JP2005317103A - Optical element and optical pickup device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical element and an optical pickup device which can improve the wavelength characteristic and the temperature characteristic. <P>SOLUTION: The optical element is for use in an optical pickup device for reproducing and/or recording information using a light flux having the wavelength λ (390 nm ≤λ≤420 nm), at least for an optical disk having the thickness d[mm] of a protective substrate. The optical element has the base member of a resin, and is composed of a mixed material in which fine particles having the refractive index variation (Δn<SB>2</SB>/Δt) according to the temperature variation reverse to the refractive index variation (Δn<SB>1</SB>/Δt) according to the temperature variation of the resin are dispersed into the resin, wherein the spherical aberration SA<SB>1</SB>[λRMS] generated when the use temperature of the optical pickup device rises by 30°C satisfies expression (1): ¾(SA<SB>1</SB>/λ<SP>2</SP>)×(Δn<SB>3</SB>/Δt)×NA<SP>4</SP>×2d×10<SP>9</SP>¾≤9.9. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an optical element used in an optical pickup device and an optical pickup device.

In recent years, in an optical pickup device, a laser light source used as a light source for reproducing information recorded on an optical disc and recording information on the optical disc has been shortened. For example, a blue-violet semiconductor laser, A laser light source having a wavelength of 405 nm such as a blue-violet SHG laser that performs wavelength conversion of an infrared semiconductor laser using harmonic generation is being put into practical use.
When these blue-violet laser light sources are used, when an objective lens having the same numerical aperture (NA) as that of a digital versatile disk (hereinafter abbreviated as DVD) is used, information of 15 to 20 GB is recorded on an optical disk having a diameter of 12 cm. Recording becomes possible, and when the NA of the objective lens is increased to 0.85, 23 to 27 GB of information can be recorded on an optical disk having a diameter of 12 cm. Hereinafter, in this specification, an optical disk and a magneto-optical disk using a blue-violet laser light source are collectively referred to as a “high density optical disk”.

  By the way, two standards are currently proposed as high-density optical disks. One is a Blu-ray disc (hereinafter abbreviated as BD) with an NA0.85 objective lens and a protective layer thickness of 0.1 mm, and the other is an NA0.65 to 0.67 objective lens. And an HD DVD (hereinafter abbreviated as HD) having a protective layer thickness of 0.6 mm. In view of the possibility that these two high-density optical discs will be distributed in the market in the future, compatible optical pickup devices capable of recording / reproducing existing DVDs on any high-density optical disc Is important, and among them, the one-lens system that is compatible with the objective lens is the most ideal form.

Conventionally, in an optical pickup device having compatibility, as a method for correcting spherical aberration caused by the difference in the wavelength of the light beam used in a plurality of optical disks and the thickness of the protective substrate, the incident light beam to the objective optical system is corrected. There are known techniques for changing the degree of divergence or providing a diffractive structure on the optical surface of an optical element constituting an optical pickup device.
Also, BD has a small spot area focused on the information recording surface, and NA is very high compared to other recording media. Therefore, when the focal depth of the objective lens is reduced and instantaneous wavelength fluctuation occurs. Since there is a problem that chromatic aberration occurs, there is known a technique for improving a lens characteristic (wavelength characteristic) against a wavelength variation by using a diffraction structure.

In addition, the optical pickup device is configured by combining various optical elements such as an objective lens, a coupling lens, and a beam expander, and these optical elements are often made of lightweight and inexpensive plastic. Has a characteristic that the refractive index changes due to a temperature change. For example, in a plastic objective lens, there arises a problem that spherical aberration occurs in the over direction due to a temperature rise.
Therefore, in order to improve the lens characteristics (temperature characteristics) against such temperature changes, a diffractive structure is provided on the optical surface of the objective lens, and spherical aberration is generated in the under direction by the diffractive structure. There is known a technique for canceling the spherical aberration generated in the above.

Thus, in recent years, diffractive structures have been used for various purposes such as achieving compatibility and improving wavelength characteristics and temperature characteristics. For example, only such diffractive structures provided in an objective lens have such functions. The problem is that lens design is difficult. Therefore, a technique is known in which the objective lens is provided with a diffractive structure, and a collimator lens provided separately from the objective lens is provided with a diffractive structure to correct chromatic aberration and achieve compatibility between two types of optical disks. (For example, refer to Patent Document 1).
JP 2001-60336 A

  However, even if the technique described in Patent Document 1 is used, the above-described wavelength characteristics and temperature characteristics cannot be improved sufficiently, and technical means capable of improving the degree of freedom in lens design are required. Yes.

  An object of the present invention is to provide an optical element and an optical pickup device that can improve the wavelength characteristics and temperature characteristics in consideration of the above-described problems.

In the present specification, in addition to the above-described BD and HD, an optical disc having a protective film with a thickness of several to several tens of nm on the information recording surface, and the protective layer or protective film has a thickness of 0 (zero). These optical disks are also included in the high density optical disk.
In this specification, DVD is a general term for DVD optical discs such as DVD-ROM, DVD-Video, DVD-Audio, DVD-RAM, DVD-R, DVD-RW, DVD + R, DVD + RW, and the like. Is a general term for optical discs of CD series such as CD-ROM, CD-Audio, CD-Video, CD-R, CD-RW and the like.

In order to solve the above-mentioned problems, the invention according to claim 1 is characterized in that at least an optical disk having a protective substrate thickness d [mm] is used for reproducing information by using a light beam having a wavelength λ (390 nm ≦ λ ≦ 420 nm). In the optical element used for the optical pickup device that performs recording, the optical element is made of resin as a base material, and the refractive index is changed by the temperature change of the resin opposite to the change in refractive index (Δn ₁ / Δt). Spherical aberration SA ₁ [λRMS], which is made of a mixed material in which fine particles having a change (Δn ₂ / Δt) are dispersed in the resin and is generated when the operating temperature of the optical pickup device is increased by 30 ° C., is (1 ) Is satisfied.
| (SA ₁ / λ ² ) · (Δn ₃ / Δt) · NA ⁴ · 2d · 10 ⁹ | ≦ 9.9 (1)
Where SA ₁ is the third-order, fifth-order, and seventh-order square sum, Δn ₃ / Δt is the refractive index change due to the temperature change of the mixed material, and NA is the numerical aperture on the exit side of the objective lens included in the optical pickup device. is there.

