JP2003167190A - Optical element for chromatic aberration correction, optical system, optical pickup device, and recording and reproducing unit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical element for chromatic aberration correction which can correct on-axis chromatic aberration effectively even when on-axis chromatic aberration remains due to a large numerical aperture of an objective lens on the side of an optical information recording medium, and to provide an optical system for optical pickup, an optical pickup device, and a recording and reproducing device using the optical element for chromatic aberration correction. <P>SOLUTION: The optical element 3 for chromatic aberration correction is arranged in an optical path between a light source which generates a light with a wavelength of 550 nm or less. An objective lens is made of a material of with Abbe's number for d-line of 95.0 or less, and has a diffraction structure consisting of a plurality of zonal step on at least one surface, and satisfies P<SB>1</SB><P<SB>0</SB><P<SB>2</SB>. In the P<SB>0</SB>is total paraxial power (mm<SP>-1</SP>) of the optical element for chromatic aberration correction at a wavelength λ<SB>0</SB>of a light generated by the light source and P<SB>1</SB>is the total paraxial power (mm<SP>-1</SP>) of the optical element for chromatic aberration correction at a wavelength λ<SB>1</SB>10 nm shorter than the wavelength λ<SB>0</SB>, and P<SB>2</SB>is the total paraxial power (mm<SP>-1</SP>) of the optical element for chromatic aberration correction at a wave length λ<SB>2</SB>10 nm longer than the wavelength λ<SB>0</SB>. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a chromatic aberration correcting optical element having a diffractive structure, an optical system including the chromatic aberration correcting optical element, an optical pickup device, and a recording / reproducing apparatus.

[0002]

2. Description of the Related Art In recent years, research on a new high-density recording optical pickup system using a blue-violet semiconductor laser light source with an oscillation wavelength λ of about 400 nm and an objective lens whose numerical aperture (NA) is increased to about 0.85.・ Development is progressing.
DVD (NA = 0.6, λ = 650 nm, storage capacity 4.
7 GB), and as an example, NA = 0.
An optical disc of 85 and λ = 400 nm can record information of 25 GB.

However, when using such a high NA objective lens or a short wavelength light source of about 400 nm, the axial chromatic aberration generated in the objective lens becomes a problem. Laser light emitted from a semiconductor laser is generally a single wavelength (single mode), and it is considered that there is no axial chromatic aberration.
Actually, the center wavelength may momentarily drop by several nm due to temperature change, output change, or the like, and mode hopping may occur.
Mode hopping is a wavelength change that occurs instantaneously so that focusing of the objective lens cannot follow, so if the chromatic aberration of the objective lens is not corrected, a defocus component is added and the wavefront aberration deteriorates. The deterioration of the wavefront aberration at the time of mode hopping becomes particularly large when an objective lens having a high NA or a short wavelength light source is used, as described below. The spherical aberration does not fluctuate with the objective lens with respect to the wavelength fluctuation Δλ, but the back focus fb fluctuates by Δfb. If the objective lens is focused in the optical axis direction with respect to the back focus fluctuation, the mean square root of the wavefront aberration is generated. Value W
_rms is 0, but if focusing is not performed W
_{The rms} is expressed by the following equation (1 ').

W _rms = 0.145 · {(NA) ² / λ} / | Δfb | (1 ′)

For example, DVD (NA = 0.6, λ = 6
(50 nm) and an optical disc with NA = 0.85 and λ = 400 nm, the wavefront aberration is degraded by 3.26 times in the latter even if Δfb is the same. That is, assuming that the allowable values of the wavefront aberration are the same, the allowable value of | Δfb | is 1
It becomes as small as /3.26, and it is necessary to reduce the axial chromatic aberration of the wavefront that is transmitted through the objective lens and focused on the recording surface of the optical disc.

As the objective lens for the cemented doublet type optical disc in which the chromatic aberration is corrected, those described in JP-A-61-3110 and JP-A-62-28609 are known, but those having a positive refractive power are known. A lens in which a lens made of a low dispersion material and a lens made of a high dispersion material having a negative refractive power are combined is not suitable for an objective lens for an optical disc, which is essential to be lightweight. Because there is a limit to the dispersion of materials, when trying to correct chromatic aberration for short wavelengths, the refractive power of each lens increases, but the positive lens is thick to secure the edge thickness of the positive lens. As a result, the objective lens itself becomes heavy.

Further, Japanese Laid-Open Patent Publication No. 11-174318 discloses an objective lens having a two-element structure having a numerical aperture of 0.85 on the optical disc side and a hologram provided on an optical surface for correcting axial chromatic aberration. Have been described. However, when the hologram has a ring-shaped structure having concentric minute steps, in a high NA objective lens in which the curvature of the optical surface tends to be small, the influence of the shadow of the ring-shaped structure is large and the light transmittance is high. Therefore, it is not suitable for a high-density recording optical pickup system as an information writing system that requires high light utilization efficiency.

A chromatic aberration correcting optical element for correcting the axial chromatic aberration of the objective lens is disclosed in Japanese Patent Laid-Open No. 6-82.
An optical element for correcting chromatic aberration described in Japanese Patent No. 725 is known, but an optical element for correcting chromatic aberration in which a plane perpendicular to the optical axis is formed stepwise as a concentric ring zone with respect to the optical axis is disclosed. When arranged in a parallel light flux, the reflected light from the diffractive structure returns in the same direction as the incident light, and a ghost signal is generated in the detection system of the optical pickup, so it is not suitable as a chromatic aberration correction optical element for an optical pickup system. .

[0009]

In view of the above-mentioned circumstances, the present invention is applied to the case where a light source having poor monochromaticity or a light source whose wavelength changes abruptly is used, for example, in a high density recording optical pickup system. Provided are an optical system for an optical pickup, which can correct axial chromatic aberration with a relatively simple configuration and can be manufactured at low cost, an optical pickup device including the optical system, and a recording / reproducing device including the optical system. The purpose is to

Further, since the numerical aperture on the side of the optical information recording medium is large, the spherical aberration is corrected, the sine condition is corrected, and the size is reduced.
An object of the present invention is to provide an optical element for correcting chromatic aberration that can correct axial chromatic aberration when used with an objective lens in which axial chromatic aberration remains for the purpose of thinning, weight reduction, and cost reduction.

