JP2001159731A - Coupling lens, optical pickup device and semiconductor laser collimating device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a coupling lens of a plastic material which is not changed in the diversion angle of an exit luminous flux even if a temperature fluctuation occurs, an optical pickup device which is not changed in an object position with respect to an objective lens even if the temperature fluctuates and is not deteriorated in the spherical aberration of the objective lens, and a semiconductor laser collimating device which can emit stable parallel luminous fluxes even if a temperature fluctuation occurs. SOLUTION: This coupling lens 2 consists of a plastic material, has a diffraction face on which a level difference is formed in a ring band form on at least either one of a first face or second face and satisfies the equation |c1+(c2-c1).ϕD/ϕC|/fc<0.15 λ (mm). The optical pickup device and the semiconductor laser collimating device include the coupling lens.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a coupling lens for an optical pickup, an optical pickup device, and a semiconductor laser collimator, and more particularly, to optical recording for recording or reproducing information on or from an information recording medium such as a magneto-optical disk or an optical disk. The present invention relates to a coupling lens that is used in an optical pickup of a reproducing apparatus and guides a divergent light from a light source to an objective lens by converting a divergence angle to an objective lens, an optical pickup device using the coupling lens, and a semiconductor laser collimating device.

[0002]

2. Description of the Related Art In an optical pickup device for recording or reproducing information on or from an information recording medium, a coupling lens is provided in front of an objective lens. This coupling lens changes the divergence angle of divergent light from a semiconductor laser as a light source. Convert and guide to objective lens. NA for coupling lens
In general, a single lens having no aberration of about 0.1 to 0.2 is used, and the divergent light from the semiconductor laser is collimated into parallel light.

[0003]

If the above-mentioned coupling lens is made of a plastic material, it can be manufactured at low cost. However, a lens made of a plastic material changes its focal length due to temperature fluctuation. Therefore, the divergence angle of the light beam emitted from the coupling lens changes with temperature fluctuation. As a result, there is a problem that an object position with respect to the objective lens changes, and spherical aberration deteriorates.

[0004] In view of the problems of the prior art, the present invention has
Made of plastic material, the divergence angle of the emitted light beam hardly changes due to temperature fluctuation, and the emitted light beam is not limited to parallel light, and even in the case of convergent light or divergent light, the degree of convergence or divergence due to temperature fluctuation is almost the same. It is an object to provide a coupling lens that does not change.

Also, an optical pickup device in which the divergence angle of the light beam emitted from the coupling lens hardly changes due to temperature fluctuation and the spherical aberration of the objective lens does not deteriorate, and a semiconductor laser collimator in which the parallel light beam does not change parallel due to temperature fluctuation. It is intended to provide a device.

[0006]

In order to achieve the above object, a coupling lens according to the present invention is a coupling lens used in an optical pickup device for recording and / or reproducing information on and from an information recording medium. A diffractive surface made of a material and having a step formed in an annular shape on at least one of the first surface and the second surface, wherein the following formula (A) is satisfied.

| C1 + (c2−c1) · φD / φC | / fc <0.15λ (mm) (A) where c1 = 1 / (n−1) · dn / dt + 1 / (n−1)・ Dn / dλ ・ dλ / dt-α c2 = 1 / λ ・ dλ / dt-2α fc: focal length (mm) of coupling lens (= 1 / φ
C) λ: Wavelength (mm) n: Refractive index of the coupling lens α: Coefficient of linear expansion of the coupling lens φD: Power of the diffractive surface (When the diffractive surfaces are provided on both surfaces, the arithmetic sum of the power of the diffractive surface is φD. ΦC: power of coupling lens dn / dt: ratio of change in refractive index to temperature change dn / dλ: ratio of change in refractive index to change in wavelength dλ / dt: ratio of change in wavelength of the light source used to change in temperature

According to this coupling lens, the divergence angle of the light beam emitted from the coupling lens hardly changes due to temperature fluctuation. Therefore, the emitted light flux is not limited to the parallel light, and the degree of convergence or the degree of divergence hardly changes due to temperature fluctuation even in the case of convergent light or divergent light.