According to a second aspect of the present invention, in the optical element of the first aspect, the expression (2) is satisfied.
| (Δn ₁ / Δt) | ≧ 2 · | (Δn ₃ / Δt) | (2)

As in the invention of claim 1, the optical element, a resin as a base material, the refractive index change (Δn ₁ / Δt) and the opposite sign change in refractive index due to temperature change due to the temperature change of the resin ([Delta] n ₂ / The spherical aberration SA _{1 that} is formed by a mixed material in which fine particles having Δt) are dispersed in the resin and that is generated when the operating temperature of the optical pickup device rises by 30 ° C. is set so as to satisfy the above formula (1). Therefore, it is possible to correct spherical aberration with respect to temperature change by suppressing the amount of change in refractive index with respect to temperature change, and the optical element that does not deteriorate the condensing performance even if the environmental temperature changes even though it is a single lens with high NA Is possible.
In this way, by mixing fine particles (for example, inorganic fine particles) in a resin (for example, plastic material), a new optical material having a reduced refractive index due to temperature change while maintaining the moldability of the plastic material. In this specification, it is called “athermal resin”.
The refractive index change (Δn ₃ / Δt) due to the temperature change of the fine particles to be dispersed does not necessarily have the opposite sign to that of the base material. A value smaller than the refractive index change (Δn ₁ / Δt) due to the temperature change of the base material may be used, but in this case, a large amount must be dispersed in order to obtain the target mixed material, resulting in poor moldability. Therefore, it is desirable that Δn ₃ / Δλ is a reverse sign of Δn ₁ / Δλ.
Further, if the optical element is a high NA optical element (emission side NA 0.6 to 0.9) and the optical element used for the optical disk pickup optical system having the wavelength λ is SA1 satisfying the expression (1), the NA Recording and reproduction can be performed without any problem on an optical disc.
For example, when using an objective lens with an NA of 0.65 for HD, it is preferable to satisfy | (SA ₁ / λ ² ) · (Δn ₃ / Δt) · NA ⁴ · 2d · 10 ⁹ | ≦ 4.0. For example, when using an objective lens with NA of 0.85 for BD, it is preferable that | (SA ₁ / λ ² ) · (Δn ₃ / Δt) · NA ⁴ · 2d · 10 ⁹ | ≦ 9.9.

  By using such an athermal resin as the material of the optical element, there is an advantage that it is possible to mass-produce a single lens which is a lens of NA 0.85 but does not require a separate correction element by injection molding. .

但し、Ａ：温度変化に対する光学素子の屈折率の変化率、ｎ：光学素子の屈折率、α：光学素子の線膨張係数、[Ｒ]：光学素子の分子屈折力 Here, the temperature change of the refractive index in the optical element of the present invention will be described. The rate of change of the refractive index with respect to the temperature change is expressed by A in the following formula (1) by differentiating the refractive index n with respect to the temperature t based on the Lorentz-Lorenz formula.

Where A: change rate of refractive index of optical element with respect to temperature change, n: refractive index of optical element, α: linear expansion coefficient of optical element, [R]: molecular refractive power of optical element

In the case of a general plastic material, the contribution of the second term is smaller than that of the first term in Equation 1, so the second term can be almost ignored. For example, in the case of acrylic resin (PMMA), the linear expansion coefficient α is 7 × 10 ^{−5, and if} it is substituted into the above equation, A = −12 × 10 ⁻⁵ , which substantially matches the actual measurement value.
Here, in the optical element of the present invention, for example, by dispersing fine particles having a diameter of 50 nm or less in a plastic material, the contribution of the second term of the above formula is substantially increased, and by the linear expansion of the first term. I try to counteract changes.

Specifically, it is preferable to suppress the refractive index change rate with respect to the temperature change, which was conventionally about −12 × 10 ⁻⁵ , to an absolute value of less than 10 × 10 ⁻⁵ . More preferably, it is preferably less than 8 × 10 ⁻⁵ , and more preferably less than 6 × 10 ⁻⁵ , in order to reduce a change in spherical aberration accompanying a temperature change.
For example, by dispersing fine particles of niobium oxide (Nb ₂ O ₅ ) in acrylic resin (PMMA), the dependency of the refractive index change on the temperature change can be eliminated.
If the refractive index change Δn ₃ / Δt due to the temperature change of the mixed material is 50% or less of the refractive index change Δn ₁ / Δt due to the temperature change of the base material as in the invention of claim 2, the environmental temperature increased by 30 ° C. It is possible to obtain an optical element in which spherical aberration occurring at this time is corrected to a Marshall limit of 0.07 [λrms] or less.

The plastic material used as the base material has a volume ratio of 80 and niobium oxide in a ratio of about 20, and these are uniformly mixed. There is a problem that the fine particles are likely to aggregate, but a technique of applying a charge to the particle surface to disperse the particles is also known, and a necessary dispersion state can be generated.
This volume ratio can be appropriately increased or decreased in order to control the rate of change in refractive index with respect to temperature change, and a plurality of types of nano-sized inorganic particles can be blended and dispersed.
The volume ratio is 80:20 in the above example, but can be appropriately adjusted between 90:10 and 60:40. If the volume ratio is smaller than 90:10, the effect of suppressing the change in refractive index is reduced. Conversely, if the volume ratio exceeds 60:40, a problem occurs in the moldability of the athermal resin, which is not preferable.

The fine particles are preferably oxides, and more preferably oxides that are saturated in oxidation state and do not oxidize any more.
In addition, it is preferable that the fine particles are inorganic in order to keep the reaction with the plastic material, which is a high molecular organic compound, low, and because it is an oxide, the transmittance deterioration due to long-term irradiation of the blue-violet laser And wavefront aberration deterioration can be prevented. In particular, oxidation is likely to be accelerated under the severe condition of being irradiated with a blue-violet laser at a high temperature. However, with such an inorganic oxide, it is possible to prevent transmittance deterioration and wave aberration deterioration due to oxidation.

  When the diameter of the fine particles dispersed in the plastic material is large, the incident light beam is easily scattered and the transmittance of the condensing lens is lowered. In a blue-violet semiconductor laser used for recording / reproducing information in a high-density optical disk, the laser power with which a stable laser oscillation can be obtained for a long time is about 30 mW, so the transmittance of the optical element with respect to the blue-violet laser is low. This is disadvantageous in terms of speeding up of information recording and compatibility with multilayer discs. Accordingly, the diameter of the fine particles dispersed in the plastic material is preferably 20 nm or less, and more preferably 10 to 15 nm or less in order to prevent a decrease in transmittance of the condenser lens.

According to a third aspect of the present invention, there is provided an optical pickup device that reproduces and / or records information using a light beam having a wavelength λ (390 nm ≦ λ ≦ 420 nm) for at least an optical disc having a protective substrate thickness d [mm]. In the optical element used, the optical element is made of resin as a base material, and has a refractive index change (Δn ₁ / Δλ) due to a wavelength change of the resin and a refractive index change (Δn ₂ / Δλ) due to a wavelength change opposite in sign. It is characterized by comprising a mixed material in which fine particles are dispersed in the resin.

