JP2001243650A - Divergent angle converting lens and optical pickup device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a divergent angle converting lens and an optical pickup device capable of emitting a stable luminous flux against various factors such as a mode hop and a change in temperature. SOLUTION: The divergent angle converting lens 1 is arranged between a laser beam source 2 of the optical pickup device and an objective lens 5, and converts the divergent angle of the luminous flux emitted from the laser beam source. A chrometic aberration on axis is within range of ±4 μm to the oscillation wavelength deviation ± 1.5 nm of the laser beam source at the environmental temperature 25 deg.C. When the focul distance is expressed by fc (mm), the paraxial image point position in the environmental temperature 25 deg.C is expressed by fB0 (mm), and the paraxial image point position in the environmental temperature 55 deg.C is expressed by fB2 (mm), 0.0007×fc-0.004<=fB2-fB0<=0.0007×fc+0.004 is satisfied.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a divergence angle conversion element used for an optical pickup device, and more particularly to a divergence angle conversion lens and an optical pickup device suitably used for a high-density optical disk.

[0002]

2. Description of the Related Art In a DVD which is a high-density optical disk at present, a semiconductor laser has a wavelength of 635 to 660 nm and an objective lens has a numerical aperture (NA) of 0.6 Gigabytes.
Storage capacity has been achieved. On the other hand, recently, wavelength 4
A blue semiconductor laser having a wavelength of about 00 nm has been commercialized, and the commercialization of a new high-density optical disk system using this blue semiconductor laser is expected. As an example, a laser wavelength of 40
0 nm and the NA of the objective lens at 0.85
Gbyte storage capacity is possible.

As described above, in order to further increase the density of an optical disk, a technique for shortening the wavelength of a laser beam and a technique for increasing the NA are indispensable. On the other hand, it could not be put to practical use.

[0004]

In introducing the above-mentioned techniques for shortening the wavelength of the laser and increasing the NA, a condensing optical system (a divergence angle conversion element and an objective lens) for forming a light spot on an information recording surface of an optical disk is required. ) Requires the following considerations.

First, in the technique of shortening the wavelength, glass materials that can be used in the light-collecting optical system are limited in terms of the degree of coloring and the internal transmittance in the short wavelength region.

[0006] Further, with respect to the technology for increasing the NA, it is necessary to suppress the occurrence of axial chromatic aberration of the condensing optical system. As an example, it is assumed that there is a wavelength variation δλ in the objective lens (the root mean square Wrms = 0 of the wavefront aberration at the best focus position) in which the spherical aberration is completely corrected with respect to the reference wavelength λ0. Here, assuming that the back focus fB changes by δfB without changing the spherical aberration at the time of wavelength change,
When focusing is not performed with respect to the change of the back focus, Wrms is expressed by the following equation (1). Wrms = 0.145 × {(NA) ² / λ} × | δfB | (1)

That is, the general DVD has an NA of 0.6 and a wavelength of 6.
Compared to the case of 55 nm, NA 0.85, wavelength 400 n
m, the effect of | δfB | is 3.3 times that of the former when the allowable amount of wavefront aberration is the same, and it is necessary to further suppress the occurrence of axial chromatic aberration.

There are various factors that cause this axial chromatic aberration, but two factors can be considered when focusing on the divergence angle conversion element. This will be described with reference to FIGS.

One of them is axial chromatic aberration caused by a change δλ in oscillation wavelength of a semiconductor laser due to mode hopping. FIG.
Is a diagram showing the paraxial image point position of the divergence angle conversion element 51 in the standard state (λ = λ0, δT = + 0 ° C.). When the paraxial image point position matches the semiconductor laser emission point 50, the divergence angle conversion element Parallel light is emitted from 51. In FIG.
The image forming position of the parallel light beam from the left to the right is set to the laser emission point 5
It is assumed that the distance between the divergence angle conversion element 51 and the laser emission point 50 is fB0. Here, as shown in FIG. 3, when the paraxial image point position of the divergence angle conversion element 51 is fB1 when the wavelength of the laser light source changes by δλ, the above-mentioned axial chromatic aberration is (fB0−fB1). And this amount of axial chromatic aberration occurs.

[0010] The other one is considered to be a possibility that axial chromatic aberration is caused by a temperature change δT. The divergence angle conversion element 51 is fixed to the holding member 53 as shown in FIG. Preferably, as shown in FIG. 4A, the holding member 53 to which the divergence angle conversion element 52 is fixed has a laser light source 52 such that one end thereof is located at a position based on the laser light source 52.
In such a case, the expansion amount δL corresponding to the linear expansion coefficient of the holding member 53 is generated when the temperature changes as shown in FIG. This is the same as a change in the position of the light source 52.

Further, the wavelength of the laser light source shifts with the temperature change δT, and the refractive index change δn of the glass material of the divergence angle conversion element 51 occurs, so that the focal length of the divergence angle conversion element is reduced as shown in FIG. It is conceivable that it changes to fB2.
Here, when (fB2−fB0) and δL are not linked, the spread angle from the divergence angle conversion element 51 changes. This means that the position of the laser emission point changes in the entire condensing optical system.

The (fB2−fB0) and δL will be described with a specific example. A blue semiconductor laser and a single ball collimator (f = 1) made of acrylic resin as a divergence angle conversion element
0 mm), a temperature change δT = + 30 ° C. is assumed.
First, as shown in FIG. 4B, a fixing member 53 holding the laser light source 52 and the divergence angle conversion element 51 due to a temperature change.
Expands by δL. Assuming that the material of the fixing member 53 is aluminum (the coefficient of linear expansion is 23 × 10 ⁻⁶ / ° C.) and the original length of the fixing member 53 is equal to the focal length of the collimator, the expansion amount δL is as follows.