Further, when dλ / dt = 2 × 10 ⁻⁷ , it is preferable that the above formula (A) is satisfied. Alternatively, when dλ / dt = 5 × 10 ⁻⁸ , it is preferable that the above formula (A) is satisfied.

Another coupling lens according to the present invention is a coupling lens used for an optical pickup device for recording and / or reproducing information on and from an information recording medium, and is made of a plastic material and has a first surface or a second surface. At least one of the surfaces has a diffractive surface having a ring-shaped step for suppressing a change in a divergence angle or a convergence angle of an emitted light beam due to a temperature change, and satisfies the following expression. −0.2 ≦ mc ≦ 0.2 (B) 2.0 ≦ fc ≦ 25 (C) where mc: magnification of the coupling lens fc: focal length of the coupling lens (mm)

According to this coupling lens, a change in the divergence angle or the convergence angle of the luminous flux emitted from the coupling lens due to the temperature fluctuation is suppressed, and when mc is equal to or more than the lower limit of the equation (B), the coupling is suppressed. When the outer diameter of the lens does not increase and is equal to or less than the upper limit, the outer diameter of the objective lens does not increase, and when applied to an optical pickup device, the size can be reduced. On the other hand, if fc is equal to or more than the lower limit of the formula (C), a diffractive surface having a high power is not so required, and it becomes easy to manufacture a diffraction zone having high diffraction efficiency. When applied to a pickup device,
Its size can be reduced.

The diffractive surface is blazed with respect to the diffracted light of the second or higher order, that is, so as to satisfy the above formula (A) or (B) and (C). Further, it is preferable that a blazed diffraction surface is formed so that the diffraction effect of the diffracted light having the second or higher order and the predetermined order is maximized.

Further, by configuring the optical pickup device to include the above-described coupling lenses, the divergence angle of the light beam emitted from the coupling lens hardly changes due to temperature fluctuation, and is stable against temperature fluctuation. An apparatus capable of performing accurate recording or reproduction can be realized.

The optical pickup device of the present invention records or reproduces information by condensing a light beam from a light source on an information recording surface of an information recording medium by an optical system including a coupling lens and an objective lens. An optical pickup device configured as described above, wherein the coupling lens is made of a plastic material, and at least one surface of the coupling lens is provided with a diffraction surface having a ring-shaped step, or In the vicinity of the ring lens, an optical element having at least one diffraction surface having a ring-shaped step is provided, and the above-described formula (A) is satisfied.

According to this optical pickup device, since the divergence angle of the light beam emitted from the coupling lens hardly changes due to temperature fluctuation, the spherical aberration of the objective lens does not deteriorate. As a result, it is possible to realize an apparatus capable of performing stable and accurate recording or reproduction with respect to temperature fluctuation.

It is preferable that the above-mentioned optical pickup device satisfies the following expression. (NAo ・ (1-mo)) ⁴・ (fo ² / fc) ・ │c1 + (c2
−c1) · φD / φCl <0.019λ Also, (NAo · (1-mo)) ⁴ · (fo ² / fc) · | c1 +
(C2-c1) · φD / φCl <0.010λ is more preferably satisfied. Where NAo: numerical aperture on the image side of the objective lens mo: lateral magnification of the objective lens fo: focal length of the objective lens

The wavelength λ of the light source is λ <0.0
0068 mm, preferably λ <0.000
It is more desirable to satisfy 45 mm.

According to another optical pickup device of the present invention, a light beam from a light source is condensed on an information recording surface of an information recording medium by an optical system including a coupling lens and an objective lens to record or reproduce information. Wherein the coupling lens is made of a plastic material, and the coupling lens is made of a plastic material to suppress a change in a divergence angle or a convergence angle of the light beam emitted from the coupling lens with respect to a temperature change. An optical element having a diffraction surface having an annular step formed on at least one surface of a ring lens, or having at least one surface having a diffraction surface having an annular step formed in the vicinity of the coupling lens. An element is provided, which satisfies the above equations (B) and (C).

