WO2009128445A1 - Objective lens and optical pickup device - Google Patents

Abstract

An optical pickup device and an objective lens which allow simple configuration and reduced costs of the optical pickup device by properly recording and/or reproducing information in/from three kinds of disks of different recording densities. On the optical surface of the objective lens, an optical path difference imparting structure is formed. The optical path difference imparting structure is obtained by superimposing a first foundation structure being a blazed structure and a second foundation structure being a stepped structure such that the positions of all the step portions of the first foundation structure coincide with the positions of the step portions of the second foundation structure.

Description

Objective lens and optical pickup device

The present invention relates to an optical pickup apparatus capable of recording and / or reproducing information interchangeably for different types of optical discs and an objective lens used therefor.

In recent years, in an optical pickup device, a laser light source used as a light source for reproducing information recorded on an optical disc and recording information on the optical disc has been shortened. For example, a blue-violet semiconductor laser, Laser light sources with wavelengths of 400 to 420 nm, such as blue SHG lasers that perform wavelength conversion of infrared semiconductor lasers using harmonics, are being put into practical use. When these blue-violet laser light sources are used, it is possible to record 15 to 20 GB of information on an optical disk having a diameter of 12 cm when an objective lens having the same numerical aperture (NA) as that of a DVD (digital versatile disk) is used. When the NA of the objective lens is increased to 0.85, 23 to 25 GB of information can be recorded on an optical disk having a diameter of 12 cm. Hereinafter, in this specification, an optical disk and a magneto-optical disk using a blue-violet laser light source are collectively referred to as a “high density optical disk”.

In a high-density optical disk using an NA 0.85 objective lens, coma aberration generated due to the inclination (skew) of the optical disk increases, so the protective layer is designed thinner than in the case of DVD (0 of DVD). Some have reduced the amount of coma due to skew. By the way, it can not be said that the value of an optical disc player / recorder (optical information recording / reproducing device) as a product is sufficient only by appropriately recording / reproducing information on such a high-density optical disc. In light of the reality that DVDs and CDs (compact discs) on which a wide variety of information is recorded are currently being sold, it is not possible to record / reproduce information on high-density optical discs. Similarly, making it possible to appropriately record / reproduce information on DVDs and CDs leads to an increase in commercial value as an optical disc player / recorder for high-density optical discs. From such a background, an optical pickup device mounted on an optical disc player / recorder for high density optical discs can appropriately receive information while maintaining compatibility with both high density optical discs, DVDs, and even CDs. It is desired to have a performance capable of recording / reproducing.

As a method for recording / reproducing information appropriately while maintaining compatibility with both high-density optical discs and DVDs, and even CDs, optical systems for high-density optical discs and optical systems for DVDs and CDs are used. A method of selectively switching the system to and from the recording density of an optical disk for recording / reproducing information is conceivable, but a plurality of optical systems are required, which is disadvantageous for miniaturization and increases the cost.

Therefore, in order to simplify the configuration of the optical pickup device and reduce the cost, the optical system for high-density optical discs and the optical system for DVDs and CDs must be shared in compatible optical pickup devices. It is preferable to reduce the number of optical components constituting the optical pickup device as much as possible. And, it is most advantageous to simplify the configuration of the optical pickup device and to reduce the cost to make the objective lens arranged facing the optical disc in common. In order to obtain an objective lens that can be used in common for a plurality of types of optical discs having different recording / reproducing wavelengths, an optical path difference providing structure having wavelength dependency of spherical aberration is formed in the objective optical system. It is necessary to reduce the spherical aberration that occurs due to the difference in thickness and the thickness of the protective layer.

Patent Document 1 describes an optical element that has an optical path difference providing structure and is used for an objective lens that can be used in common with high-density optical discs and conventional DVDs and CDs.

JP 2006-185576 A

However, according to the technique disclosed in Patent Document 1, the first optical path difference function is added to the second optical path difference function in order to enable compatibility with high-density optical discs, DVDs, and CDs. The optical path difference providing structure formed in this way is formed on the objective lens. However, when the first optical path difference function and the second optical path difference function are added without being related, in the final optical path difference providing structure, as shown in FIG. And a complex structure such as a depression at the top of the mountain, making it difficult to configure the mold, making it difficult for the material to enter the mold at the time of molding, and the optical surface of the molded objective lens to be ideal Therefore, it is difficult to obtain desired optical characteristics.

The present invention has been made in consideration of the above-mentioned problems. Even if a single lens is used as an objective lens, the recording density of the high-density optical disc (particularly BD), DVD, and CD is different. An optical pickup device and an objective lens capable of appropriately recording and / or reproducing information with respect to a disc of the above, and exhibiting desired optical characteristics, and the configuration of a molding die becomes too complicated It is an object of the present invention to provide an objective lens that can prevent this, improve transferability, simplify the configuration, and reduce the cost, and an optical pickup device using the objective lens.

In order to solve the above problems, the invention according to claim 1 is directed to information on the first optical disc having a protective layer having a thickness t1 using the first light flux having the wavelength λ1 (μm) emitted from the first light source. A second optical disk having a protective layer with a thickness t2 (t1 ≦ t2) using a second light beam having a wavelength λ2 (λ1 <λ2) emitted from the second light source, formed with a condensing spot on the recording surface. A third optical disc having a protective layer with a thickness of t3 (t2 <t3) using a third light flux of wavelength λ3 (λ2 <λ3) emitted from the third light source, forming a condensed spot on the information recording surface In an objective lens for an optical pickup device that forms a condensing spot on the information recording surface of
An optical path difference providing structure is formed on the optical surface of the objective lens,
The optical path difference providing structure includes a first basic structure that is a blaze type structure and a second basic structure that is a staircase type structure, the positions of all the step portions of the first basic structure, and the steps of the second basic structure. It is superimposed so that the position of the part matches,
Of the diffracted light generated when the first light flux is incident on the optical path difference providing structure, where L, M, and N are arbitrary integers, the L-order diffracted light has the largest amount of diffracted light, and the optical path Diffraction generated when M-th order diffracted light has the maximum amount of diffracted light among the diffracted light generated when the second light flux is incident on the difference providing structure, and the third light flux is incident on the optical path difference providing structure. Of the light, the Nth order diffracted light has the maximum amount of diffracted light.

For example, when only a blazed diffraction structure or a staircase diffraction structure is formed on a compatible objective lens, the combination of the diffraction orders of the first, second, and third light beams with high diffraction efficiency is determined. Therefore, there is a problem that the degree of freedom in design is reduced. By superimposing the basic structure as in the present invention, it is possible to select an arbitrary diffraction order, improving the degree of design freedom, and designing using a single optical path difference function. Therefore, it becomes easy to design. In addition, the optical path difference providing structure can be simplified by overlapping the positions of all the step portions of the first foundation structure so that the positions of the step portions of the second foundation structure coincide with each other. Processing of the mold for the objective lens is easy, resin and glass can easily enter the end of the mold when molding the objective lens, the manufacturing accuracy can be improved, and the light quantity close to the design value can be obtained, Light loss can be reduced.

According to a second aspect of the present invention, there is provided the objective lens according to the first aspect, wherein the second basic structure is a four-step staircase structure, and the optical axis direction of the small step of the stepped structure of the second basic structure. Length d21 (μm), the length d22 (μm) in the optical axis direction of the large step of the stepped structure of the second basic structure, and the length in the optical axis of the step portion of the first basic structure d1 (μm) is the following conditional expression:
(1.2λ1-0.4λ1) / (n−1) ≦ d1 ≦ (1.2λ1 + 0.4λ1) / (n−1)
(1.25λ1-0.2λ1) / (n−1) ≦ d21 ≦ (1.25λ1 + 0.2λ1) / (n−1)
(3.75λ1-0.2λ1) / (n−1) ≦ d22 ≦ (3.75λ1 + 0.2λ1) / (n−1)
It is characterized by satisfying. However, n represents the refractive index of the objective lens in the first light flux.

The objective lens according to claim 3 is the invention according to claim 1 or 2, wherein the first optical path difference providing structure is a four-part blazed stepped structure, which is the largest of the first optical path difference providing structure. The length d0 (μm) in the optical axis direction of the step is the following conditional expression:
(4.95λ1-0.2λ1) / (n−1) ≦ d0 ≦ (4.95λ1 + 0.2λ1) / (n−1)
It is characterized by satisfying.

The objective lens according to claim 4 is the invention according to any one of claims 1 to 3,
| L | = 2, M = 0, | N | = 1
The sign of L and N is different.

According to a fifth aspect of the present invention, there is provided the objective lens according to the first aspect, wherein the second basic structure is a six-step staircase structure, and the optical axis direction of the small step of the stepped structure of the second basic structure. Length d21 (μm), the length d22 (μm) in the optical axis direction of the large step of the stepped structure of the second basic structure, and the length in the optical axis of the step portion of the first basic structure d1 (μm) is the following conditional expression:
(Λ1−0.4λ1) / (n−1) ≦ d1 ≦ (λ1 + 0.4λ1) / (n−1)
(1.2λ1-0.2λ1) / (n−1) ≦ d21 ≦ (1.2λ1 + 0.2λ1) / (n−1)
(6λ1-0.2λ1) / (n−1) ≦ d22 ≦ (6λ1 + 0.2λ1) / (n−1)
It is characterized by satisfying. However, n represents the refractive index of the objective lens in the first light flux.

The objective lens according to claim 6 is the objective lens according to claim 1 or 5, wherein the first optical path difference providing structure is a four-part blazed stepped structure, which is the largest of the first optical path difference providing structure. The length d0 (μm) in the optical axis direction of the step is the following conditional expression:
(5λ1-0.2λ1) / (n−1) ≦ d0 ≦ (5λ1 + 0.2λ1) / (n−1)
It is characterized by satisfying.

The objective lens according to claim 7 is the invention according to claim 1, 5 or 6,
Satisfy L = 0, | M | = 2, | N | = 3,
The sign of M and N is equal.

According to an eighth aspect of the present invention, there is provided the objective lens according to the first aspect, wherein the second basic structure is a seven-stage stepped structure, and the optical axis direction of the small step of the stepped structure of the second basic structure. Length d21 (μm), the length d22 (μm) in the optical axis direction of the large step of the stepped structure of the second basic structure, and the length in the optical axis of the step portion of the first basic structure d1 (μm) is the following conditional expression:
(3λ1-0.4λ1) / (n−1) ≦ d1 ≦ (3λ1 + 0.4λ1) / (n−1)
(1.31λ1-0.2λ1) / (n−1) ≦ d21 ≦ (1.31λ1 + 0.2λ1) / (n−1)
(7.86λ1-0.2λ1) / (n−1) ≦ d22 ≦ (7.86λ1 + 0.2λ1) / (n−1)
It is characterized by satisfying. However, n represents the refractive index of the objective lens in the first light flux.

The objective lens according to claim 9 is the invention according to claim 1 or 5, wherein the first optical path difference providing structure is a seven-part blazed stepped structure, which is the largest of the first optical path difference providing structure. The length d0 (μm) in the optical axis direction of the step is the following conditional expression:
(4.86λ1-0.2λ1) / (n−1) ≦ d0 ≦ (4.86λ1 + 0.2λ1) / (n−1)
It is characterized by satisfying.

The objective lens according to claim 10 is the invention according to claim 1, 8 or 9,
| L | = 1, | M | = 3, | N | = 4,
The signs of L, M, and N are equal.

The objective lens according to claim 11 is the invention according to any one of claims 1 to 10,
The optical surface of the objective lens includes at least a ring-shaped central region including an optical axis, a ring-shaped peripheral region formed around the central region, and a ring-shaped outermost region formed around the peripheral region. Has a surrounding area,
The first light flux that has passed through the central area, the peripheral area, and the most peripheral area is condensed on the information recording surface of the first optical disc,
The second light flux that has passed through the central area and the peripheral area is condensed on the information recording surface of the second optical disc,
The third light flux that has passed through the central region is condensed on the information recording surface of the third optical disc,
The first optical path difference providing structure is provided in the central region.

The optical pickup device according to claim 12 is focused on the information recording surface of the first optical disc having a protective layer having a thickness t1 by using the first light flux of wavelength λ1 (μm) emitted from the first light source. Spot formation is performed on the information recording surface of the second optical disc having a protective layer having a thickness t2 (t1 ≦ t2) using a second light flux having a wavelength λ2 (λ1 <λ2) emitted from the second light source. With respect to the information recording surface of the third optical disk having a protective layer having a thickness t3 (t2 <t3) using a third light beam having a wavelength λ3 (λ2 <λ3) emitted from the third light source. In an optical pickup device equipped with an objective lens for forming a condensed spot,
A first optical path difference providing structure is formed on the optical surface of the objective lens,
The first optical path difference providing structure includes a first basic structure that is a blaze type structure and a second basic structure that is a staircase type structure, the positions of all the step portions of the first basic structure, and the second basic structure. Is superimposed so that the position of the step part of
L-th order diffracted light has the largest amount of diffracted light among the diffracted light generated when the first light flux is incident on the first optical path difference providing structure when L, M, and N are arbitrary integers, Of the diffracted light generated when the second light beam is incident on the first optical path difference providing structure, the Mth order diffracted light has the largest amount of diffracted light, and the third light beam is incident on the first optical path difference providing structure. Of the diffracted light generated in this case, the Nth order diffracted light has the maximum amount of diffracted light.

According to a thirteenth aspect of the present invention, in the invention according to the twelfth aspect, the second basic structure is a four-step staircase structure, and the optical axis of the small step of the stepped structure of the second basic structure. Length d21 (μm) in the direction, length d22 (μm) in the optical axis direction of the large step of the stepped structure of the second basic structure, and length in the optical axis direction of the step portion of the first basic structure D1 (μm) is the following conditional expression:
(1.2λ1-0.4λ1) / (n−1) ≦ d1 ≦ (1.2λ1 + 0.4λ1) / (n−1)
(1.25λ1-0.4λ1) / (n−1) ≦ d21 ≦ (1.25λ1 + 0.4λ1) / (n−1)
(3.75λ1-0.4λ1) / (n−1) ≦ d22 ≦ (3.75λ1 + 0.4λ1) / (n−1)
It is characterized by satisfying. However, n represents the refractive index of the objective lens in the first light flux.

An optical pickup device according to a fourteenth aspect is the invention according to the twelfth or thirteenth aspect, wherein the first optical path difference providing structure is a four-part blazed stepped structure, and is the most of the first optical path difference providing structure. The length d0 (μm) in the optical axis direction of the large step is the following conditional expression:
(4.95λ1-0.4λ1) / (n−1) ≦ d0 ≦ (4.95λ1 + 0.4λ1) / (n−1)
It is characterized by satisfying.

The optical pickup device according to claim 15 is the invention according to any one of claims 12 to 14,
| L | = 2, M = 0, | N | = 1
The sign of L and N is different.

According to a sixteenth aspect of the present invention, there is provided the optical pickup device according to the twelfth aspect, wherein the second basic structure is a six-step staircase structure, and the optical axis of the small step of the stepped structure of the second basic structure. Length d21 (μm) in the direction, length d22 (μm) in the optical axis direction of the large step of the stepped structure of the second basic structure, and length in the optical axis direction of the step portion of the first basic structure D1 (μm) is the following conditional expression:
(Λ1−0.4λ1) / (n−1) ≦ d1 ≦ (λ1 + 0.4λ1) / (n−1)
(1.2λ1-0.4λ1) / (n−1) ≦ d21 ≦ (1.2λ1 + 0.4λ1) / (n−1)
(6λ1-0.4λ1) / (n−1) ≦ d22 ≦ (6λ1 + 0.4λ1) / (n−1)
It is characterized by satisfying. However, n represents the refractive index of the objective lens in the first light flux.

In an optical pickup device according to a seventeenth aspect, in the invention according to the twelfth or sixteenth aspect, the first optical path difference providing structure is a four-part blazed stepped structure, which is the most of the first optical path difference providing structure. The length d0 (μm) in the optical axis direction of the large step is the following conditional expression:
(5λ1-0.4λ1) / (n−1) ≦ d0 ≦ (5λ1 + 0.4λ1) / (n−1)
It is characterized by satisfying.

The optical pickup device according to claim 18 is the invention according to claim 12, 16 or 17,
Satisfy L = 0, | M | = 2, | N | = 3,
The sign of M and N is equal.

An optical pickup device according to a nineteenth aspect is the optical pickup device according to the twelfth aspect, wherein the second basic structure is a seven-step staircase structure, and the optical axis of a small step of the stepped structure of the second basic structure. Length d21 (μm) in the direction, length d22 (μm) in the optical axis direction of the large step of the stepped structure of the second basic structure, and length in the optical axis direction of the step portion of the first basic structure D1 (μm) is the following conditional expression:
(3λ1-0.4λ1) / (n−1) ≦ d1 ≦ (3λ1 + 0.4λ1) / (n−1)
(1.31λ1-0.4λ1) / (n−1) ≦ d21 ≦ (1.31λ1 + 0.4λ1) / (n−1)
(7.86λ1-0.4λ1) / (n−1) ≦ d22 ≦ (7.86λ1 + 0.4λ1) / (n−1)
It is characterized by satisfying. However, n represents the refractive index of the objective lens in the first light flux.