ΔL = 30 × 23 × 10 ⁻⁶ × 10 = 0.0
069 (mm)

On the other hand, the refractive index of the plastic changes by δn due to the temperature rise, and at the same time, the plastic expands. In this case, the focal position displacement δf of the collimator lens is δf = −δn / (n−1) × f (2) ). Δn / δT of acrylic resin is δn / δT
= −1.2 × 10 ⁻⁴ , δT = + 30 ° C., n =
At 1.5, δf = 0.072 (mm). If δL and δf are approximately equal, a parallel light is emitted from the collimator lens when the temperature rises, but in the above case, δf≫δL, and a divergent light is emitted from the collimator lens. In other words, it is the same as the occurrence of positional shift of the light emitting point when viewed from the entire light collecting optical system, and it can be said that a combination of an aluminum member and a single-piece collimator made of an acrylic resin is not preferable in terms of temperature characteristics.

Assuming that the focusing optical system has an objective lens f = 1.76 mm and a collimator lens f = 10 mm, if the laser emission point moves by 4 μm, the image point shift amount δfB of the focusing optical system is 0.124 μm. is there. λ = 400 nm, N
In an optical system with A = 0.85, Wrms =
0.032λrms.

As described above, in a high-density system, in other words, in an optical pickup device having a higher NA and a shorter wavelength, the higher the NA is, the more the occurrence of mode hops and temperature changes causes. Due to the slight deviation of the light emitting point, a non-negligible aberration occurs in the entire condensing optical system.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and provides a divergence angle conversion lens and an optical pickup device capable of emitting a stable light beam with respect to various factors such as mode hop and temperature change. The purpose is to provide.

[0018]

[MEANS FOR SOLVING THE PROBLEMS] To achieve the above object
The divergence angle conversion lens according to the present invention is an optical pickup.
Placed between the laser light source of the device and the objective lens,
Divergence that converts the divergence angle of a light beam emitted from a laser light source
Angle conversion lens, laser at ambient temperature 25 ° C
Axial chromatic aberration for ± 1.5 nm oscillation wavelength shift of light source
Within ± 4 μm, focal length is fc (mm), ring
The paraxial image point position at the boundary temperature of 25 ° C. is f _B0(Mm), ring
Paraxial image point position f at boundary temperature 55 ° C_B2(Mm)
Then, 0.0007 × fc−0.004 ≦ f_B2−f_B0≦ 0.0007 × fc + 0.004 (3)

According to this divergence angle conversion lens, over-axial chromatic aberration is generated when the temperature rises, so that even if the distance between the laser light source and the divergence angle conversion lens is increased due to the temperature rise, the divergence angle is changed. A light beam can be emitted from the conversion lens at a predetermined divergence angle. Therefore, even if the temperature rises due to various external factors, a divergence angle conversion lens that can emit a stable light beam can be realized.

Further, the refractive index change dn /
It is preferable that at least a part of the material has a dT (/ ° C.) satisfying −10 × 10 ⁻⁶ ≦ dn / dT ≦ 2.0 × 10 ⁻⁶ (4). In this case, the refractive index change dn / dT (/ ° C.) with respect to the temperature change of the material is −6.0 × 10 ⁻⁶ ≦ dn / dT ≦ 1.0 × 10 ⁻⁶ (5), and is composed of the material. It is preferable that the focal length of the portion alone is positive.

Preferably, the material is glass, and an ultraviolet curable resin layer is formed on the glass. Further, it is preferable to have a portion made of the glass and a portion made of plastic. In this case, the portion made of glass and the portion made of plastic can be formed by bonding a glass lens and a plastic lens.

When the focal length of the part made of plastic is fp, the relationship with the focal length fc preferably satisfies the following equation (6).

| Fc / fp | ≦ 0.16 (6)

If the value is equal to or less than the upper limit in the equation (6), the power of the plastic lens does not become too large, and f _B2 at the time of temperature rise does not become too large than f _B0, which is preferable. In this case, it is more preferable to satisfy the following expression (7).

| Fc / fp | ≦ 0.08 (7)

Further, at least one surface can be configured to be a diffraction surface having a diffraction effect. Preferably, the divergence angle conversion lens is a collimating lens.

An optical pickup device according to the present invention includes a laser light source, a divergence angle conversion lens for converting a divergence angle of a light beam emitted from the laser light source, and an objective lens. , Disposed between the laser light source and the objective lens, and at an ambient temperature of 2.
The axial chromatic aberration is within a range of ± 4 μm with respect to an oscillation wavelength shift of the laser light source at 5 ° C. of ± 1.5 nm. The difference from the position is 3 μm or less.

Further, it is preferable that a holding member for holding the laser light source and the divergence angle conversion lens is provided, and the amount of expansion of the holding member when the ambient temperature changes from 25 ° C. to 55 ° C. is 3 μm or less. Is preferred. Further, the laser light source and the divergence angle conversion lens may be held by separate holding members.

Another optical pickup device according to the present invention includes a laser light source, a divergence angle conversion lens for converting a divergence angle of a light beam emitted from the laser light source, and an objective lens. The lens is disposed between the laser light source and the objective lens, and has an oscillation wavelength deviation of ± 1.5 nm at an ambient temperature of 25 ° C.
, The axial chromatic aberration is within the range of ± 4 μm, the focal length is fc (mm), the paraxial image point position at an environmental temperature of 25 ° C. is f _B0 (mm), and the paraxial image point at an environmental temperature of 55 ° C. When the distance is f _B2 (mm), 0.0007 × fc−0.0004 ≦ f _B2 −f _B0 ≦ 0.0007 × fc +
0.004.

Still another optical pickup device according to the present invention includes a laser light source, a divergence angle conversion lens for converting a divergence angle of a light beam emitted from the laser light source, and an objective lens. The conversion lens is disposed between the laser light source and the objective lens, and has an oscillation wavelength deviation of ± 1.5 at an ambient temperature of 25 ° C.
nm, the axial chromatic aberration is within a range of ± 4 μm,
With respect to the distance between the light emitting point of the laser light source at an environmental temperature of 25 ° C. and the divergence angle conversion lens, the expansion amount of the distance between the light emitting point of the laser light source at an environmental temperature of 55 ° C. and the divergence angle conversion lens is L μm. Environmental temperature 25 ℃
And the difference between the paraxial image point position at an environmental temperature of 55 ° C. is (L−4) μm or more and (L + 4) μm
It is characterized by the following.