According to this optical pickup device, the divergence angle or the convergence angle of the luminous flux emitted from the coupling lens is suppressed from changing due to the temperature fluctuation, and if mc is equal to or more than the lower limit of the formula (B), the coupling becomes smaller. When the outer diameter of the lens does not increase and is equal to or less than the upper limit, the outer diameter of the objective lens does not increase and the optical pickup device can be downsized. Further, when fc is equal to or more than the lower limit of the formula (C), a diffraction surface having a strong power is not so required, and it becomes easy to manufacture a diffraction zone having high diffraction efficiency.
The size of the optical pickup device can be reduced.

The semiconductor laser collimator according to the present invention is a semiconductor laser collimator comprising a semiconductor laser and a coupling lens into which a light beam from the semiconductor laser is incident and parallel light is emitted. Has a diffractive surface having a ring-shaped step formed on at least one of the first surface and the second surface, and satisfies the following expression.

| C1 + (c2-c1) · φD / φC | / f
c <0.15λ (mm) where c1 = 1 / (n-1) · dn / dt + 1 / (n-1) · dn / dλ · dλ / dt-α c2 = 1 / λ · dλ / dt -2α fc: focal length of coupling lens (mm) (= 1 /
φC) λ: wavelength of the semiconductor laser (mm) n: refractive index of the coupling lens α: linear expansion coefficient of the coupling lens φD: power of the diffractive surface (the arithmetic sum of the power of the diffractive surface when the diffractive surface is provided on both surfaces) ΦC: power of coupling lens dn / dt: ratio of refractive index change to temperature change dn / dλ: ratio of refractive index change to wavelength change dλ / dt: wavelength of semiconductor laser to temperature change Rate of change

According to this semiconductor laser collimator, since the divergence angle of the light beam emitted from the coupling lens hardly changes due to temperature fluctuation, the parallel state of the parallel light beam from the coupling lens does not change due to temperature fluctuation. Therefore, the light from the semiconductor laser can be emitted as a stable parallel light beam even when the temperature fluctuates.

Note that the optical system in the present invention is a set of two or more optical elements including a coupling lens and an objective lens capable of recording or reproducing a CD or a DVD, for example, and is provided on an information recording medium. It may mean not only the entire optical system for recording the information and / or reproducing the information on the information recording medium but also a part of the optical system. Here, the coupling lens is an optical element for converting the divergence angle of the light beam from the light source and guiding it to the objective lens, and includes a so-called collimating lens that converts the divergent light from the light source into a substantially parallel light beam. on the other hand,
The objective lens is a lens group disposed at a position closest to the optical information recording medium and opposed to the optical information recording medium when the optical information recording medium is loaded in the optical pickup device, and includes an actuator of the optical pickup device. Indicates a lens group having a light-condensing function operably provided at least in the optical axis direction. In the present invention, the optical element that can be disposed near the coupling lens may be provided separately from the lens group of the objective lens and near (or may be integrated with) the coupling lens. It is an optical element and includes, for example, an optical element having almost no refractive action. This optical element need not necessarily be provided when the diffraction surface of the present invention is provided on the coupling lens.

Further, the information recording medium of the present invention includes:
For example, various CDs such as CD, CD-R, CD-RW, CD-Video, CD-ROM, various DVDs such as DVD, DVD-ROM, DVD-RAM, DVD-R, DVD-RW, and MDs A disc-shaped information recording medium is exemplified.

Recording and / or reproduction of information on an information recording medium means recording information on the information recording surface of the information recording medium as described above, and information recorded on the information recording surface. To play. The optical pickup device in the present invention may be used for performing only recording or reproduction, or may be used for performing both recording and reproduction. Further, it may be used for recording on one information recording medium and reproducing on another information recording medium, or may be used for recording or reproducing on a certain information recording medium. It may be used for reproducing and for recording and reproducing on another information recording medium.
Note that reproduction here includes simply reading information. Therefore, the optical pickup device to which the coupling lens or the semiconductor collimating device of the present invention is applied also includes the above-described optical pickup device.

