JP2001283459A - Optical pickup device and objective lens for optical pickup device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an objective lens made of a resin material capable of securing sufficient performance against a temperature change in a use environment and capable of forming a finite conjugate optical system, and an optical pickup device using the objective lens. provide. In an optical pickup device, a low-cost and compact device configuration is achieved by configuring a finite conjugate optical system with a single resin objective lens.
In addition, by correcting the amount of axial spherical aberration change due to environmental temperature change on the base surface (envelope surface of the diffraction pattern) on the objective lens 160 and correcting spherical aberration on at least one diffraction surface, It is possible to suppress a change in on-axis spherical aberration caused by a change in refractive index due to a temperature change, which is a disadvantage of the resin lens.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical pickup device and a resin objective lens, and more particularly, to an optical pickup device suitably used for recording and / or reproduction of an optical information recording medium using an objective lens having improved temperature characteristics and aberration. And an objective lens thereof.

[0002]

2. Description of the Related Art An optical system for recording / reproducing an optical information recording medium having the accuracy required in a conventional CD reproducing apparatus (here, a recording / reproducing optical system)
The recording / reproducing optical system or the recording / reproducing apparatus referred to in this specification includes a recording optical system, a reproducing optical system, an optical system for both recording and reproduction, or an apparatus using them). Type optical system is disclosed in JP-A-57-76512, and a finite conjugate type optical system is disclosed in JP-A-61-56.
No. 314, etc. In order to reduce the occurrence of aberration due to a temperature change when a resin objective lens is used, a lens using a coupling lens is disclosed in
No. 58573. However, in recent years, due to demands for cost reduction and the like, lenses formed using a resin (plastic) material have been widely used for a recording / reproducing optical system, particularly for its objective lens.

However, in an objective lens formed of a resin material, there is a problem that an aberration generated by a change in refractive index due to a change in temperature is larger than that of a lens formed of a glass material. Generally, the change in the refractive index differs by one or more digits between the resin material and the glass material. Here, assuming that the temperature difference between the reference design temperature and the actual use environment is ΔT, the aberration that changes due to the temperature difference ΔT is mainly a third-order spherical aberration. The third-order spherical aberration component of wavefront aberration represented by rms value is defined as SA. Here, the sign is defined as SA> 0 when the spherical aberration is positive (over) and SA <0 when the spherical aberration is negative (under). . Temperature change ΔT
The third-order spherical aberration ΔSA (λrms) changed by
Using the numerical aperture NA of the objective lens on the optical information recording medium side (image side), the focal length f, the imaging magnification m, the proportionality coefficient k, and the light wavelength λ, ΔSA / ΔT = k · f (1-m) ⁴ (NA) ⁴ / λ (1). When the lens made of a resin material has a positive refractive power, the third-order spherical aberration becomes larger when the temperature rises. That is, the above equation (1)
In, the coefficient k has a positive value. When a single lens formed of a resin material is used as the objective lens, the coefficient k has a larger positive value.

[0004] In an objective lens for a compact disk which is widely used at present, since the NA is about 0.45, it can be said that the aberration generated due to the temperature change of the use environment does not reach a level that causes a problem. . However, as the density of the optical information recording medium is being promoted, the objective lens constituting the optical system of the recording / reproducing apparatus is also required to correspond thereto.

More specifically, a CD is used as an optical information recording medium.
A DVD (storage capacity: 4.7 GB), which is about the same size as (storage capacity: 640 MB) and has an increased recording density, has been developed.
It is spreading rapidly. To play a DVD,
In general, a laser beam having a predetermined wavelength whose light source has a wavelength in the range of 635 nm to 660 nm is used.
In general, a divergent light beam from a laser light source is converted into a parallel light beam by a collimating lens and then incident on an objective lens having a DVD side NA of 0.6 or more, and information is recorded through a transparent substrate of the DVD. Focused on the surface.

In particular, recently, an optical information recording medium similar to a CD or DVD having a storage capacity of 10 to 30 GB using an objective lens with a higher NA and a shorter wavelength light source has been actively developed. Promising short-wavelength light sources include a GaN blue semiconductor laser and an SHG blue laser with an oscillation wavelength of about 400 nm. In other words, the optical system in the recording / reproducing apparatus is required to have a high NA and to correspond to a laser beam having a shorter wavelength.

Considering this from the wavefront aberration, in the above equation (1), for example, the NA increases from 0.45 to 0.6, and the wavelength λ of the laser beam changes from 660 nm to 400 nm.
, The wavefront aberration Wrms becomes (0.6 /
0.45) ⁴ ÷ 400/660 = 5.17 times increase.

Here, in order to suppress the wavefront aberration based on the equation (1), it is conceivable to reduce the focal length f. However, in reality, it is necessary to secure a focusing working distance, so It is difficult to make it smaller. Further, in a finite conjugate optical system where m <0 or an infinite conjugate optical system where m = 0, in the case of a high NA, an aberration generated due to a temperature change has become a more serious problem. It is conceivable to improve the temperature characteristics by setting 0 <m <1 in an optical system using a coupling lens, but in this case, in order to secure a working distance necessary for focusing, the distance between the object and the image of the optical system is required. Or a coupling lens with a high NA is required, and the optical system and the apparatus are increased in size.

[0009]

As described above, in a conventional lens system using an objective lens formed of a resin material, an image of the objective lens caused by a change in the refractive index Δn of the resin material caused by a temperature change. Due to the occurrence of aberration proportional to the fourth power of the numerical aperture NA on the side, it has been difficult to realize a high NA optical system.

Therefore, in an optical system of an optical information recording / reproducing apparatus for achieving high-density information recording by shortening the wavelength of a laser light source and increasing the NA of an objective lens, instead of using a resin objective lens, Although the change in the refractive index with respect to a change in temperature is small, it is necessary to use a glass mold lens or a combination lens of glass which is more expensive.

To solve such a problem, see, for example,
No. 1-337818 discloses an objective lens for an optical head.
By providing a diffractive lens structure having predetermined spherical aberration characteristics,
A technique for correcting an aberration with respect to a temperature change is disclosed.

However, in order to reduce the size and cost of a recording / reproducing apparatus for an optical information recording medium, there is also a demand for reducing the number of lenses in a condensing optical system. In order to satisfy such demands, it is necessary to form a so-called finite conjugate optical system with one objective lens. However, the objective lens disclosed in Japanese Patent Application Laid-Open No. 11-337818
It does not correspond to a finite conjugate optical system.

The present invention provides an objective lens made of a resin material capable of securing sufficient performance against a temperature change in a use environment and capable of forming a finite conjugate optical system, and an optical pickup device using such an objective lens. The purpose is to:

[0014]

In order to achieve the above object, an optical pickup device according to claim 1 has a wavelength λ1.
(Nm) a light source for emitting a light beam of (nm), and a condensing optics including an objective lens for condensing the light beam emitted from the light source on an information recording surface of the optical information recording medium via a transparent substrate of the optical information recording medium. And a photodetector for receiving light reflected from the optical information recording medium, wherein the objective lens is a plastic lens, and has a diffraction pattern on at least one surface of the objective lens. Where NA (1) is the numerical aperture on the optical information recording medium side and mo1 is the imaging magnification of the objective lens, NA (1) ≧ 0.49 (1) −l / 2 ≦ mo1 ≦ −1 / While satisfying 7.5 (2), the amount of change in axial spherical aberration of the condensing optical system with respect to a temperature change ΔT (° C.) in an environmental temperature range of 20 ° C. to 30 ° C. is defined as ΔSA1. Sometimes | △ SA1 / △ T | ≦ 0.00005λr And satisfies the s / ° C (3).

Third-order spherical aberration with respect to a temperature change of a resin positive lens of which spherical aberration is corrected, such as an aspherical resin single objective lens without a diffraction pattern, which is often used for recording / reproducing of an optical information recording medium. Is given by the following equation, where ΔSA / ΔT is ∂SA / ∂T = (∂SA / ∂n) ・ (∂n / ∂T) + (∂SA / ∂n) ・ (∂n / ∂λ) ・ (∂λ / ∂T) = (∂SA / (∂n) ｛(∂n / ∂T) + (∂n / ∂λ) · (∂λ / ∂T)｝ (4) Here, the resin material is (∂n / ∂T) <0, (∂ n / ∂
λ) <0. The glass material is (∂n / ∂T) = 0,
(∂n / ∂λ) <0. The semiconductor laser is (∂λ /
(∂T)> 0, (∂λ / ∂T) = 0 for SHG lasers, solid-state lasers, gas lasers and the like.

Here, (∂n / ∂T) of the glass material is set to 0, and (∂λ) of an SHG laser, a solid laser, a gas laser or the like.
/ ∂T) was set to 0, but in fact these values are not exactly 0. However, in the field of application of the present invention, it is considered practically 0, and the description can be simplified thereby.

Now, the light source or SHG laser, solid state laser,
In the case of a gas laser or the like and (∂λ / ∂T) = 0, ∂SA / ∂T = (∂SA / n) · (∂n / ∂T) (5)

If this lens is made of glass, (∂n /
Since ∂T) = 0, ∂SA / ∂T = 0. On the other hand, if the lens is made of resin, (∂n / ∂T) <0, and since this type of lens has ∂SA / ∂T> 0, (∂SA / ∂n) <0. . When the light source is a semiconductor laser, (∂λ / ∂T)> 0.

At this time, even when the lens is made of glass, ∂SA / ∂T = (∂SA / ∂n) ・ (∂n / ∂λ) ・ (∂λ / ∂T) (6). Since ∂n / ∂λ) <0 and (∂SA / ∂n) <0, ∂SA / ∂T> 0.

Regardless of the glass material or the resin material, when the incident light has a shorter length, the absolute value of (∂n / ∂λ) increases. Therefore, when using a semiconductor laser having a short wavelength, it is necessary to pay attention to the temperature change of the spherical aberration even if the material is a glass material.

On the other hand, for a single lens made of an aspherical resin having a diffraction pattern, the amount of change in the amount of third-order spherical aberration with respect to temperature change is formulated as ∂SA / ∂T as follows. In this case, it is necessary to incorporate both the characteristics of the refractive lens portion and the characteristics of the diffraction pattern surface. Subscript R to the amount of change in the amount of spherical aberration contributed by the refracting lens portion, SA: Change in the amount of spherical aberration to be contributed by the diffraction pattern surface ∂S
A can be expressed as shown below with a lacquered letter D attached. _{∂SA / ∂T = (∂SA R /} ∂n) · (∂n / ∂T) + (∂SA R / ∂n) · (∂n / ∂λ) · (∂λ / ∂T) + (∂ SA _D / ∂λ) ・ (∂λ / ∂T) (7) Here, when the light source is an SHG laser, a solid-state laser, a gas laser, or the like, and (∂λ / ∂T) = 0, _{∂T = (∂SA R / ∂n)} · (∂n / ∂T) (8) is satisfied.

[0022] In the case of a glass lens, of course, (∂n / ∂T) = 0, and regardless of the value of _{(∂SA R / ∂n), ∂SA} / ∂T = 0 . On the other hand, if the lens is made of resin, (∂n / ∂T) <0, but (∂S
If A _R / ∂n) = 0, then ∂SA / ∂T = 0.

