JPS592966B2 - optical information reproducing device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an optical information reproducing device for optically reproducing signals from a disc-shaped record carrier such as a video disc.

FIG. 1 is a block diagram showing a conventional optical information reproducing device.

In the figure, 1 is a laser light source, 2 is light from the laser light source 1, 3 is a diffraction grating that divides into three beams: 0th-order reading light beam 3a) ± 1st-order tracking light beam 3b and 3c, 4 is a beam splitter 5; 5 is a tracking mirror; 6 is a condensing lens; T is a disc-shaped record carrier such as a video disc having an information track Ta; 8 is a motor that rotates this disc-shaped record carrier T; 9 is the above-mentioned readout Light flux 3a) Tracking light flux 3b, 10 and 3c
A photodetector 11 includes a first photodetector 9a, a second photodetector 9b, and a third photodetector 9c, each of which receives the reflected lights 10a, 10b, and 10c and converts them into electrical signals. an amplifier 12 that receives the output signals of the detector 9b and the third photodetector 9c, dynamically amplifies the difference 15, and sends out a signal for rotating the tracking mirror 5;
a, 12b and 12c are the reading light spots and tracking light spots on one side of the disc-shaped record carrier by the reading light beam 3a and the tracking light beams 3b and 3c; 13 is an output terminal for sending out a video signal; 14 is an output terminal that sends out a tracking signal.
Next, the operation of the optical information reproducing apparatus having the above configuration will be explained.

1! 5 First, the light 2 from the laser light source 1 passes through the diffraction grating 3
The diffracted beams are divided into three diffracted beams: a readout beam 3a, a tracking beam 3b and 3c, and are transmitted to a disk-shaped record carrier T through a beam splitter 4, a tracking mirror 5, and a condensing lens 6 in this order. A minute readout light spot 12a) is projected to form an image of tracking light spots 12b and 12c, which are approximately the same size as the pits to be detected on the information track Ta.

These reading light spots 12a, tracking light spots 12b and 5512c are reflected from the disk-shaped record carrier T, and the reflected lights 10a, 1□b and 1
0c is again focused by the condensing lens 6, separated from the incident optical path by the beam splitter 4 via the tracking mirror 5, and transmitted to the first photodetector 9a, second photodetector 9b and third photodetector 9c. are incident on each.

Therefore, a video signal is sent out from the first photodetector 9a, and output signals from the second photodetector 9b and third photodetector 9c are input to the amplifier 11, and the difference output thereof is sent out. Therefore, since this difference output is a signal corresponding to the deviation of the tracking optical spots 12b and 12c from the information track 7a (row of pits), if the tracking mirror 5 is controlled and shifted by this difference output, reading can be performed. Light spot 1
2a can always follow on the information track 7a,
Information can be reproduced optically. however,
According to the optical information reproducing apparatus having the above configuration, if there is a dropout (due to a pin scratch or the like) at a certain position on the information track 7a, a disturbance occurs in the video signal.

For this reason, when a dropout is detected, it must be corrected on the TV screen using an electrical circuit such as replacing the horizontal scanning line that contains the dropout with the horizontal scanning line that precedes the horizontal scanning line that contains the dropout. There were drawbacks such as the need for Therefore, an object of the present invention is to provide an optical information reproducing apparatus that performs optical correction without relying on electric circuit correction as described above. In order to achieve such an object, the present invention projects a reading light spot onto an information track of a disk-shaped recording medium, and projects a correction light spot onto an information track that is at least one information track away from this information track. an optical system, a photodetector for receiving reflected light from the fair report track by the reading light spot and transmitting a video signal, and a photodetector for receiving the reflected light from the information track by the correction light spot for correction. a correction photodetector that sends out a video signal; a dropout determination circuit that receives the video signal and detects its dropout; and cuts the video signal using the output signal of the dropout determination circuit;
The apparatus is equipped with a switch means for switching to and transmitting a correction video signal, and will be described in detail below using an embodiment.

FIG. 2 is a block diagram showing an embodiment of an optical information reproducing apparatus according to the present invention.