An optical pickup device according to a twentieth aspect is the invention according to the twelfth or nineteenth aspect, wherein the first optical path difference providing structure is a seven-part blazed stepped structure, and is the most of the first optical path difference providing structure. The length d0 (μm) in the optical axis direction of the large step is the following conditional expression
(4.86λ1-0.4λ1) / (n−1) ≦ d0 ≦ (4.86λ1 + 0.4λ1) / (n−1)
It is characterized by satisfying.

The optical pickup device according to claim 21 is the invention according to claim 12, 19 or 20,
| L | = 1, | M | = 3, | N | = 4,
The signs of L, M, and N are equal.

The optical pickup device according to claim 22 is the invention according to any one of claims 12 to 21,
The optical surface of the objective lens includes at least a ring-shaped central region including an optical axis, a ring-shaped peripheral region formed around the central region, and a ring-shaped outermost region formed around the peripheral region. Has a surrounding area,
The first light flux that has passed through the central area, the peripheral area, and the most peripheral area is condensed on the information recording surface of the first optical disc,
The second light flux that has passed through the central area and the peripheral area is condensed on the information recording surface of the second optical disc,
The third light flux that has passed through the central region is condensed on the information recording surface of the third optical disc,
The first optical path difference providing structure is provided in the central region.

An optical pickup device according to a twenty-third aspect is the optical pickup device according to any one of the twelfth to twenty-second aspects, wherein the objective lens is imaged when the first light flux is incident on the objective lens. The magnification m1 is the following equation (1), and the imaging magnification m2 of the objective lens when the second light beam is incident on the objective lens is the following equation (2), and the third light beam is incident on the objective lens. When the imaging magnification m3 of the objective lens is set to the following formula (3),
-0.02 <m1 <0.02 (1)
-0.02 <m2 <0.02 (2)
-0.02 <m3 <0.02 (3)
It is characterized by satisfying.

The optical pickup device according to the present invention has at least three light sources: a first light source, a second light source, and a third light source. Furthermore, the optical pickup device of the present invention condenses the first light flux on the information recording surface of the first optical disc, condenses the second light flux on the information recording surface of the second optical disc, and causes the third light flux to be third. It has a condensing optical system for condensing on the information recording surface of the optical disc. The optical pickup device of the present invention includes a light receiving element that receives a reflected light beam from the information recording surface of the first optical disc, the second optical disc, or the third optical disc. At this time, the first optical disc is preferably a BD (Blu-ray Disc) or HD DVD (hereinafter referred to as HD), the second optical disc is preferably a DVD, and the third optical disc is preferably a CD. Not limited. The first optical disc, the second optical disc, or the third optical disc may be a multi-layer optical disc having a plurality of information recording surfaces.

BD records and reproduces information with an objective lens with NA of 0.85, and the thickness of the protective substrate is about 0.1 mm. In the HD, information is recorded / reproduced by an objective lens having NA of 0.65 to 0.67, and the thickness of the protective substrate is about 0.6 mm. Further, DVD is a general term for DVD series optical discs in which information is recorded / reproduced by an objective lens having an NA of about 0.60 to 0.67, and the thickness of the protective substrate is about 0.6 mm. DVD-Video, DVD-Audio, DVD-RAM, DVD-R, DVD-RW, DVD + R, DVD + RW, and the like. In this specification, CD is a generic name for CD-series optical discs in which information is recorded / reproduced by an objective lens having an NA of about 0.45 to 0.53, and the thickness of the protective substrate is about 1.2 mm. Including CD-ROM, CD-Audio, CD-Video, CD-R, CD-RW and the like. As for the recording density, the recording density of BD is the highest, followed by HD, DVD, and CD in that order.

In addition, regarding the thicknesses t1, t2, and t3 of the protective substrate, the following conditional expressions (4), (5), (6),
0.0750 mm ≦ t1 ≦ 0.1125 mm or
0.5mm ≦ t1 ≦ 0.7mm (4)
0.5mm ≦ t2 ≦ 0.7mm (5)
1.0mm ≦ t3 ≦ 1.3mm (6)
However, the present invention is not limited to this.

In the present specification, the first light source, the second light source, and the third light source are preferably laser light sources. As the laser light source, a semiconductor laser, a silicon laser, or the like can be preferably used. The first wavelength λ1 of the first light beam emitted from the first light source, the second wavelength λ2 (λ2> λ1) of the second light beam emitted from the second light source, and the third of the third light beam emitted from the third light source. The wavelength λ3 (λ3> λ2) is defined by the following conditional expressions (7), (8),
1.5 × λ1 <λ2 <1.7 × λ1 (7)
1.9 × λ1 <λ3 <2.1 × λ1 (8)
It is preferable to satisfy.

In addition, when BD or HD, DVD, and CD are used as the first optical disc, the second optical disc, and the third optical disc, respectively, the first wavelength λ1 of the first light source is preferably 0.35 μm or more and 0.44 μm or less. More preferably, it is 0.38 μm or more and 0.415 μm or less, and the second wavelength λ2 of the second light source is preferably 0.57 μm or more and 0.68 μm or less, more preferably 0.63 μm or more and 0.67 μm. The third wavelength λ3 of the third light source is preferably 0.75 μm or more and 0.88 μm or less, more preferably 0.76 μm or more and 0.82 μm or less.

Also, at least two of the first light source, the second light source, and the third light source may be unitized. The unitization means that the first light source and the second light source are fixedly housed in one package, for example. However, the unitization is not limited to this, and the two light sources are fixed so that the aberration cannot be corrected. Is widely included. In addition to the light source, a light receiving element to be described later may be packaged.

As the light receiving element, a photodetector such as a photodiode is preferably used. Light reflected on the information recording surface of the optical disc enters the light receiving element, and a read signal of information recorded on each optical disc is obtained using the output signal. Furthermore, it detects the change in the light amount due to the spot shape change and position change on the light receiving element, performs focus detection and track detection, and based on this detection, the objective lens can be moved for focusing and tracking I can do it. The light receiving element may comprise a plurality of photodetectors. The light receiving element may have a main photodetector and a sub photodetector. For example, two sub photodetectors are provided on both sides of a photodetector that receives main light used for recording and reproducing information, and the sub light for tracking adjustment is received by the two sub photodetectors. It is good also as a simple light receiving element. The light receiving element may have a plurality of light receiving elements corresponding to the respective light sources.

The condensing optical system has an objective lens. The condensing optical system may include only the objective lens, but the condensing optical system may include a coupling lens such as a collimator in addition to the objective lens. The coupling lens is a single lens or a lens group that is disposed between the objective lens and the light source and changes the divergence angle of the light beam. The collimator is a type of coupling lens, and is a lens that emits light incident on the collimator as parallel light. Further, the condensing optical system has an optical element such as a diffractive optical element that divides the light beam emitted from the light source into a main light beam used for recording and reproducing information and two sub light beams used for tracking and the like. May be. In this specification, the objective lens refers to an optical system that is disposed at a position facing the optical disk in the optical pickup device and has a function of condensing the light beam emitted from the light source onto the information recording surface of the optical disk. Preferably, the objective lens is an optical system which is disposed at a position facing the optical disk in the optical pickup device and has a function of condensing the light beam emitted from the light source on the information recording surface of the optical disk, and further includes an actuator An optical system that can be integrally displaced at least in the optical axis direction. The objective lens is preferably a single objective lens, but may be formed of a plurality of optical elements. The objective lens may be a glass lens, a plastic lens, or a hybrid lens in which an optical path difference providing structure or the like is provided on a glass lens with a photocurable resin or the like. The objective lens preferably has a refractive surface that is aspheric. In the objective lens, the base surface on which the optical path difference providing structure is provided is preferably an aspherical surface.

Further, when the objective lens is a glass lens, it is preferable to use a glass material having a glass transition point Tg of 400 ° C. or lower. By using a glass material having a glass transition point Tg of 400 ° C. or lower, molding at a relatively low temperature becomes possible, so that the life of the mold can be extended. Examples of such a glass material having a low glass transition point Tg include K-PG325 and K-PG375 (both product names) manufactured by Sumita Optical Glass Co., Ltd.

By the way, since the specific gravity of the glass lens is generally larger than that of the resin lens, if the objective lens is a glass lens, the weight increases and a load is imposed on the actuator that drives the objective lens. Therefore, when the objective lens is a glass lens, it is preferable to use a glass material having a small specific gravity. Specifically, the specific gravity is preferably 3.0 or less, and more preferably 2.8 or less.

When the objective lens is a plastic lens, it is preferable to use a cyclic olefin-based resin material. Among the cyclic olefin-based materials, the refractive index at a temperature of 25 ° C. with respect to a wavelength of 405 nm is 1.52 to 1.60. The refractive index change rate dN / dT (° C. ⁻¹ ) is −20 × 10 ^{−5 to} −5 × 10 ^{− with} respect to the wavelength of 405 nm accompanying the temperature change within the temperature range of −5 ° C. to 70 ° C. ^It is more preferable to use a resin material in the range of ⁵ (more preferably, −10 × 10 ^{−5 to} −8 × 10 ⁻⁵ ). When the objective lens is a plastic lens, the coupling lens is preferably a plastic lens.

The objective lens is described below. At least one optical surface of the objective lens has a central region and a peripheral region around the central region. At least one optical surface of the objective lens may have an outermost peripheral region around the peripheral region. The central region is preferably a region including the optical axis of the objective lens, but may be a region not including the optical axis. It is preferable that the central region, the peripheral region, and the most peripheral region are provided on the same optical surface. As shown in FIG. 1, the central region CN, the peripheral region MD, and the most peripheral region OT are preferably provided concentrically around the optical axis on the same optical surface. Moreover, it is preferable that a first optical path difference providing structure is provided in the central region of the objective lens. Further, a second optical path difference providing structure may be provided in the peripheral region. In the case of having the outermost peripheral region, the outermost peripheral region may be a refractive surface, or the third optical path difference providing structure may be provided in the outermost peripheral region. The central region, the peripheral region, and the outermost peripheral region are preferably adjacent to each other, but there may be a slight gap between them.

The first optical path difference providing structure is preferably provided in a region of 70% or more of the area of the central region of the objective lens, and more preferably 90% or more. More preferably, the first optical path difference providing structure is provided on the entire surface of the central region. The second optical path difference providing structure is preferably provided in a region of 70% or more of the area of the peripheral region of the objective lens, and more preferably 90% or more. More preferably, the second optical path difference providing structure is provided on the entire surface of the peripheral region. The third optical path difference providing structure is preferably provided in a region of 70% or more of the area of the outermost peripheral region of the objective lens, and more preferably 90% or more. More preferably, the third optical path difference providing structure is provided on the entire surface of the outermost peripheral region.

In addition, the optical path difference providing structure referred to in this specification is a general term for structures that add an optical path difference to an incident light beam. The optical path difference providing structure also includes a phase difference providing structure for providing a phase difference. The phase difference providing structure includes a diffractive structure. It can be said that the optical path difference providing structure of the present invention is a diffractive structure. The optical path difference providing structure has a step, preferably a plurality of steps. This step adds an optical path difference and / or phase difference to the incident light flux. The optical path difference added by the optical path difference providing structure may be an integer multiple of the wavelength of the incident light beam or a non-integer multiple of the wavelength of the incident light beam. The steps may be arranged with a periodic interval in the direction perpendicular to the optical axis, or may be arranged with a non-periodic interval in the direction perpendicular to the optical axis.

It is preferable that the optical path difference providing structure has a plurality of concentric annular zones centered on the optical axis. In addition, the optical path difference providing structure can have various cross-sectional shapes (cross-sectional shapes in a plane including the optical axis). In particular, the first optical path difference providing structure is obtained by superimposing a first basic structure whose cross-sectional shape including the optical axis is a blazed structure and a second basic structure whose cross-sectional shape including the optical axis is a stepped structure. Is preferred.

As shown in FIGS. 2 (a) and 2 (b), the blazed structure means that the cross-sectional shape including the optical axis of an optical element having an optical path difference providing structure is a sawtooth shape. In other words, the optical path difference providing structure has an oblique surface that is neither perpendicular nor parallel to the base surface. Further, as shown in FIG. 2 (c), the staircase structure means that the cross-sectional shape including the optical axis of the optical element having the optical path difference providing structure has a plurality of small staircase shapes. In other words, the optical path difference providing structure has only a surface parallel to the base surface and a surface parallel to the optical axis, and does not have an oblique surface with respect to the base surface. This means that it has a plurality of small structures whose length in the optical axis direction changes step by step. Further, when the base structure is a stepped structure, if the base surface is a surface having a curvature, a light beam is refracted on the base surface, so that a refraction angle varies depending on the distance from the optical axis. For this reason, it is preferable to obtain a stepped structure by shifting the base surface by the same optical path length in the light traveling direction, rather than shifting the base surface parallel to the optical axis direction. In the present specification, “X division” means that a ring-shaped surface corresponding to (or facing) the vertical direction of the optical axis of one staircase structure is divided by steps and divided into X pieces. “Small step” means the smallest step in the optical axis direction in one staircase structure, and “large step” means the largest step in the optical axis direction in one staircase structure. And

When the first foundation structure and the second foundation structure are overlapped, the second foundation structure different from the first foundation structure is placed on the first foundation structure, the positions of all the step portions of the first foundation structure, and the second foundation structure. It is preferable to superimpose so that the position of the level | step-difference part matches. As a preferred mode, the deepest position P1 of the blaze structure shown in FIG. 3A and the deepest position P2 of the staircase structure shown in FIG. Thereby, the 1st optical path difference providing structure shown in FIG.3 (c) can be obtained. Thus, the structure as shown in FIG. 3C obtained by superimposing the blaze type structure and the staircase type structure with the position of the blaze type step and the position of the large step of the staircase structure being coincident with each other is obtained. In the specification, it is referred to as a blaze-type step structure. The blazed staircase structure has an optical path difference providing structure that has an oblique surface with respect to the base surface and a surface parallel to the optical axis. A structure having a plurality of small structures that change. Note that a plurality of unit zones of the second foundation structure may be superimposed on one unit zone of the first foundation structure. Further, not all the positions of the step portions of the second foundation structure need to coincide with the positions of the step portions of the first foundation structure. That is, some of the step portions of the second foundation structure may not coincide with the position of the step portion of the first foundation structure. The second optical path difference providing structure and the third optical path difference providing structure may or may not overlap the basic structure. In this case, a structure having an arbitrary shape shown in FIGS.

It should be noted that the optical path difference providing structure or the basic structure is preferably a structure in which a certain unit shape is periodically repeated. As used herein, “unit shape is periodically repeated” naturally includes shapes in which the same shape is repeated in the same cycle. In addition, the unit shape that is one unit of the cycle has regularity, and the shape in which the cycle gradually increases or decreases gradually is also included in the “unit shape is periodically repeated”. Suppose that

When the optical path difference providing structure or the basic structure has a blazed structure, the sawtooth shape as a unit shape is repeated. As shown in FIG. 2 (a), the same sawtooth shape may be repeated, and as shown in FIG. 2 (b), the size of the sawtooth shape gradually increases as it goes in the direction of the base surface. It may be a shape that increases in size or a shape that decreases. Moreover, it is good also as a shape which combined the shape where the magnitude | size of the serrated shape became large gradually and the shape where the magnitude | size of a serrated shape becomes small gradually. However, even in the case where the size of the serrated shape changes gradually, it is preferable that the size in the optical axis direction (or the direction of the passing light beam) hardly changes in the serrated shape. In the blazed structure, the length in the optical axis direction of one sawtooth shape (may be the length in the direction of the light beam passing through the sawtooth shape) is referred to as the pitch depth, and one sawtooth shape light. The length in the direction perpendicular to the axis is called the pitch width. In addition, in some areas, the blazed structure has a step opposite to the optical axis (center) side, and in other areas, the blazed structure has a step toward the optical axis (center). It is good also as a shape in which the transition area | region required in order to switch the direction of the level | step difference of a blaze | braze type | mold structure is provided in the meantime. This transition region is a region corresponding to a point that becomes an extreme value of the optical path difference function when the optical path difference added by the optical path difference providing structure, which is an optical path difference providing structure, is expressed by an optical path difference function. If the optical path difference function has an extreme point, the inclination of the optical path difference function becomes small, so that the annular zone pitch can be widened, and the decrease in transmittance due to the shape error of the optical path difference providing structure can be suppressed.

When the optical path difference providing structure or the basic structure has a staircase structure, the shape is a unit shape, which is a repeated staircase shape. There may be a shape in which the same small staircase shape of several stages (for example, a structure of five divisions as shown in FIG. 2C) is repeated as shown in FIG. Furthermore, the shape of the staircase may gradually increase in size as it proceeds in the direction of the base surface, or the shape of the staircase may gradually decrease in size. It is preferable that the length of the direction of light) hardly changes.

When the optical path difference providing structure has a binary shape as shown in FIG. 2D (such a structure can be said to be a two-step staircase structure), the optical path difference providing structure gradually increases in the direction of the base surface. A shape in which the size of the binary increases or a shape in which the size of the staircase gradually decreases may be used, but it is preferable that the length of the light beam passing through hardly changes.