[0023] Therefore, in the present invention, in order to the (∂SA R _/ ∂n) = 0 with respect to a refractive lens portion, it introduces a diffraction pattern to the non-spherical resin single lens. However, in this case, spherical aberration remains only in the refractive lens portion. However, by optimizing the diffraction pattern and correcting the spherical aberration as a whole, an objective lens suitable for recording and reproduction of the optical information recording medium can be obtained. Can be designed.

On the other hand, when the light source is a semiconductor laser, (∂λ
/ ∂T)> 0, the (case of ∂SA _R / ∂n) = 0 of the objective lens having a characteristic, ∂SA the above equation (7) / ∂T = (∂SA D / ∂λ) · (∂λ / ∂T) (9 ) and becomes generally a _{(∂SA D / ∂λ) ≠ 0} , it can be seen that the third order spherical aberration is changed by temperature.

Further, the above equation (7) can be modified as the following equation. _{∂SA / ∂T = (∂SA R /} ∂n) · {(∂n / ∂T) + (∂n / ∂λ) · (∂λ / ∂T)} + (∂SA D / ∂λ) · (∂λ / ∂T) (10)

Here, in the case of a resin lens, (ΔSA /
(∂T) <0, and since the light source is a semiconductor laser, (∂λ / ∂T)> 0, so that (∂n / ∂T) + (∂n / ∂λ) · (∂λ / ∂T) <0 (11)

The assumption, if the _{(∂SA R / ∂n) <0} , the first term is a positive value (11) from (10).
In order to set ∂SA / ∂T = 0, the second term must take a negative value, but since (∂λ / ∂T)> 0, (∂SA
_D / ∂λ) <0.

[0028] In the aspherical plastic single lens having a diffraction pattern of such properties, (∂λ / ∂T) = 0, in the above equation (8) (∂SA _R / ∂n) <0 And since (∂n / ∂T) <0, ∂SA / ∂T> 0.

Further, a temperature is constant, spherical aberration ∂SA / ∂λ when only the wavelength is _{changed, ∂SA / ∂λ = (∂SA R} / ∂n) · (∂n / ∂λ) + ( ∂SA _D / ∂λ) (12) where the first term is positive and the second term is negative. As is well known, the chromatic aberration of an aspheric single lens having a diffraction pattern is mainly Since the contribution from the diffraction pattern is large, the sign of ∂SA / ∂λ is generally determined by the second term of the above equation (12), and ∂SA / ∂λ <0 is generally satisfied.

That is, in a resin single lens in which a diffraction pattern is introduced, ΔSA / ΔT> 0 and ΔSA / Δλ <
By setting it to 0, ∂SA / ∂T = 0 can be achieved even when the light source is a semiconductor laser.

[0031] If conversely the (∂SA _R / ∂n)> 0 for the calculation is omitted in ∂SA / ∂T <0 and ∂SA / ∂λ>
By setting it to 0, ∂SA / ∂T = 0 can be achieved even when the light source is a semiconductor laser.

That is, it is only necessary that the signs of ∂SA / ∂T and ∂SA / ∂λ are opposite. At this time, the relationship of (∂SA / ∂T) · (∂SA / ∂λ) <0 (13) holds. Here, (∂SA / ∂T)> 0
Is more preferable because the load on the diffraction pattern is small because it is closer to the characteristics of an aspherical resin single lens having no diffraction pattern. According to the present invention, there is provided an objective lens capable of ensuring sufficient performance even with a temperature change in a use environment.

In an optical pickup device for recording and / or reproducing information on an optical information recording medium having a recording density equal to or less than that of a DVD, the objective lens uses an aspherical surface or a diffractive surface. , A single lens. In such a case, the objective lens forms a finite conjugate optical system that satisfies Expression (2). −l / 2 ≦ mo1 ≦ −1 / 7.5 (2)

As described above, if the objective lens can be formed as a single lens, the optical pickup device can be made more compact.

The optical pickup device according to claim 2 is
The amount of wavelength change of the light source with respect to a temperature change ΔT (° C.) within an environment temperature range of 20 ° C. to 30 ° C. is represented by Δλ1.
(Nm), 0 ≦ △ λ1 / △ T ≦ 0.5 nm / ° C (14) Therefore, the amount of change in spherical aberration with respect to a change in environmental temperature can be suppressed to be smaller, and inexpensive. The use of a semiconductor laser becomes possible.

The optical pickup device according to claim 3 is
At a wavelength of λ1 (nm), an ambient temperature of 20 ° C. to 3 ° C.
When the amount of change in the refractive index of the plastic lens material with respect to a temperature change ΔT (° C.) within a range of 0 ° C. is denoted by Δn1, −0.0002 / ° C <Δn1 / ΔT <− Since 0.00005 / ° C (15), a resin having good transmittance can be used as a material of the objective lens.

The optical pickup device according to claim 4 is
When the objective lens is driven in the direction perpendicular to the optical axis of the objective lens for tracking, the relative position with respect to the light source changes, and the astigmatic component of the wavefront aberration of the light beam emitted from the objective lens is minimized. Is a position where the optical axis of the objective lens and the center of the light beam of the light source are displaced, so that the range in which the astigmatism component is lower than a predetermined value can be expanded.

The optical pickup device according to claim 5 is
Assuming that the distance between the light source and the information recording surface of the optical information recording medium is U, 10 mm <U <40 mm (16) is satisfied, so that a more compact optical pickup device can be provided.

The optical pickup device according to claim 6 is:
A first light source having a wavelength λ1 (nm) and a wavelength λ2 (nm)
A second light source (λ2> λ1) and light beams emitted from the first light source and the second light source are collected on an information recording surface of the optical information recording medium via a transparent substrate of the optical information recording medium. A light-collecting optical system including an objective lens that emits light, and a photodetector that receives reflected light of the light flux emitted from the first light source and the second light source from the optical information recording medium; The first light beam from the light source records and / or reproduces information on the first optical information recording medium having the transparent substrate having a thickness of t1, and the second light beam from the second light source causes the transparent substrate to have a thickness of t1. Records and / or reproduces information on a second optical information recording medium at t2, wherein the objective lens is a plastic lens, and has a diffraction pattern on at least one surface of the objective lens; For recording or reproducing a recording medium at wavelength λ1 The necessary numerical aperture of the converging optical system on the optical information recording medium side is NA1, and the necessary converging optical system is on the optical information recording medium side for recording or reproducing the second optical information recording medium at wavelength λ2. When the required numerical aperture of the objective lens is NA2, t1 <t2NA1> NA2, the numerical aperture of the objective lens on the optical information recording medium side with respect to the first light flux is NA (1), and the first numerical aperture of the objective lens is When the imaging magnification with respect to the light flux is mol, NA (1) ≧ 0.56 (17) −1 / 5 ≦ mo1 ≦ −1 / 7.5 (18) is satisfied, and the ambient temperature is 20 ° C. to 30 ° C. When the amount of change in the on-axis spherical aberration of the condensing optical system with respect to the temperature change ΔT (° C.) within the range of ° C. is denoted by ΔSA1, | ΔSA1 / ΔT | ≦ 0.0005λrms / ° C. Since (19) is satisfied, light sources of different wavelengths The aberration can be properly corrected even if the light beam is used, and a finite conjugate optical system can be configured with one objective lens. Therefore, a more compact optical pickup device at lower cost is provided.

The optical pickup device according to claim 7 is
The imaging magnification of the objective lens with respect to the second light flux is mo2
| Mo2-mo1 | <0.10 (20)

The optical pickup device according to claim 8 is
It is characterized by having an optical multiplexing means capable of multiplexing the first light beam and the second light beam, for example, a beam splitter.

The optical pickup device according to the ninth aspect is
An aperture limiting means for transmitting a first light beam, transmitting a central portion of the second light beam and blocking an outer region in an optical path through which the first light beam and the second light beam pass in common. It is characterized by the following.

An optical pickup device according to a tenth aspect is characterized in that the aperture limiting means is integrated with an objective lens.

The optical pickup device according to claim 11, wherein the aperture limiting means integrated with the objective lens is provided on one surface of the objective lens, the first light beam is transmitted, and the second light beam is transmitted. Among them, the central portion is a partial dichroic coating that transmits light and reflects an outer region.

An optical pickup device according to a twelfth aspect is characterized in that the diffraction pattern is provided only on one surface of the objective lens, and the partial dichroic coating is applied on a surface having no diffraction pattern. Is what you do.

The optical pickup device according to a thirteenth aspect is characterized in that the partial dichroic coating has a reflectance of 30% to 70% for a light beam having a wavelength λ2.

In the optical pickup device according to the present invention, both surfaces of the objective lens have a diffraction pattern,
The aperture limiting means integrated with the objective lens includes a partial diffraction pattern that transmits a first light beam on one surface of the objective lens, transmits a central portion of the second light beam, and diffracts an outer region. It is characterized by being.

According to a fifteenth aspect of the present invention, in the optical pickup device, the light beam incident on the information recording surface is formed of at least an inner light beam near an optical axis, an intermediate light beam outside the inner light beam, and an outer light beam outside the intermediate light beam. When divided into three light beams, a beam spot is formed by mainly using an inner light beam and an outer light beam among the light beams from the first light source, and information is recorded on the first optical information recording medium. Recording and / or reproducing information on / from the second optical information recording medium by forming a beam spot by mainly utilizing an inner light beam and an intermediate light beam of the light beam from the second light source. It is the feature of doing.

The optical pickup device according to claim 16, wherein the third-order spherical aberration of wavefront aberration in an inner area of the light beam from the second light source, which is incident on the information recording surface of the second optical information recording medium. The component is characterized by being under.

An optical pickup device according to a seventeenth aspect is characterized in that the photodetector is common to the first light source and the second light source.

In the optical pickup device according to the eighteenth aspect, the photodetector separately includes a first photodetector for a first light source and a second photodetector for a second light source. , Are located at spatially separated positions.

In an optical pickup device according to a nineteenth aspect, at least a pair of the first light source and the first light detector or a pair of the second light source and the second light detector is unitized. It is a feature.

According to a twentieth aspect of the present invention, in the optical pickup device, the first light source, the second light source, and a common light detector (single light detector) are unitized. Things.

According to a twenty-first aspect, in the optical pickup device, in the photodetector, the first photodetector for the first light source and the second photodetector for the second light source are provided separately. Yes,
The first light source, the second light source, the first light detector, and the second light detector are unitized.

An optical pickup device according to a twenty-second aspect is characterized in that the first light source and the second light source are unitized, and are located at a position spatially separated from the photodetector. Is what you do.

According to a twenty-third aspect of the present invention, in the optical pickup device, the luminous flux from the light source is diverged in at least one of an optical path from the first light source to the objective lens and an optical path from the second light source to the objective lens. It is characterized by including a coupling lens for reducing the degree.