In the figure, reference numeral 15 indicates a position where a correction light spot 16 is projected at a position radially away from the reading light spot 12b by an amount equivalent to one track (if playback is performed from the inside to the outside, the correction light spot 16 is radially spaced from the reading light spot 12b). (located quite a bit inside)
17 is a correction photodetector that receives the reflected light 18 from the correction light spot 16 and sends out a correction signal; 19 is an output terminal for the correction signal. Further, FIG. 3 shows a signal switching section connected to the output terminals 13 and 19 of FIG. 2. In the same figure, 20 and 21 are preamplifiers that amplify and shape input video signals, respectively;
2 is a movable contact 22a, a normally closed contact 22b, and a normally open contact 2
2c is a changeover switch, and 23 is the preamplifier 20 mentioned above.
detects a change in the intensity of the dropout and determines whether or not there is a dropout.
2 movable contact 22a from normally closed contact 22b to normally open contact 22
A dropout determination circuit is connected to c, and 24 is an output terminal. Next, the operation of the optical information reproducing apparatus having the above configuration will be explained. First, light from a laser light source 1 is divided by a diffraction grating 2 into three diffracted beams: a readout beam and two tracking beams (see Figure 1). The light is projected onto the disk-shaped record carrier 7 via the lens 6 in order, and images a minute readout light spot 12a1 and tracking light spots 12b and 12c, which are approximately the same size as the pits to be detected on the information track 7a.

On the other hand, the light emitted from the correction laser light source 15 passes through the beam splitter 4, the tracking mirror 5, and the condensing lens 6 in this order and is projected onto the disk-shaped record carrier 7, forming an image on the auxiliary light spot 16. . These reading optical spots 12a, tracking optical spots 12b and 12c1 auxiliary optical spots 16 are reflected from the disk-shaped record carrier 7, and the reflected lights 10a, 10b, 10e, 18G? The light is again focused by the K condenser lens 6, separated from the incident optical path by the beam splitter 4 via the tracking mirror 5, and then sent to the first photodetector 9a.
1 enters the second photodetector 9b, the third photodetector 9c, and the correction photodetector 17. Therefore, the first photodetector 9a
A video signal is sent out from the second photodetector 9b and the third photodetector 9b.
The output signal of the photodetector 9c is input to the amplifier 11, and the difference output is sent out. Therefore, this difference output is the information track 7a of the tracking optical spots 12b and 12c.
Since the signal corresponds to the deviation from (row of parts),
If the toning mirror 5 is controlled by the differential output, the reading light spot 12a can always follow the information track 7a, and the information can be chemically reproduced. When a dropout occurs in the process of reproducing the video signal, this occurrence can be detected by a change in the carrier level of the video demodulated signal.
This can be detected by the dropout determination circuit 23.
Then, the changeover switch 22 is driven by the output signal of the dropout determination circuit 23, and the movable contact 22a is brought into contact with the normally open contact 22c. Therefore, the video signal of one screen before input to the terminal 19 can be sent out from the output terminal 24 via the preamplifier 21 and the changeover switch 22. When the end of dropout is detected by the dropout determination circuit 23, the changeover switch 22 is deactivated. Therefore, the original track video signal can be sent out again from the output terminal 24. This is because there is no major change in the image report between adjacent trucks.
No unnatural images occur due to switching. In the above description, two laser light sources are provided as light sources, but in the case of a semiconductor laser, two oscillation sections can be easily formed monolithically.

Furthermore, it goes without saying that two light beams may be created from one light source using a beam splitter, a diffraction grating, or the like. As described above in detail, according to the optical information reproducing apparatus according to the present invention, even if there is a dropout at the pit of the information track, the image is not disturbed and the television screen is stabilized.

Moreover, since there is no correction using a complicated electric circuit, there are effects such as improved reliability.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing a conventional optical information reproducing device, Fig. 2 is a block diagram showing an embodiment of the optical information reproducing device according to the present invention, and Fig. 3 is a signal switching section of Fig. 2. FIG. 1... Laser light, 2... Light, 3...
...Diffraction grating, 3a...Reading light beam, 3b
and 3c... tracking light flux, 4...
...Seam splitter, 5...Tracking mirror 6...Condensing lens, 7...Disc-shaped record carrier, 8...Motor, 9... ...
...Photodetector, 9a...First photodetector, 9b.
...Second photodetector, 9c...Third photodetector, 10a, 10b and 10c...Reflected light,
11...Anbu, 12a, 12b and 12c
...reading optical spot and tracking optical spot, 13... video signal output terminal, 1
4... Tracking signal output terminal, 15...
... Laser light source for correction, 16 ... Light spot for correction, 17 ... Photodetector for correction, 18 ...
...Reflected light, 19... Output terminal.

Claims (1)

[Claims] 1. An optical system that projects a reading light spot onto an information track of a disk-shaped recording medium and also projects a correction light spot onto an information track that is at least one information track away from the information track, and a photodetector that receives reflected light from the information track and sends out a video signal; a correction photodetector that receives reflected light from the information track by the correction light spot and sends out a correction video signal; , upon receiving the above video signal,
Optical information comprising: a dropout determination circuit that detects the dropout; and a switch means that cuts the video signal based on the output signal of the dropout determination circuit, switches to a correction video signal, and sends out the video signal. playback device.