As in the embodiment described in claim 3, the optical element, a resin as a base material, the refractive index change due to the wavelength change of the resin (Δn ₁ / Δλ) and opposite sign change in refractive index due to the wavelength change of (Δn ₂ / Δλ It is possible to suppress the amount of change in the refractive index with respect to the wavelength change, and even if the wavelength of the light source deviates from the reference wavelength, the spherical aberration is reduced. A well corrected optical element can be obtained. Furthermore, although it is a single lens having a high NA, the degree of freedom in lens design is increased as compared with the conventional lens, and the effects of reducing the chromatic aberration of the objective lens can be obtained.
The refractive index change (Δn ₃ / Δλ) due to the wavelength change of the fine particles to be dispersed does not necessarily have the opposite sign to that of the base material. The value may be smaller than the refractive index change (Δn ₁ / Δλ) due to the wavelength change of the base material. However, in order to obtain a target mixed material, a large amount of dispersion is required, and the moldability deteriorates. Therefore, it is desirable that Δn ₃ / Δλ is a reverse sign of Δn ₁ / Δλ.

According to a fourth aspect of the present invention, in the optical element according to the third aspect, the Abbe number ν _d3 of the mixed material at the d-line satisfies the expression (3).
1.1 ・ ν _d1 ≦ ν _d3 (3)
Where ν _d1 is the Abbe number of the base material on the d-line, and νd ₁ and ν _d3 are both obtained from ν _d = (n _d −1) / (n _F −n _c ), where n _d is a refractive index at the d-line of the base material, n _F is the refractive index at the F-line of the base material, the n _c is the refractive index at C line of the base material.

If the Abbe number ν _d3 in the mixed material d-line is 1.1 times or more compared to the Abbe number νd ₁ in the d-line of the base material as in the invention of claim 4, it is dispersed as compared with the conventional resin. Therefore, the spherical aberration when there is a deviation from the reference wavelength can be corrected to a Marshall limit of 0.077 [λrms] or less.

The invention according to claim 5 is the optical element according to claim 3 or 4, characterized in that the spherical aberration SA ₂ [λRMS] generated when the wavelength λ fluctuates ± 5 nm satisfies the equation (4). .
| (SA ₂ / λ ² ) · (Δn ₃ / Δλ) · NA ⁴ · 2d · 10 ⁹ | ≦ 18.5 (4)
Where SA ₁ is the third-order, fifth-order, and seventh-order square sum, Δn ₃ / Δλ is the refractive index change due to the wavelength change of the mixed material, and NA is the numerical aperture on the exit side of the objective lens included in the optical pickup device. is there.

It is well known that spherical aberration increases in proportion to the fourth power of NA. Therefore, even if it is a high NA optical element (emission side NA 0.6 to 0.9), if it is SA2 that satisfies the expression (4) as in the invention of claim 5, recording can be performed without problem on the optical disk of the corresponding NA. And can play.
For example, when an objective lens with NA of 0.65 for HD is used, it is preferable that | (SA ₂ / λ ² ) · (Δn ₃ / Δλ) · NA ⁴ · 2d · 10 ⁹ | ≦ 7.8 is satisfied. For example, when using an objective lens with NA of 0.85 for BD, it is preferable to satisfy | (SA ₂ / λ ² ) · (Δn ₃ / Δλ) · NA ⁴ · 2d · 10 ⁹ | ≦ 18.5.

According to a sixth aspect of the present invention, in the optical element according to any one of the third to fifth aspects, when the wavelength λ fluctuates ± 1 nm, the condensed spot formed on the information recording surface of the optical disc The wavefront aberration minimum position change amount Δfb [nm] in the optical axis direction satisfies the expression (5).
| Δfb / λ | ≦ 0.4 (5)

  As in the invention of claim 6, when the wavelength λ fluctuates by ± 1 nm in an optical element made of a mixed material, the change in the minimum position of wavefront aberration in the optical axis direction at the focused spot formed on the information recording surface of the optical disc If the amount Δfb (nm) is a value satisfying the expression (5), recording and reproduction can be performed without any problem on an optical disk using the corresponding λ even if a wavelength variation due to mode hop occurs. Further, in the case of an optical element with NA of 0.8 to 0.9, since spherical aberration is proportional to the fourth power of NA, when focusing on correcting spherical aberration in response to temperature change, an element with NA of around 0.65 As compared with, the aberration deterioration at the time of wavelength change becomes remarkable. If the temperature characteristic and the wavelength characteristic are satisfied at the same time, it is difficult to reduce Δfb. However, if Δfb satisfying the equation (5) is satisfied, it can be corrected by a separate complement such as a liquid crystal, and this is a problem in an optical disc of the corresponding NA Can be recorded and played back.

The invention according to claim 7 is an optical pickup device that reproduces and / or records information by using a light beam having a wavelength λ (390 nm ≦ λ ≦ 420 nm) for at least an optical disc having a protective substrate thickness d [mm]. In the optical element used, the optical element is made of resin as a base material, and has a refractive index change (Δn ₁ / Δt) due to a temperature change of the resin and a refractive index change (Δn ₂ / Δt) due to a temperature change opposite in sign. Fine particles A and fine particles B having a refractive index change (Δn ₁ / Δλ) due to a wavelength change of the resin and a refractive index change (Δn ₂ / Δλ) due to a wavelength change of the opposite sign were dispersed in the resin. It is characterized by comprising a mixed material.

As in the invention of claim 7, the optical element, a resin as a base material, the refractive index change due to the temperature change of the resin (Δn ₁ / Δt) and the opposite sign change in refractive index due to temperature change (Δn ₂ / Δt ) And fine particles B having a refractive index change (Δn ₁ / Δλ) due to a wavelength change of the resin and a refractive index change (Δn ₂ / Δλ) due to a wavelength change of the opposite sign are dispersed in the resin. By using the mixed material, it is possible to suppress both the amount of change in refractive index with respect to temperature change and the amount of change in refractive index with respect to wavelength change.

  The invention according to claim 8 is the optical element according to claim 7, wherein the fine particles A and the fine particles B are different particles.

  If the ratio of the total volume of the fine particles A and the fine particles B dispersed in the resin, which is a base material, to the volume of the base material exceeds 40:60, the moldability of the mixed material is deteriorated. If the fine particles A and the fine particles B are different from each other as described in (1), the volume ratio of the two particles A and B can be freely changed in order to obtain a target mixed material. Specifically, if importance is attached to the temperature change of the resulting mixed material, the fine particles A are more important than the other fine particles if the refractive index change in the wavelength change of the obtained mixed material is important. Many can be dispersed. Note that each of the fine particles A and the fine particles B is not necessarily one kind of fine particles.