According to a twenty-fourth aspect of the present invention, in the optical pickup device, a light source having a wavelength λ1 (nm) and a light beam emitted from the light source are transmitted through a transparent substrate of the optical information recording medium to an information recording surface of the optical information recording medium. A condensing optical system including an objective lens for converging light thereon, and a photodetector for receiving reflected light of the light beam emitted from the light source from the optical information recording medium, and a light beam from the light source, Information is recorded or reproduced on a first optical information recording medium having a thickness of t1 and a second optical information recording medium having a thickness of a transparent substrate of t2, wherein the objective lens is a plastic lens, and at least one of the objective lenses The first optical information recording medium has a diffraction pattern on one surface, and the necessary numerical aperture on the optical information recording medium side of the condensing optical system necessary for recording or reproducing the first optical information recording medium at the wavelength λ1 is NA1, Optical information recording medium When a required numerical aperture on the optical information recording medium side of the condensing optical system necessary for recording or reproducing the light at the wavelength λ1 is NA2, t1 <t2 NA1> NA2, and the imaging magnification of the objective lens Is expressed as mo1, −1 / 5 ≦ mo1 ≦ −1 / 7.5 (22) and a temperature change ΔT (° C.) in the range of the ambient temperature of 20 ° C. to 30 ° C. Assuming that the amount of change in the on-axis spherical aberration of the condensing optical system is △ SA1, | △ SA1 / △ T | ≦ 0.0005λrms / ° C (23) is satisfied, and the recording of the second optical information recording medium is further performed. And / or at the time of reproduction, there is an aperture limiting means for transmitting the central portion of the light beam from the light source and blocking the outer region, so that the aberration is appropriately corrected even if the light beam from the light source of a different wavelength is used,
In addition, since a finite conjugate optical system can be constituted by one objective lens, a compact optical pickup device at lower cost is provided.

The objective lens according to claim 25 has a wavelength λ.
A light source that emits a 1 (nm) light beam, and an objective lens that focuses the light beam emitted from the light source on an information recording surface of the optical information recording medium via a transparent substrate of the optical information recording medium. An objective lens for an optical pickup device having an optical system and a photodetector receiving light reflected from the optical information recording medium, wherein the objective lens is a plastic lens, and at least one surface of the objective lens is provided. Has a diffraction pattern, the numerical aperture of the objective lens on the optical information recording medium side is NA (1), and the imaging magnification of the objective lens is mo.
When it is set to 1, NA (1) ≧ 0.49 (1) −l / 2 ≦ mo1 ≦ −1 / 7.5 (2) is satisfied and the ambient temperature is within the range of 20 ° C. to 30 ° C. Since | SA1 / ΔT | ≦ 0.0005λrms / ° C (3) is satisfied when the amount of change in the on-axis spherical aberration of the condensing optical system with respect to the temperature change ΔT (° C) is ΔSA1, Since aberration can be properly corrected even at a high numerical aperture, it is suitable as an objective lens for an optical pickup device capable of recording and / or reproducing information on an optical information recording medium having a higher information density. Since a finite conjugate optical system can be constituted by one lens, a compact optical pickup device at lower cost is provided.

In the objective lens according to the twenty-sixth aspect, a temperature change ΔT within an environmental temperature range of 20 ° C. to 30 ° C.
(° C), the amount of change in wavelength of the light source is Δλ1 (n
m), 0 ≦ △ λ1 / △ T ≦ 0.5 nm / ° C. (14)

The objective lens according to claim 27 has a wavelength λ.
At 1 (nm), ambient temperature is 20 ° C to 30 ° C
When the amount of change in the refractive index of the plastic lens material with respect to the temperature change ΔT (° C.) in the range of Δn is Δn1, −0.0002 / ° C <Δn1 / ΔT <−0.00005 / ° C. (15).

The objective lens according to claim 28, wherein the objective lens is driven in a direction perpendicular to the optical axis of the objective lens for tracking in the optical pickup device, so that the relative position with respect to a light source changes, and The position where the astigmatism component of the wavefront aberration of the light beam emitted from the light source becomes minimum is a position where the optical axis of the objective lens and the light beam center of the light source are shifted.

According to a twenty-ninth aspect of the present invention, when the distance between the light source in the optical pickup device and the information recording surface of the optical information recording medium is U, 10 mm <U <40 mm (16) It is characterized by the following.

The objective lens according to claim 30 has a wavelength λ.
1 (nm) of a first light source and a wavelength λ2 (nm) (λ2>
λ1) a second light source, and an object for condensing light beams emitted from the first light source and the second light source on the information recording surface of the optical information recording medium via the transparent substrate of the optical information recording medium. An objective lens of an optical pickup device, comprising: a light-collecting optical system including a lens; and a photodetector that receives light reflected from the optical information recording medium of light emitted from the first light source and the second light source. The optical pickup device uses the first light flux from the first light source to reduce the thickness of the transparent substrate to t1.
Record and / or reproduce information on the first optical information recording medium, and record information on the second optical information recording medium having a thickness of t2 of the transparent substrate by the second light flux from the second light source. The objective lens is a plastic lens, has a diffraction pattern on at least one surface of the objective lens, and records or reproduces the first optical information recording medium at a wavelength λ1. The required numerical aperture on the optical information recording medium side of the converging optical system required for
A1, when a required numerical aperture on the optical information recording medium side of the condensing optical system necessary for recording or reproducing the second optical information recording medium at the wavelength λ2 is NA2, t1 <t2 NA1> NA2. When the numerical aperture of the objective lens on the optical information recording medium side with respect to the first light beam is NA (1) and the imaging magnification of the objective lens with respect to the first light beam is mol, NA (1) ≧ 0 .56 (17) −1 / 5 ≦ mo1 ≦ −1 / 7.5 (18), and the temperature change ΔT (° C) within the range of 20 ° C. to 30 ° C. Assuming that the amount of change in the on-axis spherical aberration of the optical optical system is △ SA1, | △ SA1 / △ T | ≦ 0.0005λrms / ° C (19) is satisfied, so that a light beam from a light source having a different wavelength can be used. Aberrations are properly corrected and objective lens It is possible to configure a finite conjugate optical system in sheets, compact optical pickup device is provided at a lower cost.

The objective lens according to claim 31, characterized in that when the imaging magnification of the objective lens with respect to the second light flux is mo2, | mo2-mo1 | <0.10 (20) To do.

An objective lens according to a thirty-second aspect is characterized in that the optical pickup device has optical multiplexing means for multiplexing the first light beam and the second light beam.

The objective lens according to claim 33, in the optical pickup device, wherein the first light beam is transmitted through the optical path through which the first light beam and the second light beam pass in common, and the second light beam is transmitted. Among them, there is provided an aperture limiting means for transmitting a central portion and shielding an outer region.

An objective lens according to a thirty-fourth aspect is characterized in that the aperture limiting means is integrated with the objective lens.

The objective lens according to claim 35, wherein the aperture limiting means integrated with the objective lens is provided on one surface of the objective lens, the first light beam is transmitted, and the second light beam is transmitted. The central portion is a partial dichroic coating that transmits light and reflects an outer region.

The objective lens according to claim 36, wherein the diffraction pattern is provided only on one surface of the objective lens, and the partial dichroic coating is applied to a surface having no diffraction pattern. Things.

An objective lens according to a thirty-seventh aspect is characterized in that the partial dichroic coating has a reflectance of 30% to 70% for a light beam having a wavelength λ2.

The objective lens according to claim 38, wherein both surfaces of the objective lens have a diffraction pattern, and the aperture limiting means integrated with the objective lens is provided on one surface of the objective lens. The first light beam is transmitted, and a central portion of the second light beam is transmitted, and the second light beam is a partial diffraction pattern that diffracts an outer region.

The objective lens according to claim 39, wherein in the optical pickup device, the light beam incident on the information recording surface is converted into an inner light beam near the optical axis, an intermediate light beam outside the inner light beam, and an outer light beam outside the intermediate light beam. In the case where the light beam is divided into at least three light beams of the outer light beam, a beam spot is formed by mainly using the inner light beam and the outer light beam of the light beams from the first light source, and the first optical information recording medium For recording and / or reproducing information, a beam spot is formed by mainly using the inner light beam and the intermediate light beam of the light beam from the second light source, and the information is recorded on the second optical information recording medium. It is characterized by recording and / or reproducing.

The objective lens according to claim 40, wherein in the optical pickup device, the wavefront aberration of an inner region of the light beam from the second light source, which is incident on the information recording surface of the second optical information recording medium. Is characterized in that the third-order spherical aberration component is under.

The objective lens according to claim 41, wherein the photodetector of the optical pickup device comprises a first light source and a second light source.
Are common to all the light sources.

The objective lens according to claim 42, wherein the photodetector of the optical pickup device comprises a first photodetector for a first light source and a second photodetector for a second light source. Are separately provided, and are located at spatially separated positions.

The objective lens according to claim 43, in the optical pickup device, at least a pair of the first light source and the first light detector or a pair of the second light source and the second light detector is unitized. It is characterized by having been done.

In the objective lens described in Item 44, in the optical pickup device, the first light source, the second light source, and a common light detector (single light detector) are unitized. It is characterized by the following.

The objective lens according to claim 45, wherein, in the photodetector of the optical pickup device, a first photodetector for a first light source and a second photodetector for a second light source are provided. Are separate, and the first light source, the second light source, the first photodetector, and the second photodetector are unitized.

The objective lens according to claim 46, in the optical pickup device, wherein the first light source and the second light source are unitized, and are located at a position spatially separated from the photodetector. It is characterized by having.

The objective lens according to claim 47, wherein in the optical pickup device, a light source is provided in at least one of an optical path from the first light source to the objective lens and an optical path from the second light source to the objective lens. And a coupling lens for reducing the degree of divergence of the light beam from the lens.

The objective lens according to claim 48 has a wavelength λ.
A condensing optical system including a 1 (nm) light source, and an objective lens for condensing a light beam emitted from the light source on an information recording surface of the optical information recording medium via a transparent substrate of the optical information recording medium; An objective lens for an optical pickup device having a light detector that receives reflected light of the light beam emitted from the light source from the optical information recording medium, wherein the optical pickup device includes:
The first light beam having a thickness of t1 of the transparent substrate due to the light beam from the light source.
Recording or reproducing information on or from an optical information recording medium and a second optical information recording medium having a thickness t2 of a transparent substrate, wherein the objective lens is a plastic lens, and a diffraction pattern is formed on at least one surface of the objective lens. And a required numerical aperture on the optical information recording medium side of the condensing optical system required for recording or reproducing the first optical information recording medium at the wavelength λ1.
A1, when a required numerical aperture on the optical information recording medium side of the condensing optical system required for recording or reproducing the second optical information recording medium at the wavelength λ1 is NA2, t1 <t2 NA1> NA2. When the imaging magnification of the objective lens is mo1, −1 / 5 ≦ mo1 ≦ −1 / 7.5 (22) is satisfied, and the ambient temperature is within a range of 20 ° C. to 30 ° C. Assuming that the amount of axial spherical aberration change of the condensing optical system with respect to the temperature change ΔT (° C.) is ΔSA1, | △ SA1 / ΔT | ≦ 0.0005λrms / ° C. (23) In addition, during recording and / or reproduction of the second optical information recording medium, since the central portion of the light beam from the light source is transmitted and the outer region is shielded, there is an aperture limiting means. Is properly corrected,
In addition, since a finite conjugate optical system can be constituted by one objective lens, a compact optical pickup device at lower cost is provided.

