JPS6211327B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an optical information processing apparatus, and more particularly to an optical information processing apparatus having an optical system suitable for reproducing dot information recorded on a disk using a semiconductor laser.

The dot information recorded on the disk is usually 1
It has a size of about .mu.m.phi. to 2 .mu.m.phi. and is recorded in a spiral or concentric form on the disk. Therefore, in order to accurately reproduce the signal from the dot information, it is necessary to focus the laser beam into a circular spot with a diameter of about 1 μm (half width).

Conventionally, in a video disk playback device that uses a semiconductor laser light source as a laser light source, a buried hetero structure in which the semiconductor laser light emitting area has a square shape of 1 μm x 1 μm is used, and the optical system shown in FIG. 1μmφ on top
He had gotten some spots. Here, 1 is a semiconductor laser light source, 2 is a first lens (coupling lens), 3 is a second lens (objective lens), 4 is a focused light spot, and 5 is a disk. In the optical system used in such an optical information processing device, for example, both a coupling lens and an objective lens have a magnification
A lens with a magnification of 25 times and a numerical aperture (NA) of 0.4 is used. However, when a laser having a light emitting area of 1 μm x 1 μm is used, the narrowed spot 4 has the advantage of being circular, but has the disadvantage that the laser light output is small because the light emitting area is small. Moreover, if the emission area is small, the N.
Since lens A. is required, adjust the optical system,
In particular, there is also the drawback that it is difficult to adjust the position of the coupling lens. That is, since a coupling lens with a high NA is used, the depth of focus becomes shallow, and high precision is required for positioning the semiconductor laser and the coupling lens, making position adjustment difficult. Therefore, when a signal is reproduced from dot information, a stable signal having a high signal-to-noise ratio cannot be obtained. In consideration of this point, it has been proposed to use a semiconductor laser as a light source, which has a light emitting region of 1 μm in the vertical direction and 3 μm to 5 μm in the horizontal direction, and emits a large laser output. However, the beam from this type of semiconductor laser has a large divergence angle, and the divergence angle is different in the vertical and horizontal directions, and has an elliptical distribution, so such a laser beam cannot be used as is. When narrowed down, the beam spot on the disk also becomes elliptical, and if the beam spot is irradiated with the long axis parallel to the track direction, for example, the optical reading frequency characteristics will deteriorate. On the other hand, if the light is irradiated so that the long axis is perpendicular to the track, the information on adjacent tracks will also be irradiated with the light, causing crosstalk and making it impossible to read out the information accurately. Crosstalk can be prevented by widening the distance between adjacent tracks, but in this case the recording density will decrease. Therefore, in an optical information processing device, recording density,
From the viewpoint of resolution, it is necessary to use a circular spot. A cylindrical lens is used to make the spot narrowed down on the disk closer to a circular shape, but cylindrical lenses are difficult to produce with precision in machining.
It has the drawbacks of being expensive and complicating the arrangement of the optical system, and converging the light spot into a 1 μm circular spot is affected by astigmatism because it uses a cylindrical lens. It is difficult.

In order to eliminate such drawbacks, the present invention uses a semiconductor laser as a light source that has light emitting areas with different aspect ratios and emits an elliptical beam, and furthermore, uses a semiconductor laser as a light source that emits an elliptical beam within the half width of the lateral distribution of the elliptical beam. cutting off a part of the elliptical beam with a circular aperture;
By using an optical system that forms a circular spot on the medium, it is a simple and inexpensive optical system that can process high-density information with high resolution without the need for special beam shape conversion optical elements such as cylindrical lenses. The company aims to provide information processing equipment.

Hereinafter, the present invention will be explained with reference to Examples.

In Figure 2, a spot 4 narrowed down by lenses 2 and 3 is placed on the disk 5 surface at a half-width of 1.
In order to achieve a diameter of about .mu.m.phi. (the spot diameter is the zero point of the diffracted light distribution when a circular aperture is used, the spot diameter is about 2.5 .mu.m.phi.), the following conditions must be satisfied.

1.22λ/n′≦2.5μm (1) Here, λ is the wavelength of light, which is 0.83μm in the case of a semiconductor laser. Since n' is the NA of lens 3, n'≧0.4 from equation (1).

If a lens with an NA of 0.4 or more is used as the lens 3, a lens with a magnification of 20 times or more is usually used as a microscope objective lens. However, in general, when a lens with a large magnification and NA is used, the depth of focus becomes shallow, and as shown in FIG. 2, the focus becomes blurred due to vibration during rotation of the disk 5, making it difficult to obtain a good reproduced signal.

