JPS6136296B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a tracking error detection device that uses the self-coupling effect of a semiconductor laser, and can be used, for example, in the pickup of an optical disc player.

Taking an optical pick-up for a video disc player as an example, the optical pick-up system has various advantages as it can perform non-contact reading as is well known, but it also makes the pick-up system complicated and expensive. I had the inconvenience of becoming a thing. As a solution to this problem, it has been proposed to use the self-coupling effect of semiconductor lasers. This self-coupling effect of semiconductor lasers has the effect that when the optical output of a semiconductor laser is optically fed back to the laser light source, the optical output or the terminal voltage or terminal resistance of the laser light source changes. When applied to a disk, information is read by utilizing the fact that the light fed back to the semiconductor laser light source changes depending on the presence or absence of information pits on the disk. These details are described in, for example, Journal of the Institute of Electronics and Communication Engineers 60 (1977, No. 1), pages 23 to 26, so further explanation will be omitted here.

When constructing a pickup for a video disc player by utilizing the self-coupling effect of the semiconductor laser described above, the problem is how to detect tracking errors. Conventionally, methods for detecting this tracking error include a method in which three spots of light are created using a diffraction grating and detected using a three-split receiver, and a perturbation method, but it is difficult to employ the former method due to the configuration of the pick-up optical system. In addition, adopting the latter method has the problem that the error detection range is narrow, it is necessary to develop a perturbation mechanism, and if the perturbation method is also used for focused error detection, measures to separate both error information are required.

An object of the present invention is to provide a simple and inexpensive tracking error detection device in a pickup using the self-coupling effect of a semiconductor laser.

In order to achieve the above object, the features of the present invention are as follows:
Optical spot images of a plurality of point light sources by a semiconductor laser or a group of semiconductor lasers are arranged so as to be shifted in the tracking direction, and tracking error information is obtained by combining state change information due to the self-coupling effect of all or part of the semiconductor lasers. This is what you get.

The present invention will be explained below with reference to the drawings.

FIG. 1 is an explanatory diagram of the self-coupling effect of a semiconductor laser, in which the horizontal axis shows the proportion of light that is fed back, and the vertical axis shows the optical output of the semiconductor laser. As shown in the figure, as the amount of feedback increases, the optical output also increases. As mentioned above, development such as a change in the terminal voltage of the laser light source occurs as the amount of feedback increases, but in order to avoid complexity, the present invention will be described below using a change in light output as an example.

FIG. 2 is an optical system diagram for explaining the principle of the present invention, in which 1 is a light receiver, 2 is a semiconductor laser light source, and 3 is an optical system diagram for explaining the principle of the present invention.
and 3' are lenses, and 4 is a video disc reflective surface. The light from the semiconductor laser light source 2 is focused by the lens systems 3, 3', enters the video disk reflective surface 4, is reflected there, and is reflected again by the lens systems 3, 3'.
passes in the opposite direction and returns to the original laser light source 2. The photoreceiver 1 receives the optical output of the laser light source 2, including the variation due to the self-coupling effect.

In such a configuration, the light spot on the video disk reflective surface is now located on the track 6a,
6b, the amount of reflected light is the largest and is fed back toward the laser light source, and as the spot moves toward the track position on the reflective surface, the amount of feedback light decreases.
As shown in the figure, if the horizontal axis represents the optical spot position and the vertical axis represents the laser light output, the optical output changes as shown by a curve 7.

Therefore, a pair of tracking error detection semiconductor laser light sources 2a and 2b (not shown in FIG. 2) are now connected to the recording information reading semiconductor laser light source 2.
By arranging the two laser light sources 2a and 2b on a plane substantially perpendicular to the optical axis and at positions slightly shifted from each other with the laser light source 2 in the center, these two laser light sources 2a and 2b can be light source 2
When the light spots 5a and 5b from a and 2b are positioned so as to sandwich the track (slightly shifted in the direction orthogonal to the track) as shown in FIG. The changes are as shown by curves 7a and 7b in FIG. 4, and by determining the difference in the light output between these two curves 7a and 7b, the positional relationship between the optical spot group and the track can be determined.