As the plastic material of the coupling lens, acrylic, polyolefin, polycarbonate, styrene or the like can be used, but is not limited thereto.

[0027]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an optical pickup device according to an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is a diagram showing a schematic configuration of the optical pickup device.

As shown in FIG. 1, the optical pickup device includes a semiconductor laser 1 as a light source, a coupling lens 2 for converting a divergence angle of divergent light emitted from the light source, and a light beam from the coupling lens 2. The optical information recording medium includes an objective lens that converges on an information recording surface of the optical information recording medium, and a photodetector that receives reflected light from the optical information recording medium.

The optical pickup device is further disposed between the coupling lens 2 and the objective lens 3, and a beam splitter 6 that reflects and separates reflected light from the optical information recording medium 11 toward the photodetector 4. A quarter-wave plate 7, a stop 8 in front of the objective lens 3, and a cylindrical lens 9 disposed between the beam splitter 6 and the photodetector 4.
And a focus / tracking actuator 10 that operates when reproducing information from the optical information recording medium 11.

The coupling lens 2 is formed of a resin material, and has a diffraction surface on at least one surface of which a step is formed in an annular shape. The diffraction surface is provided with diffraction zones as reliefs (surface irregularities) on the surface of a substrate lens which is a substrate. Therefore, the substrate lens is a lens having a macroscopic shape without the relief structure for diffraction.

An optical pickup device according to the present invention compensates for a change in focal length of a coupling lens due to a temperature change caused by forming the coupling lens with a resin material by giving an appropriate power to a diffraction surface. It is. That is, when the temperature rises, the oscillation wavelength of the semiconductor laser becomes longer, the power of the diffraction surface becomes stronger, and a decrease in power due to a rise in the temperature of the substrate lens of the coupling lens is compensated.

Here, a change in the wavefront aberration of the objective lens when the focal length of the coupling lens changes due to a temperature change is obtained.

First, in a system including an objective lens and a coupling lens, an object position with respect to the objective lens changes due to a change in the focal length of the coupling lens.
Consider the deterioration of the wavefront aberration of the objective lens caused by the change of the imaging magnification of the objective lens. It is assumed that the objective lens is focused on the best position.

The rate of degradation dWo / dmo of the wavefront aberration Wo (rms in mm) of the objective lens due to a change in the lateral magnification mo of the objective lens is determined by setting the image-side numerical aperture of the objective lens to NA.
o, the focal length is fo, the lateral magnification is mo, and the coefficient is β. Note that the image side means the information recording medium side.

DWo / dmo = β · (NAo · (1-m
o)) ⁴・ fo

When examined with a single lens objective lens, β
Was about ± 0.012. (The code is selected in the direction of increasing Wo.)

The ratio dmo / d of the change in the imaging magnification of the objective lens due to the change in the focal length of the coupling lens.
When f is obtained, the following equation is approximately obtained when the light emitted from the coupling lens is close to parallel light.

Dmo / dfc = -fo / fc ²

Next, a change in the focal length of the coupling lens due to a temperature change will be described. First, the power of the substrate lens is φB, the power of the diffraction surface is φD, and the power of the entire coupling lens is φC = φB + φD.
When the diffraction surfaces are provided on both surfaces, the arithmetic sum of the power of the diffraction surfaces is φD.

N is the refractive index, λ is the wavelength, α is the linear expansion coefficient,
Assuming that t is temperature and fc is the focal length,
Rate of change of focal length of coupling lens dfc / d
t is represented by the following equation.

Dfc / dt = −fc ² · dφC / dt = −fc ² · (c1 · φB + c2 · φD) where c1 = 1 / (n−1) · dn / dt + 1 / (n−1) · dn / dλ ・ dλ / dt-α c2 = 1 / λ ・ dλ / dt-2α

Alternatively, if φB = φC−φD is used, the following equation is obtained.