The objective lens according to claim 49, which is a plastic lens having a diffraction pattern on at least one surface, wherein when the astigmatism amount is ΔZ, 0.2 μm <ΔZ <0.7 μm ( 24) is characterized by the following. According to such an objective lens, even when an infinite conjugate optical system is configured, the astigmatism component caused by the optical axis shift can be effectively corrected.

The objective lens according to claim 50 is characterized in that the axial chromatic aberration is overcorrected near the wavelength for convenience. According to such an objective lens, the astigmatism component can be corrected more effectively.

The objective lens according to claim 51 has a wavelength of 6
A light source of 20 nm to 680 nm is arranged on the opposite side of the light source from a polycarbonate transparent substrate having a thickness of 0.6 mm, and the objective lens having a minimum third-order spherical aberration component of wavefront aberration measured through the transparent substrate. When the image magnification is Mmin, the plastic lens satisfies −１ ／ ≦ Mmin ≦ −1 / 12 (25) and has a diffraction pattern on at least one surface.

An objective lens according to a fifty-second aspect is characterized in that the imaging magnification Mmin satisfies −１ ／ ≦ Mmin ≦ −1 / 7.5 (26).

The objective lens of the present invention corrects the amount of axial spherical aberration change due to environmental temperature change on the base surface (envelope surface of the diffraction pattern), and corrects spherical aberration by the diffraction pattern provided on at least one surface. By doing so, it is possible to suppress a change in axial spherical aberration caused by a refractive index change due to a temperature change, which is a defect of the resin lens. Such an objective lens may be one in which a fine structure (relief) for diffraction, which is a diffraction pattern, is further formed on the surface of a lens having a refractive power. At this time, the envelope surface of the fine structure for diffraction becomes the refractive surface shape of the lens. For example, on at least one surface of an aspheric single lens objective lens,
A so-called blaze-type diffraction pattern is provided, and an annular zone having a serrated meridional section is provided on at least one entire surface thereof, and the envelope surface of one surface is an aspheric surface, and the other is an aspheric surface. The lens may have an aspheric surface or both surfaces may be aspheric.

That is, the diffraction pattern (or diffraction surface) used in the present specification means that a relief is provided on the surface of an optical element, for example, the surface of a lens, and has a function of condensing or diverging a light beam by diffraction. In other words, when one optical surface has a region where diffraction occurs and a region where diffraction does not occur, it refers to a region where diffraction occurs. As the shape of the relief, for example, on the surface of the optical element, it is formed as a substantially concentric annular zone centered on the optical axis, and when viewed in cross section on a plane including the optical axis, each annular zone is shaped like a saw tooth Are known, but include such shapes.

In the present specification, an objective lens is, in a narrow sense, a collection located at the position closest to the optical information recording medium and opposed to the optical information recording medium when the optical information recording medium is loaded in the optical pickup device. Refers to a single lens having an optical effect, and in a broad sense, refers to a lens group that can be operated at least in the optical axis direction by an actuator together with the lens. Here, such a lens group refers to at least one or more lenses, and includes a lens composed of only a single lens. Therefore, in this specification, the numerical aperture NA of the objective lens on the optical information recording medium side refers to the numerical aperture NA of the lens surface of the objective lens closest to the optical information recording medium. Further, the numerical aperture NA is a numerical aperture NA defined as a result of limiting the light flux from the light source by a component or a member provided with an aperture function such as an aperture or a filter provided in the optical pickup device.

In this specification, examples of the optical information recording medium include various CDs such as CD-R, CD-RW, CD-Video, and CD-ROM, DVD-ROM, DVD-RAM, DVD-R, DVD-RW, DVD-Video
In addition to the current optical information recording media in the form of disks such as various DVDs or MDs, next-generation recording media are also included. A transparent substrate exists on the information recording surface of many optical information recording media. However, there has been proposed or proposed a transparent substrate having a thickness of almost zero, or a transparent substrate having no transparent substrate at all. For convenience of description, the term "via a transparent substrate" may be used in the present specification, but such a transparent substrate includes a case where the thickness is zero, that is, there is no transparent substrate.

In this specification, recording and reproduction of information means recording information on the information recording surface of the information recording medium as described above, and reproducing information recorded on the information recording surface. Say. The optical pickup device of the present invention may be used to perform only recording or reproduction, or may be used to perform both recording and reproduction. Further, it may be used for recording on one information recording medium and reproducing on another information recording medium, or may be used for recording or reproducing on a certain information recording medium. It may be used for reproducing and for recording and reproducing on another information recording medium. Note that reproduction here includes simply reading information.

The optical pickup device of the present invention can be mounted on audio and / or image recording and / or reproducing devices such as various players or drives, or AV devices, personal computers and other information terminals incorporating them. Can be.

[0092]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below with reference to the drawings.

In general, the pitch of a diffraction ring zone (the position of each ring zone) is defined by using a phase difference function or an optical path difference function which will be described in detail in the embodiments described later. Specifically, the phase difference function Φ
b is expressed by the following [Equation 1] in radians, and the optical path difference function ΦB is expressed by [Equation 2] in mm.

(Equation 1)

(Equation 2)

Although these two expression methods have different units, they are equivalent in terms of expressing the pitch of the diffraction zones. That is, for the main wavelength λ (unit: mm), the coefficient b of the phase difference function
Multiplied by λ / 2π can be converted to a coefficient B of the optical path difference function, and conversely, by multiplying the coefficient B of the optical path difference function by 2π / λ, it can be converted to a coefficient b of the phase difference function.

Now, for the sake of simplicity, a diffractive lens using first-order diffracted light will be described. In the case of an optical path difference function, an annular zone is formed every time the function value exceeds an integral multiple of the principal wavelength λ, and In the case of a phase difference function, a ring zone is carved every time the function value exceeds an integral multiple of 2π.

For example, assuming a lens in which diffraction zones are formed on the object side surfaces of both cylindrical surfaces having no refracting power, the main wavelength is 0.5 μ = 0.0005 mm, the quadratic coefficient of the optical path difference function (square) Term) is -0.05 (-628.3 when converted to a second order coefficient of the phase difference function), and all the coefficients of the other orders are set to zero, the radius of the first annular zone is h = 0.1 mm, The radius of the second annular zone is h = 0.141 mm. Also,
Regarding the focal length f of this diffractive lens, f = −1 / (2 · 2) with respect to the quadratic coefficient B2 = −0.05 of the optical path difference function.
It is known that B2) = 10 mm.

Now, based on the above definition, the lens can have power by setting the secondary coefficient of the phase difference function or the optical path difference function to a non-zero value. A coefficient other than the second order of the phase difference function or the optical path difference function;
For example, the spherical aberration can be controlled by setting the fourth-order coefficient, sixth-order coefficient, eighth-order coefficient, tenth-order coefficient, and the like to non-zero values. Here, controlling means that the spherical aberration of the portion having the refracting power is corrected by generating the reverse spherical aberration, or that the entire spherical aberration is set to a desired value.

Further, the objective lenses for optical pickup of Examples 1 to 4 to be described later form a diffraction pattern on at least one optical surface and change the aspherical shape expressed by the following [Equation 3] to the optical surface. Has on both sides.

[0099]

(Equation 3)

Here, Z is the axis in the optical axis direction, h is the axis perpendicular to the optical axis (height from the optical axis: the traveling direction of light is positive), R0 is the paraxial radius of curvature, and κ is the cone The coefficient, A is the aspherical coefficient, and P is the power of the aspherical surface.

(Examples) Hereinafter, specific examples of the objective lens will be described.

In the first to third embodiments, the reference wavelength λ = 650 n
m, reference temperature T = 25 ° C., focal length f = 3.05 mm,
Numerical aperture NA = 0.6, thickness of transparent substrate of optical disk as optical information recording medium is 0.6 mm, imaging magnification mo = −1
/ 6 objective lens. Incidentally, in the lens data shown below, a power of 10 (for example, 2.5 ×
10-3) is represented using E (for example, 2.5 × E-3). The design wavelength of the optical path difference function is λ = 650.
nm.

(Example 1) Table 1 shows lens data of the objective lens according to this example, FIG. 1 shows a sectional view of the objective lens, and FIG. 2 shows a spherical aberration diagram at a reference wavelength and a reference temperature. The objective lens of the present example does not have paraxial power (refractive power ratio ΦR / ΦO = 1.0) due to the diffraction effect.
The refractive power ratio is the wavelength λ of the light source of the objective lens.
When the power at (nm) is ΦO and the refraction power is ΦR, it can be expressed as ΦR / ΦO, for example, 0.3
If ≦ ΦR / ΦO ≦ 1.5, the fluctuation of the focal position due to the fluctuation of the wavelength of the light source can be reduced.

[Table 1]

[Table 2]

For the objective lenses of Example 1 and Examples 2 and 3 described later, the reference temperature was 25 ° C. and ± 3 ° C.
Table 2 shows the calculation results of the axial spherical aberration change amount SA3 at 0 ° C. In Table 2, the change of the spherical aberration with respect to the temperature change is the third-order spherical aberration component (SA3: unit is λ).
, The value of only the third-order spherical aberration component is shown. The table shows, as a comparative example, a design example in which only the refraction system is formed with the same specifications as those of the present example.

As shown in Table 2, in Example 1,
In the comparative example, the change in spherical aberration occurring in the comparative example is favorably corrected by the change in temperature.

(Example 2) Table 3 shows lens data of the objective lens according to the present example, FIG. 3 shows a sectional view of the objective lens, and FIG. 4 shows a spherical aberration diagram at a reference wavelength and a reference temperature. The objective lens according to the present embodiment has paraxial power (refractive power ratio ΦR / ΦO = 0.9) due to the diffraction effect.

[Table 3]

As shown in Table 2, in this embodiment,
In the comparative example, the change in spherical aberration occurring in the comparative example is favorably corrected by the change in temperature.

The first and second embodiments are suitable for a light source whose wavelength does not change with temperature (such as an SHG laser). In the following embodiment, a relatively inexpensive light source (such as a semiconductor laser) is used as the light source. Generally, the wavelength of a semiconductor laser changes when the temperature of the use environment changes. In the present embodiment described below, the change in the wavelength of the laser depending on the temperature of the semiconductor laser is 0.2 nm / ° C.

(Embodiment 3) Table 4 shows lens data of the objective lens according to this embodiment, FIG. 5 shows a sectional view of the objective lens, and FIG. 6 shows a spherical aberration diagram at a reference wavelength and a reference temperature. Paraxial power due to diffraction effect (refractive power ratio ΦR / ΦO =
0.9) is the same as in the second embodiment.

