JPH056262B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an optical information processing device, and particularly to an optical information device using a semiconductor laser element as a light source.

[Conventional technology]

In recent years, optical information processing devices using semiconductor laser elements have been actively developed in place of gas lasers. Optical disks are one example. What is an optical disk? A disk is created using a semiconductor laser element.
It is used to reproduce information signals recorded on discs, or to record information at high density on discs. In other words, in order to record or reproduce information signals on a disk using a semiconductor laser, the beam emitted from the semiconductor laser element is directed onto the disk using a coupling lens and an objective lens that constitute an optical system.
It must be formed as a minute optical spot of about 1 μm.

In general, a semiconductor laser device has an anisotropic beam spread angle because its light emitting region has a different aspect ratio. The divergence angle of this semiconductor laser beam differs depending on the structure of the semiconductor laser element. That is, as shown in FIG. 1, the angles at e ^-2 in the horizontal and vertical directions of the output light distribution in the far-field image of the beam from the semiconductor laser device are θ, respectively.
If θ⊥, for example, in a CPS type semiconductor laser, θ=8°, θ⊥=24°, and θ⊥/θ=3 (1). In addition, in the BH type semiconductor laser, θ = 16°, θ⊥ = 32°, and θ⊥/θ = 2 (2), and the beam divergence angle ratio is 2 in the BH type laser and 3 in the CPS type. . Note that the horizontal axis in FIG. 1 is the spread angle, and the vertical axis is the light intensity. Second
The figure shows that when the beam divergence angle of the semiconductor laser device mentioned above is not isotropic, a diameter of 1 μm is placed on the disk.
An example of a conventional optical information processing device for forming an isotropic spot of approximately φ is shown.

In FIG. 2, a beam having a non-isotropic divergence angle emitted from one end face of the semiconductor laser element 1 is formed into a light spot 5 on a disk 4 by a coupling lens 2 and an objective lens 3. The photodetector 6 is a detector for the output of the semiconductor laser element 1. Note that A is the optical axis. In FIG. 2, the numerical aperture NA of the coupling lens 2 is the same as that between the semiconductor laser 1 and the lens 2.
If the half angle of view formed by Regarding the beam divergence angle of the semiconductor laser element 1, if the magnitudes at e ^-2 in the horizontal and vertical directions are θ and θ⊥ as described above, then using such a semiconductor laser element In order to form a square spot 5, the numerical aperture NA of the coupling lens 2 must be selected so that θθ<θ⊥ (4). That is, by reducing the numerical aperture of the coupling lens 2 and blocking off-axis rays, the optical axis A is
It is necessary to make the intensity distribution of the light emitted from the coupling lens 2 isotropic by using only the beam around (θ=0). The beam spread angle shown in Figure 1 and (1) and (3)
From equation (4), NA=0.1 and θ=5.7 for the cps type laser. (<θ<θ⊥)} (5) Then, the beam after passing through the coupling lens 2 becomes almost isotropic, and therefore an isotropic spot 5 is formed on the disk 4. .

However, when a large amount of off-axis light is blocked in this way, only a portion of the light emitted from the semiconductor laser is irradiated onto the disk, resulting in poor utilization efficiency of the light from the laser element. In particular, when recording, the metal thin film provided on the disk must be melted to form holes, which requires several times the amount of light compared to when reproducing. Furthermore, when a semiconductor laser element emits a certain amount of light or more, its lifetime becomes short. Therefore, in an optical information processing device using a semiconductor laser element, it is absolutely necessary to increase the light utilization efficiency of the laser element and to suppress the optical output as much as possible from the viewpoint of lifespan and reliability.