Dfc / dt = -fc. (C1 + (c2-
c1) ・ φD / φC)

In summary, in this system, the deterioration of the wavefront aberration of the objective lens due to the temperature fluctuation Δt in this system ΔWo (m
(rms in m) is as follows. ΔWo = (dWo / dmo) · | (dmo / dfc) · (df
c / dt) △ t |

Here, numerical examples are shown. That is, the image side numerical aperture of the objective lens is NAo = 0.6, and the focal length is fo = 3 m.
m, the lateral magnification is mo = 0, and the coefficient is β = ± 0.12, dWo / dmo = ± 0.047 (mm)

Also, let the focal length of the coupling lens be f
If c = 20 mm, dmo / dfc = −0.0075 (mm ⁻¹ )

Further, the wavelength is λ = 650 nm, the refractive index of the coupling lens is n = 1.54113, the linear expansion coefficient is α = 7 × 10 ⁻⁵ , and the temperature fluctuation of the refractive index is dn / dt = −.
Assuming that 1.2 × 10 ⁻⁴ , the temperature fluctuation of the oscillation wavelength of the semiconductor laser is dλ / dt = 2 × 10 ⁻⁷ , and the refractive index change due to the wavelength change is dn / dλ = −38, c1 = −2.97 × 10
^-4 , c2 = 1.68 × 10 ^-4 .

If the coupling lens does not have a diffractive surface, then dfc / dt = 0.0059 and Δt
= 30 degrees, ΔWo = 0.047 × | (−0.0075) × 0.00
59 × 30 | = 0.000062 mm = 0.096λ, which is worse than the Marechal discrimination value of 0.07λrms. This deterioration is greater as the focal length of the coupling lens is shorter.

According to the present invention, this deterioration can be reduced by giving an appropriate diffraction power to the coupling lens.

That is, assuming that the wavefront aberration in the reference state of the objective lens is 0, it is necessary to suppress the deterioration of the wavefront aberration to 0.07 λrms with respect to a temperature fluctuation of 30 degrees, and the following condition is obtained. 0.07λ> (dWo / dmo) · | (dmo / dfc) ·
(dfc / dt) · 30 (° C.) | Using the above relationship in this equation, the following equation (1) is obtained.

(NAo · (1-mo)) ⁴ · (fo ² /fc)·|c1+(c2−c1)·φD/φC|<0.019λ (1)

If the relationship of the above equation (1) is satisfied, the positional relationship between the light emitting point of the light source and the focal position of the coupling lens hardly changes even if the temperature changes, and the light beam emitted from the coupling lens Since the degree of divergence of the objective lens hardly changes and the angle of divergence hardly changes, it is possible to obtain an optical pickup device in which the wavefront aberration deterioration of the objective lens is small. It is more desirable to satisfy the following expression (2).

(NAo · (1-mo)) ⁴ · (fo ² /fc)|c1+(c2-c1)·φD/φC|<0.010λ (2)

As a practical condition range for the coupling lens, the image-side numerical aperture NAo of the objective lens is given by:
0.6, focal length fo = 1.0 mm, lateral magnification mo = 0
The following equation (3) is required to support the optical pickup of
It is necessary to satisfy

| C1 + (c2-c1) · φD / φC | / fc <0.15λ (mm) (3)

More preferably, the following expression (4) should be satisfied.

| C1 + (c2-c1) · φD / φC | / fc <0.037λ (mm) (4)

More preferably, the following expression (5) should be satisfied.

| C1 + (c2-c1) · φD / φC | / fc <0.009λ (mm) (5)

It is practical that the magnification mc (when the parallel light is emitted is 0) and the focal length of the coupling lens satisfy the ranges of the following equations (6) and (7), respectively.

−0.2 ≦ mc ≦ 0.2 (6)

2.0 ≦ fc ≦ 25 (7)

In this case, if mc is equal to or larger than the lower limit of the expression (6), the outer diameter of the coupling lens does not increase. The size can be reduced.