[Table 4]

By the way, in a normal lens, the third-order spherical aberration has a minimum at a predetermined temperature, and tends to gradually decrease or increase before and after the predetermined temperature. And reference temperature 25 ° C
Since the sign is inverted between the value at −30 ° C. and the value at −30 ° C., it can be determined that none of the examples has the minimum value within the range. Therefore, at least a reference temperature of 25 ° C.
Unit change in the range of ± 5 ° C (20 ° C to 30 ° C) |
SA3 / ΔT | is the average value ｛(reference temperature 25 ° C. + 30 ° C.)
) − (Value at reference temperature 25 ° C.-30 ° C.)｝ ÷ 60.

Further, as shown in the upper part of Table 2, the third-order spherical aberration change amount SA3 with respect to the temperature change ΔT (° C.) is the largest among the first to third embodiments. Therefore, the comparative example and the third embodiment will be compared and considered. Here, considering that the wavelength of the light source changes with the temperature, the actual third-order spherical aberration change amount SA3 of the third embodiment becomes small as shown in the lower part of Table 2.

As described above, even in the case of the third embodiment having the largest variation of the third-order spherical aberration, at least the reference temperature is 25 ° C. ± 5.
The unit change amount in the range of 20 ° C. (20 ° C. to 30 ° C.) is as follows: | SA3 / ΔT | = (0.001 + 0.001) (λ) ÷ 60 (° C.) = 0.000033 ≦ 0.0005, wherein , 6, 24, 25, 30, and 48. On the other hand, in the case of the comparative example, the wavelength variation of the light source is not considered, but when the wavelength varies in the comparative example, the variation of the spherical aberration is further increased, and | SA3 / ΔT |> 0.0005 It is clear that claims 1, 6, 24,
25, 30 and 48 do not satisfy the relationship. According to the present embodiment, the spherical aberration change occurring in the comparative example due to the temperature change is corrected well.

Here, in the optical pickup device using the objective lens according to the third embodiment, recording / reproduction of information on / from optical information recording media having different substrate thicknesses using light beams from light sources having different wavelengths. Is considered. At this time, the substrates were arranged such that the distance between the light source and the surface of the transparent substrate on the light source side was the same as that in Example 3 (that is, the mechanical reference surface of the transparent substrate was on the light source side). That is, the position of the detector is fixed. Accordingly, the paraxial focal position is changed, but the lens is defocused so that the focal position is adjusted. Note that the position of the detector is not constant after the fourth embodiment described later.

FIG. 7 is a spherical aberration diagram when the wavelength λ = 780 nm, the transparent substrate thickness is 1.2 mm, and the numerical aperture is 0.6.
When the numerical aperture is 0.6, the residual aberration is large and good imaging performance cannot be obtained. However, when the numerical aperture is about 0.45 like a CD (compact disc), sufficient imaging performance is obtained. . Furthermore, if a known wavelength selection filter or the like is used, the flare portion can be removed, and good imaging performance can be obtained. Therefore, different wavelengths (650 nm, 780 nm) and different substrate thicknesses (0.6 m
m, 1.2 mm), the required imaging performance can be obtained at the same time.

Next, FIG. 8 shows a spherical aberration diagram when the distance between the light source and the surface of the transparent substrate on the light source side is changed so that the spherical aberration remains even in a place where the numerical aperture is small. Unlike the above case, a sufficient imaging performance cannot be obtained even with a numerical aperture of 0.45. However, by providing a split surface on one of the optical surfaces of the objective lens by a known technique as in Example 4 described below, sufficient image forming properties can be obtained. In such a case, different wavelengths (650 nm, 780 n
m), required imaging performance can be obtained simultaneously at different substrate thicknesses (0.6 mm, 1.2 mm).

(Example 4) Table 5 shows lens data of the objective lens according to this example, and FIG. 9 shows the first light source λ1 = 650n.
m, thickness t1 of transparent substrate of first optical information recording medium = 0.6 mm
FIG. 10 shows the second light source λ2 = 780 nm,
Spherical aberration diagrams of the second optical information recording medium when the thickness t2 of the transparent substrate is 1.2 mm, and FIGS. 11 and 12 are cross-sectional views of the objective lens corresponding to each condition.

[Table 5]

In the present embodiment, even if the required numerical aperture is 0.6 for the first optical information recording medium and 0.45 for the second optical information recording medium, However, sufficient imaging performance can be obtained.

In the fourth embodiment, the objective lens of the third embodiment is provided with a ring-shaped divided surface on the surface opposite to the diffraction surface, and λ1 = 650 nm and t1 = 0.6 mm.
The temperature characteristic at is sufficiently corrected as in the third embodiment. Note that H in Table 5 represents a height from the optical axis, and defines a divided area.

Table 6 shows the refractive index with respect to the wavelength of the resin material used in Examples 1 to 4.

[Table 6]

FIG. 13 shows Embodiments 1 to 5 of the objective lens described above.
FIG. 4 is a conceptual diagram illustrating an example of an embodiment according to an optical pickup device (one light source and one detector type) to which No. 4 can be applied. In the example of this embodiment, since a semiconductor laser is used, it is particularly preferable to apply the objective lens of Example 3. In the optical pickup device 100, a light beam from a semiconductor laser 111 as a light source passes through a beam splitter 120 as an optical multiplexing unit, is stopped down to a predetermined numerical aperture by a stop 17, and is transmitted through a diffraction-integrated objective lens 160. A spot is formed on the information recording surface 220 via the transparent substrate 210 of the optical disc 200 for high density recording, which is an information recording medium. The wavelength (reference wavelength) of the semiconductor laser light is 68
It is preferably at most 0 nm, more preferably at most 500 nm. Here, 650 nm laser light was used in accordance with the specifications of the objective lenses of Examples 1 to 3.

The reflected light beam modulated by the information bit on the information recording surface 220 becomes convergent light again through the diffraction-integrated objective lens 160, passes through the stop 17, is reflected by the beam splitter 120, and is reflected by the cylindrical lens 18.
0, astigmatism and magnification conversion are performed, and the photodetector 30
It converges on the light receiving surface of 0. Reference numeral 150 in the figure is an actuator for focus control and tracking control.

Note that, including the embodiments described later, the objective lens 160 is driven by the actuator 150 in tracking direction perpendicular to the optical axis to change the relative position with respect to the semiconductor laser 111 as a light source. In such a case, the position where the astigmatism component of the wavefront aberration of the light beam emitted from the objective lens 160 is minimized is the position where the optical axis of the objective lens 160 and the center of the light beam of the semiconductor laser 111 are shifted. The range where the aberration is smaller than the predetermined value can be further expanded. The distance U between the semiconductor laser and the information recording surface of the optical information recording medium is larger than 10 mm and 4
It is preferable that the distance is smaller than 0 mm because the optical pickup device 100 can be made compact.

Further, the aperture 17 was also appropriately set so that the numerical aperture on the disk 16 side became a predetermined value in accordance with the specifications of the objective lens of the embodiment. In the present embodiment, the stop 1
A liquid crystal shutter can be provided immediately before.

FIG. 14 shows the first to fifth embodiments of the objective lens.
FIG. 4 is a conceptual diagram showing an example of an embodiment according to an optical pickup device (two light sources and two detectors) to which No. 4 can be applied. In the example of this embodiment, since two light sources are used, it is particularly desirable to apply the objective lens of Example 4. FIG.
In the optical pickup device of No. 4, when reproducing the first optical disk, the first semiconductor laser 111 uses the laser /
The photodetector 301 and the hologram 231 are unitized in the detector integrated unit 410, and the light beam emitted from the first semiconductor laser 111 passes through the hologram 231, passes through the beam splitter 190, which is an optical multiplexing unit, and further has a stop 170. And the objective lens 16
By 0, the light is focused on the information recording surface 220 via the transparent substrate 210 of the first optical disc 200.

The light flux modulated and reflected by the information pits on the information recording surface 220 is again reflected by the objective lens 16.
0, the light passes through the beam splitter 190 through the stop 170, is diffracted by the hologram 231 and is incident on the photodetector 301.
A read signal of the information recorded at 00 is obtained.

Further, a change in the light amount due to a change in the shape and position of the spot on the photodetector 301 is detected to detect focus and track, and a two-dimensional actuator 150 is used for focusing and tracking. The lens 160 is moved.

When reproducing the second optical disk, the second semiconductor laser 112 uses the integrated laser / detector unit 42.
, The light detector 302 and the hologram 232 are unitized, and the light beam emitted from the second semiconductor laser 112 passes through the hologram 232, is reflected by the beam splitter 190 as a light combining means, and further passes through the stop 170 and the objective lens 160. Then, the light is focused on the information recording surface 220 via the transparent substrate 210 of the second optical disc 200.

The light flux modulated and reflected by the information pits on the information recording surface 220 is again reflected by the objective lens 160.
And the beam passes through the aperture 170, is reflected by the beam splitter 190, is diffracted by the hologram 232, and is
Incident on the optical disk, and using the output signal thereof,
A read signal of the information recorded at 00 is obtained.

Further, by detecting a change in the light amount due to a change in the shape or position of the spot on the photodetector 302, focus detection or track detection is performed. The objective lens 160 is moved for tracking.

In the present embodiment, as well as 2
In the laser-type embodiment, when recording or reproducing the first optical disc 200 using the first light beam having the wavelength λ1, the required numerical aperture of the objective lens 160 on the optical disc side is set to NA1, and the second optical disc 200 When recording or reproducing is performed using the second light flux having the wavelength λ2, the required numerical aperture of the objective lens 160 on the optical disk side is set to N.
When A2, t1 <t2 and NA1> NA2, the numerical aperture of the objective lens 160 on the optical disc side with respect to the first light beam is NA (1), and the imaging magnification of the objective lens 160 with respect to the first light beam is mo1. Sometimes, NA (1) ≧ 0.56 (17) −1 / 5 ≦ mo1 ≦ −1 / 7.5 (18) and, as described above, at least the ambient temperature in the range of 20 ° C. to 30 ° C. And the amount of change in axial spherical aberration of the objective lens 160 with respect to the temperature change ΔT (° C.) is represented by ΔSA1.
| △ SA1 / △ T | ≦ 0.0005λrms / ° C (19)

Further, although not shown, the first light beam is on the optical path through which the first light beam and the second light beam pass in common, that is, on the surface opposite to the diffraction pattern surface of the objective lens 160. A partial dichroic coating is provided as aperture limiting means that transmits and transmits a central portion of the second light flux and reflects (shields) an outer region. Such a partial dichroic coating has a reflectance of 30% to 70% for a light beam of wavelength λ2.

As a modification of the present embodiment, both surfaces of the objective lens 160 have a diffraction pattern, and the first lens on one surface of the objective lens 160 serves as aperture limiting means integrated with the objective lens. It is also conceivable to form a partial diffraction pattern that transmits a light beam, transmits a central portion of the second light beam, and diffracts an outer region.