Now, in the configuration shown in FIG. 2, when the reflected light from the disk 4 returns to the semiconductor laser element 1, the output of the semiconductor laser 1 increases or decreases depending on the strength of the reflected light from the disk. It can be reproduced by the output of the photodetector 6. This technique is described in Japanese Patent Application Laid-open No. 49-69008.
Normally, the disk rotates with a vertical vibration of about 1 mm, and the depth of focus of the objective lens is about 2 μm, so in order to reproduce signals from the disk, the optical spot must always be kept at a diameter of about 1 μm on the disk. Focusing is necessary to achieve this.

In order to detect the deviation of the focus of the light beam from the disk, JP-A No. 53-17706 discloses a technology that detects the deviation of the focus by micro-vibrating the light source or lens in the optical axis direction and synchronously detecting the laser output. It is proposed in the official gazette. It has been previously reported that the automatic focus control pull-in range by this technique is narrow, about 10 μm (Electronic Materials, February 1979, p. 67).
Figure 3 shows when the numerical aperture of the coupling lens 2 is NA=0.1.
This figure shows the change in the output from the semiconductor laser element 1 when the disk 4 is slightly vibrated along the optical axis direction. As is clear from FIG. 3, when the numerical aperture NA of the coupling lens 2 is as small as 0.1, the automatic focusing range is only 10 μm. An optical information processing device that returns light reflected from a disk to a semiconductor laser element has the drawback of a small pull-in range, as described above. For this reason, automatic focus control was difficult and information could not be reproduced from a disk with large vertical shake.

JP-A-53-100844 describes an optical system that shapes anisotropic semiconductor laser light into an isotropic light beam using a plurality of prisms installed so that the incident plane is at right angles. ing. It has also been suggested that the optical system be applied to optical information processing devices and the like.

However, it is known that semiconductor lasers have unavoidable variations in their characteristics even if they are of the same type, and this also applies to the cross-sectional intensity pattern of the anisotropic spread of light mentioned above. The same is true. In FIG. 9 of Japanese Unexamined Patent Publication No. 100844/1984, an isotropic light beam is obtained from an anisotropic light beam using a prism. However, in this example, the light from the light source is transmitted to the cylindrical lenses 25 and 26 and the rotationally symmetrical lens 27 (corresponding to the coupling lens of the present application).
It is parallelized by . This rotationally symmetric lens is larger than the diameter of the light beam. Therefore, it is not possible to deal with variations in light emission patterns from semiconductor laser to semiconductor laser.

That is, the size of the lens that handles laser light is simply stated in equation (8) of Japanese Patent Laid-Open Publication No. 100844/1984. As a condition for the parallel light flux emitted from the condensing system, if the diameter of the light flux whose light intensity is 1/e ² or more is 89.2% of the aperture diameter of the imaging lens (that is, if the lens is made a certain percentage larger than the diameter of the light flux) This means that the intensity at the center of the image can be maximized.

In JP-A No. 53-100844, an imaging lens (a lens on the image point side, which corresponds to the objective lens in the specification of the present application)
According to the above idea, the size of is larger than the diameter of the luminous flux.
Furthermore, when designing an optical system, it is common knowledge for those skilled in the art that the relationship between the diameter of the lens and the diameter of the luminous flux is unified under the same conditions throughout the entire optical system. This is because even if a large lens is used at the rear stage of the optical system, if a small lens is used at the front stage of the optical system, the photometer that enters the rear stage lens will be limited by the front stage lens, and there is no point in specifying the rear stage lens. It is from.

Therefore, JP-A-53-100844 has no choice but to use a coupling lens (lens on the light source side) that satisfies the condition of equation (8). However, if such a large lens is used, all of the above-mentioned variations in the elliptical pattern of each semiconductor laser will be incident on the subsequent prism. Since the magnification of the prism is fixed, the size of the image converted by the prism also varies. This is particularly important when increasing magnification with multiple prisms.

[Problem to be solved by the invention]

The present invention solves the above-mentioned drawbacks and is a device using a semiconductor laser element in which the emitted diverging light does not have an isotropic spread angle and the cross-sectional intensity pattern of the spread of the emitted light varies from individual to individual. An object of the present invention is to provide an optical information processing device that can form an isotropic spot of uniform size on a recording medium with efficient use of light and without the need for troublesome adjustment of the optical system. do.