[0011]

In order to achieve the above object, a first chromatic aberration correcting optical element according to the present invention comprises 55
An optical element for chromatic aberration correction arranged in an optical path between a light source that emits light having a wavelength of 0 nm or less and an objective lens formed of a material having an Abbe number of d line of 95.0 or less, It is characterized in that it has a diffractive structure composed of a plurality of ring-shaped steps on at least one surface and satisfies the following expression (1).

P ₁ <P ₀ <P ₂ (1) where P ₀ : total paraxial power (m of the chromatic aberration correction optical element at the wavelength λ ₀ of light generated by the light source
m ⁻¹ ) P ₁ : Total paraxial power (m of the chromatic aberration correcting optical element at the wavelength λ _{1 that} is 10 nm shorter than the wavelength λ _0.
m ⁻¹ ) P ₂ : Total paraxial power (m of the chromatic aberration correcting optical element at a wavelength λ _{2 that} is 10 nm longer than the wavelength λ _0.
m ^-1 )

The above formula (1) is a light source that emits light having a wavelength of 550 nm or less, and is used in an optical pickup device that uses a light source having poor monochromaticity or a light source whose wavelength changes abruptly. A condition for correcting the axial chromatic aberration of the objective lens with respect to the total paraxial power of the chromatic aberration correcting optical element arranged between the objective lens having the residual axial chromatic aberration. The expression (1) means that the chromatic aberration correcting optical element itself causes the axial chromatic aberration so that the paraxial power becomes large at a wavelength λ _{2 which} is 10 nm longer than the wavelength λ _{0 of} the light generated by the light source. The axial chromatic aberration of the entire optical pickup optical system including the chromatic aberration correcting optical element and the objective lens is corrected by offsetting and correcting the axial chromatic aberration of the objective lens that is insufficiently corrected at the wavelength λ ₂ with overcorrection. It is a thing. By combining with the chromatic aberration correcting optical element according to the present invention, a short wavelength light source with poor monochromaticity is used, which causes a problem of residual axial chromatic aberration of the objective lens even if the objective lens does not strictly correct axial chromatic aberration. It can be used as an objective lens for an optical pickup device. The paraxial power of the chromatic aberration correcting optical element is the power of the entire chromatic aberration correcting optical element system, which is a combination of the refracting power of the refracting lens and the diffraction power of only the diffractive structure. The total paraxial power of the chromatic aberration correcting optical element refers to paraxial power obtained by combining the refracting power of the refracting lens and the diffraction power of the diffractive lens.

The second chromatic aberration correcting optical element according to the present invention comprises a light source which emits light having a wavelength of 550 nm or less, and an objective lens which is made of a material having an Abbe number of 95.0 or less for the d-line. An optical element for chromatic aberration correction arranged in the optical path between, wherein the optical element for chromatic aberration correction is
At least one surface has a diffractive structure including a plurality of ring-shaped steps, and m represented by the following equations (2) and (2 ′) is 0, ±
Step difference Δ (mm) in the optical axis direction that is an integer other than 1.
At least one ring zone step having the above is formed within the effective diameter.

M = INT (Y) (2) Y = Δ × (n−1) / (λ ₀ × 10 ⁻³ ) (2 ′) where INT (Y): an integer n obtained by rounding Y : Refractive index λ ₀ of the chromatic aberration correcting optical element at the wavelength λ ₀ (nm) of the light generated by the light source: Wavelength (nm) of the light generated by the light source

The above equation (2) is used to diffract high-order diffracted light having a diffraction order of ± 2 or more when the incident light beam is diffracted by the diffractive structure formed on the optical surface of the chromatic aberration correcting optical element. This means that the step difference Δ (mm) in the optical axis direction of the diffractive ring zone is determined so that the light amount becomes larger than the diffracted light amount of any other diffracted order.

The third chromatic-aberration correcting optical element according to the present invention comprises a light source that emits light having a wavelength of 550 nm or less, and an objective lens made of a material having an Abbe number of 95.0 or less for the d-line. An optical element for chromatic aberration correction arranged in the optical path between the two, characterized in that it has a diffractive structure having a plurality of annular zone steps on at least two surfaces.

In a general optical material, the shorter the wavelength, the greater the change in the refractive index with respect to the minute wavelength change. Therefore, when a short wavelength light source having a wavelength λ of 550 nm or less is used, a slight wavelength change occurs. On the other hand, in the objective lens, large axial chromatic aberration occurs. Therefore, the diffractive power of the diffractive lens of the chromatic aberration correcting optical element necessary for correcting the axial chromatic aberration of the objective lens becomes large. When the paraxial power of the objective lens is φ _OBJ and the total paraxial power of the chromatic aberration correcting optical element is φ _SA , the back focus of the combined system of the objective lens and the chromatic aberration correcting optical element does not change due to the change in wavelength. In order to do so, the following equation (3) may be established.

Dφ _SA / dλ = −dφ _OBJ / dλ (3)

On the other hand, the change in paraxial power with respect to the change in wavelength of the objective lens is related to the change in back focus,
The total paraxial power (that is, the diffractive power as a diffractive lens) represented by the following equation (4) when the chromatic aberration correcting optical element is a diffractive lens is proportional to the wavelength. It is represented by the formula 5).

Dφ _OBJ / dλ = − (dfB / dλ) · φ _OBJ ² (4) dφ _SA / dλ = φ _SA / λ (5)

By substituting the equations (4) and (5) into the equation (3), the diffraction power φ _SA of the chromatic aberration correcting optical element configured as the diffractive lens can be obtained by the following equation (6).

Φ _SA = (dfB / dλ) · λ · φ _OBJ ² (6)

For example, focal length 3.33 mm, wavelength used 650 nm, NA = 0.6, entrance pupil diameter φ4 mm, νd =
In a general DVD objective lens of 55, dfB
Since /dλ=0.15 μm / nm, the diffractive power φ _SA of the chromatic aberration correcting optical element is set as shown by the following expression (7).

Φ _SA = 0.15 × 10 ⁻³ · 650 · (1/3) ² = 1 / 92.3 (mm ⁻¹ ) = 1.1 × 10 ⁻² (mm ⁻¹ ) (7)

Also, the focal length is 2.35 mm and the wavelength used is 4
05 nm, NA = 0.85, entrance pupil diameter φ4 mm, νd =
In the objective lens for the high-density recording optical pickup of 55, dfB / dλ = 0.40 μm / nm, so the diffraction power φ _SA of the chromatic aberration correcting optical element is as follows (8)
It is set as shown in the formula.