Therefore, as the lens 3, a lens having a magnification of 20 to 30 times and an NA of 0.4 to 0.5 is suitable.

In Figure 2, the magnification of lens 3 is m', and the NA is
If n′, then the angle u ₄ that determines the NA shown in Figure 2 is
The relationship expressed by the following equation generally holds between and n′.

sin(u ₄ )=n' (2) In order for the spot narrowed down by the lens 3 to be sufficiently small, the entire surface of the lens 3 must be irradiated with the light from the semiconductor laser 1. In order to satisfy this condition, it is necessary to satisfy the following equation (3).

u ₃ ≧ u ₄ /m'=sin ^-1 (n')/m'
(3) Here, m′ is 20 to 30 and n′ is 0.4 to 0.5, so
The minimum value on the right side of equation (3) is 0.0133.

Therefore, the following relationship exists between the emission angles u ₂ and u ₃ of the semiconductor laser from the light source 1 shown in FIG.

u ₂ =mu ₃ (4) Here, m is the magnification of the lens 2.

From equations (3) and (4), the magnification m is expressed by the following equation (5).

m≦u ₂ /0.0133 (5) In order to determine u ₂ in equation (5), an example of the characteristics of the semiconductor laser light from the light source 1 in FIG. 2 is shown in FIG. 3. In Fig. 3, the horizontal axis indicates the emission angle u ₂ (degrees) and the vertical axis indicates the light intensity (arbitrary unit). field pattern). Third
In the figure, the half-width in the vertical and horizontal directions is
34.5° and 10°, and in the case of a light-emitting region of about 1 μm x 5 μm in length, the far-field pattern is about 34.5° and 7°.

The angle u ₂ in equation (5) is set to give the half width of the lateral far-field pattern shown in FIG. I mean,
When u ₂ is set as above, the output light distribution of the semiconductor laser will be treated as a nearly circular light distribution within the angle u ₂ in both the vertical and horizontal directions, and the light distribution entering the lens 3 will also be circular. Further, the narrowed spot 4 also has a circular shape. Therefore, the circular aperture of the lens 2 is set within the lateral half width of the semiconductor laser output light distribution. When expressed in radians, u ₂ is set to 5° x π/180 to 3.5 x π/180. However, the lateral light emitting area of the semiconductor laser light source 1 is set from 3.5 μm to 5 μm.

Taking the larger angle of 5° as u ₂ , m≦6.6 from equation (5) Therefore, it is effective to use a lens with a magnification of 7 times or less as the lens 2.

Since lens 3 has a magnification of 20 to 30 times as described above, the magnification m/m' of the optical system obtained from lenses 2 and 3 is about 0.33 or less.

Also, the NA of lens 2 is the smaller angle of u ₂
Taking 3.5°, it is necessary that sin3.5° is greater than 0.06.

If a lens 2 with a magnification higher than this is used, the spot 4 focused on the disk will not be circular but elliptical.

As explained above, according to the present invention, it is possible to use a semiconductor laser as a light source, which can obtain a relatively large light output, and whose light emitting areas have unequal aspect ratios, and to focus the light into a circular light spot, resulting in readout frequency characteristics. High-density information can be processed at high resolution without degrading the data or causing crosstalk. Moreover,
In the present invention, since an elliptical beam is made into a circular beam using the aperture of the lens that the conventional device already has, there is no need to add a special optical element such as a cylindrical lens to obtain a circular beam. A cheaper device can be realized with a simple optical system.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing a schematic configuration of an optical information processing device, FIG. 2 is a diagram explaining the configuration of an optical system used in the present invention, and FIG. 3 is a diagram showing a far-field image from a semiconductor laser. 1... Semiconductor laser, 2... Coupling lens, 3... Object lens, 5... Disc.

Claims (1)

[Claims] 1. In an optical information processing device comprising a light source and an optical system that converges a beam from the light source onto a medium, the light source has an elliptical shape with different divergence angles in the vertical and horizontal directions. a semiconductor laser that emits a beam, the optical system having a circular aperture within a half width of the lateral distribution of the elliptical beam, the beam being focused on the medium as a substantially circular spot; An optical information processing device characterized by: 2. The optical system according to claim 1, wherein the optical system has an object lens whose entire surface is irradiated with a beam from the semiconductor laser and which focuses the beam onto the medium. Information processing device. 3 The optical system has a numerical aperture of 0.06 or more when viewed from the semiconductor laser, and a magnification of the optical system.
2. The optical information processing device according to claim 1, wherein the optical information processing device is 0.33 or less.