Next, examples of various first optical path difference providing structures will be described in more detail with reference to FIGS. Note that L, M, and N shown in the following examples are the diffraction orders of the diffracted light having the maximum diffracted light quantity among the diffracted lights generated when the first light flux is incident on the first optical path difference providing structure. Next, of the diffracted light generated when the second light beam enters the first optical path difference providing structure, the diffraction order of the diffracted light having the maximum diffracted light amount is M order, and the third light beam is applied to the first optical path difference providing structure. The integers L, M, and N are shown when the diffraction order of the diffracted light having the maximum amount of diffracted light among the diffracted light generated when incident is N order.

(First optical path difference providing structure example 1)
In Example 1, as shown in FIG.6 (b), the 2nd foundation structure which is a staircase type structure is a 4 stepped staircase structure. Further, the length d21 (μm) of the small step of the stepped structure of the second basic structure in the optical axis direction, the length d22 (μm) of the large step of the stepped structure of the second basic structure, and As shown in FIG. 6 (a), the length d1 (μm) in the optical axis direction of the step portion of the first basic structure having a blaze structure is defined by the following conditional expression:
(1.2λ1-0.4λ1) / (n−1) ≦ d1 ≦ (1.2λ1 + 0.4λ1) / (n−1)
(1.25λ1-0.2λ1) / (n−1) ≦ d21 ≦ (1.25λ1 + 0.2λ1) / (n−1)
(3.75λ1-0.2λ1) / (n−1) ≦ d22 ≦ (3.75λ1 + 0.2λ1) / (n−1)
Meet. However, n represents the refractive index of the objective lens in the first light flux.

Note that the above equation indicates that the step amount d1 in the optical axis direction of the first basic structure is a step amount that gives an optical path difference of 1.2λ1 ± 0.4λ1 with respect to the wavelength λ1 of the first light flux. It can also be said that it means. Further, the step amount d21 in the direction of the small optical axis of the second foundation structure is such a step amount that gives an optical path difference of 1.25λ1 ± 0.2λ1 with respect to the wavelength λ1 of the first light beam. It can be said that the large step amount d22 in the optical axis direction is a step amount that gives an optical path difference of 3.75λ1 ± 0.2λ1 with respect to the wavelength λ1 of the first light flux.

In the blazed optical path difference providing structure such as the first basic structure, the diffraction efficiency can be calculated based on the following equation (1).

The relationship between the step amount d in the optical axis direction of the step and the diffraction order m can be expressed by m = (n−1) · d / λ.

Furthermore, in a stepped structure such as the second basic structure, the diffraction efficiency can be calculated based on the following equation (2).

In this example, as shown in FIGS. 6A and 6B, the directions of the first basic structure and the second basic structure are overlapped in the same direction. “Same orientation” means the direction of inclination of the slanted surface of the blazed structure (decreasing to the right) when the optical axis is the vertical axis and the optical axis orthogonal direction is the horizontal axis in the cross section including the optical axis of the objective lens. It means that the direction of the inclination of the slanted surface which is the envelope surface of each step of the staircase structure is the same.

The first optical path difference providing structure obtained by superimposing the first basic structure and the second basic structure is a four-part blazed stepped structure as shown in FIG. The length d0 (μm) of the largest step of the structure in the optical axis direction and the length d00 (μm) of the small step of the first optical path difference providing structure in the optical axis direction are as follows:
(4.95λ1-0.2λ1) / (n−1) ≦ d0 ≦ (4.95λ1 + 0.2λ1) / (n−1)
(1.25λ1-0.2λ1) / (n−1) ≦ d00 ≦ (1.25λ1 + 0.2λ1) / (n−1)
Meet. It is more preferable that all the step amounts d0 and d00 of the first optical path difference providing structure in the central region satisfy the above conditional expression. However, in the case of a step away from the optical axis, the aspheric surface of the objective lens is curved. The step amount must be taken into consideration, and the step amounts d0 and d00 of the step away from the optical axis tend to increase gradually, and there may be a step slightly larger than the above conditional expression. Therefore, it is preferable that d0 and d00 closest to the optical axis of the first optical path difference providing structure satisfy at least the above conditional expression.

Further, the above equation is a step amount such that the small step amount d00 in the optical axis direction of the first optical path difference providing structure gives an optical path difference of 1.25λ1 ± 0.2λ1 with respect to the wavelength λ1 of the first light flux. This means that the large step amount d0 in the optical axis direction of the first optical path difference providing structure is a step amount that gives an optical path difference of 4.95λ1 ± 0.2λ1 with respect to the wavelength λ1 of the first light flux. It can be said that they are doing.

In this example, | L | = 2, M = 0, and | N | = 1 are satisfied, and the signs of L and N are different. L is preferably positive.

Note that the phase of the first light beam that has passed through the first optical path difference providing structure increases as it moves away from the optical axis, and the phase of the third light beam that has passed through the first optical path difference providing structure is delayed as it moves away from the optical axis. In such a case, the phase of the first light flux that has passed through the first optical path difference providing structure is delayed as the distance from the optical axis increases, and the phase of the third light flux that has passed through the first optical path difference providing structure is increased as the distance from the optical axis increases. Can be said to be different in the sign of L and N. In addition, when the first optical path difference providing structure is a staircase-shaped repetitive structure, it is preferable that the phase advance and the phase delay occur in one staircase shape that is a unit structure.

In the first optical path difference providing structure of Example 1, the first wavelength of the first light beam is about 405 nm, the second wavelength of the second light beam is about 655 nm, and the third wavelength of the third light beam is about 785 nm. The diffraction efficiency can be about 77% for the first beam, about 68% for the second beam, and about 57% for the third beam. According to this example, the order that cannot be obtained with a normal blazed structure or a diffractive structure with a staircase structure can be set to the maximum diffraction efficiency.

In the optical path difference providing structure, the diffraction efficiency can also be calculated based on the following equation (3).

(First optical path difference providing structure example 2)
In Example 2, as shown in FIG.7 (b), the 2nd foundation structure which is a staircase type structure is a 6-step staircase type structure. Further, the length d21 (μm) of the small step of the stepped structure of the second basic structure in the optical axis direction, the length d22 (μm) of the large step of the stepped structure of the second basic structure, and As shown in FIG. 7 (a), the length d1 (μm) in the optical axis direction of the step portion of the first basic structure having a blaze structure is defined by the following conditional expression:
(Λ1−0.4λ1) / (n−1) ≦ d1 ≦ (λ1 + 0.4λ1) / (n−1)
(1.2λ1-0.2λ1) / (n−1) ≦ d21 ≦ (1.2λ1 + 0.2λ1) / (n−1)
(6λ1-0.2λ1) / (n−1) ≦ d22 ≦ (6λ1 + 0.2λ1) / (n−1)
Meet.

In this example, as shown in FIGS. 7A and 7B, the directions of the first basic structure and the second basic structure are superimposed in different directions. “Different orientation” refers to the direction of inclination of a slanted surface of a blazed structure (decrease to the right) when the optical axis is the vertical axis and the optical axis orthogonal direction is the horizontal axis in the cross section including the optical axis of the objective lens It means that the inclination direction of the slanted surface, which is the envelope surface of each step of the staircase structure, is reversed.

Further, the first optical path difference providing structure obtained by superimposing the first basic structure and the second basic structure is a six-part blazed stepped structure as shown in FIG. The length d0 (μm) of the largest step of the structure in the optical axis direction and the length d00 (μm) of the small step of the first optical path difference providing structure in the optical axis direction are as follows:
(5λ1-0.2λ1) / (n−1) ≦ d0 ≦ (5λ1 + 0.2λ1) / (n−1)
(1.2λ1-0.2λ1) / (n−1) ≦ d00 ≦ (1.2λ1 + 0.2λ1) / (n−1)
Meet. It is more preferable that all the step amounts d0 and d00 of the first optical path difference providing structure in the central region satisfy the above conditional expression. However, in the case of a step away from the optical axis, the aspheric surface of the objective lens is curved. The step amount must be taken into consideration, and the step amounts d0 and d00 of the step away from the optical axis tend to increase gradually, and there may be a step slightly larger than the above conditional expression. Therefore, it is preferable that d0 and d00 closest to the optical axis of the first optical path difference providing structure satisfy at least the above conditional expression.

In this example, L = 0, | M | = 2, and | N | = 3 are satisfied, and the signs of M and N are equal. It is preferred that both M and N are positive.

The phase of the second light flux that has passed through the first optical path difference providing structure is advanced as the distance from the optical axis increases, and the phase of the second light flux that has passed through the first optical path difference providing structure is advanced as it is further away from the optical axis. In such a case, the phase of the second light flux that has passed through the first optical path difference providing structure is delayed as the distance from the optical axis increases, and the phase of the third light flux that has passed through the first optical path difference providing structure is also determined to be away from the optical axis. Is delayed, it can be said that the signs of M and N are equal. In addition, when the first optical path difference providing structure is a staircase-shaped repetitive structure, it is preferable that the phase advance and the phase delay occur in one staircase shape that is a unit structure.

In the first optical path difference providing structure of Example 2, the first wavelength of the first light beam is about 405 nm, the second wavelength of the second light beam is about 655 nm, and the third wavelength of the third light beam is about 785 nm. The diffraction efficiency can be about 80% for the first beam, about 62% for the second beam, and about 54% for the third beam. According to this example, the order that cannot be obtained with a normal blazed structure or a diffractive structure with a staircase structure can be set to the maximum diffraction efficiency.

(First optical path difference giving structure example 3)
In Example 3, as shown in FIG.8 (b), the 2nd foundation structure which is a staircase type structure is a 7-step staircase type structure. Further, the length d21 (μm) of the small step of the stepped structure of the second basic structure in the optical axis direction, the length d22 (μm) of the large step of the stepped structure of the second basic structure, and As shown in FIG. 8 (a), the length d1 (μm) in the optical axis direction of the step portion of the first basic structure having a blaze structure is defined by the following conditional expression:
(3λ1-0.4λ1) / (n−1) ≦ d1 ≦ (3λ1 + 0.4λ1) / (n−1)
(1.31λ1-0.2λ1) / (n−1) ≦ d21 ≦ (1.31λ1 + 0.2λ1) / (n−1)
(7.86λ1-0.2λ1) / (n−1) ≦ d22 ≦ (7.86λ1 + 0.2λ1) / (n−1)
Meet.

In this example, as shown in FIGS. 8A and 8B, the directions of the first basic structure and the second basic structure are superimposed in different directions.

Further, the first optical path difference providing structure obtained by superimposing the first basic structure and the second basic structure is a seven-part blazed stepped structure as shown in FIG. The length d0 (μm) of the largest step of the structure in the optical axis direction and the length d00 (μm) of the small step of the first optical path difference providing structure in the optical axis direction are as follows:
(4.86λ1-0.2λ1) / (n−1) ≦ d0 ≦ (4.86λ1 + 0.2λ1) / (n−1)
(1.31λ1-0.2λ1) / (n−1) ≦ d00 ≦ (1.31λ1 + 0.2λ1) / (n−1)
Meet. It is more preferable that all the step amounts d0 and d00 of the first optical path difference providing structure in the central region satisfy the above conditional expression. However, in the case of a step away from the optical axis, the aspheric surface of the objective lens is curved. The step amount must be taken into consideration, and the step amounts d0 and d00 of the step away from the optical axis tend to increase gradually, and there may be a step slightly larger than the above conditional expression. Therefore, it is preferable that d0 and d00 closest to the optical axis of the first optical path difference providing structure satisfy at least the above conditional expression.

In this example, | L | = 1, | M | = 3, and | N | = 4 are satisfied, and the signs of L, M, and N are equal. Moreover, it is preferable that L, M, and N are all positive.

In the first optical path difference providing structure of Example 3, the first wavelength of the first light beam is about 405 nm, the second wavelength of the second light beam is about 655 nm, and the third wavelength of the third light beam is about 785 nm. The diffraction efficiency can be about 69% for the first beam, about 65% for the second beam, and about 64% for the third beam. According to this example, the order that cannot be obtained with a normal blazed structure or a diffractive structure with a staircase structure can be set to the maximum diffraction efficiency.

(First optical path difference providing structure example 4)
In Example 4, as shown in FIG. 9B, the second basic structure having a stepped structure is a seven-stage stepped structure. Further, the length d21 (μm) of the small step of the stepped structure of the second basic structure in the optical axis direction, the length d22 (μm) of the large step of the stepped structure of the second basic structure, and As shown in FIG. 9 (a), the length d1 (μm) in the optical axis direction of the step portion of the first basic structure having a blaze structure is defined by the following conditional expression:
(4λ1−0.4λ1) / (n−1) ≦ d1 ≦ (4λ1 + 0.4λ1) / (n−1)
(1.28λ1-0.2λ1) / (n−1) ≦ d21 ≦ (1.28λ1 + 0.2λ1) / (n−1)
(7.68λ1-0.2λ1) / (n−1) ≦ d22 ≦ (7.68λ1 + 0.2λ1) / (n−1)
Meet.

In this example, as shown in FIGS. 9A and 9B, the directions of the first basic structure and the second basic structure are superimposed in different directions.

Further, the first optical path difference providing structure obtained by superimposing the first basic structure and the second basic structure is a seven-part blazed stepped structure as shown in FIG. The length d0 (μm) of the largest step of the structure in the optical axis direction and the length d00 (μm) of the small step of the first optical path difference providing structure in the optical axis direction are as follows:
(3.68λ1-0.2λ1) / (n−1) ≦ d0 ≦ (3.68λ1 + 0.2λ1) / (n−1)
(1.28λ1-0.2λ1) / (n−1) ≦ d00 ≦ (1.28λ1 + 0.2λ1) / (n−1)
Meet. It is more preferable that all the step amounts d0 and d00 of the first optical path difference providing structure in the central region satisfy the above conditional expression. However, in the case of a step away from the optical axis, the aspheric surface of the objective lens is curved. The step amount must be taken into consideration, and the step amounts d0 and d00 of the step away from the optical axis tend to increase gradually, and there may be a step slightly larger than the above conditional expression. Therefore, it is preferable that d0 and d00 closest to the optical axis of the first optical path difference providing structure satisfy at least the above conditional expression.

In this example, | L | = 2, | M | = 4, and | N | = 5 are satisfied, and the signs of L, M, and N are equal. Moreover, it is preferable that L, M, and N are all positive.

In the first optical path difference providing structure of Example 4, the first wavelength of the first light beam is about 405 nm, the second wavelength of the second light beam is about 655 nm, and the third wavelength of the third light beam is about 785 nm. The diffraction efficiency can be about 67% for the first beam, about 68% for the second beam, and about 60% for the third beam. According to this example, the order that cannot be obtained with a normal blazed structure or a diffractive structure with a staircase structure can be set to the maximum diffraction efficiency.

(First optical path difference providing structure example 5)
In Example 5, as shown in FIG.10 (b), the 2nd foundation structure which is a staircase type structure is a 5-step staircase type structure. Further, the length d21 (μm) of the small step of the stepped structure of the second basic structure in the optical axis direction, the length d22 (μm) of the large step of the stepped structure of the second basic structure, and As shown in FIG. 10 (a), the length d1 (μm) in the optical axis direction of the step portion of the first basic structure having a blaze structure is defined by the following conditional expression:
(2λ1-0.4λ1) / (n−1) ≦ d1 ≦ (2λ1 + 0.4λ1) / (n−1)
(1.2λ1-0.2λ1) / (n−1) ≦ d21 ≦ (1.2λ1 + 0.2λ1) / (n−1)
(4.8λ1-0.2λ1) / (n−1) ≦ d22 ≦ (4.8λ1 + 0.2λ1) / (n−1)
Meet.

In this example, as shown in FIGS. 10A and 10B, the directions of the first basic structure and the second basic structure are overlapped in the same direction.

Further, the first optical path difference providing structure obtained by superimposing the first basic structure and the second basic structure is a five-part blazed staircase structure as shown in FIG. The length d0 (μm) of the largest step of the structure in the optical axis direction and the length d00 (μm) of the small step of the first optical path difference providing structure in the optical axis direction are as follows:
(6.8λ1-0.2λ1) / (n−1) ≦ d0 ≦ (6.8λ1 + 0.2λ1) / (n−1)
(1.2λ1-0.2λ1) / (n−1) ≦ d00 ≦ (1.2λ1 + 0.2λ1) / (n−1)
Meet. It is more preferable that all the step amounts d0 and d00 of the first optical path difference providing structure in the central region satisfy the above conditional expression. However, in the case of a step away from the optical axis, the aspheric surface of the objective lens is curved. The step amount must be taken into consideration, and the step amounts d0 and d00 of the step away from the optical axis tend to increase gradually, and there may be a step slightly larger than the above conditional expression. Therefore, it is preferable that d0 and d00 closest to the optical axis of the first optical path difference providing structure satisfy at least the above conditional expression.

In this example, | L | = 3, M = 0, and | N | = 1 are satisfied, and the signs of L and N are different. Moreover, it is preferable that L is positive.

In the first optical path difference providing structure of Example 5, the first wavelength of the first light beam is about 405 nm, the second wavelength of the second light beam is about 655 nm, and the third wavelength of the third light beam is about 785 nm. The diffraction efficiency can be about 88% for the first beam, about 70% for the second beam, and about 57% for the third beam. According to this example, the order that cannot be obtained with a normal blazed structure or a diffractive structure with a staircase structure can be set to the maximum diffraction efficiency.