FIG. 6 is an optical system diagram for explaining one embodiment of the present invention, in which 1 and 2 are a light receiver and a semiconductor laser light source for reading recorded information, and 3 and 3'
4 is a lens, 4 is a video disk reflective surface, 2a and 2b are a pair of semiconductor laser light sources for reading recorded information, 1a and 1b are light receivers that receive the optical outputs of laser light sources 2a and 2b, respectively, and 8 calculates a tracking error signal. 9 is a tracking error output terminal. Semiconductor laser light source 2, 2
a and 2b are arranged so that when the light spot 5 from the light source 2 is located exactly on the track, the light spots 5a and 5b from the light sources 2a and 2b are located sandwiching the track. The light sources are arranged so that the light emitting surface of each light source lies on a plane substantially perpendicular to the axis.

With the above configuration, the optical output from the tracking error detection semiconductor laser light sources 2a and 2b changes as shown by the curves 7a and 7b in FIG. 4 according to the position change of the optical spot 5, and the differential amplifier By determining the difference between curves 7a and 7b at step 8, output terminal 9
From this, a tracking error signal like the curve shown in FIG. 7 can be obtained.

FIG. 8 is a front view of the light emitting surface of a semiconductor laser light source showing another embodiment of the present invention, and this is a rectangular shape larger than the semiconductor laser light source 2 for reading recorded information as the semiconductor laser light sources 2a and 2b for tracking error detection. This is when using a device with a light emitting surface.
In this way, it becomes possible to reduce the interference with the tracking error detection operation due to the pit structure of the track on the video disc reflective surface 4, and in conjunction with this, the semiconductor laser light sources 2a and 2b for tracking error detection can be reduced. Since each light emitting area increases,
As a result of narrowing the spread angle of the emitted light beam, the eclipse loss due to lenses and the like is reduced, and therefore the feedback light amount ratio is increased, which has the advantage of making it easier to cause the self-coupling effect of the semiconductor laser.

As described above, according to the present invention, tracking error detection in a semiconductor laser pickup using the self-coupling effect is possible with a simple and inexpensive configuration, and the configuration of the pickup is facilitated.

[Brief explanation of the drawing]

Fig. 1 is a characteristic diagram for explaining the self-coupling effect of a semiconductor laser, Figs. 2 to 5 are illustrations for explaining the principle of the present invention, Fig. 2 is an optical system diagram, and Fig. 3 is a diagram of a video disc reflective surface. Fig. 4 is a plan view of the main part, Fig. 4 is a characteristic diagram of optical output, Fig. 5 is a plan view of the main part showing the positional relationship of light spots on the reflective surface, and Fig. 6 is an optical system diagram of an embodiment of the present invention. , FIG. 7 is a characteristic diagram showing an example of the error detection signal according to FIG. 6, and FIG. 8 is a front view showing another embodiment of the present invention. Explanation of symbols: 1, 1a, 1b... Light receiver, 2... Semiconductor laser light source for reading recorded information, 2a, 2b... Semiconductor laser light source for tracking error detection, 3.
3'...Lens, 4...Video disc reflective surface, 5,
5a, 5b... optical spot, 6a, 6b... track, 8... differential amplifier, 9... output terminal.

Claims (1)

[Scope of Claims] 1 A plurality of light spot images corresponding to a plurality of semiconductor laser light sources are placed on a track having a reflectance that is effectively different from that of other parts, and at least one of the spot images is
position by shifting the part in a direction perpendicular to the track,
A mutual positional relationship between at least one light spot image from the laser group and the track is detected by detecting a state change due to a self-coupling effect of all or some of the semiconductor lasers in the semiconductor laser group. tracking error detection device. 2. The tracking error detection device according to claim 1, wherein the shape of the light emitting surface of the semiconductor laser light source for tracking error detection is made different from the shape of the light emitting surface of the semiconductor laser light source for reading recorded information.