According to each of the optical pickup devices described above, the divergence angle conversion lens is configured to generate excessive axial chromatic aberration when the temperature rises, so that the distance between the laser light source and the divergence angle conversion lens increases due to the temperature rise. Even if
The light beam can be emitted from the divergence angle conversion lens at a predetermined divergence angle. Therefore, even if the temperature rises due to various external factors, a divergence angle conversion lens that can emit a stable light beam can be realized, and a stable light irradiation operation can be realized in the optical pickup device.

The divergence angle conversion lens is made of a material whose refractive index change dn / dT (/ ° C.) with respect to temperature change satisfies -10.0 × 10 ⁻⁶ ≦ dn / dT ≦ 2.0 × 10 ^-6. It is preferable to have the refractive index change dn at least in part with respect to a temperature change of the material.
It is preferable that / dT (/ ° C.) is −6.0 × 10 ⁻⁶ ≦ dn / dT ≦ 1.0 × 10 ⁻⁶ , and that the focal length of the partial simple substance made of the material is positive.

Preferably, the material is glass, and an ultraviolet curable resin layer is formed on the glass. The material is glass, and a portion made of glass and a material made of plastic are used. It is preferable to have a portion which is provided.

The portion made of glass and the portion made of plastic can be formed by bonding a glass lens and a plastic lens.

When the focal length of the divergence angle conversion lens is fc, and the focal length of a part of the divergence angle conversion lens made of plastic is fp, the relationship with the focal length fc is as follows: It is preferable that the following expression (6) is satisfied.

| Fc / fp | ≦ 0.16 (6)

If it is less than the upper limit, the power of the plastic lens does not become too large, and f _B2 when the temperature rises is f _B0
It does not become too large, and is preferable. In this case, it is more preferable to satisfy Expression (7).

| Fc / fp | ≦ 0.08 (7)

Further, at least one surface of the divergence angle conversion lens may be a diffraction surface having a diffraction effect. Preferably, the divergence angle conversion lens is a collimating lens.

The objective lens has a numerical aperture of 0.65.
That is all. Further, the above-mentioned optical pickup device in which the wavelength of the laser light source is 450 nm or less can realize a new high-density optical disk system using a blue semiconductor laser or the like.

Still another optical pickup device according to the present invention has a laser light source, a divergence angle conversion lens for converting a divergence angle of a light beam emitted from the laser light source, and an objective lens. The conversion lens is disposed between the laser light source and the objective lens, is held by the holding member together with the laser light source, and has an axial chromatic aberration with respect to an oscillation wavelength deviation of the laser light source at an environmental temperature of 25 ° C. ± 1.5 nm. Is within the range of ± 4 μm, and the focal length is fc (m
m) and the paraxial image point position at an environmental temperature of 25 ° C. is represented by f _B0 (m
m), paraxial image point distance f _B2 (m
m), assuming that the linear expansion coefficient of the holding member is α, 30 × α × fc−0.004 ≦ f _B2 −f _B0 ≦ 30 × α × fc + 0.004 (8). .

According to this optical pickup device, the divergence angle conversion lens is configured to generate excessive axial chromatic aberration when the temperature rises, so that the temperature rise increases the distance between the laser light source and the divergence angle conversion lens in the holding member. Even when the divergence angle conversion lens is extended, it is possible to emit a light beam at a predetermined divergence angle. Therefore, even if the temperature rises due to various external factors, a divergence angle conversion lens that can emit a stable light beam can be realized, and a stable light irradiation operation can be realized in the optical pickup device.

Each of the above-described optical pickup devices condenses a light beam from a laser light source on a recording surface of an optical information recording medium via a divergence angle conversion lens and an objective lens, and condenses the light from the optical information recording medium. By detecting with the detector, recording and / or reproduction of information on the optical information recording medium can be performed. This optical information recording medium includes, for example, C
Various CDs such as D, CD-R, CD-RW, CD-Video, CD-ROM, DVD,
Various types of DVDs, such as DVD-ROM, DVD-RAM, DVD-R, and DVD-RW, and disc-shaped information recording media such as MDs, are also available. Including. In particular, the optical pickup device is useful for a new information recording medium that requires a high numerical aperture NA for the objective lens and / or a short wavelength for the light source.

[0044]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in more detail by embodiments of the present invention with reference to the drawings.

<First Embodiment> A first embodiment will be described. FIG. 1 is a schematic configuration diagram of an optical pickup device according to the first embodiment.

The optical pickup device shown in FIG. 1 stores a GaN blue semiconductor laser 2 as a laser light source, a collimator lens (focal length fc) 1 as a divergence angle conversion lens, and stores laser light from the blue semiconductor laser 2 as optical information. Objective lens 5 for focusing light on the information recording surface of an optical disk 6 as a medium
And a holding member 3 for fixing the collimator 1 and the blue semiconductor laser 2 respectively.

Further, in the optical pickup device shown in FIG. 1, a beam shaping element 4 is disposed between the collimator lens 1 and the objective lens 5, whereby the astigmatic difference of the blue semiconductor laser 1 is reduced. A substantially circular light beam is incident on the objective lens 5 (by enlarging the direction in which the angle is small). That is, the light emitted from the blue semiconductor laser 2 is converted into a parallel light beam by the collimator lens 1,
Is converted into a circular parallel light beam. A stop 8 is arranged on the side of the semiconductor laser 1 of the objective lens 5 to limit the beam diameter. The light beam incident on the objective lens 5 is condensed on the information recording surface of the optical disk 6, and at this time, the objective lens 5 is focused by the actuator 7.
The optical pickup device includes a light receiver (not shown) for receiving light from the information recording surface of the optical disc 6.