(First optical path difference providing structure example 6)
In Example 6, as shown in FIG. 11B, the second basic structure having a stepped structure is a two-step stepped structure (binary structure). Further, the length d21 (μm) of the small step of the stepped structure of the second basic structure in the optical axis direction, the length d22 (μm) of the large step of the stepped structure of the second basic structure, and As shown in FIG. 11 (a), the length d1 (μm) in the optical axis direction of the step portion of the first basic structure having a blaze structure is defined by the following conditional expression:
(4λ1−0.4λ1) / (n−1) ≦ d1 ≦ (4λ1 + 0.4λ1) / (n−1)
(1.1λ1-0.2λ1) / (n−1) ≦ d21 ≦ (1.1λ1 + 0.2λ1) / (n−1)
(1.1λ1-0.2λ1) / (n−1) ≦ d22 ≦ (1.1λ1 + 0.2λ1) / (n−1)
Meet. Here, the case of d21 = d22 is included (the same applies to Examples 7, 8, 18, and 19).

In this example, as shown in FIGS. 11A and 11B, the directions of the first foundation structure and the second foundation structure are superimposed in different directions.

The first optical path difference providing structure obtained by superimposing the first basic structure and the second basic structure is a two-part blazed staircase structure as shown in FIG. The length d0 (μm) of the largest step of the structure in the optical axis direction and the length d00 (μm) of the small step of the first optical path difference providing structure in the optical axis direction are as follows:
(2.9λ1-0.2λ1) / (n−1) ≦ d0 ≦ (2.9λ1 + 0.2λ1) / (n−1)
(1.1λ1-0.2λ1) / (n−1) ≦ d00 ≦ (1.1λ1 + 0.2λ1) / (n−1)
Meet. It is more preferable that all the step amounts d0 and d00 of the first optical path difference providing structure in the central region satisfy the above conditional expression. However, in the case of a step away from the optical axis, the aspheric surface of the objective lens is curved. The step amount must be taken into consideration, and the step amounts d0 and d00 of the step away from the optical axis tend to increase gradually, and there may be a step slightly larger than the above conditional expression. Therefore, it is preferable that d0 and d00 closest to the optical axis of the first optical path difference providing structure satisfy at least the above conditional expression.

In this example, | L | = 4, | M | = 3, and | N | = 3 are satisfied, and the signs of L, M, and N are equal. L, M, and N are preferably positive.

In the first optical path difference providing structure of Example 6, the first wavelength of the first light beam is about 405 nm, the second wavelength of the second light beam is about 655 nm, and the third wavelength of the third light beam is about 785 nm. The diffraction efficiency can be about 97% for the first beam, about 74% for the second beam, and about 45% for the third beam. According to this example, the order that cannot be obtained with a normal blazed structure or a diffractive structure with a staircase structure can be set to the maximum diffraction efficiency.

(First optical path difference providing structure example 7)
In Example 7, as shown in FIG. 12B, the second basic structure having a stepped structure is a two-stage stepped structure (binary structure). Further, the length d21 (μm) of the small step of the stepped structure of the second basic structure in the optical axis direction, the length d22 (μm) of the large step of the stepped structure of the second basic structure, and As shown in FIG. 12 (a), the length d1 (μm) in the optical axis direction of the step portion of the first basic structure having a blaze structure is defined by the following conditional expression:
(Λ1−0.4λ1) / (n−1) ≦ d1 ≦ (λ1 + 0.4λ1) / (n−1)
(2λ1-0.2λ1) / (n−1) ≦ d21 ≦ (2λ1 + 0.2λ1) / (n−1)
(2λ1-0.2λ1) / (n−1) ≦ d22 ≦ (2λ1 + 0.2λ1) / (n−1)
Meet.

In this example, as shown in FIGS. 12A and 12B, the directions of the first basic structure and the second basic structure are overlapped in the same direction.

The first optical path difference providing structure obtained by superimposing the first basic structure and the second basic structure is a two-part blazed stepped structure as shown in FIG. The length d0 (μm) of the largest step of the structure in the optical axis direction and the length d00 (μm) of the small step of the first optical path difference providing structure in the optical axis direction are as follows:
(3λ1-0.2λ1) / (n−1) ≦ d0 ≦ (3λ1 + 0.2λ1) / (n−1)
(2λ1-0.2λ1) / (n−1) ≦ d00 ≦ (2λ1 + 0.2λ1) / (n−1)
Meet. It is more preferable that all the step amounts d0 and d00 of the first optical path difference providing structure in the central region satisfy the above conditional expression. However, in the case of a step away from the optical axis, the aspheric surface of the objective lens is curved. The step amount must be taken into consideration, and the step amounts d0 and d00 of the step away from the optical axis tend to increase gradually, and there may be a step slightly larger than the above conditional expression. Therefore, it is preferable that d0 and d00 closest to the optical axis of the first optical path difference providing structure satisfy at least the above conditional expression.

In this example, | L | = 1, | M | = 1, | N | = 1 are satisfied, and the signs of L, M, and N are equal. L, M, and N are preferably positive.

In the first optical path difference providing structure of Example 7, the first wavelength of the first light beam is about 405 nm, the second wavelength of the second light beam is about 655 nm, and the third wavelength of the third light beam is about 785 nm. The diffraction efficiency can be about 82% for the first beam, about 91% for the second beam, and about 57% for the third beam. According to this example, higher diffraction efficiency can be obtained as compared with the blazed structure.

(First optical path difference providing structure example 8)
In Example 8, as shown in FIG. 13B, the second basic structure having a stepped structure is a two-stage stepped structure (binary structure). Further, the length d21 (μm) of the small step of the stepped structure of the second basic structure in the optical axis direction, the length d22 (μm) of the large step of the stepped structure of the second basic structure, and As shown in FIG. 13 (a), the length d1 (μm) in the optical axis direction of the step portion of the first basic structure having a blaze structure is defined by the following conditional expression:
(Λ1−0.4λ1) / (n−1) ≦ d1 ≦ (λ1 + 0.4λ1) / (n−1)
(3.1λ1-0.2λ1) / (n−1) ≦ d21 ≦ (3.1λ1 + 0.2λ1) / (n−1)
(3.1λ1-0.2λ1) / (n−1) ≦ d22 ≦ (3.1λ1 + 0.2λ1) / (n−1)
Meet.

In this example, as shown in FIGS. 13A and 13B, the directions of the first foundation structure and the second foundation structure are superimposed in different directions.

The first optical path difference providing structure obtained by superimposing the first basic structure and the second basic structure is a two-part blazed staircase structure as shown in FIG. The length d0 (μm) of the largest step of the structure in the optical axis direction and the length d00 (μm) of the small step of the first optical path difference providing structure in the optical axis direction are as follows:
(3.1λ1-0.2λ1) / (n−1) ≦ d0 ≦ (3.1λ1 + 0.2λ1) / (n−1)
(2.1λ1-0.2λ1) / (n−1) ≦ d00 ≦ (2.1λ1 + 0.2λ1) / (n−1)
Meet. It is more preferable that all the step amounts d0 and d00 of the first optical path difference providing structure in the central region satisfy the above conditional expression. However, in the case of a step away from the optical axis, the aspheric surface of the objective lens is curved. The step amount must be taken into consideration, and the step amounts d0 and d00 of the step away from the optical axis tend to increase gradually, and there may be a step slightly larger than the above conditional expression. Therefore, it is preferable that d0 and d00 closest to the optical axis of the first optical path difference providing structure satisfy at least the above conditional expression.

In this example, | L | = 1, | M | = 1, | N | = 1 are satisfied, and the signs of L, M, and N are equal. L, M, and N are preferably positive.

In the first optical path difference providing structure of Example 8, the first wavelength of the first light beam is about 405 nm, the second wavelength of the second light beam is about 655 nm, and the third wavelength of the third light beam is about 785 nm. The diffraction efficiency can be about 90% for the first beam, about 85% for the second beam, and about 50% for the third beam. According to this example, higher diffraction efficiency can be obtained as compared with the blazed structure.

(First optical path difference providing structure example 9)
In Example 9, as shown in FIG. 14B, the second basic structure having a stepped structure is a seven-step stepped structure. Further, the length d21 (μm) of the small step of the stepped structure of the second basic structure in the optical axis direction, the length d22 (μm) of the large step of the stepped structure of the second basic structure, and As shown in FIG. 14 (a), the length d1 (μm) in the optical axis direction of the step portion of the first basic structure having a blaze structure is defined by the following conditional expression:
(Λ1−0.4λ1) / (n−1) ≦ d1 ≦ (λ1 + 0.4λ1) / (n−1)
(1.29λ1-0.2λ1) / (n−1) ≦ d21 ≦ (1.29λ1 + 0.2λ1) / (n−1)
(7.74λ1-0.2λ1) / (n−1) ≦ d22 ≦ (7.74λ1 + 0.2λ1) / (n−1)
Meet.

In this example, as shown in FIGS. 14A and 14B, the directions of the first basic structure and the second basic structure are superimposed in different directions.

Further, the first optical path difference providing structure obtained by superimposing the first basic structure and the second basic structure is a seven-part blazed stepped structure as shown in FIG. The length d0 (μm) of the largest step of the structure in the optical axis direction and the length d00 (μm) of the small step of the first optical path difference providing structure in the optical axis direction are as follows:
(6.74λ1-0.2λ1) / (n−1) ≦ d0 ≦ (6.74λ1 + 0.2λ1) / (n−1)
(1.29λ1-0.2λ1) / (n−1) ≦ d00 ≦ (1.29λ1 + 0.2λ1) / (n−1)
Meet. It is more preferable that all the step amounts d0 and d00 of the first optical path difference providing structure in the central region satisfy the above conditional expression. However, in the case of a step away from the optical axis, the aspheric surface of the objective lens is curved. The step amount must be taken into consideration, and the step amounts d0 and d00 of the step away from the optical axis tend to increase gradually, and there may be a step slightly larger than the above conditional expression. Therefore, it is preferable that d0 and d00 closest to the optical axis of the first optical path difference providing structure satisfy at least the above conditional expression.

In this example, | L | = 1, | M | = 2, and | N | = 3 are satisfied, and the signs of L and the signs of M and N are different for positive and negative signs. The signs are equal. L is preferably negative.

In the first optical path difference providing structure of Example 9, the first wavelength of the first light beam is about 405 nm, the second wavelength of the second light beam is about 655 nm, and the third wavelength of the third light beam is about 785 nm. The diffraction efficiency can be about 76% for the first beam, about 76% for the second beam, and about 64% for the third beam. According to this example, the order that cannot be obtained with a normal blazed structure or a diffractive structure with a staircase structure can be set to the maximum diffraction efficiency.

(First optical path difference providing structure example 10)
In Example 10, as shown in FIG.15 (b), the 2nd foundation structure which is a step type structure is a step type structure of 8 divisions. Further, the length d21 (μm) of the small step of the stepped structure of the second basic structure in the optical axis direction, the length d22 (μm) of the large step of the stepped structure of the second basic structure, and As shown in FIG. 15 (a), the length d1 (μm) in the optical axis direction of the step portion of the first basic structure having a blaze structure is defined by the following conditional expression:
(Λ1−0.4λ1) / (n−1) ≦ d1 ≦ (λ1 + 0.4λ1) / (n−1)
(1.13λ1-0.2λ1) / (n−1) ≦ d21 ≦ (1.13λ1 + 0.2λ1) / (n−1)
(7.91λ1-0.2λ1) / (n−1) ≦ d22 ≦ (7.91λ1 + 0.2λ1) / (n−1)
Meet.

In this example, as shown in FIGS. 15A and 15B, the directions of the first basic structure and the second basic structure are superimposed in different directions.

Further, the first optical path difference providing structure obtained by superimposing the first basic structure and the second basic structure is an eight-divided blazed staircase structure as shown in FIG. The length d0 (μm) of the largest step of the structure in the optical axis direction and the length d00 (μm) of the small step of the first optical path difference providing structure in the optical axis direction are as follows:
(6.91λ1-0.2λ1) / (n−1) ≦ d0 ≦ (6.91λ1 + 0.2λ1) / (n−1)
(1.13λ1-0.2λ1) / (n−1) ≦ d00 ≦ (1.13λ1 + 0.2λ1) / (n−1)
Meet. It is more preferable that all the step amounts d0 and d00 of the first optical path difference providing structure in the central region satisfy the above conditional expression. However, in the case of a step away from the optical axis, the aspheric surface of the objective lens is curved. The step amount must be taken into consideration, and the step amounts d0 and d00 of the step away from the optical axis tend to increase gradually, and there may be a step slightly larger than the above conditional expression. Therefore, it is preferable that d0 and d00 closest to the optical axis of the first optical path difference providing structure satisfy at least the above conditional expression.

In this example, | L | = 2, | M | = 2, and | N | = 3 are satisfied, and the signs of L and the signs of M and N are different for positive and negative signs. The signs are equal. Moreover, it is preferable that L is positive.

In the first optical path difference providing structure of Example 10, the first wavelength of the first light beam is about 405 nm, the second wavelength of the second light beam is about 655 nm, and the third wavelength of the third light beam is about 785 nm. The diffraction efficiency can be about 95% for the first beam, about 70% for the second beam, and about 51% for the third beam. According to this example, the order that cannot be obtained with a normal blazed structure or a diffractive structure with a staircase structure can be set to the maximum diffraction efficiency.

(First optical path difference providing structure example 11)
In Example 11, as shown in FIG.16 (b), the 2nd foundation structure which is a step type structure is a step type structure of 8 divisions. Further, the length d21 (μm) of the small step of the stepped structure of the second basic structure in the optical axis direction, the length d22 (μm) of the large step of the stepped structure of the second basic structure, and As shown in FIG. 16 (a), the length d1 (μm) in the optical axis direction of the step portion of the first basic structure having a blaze structure is defined by the following conditional expression:
(3λ1-0.4λ1) / (n−1) ≦ d1 ≦ (3λ1 + 0.4λ1) / (n−1)
(1.37λ1-0.2λ1) / (n−1) ≦ d21 ≦ (1.37λ1 + 0.2λ1) / (n−1)
(9.59λ1-0.2λ1) / (n−1) ≦ d22 ≦ (9.59λ1 + 0.2λ1) / (n−1)
Meet.

In this example, as shown in FIGS. 16A and 16B, the directions of the first basic structure and the second basic structure are superimposed in different directions.

Further, the first optical path difference providing structure obtained by superimposing the first basic structure and the second basic structure is an eight-divided blazed staircase structure as shown in FIG. The length d0 (μm) of the largest step of the structure in the optical axis direction and the length d00 (μm) of the small step of the first optical path difference providing structure in the optical axis direction are as follows:
(6.59λ1-0.2λ1) / (n−1) ≦ d0 ≦ (6.59λ1 + 0.2λ1) / (n−1)
(1.37λ1-0.2λ1) / (n−1) ≦ d00 ≦ (1.37λ1 + 0.2λ1) / (n−1)
Meet. It is more preferable that all the step amounts d0 and d00 of the first optical path difference providing structure in the central region satisfy the above conditional expression. However, in the case of a step away from the optical axis, the aspheric surface of the objective lens is curved. The step amount must be taken into consideration, and the step amounts d0 and d00 of the step away from the optical axis tend to increase gradually, and there may be a step slightly larger than the above conditional expression. Therefore, it is preferable that d0 and d00 closest to the optical axis of the first optical path difference providing structure satisfy at least the above conditional expression.

In this example, L = 0, | M | = 3, and | N | = 4 are satisfied, and the positive and negative signs of M and N are equal. Moreover, it is preferable that M and N are positive.

In the first optical path difference providing structure of Example 11, the first wavelength of the first light beam is about 405 nm, the second wavelength of the second light beam is about 655 nm, and the third wavelength of the third light beam is about 785 nm. The diffraction efficiency can be about 61% for the first beam, about 81% for the second beam, and about 71% for the third beam. According to this example, the order that cannot be obtained with a normal blazed structure or a diffractive structure with a staircase structure can be set to the maximum diffraction efficiency.

(First optical path difference providing structure example 12)
In Example 12, as shown in FIG. 17 (b), the second basic structure having a stepped structure is a nine-stage stepped structure. Further, the length d21 (μm) of the small step of the stepped structure of the second basic structure in the optical axis direction, the length d22 (μm) of the large step of the stepped structure of the second basic structure, and As shown in FIG. 17 (a), the length d1 (μm) in the optical axis direction of the step portion of the first basic structure having a blaze structure is defined by the following conditional expression:
(2λ1-0.4λ1) / (n−1) ≦ d1 ≦ (2λ1 + 0.4λ1) / (n−1)
(1.11λ1-0.2λ1) / (n−1) ≦ d21 ≦ (1.11λ1 + 0.2λ1) / (n−1)
(8.88λ1-0.2λ1) / (n−1) ≦ d22 ≦ (8.88λ1 + 0.2λ1) / (n−1)
Meet.

In this example, as shown in FIGS. 17A and 17B, the directions of the first basic structure and the second basic structure are superimposed in different directions.