If fc is equal to or more than the lower limit of the expression (7), a diffraction surface having a high power is not required so much to obtain the above-mentioned temperature compensation effect, so that a diffraction ring with high diffraction efficiency can be manufactured. When the temperature is below the upper limit, the size of the optical pickup device can be reduced.

If the distance between the diffraction zones is too small, the production becomes difficult. To avoid this problem, it is necessary to provide diffraction surfaces on both sides or to use a higher-order diffracted light beam to make the surface blazed. It is valid. In addition, by applying the present invention to an optical pickup device using a short wavelength light source, an optical pickup device capable of high-density recording or reproduction can be obtained. For this reason, if the wavelength λ of the light source is λ <0.000
68 mm, more preferably λ <0.00045 mm,
It is desirable to satisfy

[0066]

Next, Examples 1, 2, and 3 of the coupling lens according to the present invention will be described. Examples 1 and 2 have a reference wavelength of 650 nm, and Example 3 has a reference wavelength of 400 nm. Table 1 below shows the specification values of each embodiment.
Also, the lowermost row of Table 1 shows the value of the above-described equation (1) for the pickup device.

[0067]

[Table 1]

In the third embodiment, compared to the first and second embodiments, a short-wavelength laser having a smaller dλ / dt is used, so that a strong diffraction surface power is required.

The diffractive surface is represented by the following optical path difference function Φ (h), and a diffraction ring zone is provided every time the value of the optical path difference function changes by mλ (m is the diffraction order).

[0070] Φ (h) = b2 · h 2 + b4 · h 4 + b6 · h 6 + ··· however, h: distance from the optical axis b2, b4, b6, ···: coefficients of the optical path difference function

The aspheric surface is represented by the following equation.

X = (h ² / r) / (1 + √ (1- (1 + K) h ² )
^{/ R 2)) + A2 ·} h 2 + A4 · h 4 + A6 · h 6 + ··· However, A2, A4, A6, ··· : aspheric coefficient K: conical coefficient r: paraxial radius of curvature

<Example 1>

Table 2 shows the lens data of the first embodiment. As shown in Table 1, when the light source wavelength is λ650 nm, the focal length fc is 14.0 mm and the light source side numerical aperture NA is 0.107.

[0075]

[Table 2]

FIG. 2 is a lens cross-sectional view of the coupling lens of the first embodiment, and FIG. 3 is a spherical aberration diagram of the coupling lens of the first embodiment (reference wavelength λ650 nm, light source side numerical aperture NA 0.107). From FIG. 3, it can be seen that the spherical aberration is sufficiently corrected at the reference wavelength λ = 650 nm in the coupling lens of Example 1.

<Embodiment 2>

Table 3 shows lens data of the second embodiment. As shown in Table 1, when the light source wavelength is λ650 nm, the focal length fc is 8.0 mm, and the light source side numerical aperture NA is 0.188.

[0079]

[Table 3]

FIG. 4 is a lens sectional view of the coupling lens of the second embodiment, and FIG. 5 is a spherical aberration diagram of the coupling lens of the second embodiment (reference wavelength λ650 nm, light source side numerical aperture NA 0.188). FIG. 5 shows that the spherical aberration is sufficiently corrected at the reference wavelength λ = 650 nm in the coupling lens of Example 2.

<Embodiment 3>

Table 4 shows lens data of the third embodiment. As shown in Table 1, when the light source wavelength is λ400 nm, the focal length fc is 8.0 mm and the light source side numerical aperture NA is 0.188.

[0083]

[Table 4]

FIG. 6 is a lens sectional view of the coupling lens of the second embodiment, and FIG. 7 is a spherical aberration diagram of the coupling lens of the third embodiment (reference wavelength λ 400 nm, numerical aperture NA 0.188 on the light source side). FIG. 7 shows that the spherical aberration was sufficiently corrected at the reference wavelength λ = 400 nm in the coupling lens of Example 3.