The collimator lens 1 of the present embodiment corrects axial chromatic aberration due to a difference in wavelength in an environment where there is no temperature change (δT = 0 ° C .: room temperature 25 ° C.). For example, the correction can be made such that fB0 ≒ fB1 in FIGS. There are various correction means. When the collimator lens 1 is a single lens, it is preferable that the dispersion value (Abbe number) ν is simply large. As an example of the case of correcting with two balls, there is a laminated lens of convex crown glass and concave flint glass which is a general achromatic lens. Further, a diffraction surface may be formed on the collimator lens 1 to correct longitudinal chromatic aberration. As a result, even when a wavelength shift of the laser light source occurs due to mode hopping, the collimator emits a parallel light beam.

Further, it is preferable to hold the blue semiconductor laser and the collimator lens with a material whose linear expansion coefficient is sufficiently smaller than that of aluminum. Alternatively, the blue semiconductor laser and the collimator lens may be attached to separate frames so that the distance between the laser and the collimator does not change when the temperature rises. This example will be described with reference to FIG. 6. When the collimator lens 1 is attached and held on the frame 11 and the laser light source 2 is attached and held on another frame 12, δL ≒ 0 in FIG. 4B. To do.

As described above, the amount of deviation δf of the focal position of the collimator lens at the time of temperature change may be set within ± 3 μm. This δf is represented by δf =
fB2−fB0 ≒ 0. In the case of a single ball collimator, it is sufficient that δn ≒ 0, as is clear from equation (2), that is, dn / dT ≒ 0. As an example of such a glass material, there is a glass “S-FSL5” manufactured by Ohara Corporation. Further, when the collimator lens is formed of two types of glass materials, if the following equation (9) is satisfied, the focal position shift amount δf of the collimator lens when the temperature changes can be reduced. ｛−δn1 / (n1-1) × f1 + δn2 / (n2-1) × f2｝ ≒ 0 (9) where ni and fi are the refractive index and the focal length of the i-th glass material. 1 / fc = 1 / f1 + 1 / f2.

There are various solutions satisfying the expression (9) such as a combination of convex and convex, a combination of concave and convex, and the like. Further considering the normal achromatizing condition, f1 = fc (ν1−ν2) / ν1 f2 = fc (ν2−ν1) / ν2 where νi is the i-th dispersion value, and therefore, it is sufficient to select a glass material satisfying these from the above-described paraxial calculation, and then actually perform the aberration correction design.

The present invention is not limited to the embodiment. Any divergence angle conversion lens (so-called coupling lens) that is disposed between the laser light source of the optical pickup device and the objective lens and converts the divergence angle of the light beam emitted from the laser light source may be used. That is, although the embodiment of the collimator lens in which the parallel light beam enters the objective lens has been described, the present invention is not limited thereto, and a coupling lens in which the non-parallel light beam enters the objective lens may be used. The point is that almost the same luminous flux can be stably incident on the objective lens regardless of the laser oscillation wavelength change due to the mode hop or the laser oscillation wavelength shift due to the temperature change.

Although the beam shaping element is inserted between the collimator lens and the objective lens, it may be omitted. When elements having different powers in the two axial directions are introduced, astigmatism occurs due to a shift in the light emitting point. This astigmatism cannot be eliminated by focusing the objective lens. Therefore, if the performance of the blue semiconductor laser is improved and the laser output is large in the future, or if a blue semiconductor laser having a small astigmatism is commercialized, it is sufficiently possible to omit this beam shaping element.

Further, it goes without saying that the present invention is not limited to a blue semiconductor laser, but is also effective for an optical system in which a conventional red semiconductor laser of about 650 nm has an objective lens with a high NA (≧ 0.65).

<Second Embodiment>

Next, a second embodiment will be described. The optical pickup device using the divergence angle conversion lens according to this embodiment has a structure in which the member holding the blue semiconductor laser and the collimator lens expands when the temperature rises, and the divergence angle conversion lens cancels the displacement of the light emitting point position. Except for the generation of the chromatic aberration, it is the same as that described above, and the description of the overlapping portions will be omitted. A collimator lens (focal length fc) as a divergence angle conversion lens in the present embodiment will be described.

The collimator lens according to the present embodiment corrects axial chromatic aberration due to a difference in wavelength at δT = 0 ° C. in an environment where there is no temperature change. There are various correction means. When the collimator lens 1 is a single lens, it is preferable that the dispersion value (Abbe number) ν is simply large. As an example of the case of correcting with two balls, there is a laminated lens of convex crown glass and concave flint glass which is a general achromatic lens. Further, a diffraction surface may be formed on the collimator lens to correct longitudinal chromatic aberration.

Here, the holding member 3 (FIG. 1) holding the blue semiconductor laser and the collimator lens expands due to the temperature rise δT, and the amount of expansion δL is as described above, where the linear expansion coefficient of the holding member 3 is α. Thus, it can be approximated by δL = α × δT × fc (mm) (see FIG. 4).

On the other hand, as the temperature rises, the oscillation wavelength of the blue semiconductor laser shifts, and for the collimator lens, the refractive index changes with the wavelength and the temperature, and as a result, the focal position shift δf occurs. The focal position deviation δf and the expansion amount δ of the holding member 3
By making L substantially the same, it is possible to reduce the displacement of the light emitting point due to the temperature rise. That is, it is preferable that the power of the collimator lens becomes weak when the temperature rises. In ordinary glass materials, the refractive index decreases as the wavelength increases, but many glass materials have a positive dn / dT with respect to the change in refractive index. When the collimator lens is a single convex lens, the positive power must be weakened, so that it is desirable that the refractive index be lowered when the temperature rises. Such a d
As a glass material satisfying n / dT ≦ 0, for example, there is “S-FPL51” manufactured by Ohara Corporation. Such dn / dT
Although a small number of glass materials satisfy ≦ 0, these glass materials tend to have a large ν value and a high internal transmittance at a short wavelength, and are preferable as a collimator lens for a short wavelength.