Further, the first optical path difference providing structure obtained by superimposing the first basic structure and the second basic structure is a nine-part blazed stepped structure as shown in FIG. The length d0 (μm) of the largest step of the structure in the optical axis direction and the length d00 (μm) of the small step of the first optical path difference providing structure in the optical axis direction are as follows:
(6.88λ1-0.2λ1) / (n−1) ≦ d0 ≦ (6.88λ1 + 0.2λ1) / (n−1)
(1.11λ1-0.2λ1) / (n−1) ≦ d00 ≦ (1.11λ1 + 0.2λ1) / (n−1)
Meet. It is more preferable that all the step amounts d0 and d00 of the first optical path difference providing structure in the central region satisfy the above conditional expression. However, in the case of a step away from the optical axis, the aspheric surface of the objective lens is curved. The step amount must be taken into consideration, and the step amounts d0 and d00 of the step away from the optical axis tend to increase gradually, and there may be a step slightly larger than the above conditional expression. Therefore, it is preferable that d0 and d00 closest to the optical axis of the first optical path difference providing structure satisfy at least the above conditional expression.

In this example, | L | = 1, | M | = 4, | N | = 5 is satisfied, and the positive and negative signs of L, M, and N are equal. L, M, and N are preferably positive.

In the first optical path difference providing structure of Example 12, the first wavelength of the first light beam is about 405 nm, the second wavelength of the second light beam is about 655 nm, and the third wavelength of the third light beam is about 785 nm. The diffraction efficiency can be about 91% for the first beam, about 66% for the second beam, and about 48% for the third beam. According to this example, the order that cannot be obtained with a normal blazed structure or a diffractive structure with a staircase structure can be set to the maximum diffraction efficiency.

(First optical path difference providing structure example 13)
In Example 13, as shown in FIG.18 (b), the 2nd basic structure which is a staircase type structure is a 10-step staircase type structure. Further, the length d21 (μm) of the small step of the stepped structure of the second basic structure in the optical axis direction, the length d22 (μm) of the large step of the stepped structure of the second basic structure, and As shown in FIG. 18 (a), the length d1 (μm) in the optical axis direction of the step portion of the first basic structure having a blaze structure is defined by the following conditional expression:
(2λ1-0.4λ1) / (n−1) ≦ d1 ≦ (2λ1 + 0.4λ1) / (n−1)
(1.2λ1-0.2λ1) / (n−1) ≦ d21 ≦ (1.2λ1 + 0.2λ1) / (n−1)
(10.8λ1-0.2λ1) / (n−1) ≦ d22 ≦ (10.8λ1 + 0.2λ1) / (n−1)
Meet.

In this example, as shown in FIGS. 18A and 18B, the directions of the first basic structure and the second basic structure are superimposed in different directions.

Further, the first optical path difference providing structure obtained by superimposing the first basic structure and the second basic structure is a 10-part blazed staircase structure as shown in FIG. The length d0 (μm) of the largest step of the structure in the optical axis direction and the length d00 (μm) of the small step of the first optical path difference providing structure in the optical axis direction are as follows:
(8.8λ1-0.2λ1) / (n−1) ≦ d0 ≦ (8.8λ1 + 0.2λ1) / (n−1)
(1.2λ1-0.2λ1) / (n−1) ≦ d00 ≦ (1.2λ1 + 0.2λ1) / (n−1)
Meet. It is more preferable that all the step amounts d0 and d00 of the first optical path difference providing structure in the central region satisfy the above conditional expression. However, in the case of a step away from the optical axis, the aspheric surface of the objective lens is curved. The step amount must be taken into consideration, and the step amounts d0 and d00 of the step away from the optical axis tend to increase gradually, and there may be a step slightly larger than the above conditional expression. Therefore, it is preferable that d0 and d00 closest to the optical axis of the first optical path difference providing structure satisfy at least the above conditional expression.

In this example, L = 0, | M | = 4, | N | = 5 is satisfied, and the positive and negative signs of M and N are equal. Moreover, it is preferable that M and N are positive.

In the first optical path difference providing structure of Example 13, the first wavelength of the first light beam is about 405 nm, the second wavelength of the second light beam is about 655 nm, and the third wavelength of the third light beam is about 785 nm. The diffraction efficiency can be about 88% for the first beam, about 76% for the second beam, and about 57% for the third beam. According to this example, the order that cannot be obtained with a normal blazed structure or a diffractive structure with a staircase structure can be set to the maximum diffraction efficiency.

(First optical path difference providing structure example 14)
In Example 14, as shown in FIG. 19B, the second basic structure having a stepped structure is a ten-step divided structure. Further, the length d21 (μm) of the small step of the stepped structure of the second basic structure in the optical axis direction, the length d22 (μm) of the large step of the stepped structure of the second basic structure, and As shown in FIG. 19 (a), the length d1 (μm) in the optical axis direction of the step portion of the first basic structure having a blaze structure is defined by the following conditional expression:
(3λ1-0.4λ1) / (n−1) ≦ d1 ≦ (3λ1 + 0.4λ1) / (n−1)
(1.33λ1-0.2λ1) / (n−1) ≦ d21 ≦ (1.33λ1 + 0.2λ1) / (n−1)
(11.97λ1-0.2λ1) / (n−1) ≦ d22 ≦ (11.97λ1 + 0.2λ1) / (n−1)
Meet.

In this example, as shown in FIGS. 19A and 19B, the directions of the first basic structure and the second basic structure are superimposed in different directions.

Further, the first optical path difference providing structure obtained by superimposing the first basic structure and the second basic structure is a 10-part blazed staircase structure as shown in FIG. The length d0 (μm) of the largest step of the structure in the optical axis direction and the length d00 (μm) of the small step of the first optical path difference providing structure in the optical axis direction are as follows:
(8.97λ1-0.2λ1) / (n−1) ≦ d0 ≦ (8.97λ1 + 0.2λ1) / (n−1)
(1.33λ1-0.2λ1) / (n−1) ≦ d00 ≦ (1.33λ1 + 0.2λ1) / (n−1)
Meet. It is more preferable that all the step amounts d0 and d00 of the first optical path difference providing structure in the central region satisfy the above conditional expression. However, in the case of a step away from the optical axis, the aspheric surface of the objective lens is curved. The step amount must be taken into consideration, and the step amounts d0 and d00 of the step away from the optical axis tend to increase gradually, and there may be a step slightly larger than the above conditional expression. Therefore, it is preferable that d0 and d00 closest to the optical axis of the first optical path difference providing structure satisfy at least the above conditional expression.

In this example, L = 0, | M | = 4, | N | = 5 is satisfied, and the positive and negative signs of M and N are equal. Moreover, it is preferable that M and N are positive.

In the first optical path difference providing structure of Example 14, the first wavelength of the first light beam is about 405 nm, the second wavelength of the second light beam is about 655 nm, and the third wavelength of the third light beam is about 785 nm. The diffraction efficiency can be about 74% for the first beam, about 85% for the second beam, and about 65% for the third beam. According to this example, the order that cannot be obtained with a normal blazed structure or a diffractive structure with a staircase structure can be set to the maximum diffraction efficiency.

(First optical path difference providing structure example 15)
In Example 15, as shown in FIG. 20B, the second basic structure that is a stepped structure is a six-step staircase structure. Further, the length d21 (μm) of the small step of the stepped structure of the second basic structure in the optical axis direction, the length d22 (μm) of the large step of the stepped structure of the second basic structure, and As shown in FIG. 20 (a), the length d1 (μm) in the optical axis direction of the step portion of the first basic structure having a blaze structure is defined by the following conditional expression:
(Λ1−0.4λ1) / (n−1) ≦ d1 ≦ (λ1 + 0.4λ1) / (n−1)
(1.19λ1-0.2λ1) / (n−1) ≦ d21 ≦ (1.19λ1 + 0.2λ1) / (n−1)
(5.95λ1-0.2λ1) / (n−1) ≦ d22 ≦ (5.95λ1 + 0.2λ1) / (n−1)
Meet.

Also, in this example, as shown in FIGS. 20A and 20B, the directions of the first basic structure and the second basic structure are overlapped in the same direction.

Further, the first optical path difference providing structure obtained by superimposing the first basic structure and the second basic structure is a six-part blazed stepped structure as shown in FIG. The length d0 (μm) of the largest step of the structure in the optical axis direction and the length d00 (μm) of the small step of the first optical path difference providing structure in the optical axis direction are as follows:
(6.95λ1-0.2λ1) / (n−1) ≦ d0 ≦ (6.95λ1 + 0.2λ1) / (n−1)
(1.19λ1-0.2λ1) / (n−1) ≦ d00 ≦ (1.19λ1 + 0.2λ1) / (n−1)
Meet. It is more preferable that all the step amounts d0 and d00 of the first optical path difference providing structure in the central region satisfy the above conditional expression. However, in the case of a step away from the optical axis, the aspheric surface of the objective lens is curved. The step amount must be taken into consideration, and the step amounts d0 and d00 of the step away from the optical axis tend to increase gradually, and there may be a step slightly larger than the above conditional expression. Therefore, it is preferable that d0 and d00 closest to the optical axis of the first optical path difference providing structure satisfy at least the above conditional expression.

Also, in this example, | L | = 2, | M | = 1, | N | = 2, and the sign of L is different from the sign of M and N for positive and negative signs. Are equal. Moreover, it is preferable that L is positive.

In the first optical path difference providing structure of Example 15, the first wavelength of the first light beam is about 405 nm, the second wavelength of the second light beam is about 655 nm, and the third wavelength of the third light beam is about 785 nm. The diffraction efficiency can be about 86% for the first beam, about 74% for the second beam, and about 54% for the third beam. According to this example, the order that cannot be obtained with a normal blazed structure or a diffractive structure with a staircase structure can be set to the maximum diffraction efficiency.

(First optical path difference providing structure example 16)
In Example 16, as shown in FIG. 21 (b), the second basic structure having a stepped structure is a four-step stepped structure. Further, the length d21 (μm) of the small step of the stepped structure of the second basic structure in the optical axis direction, the length d22 (μm) of the large step of the stepped structure of the second basic structure, and As shown in FIG. 21 (a), the length d1 (μm) in the optical axis direction of the step portion of the first basic structure having a blaze structure is defined by the following conditional expression:
(Λ1−0.4λ1) / (n−1) ≦ d1 ≦ (λ1 + 0.4λ1) / (n−1)
(3.25λ1-0.2λ1) / (n−1) ≦ d21 ≦ (3.25λ1 + 0.2λ1) / (n−1)
(9.75λ1-0.2λ1) / (n−1) ≦ d22 ≦ (9.75λ1 + 0.2λ1) / (n−1)
Meet.

Further, in this example, as shown in FIGS. 21A and 21B, the directions of the first basic structure and the second basic structure are superimposed in different directions.

The first optical path difference providing structure obtained by superimposing the first basic structure and the second basic structure is a four-part blazed stepped structure as shown in FIG. The length d0 (μm) of the largest step of the structure in the optical axis direction and the length d00 (μm) of the small step of the first optical path difference providing structure in the optical axis direction are as follows:
(8.75λ1-0.2λ1) / (n−1) ≦ d0 ≦ (8.75λ1 + 0.2λ1) / (n−1)
(3.25λ1-0.2λ1) / (n−1) ≦ d00 ≦ (3.25λ1 + 0.2λ1) / (n−1)
Meet. It is more preferable that all the step amounts d0 and d00 of the first optical path difference providing structure in the central region satisfy the above conditional expression. However, in the case of a step away from the optical axis, the aspheric surface of the objective lens is curved. The step amount must be taken into consideration, and the step amounts d0 and d00 of the step away from the optical axis tend to increase gradually, and there may be a step slightly larger than the above conditional expression. Therefore, it is preferable that d0 and d00 closest to the optical axis of the first optical path difference providing structure satisfy at least the above conditional expression.

In this example, L = 0, | M | = 1, | N | = 2, and the positive and negative signs of M and N are equal. Moreover, it is preferable that M and N are positive.

In the first optical path difference providing structure of Example 16, the first wavelength of the first light beam is about 405 nm, the second wavelength of the second light beam is about 655 nm, and the third wavelength of the third light beam is about 785 nm. The diffraction efficiency can be about 81% for the first beam, about 89% for the second beam, and about 61% for the third beam. According to this example, higher diffraction efficiency can be obtained as compared with the stepped structure.

(First optical path difference providing structure example 17)
In Example 17, as shown in FIG.22 (b), the 2nd foundation structure which is a staircase type structure is a 4 stepped staircase type structure. Further, the length d21 (μm) of the small step of the stepped structure of the second basic structure in the optical axis direction, the length d22 (μm) of the large step of the stepped structure of the second basic structure, and As shown in FIG. 22 (a), the length d1 (μm) in the optical axis direction of the step portion of the first basic structure having a blaze structure is defined by the following conditional expression:
(Λ1−0.4λ1) / (n−1) ≦ d1 ≦ (λ1 + 0.4λ1) / (n−1)
(3.22λ1-0.2λ1) / (n−1) ≦ d21 ≦ (3.22λ1 + 0.2λ1) / (n−1)
(9.66λ1-0.2λ1) / (n−1) ≦ d22 ≦ (9.66λ1 + 0.2λ1) / (n−1)
Meet.

In this example, as shown in FIGS. 22A and 22B, the directions of the first basic structure and the second basic structure are overlapped in the same direction.

The first optical path difference providing structure obtained by superimposing the first basic structure and the second basic structure is a four-part blazed stepped structure as shown in FIG. The length d0 (μm) of the largest step of the structure in the optical axis direction and the length d00 (μm) of the small step of the first optical path difference providing structure in the optical axis direction are as follows:
(10.66λ1-0.2λ1) / (n−1) ≦ d0 ≦ (10.66λ1 + 0.2λ1) / (n−1)
(3.22λ1-0.2λ1) / (n−1) ≦ d00 ≦ (3.22λ1 + 0.2λ1) / (n−1)
Meet. It is more preferable that all the step amounts d0 and d00 of the first optical path difference providing structure in the central region satisfy the above conditional expression. However, in the case of a step away from the optical axis, the aspheric surface of the objective lens is curved. The step amount must be taken into consideration, and the step amounts d0 and d00 of the step away from the optical axis tend to increase gradually, and there may be a step slightly larger than the above conditional expression. Therefore, it is preferable that d0 and d00 closest to the optical axis of the first optical path difference providing structure satisfy at least the above conditional expression.

In this example, | L | = 2, M = 0, and | N | = 1 are satisfied, and the signs of L and N are different. Moreover, it is preferable that L is positive.

In the first optical path difference providing structure of Example 17, the first wavelength of the first light beam is about 405 nm, the second wavelength of the second light beam is about 655 nm, and the third wavelength of the third light beam is about 785 nm. The diffraction efficiency can be about 78% for the first beam, about 72% for the second beam, and about 58% for the third beam. According to this example, the order that cannot be obtained with a normal blazed structure or a diffractive structure with a staircase structure can be set to the maximum diffraction efficiency.

(First optical path difference providing structure example 18)
In Example 18, as shown in FIG. 23B, the second basic structure having a stepped structure is a two-step staircase structure (binary structure). Further, the length d21 (μm) of the small step of the stepped structure of the second basic structure in the optical axis direction, the length d22 (μm) of the large step of the stepped structure of the second basic structure, and As shown in FIG. 23 (a), the length d1 (μm) in the optical axis direction of the step portion of the first basic structure having a blaze structure is defined by the following conditional expression:
(2λ1-0.4λ1) / (n−1) ≦ d1 ≦ (2λ1 + 0.4λ1) / (n−1)
(3.05λ1-0.2λ1) / (n−1) ≦ d21 ≦ (3.05λ1 + 0.2λ1) / (n−1)
(3.05λ1-0.2λ1) / (n−1) ≦ d22 ≦ (3.05λ1 + 0.2λ1) / (n−1)
Meet.

Further, in this example, as shown in FIGS. 23A and 23B, the directions of the first basic structure and the second basic structure are overlapped in the same direction.

The first optical path difference providing structure obtained by superimposing the first basic structure and the second basic structure is a two-part blazed stepped structure as shown in FIG. The length d0 (μm) of the largest step of the structure in the optical axis direction and the length d00 (μm) of the small step of the first optical path difference providing structure in the optical axis direction are as follows:
(5.05λ1-0.2λ1) / (n−1) ≦ d0 ≦ (5.05λ1 + 0.2λ1) / (n−1)
(3.05λ1-0.2λ1) / (n−1) ≦ d00 ≦ (3.05λ1 + 0.2λ1) / (n−1)
Meet. It is more preferable that all the step amounts d0 and d00 of the first optical path difference providing structure in the central region satisfy the above conditional expression. However, in the case of a step away from the optical axis, the aspheric surface of the objective lens is curved. The step amount must be taken into consideration, and the step amounts d0 and d00 of the step away from the optical axis tend to increase gradually, and there may be a step slightly larger than the above conditional expression. Therefore, it is preferable that d0 and d00 closest to the optical axis of the first optical path difference providing structure satisfy at least the above conditional expression.

In this example, | L | = 2, | M | = 1, N = 0 are satisfied, and the positive and negative signs of L and M are equal. Moreover, it is preferable that L and M are positive.