[0027]   φ_SA= 0.40 x 10^-3・ 405 ・ (1 / 2.35)^Two= 1 / 34.1 (mm ^-1 ) = 2.9 × 10^-2(Mm^-1) (8)

That is, the chromatic aberration correcting optical element for the high-density recording optical pickup requires about 2.7 times the diffraction power as compared with the DVD chromatic aberration correcting optical element.
In reality, since the objective lens for a high-density recording optical pickup having a large NA has a small depth of focus, it is necessary to rigorously correct axial chromatic aberration. The required diffraction power is larger than that of equation (8).

By the way, the optical path difference Φ added to the transmitted wave front by the chromatic aberration correcting optical element of the diffraction power φ _SA is expressed by the following equation (9) as a function of the height h from the optical axis.

Φ = (φ _SA / 2) · h ² (9)

Further, the interval Λ measured in the direction perpendicular to the optical axis of the adjacent ring zones of the diffractive ring zone structure formed in the chromatic aberration correcting optical element has an optimized wavelength of the ring zone structure of λ ₀ , which is the maximum. When the diffraction order of the diffracted light having the diffracted light amount is m, it is expressed by the following equation (10).

Λ = m · λ ₀ / (dΦ / dh) (10)

Substituting equation (10) into equation (9), the spacing Λ of the diffractive ring zone structure is determined by equation (11) below.

Λ = m · λ ₀ / (φ _SA · h) (11)

Therefore, in the above-mentioned optical element for correcting chromatic aberration for DVD, the interval Λ ₆₅₀ of the diffractive ring structure at a height of 2 mm from the optical axis has an optimized wavelength of the ring structure of 65.
When the thickness is 0 nm, the following expression (12) is obtained. Λ ₆₅₀ = m · 650 × 10 ⁻³ /(1/92.3·2)=30·m (μm) (12)

On the other hand, in the chromatic aberration correcting optical element for the high-density recording optical pickup described above, the interval Λ ₄₀₅ of the diffractive ring zone structure at a height of 2 mm from the optical axis is 405 nm when the optimized wavelength of the ring zone structure is 405 nm. The following expression (13) is obtained.

Λ ₄₀₅ = m · 405 × 10 ⁻³ /(1/34.1·2)=6.9·m (μm) (13)

In the equation (13), when the diffraction ring zone structure is determined so that the first-order diffracted light has the maximum diffracted light amount,
Since the distance between the diffraction ring structure at the position corresponding to the entrance pupil diameter of the objective lens is 6.9 μm, it is possible to transfer the tip shape of the diamond tool when cutting the injection molding mold by SPDT. There is a possibility that the influence of the light amount loss due to the phase-mismatched portion of the generated annular zone step becomes large. Further, if the spacing between the diffractive ring zone structures is small, it is difficult to accurately transfer the ring zone shape at the time of molding, and this also increases the influence of the light amount loss due to the phase mismatch portion.

From the above, as in the second chromatic aberration correcting optical element of the present invention, the diffracted light quantity of the high-order diffracted light having the diffraction order of ± m (where m is an integer other than 0 and ± 1) or higher is obtained. , The amount of step difference Δ (m
When m) is determined, the interval of the diffractive ring zone structure can be increased by m times according to the above equation (13), so that the influence of the light amount loss due to the phase mismatch portion can be reduced.

Further, like the third chromatic aberration correcting optical element of the present invention, a diffractive ring zone structure is formed on an optical surface of n (where n is an integer of 2 or more) surfaces or more, and the chromatic aberration correcting optical element is formed. If the diffracted power φ _SA required for the element is evenly distributed to the n optical surfaces, the diffracted power per surface becomes 1 / n times, and the interval of the diffractive ring zone structure is n by the above formula (11).
Since it can be doubled, it is possible to reduce the influence of the light amount loss due to the phase mismatch portion. Here, for simplification of description, it is explained that the diffractive power required for the chromatic aberration correcting optical element is evenly distributed to the n optical surfaces, but it is needless to say that the distribution is not even. .

For example, a diffracted ring zone structure is formed on two optical surfaces, and the amount of diffracted light of higher-order diffracted light having a second-order diffracted order is larger than that of diffracted light of any other diffracted order. When the step difference Δ (mm) in the optical axis direction of the diffractive ring zone is determined so as to be large, the diffractive ring at the position corresponding to the entrance pupil diameter of the objective lens described above is calculated by the equations (11) and (13). The interval between the band structures can be 27.6 μm.

A fourth chromatic aberration correcting optical element according to the present invention comprises a light source which emits light having a wavelength of 550 nm or less and an objective lens which is made of a material having an Abbe number of 95.0 or less for d-line. A chromatic aberration correcting optical element arranged in an optical path between the chromatic aberration correcting optical elements is a single lens, and when viewed macroscopically, a diffractive structure composed of a plurality of plane annular zone steps is formed. One optical surface and the other optical surface formed on the opposite refractive surface which is a concave refracting surface.

When the diffractive ring zone structure is formed on a plane, the light reflected by the diffractive structure travels in a direction different from that of the incident light, so that the generation of a ghost signal in the detection system of the optical pickup can be prevented. Further, the total paraxial power of the optical surface on which the diffractive structure is formed, which is obtained by combining the refracting power and the diffracting power, is given by the above equation (6) because the refracting power is 0. Therefore, the optical surface on the side opposite to the optical surface on which the diffractive structure is formed is made a refracting surface having a negative refracting power such that the absolute value of the paraxial power becomes the same as that of the expression (6). Since the total paraxial power of the optical element for use can be set to 0, it is easy to arrange it in the parallel light flux.

Further, when the diffractive ring zone structure is formed on a plane, the spacing of the diffractive ring zone structure becomes several μm as given by the above equation (13), and a chromatic aberration correcting optical element for a high density recording optical pickup. Can be manufactured by electron beam drawing capable of forming a fine diffraction structure without a shape error. A method for producing a fine diffraction structure by electron beam writing is described in "OPTICS DESIGN Optical Design Research Group Journal No.20 2000.2.25 p.26-p.31". Here, “a plane when viewed macroscopically” means that a ring-shaped step is formed on a plane optical surface, which will be described later with reference to FIG.
In (a), it is synonymous with that the line L1 (envelope) connecting the vertices of each ring zone step becomes a straight line.

Further, in the first to fourth chromatic aberration correcting optical elements according to the present invention, it is preferable that the following expression (14) is satisfied.