Further, a solution with two balls and a solution provided with a diffractive surface can also exist, and will be described in the following embodiments.

The present invention is not limited to the present embodiment. Any divergence angle conversion lens (so-called coupling lens) that is arranged between the main laser source of the optical pickup device and the objective lens and converts the divergence angle of the light beam emitted from the laser light source may be used. That is, although the embodiment of the collimator lens in which the parallel light beam enters the objective lens has been described, the present invention is not limited thereto, and a coupling lens in which the non-parallel light beam enters the objective lens may be used. The point is that almost the same luminous flux can be stably incident on the objective lens regardless of the laser oscillation wavelength change due to the mode hop or the laser oscillation wavelength shift due to the temperature change.

Although the beam shaping element is inserted between the collimator lens and the objective lens, it may be omitted. When elements having different powers in the two axial directions are introduced, astigmatism occurs due to a shift in the light emitting point. This astigmatism cannot be eliminated by focusing the objective lens. Therefore, if the performance of the blue semiconductor laser is improved and the laser output is large in the future, or if a blue semiconductor laser having a small astigmatism is commercialized, it is sufficiently possible to omit this beam shaping element.

Further, it is needless to say that the present invention is not limited to the blue semiconductor laser, but can be applied to an optical system having a high NA (≧ 0.65) with an objective lens using a conventional red semiconductor laser of about 650 nm.

[0064]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments 1 to 7 of the present invention will be described below.

(Example 1)

Example 1 is an example relating to the above-described second embodiment. Blue semiconductor laser wavelength λ = 40
5 nm, dλ / dT = + 0.05 nm / ° C., and the focal length fc = 1 of the collimator lens as the divergence angle conversion element
0 mm. The blue semiconductor laser and the collimator lens are mounted on the same holding member as shown in FIG.
The material of the member is aluminum. Therefore, the temperature rise δ
When T = + 30 ° C., the expansion amount δL of the holding member is δL ≒ 0.0069 (mm) as described above. The collimator lens is a single-sided aspherical glass single lens, and the glass material is "S-FPL51" (dn / dT) manufactured by Ohara.
= −5.3 × 10 ⁻⁶ / ° C.). Table 1 shows lens data of the collimator lens.

[0067]

[Table 1]

In Table 1, an optical system in which a parallel light beam enters from the objective lens side is shown. Therefore, when the position of the image point coincides with the position of the laser emission point, in an actual optical pickup device, a parallel light beam is emitted from the collimator lens. Also, r indicates the radius of curvature of the surface, d indicates the surface interval between the i-th surface and the (i + 1) -th surface, and n indicates the refractive index. The first surface is a stop, and the stop diameter φ =
3.0 mm.

The formula of the aspherical surface is based on the following equation (1). Here, X is an axis in the optical axis direction, H is an axis perpendicular to the optical axis, and the traveling direction of light is positive. Κ is a cone coefficient, Aj is an aspheric coefficient, and Pj is a power of the aspheric surface.

[0070]

(Equation 1)

As is apparent from Table 1, the axial chromatic aberration when a wavelength shift occurs in mode hop is | fB
0-fB1 | = 2.7 μm (wavelength shift δλ = + 1.5 nm in an environment of δT = 0 ° C.). When the temperature rises, the refractive index change due to the wavelength change and the focal position shift δf (= fB2−fB0) = + 5.7 μm resulting from the change in the refractive index, and chromatic aberration that cancels the expansion amount δL of the holding member is generated. I understand. Here, temporarily, d of “S-FPL51”
When n / dT is + 2.0 × 10 ⁻⁶ / ° C., the above δf
Are respectively +1.5 μm, and δL cannot be canceled, which is not preferable.

(Example 2)

Example 2 is an example relating to the above-described second embodiment. Blue semiconductor laser wavelength λ = 40
5 nm, dλ / dT = + 0.05 nm / ° C., and the focal length fc = 1 of the collimator lens as the divergence angle conversion element
0 mm. The blue semiconductor laser and the collimator lens are mounted on the same holding member, and the material of the holding member is aluminum. Therefore, the temperature rise δT = + 3
In the case of 0 ° C., the expansion amount δL of the member is similarly δL ≒ 0.
0069 (mm).

A collimator lens is formed on one surface of a glass lens having a spherical surface on both sides (single focal length f = 10.429 mm).
This is a hybrid lens in which an ultraviolet curable resin layer having a weak positive power (single focal length f = 224 mm) is provided, and this resin layer is aspheric. The glass material is "S" manufactured by OHARA
−FSL5 ”(dn / dT = 0 / ° C.), and δn / δT of the ultraviolet curable resin is −1.2 × 10 −4. Table 2
Shows lens data of the collimator lens.

[0075]

[Table 2]

As is clear from Table 2, the axial chromatic aberration when the wavelength shift occurs in mode hop is fB0
−fB1 = 3.3 μm (wavelength shift δλ = + 1.5 nm in an environment of δT = 0 ° C.). When the temperature rises, the refractive index change due to the wavelength change and the focal position shift δ resulting from the refractive index change
f (= fB2−fB0) = + 6.5 μm, which indicates that chromatic aberration that cancels the expansion amount δL of the member is generated. Here, if the dn / dT of “S-FSL5” is −10.0 × 10 ⁻⁶ / ° C., the above δf becomes +12 μm, and δL cannot be canceled, which is not preferable.

(Example 3)

Example 3 is an example relating to the above-described second embodiment. Blue semiconductor laser wavelength λ = 40
5 nm, dλ / dT = + 0.05 nm / ° C., and the focal length fc of the collimator lens as the divergence angle conversion element is 1
0 mm. The blue semiconductor laser and the collimator lens are mounted on the same holding member, and the material of the holding member is aluminum. Therefore, the temperature rise δT = + 3
In the case of 0 ° C., the expansion amount δL of the holding member is similarly δL ≒
0.0069 (mm).