In the first optical path difference providing structure of Example 18, the first wavelength of the first light beam is about 405 nm, the second wavelength of the second light beam is about 655 nm, and the third wavelength of the third light beam is about 785 nm. The diffraction efficiency can be about 98% for the first beam, about 91% for the second beam, and about 41% for the third beam. According to this example, the order that cannot be obtained with a normal blazed structure or a diffractive structure with a staircase structure can be set to the maximum diffraction efficiency.

(First optical path difference providing structure example 19)
In Example 19, as shown in FIG. 24B, the second basic structure having a stepped structure is a two-stage stepped structure (binary structure). Further, the length d21 (μm) of the small step of the stepped structure of the second basic structure in the optical axis direction, the length d22 (μm) of the large step of the stepped structure of the second basic structure, and As shown in FIG. 24 (a), the length d1 (μm) in the optical axis direction of the step portion of the first basic structure having a blaze structure is defined by the following conditional expression:
(Λ1−0.4λ1) / (n−1) ≦ d1 ≦ (λ1 + 0.4λ1) / (n−1)
(5λ1-0.2λ1) / (n−1) ≦ d21 ≦ (5λ1 + 0.2λ1) / (n−1)
(5λ1-0.2λ1) / (n−1) ≦ d22 ≦ (5λ1 + 0.2λ1) / (n−1)
Meet.

Further, in this example, as shown in FIGS. 24A and 24B, the directions of the first basic structure and the second basic structure are superimposed in different directions.

The first optical path difference providing structure obtained by superimposing the first basic structure and the second basic structure is a two-part blazed stepped structure as shown in FIG. The length d0 (μm) of the largest step of the structure in the optical axis direction and the length d00 (μm) of the small step of the first optical path difference providing structure in the optical axis direction are as follows:
(5λ1-0.2λ1) / (n−1) ≦ d0 ≦ (5λ1 + 0.2λ1) / (n−1)
(4λ1-0.2λ1) / (n-1) ≦ d00 ≦ (4λ1 + 0.2λ1) / (n−1)
Meet. It is more preferable that all the step amounts d0 and d00 of the first optical path difference providing structure in the central region satisfy the above conditional expression. However, in the case of a step away from the optical axis, the aspheric surface of the objective lens is curved. The step amount must be taken into consideration, and the step amounts d0 and d00 of the step away from the optical axis tend to increase gradually, and there may be a step slightly larger than the above conditional expression. Therefore, it is preferable that d0 and d00 closest to the optical axis of the first optical path difference providing structure satisfy at least the above conditional expression.

In this example, | L | = 1, | M | = 1, N = 0 are satisfied, and the positive and negative signs of L and M are equal. Moreover, it is preferable that L and M are positive.

In the first optical path difference providing structure of Example 19, the first wavelength of the first light beam is about 405 nm, the second wavelength of the second light beam is about 655 nm, and the third wavelength of the third light beam is about 785 nm. The diffraction efficiency can be about 82% for the first beam, about 83% for the second beam, and about 54% for the third beam. According to this example, higher diffraction efficiency can be obtained as compared with the stepped structure.

(First optical path difference providing structure example 20)
In Example 20, as shown in FIG.25 (b), the 2nd foundation structure which is a staircase type structure is a three-step staircase type structure. Further, the length d21 (μm) of the small step of the stepped structure of the second basic structure in the optical axis direction, the length d22 (μm) of the large step of the stepped structure of the second basic structure, and As shown in FIG. 25 (a), the length d1 (μm) in the optical axis direction of the step portion of the first basic structure having a blaze structure is defined by the following conditional expression:
(Λ1−0.4λ1) / (n−1) ≦ d1 ≦ (λ1 + 0.4λ1) / (n−1)
(2λ1-0.2λ1) / (n−1) ≦ d21 ≦ (2λ1 + 0.2λ1) / (n−1)
(4λ1−0.2λ1) / (n−1) ≦ d22 ≦ (4λ1 + 0.2λ1) / (n−1)
Meet.

Further, in this example, as shown in FIGS. 25A and 25B, the directions of the first basic structure and the second basic structure are superimposed in different directions.

Further, the first optical path difference providing structure obtained by superimposing the first basic structure and the second basic structure is a three-part blazed stepped structure as shown in FIG. The length d0 (μm) of the largest step of the structure in the optical axis direction and the length d00 (μm) of the small step of the first optical path difference providing structure in the optical axis direction are as follows:
(3λ1-0.2λ1) / (n−1) ≦ d0 ≦ (3λ1 + 0.2λ1) / (n−1)
(2λ1-0.2λ1) / (n−1) ≦ d00 ≦ (2λ1 + 0.2λ1) / (n−1)
Meet. It is more preferable that all the step amounts d0 and d00 of the first optical path difference providing structure in the central region satisfy the above conditional expression. However, in the case of a step away from the optical axis, the aspheric surface of the objective lens is curved. The step amount must be taken into consideration, and the step amounts d0 and d00 of the step away from the optical axis tend to increase gradually, and there may be a step slightly larger than the above conditional expression. Therefore, it is preferable that d0 and d00 closest to the optical axis of the first optical path difference providing structure satisfy at least the above conditional expression.

In this example, | L | = 1, M = 0, and | N | = 1 are satisfied, and the signs of L and N are equal. Moreover, it is preferable that L and N are positive.

In the first optical path difference providing structure of Example 20, the first wavelength of the first light beam is about 405 nm, the second wavelength of the second light beam is about 655 nm, and the third wavelength of the third light beam is about 785 nm. The diffraction efficiency can be about 100% for the first beam, about 88% for the second beam, and about 44% for the third beam. According to this example, higher diffraction efficiency can be obtained as compared with the stepped structure.

(First optical path difference providing structure example 21)
In Example 21, as shown in FIG.26 (b), the 2nd foundation structure which is a staircase type structure is a three-step staircase type structure. Further, the length d21 (μm) of the small step of the stepped structure of the second basic structure in the optical axis direction, the length d22 (μm) of the large step of the stepped structure of the second basic structure, and As shown in FIG. 26 (a), the length d1 (μm) in the optical axis direction of the step portion of the first basic structure having a blaze structure is defined by the following conditional expression:
(Λ1−0.4λ1) / (n−1) ≦ d1 ≦ (λ1 + 0.4λ1) / (n−1)
(3λ1-0.2λ1) / (n−1) ≦ d21 ≦ (3λ1 + 0.2λ1) / (n−1)
(6λ1-0.2λ1) / (n−1) ≦ d22 ≦ (6λ1 + 0.2λ1) / (n−1)
Meet.

Further, in this example, as shown in FIGS. 26A and 26B, the directions of the first basic structure and the second basic structure are superimposed in different directions.

Further, the first optical path difference providing structure obtained by superimposing the first basic structure and the second basic structure is a three-part blazed staircase structure as shown in FIG. The length d0 (μm) of the largest step of the structure in the optical axis direction and the length d00 (μm) of the small step of the first optical path difference providing structure in the optical axis direction are as follows:
(5λ1-0.2λ1) / (n−1) ≦ d0 ≦ (5λ1 + 0.2λ1) / (n−1)
(3λ1-0.2λ1) / (n−1) ≦ d00 ≦ (3λ1 + 0.2λ1) / (n−1)
Meet. It is more preferable that all the step amounts d0 and d00 of the first optical path difference providing structure in the central region satisfy the above conditional expression. However, in the case of a step away from the optical axis, the aspheric surface of the objective lens is curved. The step amount must be taken into consideration, and the step amounts d0 and d00 of the step away from the optical axis tend to increase gradually, and there may be a step slightly larger than the above conditional expression. Therefore, it is preferable that d0 and d00 closest to the optical axis of the first optical path difference providing structure satisfy at least the above conditional expression.

In this example, | L | = 1, | M | = 1, | N | = 2, and the signs of L, M, and N are equal. L, M, and N are preferably positive.

In the first optical path difference providing structure of Example 21, the first wavelength of the first light beam is about 405 nm, the second wavelength of the second light beam is about 655 nm, and the third wavelength of the third light beam is about 785 nm. The diffraction efficiency can be about 100% for the first beam, about 80% for the second beam, and about 40% for the third beam. According to this example, the order that cannot be obtained with a normal blazed structure or a diffractive structure with a staircase structure can be set to the maximum diffraction efficiency.

In addition to the first optical path difference providing structure provided in the central area of the objective lens, when the second optical path difference providing structure is provided in the peripheral area of the objective lens, it may be provided on different optical surfaces of the objective lens, but the same It is preferably provided on the optical surface. Providing them on the same optical surface is preferable because it makes it possible to reduce eccentricity errors during manufacturing. Moreover, it is preferable that the first optical path difference providing structure and the second optical path difference providing structure are provided on the light source side surface of the objective lens rather than the optical disk side surface of the objective lens.

The objective lens condenses the first light beam, the second light beam, and the third light beam that pass through the central region where the first optical path difference providing structure of the objective lens is provided so as to form a condensed spot. Preferably, the objective lens is capable of recording and / or reproducing information on the information recording surface of the first optical disc, with the first light beam passing through the central region provided with the first optical path difference providing structure of the objective lens. Condensate. In addition, the objective lens collects the second light flux that passes through the central region where the first optical path difference providing structure of the objective lens is provided so that information can be recorded and / or reproduced on the information recording surface of the second optical disc. Shine. Further, the objective lens collects the third light flux that passes through the central region where the first optical path difference providing structure of the objective lens is provided so that information can be recorded and / or reproduced on the information recording surface of the third optical disc. Shine. In addition, when the thickness t1 of the protective substrate of the first optical disc and the thickness t2 of the protective substrate of the second optical disc are different, the first optical path difference providing structure includes the first light flux passing through the first optical path difference providing structure and the second optical flux. It occurs due to the spherical aberration generated by the difference between the thickness t1 of the protective substrate of the first optical disk and the thickness t2 of the protective substrate of the second optical disk and / or the difference in the wavelengths of the first and second light beams. It is preferable to correct spherical aberration. Further, the first optical path difference providing structure has a thickness t1 of the protective substrate of the first optical disc and a thickness of the protective substrate of the third optical disc with respect to the first light beam and the third light beam that have passed through the first optical path difference providing structure. It is preferable to correct spherical aberration generated due to a difference from t3 and / or spherical aberration generated due to a difference in wavelength between the first light flux and the third light flux.

When the focal length of the first light beam of the objective lens is f1 (mm) and the center thickness of the objective lens is d (mm), the following formula (7),
0.7 ≦ d / f1 ≦ 2.0 (7)
It is preferable to satisfy.

In addition, the following formula (7) ′,
1.0 ≦ d / f1 ≦ 1.5 (7) ′
It is more preferable to satisfy.

With the above configuration, the working distance of the CD as the third optical disk can be secured without reducing the pitch of the optical path difference providing structure, and the objective lens can be easily manufactured. In addition, the light use efficiency is increased. Can be maintained.

Moreover, it is preferable to satisfy the following conditional expressions.
2.1mm ≦ Φ ≦ 4.2mm
Φ represents the effective diameter of the objective lens when the first optical disk is used. By satisfying the above range, the working distance of the CD as the third optical disk is secured at a distance that does not cause a problem in practical use, and even if the objective lens is a plastic lens, for example, the aberration change when the temperature changes It can be maintained at a problem-free level.

Further, when the objective lens is provided with the second optical path difference providing structure, the objective lens condenses the first light flux and the second light flux that pass through the peripheral region so as to form a condensed spot, respectively. To do. Preferably, the objective lens is capable of recording and / or reproducing information on the information recording surface of the first optical disc, with the first light flux passing through the peripheral region provided with the second optical path difference providing structure of the objective lens. Condensate. Further, when the objective lens is provided with the second optical path difference providing structure, the objective lens records the information on the information recording surface of the second optical disk and / or records the second light flux that passes through the peripheral region. Light is collected so that it can be regenerated. Further, it is preferable that the second optical path difference providing structure corrects chromatic spherical aberration caused by a difference in wavelength between the first light beam and the second light beam that pass through the second optical path difference providing structure.

Also, as a preferred mode, there is a mode in which the third light flux that has passed through the peripheral area is not used for recording and / or reproduction of the third optical disk. It is preferable that the third light flux that has passed through the peripheral region does not contribute to the formation of a focused spot on the information recording surface of the third optical disc. That is, when the objective lens is provided with the second optical path difference providing structure, it is preferable that the third light flux passing through the peripheral region thereby forms a flare on the information recording surface of the third optical disc. As shown in FIG. 4, in the spot formed on the information recording surface of the third optical disc by the third light flux that has passed through the objective lens, the light amount density is high in the order from the optical axis side (or the spot center) to the outside. The spot center portion SCN, the spot intermediate portion SMD whose light intensity density is lower than that of the spot center portion, and the spot peripheral portion SOT whose light intensity density is higher than that of the spot intermediate portion and lower than that of the spot center portion. The center portion of the spot is used for recording and / or reproducing information on the optical disc, and the spot intermediate portion and the spot peripheral portion are not used for recording and / or reproducing information on the optical disc. In the above, this spot peripheral part is called flare. That is, it is preferable that the third light flux that has passed through the second optical path difference providing structure provided in the peripheral region of the objective lens forms a spot peripheral portion on the information recording surface of the third optical disc. However, even if the flare is not as described above, there may be a spot peripheral portion around the spot center portion where the light density is high and there is no spot middle portion, and the light spot density is lower than the spot center portion. The periphery of the spot is called flare. In addition, it is preferable that the condensing spot or spot of a 3rd light beam here is a spot in 1st best focus.

Moreover, as a preferable aspect in the case of having the outermost peripheral area, the first light flux that has passed through the outermost peripheral area is used for recording and / or reproduction of the first optical disc, and the second and third light fluxes that have passed through the outermost peripheral area. Includes an aspect that is not used for recording and / or reproduction of the second optical disc and the third optical disc. It is preferable that the second light flux and the third light flux that have passed through the outermost peripheral region do not contribute to the formation of a condensed spot on the information recording surfaces of the second optical disc and the third optical disc, respectively. That is, when the objective lens has the outermost peripheral area, the second light flux and the third light flux that pass through the outermost peripheral area of the objective lens preferably form a flare on the information recording surfaces of the second optical disc and the third optical disc. . In other words, it is preferable that the second light flux and the third light flux that have passed through the most peripheral area of the objective lens form a spot peripheral portion on the information recording surface of the second optical disc and the third optical disc.

When the outermost peripheral region has the third optical path difference providing structure, the third optical path difference providing structure is generated by a slight variation in the wavelength of the first light source with respect to the first light flux that has passed through the third optical path difference providing structure. Spherochromatism (chromatic spherical aberration) may be corrected. A slight change in wavelength refers to a change within ± 10 nm. For example, when the first light beam changes by ± 5 nm from the wavelength λ1, the third optical path difference providing structure compensates for the variation in spherical aberration of the first light beam that has passed through the most peripheral region, and on the information recording surface of the first optical disc. It is preferable that the amount of change in the wavefront aberration at 0.001λ2 rms or more and 0.070λ2 rms or less.

The second optical path difference providing structure may be a single stepped structure or a single blazed structure, or a blazed structure and a rougher (large pitch) blazed structure are superimposed. The structure which becomes may be sufficient. When the second optical path difference providing structure is the superposition structure, the first wavelength λ1 of the first light flux is used for the blaze structure (in the case of the second optical path difference providing structure, a diffractive structure that is not rough (small pitch)). An optical path difference corresponding to an even multiple of the first light flux may be imparted to the first light flux so that the phase of the wavefront of the first light flux does not change. Further, when the third wavelength λ3 of the third light flux is a wavelength that is substantially an even multiple of the first wavelength of the first light flux, an optical path difference of an integral multiple is given to the third light flux. There is no change in the phase of the wavefront of the three light beams. With such a configuration, there is an advantage that the first light flux and the third light flux are not affected by the diffraction structure. Note that “even multiples” means a range of (2n−0.1) × λ1 or more and (2n + 0.1) × λ1 or less when n is a natural number.

Note that by forming the first optical path difference providing structure by superimposing the first basic structure and the second basic structure, all of the first, second, and third light beams that have passed through the first optical path difference providing structure are output. Since the directions of the incident light can be made different, even if all the first, second, and third light beams are incident on the objective lens with the same imaging magnification (for example, all parallel light beams), they are different. Aberrations caused by using different types of optical discs can be corrected, and compatibility is possible.

When the objective lens is a plastic lens, the third basic structure as the temperature characteristic correcting structure may be further overlapped with the first basic structure and the second basic structure as the first optical path difference providing structure. However, when the first optical disc is an HD, the influence of temperature change is not so great, so that the objective lens does not have to be provided with a basic structure as a temperature characteristic correcting structure. Specifically, the step difference in the optical axis direction of the third basic structure gives an optical path difference of about 10 wavelengths of the first wavelength to the first light flux, and about 6 of the second wavelength to the second light flux. It is preferable that the difference in level be such that an optical path difference corresponding to the wavelength is given and an optical path difference equivalent to about 5 wavelengths of the third wavelength is given to the third light flux.