[0046]   0.5 x 10^-2<P_D<15.0 x 10^-2                (14) However, P_D: Formed on the i-th surface of the chromatic aberration correcting optical element
Diffractive structure transmits the chromatic aberration correction optical element
Optical path difference Φ added to wavefront_biIs the height h from the optical axis
_iAs a function of (mm) Φ_bi= Ni ・ (b_2i・ Hi^Two+ b_4i・ Hi^Four+ b_6i・
hi⁶+ ...) When expressed by the optical path difference function defined by
i represents the diffracted light generated by the diffractive structure formed on the i-th surface.
And the diffraction order of the diffracted light having the maximum diffracted light amount, b _2i,
b_4i, B_6i... are 2nd, 4th, 6th,
Is an optical path difference function coefficient (also referred to as a diffractive surface coefficient) of
), P_D= Σ (-2 · b_2i・ Ni) Diffractive power as a diffractive lens defined by (mm
^-1)

As described above, the high density recording optical pickup
The chromatic aberration correction optical element for
2.35 mm, working wavelength 405 nm, NA = 0.85,
Axis of the objective lens with entrance pupil diameter φ4 mm and νd = 55
To correct the upper chromatic aberration, φ _SA= 2.9 × 10^-2
(Mm^-1) Diffraction power of the order of magnitude is required. actually
Is an objective lens for a high-density recording optical pickup with a large NA.
Since the depth of focus of the lens is small, axial chromatic aberration is more severe
Must be corrected, and for high density recording optical pickup
The diffraction power required for the chromatic aberration correction optical element is the above value.
Grows bigger. In addition, the number of times required for the chromatic aberration correction optical element
Folding power depends on the focal length of the objective lens and the Abbe number.
Therefore, it also changes. Therefore, high-density recording optical pickup
Range of Diffraction Power of Optical Element for Correcting Chromatic Aberration
As the above, the condition as shown in the above equation (14) is defined.

Above the lower limit of equation (14), the axial chromatic aberration of the wavefront focused on the information recording surface of the optical information recording medium is not overcorrected, and below the upper limit of equation (14), The axial chromatic aberration of the wavefront focused on the information recording surface of the optical information recording medium is not overcorrected. In order to achieve the above operation, it is more preferable to satisfy the following expression (15).

1.0 × 10 ⁻² <P _D <10.0 × 10 ⁻² (15)

The above-mentioned chromatic aberration correcting optical elements are
It is preferable that the total paraxial power P _{0 of the} chromatic aberration correcting optical element at the wavelength λ ₀ of the light generated by the light source is substantially zero, and it is easy to dispose in the parallel light flux. Specifically, it is to satisfy the following expressions (16) to (18).

P _D > 0 (16) P _R <0 (17) −0.9 <P _D / P _R <−1.1 (18) where P _R : as a refraction lens of the chromatic aberration correcting optical element Refraction power (mm ^-1 )

Further, in the above-mentioned first to fourth chromatic aberration correcting optical elements, the spherical aberration of the outgoing light beam is insufficiently corrected when the wavelength of the incoming light beam changes to the long wavelength side, or
It is preferable to have at least one surface having a spherical aberration characteristic that changes in the direction of overcorrection and having a diffractive structure that satisfies the following expression (19). 0.2 ≦ | (P _hf / P _hm ) −2 | ≦ 6.0 (19) where P _{hf is} a ring zone in a direction perpendicular to the optical axis of the diffractive structure at a position hf that is half the maximum effective diameter hm. Interval P _hm : annular zone interval in the direction perpendicular to the optical axis of the diffractive structure at the maximum effective diameter hm

When a short wavelength light source having a wavelength of 550 nm or less, particularly about 400 nm, is used, as described above, the change in the refractive index with respect to the minute wavelength change of the lens material is large, so that when the minute wavelength change occurs, the objective lens In addition to the axial chromatic aberration, spherical aberration also changes. For example, an objective lens with a single lens configuration has a wavelength of 10 nm from the design wavelength.
When it changes to the long wavelength side, the spherical aberration changes in the direction of overcorrection. Further, in the two-group objective lens, the spherical aberration when the wavelength changes to the long wavelength side of 10 nm from the design wavelength changes to the overcorrection direction or the undercorrection direction depending on the paraxial power arrangement of the lens groups. To do

The above equation (19) is a condition for correcting the spherical aberration change of the objective lens by the diffractive action of the chromatic aberration correcting optical element when a slight wavelength change occurs. If the optical path difference function has only a second-order optical path difference function coefficient (also referred to as a diffractive surface coefficient), (P _hf / P _hm ) −2 = 0
However, since the chromatic aberration correcting optical element according to the present invention satisfactorily corrects the change in spherical aberration that occurs in the objective lens due to a minute wavelength change from the design wavelength, due to the diffractive action of the diffractive structure of the chromatic aberration correcting optical element. The high-order optical path difference function coefficient of the optical path difference function is used for. At this time, (P
It is preferable that _hf / P _hm ) -2 be a value that is apart from 0 to some extent, and if the expression (19) is satisfied, the above-described change in spherical aberration can be effectively canceled by the diffraction effect.

In the above-mentioned first to fourth chromatic aberration correcting optical elements, it is preferable that the wavelength at which the diffraction efficiency is maximum is 550 nm or less. More preferably, the design wavelength of the objective lens and the wavelength that maximizes the diffraction efficiency are substantially the same.

Further, it is preferable that the first to fourth chromatic aberration correcting optical elements are plastic lenses. When the chromatic aberration correcting optical element of the present invention is arranged in the optical pickup optical system as an element separate from the objective lens, it is thinned for securing a working distance and reducing the weight like the objective lens, Since there is no strong demand for miniaturization, the lens of the diffractive / refractive integrated optical element made of a plastic material can be easily manufactured at low cost by an injection molding method using a mold.

In the present specification, the diffractive surface means a surface provided with a relief on the surface of an optical element, for example, the surface of a lens, to have a function of diffracting an incident light beam. When there is a region where diffraction occurs and a region where diffraction does not occur, it means a region where diffraction occurs. Further, the diffractive structure or the diffractive pattern means a region where this diffraction occurs. As the relief shape, for example, on the surface of the optical element, it is formed as a ring of substantially concentric circles centered on the optical axis, and when viewed in a plane including the optical axis, each ring zone is sawtooth-shaped or stairs. A shape like a shape is known, but includes such a shape.