[Means to solve the problem]

To achieve this object, the present invention provides a semiconductor laser that emits light whose intensity distribution around an optical axis is anisotropic, an information recording medium, and a rotating device that collimates the light beam from the semiconductor laser. a symmetrical coupling lens, a plurality of prisms for enlarging or reducing the collimated light beam, an optical system for converging the light from the prisms onto the medium, and detecting a change in the light amount of the light beam from the medium. In the optical information processing device, the rotationally symmetrical coupling lens satisfies the following conditions, and each of the plurality of prisms has an equal angle formed by an input end face and an output end face, and has the same refractive index.

Conditions: θ<θ≦θ⊥ NA=sinθ (However, let θ and θ⊥ be the angles at e ^-2 in the horizontal and vertical directions of the output light distribution in the far-field image of the light beam from the semiconductor laser, respectively,
Let NA be the numerical aperture of the above coupling lens. ) [Function] By having the above configuration, the present invention can produce an isotropic spot on a medium with a simple optical system, even if a semiconductor laser element that does not have an isotropic spread angle is used as a light source. This has the effect that it can be formed well.

In other words, the present invention solves the problem that when shaping a semiconductor laser beam using a plurality of prisms, the shape and size of the image vary due to variations in the characteristics of the semiconductor laser, by specifying the size of the coupling lens. It is solved by this. In other words, the pattern of the elliptical beam emitted by the semiconductor laser has large variations in output from one solid to the next, especially in areas where the intensity is weak. Therefore, in the present invention, by defining the diameter of the lens as θ<θ≦θ⊥, the diameter of the lens is defined as θ<θ≦θ⊥.
Turn on the laser beam (part below e ^-2 ). By arranging the shapes of the beams incident on the prism in this way, it becomes easy to determine the magnification m of the prism, and an isotropic beam can be reliably obtained.

〔Example〕

As mentioned above, in order to form an isotropic spot 5 on the disk 4 using the semiconductor laser element 1 having an anisotropic divergence angle, the numerical aperture of the coupling lens 2 is set to (4) and (5). ) must be made small as shown in the formula. However, in this case, only a portion of the light emitted from the semiconductor laser element is irradiated onto the disk, resulting in poor utilization efficiency of the light from the laser element. Moreover, due to the displacement of the disk,
The focal position of the reflected return light spot near the end face of the laser element changes significantly. That is, the reflected return light spot on the end face of the laser element is significantly blurred due to the focal shift, and as a result, the automatic focusing range becomes as small as 10 μm.

Therefore, the present inventors ignored equation (4), which is the condition of the coupling lens that the light spot 5 on the disk 4 is isotropic, and investigated the focus pull-in when the numerical aperture NA of the coupling lens 2 is increased. I tried to find the range experimentally. FIG. 4 shows changes in the output from the semiconductor laser element when the disk 4 is slightly moved along the optical axis direction for several types of coupling lenses with different numerical apertures NA (sin θ). As is clear from FIG. 4, the larger the numerical aperture of the combined lens, the wider the automatic focusing range, and complete automatic focusing can be achieved against vertical movement of the disk. Moreover, as the numerical aperture of the coupling lens increases, more beams from the semiconductor laser element are incident on the coupling lens, increasing the light utilization efficiency. However, if the numerical aperture NA of the coupling lens approximately satisfies the vertical divergence angle θ⊥ at e ^-2 of the far-field image shown in Figure 1, then the coupling lens will substantially absorb most of the beam from the semiconductor laser element. It will be injected into. Therefore, in reality, it is sufficient to satisfy θ<θ≦θ⊥ (6).

