JPH0754376B2 - Optical disk device - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to an optical disc device using a semiconductor laser pen that emits a parallel beam having an isotropic light intensity distribution by using a semiconductor laser as a light source.

[Background of the Invention]

A laser beam emitted from a semiconductor laser has a large divergence angle and is a beam having a different divergence angle in a direction parallel to a direction perpendicular to the pn junction surface of the semiconductor laser. Since the divergence angle is large at and small in the parallel direction, the optical axis cross section has an elliptical distribution. When such a semiconductor laser beam is used in an optical information processing device such as an optical disc, a laser printer or a laser reading device, it can be converted into a parallel beam having a circular or pseudo-circular distribution because it is focused on a circular spot and used. is important.

Conventionally, in order to obtain this parallel circular beam, a combination of two cylindrical lenses having a lens action only in one direction (US Pat. No. 4203652) or a combination of a lens and a prism which are rotationally symmetric with respect to the optical axis ( Those disclosed in JP-A-56-41 and JP-A-56-152942) are known. However, the techniques disclosed in these publications do not recognize the problem of output change and temperature change of the semiconductor laser.

[Object of the Invention]

The present invention relates to a semiconductor laser pen that converts a semiconductor laser beam into a parallel circular beam and emits it by using a combination of a rotationally symmetric lens and a prism. It is an object of the present invention to provide an optical disk device using a semiconductor laser pen that suppresses the invention of angle change and astigmatism.

[Outline of Invention]

According to the present invention, a plurality of prisms made of different materials are used as a beam shape conversion element to compensate for a change in a refraction angle due to a change in a wavelength of a semiconductor laser beam so as to keep an emission angle constant, and a semiconductor laser, a lens and a prism. It is characterized by compensating the positional deviation due to the focal position of the lens and the temperature of the semiconductor laser by forming the housing for fixing and holding the same with a plurality of members made of different materials.

Specifically, a semiconductor laser that emits divergent laser light whose optical axis cross section has an elliptical distribution, a lens that makes the laser light emitted from this semiconductor laser a parallel beam, and a beam width in one direction of the parallel beam is expanded or reduced. A prism and
In an optical disc device for reproducing information by irradiating a light beam from a semiconductor laser pen having a casing for fixing a lens and a prism as a narrowed spot on an optical disc, the casing has a first portion for holding the lens and the prism, Disposed between the first portion and the semiconductor laser,
Having a second part having a coefficient of thermal expansion different from that of the first part, so that the following conditions are satisfied:
It is characterized in that the light emitted from the lens is kept in a parallel beam regardless of the temperature change and is incident on the prism to correct the astigmatism of the narrowed spot on the optical disc.

Condition: Δl1 = Δl2 + Δl3 + Δl4 where Δl1 is the elongation amount of the second portion due to temperature change,
Δl2 is the amount of movement of the lens in the direction of the semiconductor laser due to temperature change, Δl3 is the amount of change of the working distance of the lens due to temperature change, and Δl4 is the amount of movement of the semiconductor laser in the lens direction due to temperature change.

Example of Invention

First, a problem caused by a change in output of the semiconductor laser or a change in temperature will be described.

FIG. 1 is a schematic configuration diagram of a semiconductor laser pen that emits a circular parallel beam, in which light emitted from the semiconductor laser 1 is converted into a parallel beam by a coupling lens 2 that is rotationally symmetric with respect to the optical axis. The intensity distribution of the laser light emitted from the semiconductor laser 1 is flat, and the parallel beam has an elliptical distribution whose optical axis cross section has a major axis in the direction perpendicular to the joint surface.
In the short axis direction of the parallel beam (parallel to the joint surface)
The beam width of is expanded and converted into an isotropic light intensity distribution.
The wavelength of the semiconductor laser 1 slightly changes depending on the emission output and the temperature change, and for example, the wavelength changes from 830 nm to about 5 nm.
On the other hand, since the refractive index of the optical glass varies depending on the wavelength, the focal position of the coupling lens 2 varies depending on the wavelength, which is called chromatic aberration. Coupling lens 2
If there is chromatic aberration, the light emitted from the coupling lens will deviate from the parallel beam. Further, if one triangular prism 3 is used as the beam shape conversion element, the emission angle changes due to the change in the refractive index due to the change in the wavelength of the laser light. For example, if the triangular prism 3 is composed of SF-11, its apex angle α is set to 30.79 degrees, and its incident angle θ is set to 64.56 degrees, the beam width in the minor axis direction is doubled and it is almost perpendicular to the exit surface. Outgoing.
When the wavelength changes from 830 nm to 835 nm, the refractive index of SF-11 becomes
Change from 1.7630661 to 1.7628084, emission angle is 8.8 × 10 ^-3
Change. For example, by using this laser pen in an optical disk device, a focusing lens having a focal length of 4.5 mm is used to focus a laser spot of about 1 μm on a disk having a track pitch of 1.6 μm. When the laser emission output is increased to record information, the wavelength changes by about 5 nm and the laser beam emission angle is inclined by 8.8 × 10 ^-3 degrees, so the laser spot is about 0.7 μm.
It shifts by m. When it is displaced in the direction perpendicular to the track direction, information is recorded at a position displaced by 0.7 μm from the center of the track, which makes reproduction difficult. Also, when it is displaced in the track direction, it becomes a jitter.