Further, the optical system according to the present invention is 550 nm.
A light source that emits light of the following wavelength and an Abbe number of d-line is 9
Information from an information recording surface of an optical information recording medium having an objective lens formed of a material of 5.0 or less and an optical element for chromatic aberration correction arranged in an optical path between the light source and the objective lens. Is an optical system for reproducing information and / or recording information on an information recording surface, characterized by comprising any one of the above-mentioned chromatic aberration correcting optical elements as the chromatic aberration correcting optical element.

Further, the optical pickup device according to the present invention comprises a light source which emits light having a wavelength of 550 nm or less, an objective lens formed of a material having an Abbe number of d line of 95.0 or less, the light source and the light source. An optical system having a chromatic aberration correcting optical element arranged in the optical path between the objective lens and the objective lens, reproducing information from the information recording surface of the optical information recording medium and / or An optical pickup device for recording information, characterized by having the above-mentioned optical system as the condensing optical system.

According to the above-mentioned optical system, even when a light source having poor monochromaticity or a light source whose wavelength changes abruptly is used in, for example, a high-density recording optical pickup system, the axis is relatively simple. Can correct upper chromatic aberration,
Moreover, an optical system for an optical pickup and an optical pickup device that can be manufactured at low cost can be realized.

In the present specification, examples of the optical information recording medium include various CDs such as CD, CD-R, CD-RW, CD-Video, and CD-ROM, DVD, DVD-ROM, DVD-RAM. , Various DVDs such as DVD-R, DVD-RW, and DVD + RW, and present disc-shaped optical information recording media such as MD, as well as next-generation high-density recording media.

In this specification, information recording and reproduction means recording information on the information recording surface of the optical information recording medium as described above and reproducing the information recorded on the information recording surface. Say that. The condensing optical system 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 optical information recording medium and reproducing on another optical information recording medium, or for one optical information recording medium. Alternatively, it may be used for performing reproduction and recording and reproduction for another optical information recording medium. Note that the reproduction here includes simply reading information.

The optical pickup device according to the present invention described above is, for example, a CD, a CD-R, a CD-RW, a CD-Video, a CD-ROM, a DVD or a DVD-DVD-
Players, drives, etc. compatible with optical information recording media such as ROM, DVD-RAM, DVD-R, DVD-RW, DVD + RW, MD, etc., or AV devices, personal computers, etc. incorporating them.
It can be installed in a recording device and / or reproducing device for audio and / or images such as other information terminals.

[0064]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram schematically showing a configuration of an optical pickup device including a condensing optical system for an optical pickup according to this embodiment, and FIG. 2A is a side view of the chromatic aberration correcting optical element of FIG. 2B is a plan view seen from the arrow direction A in FIG.

The optical pickup device 1 shown in FIG. 1 includes a semiconductor laser 2 as a light source, a chromatic aberration correcting optical element 3 of a diffraction integrated type, and an objective lens 4. The semiconductor laser 2 is a GaN-based blue-violet laser that emits a light flux with a wavelength of about 400 nm. As a light source that emits a light flux with a wavelength of about 400 nm, in addition to the above-mentioned GaN blue-violet laser, S
It may be an HG blue-violet laser.

Further, as shown in FIGS. 2 (a) and 2 (b),
On the surface S1 of the chromatic aberration correcting optical element 3 on the semiconductor laser 2 side, a substantially concentric circular diffraction pattern p is provided on a flat optical surface. The diffraction power of the diffraction pattern p is determined so as to satisfy the above formula (14), and the interval in the direction perpendicular to the optical axis of the diffraction pattern p is determined by the above formula (11). Further, the chromatic aberration correcting optical element 3
The surface S2 on the objective lens 4 side is a concave surface having a negative refractive power, and by setting the absolute values of the diffraction power of the diffraction pattern and the refractive power of the concave surface to be equal, the power of the entire system of the chromatic aberration correcting optical element 3 is set. Is set to 0.

The substantially concentric circular diffraction pattern may be provided on the surface of the chromatic aberration correcting optical element 3 on the objective lens 4 side, or on both the light source side surface and the objective lens 4 side surface. May be. Although the total paraxial power of the chromatic aberration correcting optical element 3 is set to 0, this total paraxial power may be positive or negative. Although the diffraction pattern of the chromatic aberration correcting optical element 3 is substantially concentric with the optical axis, other diffraction patterns may be provided. Further, in the optical pickup device 1 of FIG. 1, the chromatic aberration correcting optical element 3 is composed of one lens, but it may be composed of a plurality of lenses without departing from the scope of the present invention. Further, in the optical pickup device 1 of FIG. 1, the chromatic aberration correction optical element 3 is arranged as a separate element from the objective lens 4, but the chromatic aberration correction optical element 3 and the objective lens 4 are provided with a lens frame, an adhesive, or the like. May be integrated with. In this case, the chromatic aberration correcting optical element 3 and the objective lens 4 are integrally controlled by the biaxial actuator 10 for tracking control, so that good tracking characteristics can be obtained.

Further, the objective lens 4 of FIG. 1 is a lens for condensing the light flux from the chromatic aberration correcting optical element 3 on the information recording surface 5'of the optical disk 5 within the diffraction limit, and is composed of one lens. And has at least one aspherical surface. Further, the objective lens 4 has a flange portion 4 ′ having a surface extending perpendicularly to the optical axis, and the objective lens 4 can be accurately attached to the optical pickup device 1 by this flange portion 4 ′. The numerical aperture of the objective lens 4 on the optical disk 5 side is preferably 0.65 or more,
It is more preferably 0.75 or more. Although the objective lens 4 is composed of one lens,
It may be composed of one or more lenses.

The divergent light beam emitted from the semiconductor laser 2 passes through the deflecting beam splitter 6, passes through the collimating lens 7 and the quarter wave plate 8 to become a circularly polarized parallel light beam, and the chromatic aberration correcting optical element 3, After passing through the diaphragm 9, it becomes a spot formed on the information recording surface 5 ′ by the objective lens 4 through the transparent substrate 5 ″ of the high density recording optical disc 5. The objective lens 4 is focus-controlled and tracking-controlled by a biaxial actuator 10 arranged around the objective lens 4.

The reflected light beam modulated by the information pits on the information recording surface 5 ', again passes through the objective lens 4, the chromatic aberration correcting optical element 3, the quarter-wave plate 8 and the collimating lens 7, and becomes a convergent light beam. , Deflection beam splitter 6
Is reflected by, and astigmatism is given by passing through the cylindrical lens 11 and converges on the photodetector 12. Then, the information recorded on the optical disk 5 can be read using the output signal of the photodetector 12.