  The invention according to claim 9 is the optical element according to claim 7, wherein the fine particles A and the fine particles B are the same particles.

  If the ratio of the volume of the fine particles dispersed in the resin as the base material to the volume of the base material exceeds 40:60, the moldability of the mixed material deteriorates. When A and the fine particles B are the same particles, an athermal resin that has a sufficient effect of suppressing the refractive index change and does not affect the moldability can be obtained.

According to a tenth aspect of the present invention, in the optical element according to any one of the seventh to ninth aspects, the spherical aberration SA ₁ [λRMS] generated when the operating temperature of the optical pickup device increases by 30 ° C. is (1). ) Is satisfied.
| (SA ₁ / λ ² ) · (Δn ₃ / Δt) · NA ⁴ · 2d · 10 ⁹ | ≦ 9.9 (1)
Where SA ₁ is the third-order, fifth-order, and seventh-order square sum, Δn ₃ / Δt is the refractive index change due to the temperature change of the mixed material, and NA is the numerical aperture on the exit side of the objective lens included in the optical pickup device. is there.

  If the spherical aberration SA1 [λrms] generated when the environmental temperature rises by 30 ° C. is a numerical value satisfying the expression (1) as in the invention of claim 10, SA1 is equal to or less than the Marshall limit of 0.07 [λrms]. Yes, recording and reproduction can be performed without any problem with the corresponding NA on an optical disk having a protective substrate thickness d [mm].

An eleventh aspect of the present invention is the optical element according to the tenth aspect, wherein the expression (2) is satisfied.
| (Δn ₁ / Δt) | ≧ 2 · | (Δn ₃ / Δt) | (2)

As in the invention of claim 11, fine particles A having a refractive index change (Δn ₂ / Δt) due to temperature and fine particles B having a refractive index change (Δn ₂ / Δλ) due to a wavelength change are used as the base resin. If the refractive index change (Δn ₃ / Δt) due to the temperature change of the dispersed mixed material is 50% or less of the refractive index change (Δn ₁ / Δt) due to the temperature change of the base material, when the environmental temperature increases by 30 ° C. It is possible to obtain an optical element in which the generated spherical aberration is corrected to a Marechal limit of 0.07 [λrms] or less.

The invention according to claim 12 is the optical element according to any one of claims 7 to 11, wherein the Abbe number ν _d3 of the mixed material at the d-line satisfies the expression (3).
1.1 ・ ν _d1 ≦ ν _d3 (3)
Where ν _d1 is the Abbe number of the base material at the d-line, and νd ₁ and ν _d3 are both obtained from ν _d = (n _d −1) / (n _F −n _c ), where n _d is a refractive index at the d-line of the base material, n _F is the refractive index at the F-line of the base material, the n _c is the refractive index at C line of the base material.

If the Abbe number ν _d3 in the mixed material d-line is 1.1 times or more compared to the Abbe number νd ₁ in the d-line of the base material as in the invention of claim 12, it is dispersed as compared with the conventional resin. Therefore, it is possible to correct the spherical aberration when there is a deviation from the reference wavelength to a marginal limit of 0.07 [λrms] or less.

According to a thirteenth aspect of the present invention, in the optical element according to any one of the seventh to twelfth aspects, the spherical aberration SA ₂ [λRMS] generated when the wavelength λ fluctuates ± 5 nm satisfies the equation (4). It is characterized by that.
| (SA ₂ / λ ² ) · (Δn ₃ / Δλ) · NA ⁴ · 2d · 10 ⁹ | ≦ 18.5 (4)
Where SA ₁ is the third-order, fifth-order, and seventh-order square sum, Δn ₃ / Δλ is the refractive index change due to the wavelength change of the mixed material, and NA is the numerical aperture on the exit side of the objective lens included in the optical pickup device. is there.

  The spherical aberration SA2 that occurs when the wavelength λ ′ (390 nm to 420 nm) is changed by ± 5 nm increases in proportion to the fourth power of NA. Therefore, if the SA2 satisfies the expression (4) as in the thirteenth aspect of the invention, recording and reproduction can be performed without any problem on the optical disk having the NA.

A fourteenth aspect of the present invention is the optical element according to any one of the seventh to thirteenth aspects, wherein the condensed spot formed on the information recording surface of the optical disc when the wavelength λ varies ± 1 nm. The wavefront aberration minimum position change amount Δfb [nm] in the optical axis direction satisfies the expression (5).
| Δfb / λ | ≦ 0.4 (5)

  As in the invention of claim 14, when the wavelength λ varies ± 1 nm in an optical element made of a mixed material, the change in the minimum position of wavefront aberration in the optical axis direction at the focused spot formed on the information recording surface of the optical disc If the amount Δfb (nm) is a value satisfying the equation (5), recording and reproduction can be performed without any problem on an optical disk using the corresponding λ even if wavelength variation due to mode hops occurs.

According to a fifteenth aspect of the present invention, in the optical element according to any one of the third to fourteenth aspects, the refractive indexes of the base material and the mixed material with respect to the light flux having the wavelength λ are N ₁ and N ₃ , respectively. when defined maximum effective diameter h _max of the light source side optical surface of the optical element, the angle formed by the tangent and the optical axis in the h _max of the optical surface and alpha, satisfies the expression (6) and (7) It is characterized by that.
N ₁ <N ₃ (6)
26.0 ° ≦ α (7)

As in the invention described in claim 15, under the condition of N ₁ <N ₃ , the angle α formed by the tangent and the optical axis at the maximum effective diameter h _max of the optical surface satisfies the above expression (7). The curvature of the optical surface on the light source side can be suppressed. When the lens surface is relatively shifted and tilted (decentered) due to the gentle curvature, coma aberration deterioration is smaller than that of an optical element having a large curvature. Therefore, by satisfying the expression (7), the tolerance for eccentricity in manufacturing can be increased and the productivity can be improved.

  The invention according to claim 16 is the optical element according to any one of claims 1 to 15, wherein an average particle diameter of the fine particles in the mixed material is 50 nm or less.

When the average particle size of the fine particles exceeds 50 nm, the resulting mixed material becomes cloudy and the transparency is lowered, and the light transmittance of the optical element becomes 70% or less. Preferably it is 20 nm or less, More preferably, it is 10-15 nm or less.
Examples of the fine particles used in the present invention include oxide fine particles. More specifically, for example, titanium oxide, zinc oxide, aluminum oxide, zirconium oxide, hafnium oxide, niobium oxide, tantalum oxide, magnesium oxide, calcium oxide, strontium oxide, barium oxide, yttrium oxide, lanthanum oxide, cerium oxide, Phosphate and sulfate formed in combination with oxides such as indium oxide, tin oxide, lead oxide, and lithium oxides of double oxide such as lithium niobate, potassium niobate, and lithium tantalate Etc.