In the above embodiments, an example in which the diffraction surface of the present invention is provided on the coupling lens has been described.
Instead of providing the coupling lens, an optical element that does not substantially change the divergence angle of the incident light beam may be provided near the coupling lens, and the optical element may be provided with the diffraction surface of the present invention.

[0086]

According to the present invention, the divergence angle of the light beam emitted from the coupling lens made of a plastic material hardly changes even if the temperature changes. Therefore, if this coupling lens light is used for the pickup device, the object position with respect to the objective lens does not change even if the temperature fluctuates,
A pickup device in which the spherical aberration of the objective lens does not deteriorate can be provided. Further, it is possible to provide a semiconductor laser collimator capable of emitting a stable parallel light beam even when a temperature change occurs.

[Brief description of the drawings]

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

FIG. 2 is a lens cross-sectional view of the coupling lens of Example 1 according to the embodiment of the present invention.

FIG. 3 shows a reference wavelength λ of the coupling lens of Example 1;
It is a spherical aberration figure with respect to 650 nm.

FIG. 4 is a lens cross-sectional view of a coupling lens of Example 2 according to the embodiment of the present invention.

FIG. 5 shows a reference wavelength λ of the coupling lens according to the second embodiment.
It is a spherical aberration figure with respect to 650 nm.

FIG. 6 is a lens cross-sectional view of a coupling lens of Example 3 according to the embodiment of the present invention.

FIG. 7 shows a reference wavelength λ of the coupling lens according to the third embodiment.
It is a spherical aberration figure with respect to 400 nm.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Semiconductor laser (light source) 2 Coupling lens 3 Objective lens 4 Photodetector 5 Information recording surface 11 Optical information recording medium

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2H087 KA13 LA25 NA08 PA01 PA17 PB01 QA03 QA07 QA12 QA15 QA31 QA32 RA05 RA13 RA42 RA46 UA01 5D119 AA09 AA21 BA01 DA01 DA05 EC01 FA05 JA02 JA04 JB03 9A001 KK13 KK16

Claims (13)