Further, when the objective lens is a plastic lens, the basic structure may be used as the temperature characteristic correcting structure, and the stacked structure may be used as the second optical path difference providing structure. However, when the first optical disc is an HD, the influence of temperature change is not so great, so that the objective lens does not have to be provided with a basic structure as a temperature characteristic correcting structure. Specifically, the step difference in the optical axis direction of the third basic structure gives an optical path difference corresponding to approximately five wavelengths of the first wavelength to the first light flux, and approximately the second wavelength relative to the second light flux. It is preferable that the step amount is such that an optical path difference for three wavelengths is given and an optical path difference for about two wavelengths of the third wavelength is given to the third light flux.

In the case where the outermost peripheral region is provided and the objective lens is made of plastic, it is preferable to further provide the third optical path difference providing structure in the outermost peripheral region. It is good also as a structure which has a basic structure.

As described above, it is preferable that the level difference is not too large. If the level difference of the annular zone with the optical path difference providing structure that is the basis obtained by superimposing multiple foundation structures is higher than the reference value, the level difference of the annular zone is only 10 · λB / (n-1) (μm) By making it low, it becomes possible to reduce an excessively large step amount without affecting the optical performance. An arbitrary value can be set as the reference value, but it is preferable to set 10 · λB / (n−1) (μm) as the reference value.

Further, from the viewpoint that it is preferable from the viewpoint of production that the number of elongated ring zones is small, it is preferable that the value of (step amount / pitch width) is 1 or less in all the ring zones of the first optical path difference providing structure, and more preferable. Is 0.8 or less. More preferably, the value of (step difference / pitch width) is preferably 1 or less, and more preferably 0.8 or less, in all annular zones of all optical path difference providing structures.

The objective-side numerical aperture of the objective lens necessary for reproducing and / or recording information on the first optical disk is NA1, and the objective lens necessary for reproducing and / or recording information on the second optical disk The image-side numerical aperture is NA2 (NA1 ≧ NA2), and the image-side numerical aperture of the objective lens necessary for reproducing and / or recording information on the third optical disk is NA3 (NA2> NA3). NA1 is preferably 0.6 or more and 0.9 or less. In particular, NA1 is preferably 0.85. NA2 is preferably 0.55 or more and 0.7 or less. In particular, NA2 is preferably 0.60 or 0.65. NA3 is preferably 0.4 or more and 0.55 or less. In particular, NA3 is preferably 0.45 or 0.53.

The boundary between the central region and the peripheral region of the objective lens is 0.9 · NA3 or more and 1.2 · NA3 or less (more preferably 0.95 · NA3 or more, 1.15 · NA3) when the third light flux is used. It is preferably formed in a portion corresponding to the following range. More preferably, the boundary between the central region and the peripheral region of the objective lens is formed in a portion corresponding to NA3. The boundary between the peripheral area and the most peripheral area of the objective lens is 0.9 · NA 2 or more and 1.2 · NA 2 or less (more preferably 0.95 · NA 2 or more, 1. 15 · NA2 or less) is preferable. More preferably, the boundary between the peripheral region and the most peripheral region of the objective lens is formed in a portion corresponding to NA2.

When the third light flux that has passed through the objective lens is condensed on the information recording surface of the third optical disc, it is preferable that the spherical aberration has at least one discontinuous portion. In that case, the discontinuous portion has a range of 0.9 · NA 3 or more and 1.2 · NA 3 or less (more preferably 0.95 · NA 3 or more and 1.15 · NA 3 or less) when the third light flux is used. It is preferable that it exists in.

In addition, when spherical aberration is continuous and does not have a discontinuous portion and the third light flux that has passed through the objective lens is condensed on the information recording surface of the third optical disc, NA2 It is preferable that the absolute value of the spherical aberration is 0.03 μm or more, and in NA3, the absolute value of the longitudinal spherical aberration is 0.02 μm or less. More preferably, in NA2, the absolute value of longitudinal spherical aberration is 0.08 μm or more, and in NA3, the absolute value of longitudinal spherical aberration is 0.01 μm or less.

Also, the diffraction efficiency for each wavelength in the central region can be set as appropriate according to the use of the optical pickup device. For example, in the case of an optical pickup device that performs recording and reproduction on the first optical disc and only reproduction on the second and third optical discs, the diffraction efficiency of the central region and / or the peripheral region is expressed as It is preferable to set with emphasis. On the other hand, in the case of an optical pickup device that performs only reproduction with respect to the first optical disc and performs recording and reproduction with respect to the second and third optical discs, the second and third light fluxes are emphasized with respect to the diffraction efficiency of the central region. It is preferable to set the diffraction efficiency of the peripheral region with the second light flux as important.

In any case, by satisfying the following conditional expression (9), it is possible to ensure high diffraction efficiency of the first light flux calculated by the area weighted average of each region.
η11 ≦ η21 (9)
However, η11 represents the diffraction efficiency of the first light flux in the central region, and η21 represents the diffraction efficiency of the first light flux in the peripheral region. When the diffraction efficiency of the central region is focused on the light fluxes of the second and third wavelengths, the diffraction efficiency of the first light flux of the central region is low, but the numerical aperture of the first optical disc is the numerical aperture of the third optical disc. If it is larger than, the lowering of the diffraction efficiency in the central region does not have a significant effect when considering the entire effective diameter of the first light flux.

In addition, the diffraction efficiency in this specification can be defined as follows.
[1] The transmittance of an objective lens that has the same focal length, lens thickness, and numerical aperture, is formed of the same material, and does not have the first and second optical path difference providing structures is formed in the central region and the peripheral region. Separately measure. At this time, the transmittance of the central region is measured by blocking the light beam incident on the peripheral region, and the transmittance of the peripheral region is measured by blocking the light beam incident on the central region.
[2] The transmittance of the objective lens having the first and second optical path difference providing structures is measured separately for the central region and the peripheral region.
[3] The value obtained by dividing the result of [2] by the result of [1] is the diffraction efficiency of each region.

The light utilization efficiency of any two of the first to third light fluxes is 70% or more, and the light utilization efficiency of the remaining one light flux is 30% or more and 70% or less. Good. The light utilization efficiency of the remaining one light beam may be 40% or more and 60% or less. In this case, it is preferable that the light beam having the light use efficiency of 30% or more and 70% or less (or 40% or more and 60% or less) is the third light beam.

Here, the light utilization efficiency is the information recording on the optical disk by the objective lens in which the first optical path difference providing structure is formed (the second optical path difference providing structure and the third optical path difference providing structure may be formed). The amount of light in the Airy disk of the focused spot formed on the surface is A, and the first optical path is formed from the same material and has the same focal length, axial thickness, numerical aperture, and wavefront aberration. The amount of light in the Airy disk of the focused spot formed on the information recording surface of the optical information recording medium by the objective lens in which the difference providing structure, the second optical path difference providing structure, and the third optical path difference providing structure are not formed is defined as B. When calculating by A / B. Here, the Airy disk refers to a circle having a radius r ′ centered on the optical axis of the focused spot. r ′ = 0.61 · λ / NA.

The first light beam, the second light beam, and the third light beam may be incident on the objective lens as parallel light, or may be incident on the objective lens as divergent light or convergent light. Preferably, the imaging magnification m1 of the objective lens when the first light beam enters the objective lens is expressed by the following formula (1),
-0.02 <m1 <0.02 (1)
Is to satisfy.

On the other hand, when the first light flux is incident on the objective lens as diverging light, the imaging magnification m1 of the objective lens when the first light flux is incident on the objective lens is expressed by the following equation (1 ′),
-0.10 <m1 <0 (1 ')
It is preferable to satisfy.

Further, when the second light flux is incident on the objective lens as parallel light or substantially parallel light, the imaging magnification m2 of the objective lens when the second light flux is incident on the objective lens is expressed by the following equation (2):
-0.02 <m2 <0.02 (2)
It is preferable to satisfy.

On the other hand, when the second light flux is incident on the objective lens as diverging light, the imaging magnification m2 of the objective lens when the second light flux is incident on the objective lens is expressed by the following equation (2 ′):
-0.10 <m2 <0 (2 ')
It is preferable to satisfy.

In addition, when the third light beam is incident on the objective lens as parallel light or substantially parallel light, the imaging magnification m3 of the objective lens when the third light beam enters the objective lens satisfies the following expression (3). Is preferred. When the third light flux is parallel light, a problem easily occurs in tracking. However, even if the third light flux is parallel light, the present invention can obtain good tracking characteristics, and can be used for three different optical disks. On the other hand, recording and / or reproduction can be appropriately performed.
-0.02 <m3 <0.02 (3)
On the other hand, when the third light beam is incident on the objective lens as diverging light, the imaging magnification m3 of the objective lens when the third light beam enters the objective lens is expressed by the following equation (3 ′):
-0.10 <m3 <0 (3 ')
It is preferable to satisfy.

The working distance (WD) of the objective lens when using the third optical disk is preferably 0.20 mm or more and 1.5 mm or less. Preferably, it is 0.3 mm or more and 1.20 mm or less. Next, the WD of the objective lens when using the second optical disk is preferably 0.4 mm or more and 1.3 mm or less. Further, the WD of the objective lens when using the first optical disk is preferably 0.4 mm or more and 1.2 mm or less.

An optical information recording / reproducing apparatus according to the present invention includes an optical disc drive apparatus having the above-described optical pickup apparatus.

Here, the optical disk drive apparatus provided in the optical information recording / reproducing apparatus will be described. The optical disk drive apparatus can hold an optical disk mounted from the optical information recording / reproducing apparatus main body containing the optical pickup apparatus or the like. There are a system in which only the tray is taken out, and a system in which the optical disc drive apparatus main body in which the optical pickup device is stored is taken out to the outside.

The optical information recording / reproducing apparatus using each method described above is generally equipped with the following components, but is not limited thereto.

An optical pickup device housed in a housing or the like, a drive source of an optical pickup device such as a seek motor that moves the optical pickup device together with the housing toward the inner periphery or outer periphery of the optical disc, and the optical pickup device housing the inner periphery or outer periphery of the optical disc These include a transfer means of an optical pickup device having a guide rail or the like that guides toward the head, a spindle motor that rotates the optical disk, and the like.

In addition to these components, the former method is provided with a tray that can be held in a state in which an optical disk is mounted and a loading mechanism for sliding the tray, and the latter method has no tray and loading mechanism. It is preferable that each component is provided in a drawer corresponding to a chassis that can be pulled out to the outside.

According to the present invention, the desired optical characteristics can be exhibited, the molding die configuration can be prevented from becoming too complicated, the transferability can be improved, and the configuration can be simplified and reduced in cost. It is possible to provide a possible objective lens and an optical pickup device using the same.

(A) is the figure which looked at an example of objective-lens OBJ which concerns on this invention from the optical axis direction, (b) is sectional drawing. FIG. 3 is a cross-sectional view schematically showing several examples (a) to (d) of an optical path difference providing structure provided in the objective lens OBJ according to the present invention. It is a figure which shows the superimposition of the optical path difference providing structure. It is the figure which showed the shape of the spot by the objective lens which concerns on this invention. It is a figure which shows schematically the structure of the optical pick-up apparatus which concerns on this invention. In the optical path difference providing structure according to Example 1, (a) a cross section of the first basic structure, (b) a cross section of the second basic structure, and (c) a cross section of the superimposed optical path difference providing structure. In the optical path difference providing structure according to Example 2, (a) a cross section of the first basic structure, (b) a cross section of the second basic structure, and (c) a cross section of the superimposed optical path difference providing structure. In the optical path difference providing structure according to Example 3, (a) a cross section of the first basic structure, (b) a cross section of the second basic structure, and (c) a cross section of the superimposed optical path difference providing structure. In the optical path difference providing structure according to Example 4, (a) a cross section of the first basic structure, (b) a cross section of the second basic structure, and (c) a cross section of the superimposed optical path difference providing structure. In the optical path difference providing structure according to Example 5, (a) a cross section of the first basic structure, (b) a cross section of the second basic structure, and (c) a cross section of the superimposed optical path difference providing structure. In the optical path difference providing structure according to Example 6, (a) a cross section of the first basic structure, (b) a cross section of the second basic structure, (c) a cross section of the superimposed optical path difference providing structure. In the optical path difference providing structure according to Example 7, (a) a cross section of the first basic structure, (b) a cross section of the second basic structure, and (c) a cross section of the superimposed optical path difference providing structure. In the optical path difference providing structure according to Example 8, (a) a cross section of the first basic structure, (b) a cross section of the second basic structure, (c) a cross section of the superimposed optical path difference providing structure. In the optical path difference providing structure according to Example 9, (a) a cross section of the first basic structure, (b) a cross section of the second basic structure, (c) a cross section of the superimposed optical path difference providing structure. In the optical path difference providing structure according to Example 10, (a) a cross section of the first basic structure, (b) a cross section of the second basic structure, and (c) a cross section of the superimposed optical path difference providing structure. In the optical path difference providing structure according to Example 11, (a) a cross section of the first basic structure, (b) a cross section of the second basic structure, and (c) a cross section of the superimposed optical path difference providing structure. In the optical path difference providing structure according to Example 12, (a) a cross section of the first basic structure, (b) a cross section of the second basic structure, and (c) a cross section of the superimposed optical path difference providing structure. In the optical path difference providing structure according to Example 13, (a) a cross section of the first basic structure, (b) a cross section of the second basic structure, and (c) a cross section of the superimposed optical path difference providing structure. In the optical path difference providing structure according to Example 14, (a) a cross section of the first basic structure, (b) a cross section of the second basic structure, and (c) a cross section of the superimposed optical path difference providing structure. In the optical path difference providing structure according to Example 15, (a) a cross section of the first basic structure, (b) a cross section of the second basic structure, and (c) a cross section of the superimposed optical path difference providing structure. In the optical path difference providing structure according to Example 16, (a) a cross section of the first basic structure, (b) a cross section of the second basic structure, (c) a cross section of the superimposed optical path difference providing structure. In the optical path difference providing structure according to Example 17, (a) a cross section of the first basic structure, (b) a cross section of the second basic structure, (c) a cross section of the superimposed optical path difference providing structure. In the optical path difference providing structure according to Example 18, (a) a cross section of the first basic structure, (b) a cross section of the second basic structure, and (c) a cross section of the superimposed optical path difference providing structure. In the optical path difference providing structure according to Example 19, (a) the cross section of the first basic structure, (b) the cross section of the second basic structure, (c) the cross section of the superimposed optical path difference providing structure. In the optical path difference providing structure according to Example 20, (a) a cross section of the first basic structure, (b) a cross section of the second basic structure, and (c) a cross section of the superimposed optical path difference providing structure. In the optical path difference providing structure according to Example 21, (a) a cross section of the first basic structure, (b) a cross section of the second basic structure, (c) a cross section of the superimposed optical path difference providing structure.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 5 is a diagram schematically showing a configuration of the optical pickup device PU1 of the present embodiment that can appropriately record and / or reproduce information on BD, DVD, and CD, which are different optical disks. Such an optical pickup device PU1 can be mounted on an optical information recording / reproducing device. Here, the first optical disc is a BD, the second optical disc is a DVD, and the third optical disc is a CD. The present invention is not limited to the present embodiment.

The optical pickup device PU1 emits a laser beam (first beam) having a wavelength λ1 = 405 nm that is emitted when information is recorded / reproduced with respect to the objective lens OBJ, aperture ST, collimator lens CL, dichroic prism PPS, and BD. A unit MD1, a laser module LM, and the like in which a first semiconductor laser LD1 (first light source) and a first light receiving element PD1 that receives a reflected light beam from the information recording surface RL1 of the BD are integrated.

The laser module LM includes a second semiconductor laser EP1 (second light source) that emits a laser beam (second beam) having a wavelength λ2 = 658 nm and is emitted when information is recorded / reproduced with respect to a DVD, and a CD. A third semiconductor laser EP2 (third light source) that emits a laser beam (third beam) having a wavelength λ3 = 785 nm and is reflected from the information recording surface RL2 of the DVD. It has a second light receiving element DS1 that receives the light beam, a third light receiving element DS2 that receives the reflected light beam from the information recording surface RL3 of the CD, and a prism PS.

As shown in FIGS. 1A and 1B, in the objective lens OBJ of the present embodiment, a central region CN including the optical axis on the aspherical optical surface on the light source side, and a peripheral region disposed around the central region CN The MD and the outermost peripheral region OT disposed around the MD are formed concentrically around the optical axis. Although not shown, a first optical path difference providing structure in which the first basic structure and the second basic structure are superimposed is formed in the central area CN, and a second optical path difference providing structure is formed in the peripheral area MD. Yes. In the outermost peripheral region OT, there are a structure in which the third optical path difference providing structure is formed and a structure in which the third optical path difference providing structure is not formed and a refractive surface. In the first optical path difference providing structure, for example, the 0th-order diffracted light amount of the first light beam that has passed is made larger than any other order diffracted light amount, and the second-order diffracted light amount of the second light beam is made any other order of diffraction A structure in which the third-order diffracted light quantity of the third light beam is made larger than any other order diffracted light quantity can be used, but examples of the first optical path difference providing structure in this specification are 1 to Any of those described in 21 can be used. Furthermore, the second optical path difference providing structure and the third optical path difference providing structure can be arbitrarily selected according to the first optical path difference providing structure. For example, when the first optical path difference providing structure is Example 1 described above, the second optical path difference providing structure is preferably a structure in which the fourth basic structure and the fifth basic structure are superimposed. The fourth basic structure has a structure that maximizes the first-order diffracted light amount in the first light beam and the second light beam, the fifth basic structure has the maximum zero-order diffracted light amount in the first light beam, and the second light beam is − A structure that maximizes the first-order diffracted light amount is preferable. Moreover, when it has a 3rd optical path difference providing structure, it is preferable that the 3rd optical path difference providing structure is formed only by the 7th foundation structure. The seventh basic structure is a blazed structure in which the second-order diffracted light amount of the first light beam that has passed is made larger than any other order of diffracted light amount, and the first-order diffracted light amount of the second light beam is made to be any other The first order diffracted light amount of the third light flux is made larger than any other order diffracted light amount. Note that the ratios of the areas of the central region, the peripheral region, and the outermost peripheral region in FIGS. 1A and 1B are not accurately represented.

