JPS6136295B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a focus 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 a semiconductor laser is an effect in which 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 the focus error. Conventionally, a method using a 4-split photodetector and a cylindrical lens or a perturbation method have been adopted to detect this focus error, but the former method is difficult to employ due to the configuration of the pickup optical system, and the latter method Adopting this method requires the development of a perturbation mechanism with a narrow detection range, and if the perturbation method is also used for tracking error detection, there are problems in that measures to separate both types of error information are also required.

SUMMARY OF THE INVENTION An object of the present invention is to provide a simple and inexpensive focus 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:
A semiconductor laser light source for focus error detection is placed at the front and rear positions in the optical axis direction with a semiconductor laser light source for reading recorded information in the center, a lens system that focuses the light from these laser light sources, and a lens system that focuses the focused light. A reflecting surface that reflects the light back to the original laser light source, a group of light receivers that receive the light output from each laser light source including changes due to self-coupling effects, and a group of light receivers for detecting the error in this group of light receivers. a differential amplifier that receives outputs from a light receiver corresponding to the laser light source at two inputs, calculates the difference therebetween, and outputs the difference as focus error information on the reflective surface of the laser light source for reading recorded information; There is something to do.

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 represents the proportion of light that is fed back, and the vertical axis represents the optical output of the semiconductor laser. As shown in the figure, as the amount of feedback increases, the optical output also increases. Phenomena such as changes in the terminal voltage of the laser light source occur as the amount of feedback increases, but in order to avoid complexity, the present invention will be described below using changes in optical 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 light receiver 1 receives the optical output of the laser light source 2, including the variation due to the self-coupling effect.

In such a configuration, when the video disc reflective surface 4 is located at a position where the incident light beam forms an image on this surface, the reflected light is best fed back to the laser light source side, and the video disc reflective surface 4 4 moves forward or backward in the optical axis direction from that position, the amount of feedback light decreases. Therefore, if we take the position of the video disc reflective surface 4 on the horizontal axis and the light output from the laser light source on the vertical axis, we can calculate the amount of light. The output changes as shown by curve 5 in FIG. Therefore, laser light sources for focus error detection (not shown in FIG. 2) are installed at positions close to the laser light source 2 and slightly shifted forward and backward in the optical axis direction, respectively.
If a light receiver (not shown) is provided to receive the light output from each laser light source, the light output of the focus error detection laser light source placed at the front position in the optical axis direction will be as shown by curve 5a in FIG. 3, for example. The optical output of the laser light source for focus error detection placed at the rear position in the optical axis direction changes as shown by curve 5b in FIG. 3. Therefore, by determining the difference between the optical outputs shown by these two curves 5a and 5b, information indicating the focused state of the desired spot of the laser light source 2 can be obtained.

FIG. 4 is an optical system diagram for explaining one embodiment of the present invention, and 1, 2, 3, 3', and 4 are light receivers and semiconductors for reading recorded information, respectively, having the same functions as in FIG. 2. Laser light source, lens system for focusing light,
Video disk reflective surface. 2a and 2b are
These are laser light sources for focus error detection, and are arranged so as to be located on the optical axis and before and after the recorded information reading laser light source 2 in the optical axis direction. 1a is a light receiver that receives the light output from the laser light source 2a for focus error detection, and 1b is a light receiver that receives the light output from the laser light source 2b for focus error detection. 6 is a differential amplifier, which converts the output signals from the photodetectors 1a and 1b into 2
It receives input, calculates the difference, and outputs it. Reference numeral 7 denotes an output terminal of the differential amplifier 6, which is a terminal to which the focus error is output.

With the above configuration, the output terminal 7 outputs the fifth signal depending on the position of the video disc reflective surface 4.
A desired focus error signal that changes like the curve shown in the figure is obtained. The above description has been made using an example in which separate lasers are used for reading recorded information and detecting focus errors. It is also possible to configure it to be used also for error detection.

FIG. 6 is a diagram illustrating another embodiment of the present invention,
This is the laser light source 2a, 2b for focus error detection.
This is a case where a laser light source with a rectangular light emitting surface is used, and by doing so, the detection range can be expanded. Furthermore, if the area of the light emitting surface of the semiconductor laser light source for focus error detection is configured to be larger than the area of the semiconductor laser light source for reading recorded information, the influence of recording pits on the video disc can be reduced. .

The present invention has the above-described configuration and operation.According to the present invention, focus error detection in semiconductor laser pickup using the self-coupling effect is possible with a simple configuration, and the device is inexpensive. be able to.

[Brief explanation of the drawing]

Figure 1 is a characteristic diagram for explaining the self-coupling effect of a semiconductor laser, Figure 2 is an optical system diagram for explaining the principle of the present invention, Figure 3 is a characteristic curve diagram for explaining the operation of Figure 2, and Figure 4 is a diagram for explaining the operation of the semiconductor laser. The figure is an optical system diagram for explaining one embodiment of the present invention, FIG. 5 is an output characteristic diagram in FIG. 4, and FIG.
The figure is a front view showing the main parts of 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 focus error detection, 3, 3'...
Lens, 4... Video disc reflective surface, 5, 5a,
5b... Optical output change curve, 6... Differential amplifier, 7... Output terminal.

Claims (1)

[Claims] 1. A plurality of semiconductor laser light sources disposed at front and back positions in the optical axis direction; a lens system that focuses light from these laser light sources; and a lens system corresponding to each of the plurality of laser light sources. a plurality of light receiving means provided for receiving reflected light of the laser light output from the laser light source and detecting a state change due to a self-coupling effect of each laser light source; connected to the light receiving means;
A focus error detection device comprising: a differential amplifier that compares output signals of each light receiving means and outputs focus error information on a reflective surface of an object irradiated with laser light from the laser light source. 2. The semiconductor laser light source for focus error detection is characterized in that the semiconductor laser light source for focus error detection is arranged such that its light emitting surface is rectangular or elliptical and its longitudinal direction is perpendicular to the optical axis. A focus error detection device according to claim 1. 3. The focus error detection device according to claim 1, wherein the area of the light emitting surface of the semiconductor laser light source for focus error detection is larger than the area of the light emitting surface of the semiconductor laser light source for reading recorded information.