However, since the light beam passing through the coupling lens 2 that satisfies equation (6) is not isotropic, the light spot 5 is also not isotropic. In the present invention,
In order to solve this problem, as shown in Figure 5,
Prisms 7 and 8 are placed after the coupling lens 2 that satisfies the formula. In Fig. 5, prism 7,
8 is a right-angle prism whose apex angle is θ〓, the refractive index is N, the incident angle is θ _i , and the ratio of the incident beam diameter I to the refracted beam diameter O (beam magnification) is m = O/I, These are respectively given by the following equations.

Further, the reflectance of P-polarized light (polarized light vibrating parallel to the plane of the paper) at the incident surface of the prism is given by the following equation.

Here, if θ _i +θ=90°, R _P =0, and the loss of light at the incident surface of the prism becomes zero.

(In the case of θ _i = θ〓, there is no effect of the prism because it is perpendicular incidence.) Here, R _p = 0 because tan ² θ _i
=N. At this time, equation (7) has the following relationship.

However, the beam magnification m is set depending on the structure of the semiconductor laser device used. That is, the prism extends the horizontal direction of the spread of the beam from the semiconductor laser element so that it coincides with the vertical direction, thereby making the intensity distribution of the light emitted from the prism isotropic. Therefore, when most of the beam from the semiconductor laser device is incident on the coupling lens, in order to obtain an isotropic beam, the beam magnification m must be made to match the beam divergence angle ratio θ⊥/θ. There is a need. For example, when using a CPS type semiconductor laser element, the beam magnification m is set to 3 from equation (1). At this time, the shapes of the prisms 7 and 8 are as follows from equation (9): m=3 N=1.732 θ _i =60° θ=30° R _p =0 (10).

Therefore, for a CSP type semiconductor laser having a beam divergence angle expressed by equation (1), the prisms 7 and 8 expressed by equation (10) can be inserted immediately after the coupling lens 2 in FIG. Therefore, it is possible to convert the beam into an isotropic beam using the prisms 7 and 8. This isotropic light beam makes it possible to obtain an isotropic spot 5 on the disk 4 through the objective lens 3, and almost all of the beam from the laser element is irradiated onto the disk. Moreover, since the numerical aperture of the coupling lens 2 is increased,
The retraction range of the self-cutting focus has been expanded. Also,
The light utilization efficiency is excellent because there is no loss of light due to incidence on the prism.

In FIG. 5, the beam from the semiconductor laser element 1 is set to be P-polarized light (the plane of polarization vibrates parallel to the plane of the paper) as indicated by the arrow in the figure.

FIG. 6 is a diagram showing the configuration of another embodiment of the present invention, in which the same reference numerals as in FIG. 5 indicate the same or equivalent parts. In the embodiment shown in FIG. 6, unlike the embodiment shown in FIG. The arrangement is opposite to that of the embodiment of FIG. That is, the beam from the semiconductor laser element 1 is set to S-polarized light (the plane of polarization vibrates perpendicular to the plane of the paper) as shown by the black circle in the figure, and this is converted to P-polarized light by the half-wave plate 9. The light is then incident on prisms 7 and 8. By doing so, the objective lens 3 can be made smaller.

FIG. 7 is a diagram showing the configuration of another embodiment of the present invention. In the configuration of the embodiment shown in FIG. 5, a prism 11 is disposed between the prism 8 and the objective lens 3. This embodiment makes it possible to detect changes in the reflected light from the disk 4 from the prism 11. Note that 10 is a quarter wavelength plate, and 12 is a photodetector.

Furthermore, in the description of the embodiments above, a case has been described in which a change in the amount of light reflected from the disk is detected as a change in laser light from the other direction of the semiconductor laser.
Even when detecting as a change in the drive current,
It goes without saying that the present invention is applicable.