As the inorganic fine particles of the present invention, fine particles having a semiconductor crystal composition can also be preferably used. Although there is no restriction | limiting in particular in this semiconductor crystal composition, What does not produce absorption, light emission, fluorescence, etc. in the wavelength range used as an optical element is desirable. Specific examples of the composition include simple elements of Group 14 elements of the periodic table such as carbon, silicon, germanium and tin, simple elements of Group 15 elements of the periodic table such as phosphorus (black phosphorus), and periodic tables such as selenium and tellurium. A single group 16 element, a compound comprising a plurality of group 14 elements such as silicon carbide (SiC), tin (IV) (SnO2), tin sulfide (II, IV) (Sn (II) Sn (IV) S3), tin sulfide (IV) (SnS2), tin sulfide (II) (SnS), tin selenide (II) (SnSe), tin telluride (II) (SnTe), lead sulfide (II) (PbS), Compound of periodic table group 14 element and periodic table group 16 element such as lead (II) selenide (PbSe), lead telluride (II) (PbTe), boron nitride (BN), boron phosphide (BP) Boron arsenide (BAs), aluminum nitride (AlN), aluminum phosphide (AlP) Aluminum arsenide (AlAs), aluminum antimonide (AlSb), gallium nitride (GaN), gallium phosphide (GaP), gallium arsenide (GaAs), gallium antimonide (GaSb), indium nitride (InN), indium phosphide (InP) ), Indium arsenide (InAs), indium antimonide (InSb), etc., compounds of Group 13 elements of the periodic table and Group 15 elements of the periodic table (or III-V compound semiconductors), aluminum sulfide (Al2S3), selenide Aluminum (Al2Se3), Gallium sulfide (Ga2S3), Gallium selenide (Ga2Se3), Gallium telluride (Ga2Te3), Indium oxide (In2O3), Indium sulfide (In2S3), Indium selenide (In2Se3), Indium telluride (I Compounds of Group 13 elements of the periodic table and Group 16 elements of the periodic table, such as 2Te3), thallium chloride (I) (TlCl), thallium bromide (I) (TlBr), thallium iodide (I) (TlI), etc. A compound of a periodic table group 13 element and a periodic table group 17 element, zinc oxide (ZnO), zinc sulfide (ZnS), zinc selenide (ZnSe), zinc telluride (ZnTe), cadmium oxide (CdO), Periodic table Group 12 elements such as cadmium sulfide (CdS), cadmium selenide (CdSe), cadmium telluride (CdTe), mercury sulfide (HgS), mercury selenide (HgSe), mercury telluride (HgTe) and the periodic table Compounds with group 16 elements (or II-VI compound semiconductors), arsenic (III) sulfide (As2S3), arsenic selenide (III) (As2Se3), arsenic telluride (III) (As Te3), antimony sulfide (III) (Sb2S3), antimony selenide (III) (Sb2Se3), antimony telluride (III) (Sb2Te3), bismuth sulfide (III) (Bi2S3), bismuth selenide (III) (Bi2Se3) , Bismuth telluride (III) (Bi2Te3) periodic table group 15 element and periodic table group 16 element compound, copper (I) (Cu2O), selenide copper (I) (Cu2Se), etc. Compounds of Group 11 elements and Periodic Group 16 elements, copper (I) (CuCl), copper (I) (CuBr), copper (I) (CuI), silver chloride (AgCl) A compound of a periodic table group 11 element such as silver bromide (AgBr) and a periodic table group 17 element, a periodic table group 10 element such as nickel (II) (NiO), and a group 16 element of the periodic table; The compound of oxide (II) (CoO), cobalt sulfide (II) (CoS) periodic table group 9 element and periodic table group 16 element compound, triiron tetroxide (Fe3O4), iron sulfide (II) (FeS) ), Etc., compounds of Group 8 elements of the Periodic Table, elements of Group 16 of the Periodic Table, compounds of Group 7 elements of the Periodic Table, such as manganese (II) (MnO), and Group 16 elements of the Periodic Table, molybdenum sulfide ( IV) (MoS2), tungsten oxide (IV) (WO2) and other compounds of Group 6 elements of the periodic table and Group 16 elements of the periodic table, vanadium oxide (II) (VO), vanadium oxide (IV) (VO2) A compound of a periodic table group 5 element such as tantalum (V) (Ta2O5) and a periodic table group 16 element, a periodic table group 4 element such as titanium oxide (TiO2, Ti2O5, Ti2O3, Ti5O9, etc.) and a period Table 16. Compounds with Group 16 elements, Magnesium sulfide (MgS), magnesium selenide (MgSe) and the like, compounds of Group 2 elements of the periodic table and Group 16 elements of the periodic table, cadmium (II) chromium (III) (CdCr 2 O 4), cadmium selenide (II) chromium ( III) (CdCr2Se4), copper sulfide (II) chromium (III) (CuCr2S4), chalcogen spinels such as mercury selenide (II) chromium (III) (HgCr2Se4), barium titanate (BaTiO3), and the like. In addition, G. Schmid et al .; Adv. Mater. 4, 494 (1991) (BN) 75 (BF2) 15F15 and D.C. Fenske et al .; Angew. Chem. Int. Ed. Engl. 29, page 1452 (1990), a semiconductor cluster whose structure is determined like Cu146Se73 (triethylphosphine) 22 reported in the same manner is also exemplified.
As these fine particles, one kind of inorganic fine particles may be used, or a plurality of kinds of inorganic fine particles may be used in combination.

  The invention according to claim 17 is the optical element according to any one of claims 1 to 16, wherein the optical element is constituted by a single lens.

  In the conventional plastic optical element, there is a technique of using two components to correct spherical aberration when the environmental temperature rises by 30 ° C., but the assembly adjustment of two lenses and the number of parts increase. The cost increase is inevitable. In addition, it is desired that a pickup for a personal computer is lightweight and thin. Therefore, according to the seventeenth aspect, by using one optical element, the problem of the two-element structure can be solved, and the pickup can be made light and compact.

  An eighteenth aspect of the invention includes the optical element according to any one of the first to seventeenth aspects.

  According to the present invention, an optical element and an optical pickup device that can improve wavelength characteristics and temperature characteristics can be obtained.

Hereinafter, the best mode for carrying out the present invention will be described in detail with reference to the drawings.
FIG. 1 is a diagram schematically showing a configuration of an optical pickup apparatus 10 that can appropriately record / reproduce information to / from a BD 20 (optical disc). The optical specifications of the BD are wavelength λ = 405 nm, protective layer 22 thickness d = 0.1 mm, and numerical aperture NA = 0.85.
However, the combination of the wavelength, the thickness of the protective layer, and the numerical aperture is not limited to this. Further, as the optical disc, an HD having a numerical aperture NA of about 0.65 and a thickness d of the protective layer PL of about 0.6 mm may be used.