Also, when the temperature changes by 25 ° C, the refractive index of SF-11 is 2.3 × 10
-Because it changes about ^{-4, the} light emitted from the laser pen is 5 nm.
The change is 7.6 × 10 ^-3 degrees, which is about the same as the case of the wavelength change.

Next, the distance (working distance) between the laser-side end surface 6 of the coupling lens 3 and the focus position changes depending on the temperature. For example, with a focal length of 9.55 mm, a working distance of 2 mm, and a coupling lens with a four-lens configuration, the working distance changes with temperature.
Climb 5.25μm at 25 ℃. If the tube of the coupling lens is made of aluminum and the housing 7 is also made of aluminum, the distance between the end face 6 and the laser 1 is 1.15μ at a temperature change of 25 ° C.
m grows. As a result, the focal position of the laser 1 and the coupling lens 2 shifts by 6.4 μm at a temperature change of 25 ° C., the emitted light of the coupling lens 2 shifts from the parallel beam, and the triangular prism 3 doubles the beam width in one direction. Since it is enlarged, the focusing spot on the optical disc causes astigmatism (an astigmatic difference of about 1 μm), and the reproduced signal of information is reduced.

The present invention is to solve such a problem, and uses a compound prism made of different materials as a beam shape conversion element, and a laser pen housing having a temperature compensation structure composed of a plurality of portions having different thermal expansions. Is.

Next, embodiments of the present invention will be described in detail with reference to the drawings. Second
FIG. 1 is a sectional view showing an embodiment of the present invention. Reference numeral 11 is a semiconductor laser that emits a beam having an elliptical distribution in its optical axis cross section. Here, it is assumed that the elliptical distribution beam from this semiconductor laser has a short axis in a direction parallel to the paper surface. Reference numeral 12 denotes a coupling lens for converting the beam from the semiconductor laser 11 into a parallel beam, and is composed of a combination lens in which various convex lenses and concave lenses made of different materials are combined in order to eliminate chromatic aberration. Various types of such combination lenses having no chromatic aberration are known. 13 is a beam width conversion optical system for converting the elliptical parallel beam from the coupling lens 12 into a parallel beam having a circular or pseudo-circular distribution,
The composite prism is formed by combining at least two types of prisms made of materials having different wavelength dispersions of the refractive index. Here, the composite prism 13 will be described in detail with reference to FIG.

In the figure, reference numeral 13 denotes a first prism 13A made of a first material having a refractive index of n ₁ and a second prism 13B made of a second material having a refractive index of n ₂ . It is a composite prism bonded on the surface M.

In the following description, a case will be considered in which a light beam entering the compound prism 2 at an angle θ ₁ from the air layer exits the compound prism 13 perpendicularly to its exit surface. In order for the emitted light to be emitted perpendicularly from the emission surface of the compound prism 13, it is sufficient that the angle indicated by α ₂ in the drawing does not change with respect to the change in wavelength.

According to Snell's law, sin θ ₁ = n ₁ sin θ ₂ (1) n ₁ sin α ₁ = n ₂ sin α ₂ (2) holds, and θ ₂ + α ₁ = ₁ (3) α ₂ = ₂ (4).

Refractive index n ₁ , n ₂ ; angle α ₁ , α ₂ ,
The changes in θ ₂ etc. are calculated as Δn ₁ , Δn ₂ ; Δα ₁ , Δα ₂ , Δθ, respectively.
₂ and so on (angle θ ₁ is invariant), and from equation (1) Further, (2) from equation _{Δn 1 sinα 1 + n 1 cosα} 1 Δα 1 -Δn 2 sinα 2 = n 2 cosα 2 Δα 2 ...... (6) is obtained.