The divergent light beam of the first light beam (λ1 = 405 nm) emitted from the blue-violet semiconductor laser LD1 is transmitted through the dichroic prism PPS, converted into a parallel light beam by the collimator lens CL, and then linearly polarized by a λ1 / 4 wavelength plate (not shown). To circularly polarized light, the diameter of the light beam is regulated by the stop ST, and enters the objective lens OBJ. Here, the light beam condensed by the central region, the peripheral region, and the outermost peripheral region of the objective lens OBJ is a spot formed on the information recording surface RL1 of the BD via the protective substrate PL1 having a thickness of 0.1 mm. Become.

The reflected light beam modulated by the information pits on the information recording surface RL1 passes through the objective lens OBJ and the aperture stop ST again, is converted from circularly polarized light to linearly polarized light by a λ1 / 4 wavelength plate (not shown), and is converged by the collimating lens CL. After being transmitted through the dichroic prism PPS, it is converged on the light receiving surface of the first light receiving element PD1. Then, by using the output signal of the first light receiving element PD1 to focus or track the objective lens OBJ by the biaxial actuator AC, it is possible to read information recorded on the BD.

The divergent light beam of the second light beam (λ2 = 658 nm) emitted from the red semiconductor laser EP1 is reflected by the prism PS, then reflected by the dichroic prism PPS, converted into a parallel light beam by the collimator lens CL, and then λ1 (not shown). Polarized light is converted by the / 4 wavelength plate and enters the objective lens OBJ. Here, the light beam condensed by the central region and the peripheral region of the objective lens OBJ (the light beam that has passed through the most peripheral region is flared and forms a spot peripheral part) is passed through the protective substrate PL2 having a thickness of 0.6 mm. Thus, the spot is formed on the information recording surface RL2 of the DVD, and the center of the spot is formed.

The reflected light beam modulated by the information pits on the information recording surface RL2 is again transmitted through the objective lens OBJ and the aperture stop ST, is then polarized by a λ1 / 4 wave plate (not shown), is converted into a convergent light beam by the collimator lens CL, and is dichroic. After being reflected by the prism PPS, then after being reflected twice in the prism, it converges on the second light receiving element DS1. The information recorded on the DVD can be read using the output signal of the second light receiving element DS1. It should be noted that the light utilization efficiency can be increased by performing polarization conversion with the λ1 / 4 wavelength plate in the round-trip path as compared with the case where there is no λ1 / 4 wavelength plate.

The divergent light beam of the third light beam (λ3 = 785 nm) emitted from the infrared semiconductor laser EP2 is reflected by the prism PS, then reflected by the dichroic prism PPS, converted into a parallel light beam by the collimator lens CL, and is not shown in the figure. Polarized light is converted by the λ1 / 4 wave plate and enters the objective lens OJT. Here, the light beam condensed by the central region of the objective lens OBJ (the light beam that has passed through the peripheral region and the most peripheral region is flared and forms a spot peripheral part) is passed through the protective substrate PL3 having a thickness of 1.2 mm. Thus, the spot is formed on the information recording surface RL3 of the CD.

The reflected light beam modulated by the information pits on the information recording surface RL3 is again transmitted through the objective lens OBJ and the aperture stop ST, and then is converted by the λ1 / 4 wavelength plate (not shown), and is converted into a convergent light beam by the collimator lens CL. After being reflected by the prism PPS, then after being reflected twice in the prism, it converges on the third light receiving element DS2. The information recorded on the CD can be read using the output signal of the third light receiving element DS2. It should be noted that the light utilization efficiency can be increased by performing polarization conversion with the λ1 / 4 wavelength plate in the round-trip path as compared with the case where there is no λ1 / 4 wavelength plate.

AC biaxial actuator PPS dichroic prism CL collimating lens LD1 blue-violet semiconductor laser LM laser module OBJ objective lens PL1 protective substrate PL2 protective substrate PL3 protective substrate PU1 optical pickup device RL1 information recording surface RL2 information recording surface RL3 information recording surface CN central region MD Peripheral area OT Most peripheral area

Claims (23)

Using a first light beam having a wavelength λ1 (μm) emitted from the first light source, a condensing spot is formed on the information recording surface of the first optical disc having a protective layer having a thickness t1, and emitted from the second light source. Using a second light beam having a wavelength λ2 (λ1 <λ2), a condensing spot is formed on the information recording surface of the second optical disc having a protective layer having a thickness t2 (t1 ≦ t2) and emitted from the third light source. For an optical pickup device that forms a condensing spot on the information recording surface of a third optical disc having a protective layer with a thickness t3 (t2 <t3) using a third light beam having a wavelength λ3 (λ2 <λ3). In the objective lens,
A first optical path difference providing structure is formed on the optical surface of the objective lens,
The first optical path difference providing structure includes a first basic structure that is a blaze type structure and a second basic structure that is a staircase type structure, the positions of all the step portions of the first basic structure, and the second basic structure. Is superimposed so that the position of the step part of
L-th order diffracted light has the largest amount of diffracted light among the diffracted light generated when the first light flux is incident on the first optical path difference providing structure when L, M, and N are arbitrary integers, Of the diffracted light generated when the second light beam is incident on the first optical path difference providing structure, the Mth order diffracted light has the largest amount of diffracted light, and the third light beam is incident on the first optical path difference providing structure. An objective lens, wherein the Nth-order diffracted light among the diffracted light generated in this case has the maximum amount of diffracted light. The second foundation structure is a four-step staircase structure, and the length d21 (μm) of a small step in the optical axis direction of the step structure of the second foundation structure is large and the step structure of the second foundation structure is large. The length d22 (μm) in the optical axis direction of the step and the length d1 (μm) in the optical axis direction of the step portion of the first basic structure satisfy the following conditional expression. Objective lens described in 1.
(1.2λ1-0.4λ1) / (n−1) ≦ d1 ≦ (1.2λ1 + 0.4λ1) / (n−1)
(1.25λ1-0.2λ1) / (n−1) ≦ d21 ≦ (1.25λ1 + 0.2λ1) / (n−1)
(3.75λ1-0.2λ1) / (n−1) ≦ d22 ≦ (3.75λ1 + 0.2λ1) / (n−1)
However, n represents the refractive index of the objective lens in the first light flux. The first optical path difference providing structure is a four-divided blaze step structure, and the length d0 (μm) of the largest step of the first optical path difference providing structure in the optical axis direction satisfies the following conditional expression: The objective lens according to claim 1 or 2, characterized in that
(4.95λ1-0.2λ1) / (n−1) ≦ d0 ≦ (4.95λ1 + 0.2λ1) / (n−1) | L | = 2, M = 0, | N | = 1
The objective lens according to any one of claims 1 to 3, wherein L and N have different signs. The second foundation structure is a six-step staircase structure, and the length d21 (μm) in the optical axis direction of the small step of the step structure of the second foundation structure and the step structure of the second foundation structure are large. The length d22 (μm) in the optical axis direction of the step and the length d1 (μm) in the optical axis direction of the step portion of the first basic structure satisfy the following conditional expression. Objective lens described in 1.
(Λ1−0.4λ1) / (n−1) ≦ d1 ≦ (λ1 + 0.4λ1) / (n−1)
(1.2λ1-0.2λ1) / (n−1) ≦ d21 ≦ (1.2λ1 + 0.2λ1) / (n−1)
(6λ1-0.2λ1) / (n−1) ≦ d22 ≦ (6λ1 + 0.2λ1) / (n−1)
However, n represents the refractive index of the objective lens in the first light flux. The first optical path difference providing structure is a four-divided blaze step structure, and the length d0 (μm) of the largest step of the first optical path difference providing structure in the optical axis direction satisfies the following conditional expression: The objective lens according to claim 1 or 5, characterized in that
(5λ1-0.2λ1) / (n−1) ≦ d0 ≦ (5λ1 + 0.2λ1) / (n−1) Satisfy L = 0, | M | = 2, | N | = 3,
The objective lens according to claim 1, wherein M and N have the same sign. The second foundation structure is a seven-step staircase structure, and the length d21 (μm) in the optical axis direction of a small step of the step structure of the second foundation structure is larger than the step structure of the second foundation structure. The length d22 (μm) in the optical axis direction of the step and the length d1 (μm) in the optical axis direction of the step portion of the first basic structure satisfy the following conditional expression. Objective lens described in 1.
(3λ1-0.4λ1) / (n−1) ≦ d1 ≦ (3λ1 + 0.4λ1) / (n−1)
(1.31λ1-0.2λ1) / (n−1) ≦ d21 ≦ (1.31λ1 + 0.2λ1) / (n−1)
(7.86λ1-0.2λ1) / (n−1) ≦ d22 ≦ (7.86λ1 + 0.2λ1) / (n−1)
However, n represents the refractive index of the objective lens in the first light flux. The first optical path difference providing structure is a seven-part blazed stepped structure, and the length d0 (μm) in the optical axis direction of the largest step of the first optical path difference providing structure satisfies the following conditional expression: The objective lens according to claim 1 or 5, characterized in that
(4.86λ1-0.2λ1) / (n−1) ≦ d0 ≦ (4.86λ1 + 0.2λ1) / (n−1) | L | = 1, | M | = 3, | N | = 4,
The objective lens according to claim 1, wherein L, M, and N have the same sign. The optical surface of the objective lens includes at least a ring-shaped central region including an optical axis, a ring-shaped peripheral region formed around the central region, and a ring-shaped outermost region formed around the peripheral region. Has a surrounding area,
The first light flux that has passed through the central area, the peripheral area, and the most peripheral area is condensed on the information recording surface of the first optical disc,
The second light flux that has passed through the central area and the peripheral area is condensed on the information recording surface of the second optical disc,
The third light flux that has passed through the central region is condensed on the information recording surface of the third optical disc,
The objective lens according to any one of claims 1 to 10, wherein the first optical path difference providing structure is provided in the central region. Using a first light beam having a wavelength λ1 (μm) emitted from the first light source, a condensing spot is formed on the information recording surface of the first optical disc having a protective layer having a thickness t1, and emitted from the second light source. Using a second light beam having a wavelength λ2 (λ1 <λ2), a condensing spot is formed on the information recording surface of the second optical disc having a protective layer having a thickness t2 (t1 ≦ t2) and emitted from the third light source. And an objective lens for forming a condensing spot on the information recording surface of the third optical disk having a protective layer having a thickness of t3 (t2 <t3) using a third light beam of wavelength λ3 (λ2 <λ3). In the optical pickup device,
A first optical path difference providing structure is formed on the optical surface of the objective lens,
The first optical path difference providing structure includes a first basic structure that is a blaze type structure and a second basic structure that is a staircase type structure, the positions of all the step portions of the first basic structure, and the second basic structure. Is superimposed so that the position of the step part of
L-th order diffracted light has the largest amount of diffracted light among the diffracted light generated when the first light flux is incident on the first optical path difference providing structure when L, M, and N are arbitrary integers, Of the diffracted light generated when the second light beam is incident on the first optical path difference providing structure, the Mth order diffracted light has the largest amount of diffracted light, and the third light beam is incident on the first optical path difference providing structure. An optical pickup device characterized in that the Nth order diffracted light has the maximum amount of diffracted light among the diffracted light generated. The second foundation structure is a four-step staircase structure, and the length d21 (μm) of a small step in the optical axis direction of the step structure of the second foundation structure is large and the step structure of the second foundation structure is large. The length d22 (μm) in the optical axis direction of the step and the length d1 (μm) in the optical axis direction of the step portion of the first basic structure satisfy the following conditional expression. The optical pickup device described in 1.
(1.2λ1-0.4λ1) / (n−1) ≦ d1 ≦ (1.2λ1 + 0.4λ1) / (n−1)
(1.25λ1-0.4λ1) / (n−1) ≦ d21 ≦ (1.25λ1 + 0.4λ1) / (n−1)
(3.75λ1-0.4λ1) / (n−1) ≦ d22 ≦ (3.75λ1 + 0.4λ1) / (n−1)
However, n represents the refractive index of the objective lens in the first light flux. The first optical path difference providing structure is a four-divided blaze step structure, and the length d0 (μm) of the largest step of the first optical path difference providing structure in the optical axis direction satisfies the following conditional expression: The optical pickup device according to claim 12 or 13, characterized in that:
(4.95λ1-0.4λ1) / (n−1) ≦ d0 ≦ (4.95λ1 + 0.4λ1) / (n−1) | L | = 2, M = 0, | N | = 1
The optical pickup device according to any one of claims 12 to 14, wherein L and N have different positive and negative signs. The second foundation structure is a six-step staircase structure, and the length d21 (μm) in the optical axis direction of the small step of the step structure of the second foundation structure and the step structure of the second foundation structure are large. The length d22 (μm) in the optical axis direction of the step and the length d1 (μm) in the optical axis direction of the step portion of the first basic structure satisfy the following conditional expression. The optical pickup device described in 1.
(Λ1−0.4λ1) / (n−1) ≦ d1 ≦ (λ1 + 0.4λ1) / (n−1)
(1.2λ1-0.4λ1) / (n−1) ≦ d21 ≦ (1.2λ1 + 0.4λ1) / (n−1)
(6λ1-0.4λ1) / (n−1) ≦ d22 ≦ (6λ1 + 0.4λ1) / (n−1)
However, n represents the refractive index of the objective lens in the first light flux. The first optical path difference providing structure is a four-divided blaze step structure, and the length d0 (μm) of the largest step of the first optical path difference providing structure in the optical axis direction satisfies the following conditional expression: The optical pickup device according to claim 12 or 16, characterized in that:
(5λ1-0.4λ1) / (n−1) ≦ d0 ≦ (5λ1 + 0.4λ1) / (n−1) Satisfy L = 0, | M | = 2, | N | = 3,
18. The optical pickup device according to claim 12, 16 or 17, wherein the signs of M and N are equal. The second foundation structure is a seven-step staircase structure, and the length d21 (μm) in the optical axis direction of a small step of the step structure of the second foundation structure is larger than the step structure of the second foundation structure. The length d22 (μm) in the optical axis direction of the step and the length d1 (μm) in the optical axis direction of the step portion of the first basic structure satisfy the following conditional expression. The optical pickup device described in 1.
(3λ1-0.4λ1) / (n−1) ≦ d1 ≦ (3λ1 + 0.4λ1) / (n−1)
(1.31λ1-0.4λ1) / (n−1) ≦ d21 ≦ (1.31λ1 + 0.4λ1) / (n−1)
(7.86λ1-0.4λ1) / (n−1) ≦ d22 ≦ (7.86λ1 + 0.4λ1) / (n−1)
However, n represents the refractive index of the objective lens in the first light flux. The first optical path difference providing structure is a seven-part blazed stepped structure, and the length d0 (μm) in the optical axis direction of the largest step of the first optical path difference providing structure satisfies the following conditional expression: The optical pickup device according to claim 12 or 19, characterized in that:
(4.86λ1-0.4λ1) / (n−1) ≦ d0 ≦ (4.86λ1 + 0.4λ1) / (n−1) | L | = 1, | M | = 3, | N | = 4,
21. The optical pickup device according to claim 12, 19 or 20, wherein the signs of L, M, and N are equal. The optical surface of the objective lens includes at least a ring-shaped central region including an optical axis, a ring-shaped peripheral region formed around the central region, and a ring-shaped outermost region formed around the peripheral region. Has a surrounding area,
The first light flux that has passed through the central area, the peripheral area, and the most peripheral area is condensed on the information recording surface of the first optical disc,
The second light flux that has passed through the central area and the peripheral area is condensed on the information recording surface of the second optical disc,
The third light flux that has passed through the central region is condensed on the information recording surface of the third optical disc,
The optical pickup device according to any one of claims 12 to 21, wherein the first optical path difference providing structure is provided in the central region. The imaging magnification m1 of the objective lens when the first light beam is incident on the objective lens satisfies the following formula (1), and the objective lens when the second light beam is incident on the objective lens. The imaging magnification m2 satisfies the following formula (2), and the imaging magnification m3 of the objective lens satisfies the following formula (3) when the third light beam enters the objective lens. The optical pickup device according to any one of claims 12 to 22.
-0.02 <m1 <0.02 (1)
-0.02 <m2 <0.02 (2)
-0.02 <m3 <0.02 (3)

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