The optical pickup device 10 includes a blue-violet semiconductor laser 11 as a light source, a polarizing beam splitter 12, a quarter-wave plate 16, a collimating lens 13, an aperture 18, an objective lens 30 (optical element of the present invention), and focusing / tracking. It comprises a biaxial actuator 19, a cylindrical lens 17, a concave lens 14, and a photodetector 15.
The divergent light beam emitted from the blue-violet semiconductor laser 11 passes through the polarization beam splitter 12, passes through the quarter-wave plate 16 and the collimating lens 13, and becomes a circularly polarized parallel light beam. It is regulated and becomes a spot formed on the information recording surface 21 by the objective lens 30 via the protective layer 22 of the high-density optical disc 20.

The reflected light beam modulated by the information pits on the information recording surface 21 becomes a converged light beam again through the objective lens 30, the diaphragm 18 and the collimator lens 13, and then passes through the quarter-wave plate 16 to become linearly polarized light. Astigmatism is given by being reflected by the polarization beam splitter 12, passing through the cylindrical lens 17 and the concave lens 14, and converges on the photodetector 15. Then, the information recorded on the information recording surface 21 of the high-density optical disc 20 can be read using the output signal of the photodetector 15.
As a light source for emitting laser light having a wavelength of about 400 nm, an SHG blue-violet laser using a second harmonic generation method may be used instead of the blue-violet semiconductor laser.

Next, the configuration of the objective lens 30 will be described.
The objective lens is a single lens made of athermal resin having a group of one element in which both the optical surface on the light source side and the optical surface on the optical disk side are aspherical.

Athermal resin disperses fine particles having a refractive index change (Δn ₁ / Δt) due to a temperature change of this resin and a refractive index change (Δn ₂ / Δt) due to a temperature change opposite to that of the resin as a base material. The spherical aberration SA ₁ [λRMS] generated when the operating temperature of the optical pickup device 10 is increased by 30 ° C. is set so as to satisfy the expression (1).
0.6 ≦ | (SA ₁ / λ ² ) · (Δn ₃ / Δt) · NA ² · 2d · 10 ⁸ | ≦ 1.3 (1)
Where SA ₁ is the sum of squares of the third, fifth and seventh orders, Δn ₃ / Δt is the refractive index change due to the temperature change of the mixed material, and NA is the numerical aperture of the objective lens of the optical pickup device.

  A phase structure is provided on the optical surface of the objective lens. The phase structure may be either a diffractive structure or an optical path difference providing structure. As schematically shown in FIG. 2, the diffractive structure includes a plurality of annular zones 100 and includes a cross-sectional shape including the optical axis. 3 has a sawtooth shape, or, as schematically shown in FIG. 3, the step 101 is composed of a plurality of annular zones 102 having the same direction within the effective diameter, and the cross-sectional shape including the optical axis is a staircase shape. As shown schematically in FIG. 4, a plurality of annular zones 103 in which a staircase structure is formed, and as shown schematically in FIG. 5, the direction of the step 104 is the effective diameter. Some of them are composed of a plurality of annular zones 105 that are interchanged, and the cross-sectional shape including the optical axis is a staircase shape. Further, as schematically shown in FIG. 5, the optical path difference providing structure is composed of a plurality of annular zones 105 in which the direction of the step 104 is changed in the middle of the effective diameter, and the cross-sectional shape including the optical axis is a staircase shape. There is. Therefore, the structure schematically shown in FIG. 5 may be a diffractive structure or an optical path difference providing structure. 2 to 5 schematically show the case where each phase structure is formed on a plane, but each phase structure may be formed on a spherical surface or an aspherical surface. In this specification, a diffraction structure composed of a plurality of annular zones as shown in FIGS. 2, 3 and 5 is represented by a symbol “DOE”, and a staircase structure is formed inside as shown in FIG. A diffractive structure composed of a plurality of annular zones is represented by the symbol “HOE”.

  By providing such a phase structure, for example, when a semiconductor laser whose oscillation wavelength is deviated from the reference wavelength due to a manufacturing error is used or when spherical aberration is suppressed when the wavelength of the semiconductor laser is changed due to a temperature change. The recording / reproducing characteristics can be maintained even when the wavelength of the incident light beam is instantaneously changed by suppressing the spherical aberration or by the mode hopping of the laser.

  In the present embodiment, the optical pickup device 10 includes one laser light source 11 and reproduces / records information with respect to an optical disc (BD in the present embodiment) of one kind of standard (or recording density). However, the present invention is not limited to this, and two or more light sources are used and two or more types of optical discs (for example, compatibility between a high-density optical disc and a DVD or a high-density optical disc and a DVD and a CD) For example, when an optical pickup device having compatibility between a high-density optical disc and a DVD is used, a phase structure provided in the objective lens is used to obtain a first optical disc device for a high-density optical disc. Chromatic aberration due to the wavelength difference between one wavelength λ1 and the second wavelength λ2 for DVD and / or the difference in thickness between the protective layer of the high-density optical disc and the protective layer of the DVD Note that the chromatic aberration here refers to the minimum position fluctuation of the wavefront aberration in the optical axis direction caused by the wavelength difference, for example, the phase structure of the light beams having the wavelengths λ1 and λ2. By using a diffractive structure that imparts a positive diffractive action to at least one light beam, chromatic aberration that occurs due to wavelength fluctuations of the light beam that has been diffracted can be suppressed.

As described above, according to the objective lens (optical element) and the optical pickup device described in the present embodiment, the objective lens is made of a refractive index change (Δn) due to a temperature change of the resin with respect to the resin as a base material. ₁ / Δt), which is composed of a single lens made of a mixed material (athermal resin) in which fine particles having a refractive index change (Δn ₂ / Δt) with a temperature change of the opposite sign is used, and the optical pickup device 10 is used. The spherical aberration SA ₁ [λRMS] generated when the temperature rises by 30 ° C. is set so as to satisfy the above equation (1).

  Thus, the refractive index change (dn / dt) due to a temperature change is obtained by mixing fine particles having dn / dt of the opposite sign to that of a resin (plastic resin) generally used in the past, into the resin. As a material for the objective lens, an athermal resin with a reduced squeezing can suppress the amount of change in the refractive index with respect to temperature change, and it is a single lens with high NA, but it can collect light even if the environmental temperature changes. An optical element whose performance is not deteriorated can be obtained.