The collimator lens is a combination of a convex glass lens having a spherical surface on both sides (single focal length f = 5.165 mm) and a glass lens having a concave power on both spherical surfaces (single focal length f = -10.65 mm). It is a compound lens.
The glass material is "S-BAL3" (dn / dT) manufactured by OHARA
= + 0.5 × 10 ⁻⁶ / ° C.) and “S-LA” manufactured by OHARA
H53 "(dn / dT = + 9.2 × 10 ⁻⁶ / ° C.). Table 3 shows the lens data of the collimator lens.

[0080]

[Table 3]

As is apparent from Table 3, the axial chromatic aberration when the wavelength shift occurs in mode hop is fB0
−fB1 = 3.2 μm (wavelength shift δλ = + 1.5 nm in an environment of δT = 0 ° C.). When the temperature rises, the refractive index change due to the wavelength change and the focal position shift δ resulting from the refractive index change
f (= fB2−fB0) = + 5.4 μm, which indicates that chromatic aberration that cancels the expansion amount δL of the member is generated.

(Embodiment 4)

Embodiment 4 is an embodiment relating to the above-described second embodiment. Blue semiconductor laser wavelength λ = 40
5 nm, dλ / dT = + 0.05 nm / ° C., and the focal length fc of the collimator lens as the divergence angle conversion element is 1
0 mm. The blue semiconductor laser and the collimator lens are mounted on the same holding member, and the material of the holding member is aluminum. Therefore, the temperature rise δT = + 3
In the case of 0 ° C., the expansion amount δL of the holding member is similarly δL ≒
0.0069 (mm).

The collimator lens includes a plano-convex glass lens (single focal length f = 10.65 mm) and a single-sided aspherical single-sided plastic lens having weak positive power (single focal length f = 146.4 mm). Is a laminated lens. The glass material is "S-FSL" manufactured by OHARA
5 "(dn / dT = 0 / ° C.), and δn / δT of the plastic lens is -1.2 × 10 ^-4 . Table 4 shows lens data of the collimator lens.

[0085]

[Table 4]

As is apparent from Table 4, the axial chromatic aberration when the wavelength shift occurs in mode hop is fB0
−fB1 = 3.3 μm (wavelength shift δλ = + 1.5 nm in an environment of δT = 0 ° C.). When the temperature rises, the refractive index change due to the wavelength change and the focal position shift δ resulting from the refractive index change
f (= fB2−fB0) = + 5.9 μm, which indicates that chromatic aberration that cancels the expansion amount δL of the member is generated.

(Embodiment 5)

Example 5 is an example relating to the above-described second embodiment. Blue semiconductor laser wavelength λ = 40
5 nm, dλ / dT = + 0.05 nm / ° C., and the focal length fc of the collimator lens as the divergence angle conversion element is 1
0 mm. The blue semiconductor laser and the collimator lens are mounted on the same holding member, and the material of the holding member is aluminum. Therefore, the temperature rise δT = + 3
In the case of 0 ° C., the expansion amount δL of the member is similarly δL ≒ 0.
0069 (mm). The collimator lens is a single aspherical glass lens, and the glass material is "S" manufactured by OHARA.
−FPL51 ”(dn / dT = −5.3 × 10 ⁻⁶ / ° C.)
And Table 5 shows the lens data of the collimator lens.

[0089]

[Table 5]

Then, on the second surface of the collimator lens,
A diffraction pattern (diffraction ring zone) is provided concentrically with the optical axis. Generally, the pitch of a diffraction ring zone is defined using a phase difference function or an optical path difference function. Specifically, the phase difference function ΦB is expressed by the following equation 2 with the unit being radian,
The optical path difference function Φb is expressed by the following Equation 3 with the unit being mm.

[0091]

(Equation 2)

(Equation 3)

Although these two expression methods have different units, they are equivalent in terms of expressing the pitch of the diffraction ring zone. That is, by multiplying the coefficient B of the phase difference function whose unit is radian by λ / 2π with respect to the main wavelength λ (mm), it can be converted into the coefficient b of the optical path difference function, and conversely, the optical path difference whose unit is mm By multiplying the coefficient b of the function by 2π / λ, the coefficient B of the phase difference function
Can be converted to In the following embodiment, λ is the main wavelength 405 nm of the blue semiconductor laser.

As is apparent from Table 5, the axial chromatic aberration when the wavelength shift occurs in mode hop is fB0
−fB1 = 0.2 μm (wavelength shift δλ = + 1.5 nm in an environment of δT = 0 ° C.). When the temperature rises, the refractive index change due to the wavelength change and the focal position shift δ resulting from the refractive index change
f (= fB2−fB0) = + 3.0 μm, which indicates that chromatic aberration that cancels the expansion amount δL of the member is generated.

(Embodiment 6)

Example 6 is an example relating to the above-described second embodiment. Blue semiconductor laser wavelength λ = 40
5 nm, dλ / dT = + 0.05 nm / ° C., and the focal length fc of the collimator lens as the divergence angle conversion element is 1
0 mm. The blue semiconductor laser and the collimator lens are mounted on the same holding member, and the material of the holding member is aluminum. Therefore, the temperature rise δT = + 3
In the case of 0 ° C., the expansion amount δL of the member is similarly δL ≒ 0.
0069 (mm).

The collimator lens is an example in which an ultraviolet curable resin layer is formed on the surface of a glass lens, and annular diffraction is provided on the surface side of the resin layer. The glass material is “S-FSL5” (dn / dT = 0 / ° C.) manufactured by OHARA CORPORATION, and δn / δT of the resin layer is −1.2 × 10 ⁻⁴ . Table 6 shows the lens data of the collimator lens.