Further, if near the point N=√ where R _p =0, R _p is almost 0. As a practical matter, even if the refractive index of prisms 7 and 8 cannot be exactly √, the refractive index N that makes R _p = 0
(=√), R _p is almost zero, so a refractive index in that vicinity can be used satisfactorily. FIG. 8 shows the relationship between the beam magnification m and the reflectance R _p at the entrance surface of the prism. If the prism is composed of one prism, and the light reflectance is set to be low and the beam magnification m is set to m=2 to 3, a prism with a considerably large refractive index N is required. In the diagram
The relationship when one prism made of BK-7 (N=1.51) and SF-11 (N=1.764) is used is shown by a dashed line and a broken line, respectively. θ of semiconductor laser beam
Since the ratio of ⊥ and θ is usually about 2 to 4 times,
It is quite difficult to configure it with just one piece.
When configured with two pieces as in this embodiment, it is possible to eliminate the above-mentioned drawbacks when configured with one piece. In the figure, the solid line shows the relationship when two prisms made of BK-7 are used. In the case of BK-7, which is generally widely known, the refractive index N=1.51 near the wavelength of 8000 Å. In this case, R _p =0 when m=2.28 times. Moreover, the transmittance is 99.9% or more in the region of m≒2.1 to 2.5. If it is allowed up to 99%, m≒1.8 to 3 can be used.

As described above, according to the present invention, the beam magnification can be increased with less reflection loss using a prism with a small refractive index N, and the range of use thereof can also be expanded. Therefore, it has the advantage of being able to perform beam shaping with excellent light utilization efficiency using ordinary optical glass.

〔Effect of the invention〕

As explained above, according to the present invention, by specifying the conditions of the coupling lens and using a plurality of prisms having the same refractive index and apex angle, it is possible to eliminate the isotropic divergence angle and To form an isotropic spot on a recording medium with efficient light utilization without changing characteristics such as prism magnification for each device in an optical information processing device using a semiconductor laser element whose angle of deflection varies from device to device. be able to.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing a far-field image of a semiconductor laser beam, FIG. 2 is a diagram for explaining a conventional optical information processing device, and FIG. 3 is a diagram for explaining a conventional autofocus pull-in range. , FIG. 4 is a diagram explaining the automatic focus pull-in range according to the present invention, FIG. 5, and FIG.
7 and 7 are diagrams showing the configuration of an embodiment of the present invention, and FIG. 8 is a diagram showing the relationship between the reflectance on the entrance surface of the prism and the beam magnification. Explanation of symbols, 1... Semiconductor laser, 2... Coupling lens, 3... Objective lens, 4... Disk,
7, 8...prism.

Claims (1)

[Scope of Claims] 1. A semiconductor laser that emits light with an anisotropic intensity distribution around the optical axis, an information recording medium, and a rotationally symmetrical coupling that collimates the light beam from the semiconductor laser. A lens, a plurality of prisms for enlarging or reducing the collimated light beam, an optical system for converging the light from the prisms onto the medium, and a means for detecting a change in the light amount of the light beam from the medium. In the optical information processing device, the rotationally symmetric coupling lens satisfies the following conditions,
An optical information processing device characterized in that each of the plurality of prisms has an angle formed by an incident end face and an outgoing end face and an equal refractive index. Conditions: θ<θ≦θ⊥ NA=sinθ (However, let θ and θ⊥ be the angles at e ^-2 in the horizontal and vertical directions of the output light distribution in the far-field image of the light beam from the semiconductor laser, respectively,
Let NA be the numerical aperture of the above coupling lens. ) 2 The semiconductor laser is a semiconductor laser element that outputs a non-uniformly distributed light beam polarized in the minor axis direction, and the optical system is arranged so that the light beam from the laser element is polarized within the incident plane. Claim 1, characterized in that the prism has a
The optical information processing device described in Section 1. 3. A 1/2 wavelength plate is provided in the optical path between the prism and the laser element, and the prism is arranged so that the light beam from the wavelength plate enters perpendicularly. Optical information processing device according to scope 2.