Further, as another modified example of the present embodiment, a light beam incident on the information recording surface 220 of the optical disc 200 is converted into an inner light beam near the optical axis, an intermediate light beam outside the inner light beam, and an intermediate light beam. In the case where the light is divided into at least three light beams of the outer light beam, the first semiconductor laser 1
A beam spot is formed by mainly using the inner light beam and the outer light beam among the light beams from the light source 11, and information is recorded and / or reproduced on the first optical disc 200. A beam spot may be formed by mainly using the inner light beam and the intermediate light beam of the light beam to record and / or reproduce information on and from the second optical disc 200.

By configuring the aperture limiting means as described above, the spot diameter on the information recording surface 220 can be adjusted, thereby enabling appropriate recording or reproduction of information on different types of optical discs.

In the light beam from the second semiconductor laser 112, it is preferable that the third-order spherical aberration component of the wavefront aberration in the inner region incident on the information recording surface 220 of the second optical disc 200 is under (see FIG. 10). reference).

The third optical pickup device (two light sources, two detectors) shown in FIG. 15 has a configuration suitable for an optical system for recording and reproduction. The recording and reproduction modes of information will be described.

When reproducing the first optical disc 200,
A coupling ring lens 60 that emits a beam from a first semiconductor laser 111 as a first light source and reduces the degree of divergence of a divergent light beam, and a beam splitter 1 as an optical multiplexing unit.
90, transmitted through the beam splitter 120,
70, and the information recording surface 2 through the transparent substrate 210 of the first optical disc 200 by the objective lens 160.
It is condensed on 20.

The light flux modulated and reflected by the information bits on the information recording surface 220 is again reflected by the objective lens 160,
The light passes through the stop 170, enters the beam splitter 120, is reflected there, is given astigmatism by the cylindrical lens 180, and is transmitted through the concave lens 50 to the photodetector 30.
1, and a read signal of information recorded on the first optical disc 200 is obtained using the output signal.

Further, by detecting a change in the light amount due to a change in the shape and position of the spot on the photodetector 301, focus detection and track detection are performed. Based on this detection, the two-dimensional actuator 150 moves the objective lens 160 so that the light beam from the first semiconductor laser 111 is focused on the recording surface 220 of the first optical disc 200, and the light beam from the semiconductor laser 111 is The objective lens 160 is moved so that an image is formed on a predetermined track.

The second semiconductor laser 112 as a second light source for reproducing the second optical disk is unitized with the photodetector 302 and the hologram 230 in the integrated laser / detector unit 400. “Unit” or “unitization” means that the members and means that are unitized can be integrated into an optical pickup device, and are assembled as one part when assembling the device. It can be attached.

The light beam emitted from the second semiconductor laser 112 passes through the hologram 230, is reflected by the beam splitter 190 which is an optical multiplexing means, and
The light passes through the aperture 20 and is further focused on the information recording surface 220 via the transparent substrate 210 of the second optical disc 200 via the stop 170 and the objective lens 160.

The light flux modulated and reflected by the information pits on the information recording surface 220 is again reflected by the objective lens 16.
0, transmitted through the aperture 170 and the beam splitter 120, reflected by the beam splitter 190, diffracted by the hologram 230 and incident on the photodetector 302, and the information recorded on the second optical disc 200 using the output signal. Is obtained.

Further, by detecting a change in the light amount due to a change in the shape and position of the spot on the photodetector 302, focus detection and track detection are performed, and a two-dimensional actuator 150 is used for focusing and tracking. The lens 160 is moved.

In the optical pickup device (two light sources, one detector type) according to the fourth embodiment shown in FIG. 16, a semiconductor laser 111 serving as a first light source for reproducing a first optical disk, and a second light source are provided. A semiconductor laser 112 as a second light source for reproducing an optical disk.

First, when reproducing the first optical disk, a beam is emitted from the first semiconductor laser 111, and the emitted luminous flux passes through the beam splitter 190, which is a means for multiplexing the light emitted from both the semiconductor lasers 111 and 112. The first optical disc 200 is transmitted through the beam splitter 120, is stopped down by the stop 17, and is stopped by the objective lens 160.
Is focused on the information recording surface 220 via the transparent substrate 210 of FIG.

The light flux modulated and reflected by the information bit on the information recording surface 220 is again reflected by the objective lens 16.
0, the light passes through the stop 17, enters the beam splitter 120, is reflected there, is given astigmatism by the cylindrical lens 180, enters the photodetector 300, and uses the output signal thereof to generate a first signal. A read signal of information recorded on the optical disc 200 is obtained.

Further, by detecting a change in the light amount due to a change in the shape and position of the spot on the photodetector 300, focus detection and track detection are performed. Based on this detection, the two-dimensional actuator 150 moves the objective lens 160 so that the light beam from the first semiconductor laser 111 forms an image on the recording surface 220 of the first optical disc 200, and the light beam from the semiconductor laser 111 The objective lens 160 is moved so that is imaged on a predetermined track.

When reproducing the second optical disk, a beam is emitted from the second semiconductor laser 112, and the emitted light beam is reflected by the beam splitter 190, which is an optical multiplexing means, and is combined with the light beam from the first semiconductor 111. Similarly, the light is focused on the information recording surface 220 via the transparent substrate 210 of the second optical disc 200 via the beam splitter 190, the aperture 17, and the objective lens 160.

The light flux modulated and reflected by the information pits on the information recording surface 220 is again reflected by the objective lens 16.
0, the aperture 17, the beam splitter 190, and the incident light on the photodetector 300 via the cylindrical lens 180,
Using the output signal, a read signal of information recorded on the second optical disc 200 is obtained.

As in the case of the first optical disk, a change in the light amount due to a change in the shape and position of the spot on the photodetector 300 is detected, and focus detection and track detection are performed. The objective lens 160 is moved for focusing and tracking.

In the optical pickup device (two light sources, one detector, one unit type) of the fifth embodiment shown in FIG. 17, the first semiconductor laser 111 as the first light source and the second
A second semiconductor laser 112 as a light source, a photodetector 30,
Hologram 230 has integrated laser / detector unit 430
As a unit.

When reproducing the first optical disk, the luminous flux emitted from the first semiconductor laser 111 is reflected on the hologram 2
The light passes through the aperture 30, is further stopped down by the stop 170, and is focused on the information recording surface 220 by the objective lens 160 via the transparent substrate 210 of the first optical disc 200.

The light flux modulated and reflected by the information pits on the information recording surface 220 is again reflected by the objective lens 16.
0, transmitted through the stop 170, diffracted by the hologram 230 and incident on the photodetector 300, and using the output signal thereof,
A read signal of information recorded on the first optical disc 200 is obtained.

Further, by detecting a change in the light amount due to a change in the shape and position of the spot on the photodetector 300, focus detection and track detection are performed, and a two-dimensional actuator 150 is used for focusing and tracking. The lens 160 is moved.

When reproducing the second optical disk, the luminous flux emitted from the second semiconductor laser 112 is the hologram 2
The light passes through 30 and becomes a substantially parallel light beam. Further aperture 17
0, the second optical disc 200 via the objective lens 160
Is focused on the information recording surface 220 via the transparent substrate 210 of FIG.

The light beam modulated and reflected by the information pits on the information recording surface 220 is again reflected by the objective lens 16.
0, transmitted through the stop 170, diffracted by the hologram 230 and incident on the photodetector 300, and using the output signal thereof,
A read signal of information recorded on the second optical disc 200 is obtained.

Further, a change in the light amount due to a change in the shape or position of the spot on the photodetector 300 is detected, and focus detection and track detection are performed. The objective lens 160 is moved for tracking.

Optical pickup device according to the sixth embodiment shown in FIG. 18 (two light sources, two detectors, one unit type)
, The first semiconductor laser 11 as the first light source
1. Second semiconductor laser 112 as second light source, first photodetector 301, second photodetector 302, hologram 2
30 is unitized as a laser / detector integrated unit 430.

When reproducing the first optical disk, the luminous flux emitted from the first semiconductor laser 111 is applied to the hologram 2
The light passes through the surface of the disk 30 on the disk side, is further stopped down by the stop 170, and is condensed by the objective lens 160 onto the information recording surface 220 via the transparent substrate 210 of the first optical disk 200.

The light flux modulated and reflected by the information pits on the information recording surface 220 is again reflected by the objective lens 16.
0, transmitted through the stop 170, diffracted by the disk-side surface of the hologram 230, and detected by the photodetector 30 corresponding to the first light source.
1 and the read signal of the information recorded on the first optical disc 200 is obtained by using the output signal.

Further, a change in the light amount due to a change in the shape and position of the spot on the photodetector 301 is detected, and focus detection and track detection are performed. The lens 160 is moved.

When reproducing the second optical disk, the luminous flux emitted from the second semiconductor laser 112 is the hologram 2
The light is diffracted by the surface 30 on the semiconductor laser side. The surface of the hologram on the semiconductor laser side functions as a light combining means. The diffracted light is further transmitted to the transparent substrate 2 of the second optical disc 200 through the stop 170 and the objective lens 160.
The light is condensed on the information recording surface 220 via.

The light flux modulated and reflected by the information pits on the information recording surface 220 is again reflected by the objective lens 16.
0, the photodetector 30 transmitted through the stop 170 and diffracted by the disk-side surface of the hologram 230 and corresponding to the second light source
2 and the read signal of the information recorded on the second optical disc 200 is obtained by using the output signal.

Further, a change in the light amount due to a change in the shape and position of the spot on the photodetector 302 is detected, and focus detection and track detection are performed. The objective lens 160 is moved for tracking.

In the optical pickup device (two light sources, one package type) according to the seventh embodiment shown in FIG. 19, the beam emitted from the first semiconductor laser 111 as the first light source is an optical multiplexing means. The light passes through the beam splitter 120, is further stopped down by the stop 17, and is transmitted by the objective lens 16 to the transparent substrate 21 of the first optical disc 20.
Is focused on the information recording surface 22 via the.

The light flux modulated and reflected by the information bits on the information recording surface 22 passes through the objective lens 16 and the aperture 17 again, enters the beam splitter 12, is reflected there, and is reflected by the cylindrical lens 180. An aberration is given, the light is incident on the photodetector 301 via the concave lens 50, and a read signal of information recorded on the first optical disc 20 is obtained using the output signal.

Also, by detecting a change in the light amount due to a change in the shape and position of the spot on the photodetector 301, focus detection and track detection are performed. Based on this detection, a two-dimensional actuator (not shown) moves the objective lens 16 so that the light beam from the first semiconductor laser 111 forms an image on the recording surface 22 of the first optical disk 20, and the two-dimensional actuator (not shown) The objective lens 16 is moved so that the light beam is focused on a predetermined track.

The beam emitted from the second semiconductor laser 112 passes through a beam splitter 120 which is an optical multiplexing means, and further passes through a stop 17 and an objective lens 16 via a transparent substrate 21 of a second optical disc 20. Recording surface 22
Is collected.

The light flux modulated and reflected by the information pits on the information recording surface 22 is reflected again by the objective lens 16, the diaphragm 17 and the beam splitter 120, is given astigmatism by the cylindrical lens 180, and is given a concave lens 5.
The light is incident on the photodetector 301 via the optical disc 0, and a read signal of the information recorded on the second optical disc 20 is obtained using the output signal.