In the above-described embodiment, the objective lens uses a resin as a base material, and the refractive index change (Δn ₁ / Δt) due to a temperature change of the resin and the refractive index change (Δn ₂ / Δt) due to a temperature change opposite to the sign. However, the present invention is not limited to this, and the objective lens is made of a resin as a base material, and the refractive index change (Δn ₁ / [Delta] [lambda]) and fine particles having a refractive index change ([Delta] n < ₂ > / [Delta] [lambda]) due to a wavelength change of the opposite sign may be constituted by a mixed material dispersed in the resin, or a resin as a base material, A fine particle A having a refractive index change (Δn ₁ / Δt) due to a temperature change and a refractive index change (Δn ₂ / Δt) due to a temperature change of the opposite sign, and a refractive index change (Δn ₁ / Δλ) due to a wavelength change of the resin. Refractive index due to wavelength change with opposite sign You may comprise by the mixed material which disperse | distributed the fine particle B which has a change ((DELTA) n < ₂ > / (DELTA) (lambda)) in resin.

As a result, it is possible to suppress the amount of change in the refractive index with respect to the wavelength change, and the degree of freedom in lens design is increased as compared with the conventional lens even though it is a single lens having a high NA. Effects such as increasing the tolerance and reducing the chromatic aberration of the objective lens can be obtained.
In addition, by combining the function of such an athermal resin and the function of the phase structure provided on the optical surface of the objective lens, for example, spherical aberration when the wavelength of the semiconductor laser changes due to temperature change can be reduced. Suppressing, suppressing spherical aberration when using a semiconductor laser whose oscillation wavelength deviates from the reference wavelength due to manufacturing errors, or when the wavelength of the incident light beam changes instantaneously due to laser mode hopping Recording / reproduction characteristics can be further improved.

Next, examples of the optical element shown in the above embodiment will be described.
Table 1 shows lens data of Example 1.

  As shown in Table 1, in this example, the optical element of the present invention is applied to an objective lens. This objective lens is used exclusively for BD, and is set to a focal length f1 = 1.78 mm and a magnification = 0 when the wavelength λ = 405 nm.

The entrance surface (second surface) and the exit surface (third surface) of the objective lens are aspherical surfaces that are axisymmetric about the optical axis L and are defined by a mathematical formula in which the coefficients shown in Table 1 are substituted into the following equation (2). Is formed.

なお、回折構造ＤＯＥのブレーズ化波長λＢは１．０ｍｍである。
また、本実施例の対物レンズにおいては、ＳＡ₁＝０．０５９λｒｍｓ、Δｎ₃／Δｔ＝−５．３１×１０^-05、ＮＡ＝０．８５０、ｄ＝０．１００（ｍｍ）に設定されており、｜（ＳＡ₁／λ²）・(Δｎ₃／Δｔ)・ＮＡ⁴・２ｄ・１０⁹｜＝８．０８となることから、上記（１）式を満たすことが分かる。
また、Δｎ₁／Δｔ＝−９．８１×１０^-05、Δｎ₃／Δｔ＝−５．３１×１０^-05に設定されており、（Δｎ₁／Δｔ）／（Δｎ₃／Δｔ）＝１．８５となることから、上記（２）式を満たすことが分かる。 Here, x is an axis in the optical axis direction (the light traveling direction is positive), κ is a conic coefficient, and A _2i is an aspheric coefficient.
A diffractive structure DOE is formed on the third surface. This diffractive structure DOE is represented by an optical path difference added to the transmitted wavefront by this structure. The optical path difference is such that h (mm) is the height in the direction perpendicular to the optical axis, B _2i is the optical path difference function coefficient, n is the diffraction order of the diffracted light having the maximum diffraction efficiency out of the diffracted light of the incident light flux, λ When (nm) is the wavelength of the light beam incident on the diffractive structure and λB (nm) is the manufacturing wavelength of the diffractive structure, the optical path difference function φ () defined by substituting the coefficient shown in Table 1 into the following equation (3) h) Expressed in mm.

The blazed wavelength λB of the diffractive structure DOE is 1.0 mm.
In the objective lens of the present _{example, SA 1 = 0.059λrms, Δn 3} /Δt=-5.31×10 -05, NA = 0.850, is set to d = 0.100 (mm) Since | (SA ₁ / λ ² ) · (Δn ₃ / Δt) · NA ⁴ · 2d · 10 ⁹ | = 8.08, it is understood that the above equation (1) is satisfied.
Further, Δn ₁ /Δt=-9.81×10 ^-05, is set to ^{_{Δn 3 /Δt=-5.31×10 -05, (Δn 1}} / Δt) / (Δn 3 / Δt) = 1 .85, it is understood that the above expression (2) is satisfied.

Table 2 shows lens data of Example 2.

  As shown in Table 2, in this example, the optical element of the present invention is applied to an objective lens. This objective lens is used exclusively for BD, and is set to a focal length f1 = 1.77 mm and a magnification = 0 when the wavelength λ = 405 nm.

The entrance surface (second surface) and the exit surface (third surface) of the objective lens are aspherical surfaces that are axisymmetric about the optical axis L and are defined by a mathematical formula in which the coefficients shown in Table 2 are substituted into the formula (2). Is formed.
A diffractive structure DOE is formed on the third surface. This diffractive structure DOE is represented by an optical path difference added to the transmitted wavefront by this structure. Such an optical path difference is represented by an optical path difference function φ (h) (mm) defined by substituting the coefficient shown in Table 2 into the above equation (3).
The blazed wavelength λB of the diffractive structure DOE is 1.0 mm.
Further, in the objective lens of this example, ν _d1 = 57 and ν _d3 = 63 are set, and 1.1 × ν _d1 = 62.7, so that the above expression (3) is satisfied. I understand.
SA ₂ = 0.048λrms, Δn ₃ /Δλ=−1.468×10 ⁻⁰⁴ , NA = 0.850, d = 0.100 (mm) are set, and | (SA ₂ / λ ² ) · (Δn ₃ / Δt) · NA ⁴ · 2d · 10 ⁹ | = 18.16, it is understood that the above expression (4) is satisfied.
Moreover, since Δfb = 152 nm and | Δfb / λ | = 0.375, it is understood that the above expression (5) is satisfied.
Further, since N ₁ = 1.5603, N ₃ = 1.5619, h _max = 3.0 mm, and α = 26.28 °, the above expressions (6) and (7) are satisfied. I understand.

