JPH0239022B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention uses a semiconductor laser as a light source.
The present invention relates to an information reproducing device such as an optical video disc device.

In conventional optical video disk devices, a He--Ne gas laser was used primarily as a light source.
However, He-Ne gas lasers are large in size and expensive, making the structure of optical video disc playback devices complex and increasing costs. In response, development efforts have been made to solve the above problems by using semiconductor lasers as light sources. However, conventional semiconductor lasers generally have a light emission shape that is not completely isotropic, and therefore, when the laser beam is focused onto an information recording medium such as a disk, it is usually recorded at a high frequency of MHz or higher. This method has the disadvantage that several pits of video information are simultaneously irradiated in the direction of arrangement on the track, distorting the reproduced signal waveform and lowering the degree of modulation of the signal.

The present invention has been made in order to solve the above-mentioned drawbacks, and is a compact, low-cost information processing device with a simple configuration using a semiconductor laser, which can obtain a reproduced signal with little waveform distortion and a high degree of modulation. The purpose is to obtain a playback device.

In order to achieve this object, the information reproducing apparatus of the present invention provides information as a plurality of pits on an information track, and the length of these pits in the direction of the information track is equal to the length of the pit in the direction perpendicular to the information track. An elliptical spot obtained by using an information recording medium that is larger than the length of the information recording medium and focusing an elliptical beam emitted from a semiconductor laser onto the information recording medium by optical means, and whose short axis direction is the direction of the information track. The invention is characterized in that the plurality of pits are reproduced using elliptical spots that substantially match the pits.

Hereinafter, the present invention will be explained in detail along with examples. FIG. 1 shows a first embodiment of the invention. A laser beam 2 emitted from a semiconductor laser 1 passes through a lens 3, a mirror deflector 4, and a focusing lens 5, and is focused onto an information track 7 on an information recording medium 6 (for example, a disk or tape). At this time, the junction surface of the semiconductor laser is in the x direction, and this x
The direction is orthogonal to the direction y' of the information track. The effects of such an arrangement will be explained with reference to FIG. In FIG. 2, the oval direction of the focused laser spot 8 is perpendicular to the information track 7 on the information recording medium 6. In this way, if the major axis direction of the narrowed-down elliptical spot is made almost orthogonal to the direction of the information track, and the minor axis direction is made to match the direction of the information track, each pit will be Therefore, the amount of light is sufficiently reduced at the center of the pits, and at the same time at intermediate positions between the pits, the amount of light increases sufficiently because the spots are not covered by the pits, causing waveform distortion. Therefore, a reproduced signal with a large modulation degree can be obtained. For example, the size of the information pit is 0.8 μm on the axis, 1.5 μm in length, and the pitch between the pits is 0.8 μm.
The pits are approximately 1.5 μm long in the track direction. Further, the size of the laser spot is approximately 3 μm in the long axis direction and 1.5 μm in the short axis direction when a normal double heterostructure semiconductor laser is used at the very edge of the oscillation threshold. Buried heterostructure semiconductor lasers (For buried heterostructure lasers, see the Journal of Applied Physics
Volume45November1974Number11 4899〜4906
Shown on page. ), the size of the laser spot is usually about 1.5 μm x 2 μm.
Therefore, if the bonding surface direction is made parallel to the information track direction, two or more information pits will be irradiated at the same time. However, as described above, in the present invention, since the joint surface direction is orthogonal to the information track direction, the two information pits are not illuminated, or even if it is, the influence is small;
A reproduced video signal with little waveform distortion and a high degree of modulation can be obtained. On the other hand, the interval between information tracks is usually 2 to 2.5 .mu.m, and in this direction, even if the laser track has a width of about 3.2 to 4.2 .mu.m, crosstalk will not occur and there will be no problem.