Also, a change in the light amount due to a change in the shape and position of the spot on the photodetector 302 is detected to detect focusing and tracking, and a two-dimensional actuator (not shown) performs focusing and tracking. Objective lens 1
6 is moved.

[0171]

As described above, according to the present invention, in a finite conjugate optical system, even when a material whose refractive index changes according to the ambient temperature is used, the spherical aberration change due to the temperature change can be achieved with a relatively simple structure. Can be corrected,
Further, even if the light source is an optical system whose wavelength varies with the environmental temperature, it is possible to correct both the change in spherical aberration due to the wavelength variation and the change in spherical aberration due to the variation in the refractive index of the material. Further, by combining with a known technique, sufficient imaging performance can be obtained for optical information recording media having different wavelengths and different thicknesses. Therefore,
An objective lens for an optical pickup device that can be manufactured at low cost, an optical pickup device including the objective lens, and a recording / reproducing device including the objective lens can be obtained.

[Brief description of the drawings]

FIG. 1 is a sectional view of an objective lens according to a first embodiment.

FIG. 2 is a diagram of spherical aberration at a reference wavelength and a reference temperature by the objective lens of Example 1;

FIG. 3 is a sectional view of an objective lens according to a second embodiment.

FIG. 4 is a diagram of spherical aberration at a reference wavelength and a reference temperature by the objective lens of Example 3;

FIG. 5 is a sectional view of an objective lens according to a third embodiment.

FIG. 6 is a spherical aberration diagram at a reference wavelength and a reference temperature by the objective lens of Example 3;

FIG. 7: wavelength λ = 780 nm, transparent substrate thickness 1.2 mm,
FIG. 4 is a spherical aberration diagram when the numerical aperture is 0.6.

FIG. 8 is a spherical aberration diagram when the distance between the light source and the surface of the transparent substrate on the light source side is changed with respect to FIG. 7;

FIG. 9 is a spherical aberration diagram when the first light source λ1 = 650 nm and the transparent substrate thickness t1 of the first optical information recording medium is 0.6 mm.

FIG. 10 is a spherical aberration diagram when the second light source λ2 = 780 nm and the transparent substrate thickness t2 of the second optical information recording medium is 1.2 mm.

FIG. 11 is a cross-sectional view of the objective lens of Example 4 corresponding to FIG.

FIG. 12 is a cross-sectional view of the objective lens of Example 4 corresponding to FIG.

FIG. 13 is a conceptual diagram of an optical pickup device according to the first embodiment.

FIG. 14 is a conceptual diagram of an optical pickup device according to a second embodiment.

FIG. 15 is a conceptual diagram of an optical pickup device according to a third embodiment.

FIG. 16 is a conceptual diagram of an optical pickup device according to a fourth embodiment.

FIG. 17 is a conceptual diagram of an optical pickup device according to a fifth embodiment.

FIG. 18 is a conceptual diagram of an optical pickup device according to a sixth embodiment.

FIG. 19 is a conceptual diagram of an optical pickup device according to a seventh embodiment.

[Explanation of symbols]

 REFERENCE SIGNS LIST 100 Optical pickup device 200 Actuator 111 Semiconductor laser (first semiconductor laser) 112 Second semiconductor laser 160 Objective lens 300 Photodetector 201 First photodetector 302 Second photodetector

Claims (52)