[Claims] 1. A coupling lens for use in an optical pickup device for recording and / or reproducing information on and from an information recording medium, wherein the coupling lens is made of a plastic material, and at least one of a first surface and a second surface has an annular step. A coupling lens having a diffraction surface formed and satisfying the following expression. | C1 + (c2-c1) · φD / φC | / fc <0.15
λ (mm) where c1 = 1 / (n-1) · dn / dt + 1 / (n-1) · dn / dλ · dλ / dt-α c2 = 1 / λ · dλ / dt-2α fc: Focal length of coupling lens (mm) (= 1 /
φC) λ: Wavelength (mm) n: Refractive index of coupling lens α: Coefficient of linear expansion of coupling lens φD: Power of diffractive surface (If diffractive surfaces are provided on both surfaces, the arithmetic sum of the power of the diffractive surface is φD ΦC: power of coupling lens dn / dt: ratio of change in refractive index to temperature change dn / dλ: ratio of change in refractive index to change in wavelength dλ / dt: ratio of change in wavelength of the light source used to change in temperature 2. The method according to claim 1, wherein dλ / dt = 2 × 10 ^−7.
The coupling lens according to 1. 3. The method according to claim 1, wherein dλ / dt = 5 ^* 10 ^-8.
The coupling lens according to 1. 4. A coupling lens for use in an optical pickup device for recording and / or reproducing information recorded on an information recording medium, wherein the coupling lens is made of a plastic material, and is provided on at least one of a first surface and a second surface with respect to temperature fluctuation. A coupling lens for suppressing a change in a divergence angle or a convergence angle of a light beam, having a diffractive surface having a ring-shaped step, and satisfying the following expression. −0.2 ≦ mc ≦ 0.2 2.0 ≦ fc ≦ 25 where mc: magnification of the coupling lens fc: focal length of the coupling lens (mm) 5. The coupling lens according to claim 1, wherein said diffractive surface is blazed for diffracted light of the second or higher order. 6. An optical pickup device having the coupling lens according to claim 1. 7. An optical pickup device configured to record or reproduce information by condensing a light beam from a light source on an information recording surface of an information recording medium by an optical system including a coupling lens and an objective lens. Wherein the coupling lens is made of a plastic material, and at least one surface of the coupling lens is provided with a diffraction surface having a step formed in an annular shape, or an annular shape is provided in the vicinity of the coupling lens. An optical element having a diffraction surface having a step formed on at least one surface thereof, wherein the following formula is satisfied. | C1 + (c2-c1) · φD / φC | / fc <0.15
λ (mm) where c1 = 1 / (n-1) · dn / dt + 1 / (n-1) · dn / dλ · dλ / dt-α c2 = 1 / λ · dλ / dt-2α fc: Focal length of coupling lens (mm) (= 1 /
φC) λ: Wavelength (mm) n: Refractive index of coupling lens α: Coefficient of linear expansion of coupling lens φD: Power of diffractive surface ΦC: power of coupling lens dn / dt: ratio of change in refractive index to temperature change dn / dλ: ratio of change in refractive index to change in wavelength dλ / dt: ratio of change in wavelength of light source to change in temperature 8. The method according to claim 7, wherein the following expression is satisfied.
An optical pickup device according to item 1. (NAo ・ (1-mo)) ⁴・ (fo ² / fc) ・ │c1 + (c2
−c1) · φD / φCl <0.019λ where NAo: numerical aperture on the image side of the objective lens mo: lateral magnification of the objective lens fo: focal length of the objective lens 9. The method according to claim 8, wherein the following expression is satisfied.
An optical pickup device according to item 1. (NAo ・ (1-mo)) ⁴・ (fo ² / fc) ・ │c1 + (c2
−c1) · φD / φCl <0.010λ 10. The optical pickup device according to claim 7, wherein the following expression is satisfied. λ <0.00068mm 11. The optical pickup device according to claim 7, wherein the following expression is satisfied. λ <0.00045mm 12. An optical pickup device configured to record or reproduce information by condensing a light beam from a light source on an information recording surface of an information recording medium by an optical system including a coupling lens and an objective lens. Wherein the coupling lens is made of a plastic material, and a ring is formed on at least one surface of the coupling lens in order to suppress a change in a divergence angle or a convergence angle of a light beam emitted from the coupling lens with respect to a temperature change. Either providing a diffraction surface having a band-shaped step or providing an optical element having a diffraction surface having a ring-shaped step on at least one surface in the vicinity of the coupling lens, and satisfying the following expression. An optical pickup device characterized by the following. −0.2 ≦ mc ≦ 0.2 2.0 ≦ fc ≦ 25 where mc: magnification of the coupling lens fc: focal length of the coupling lens (mm) 13. A semiconductor laser collimator comprising: a semiconductor laser; and a coupling lens that receives a light beam from the semiconductor laser and emits parallel light, wherein the coupling lens is made of a plastic material. A semiconductor laser collimator comprising: a diffraction surface having a step formed in an annular shape on at least one of a surface and a second surface; | C1 + (c2-c1) · φD / φC | / fc <0.15
λ (mm) where c1 = 1 / (n-1) · dn / dt + 1 / (n-1) · dn / dλ · dλ / dt-α c2 = 1 / λ · dλ / dt-2α fc: Focal length of coupling lens (mm) (= 1 /
φC) λ: wavelength of the semiconductor laser (mm) n: refractive index of the coupling lens α: linear expansion coefficient of the coupling lens φD: power of the diffractive surface (the arithmetic sum of the power of the diffractive surface when the diffractive surface is provided on both surfaces) ΦC: power of coupling lens dn / dt: ratio of refractive index change to temperature change dn / dλ: ratio of refractive index change to wavelength change dλ / dt: wavelength of semiconductor laser to temperature change Rate of change