Since it is necessary that a [Delta] [alpha] ₂ = 0 with respect to the wavelength change, is necessary to established _{(6) Δn 1 sinα 1 +} n 1 cosα 1 -Δn 2 sinα 2 = 0 ...... from the equation (7) Further, both sides of the equation (3) are differentiated to obtain Δθ ₂ = −Δα ₁ (8) Therefore, from the equations (2) and (7), Is obtained. By substituting the relationship shown in Expression (8) into Expression (9), Becomes Here, by substituting the relationship represented by the equation (5) into the equation (10) and eliminating Δθ ₂ , Is obtained, and further organized However, the condition is that the emission angle does not change with respect to the wavelength change.

Materials having a refractive index and wavelength dispersion satisfying the above conditions can exist as described below.

For example, the theta ₂ = alpha _1, and, given that a n ₁ ≒ n _2, a 2Δn ₁ ≒ Δn _2. According to the optical glass list of Ohara Optical Glass Co., Ltd., the value of Δn ₁ / Δn ₂ is Since it can be taken to some extent, a real system can be constructed.

Since the two prisms 13A and 13B are used in the composite prism 13 configured as described above, the number of refracting surfaces increases and the reflection loss increases. In order to reduce this as much as possible, the materials forming the above two prisms may be selected so that n ₁ = n ₂ at a specific wavelength (center wavelength).

In the above description, the first prism 13A and the second prism 13B
The composite prism 13 in which the and are bonded together on the surface M has been described. However, if the composite prism 13 keeps the exit surface of the prism 13A and the entrance surface of the prism 13B parallel to each other, another composite material between them is used. One or more layers may be interposed. However, it is preferable to use a material having a high light transmittance for this flat plate, and the prisms 13A and 13B.
Needless to say, the air layer may be interposed between the two so as to be separated from each other.

It goes without saying that the prism optical system operates similarly even if the incident direction and the outgoing direction are reversed. However,
In this case, it acts in a direction to reduce one direction of the incident light beam.

For example, of the two prisms constituting the composite prism 13, the first prism 13A is the LaSF-016 (n ₁ = 1.760304 at λ = 830 nm) manufactured by Ohara Optical Glass Mfg. Co., Ltd.
Prism 11B of the same is SF-11 (same n ₂ = 1.7630661), the apex angle ₁ of the first prism 13A is 75.49 degrees, and the second prism 13B
If the apex angle ₂ is 44.70 degrees and the incident angle θ ₁ of the incident light beam is 63.99 degrees, the beam width can be expanded almost twice, and when a laser with an elliptic ratio of 1: 2 is used, it is almost circular. Can be converted into a beam.

The refractive index of LaSF-016 at λ = 830 nm is 1.760304,
1.7601429 at λ = 835 nm, refractive index of SF-11 at λ = 830 nm is 1.
7630661, λ = 835nm, 1.7628084, wavelength λ is 830n
Refractive index change when changing from m to 835 nm by 5 nm Δn ₁ , Δn
₂ are -0.0001611 and -0.0002577, respectively.
When the wavelength λ actually changes from 830 nm to 835 nm, the change of the emission angle is 9.9 × 10 ^-6 degrees, which is 1/1000 of the case of the prism made of a single material. Moreover, the refractive index of LaSF-016 changes by about 1.05 × 10 ^-4 with a temperature change of 25 ° C.
Since the refractive index of −11 changes by about 2.3 × 10 ⁻⁴ , the exit angle changes by 1.8 × 10 ⁻³ degrees with a temperature change of 25 ° C. This is one-fourth that of a prism made of a single material. The composite prism of the present embodiment has a high performance especially with respect to a wavelength change, but the invention is not limited to this, and it can have a high performance with respect to a temperature change.