In the present embodiment, the chromatic aberration correcting optical element 3 is provided with the above-described substantially concentric circular diffraction pattern on the optical surface, so that the semiconductor laser 2
The axial chromatic aberration having the opposite sign to that of the objective lens 4 and the absolute value of which substantially coincides with respect to the oscillation wavelength of. Therefore, the light flux emitted from the semiconductor laser 2 passes through the chromatic aberration correcting optical element 3 and the objective lens 4 and thereby has almost no axial chromatic aberration, and thus the information recording surface 5 ′ of the optical disk 5 is substantially free.
Can be focused on.

The optical pickup device 1 as shown in FIG. 1 is, for example, a CD, a CD-R, a CD-RW, a CD-Video, a CD-ROM, a DV.
Players or drives compatible with optical information recording media such as D, DVD-ROM, DVD-RAM, DVD-R, DVD-RW, DVD + RW, and MD, or AV devices, personal computers, etc. incorporating them It can be installed in a sound and / or image recording device and / or reproducing device such as the information terminal.

[0073]

EXAMPLES FIGS. 3 and 4 show examples of objective lenses in which axial chromatic aberration is corrected by the chromatic aberration correcting optical element according to the present invention. FIG. 3 shows an objective lens (focal length 1.76) whose axial chromatic aberration is corrected by the chromatic aberration correcting optical element of the present invention.
FIG. 8 is an optical path diagram with an image side numerical aperture of 0.85 mm. This objective lens is formed of an olefin resin having an Abbe number of 56.5 for d line. FIG. 4 is a graph showing spherical aberration and axial chromatic aberration at a wavelength of 405 ± 10 nm of this objective lens, showing that when the wavelength changes to the 10 nm long wavelength side, the focus changes to the over side by about 3 μm. There is.

Next, Examples 1 to 3 relating to the optical system of the optical pickup according to the present invention will be described. The aspherical surface in this embodiment is represented by the following formula 1 when the optical axis direction is the X axis, the height in the direction perpendicular to the optical axis is h, and the radius of curvature of the refracting surface is r. However, κ is a cone coefficient and A _2i is an aspherical surface coefficient.

[0075]

[Equation 1]

The ring-shaped diffractive surface provided on the lens of this embodiment can be expressed by the following equation 2 as the optical path difference function Φ _b . Here, n is the diffraction order of the diffracted light having the maximum diffracted light amount among the diffracted light generated on the diffractive surface, and h
Is the height perpendicular to the optical axis, and b _2j is the coefficient of the optical path difference function.

[0077]

[Equation 2]

<Example 1>

Table 1 shows data relating to the optical pickup optical system of Example 1, and FIG. 5 shows an optical path diagram of the optical pickup optical system of Example 1.

[0080]

[Table 1]

In Example 1, the chromatic aberration correcting optical element was formed of an olefin resin, and the axial chromatic aberration of the objective lens was corrected by making both the light source side surface and the objective lens side optical surface diffractive. . Further, the refracting power on each optical surface is negative, the absolute value thereof is the same as the absolute value of the diffraction power, and the total paraxial power of each optical surface is set to 0, so that the chromatic aberration correcting optical element exits. The diameter of the light flux is set to be unchanged relative to the diameter of the incident light flux. further,
The coefficient of the optical path difference function in Table 1 was determined so that the second-order diffracted light had the maximum diffracted light amount.

FIG. 6 is a graph showing spherical aberration and axial chromatic aberration at a wavelength of 405 ± 10 nm in the optical pickup optical system of Example 1, showing that the focus hardly moves regardless of the wavelength.

Further, the diffracting power of the chromatic aberration correcting optical element is determined so that the axial chromatic aberration of the combined system with the objective lens is overcorrected, and further, the spherical aberration on the long wavelength side and the short wavelength side of the combined system are determined. The remaining spherical aberration of over-correction and over-correction of each are left, and the spherical aberration graph of the reference wavelength and the spherical aberration graph of the long wavelength side and the short wavelength side are tolerated to obtain the best image point position when the wavelength changes. , The defocus component of the wavefront aberration when the mode hopping of +1 nm occurs can be reduced to 0.002λrms (calculated value).

When the chromatic aberration of the composite system is corrected as described above, the axial chromatic aberration of the composite system is almost completely corrected, and the spherical aberration on the long wavelength side and the spherical aberration on the short wavelength side are almost completely corrected. Since the gap between the diffraction ring zone structures of the optical element for correcting chromatic aberration can be increased as compared with the case where the movement of the best image point position at the time of wavelength change is suppressed by correction, the shape error of the diffraction ring zone structure at the time of fabrication can be increased. It is possible to reduce the light amount loss due to.

<Example 2>

Table 2 shows data relating to the optical pickup optical system of Example 2, and FIG. 7 shows an optical path diagram of the optical pickup optical system of Example 2.

[0087]

[Table 2]

In Example 2, the chromatic aberration-correcting optical element was formed of an olefin resin, and the optical surface on the light source side was macroscopically a planar diffraction surface to correct the axial chromatic aberration of the objective lens. Further, the refractive power of the optical surface on the objective lens side is made negative, and the absolute value thereof is made equal to the absolute value of the diffraction power of the optical surface on the light source side, whereby the total paraxial power of the chromatic aberration correcting optical element is set to 0. did. Further, the coefficient of the optical path difference function in Table 2 was determined so that the second-order diffracted light has the maximum diffracted light amount.

FIG. 8 is a graph showing spherical aberration and axial chromatic aberration at a wavelength of 405 ± 10 nm in the optical pickup optical system of Example 2, showing that the focus hardly moves regardless of the wavelength.

<Example 3>

Table 3 shows data relating to the optical pickup optical system of Example 3, and FIG. 9 shows an optical path diagram of the optical pickup optical system of Example 3.

[0092]

[Table 3]

In Example 3, the chromatic aberration-correcting optical element was formed of an olefin resin, and the optical surface on the light source side was a diffractive surface to correct the axial chromatic aberration of the objective lens. Also,
By making the refracting power of the optical surface on the light source side negative, and making its absolute value the same as the absolute value of the diffraction power, and making the optical surface on the objective lens side a plane, the total paraxial axis of the chromatic aberration correction optical element The power was set to 0. Further, the coefficient of the optical path difference function in Table 3 was determined so that the second-order diffracted light had the maximum light amount. In addition, by using a term of the second or higher order of the coefficient of the optical path difference function, and by using a diffractive surface having a spherical aberration characteristic such that the spherical aberration changes in the undercorrection direction when the wavelength changes to the long wavelength side, The change in spherical aberration that occurs in the objective lens when the wavelength changes to the long wavelength side is offset and corrected.