[Claims] 1. A light source for emitting a light beam having a wavelength of λ1 (nm), and a light beam emitted from the light source is condensed on an information recording surface of the optical information recording medium via a transparent substrate of the optical information recording medium. A focusing optical system including an objective lens, and a photodetector receiving light reflected from the optical information recording medium, wherein the objective lens is a plastic lens, and a diffraction pattern is formed on at least one surface of the objective lens. Wherein the numerical aperture of the objective lens on the optical information recording medium side is NA
(1) Assuming that the imaging magnification of the objective lens is mo1, NA (1) ≧ 0.49−1 / 2 ≦ mo1 ≦ −1 / 7.5 is satisfied, and the ambient temperature is 20 ° C. to 30 ° C. Assuming that the amount of change in the on-axis spherical aberration of the condensing optical system with respect to the temperature change ΔT (° C.) in the range of ° C. is ΔSA1, | ΔSA1 / ΔT | ≦ 0.0005λrms / ° C. An optical pickup device characterized by satisfying. 2. When the wavelength change amount of the light source with respect to a temperature change ΔT (° C.) within an environment temperature range of 20 ° C. to 30 ° C. is defined as Δλ1 (nm), 0 ≦ Δλ1 / 2. The optical pickup device according to claim 1, wherein ΔT ≦ 0.5 nm / ° C. 3. At the wavelength λ1 (nm), the ambient temperature 2
Temperature change ΔT (° C.) within the range of 0 ° C. to 30 ° C.
When the amount of change in the refractive index of the plastic lens material with respect to C) is Δn1, −0.0002 / ° C <Δn1 / ΔT <−0.00000
The optical pickup device according to claim 1, wherein the temperature is 5 / ° C. 4. 4. The objective lens is driven in a direction perpendicular to the optical axis of the objective lens for tracking, so that a relative position with respect to a light source changes, and a wavefront aberration of a light beam emitted from the objective lens is reduced. 4. The optical pickup device according to claim 1, wherein the position where the astigmatism component is minimized is a position where the optical axis of the objective lens and the center of the light beam of the light source are shifted. 5. The optical recording medium according to claim 1, wherein when a distance between the light source and the information recording surface of the optical information recording medium is U, 10 mm <U <40 mm is satisfied. Optical pickup device. 6. A first light source having a wavelength of λ1 (nm), a second light source having a wavelength of λ2 (nm) (λ2> λ1), and a light beam emitted from the first light source and the second light source. A condensing optical system including an objective lens for converging light on an information recording surface of the optical information recording medium via a transparent substrate of the optical information recording medium; and a light beam emitted from the first light source and the second light source. And a photodetector for receiving the reflected light from the optical information recording medium, wherein the thickness of the transparent substrate is t by the first light flux from the first light source.
Recording and / or reproducing information on and from the first optical information recording medium, and the thickness of the transparent substrate is t by the second light flux from the second light source.
Recording and / or reproducing information on and from the second optical information recording medium, wherein the objective lens is a plastic lens, and has a diffraction pattern on at least one surface of the objective lens; The necessary numerical aperture on the optical information recording medium side of the condensing optical system necessary for recording or reproducing the medium at the wavelength λ1 is NA1, and the required numerical aperture for recording or reproducing the second optical information recording medium at the wavelength λ2. When the required numerical aperture of the condensing optical system on the optical information recording medium side is NA2, t1 <t2NA1> NA2, and the numerical aperture of the objective lens on the optical information recording medium side with respect to the first light flux is NA. (1) The imaging magnification of the objective lens with respect to the first light flux is mo.
l, NA (1) ≧ 0.56−1 / 5 ≦ mo1 ≦ −1 / 7.5, and a temperature change ΔT (T) within an environmental temperature range of 20 ° C. to 30 ° C. An optical pickup device characterized by satisfying | △ SA1 / △ T | ≦ 0.0005λrms / ° C, where 上 SA1 is the amount of change in axial spherical aberration of the focusing optical system with respect to (° C). 7. The optical pickup device according to claim 6, wherein | mo2−mo1 | <0.10 when an imaging magnification of the objective lens with respect to the second light flux is mo2. 8. The optical pickup device according to claim 6, further comprising an optical multiplexing unit that can multiplex the first light beam and the second light beam. 9. An opening for transmitting a first light beam, transmitting a central portion of the second light beam, and blocking an outer region in an optical path through which the first light beam and the second light beam pass in common. 9. The optical pickup device according to claim 6, further comprising a limiting unit. 10. The optical pickup device according to claim 9, wherein said aperture limiting means is integrated with an objective lens. 11. An aperture limiting means integrated with the objective lens is provided on one surface of the objective lens, and transmits a first light beam, transmits a central portion of a second light beam, and transmits an outer light beam. The optical pickup device according to claim 10, wherein the optical pickup device is a partial dichroic coating that reflects an area. 12. The optical pickup device according to claim 11, wherein the diffraction pattern is provided only on one surface of the objective lens, and the partial dichroic coating is applied on a surface having no diffraction pattern. . 13. The optical pickup device according to claim 11, wherein the partial dichroic coating has a reflectance of 30% to 70% for a light beam having a wavelength of λ2. 14. An objective lens, wherein both surfaces of the objective lens have a diffraction pattern, and the aperture limiting means integrated with the objective lens transmits a first light beam on one surface of the objective lens, 11. The optical pickup device according to claim 10, wherein the central portion of the two light beams is a partial diffraction pattern that transmits a central portion and diffracts an outer region. 15. A light beam incident on the information recording surface may be an inner light beam near an optical axis, an intermediate light beam outside the inner light beam,
When divided into at least three light beams of the outer light beam outside the intermediate light beam, a beam spot is formed by mainly using the inner light beam and the outer light beam among the light beams from the first light source,
Recording and / or reproducing information on and from a first optical information recording medium, forming a beam spot by mainly utilizing an inner light beam and an intermediate light beam of the light beam from the second light source;
15. The optical pickup device according to claim 6, wherein information is recorded on and / or reproduced from the optical information recording medium. 16. The tertiary spherical aberration component of wavefront aberration in an inner area of the light beam from the second light source, which is incident on an information recording surface of the second optical information recording medium, is under. 16. The optical pickup device according to claim 15, wherein: 17. The optical pickup device according to claim 6, wherein the photodetector is common to the first light source and the second light source. 18. The photodetector according to claim 18, wherein said photodetector comprises a first light source.
The optical pickup according to any one of claims 6 to 16, wherein the optical pickup according to any one of claims 6 to 16 is separately provided with a photodetector for the second light source and a second photodetector for the second light source. apparatus. 19. The light according to claim 18, wherein at least a pair of the first light source and the first light detector or a pair of the second light source and the second light detector is unitized. Pickup device. 20. The optical pickup device according to claim 17, wherein the first light source, the second light source, and a common photodetector (single photodetector) are unitized. 21. The photodetector, wherein a first photodetector for a first light source and a second photodetector for a second light source are separate bodies, and the first light source and the second 17. The optical pickup device according to claim 6, wherein the two light sources, the first light detector, and the second light detector are unitized. 22. The apparatus according to claim 6, wherein the first light source and the second light source are unitized, and are located at a position spatially separated from the photodetector. An optical pickup device according to item 1. 23. At least one of an optical path from the first light source to the objective lens and an optical path from the second light source to the objective lens includes a coupling lens for reducing the degree of divergence of a light beam from the light source. 23. The optical pickup device according to claim 6, wherein: 24. A light source having a wavelength λ1 (nm), and an objective lens for condensing a light beam emitted from the light source on an information recording surface of the optical information recording medium via a transparent substrate of the optical information recording medium. A light-condensing optical system, and a photodetector that receives reflected light of the light beam emitted from the light source from the optical information recording medium, wherein the light beam from the light source causes the first transparent substrate to have a thickness of t1.
Recording or reproducing information on or from an optical information recording medium and a second optical information recording medium having a transparent substrate with a thickness of t2, wherein the objective lens is a plastic lens, and a diffraction pattern is formed on at least one surface of the objective lens. The required numerical aperture of the converging optical system on the optical information recording medium side required for recording or reproducing the first optical information recording medium at the wavelength λ1 is NA1, and the second optical information recording medium is the wavelength λ1. When the necessary numerical aperture on the optical information recording medium side of the condensing optical system required for recording or reproducing in the above is defined as NA2, t1 <t2NA1> NA2, and the imaging magnification of the objective lens is defined as mo1. In some cases, −１ ／ ≦ mo1 ≦ −1 / 7.5 is satisfied, and the axis of the condensing optical system with respect to a temperature change ΔT (° C.) within an environmental temperature range of 20 ° C. to 30 ° C. Upper spherical aberration change △ SA1 / ΔT | ≦ 0.0005λrms / ° C, and the central portion of the light flux from the light source is transmitted during recording and / or reproduction of the second optical information recording medium. An optical pickup device comprising an aperture limiting means for shielding an outside area. 25. A light source for emitting a light beam having a wavelength of λ1 (nm), and a light beam emitted from the light source is condensed on an information recording surface of the optical information recording medium via a transparent substrate of the optical information recording medium. An objective lens for an optical pickup device, comprising: a condensing optical system including an objective lens; and a photodetector that receives reflected light from the optical information recording medium, wherein the objective lens is a plastic lens, A lens has a diffraction pattern on at least one surface thereof, and the numerical aperture of the objective lens on the optical information recording medium side is NA
(1) Assuming that the imaging magnification of the objective lens is mo1, NA (1) ≧ 0.49−1 / 2 ≦ mo1 ≦ −1 / 7.5 is satisfied, and the ambient temperature is 20 ° C. to 30 ° C. Assuming that the amount of change in the on-axis spherical aberration of the condensing optical system with respect to the temperature change ΔT (° C.) in the range of ° C. is ΔSA1, | ΔSA1 / ΔT | ≦ 0.0005λrms / ° C. An objective lens characterized by satisfying. 26. When a wavelength change amount of the light source with respect to a temperature change ΔT (° C.) within an environment temperature range of 20 ° C. to 30 ° C. is set to Δλ1 (nm), 0 ≦ Δλ1 / The objective lens according to claim 25, wherein ΔT ≦ 0.5 nm / ° C. 27. At a wavelength λ1 (nm), a temperature change ΔT (°) within an environmental temperature range of 20 ° C. to 30 ° C.
When the amount of change in the refractive index of the plastic lens material with respect to C) is Δn1, −0.0002 / ° C <Δn1 / ΔT <−0.00000
The objective lens according to claim 26 or 27, wherein 5 / ° C. 28. The objective lens, when driven in a direction perpendicular to the optical axis of the objective lens for tracking in the optical pickup device, changes its relative position with respect to a light source and emits the objective lens. The position where the astigmatism component of the wavefront aberration of the light beam becomes minimum is a position where the optical axis of the objective lens and the light beam center of the light source are shifted. Objective lens. 29. The optical pickup according to claim 25, wherein when the distance between the light source in the optical pickup device and the information recording surface of the optical information recording medium is U, 10 mm <U <40 mm is satisfied. Objective lens written in one of them. 30. A first light source having a wavelength of λ1 (nm), a second light source having a wavelength of λ2 (nm) (λ2> λ1), and a light beam emitted from the first light source and the second light source. A condensing optical system including an objective lens for converging light on an information recording surface of the optical information recording medium via a transparent substrate of the optical information recording medium; and a light beam emitted from the first light source and the second light source. An objective lens of an optical pickup device having a photodetector that receives reflected light from an optical information recording medium, wherein the optical pickup device has a thickness of a transparent substrate by a first light beam from a first light source. t
Recording and / or reproducing information on and from the first optical information recording medium, and the thickness of the transparent substrate is t by the second light flux from the second light source.
2 for recording and / or reproducing information on and from a second optical information recording medium, wherein the objective lens is a plastic lens, and has a diffraction pattern on at least one surface of the objective lens; The required numerical aperture of the converging optical system on the optical information recording medium side required for recording or reproducing the first optical information recording medium at the wavelength λ1 is NA1, and the second optical information recording medium is recorded or reproduced at the wavelength λ2. When the required numerical aperture on the optical information recording medium side of the condensing optical system required to perform the operation is NA2, t1 <t2 NA1> NA2, and the optical information recording medium side for the first light flux of the objective lens Is the numerical aperture of NA (1), and the imaging magnification of the objective lens with respect to the first light flux is mo.
l, NA (1) ≧ 0.56−1 / 5 ≦ mo1 ≦ −1 / 7.5, and a temperature change ΔT (T) within an environmental temperature range of 20 ° C. to 30 ° C. An objective lens characterized by satisfying | △ SA1 / △ T | ≦ 0.0005λrms / ° C, where △ SA1 represents the amount of change in axial spherical aberration of the focusing optical system with respect to (° C). 31. The objective lens according to claim 30, wherein, when an imaging magnification of the objective lens with respect to the second light flux is mo2, | mo2−mo1 | <0.10. 32. The optical pickup device, comprising:
The objective lens according to claim 30, further comprising a light multiplexing unit that can multiplex the light flux of the second light flux with the light flux of the second light flux. 33. In the optical pickup device, an optical path through which the first light beam and the second light beam pass in common:
33. The objective lens according to claim 30, further comprising an aperture limiting unit that transmits the first light beam, transmits a central portion of the second light beam, and shields an outer region. 34. The objective lens according to claim 33, wherein said aperture limiting means is integrated with an objective lens. 35. An aperture limiting means integrated with the objective lens is provided on one surface of the objective lens, and transmits a first light beam, transmits a central portion of a second light beam and transmits an outer light beam. The objective lens according to claim 34, wherein the objective lens is a partial dichroic coating that reflects an area. 36. The objective lens according to claim 35, wherein the diffraction pattern is provided only on one surface of the objective lens, and the partial dichroic coating is applied on a surface having no diffraction pattern. 37. The objective lens according to claim 35, wherein the partial dichroic coating has a reflectance of 30% to 70% for a light beam having a wavelength of λ2. 38. Both surfaces of the objective lens have a diffraction pattern, and the aperture limiting means integrated with the objective lens transmits a first light beam on one surface of the objective lens, 35. The objective lens according to claim 34, wherein a central portion of the two light beams is a partial diffraction pattern that transmits the light and diffracts an outer region. 39. In the optical pickup device, a light beam incident on the information recording surface is converted into an inner light beam near an optical axis,
In the case where the light beam is divided into at least three light beams of an intermediate light beam outside the inner light beam and an outer light beam outside the intermediate light beam, by mainly using the inner light beam and the outer light beam among the light beams from the first light source. Forming a beam spot,
Recording and / or reproducing information on and from a first optical information recording medium, forming a beam spot by mainly utilizing an inner light beam and an intermediate light beam of the light beam from the second light source;
The objective lens according to any one of claims 30 to 38, characterized in that information is recorded and / or reproduced with respect to the optical information recording medium of (1). 40. The optical pickup device, wherein a third-order spherical aberration component of wavefront aberration in an inner area of the light beam from the second light source, which is incident on an information recording surface of the second optical information recording medium, is under. The objective lens according to claim 39, wherein: 41. The objective lens according to claim 30, wherein the photodetector of the optical pickup device is common to a first light source and a second light source. 42. The photodetector of the optical pickup device includes a first photodetector for a first light source and a second photodetector for a second light source, each of which is spatially separated. The objective lens according to any one of claims 30 to 40, wherein the objective lens is located at a distance from the object lens. 43. In the optical pickup device, at least a pair of the first light source and the first light detector or a pair of the second light source and the second light detector is unitized. The objective lens according to claim 42. 44. The optical pickup device according to claim 41, wherein the first light source, the second light source, and a common light detector (single light detector) are unitized. The objective lens as described. 45. The photodetector of the optical pickup device, wherein a first photodetector for a first light source and a second photodetector for a second light source are separate bodies, The light source, the second light source, the first light detector, and the second light detector are unitized.
0. The objective lens according to any one of 0. 46. The optical pickup device, wherein the first light source and the second light source are unitized,
The objective lens according to any one of claims 30 to 40, wherein the objective lens is spatially separated from the photodetector. 47. In the optical pickup device, the divergence of a light beam from the light source is reduced in at least one of an optical path from the first light source to the objective lens and an optical path from the second light source to the objective lens. The objective lens according to any one of claims 30 to 46, further comprising a coupling lens. 48. A light source having a wavelength λ1 (nm), and an objective lens for condensing a light beam emitted from the light source on an information recording surface of the optical information recording medium via a transparent substrate of the optical information recording medium. An objective lens for an optical pickup device, comprising: a condensing optical system; and a photodetector that receives reflected light of the light flux emitted from the light source from the optical information recording medium. By luminous flux,
Recording or reproducing information on a first optical information recording medium having a transparent substrate thickness of t1 and a second optical information recording medium having a transparent substrate thickness of t2, wherein the objective lens is a plastic lens; The lens has a diffraction pattern on at least one surface, and the required numerical aperture on the optical information recording medium side of the condensing optical system required for recording or reproducing the first optical information recording medium at the wavelength λ1 is NA1, When a required numerical aperture on the optical information recording medium side of the condensing optical system required for recording or reproducing the second optical information recording medium at the wavelength λ1 is NA2, t1 <t2 NA1> NA2, and Assuming that the imaging magnification of the objective lens is mo1, −1 / 5 ≦ mo1 ≦ −1 / 7.5 is satisfied, and a temperature change ΔT (° in the range of the ambient temperature of 20 ° C. to 30 ° C. The collection for C) When the amount of change in the on-axis spherical aberration of the optical system is △ SA1, | △ SA1 / △ T | ≦ 0.0005λrms / ° C is satisfied, and the light source is used for recording and / or reproduction of the second optical information recording medium. An aperture limiting means for transmitting a central portion of the light flux from the lens and blocking an outer region. 49. A plastic lens having a diffraction pattern on at least one surface, wherein the astigmatism amount is ΔZ
Where 0.2 μm <ΔZ <0.7 μm.
Or an objective lens for reproduction. 50. The objective lens for recording and / or reproducing information on an optical information recording medium according to claim 49, wherein the axial chromatic aberration is overcorrected near the wavelength for convenience. 51. A light source having a wavelength of 620 nm to 680 nm, and a polycarbonate transparent substrate having a thickness of 0.6 mm disposed on the side opposite to the light source, and a third-order spherical aberration component of wavefront aberration measured through the transparent substrate is minimized. When the imaging magnification of the objective lens is Mmin, the plastic lens satisfies −１ ／ ≦ Mmin ≦ −1 / 12 and has a diffraction pattern on at least one surface. Objective lens for recording and / or reproducing media. 52. An imaging magnification Mmin of the objective lens
52. The objective lens for recording and / or reproducing information on an optical information recording medium according to claim 51, wherein satisfies −１ ／ ≦ Mmin ≦ −1 / 7.5.