[0097]

[Table 6]

As is clear from Table 6, the axial chromatic aberration when the wavelength shift occurs in mode hop is fB0
−fB1 = 0.1 μm (under an environment of δT = 0 ° C., wavelength shift δλ = + 1.5 nm). When the temperature rises, the refractive index change due to the wavelength change and the focal position shift δ resulting from the refractive index change
f (= fB2−fB0) = + 6.0 μm, which indicates that chromatic aberration that cancels the expansion amount δL of the member is generated.

(Embodiment 7)

Example 7 is an example of the above-described second embodiment. Blue semiconductor laser wavelength λ = 405n
m, dλ / dT = + 0.05 nm / ° C., and the focal length fc of the collimator lens as the divergence angle conversion element is 10 m.
m. The blue semiconductor laser and the collimator lens are mounted on the same holding member, and the material of the holding member is aluminum. Therefore, the temperature rise δT = + 30 ° C.
, The expansion amount δL of the holding member is similarly δL は 0.
0069 (mm).

The collimator lens is an example in which an ultraviolet curing resin layer is formed on the surface of a glass lens and a so-called bonded portion is provided. The glass material is “S-FSL5” (dn / dT = 0 / ° C.) manufactured by OHARA CORPORATION, and δn / δT of the resin layer is −1.2 × 10 ⁻⁴ . Table 7 shows lens data of the collimator lens.

[0102]

[Table 7]

As is clear from Table 7, the axial chromatic aberration when a wavelength shift occurs in mode hop is fB0
−fB1 = 0.2 μm (wavelength shift δλ = + 1.5 nm in an environment of δT = 0 ° C.). When the temperature rises, the refractive index change due to the wavelength change and the focal position shift δ resulting from the refractive index change
f (= fB2−fB0) = + 6.0 μm, which indicates that chromatic aberration that cancels the expansion amount δL of the member is generated.

The embodiment according to the second embodiment has been described above. However, even when the temperature rises, the distance between the laser light source and the collimator lens does not expand (δL ≒ 0).
That is, also in the first embodiment, the dn / d
If T and dn / dλ are selected in consideration, fB2−fB0 = 0 can be set, and the description is omitted.

[0105]

As described above, the divergence angle conversion element (particularly, preferably, a collimator lens) and the optical pickup device of the present invention can provide axial chromatic aberration even when the oscillation wavelength shifts due to the mode hop of the semiconductor laser. Is corrected, a luminous flux having a desired divergence angle can be emitted from the divergence angle conversion element. In particular, it is possible to maintain the emission of a parallel light beam from the collimator lens. Furthermore, even if the distance between the semiconductor laser and the divergence angle conversion element (for example, a collimator lens) changes with the temperature rise or the optical pickup device does not change, the dn of the material of the divergence angle conversion element (collimator) will not change. / DT, dn /
Since chromatic aberration for canceling the interval change is generated in consideration of dλ, a light beam having a desired divergence angle can be emitted from the divergence angle conversion element. In particular,
The collimator lens can keep the parallel light beam emitted.

[Brief description of the drawings]

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

FIG. 2 is a diagram illustrating a paraxial image point position of a divergence angle conversion element 51 in a standard state (λ = λ0, δT = + 0 ° C.).

3 is a diagram showing a paraxial image point position of a divergence angle conversion element 51 in a state where the wavelength of the laser beam has changed from the state of FIG. 2 (λ = λ0 + δλ, δT = + 0 ° C.).

FIG. 4 is a diagram showing a divergence angle conversion element 51 and a semiconductor laser 52 held by a holding member 53, respectively.
The case of 0 ° C. (a) and the case of δT> 0 ° C. (b) are shown.

5 is a diagram showing a paraxial image point position of the divergence angle conversion element 51 in a state where the wavelength and temperature of the laser beam have changed from the state of FIG. 2 (λ = λ0 + δλ, δT = + 30 ° C.).

FIG. 6 is a view showing a modification of the holding member in the optical pickup device according to the first embodiment.

[Explanation of symbols]

 Reference Signs List 1 collimator lens (divergence angle conversion lens) 2 blue semiconductor laser (laser light source) 3 holding member 4 beam shaping element 5 objective lens 6 optical disk 11, 12 frame

 ────────────────────────────────────────────────── ─── Continued on the front page F term (reference) 2H087 KA13 LA25 PA01 PA17 PA18 PB01 QA02 QA07 QA14 QA22 QA37 QA41 RA05 RA12 RA13 UA01 5D119 AA43 BA01 FA02 JA02 JA43 JB01 JB02 JB03 JC04 LB05 9A001 GG01 KK16

Claims (28)