FIG. 10 is a graph showing the spherical aberration and the axial chromatic aberration at the wavelength of 405 ± 10 nm of the optical pickup optical system of Example 3, showing that the focal point and the spherical aberration hardly change regardless of the wavelength. .

In the above table or figure, E (or e) is used to express the power of 10, for example, E-02.
It may be expressed as (= 10 ⁻² ). The chromatic aberration correcting optical element in the present invention is defined as follows. That is, the best image point position when light with a certain wavelength λ of 550 nm or less is incident on the objective lens is fB1, and the best image point position when light with a wavelength 10 nm longer than λ is incident on this objective lens. Is fB2, and the best image point position when light of wavelength λ via “a certain optical element” is incident on this objective lens is fB1 ′, and a wavelength 10 nm longer than λ via this “a certain optical element”. When the best image point position when this light is incident on this objective lens is fB2 ', |
When fB2-fB1 |> | fB1'-fB2 '| is satisfied, this "certain optical element" is defined as the chromatic aberration correcting optical element according to the present invention. Further, in the present specification,
The refraction power refers to the power determined by the radius of curvature, the axial thickness, and the paraxial amount of the refractive index. The diffractive power is the optical path difference added to the transmitted wavefront by the diffractive structure by the mathematical formula 2 above.
When expressed by the optical path difference function of, PD = Σ (−2 · b2i · ni) indicates the power of the diffractive structure. The total paraxial power of the optical element and the optical surface refers to the power obtained by combining the refracting power and the diffracting power. That is, when the diffractive structure is not formed on the optical element or the optical surface, the total paraxial power of the optical element or the optical surface is equal to the refractive power of the optical element or the optical surface, and the diffractive structure is formed on the optical element or the optical surface. However, when the refracting power of the optical element or the optical surface is zero, the total paraxial power of the optical element or the optical surface is equal to the diffraction power of the optical element or the optical surface.

[0096]

According to the present invention, since the numerical aperture on the side of the optical information recording medium is large, the axial aberration is corrected for the purpose of correcting spherical aberration, correcting sine conditions and reducing the size, thickness, weight and cost. It is possible to provide a chromatic aberration correcting optical element capable of correcting axial chromatic aberration when used with an objective lens in which chromatic aberration remains.

Further, even when a light source having poor monochromaticity or a light source whose wavelength changes abruptly is used in, for example, a high-density recording optical pickup system, axial chromatic aberration can be corrected with a relatively simple structure. Moreover, it is possible to provide an optical system for an optical pickup that can be manufactured at low cost, an optical pickup device including the optical system, and a recording / reproducing device including the optical system.

[Brief description of drawings]

FIG. 1 is a diagram schematically showing an optical pickup device according to an embodiment of the present invention.

2 (a) is a side view of the chromatic aberration correcting optical element of FIG. 1, and FIG. 2 (b) is a chromatic aberration correcting optical element of FIG. 1 viewed from the arrow direction A of FIG. 2 (a). FIG.

FIG. 3 is a diagram showing an embodiment of an objective lens in which axial chromatic aberration is corrected by a chromatic aberration correcting optical element according to the present invention, and is an optical path diagram of this objective lens.

4 is a graph showing spherical aberration and axial chromatic aberration at a wavelength of 405 ± 10 nm of the objective lens in FIG.

5 is an optical path diagram of the optical pickup optical system of Example 1. FIG.

FIG. 6 is a wavelength 405 of the optical pickup optical system according to the first embodiment.
6 is a graph showing spherical aberration and axial chromatic aberration at ± 10 nm.

FIG. 7 is an optical path diagram of an optical pickup optical system of Example 2.

FIG. 8 is a wavelength 405 of the optical pickup optical system according to the second embodiment.
6 is a graph showing spherical aberration and axial chromatic aberration at ± 10 nm.

FIG. 9 is an optical path diagram of an optical pickup optical system according to a third embodiment.

FIG. 10 is a wavelength 40 of the optical pickup optical system according to the third embodiment.
6 is a graph showing spherical aberration and axial chromatic aberration at 5 ± 10 nm.

[Explanation of symbols]

1 Optical Pickup Device 2 Semiconductor Laser (Light Source) 3 Chromatic Aberration Correction Optical Element 4 Objective Lens 5 Optical Disk (Optical Information Recording Medium) 5 ′ Information Recording Surface S1 Chromatic Aberration Correction Optical Element 3 Surface S2 on the Light Source Side Chromatic Aberration Correction Optical Element Objective lens 3
Side surface p diffraction pattern

   ─────────────────────────────────────────────────── ─── Continued front page    F-term (reference) 2H087 KA13 LA01 NA04 NA14 PA03                       PA17 PB03 QA03 QA05 QA21                       QA25 QA33 QA41 RA05 RA12                       RA13 RA42 RA46 UA01                 5D119 AA02 AA11 AA22 AA40 BA01                       BB01 BB02 BB03 BB04 BB05                       DA01 DA05 EB02 EC03 EC07                       FA05 JA02 JA09 JA12 JA29                       JA32 JA43 JA44 JB01 JB04

Claims (15)