It is a principal part top view which shows the structure of an optical pick-up apparatus. It is drawing (a) and (b) which show a phase structure. It is drawing (a) and (b) which show a phase structure. It is drawing (a) and (b) which show a phase structure. It is drawing (a) and (b) which show a phase structure.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Optical pick-up apparatus 11 Blue-violet semiconductor laser 12 Polarization beam splitter 13 Collimating lens 20 High-density optical disk 30 Objective lens

Claims (18)

At least an optical element used in an optical pickup device that reproduces and / or records information using a light beam having a wavelength λ (390 nm ≦ λ ≦ 420 nm) with respect to an optical disc having a protective substrate thickness d [mm].
The optical element uses resin as a base material, and fine particles having a refractive index change (Δn ₁ / Δt) due to a temperature change of the resin and a refractive index change (Δn ₂ / Δt) due to a temperature change opposite to the sign in the resin. Composed of a mixed material dispersed in
An optical element characterized in that spherical aberration SA ₁ [λRMS] generated when the operating temperature of the optical pickup device rises by 30 ° C. satisfies the expression (1).
| (SA ₁ / λ ² ) · (Δn ₃ / Δt) · NA ⁴ · 2d · 10 ⁹ | ≦ 9.9 (1)
Where SA ₁ is the third-order, fifth-order, and seventh-order square sum, Δn ₃ / Δt is the refractive index change due to the temperature change of the mixed material, and NA is the numerical aperture on the exit side of the objective lens included in the optical pickup device. is there. The optical element according to claim 1, wherein the expression (2) is satisfied.
| (Δn ₁ / Δt) | ≧ 2 · | (Δn ₃ / Δt) | (2) At least an optical element used in an optical pickup device that reproduces and / or records information using a light beam having a wavelength λ (390 nm ≦ λ ≦ 420 nm) with respect to an optical disc having a protective substrate thickness d [mm].
The optical element uses resin as a base material, and fine particles having a refractive index change (Δn ₁ / Δλ) due to a wavelength change of the resin and a refractive index change (Δn ₂ / Δλ) due to a wavelength change of the opposite sign are contained in the resin. An optical element comprising a mixed material dispersed in an optical element. The optical element according to claim 3, wherein an Abbe number ν _d3 of the mixed material at the d-line satisfies the expression (3).
1.1 ・ ν _d1 ≦ ν _d3 (3)
Where ν _d1 is the Abbe number of the base material at the d-line, and νd ₁ and ν _d3 are both obtained from ν _d = (n _d −1) / (n _F −n _c ), where n _d is a refractive index at the d-line of the base material, n _F is the refractive index at the F-line of the base material, the n _c is the refractive index at C line of the base material. 5. The optical element according to claim 3, wherein spherical aberration SA ₂ [λRMS] generated when the wavelength λ fluctuates by ± 5 nm satisfies the expression (4).
| (SA ₂ / λ ² ) · (Δn ₃ / Δλ) · NA ⁴ · 2d · 10 ⁹ | ≦ 18.5 (4)
Where SA ₁ is the third-order, fifth-order, and seventh-order square sum, Δn ₃ / Δλ is the refractive index change due to the wavelength change of the mixed material, and NA is the numerical aperture on the exit side of the objective lens included in the optical pickup device. is there. When the wavelength λ fluctuates ± 1 nm, the minimum amount of change Δfb [nm] in the optical axis direction of the focused spot formed on the information recording surface of the optical disk satisfies the equation (5). The optical element according to any one of claims 3 to 5.
| Δfb / λ | ≦ 0.4 (5) At least an optical element used in an optical pickup device that reproduces and / or records information using a light beam having a wavelength λ (390 nm ≦ λ ≦ 420 nm) with respect to an optical disc having a protective substrate thickness d [mm].
The optical element has a resin as a base material, fine particles A having a refractive index change (Δn ₁ / Δt) due to a temperature change of the resin and a refractive index change (Δn ₂ / Δt) due to a temperature change of the opposite sign, and It is composed of a mixed material in which fine particles B having refractive index change (Δn ₁ / Δλ) due to wavelength change of resin and refractive index change (Δn ₂ / Δλ) due to wavelength change of opposite sign are dispersed in the resin. An optical element.   The optical element according to claim 7, wherein the fine particles A and the fine particles B are different particles.   The optical element according to claim 7, wherein the fine particles A and the fine particles B are the same particles. 10. The optical element according to claim 7, wherein spherical aberration SA ₁ [λRMS] generated when the operating temperature of the optical pickup device is increased by 30 ° C. satisfies the expression (1).
| (SA ₁ / λ ² ) · (Δn ₃ / Δt) · NA ⁴ · 2d · 10 ⁹ | ≦ 9.9 (1)
Where SA ₁ is the third-order, fifth-order, and seventh-order square sum, Δn ₃ / Δt is the refractive index change due to the temperature change of the mixed material, and NA is the numerical aperture on the exit side of the objective lens included in the optical pickup device. is there. The optical element according to claim 10, wherein the expression (2) is satisfied.
| (Δn ₁ / Δt) | ≧ 2 · | (Δn ₃ / Δt) | (2) The optical element according to claim 7, wherein an Abbe number ν _d3 of the mixed material at the d-line satisfies the expression (3).
1.1 ・ ν _d1 ≦ ν _d3 (3)
Where ν _d1 is the Abbe number of the base material on the d-line, and νd ₁ and ν _d3 are both obtained from ν _d = (n _d −1) / (n _F −n _c ), where n _d is a refractive index at the d-line of the base material, n _F is the refractive index at the F-line of the base material, the n _c is the refractive index at C line of the base material. The optical element according to claim 7, wherein spherical aberration SA ₂ [λRMS] generated when the wavelength λ fluctuates by ± 5 nm satisfies the expression (4).
| (SA ₂ / λ ² ) · (Δn ₃ / Δλ) · NA ⁴ · 2d · 10 ⁹ | ≦ 18.5 (4)
Where SA ₁ is the third-order, fifth-order, and seventh-order square sum, Δn ₃ / Δλ is the refractive index change due to the wavelength change of the mixed material, and NA is the numerical aperture on the exit side of the objective lens included in the optical pickup device. is there. When the wavelength λ fluctuates ± 1 nm, the minimum amount of change Δfb [nm] in the optical axis direction of the focused spot formed on the information recording surface of the optical disk satisfies the equation (5). The optical element according to any one of claims 7 to 13.
| Δfb / λ | ≦ 0.4 (5) The refractive indexes of the base material and the mixed material with respect to the light flux of the wavelength λ are N ₁ and N ₃ , the maximum effective diameter of the optical surface on the light source side of the optical element is h _max , and the tangent line at the h _max of the optical surface The optical element according to any one of claims 3 to 14, wherein the expression (6) and the expression (7) are satisfied when an angle between the optical axis and the optical axis is defined as α.
N ₁ <N ₃ (6)
26.0 ° ≦ α (7)   The optical element according to claim 1, wherein an average particle diameter of the fine particles in the mixed material is 50 nm or less.   The optical element according to claim 1, comprising a single lens.   An optical pickup device comprising the optical element according to claim 1.

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