[Claims] 1. A divergence angle conversion lens disposed between a laser light source of an optical pickup device and an objective lens for converting a divergence angle of a light beam emitted from the laser light source, wherein the laser light source at an environmental temperature of 25 ° C. Oscillation wavelength deviation of ±
The axial chromatic aberration is within a range of ± 4 μm for 1.5 nm, the focal length is fc (mm), the paraxial image point position at an ambient temperature of 25 ° C. is f _B0 (mm), and the paraxial at an environmental temperature of 55 ° C. When the image point position is f _B2 (mm), 0.0007 × fc−0.0004 ≦ f _B2 −f _B0 ≦ 0.0007 × fc +
A divergence angle conversion lens satisfying 0.004. 2. A refractive index change dn / dT with respect to a temperature change.
(/ ° C.) is divergent light conversion lens according to claim 1, characterized in that it comprises at least a portion of the material which satisfies ^{-10.0 × 10 -6 ≦ dn / dT} ≦ 2.0 × 10 -6. 3. The material has a refractive index change dn / dT (/ ° C.) with respect to a temperature change of −6.0 × 10 ⁻⁶ ≦ dn / dT ≦ 1.0 × 10 ⁻⁶ , and is made of the material. 3. The divergence angle conversion lens according to claim 2, wherein the focal length of the portion alone is positive. 4. The divergence angle conversion lens according to claim 3, wherein the material is glass, and an ultraviolet curable resin layer is formed on the glass. 5. The divergence angle conversion lens according to claim 3, wherein said material is glass, and has a portion made of glass and a portion made of plastic. 6. The divergence angle according to claim 5, wherein the portion made of glass and the portion made of plastic are formed by bonding a glass lens and a plastic lens. Conversion lens. 7. The relationship between the focal length fc and the focal length fc of a single unit made of plastic, which satisfies | fc / fp | ≦ 0.16. The divergence angle conversion lens according to 5 or 6. 8. The focal length fc and the focal length fp
The divergence angle conversion lens according to claim 7, wherein the relationship of | fc / fp | ≦ 0.08 is satisfied. 9. The method according to claim 1, wherein at least one surface is a diffraction surface having a diffraction effect.
The divergence angle conversion lens according to the item. 10. A divergence angle conversion lens according to claim 1, wherein the divergence angle conversion lens is a collimator lens. 11. A laser light source, a divergence angle conversion lens for converting a divergence angle of a light beam emitted from the laser light source,
In an optical pickup device having an objective lens, the divergence angle conversion lens is disposed between the laser light source and the objective lens, and has an oscillation wavelength shift of the laser light source at an environmental temperature of 25 ° C.
The axial chromatic aberration is within a range of ± 4 μm for 1.5 nm, and the paraxial image point position at an environmental temperature of 25 ° C. and the environmental temperature 55
An optical pickup device, wherein a difference from a paraxial image point position at 3 ° C. is 3 μm or less. 12. A laser light source, a divergence angle conversion lens for converting a divergence angle of a light beam emitted from the laser light source,
In the optical pickup device having an objective lens, the divergence angle conversion lens is disposed between the laser light source and the objective lens, and has an oscillation wavelength shift of the laser light source at an environmental temperature of 25 ° C.
The axial chromatic aberration is within a range of ± 4 μm with respect to 1.5 nm. When the expansion amount of the distance between the light emitting point of the light source and the divergence angle conversion lens is L μm, the ambient temperature is 25 ° C.
And the difference between the paraxial image point position at an environmental temperature of 55 ° C. is (L−4) μm or more and (L + 4) μm
An optical pickup device characterized by the following. 13. The optical pickup device according to claim 11, further comprising a holding member that holds the laser light source and the divergence angle conversion lens. 14. The optical pickup device according to claim 13, wherein the amount of expansion of the holding member when the environmental temperature changes from 25 ° C. to 55 ° C. is 3 μm or less. 15. A laser light source, a divergence angle conversion lens for converting a divergence angle of a light beam emitted from the laser light source,
In the optical pickup device having an objective lens, the divergence angle conversion lens is disposed between the laser light source and the objective lens, is held by a holding member together with the laser light source, and oscillates the laser light source at an ambient temperature of 25 ° C. Wavelength deviation ±
The axial chromatic aberration is within a range of ± 4 μm with respect to 1.5 nm, the focal length is fc (mm), the paraxial image point position at an ambient temperature of 25 ° C. is f _B0 (mm), and the When the axial image point distance f _B2 (mm) and the linear expansion coefficient of the holding member are α, 30 × α × fc−0.004 ≦ f _B2 −f _B0 ≦ 30 × α × fc +
An optical pickup device satisfying 0.004. 16. A laser light source, a divergence angle conversion lens for converting a divergence angle of a light beam emitted from the laser light source,
In the optical pickup device having an objective lens, the divergence angle conversion lens is disposed between the laser light source and the objective lens, and has an oscillation wavelength shift of the laser light source at an environmental temperature of 25 ° C.
The axial chromatic aberration is within a range of ± 4 μm with respect to 1.5 nm, the focal length is fc (mm), the paraxial image point position at an ambient temperature of 25 ° C. is f _B0 (mm), and the When the axial image point distance is f _B2 (mm), 0.0007 × fc−0.004 ≦ f _B2 −f _B0 ≦ 0.0007 × fc +
An optical pickup device satisfying 0.004. 17. The optical pickup device according to claim 11, wherein the laser light source and the divergence angle conversion lens are held by separate holding members. 18. The divergence angle conversion lens is made of a material whose refractive index change dn / dT (/ ° C.) with respect to temperature change satisfies -10.0 × 10 ⁻⁶ ≦ dn / dT ≦ 2.0 × 10 ^−6. The optical pickup device according to claim 11, wherein the optical pickup device is provided at least in part. 19. The material has a refractive index change dn / dT (/ ° C.) with respect to a temperature change of −6.0 × 10 ⁻⁶ ≦ dn / dT ≦ 1.0 × 10 ⁻⁶ , and is composed of the material. 19. The optical pickup device according to claim 18, wherein the focal length of the single part is positive. 20. The optical pickup device according to claim 19, wherein the material is glass, and an ultraviolet curable resin layer is formed on the glass. 21. The optical pickup device according to claim 19, wherein the material is glass, and has a portion made of glass and a portion made of plastic. 22. The optical pickup according to claim 21, wherein the portion made of glass and the portion made of plastic are formed by bonding a glass lens and a plastic lens. apparatus. 23. The focal length of the divergence angle conversion lens is f
23. The optical system according to claim 21, wherein: | c / fp | ≦ 0.16, where fp is the focal length of a single unit made of the plastic of the divergence angle conversion lens. An optical pickup device as described in the above. 24. The focal length fc and the focal length f
The optical pickup device according to claim 23, wherein the relationship with p satisfies | fc / fp | ≦ 0.08. 25. At least one of the divergence angle conversion lenses
25. The optical pickup device according to claim 11, wherein the surface is a diffraction surface having a diffraction effect. 26. The optical pickup device according to claim 11, wherein the divergence angle conversion lens is a collimator lens. 27. The optical pickup device according to claim 11, wherein a numerical aperture of the objective lens is 0.65 or more. 28. The optical pickup device according to claim 11, wherein a wavelength of said laser light source is 450 nm or less.