Note that the elliptical beam 2 emitted from the semiconductor laser 1 is polarized in a direction parallel to the cemented surface, and is linearly polarized light with almost no vertical component.This light is focused by the lens 5 to form an elliptical spot. Since the long axis direction of the laser beam 8 coincides with the direction parallel to the bonding surface, the polarization direction of the semiconductor laser 1 coincides with the long axis direction of the focused elliptical spot 8. In other words, the elliptical emission pattern (near-field pattern) on the emission end facet of a semiconductor laser first becomes an elliptical-shaped divergent beam (far-field pattern) with its major axis rotated by 90 degrees due to diffraction, and this is then converted into an elliptical divergent beam (far-field pattern) by optical means. When the light is narrowed down, the long axis direction returns to its original state on the focusing surface, and the near field pattern becomes an elliptical focusing spot with the same long axis direction on the exit surface.
Reading out pits using a light spot linearly polarized in such a direction has the effect of increasing the degree of modulation of the reproduced signal. This is because when considering light as an electromagnetic wave, the magnitude of reflection changes depending on the vibration direction of the electromagnetic vector (the polarization direction of the light). Reflected light on the surface of the recording medium is caused by vibration of free electrons due to the electric field of the incident light. Electrons move easily in the direction along the pit edge, so
Incident light with an electric field in this direction is easily reflected, and conversely, electrons have difficulty moving in a direction perpendicular to the pit edge, so incident light with an electric field in this direction is difficult to reflect.
Therefore, when a pit that is elongated in the direction of the information track is irradiated with a spot polarized in the direction perpendicular to the information track, the edge portions that are difficult to reflect (edges in the track direction) will be divided into the edge portions that are easy to reflect (edges in the track direction). (edges in the orthogonal direction), the diffraction of light by the original pit is greater than when irradiating with a spot polarized in the direction of the information track (in this case, the edges in the track direction are more likely to reflect). In addition, the reflectance at the edge of the pit is greatly reduced, and as a result, a larger reproduced signal can be obtained.

Although FIG. 1 shows a configuration in which laser light from a semiconductor laser is guided to an information recording medium using two lenses and a mirror deflector, it is of course not limited to this configuration. I would like to add this. Furthermore, it should be noted that the present invention exhibits its effects when using the above-mentioned buried heterostructure semiconductor laser.

As shown above, by using the information reproducing device of the present invention, a semiconductor laser can be used in place of the conventional gas laser such as He-Ne, which simplifies the configuration of the device and at the same time reduces the size and cost of the device. It can be priced. In particular, the present invention uses an elliptical spot obtained by focusing an elliptical beam emitted from a semiconductor laser by an optical means, so there is no need for anamorphic optical means such as a cylindrical lens or prism to obtain an elliptical spot. The structure of the optical means is also simple.

To significantly reduce the distortion of the reproduced signal waveform and to increase the degree of modulation of the reproduced signal, compared to the case where the semiconductor laser is arranged so that the major axis direction of the focused elliptical spot coincides with the direction of the information track. Can be done.

In addition to the increase in the degree of signal modulation due to the spot shape, the degree of signal modulation also increases due to the effect of polarization. That is, the present invention provides an information recording medium in which information is provided as a plurality of pits on an information track, and the length of these pits in the information track direction is larger than the length in the direction perpendicular to the information track, and an information recording medium in which information is provided as a plurality of pits on an information track, and a semiconductor laser emitted from the information recording medium. By combining this with an elliptical spot obtained by narrowing down the elliptical beam, the degree of modulation of the reproduced signal is improved far beyond what can be estimated from the spot shape.

[Brief explanation of drawings]

FIG. 1 shows one embodiment of the present invention, and FIG. 2 is a supplementary diagram thereof.

Claims (1)

[Claims] 1 Information is provided as a plurality of pits on an information track, and the length of the pits in the direction of the information track is larger than the length of the pits in the direction orthogonal to the information track, and the information recording medium is The junction surface of the semiconductor laser is aligned with the information track so that the short axis direction of the ellipse spot obtained by focusing the ellipse beam emitted from the semiconductor laser onto the medium substantially coincides with the direction of the information track. An information reproducing apparatus characterized in that the plurality of pits are reproduced using the elliptical spots arranged in alignment with orthogonal directions.