The housing 14 is a first cylinder 14 that fixedly supports the semiconductor laser 11.
A and a second cylinder 14B that fixedly supports the coupling lens 12 and the compound prism 13, and the first and second cylinders are made of materials having different thermal expansion coefficients. For example, the first cylindrical portion 14A is made of Invar and the second cylindrical portion 14B is made of aluminum. The length of the invar portion 14A is l ₁ , and the length of the coupling lens 2 (the lens barrel is made of aluminum) from the aluminum portion 14B to the invar portion 14A is l ₂ ,
The working distance is l ₃ , and the length of the chip support (made of copper) of the semiconductor laser 11 is l ₄ . l ₁ = l ₂ + l ₃ + l ₄ . The elongations of l ₁ , l ₂ , l ₃ and l ₄ due to temperature are Δn ₁ , Δl ₂ , Δl ₃ and Δ
When l ₄ is satisfied, if Δl ₁ = Δl ₂ + Δl ₃ + Δl ₄ is satisfied, the light emitted from the coupling lens 2 is kept in a parallel beam, and the light emitted from the laser pen does not cause astigmatism. For example, the thermal expansion coefficients of aluminum, copper and Invar are 23 × 10 ⁻⁶ , 16.8 × 10 ⁻⁶ and 1 × 10 ⁻⁶ , respectively, and the working distance l ₃ of the coupling lens 2 per 1 ° C. As mentioned above, when set to -0.21 μm, l ₁ = 11.65 m
m, l ₂ = 8.65 mm, l ₃ = 2 mm, l ₄ = 1 mm. Semiconductor laser 11
Needless to say, the portion 14A that supports is not limited to Invar and can be made of other materials.

According to this embodiment, the change in the emission angle due to the change in the wavelength of the semiconductor laser beam can be reduced to 1/1000 of the conventional value, and the change in the emission angle due to the change in temperature can be reduced to 1/4 of the conventional value. Therefore, a semiconductor laser pen that does not produce astigmatism can be realized.

〔The invention's effect〕

As described above, according to the present invention, the change in the angle of the emitted light is extremely small due to the change in the laser output and the change in temperature, and
Since a high-performance semiconductor laser that does not generate astigmatism can be provided, there is an effect that a highly accurate optical information processing device can be realized.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of a semiconductor laser pen, and FIG. 2 is
FIG. 3 is a sectional view showing an embodiment of a semiconductor laser pen according to the present invention, and FIG. 3 is a view showing a compound prism used in the present invention. 11 …… Semiconductor laser, 12 …… Coupling lens, 13 …… Composite prism, 14 …… Housing.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Takeshi Maeda 1-280, Higashi Koigakubo, Kokubunji, Tokyo, Central Research Laboratory, Hitachi, Ltd. (72) Masateru Watanabe 2880, Kozu, Odawara, Kanagawa Prefecture Hitachi, Ltd. Odawara In the factory (72) Inventor Toshinasa Kamijo 2880 Kozu, Odawara-shi, Kanagawa Stock company Hitachi Ltd. Odawara factory (56) References JP 59-15205 (JP, A) JP 58-203405 (JP, A) Actual development Sho 59-33020 (JP, U) Yamagata Kogoro "Geometrical Optics 2" P. 267-269 Published September 10, 1979 Optical Technology Research Association

Claims (5)

[Claims] 1. A semiconductor laser that emits a divergent laser beam having an elliptical distribution in its optical axis cross section, a lens that makes the laser beam emitted from the semiconductor laser a parallel beam, and a beam width in one direction of the parallel beam is expanded or In an optical disc apparatus for reproducing information by irradiating a light beam from a semiconductor laser pen having a prism for contracting and a housing for fixing the lens and the prism as a narrowed spot on the optical disc, the cylindrical body has the lens and A first portion that holds the prism; and a second portion that is disposed between the first portion and the semiconductor laser and that has a coefficient of thermal expansion different from that of the first portion. Therefore, the following conditions are satisfied, and the light emitted from the lens is kept in a parallel beam regardless of the temperature change and is incident on the prism. Optical disc apparatus characterized by correcting astigmatism of narrowing spot on click. Condition: Δl1 = Δl2 + Δl3 + Δl4 where Δl1 is the elongation amount of the second portion due to temperature change,
Δl2 is the amount of movement of the lens in the direction of the semiconductor laser due to temperature change, Δl3 is the amount of change of the working defect of the lens due to temperature change, and Δl4 is the amount of movement of the semiconductor laser in the direction of the lens due to temperature change. . 2. The optical disk device according to claim 1, wherein the first portion comprises a lens barrel for holding the lens and a coupling member for coupling the lens barrel and the prism. . 3. The optical disk device according to claim 2, wherein the lens barrel projects from the coupling member toward the second portion. 4. The semiconductor laser is mounted on a chip support base, and the second portion is arranged between the first portion and the chip support base so as to engage with each other. The optical disk device according to claim 3. 5. The optical disk device according to claim 1, wherein the prism is composed of a plurality of prisms made of different materials.