[Claims] 1. An optical element for correcting chromatic aberration arranged in an optical path between a light source which emits light having a wavelength of 550 nm or less and an objective lens formed of a material having an Abbe number of d line of 95.0 or less. An optical element for correcting chromatic aberration, wherein the optical element for correcting chromatic aberration has a diffractive structure including a plurality of annular zone steps on at least one surface and satisfies the following expression. P ₁ <P ₀ <P ₂ where P ₀ : the total paraxial power (m of the chromatic aberration correcting optical element at the wavelength λ ₀ of the light generated by the light source)
m ⁻¹ ) P ₁ : Total paraxial power (m of the chromatic aberration correcting optical element at the wavelength λ _{1 that} is 10 nm shorter than the wavelength λ _0.
m ⁻¹ ) P ₂ : Total paraxial power (m of the chromatic aberration correcting optical element at a wavelength λ _{2 that} is 10 nm longer than the wavelength λ _0.
m ^-1 ) 2. An optical element for correcting chromatic aberration which is arranged in an optical path between a light source which emits light having a wavelength of 550 nm or less and an objective lens which is made of a material having an Abbe number of d line of 95.0 or less. The chromatic aberration correcting optical element has a diffractive structure composed of a plurality of annular zone steps on at least one surface, and m represented by the following equation is an integer other than 0 and ± 1. An optical element for chromatic aberration correction, wherein at least one ring zone step having a step difference Δ (mm) in the optical axis direction is formed within an effective diameter. m = INT (Y) Y = Δ × (n−1) / (λ ₀ × 10 ⁻³ ) where INT (Y): an integer obtained by rounding Y: n: wavelength λ of light generated by the light source Refractive index λ ₀ of the chromatic aberration correcting optical element at ₀ (nm): wavelength (nm) of light generated by the light source 3. An optical element for correcting chromatic aberration arranged in an optical path between a light source that emits light having a wavelength of 550 nm or less and an objective lens made of a material having an Abbe number of d line of 95.0 or less. An optical element for correcting chromatic aberration, wherein the optical element for correcting chromatic aberration has a diffractive structure having a plurality of annular zone steps on at least two surfaces. 4. An optical element for correcting chromatic aberration arranged in an optical path between a light source that emits light having a wavelength of 550 nm or less and an objective lens formed of a material having an Abbe number of d-line of 95.0 or less. The element, wherein the chromatic aberration correcting optical element is a single lens, and when viewed macroscopically, one optical surface on which a diffractive structure composed of a plurality of flat annular zones is formed, and the opposite surface. And the other optical surface formed on the concave refracting surface, and a chromatic aberration correcting optical element. 5. The optical element for correcting chromatic aberration satisfies the following equation.
It adds to any one of Claims 1 thru | or 4 characterized by the above-mentioned.
An optical element for chromatic aberration correction described. 0.5 x 10^-2<P_D<15.0 x 10^-2 However, P_D: Formed on the i-th surface of the chromatic aberration correcting optical element
Diffractive structure transmits the chromatic aberration correction optical element
Optical path difference Φ added to wavefront_biIs the height h from the optical axis
_iAs a function of (mm) Φ_bi= Ni ・ (b_2i・ Hi^Two+ b_4i・ Hi^Four+ b_6i・
hi⁶+ ...) When expressed by the optical path difference function defined by
i represents the diffracted light generated by the diffractive structure formed on the i-th surface.
And the diffraction order of the diffracted light having the maximum diffracted light amount, b _2i,
b_4i, B_6i... are 2nd, 4th, 6th,
Is an optical path difference function coefficient (also referred to as a diffractive surface coefficient) of
), P_D= Σ (-2 · b_2i・ Ni) Diffractive power as a diffractive lens defined by (mm
^-1) 6. The chromatic aberration correcting optical element according to claim 5, wherein the chromatic aberration correcting optical element satisfies the following expression. 1.0 × 10 ⁻² <P _D <10.0 × 10 ⁻² 7. A plurality of ring steps on at least one surface
Is characterized by satisfying the following formula:
Optical element for chromatic aberration correction. 1.0 x 10^-2<P_D<10.0 x 10^-2 However, P_D: Formed on the i-th surface of the chromatic aberration correcting optical element
Diffractive structure transmits the chromatic aberration correction optical element
Optical path difference Φ added to wavefront_biIs the height h from the optical axis
_iAs a function of (mm) Φ_bi= Ni ・ (b_2i・ Hi^Two+ b_4i・ Hi^Four+ b_6i・
hi⁶+ ...) When expressed by the optical path difference function defined by
i represents the diffracted light generated by the diffractive structure formed on the i-th surface.
And the diffraction order of the diffracted light having the maximum diffracted light amount, b _2i,
b_4i, B_6i... are 2nd, 4th, 6th,
Is an optical path difference function coefficient (also referred to as a diffractive surface coefficient) of
), P_D= Σ (-2 · b_2i・ Ni) Diffractive power as a diffractive lens defined by (mm
^-1) 8. The chromatic aberration correcting optical element is characterized in that a total paraxial power P _{0 of the} chromatic aberration correcting optical element at a wavelength λ ₀ of light generated by the light source is substantially zero. 8. The chromatic aberration correcting optical element according to any one of 1 to 7. 9. The chromatic aberration correcting optical element according to claim 8, wherein the chromatic aberration correcting optical element satisfies the following equation. P _D > 0 P _R <0 −0.9 <P _D / P _R <−1.1, where P _R : refraction power (mm ⁻¹ ) of the chromatic aberration correction optical element as a refraction lens. 10. A spherical aberration characteristic that, when the wavelength of an incident light beam is changed to a long wavelength side, the spherical aberration of the emitted light beam is changed so as to be undercorrected or overcorrected. 10. At least one surface having a diffractive structure satisfying the formula is provided.
The optical element for correcting chromatic aberration according to any one of 1. 0.2 ≦ | (P _hf / P _hm ) −2 | ≦ 6.0, where P _hf : annular zone spacing P _{hm in} a direction perpendicular to the optical axis of the diffractive structure at a position hf that is half the maximum effective diameter _hm. : Ring spacing in the direction perpendicular to the optical axis of the diffractive structure at the maximum effective diameter hm 11. The wavelength at which the diffraction efficiency is maximum is 550 n.
The chromatic aberration correcting optical element according to any one of claims 1 to 10, wherein the optical element is m or less. 12. The chromatic aberration correcting optical element according to claim 1, wherein the chromatic aberration correcting optical element is a plastic lens. 13. A light source that emits light having a wavelength of 550 nm or less, an objective lens formed of a material having an Abbe number of d-line of 95.0 or less, and an optical path between the light source and the objective lens. And an optical element for chromatic aberration correction arranged in, reproducing information from the information recording surface of the optical information recording medium,
And / or an optical system for recording information on an information recording surface, comprising the chromatic aberration correcting optical element according to any one of claims 1 to 12 as the chromatic aberration correcting optical element. And optical system. 14. A light source for generating light having a wavelength of 550 nm or less, an objective lens formed of a material having an Abbe number of 95.0 or less for d-line, and an optical path between the light source and the objective lens. An optical pickup for reproducing information from an information recording surface of an optical information recording medium and / or recording information on the information recording surface, comprising a condensing optical system having a chromatic aberration correcting optical element arranged in An optical pickup device comprising the optical system according to claim 13 as the condensing optical system. 15. An audio and / or image recording device, and / or an audio and / or image reproducing device, comprising the optical pickup device according to claim 14.