JPS6132735B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an optical video disk device, and particularly to a simple and low-cost optical video disk device.

Generally, in order to correctly reproduce the information recorded on a video disc, the reading laser beam must be accurately tracked on the information track.
Moreover, it is necessary to focus accurately.
For this purpose, conventionally, for tracking, three
one light spot illuminates the information track,
Each reflected light is captured by three photodetectors, and the amount and direction of tracking position shift are detected by taking the difference in each light output, and this signal is used to deflect the galvano mirror to accurately Tracking is carried out. The video information contained in the information track is detected by the central one of the three photodetectors. However, this method has several problems. First of all, since it is necessary to divide the laser beam into three parts, a relatively large output power is required as a laser light source. Second,
As many as three photodetectors are required, and relatively high placement accuracy is required. One method for solving the above problem to some extent is the method described in Japanese Patent Application Laid-Open No. 49-98113. In this method, the video signal and track signal are detected by capturing the diffracted light component of the laser light due to the information track with a photodetector, which solves the first problem mentioned above and uses a relatively low-power laser light source. Although it allows the use of
This method has the disadvantage that at least four photodetectors are required.

The present invention provides a simple and inexpensive information reproducing device that eliminates the drawbacks of the conventional methods described above.

The outline of the present invention is to record an information track on an information recording medium with unevenness, to make the optical depth of the nuclear mark not an integral multiple of λ/4 with respect to the wavelength λ of a laser beam, and to prevent reflection from the information track. Alternatively, there are at least two or more detection surfaces in the transmitted laser beam. The present invention provides an information reproducing device in which a photodetector is arranged, a video signal is detected by the sum of signal outputs from each detection surface, and a tracking signal is detected by the output difference.

The present invention will be explained in detail below based on examples.

FIG. 1 shows a first embodiment of the present invention. He-
The laser beam 2 emitted from the Ne laser 1 is passed through the lens 3,
Passes through the galvanometer mirror 4 and is then processed by the lens 5.
The reflected light beam is focused on an information track 7 on an information recording medium (disk, sheet, tape, etc.) 6 and guided onto photodetectors 9 and 10 by a half mirror 8. At this time, the optical depth of the uneven markings (pits) constituting the information track is set to an integer multiple of λ/4 with respect to the He-Ne laser wavelength λ (6328 Å). The optical depth here is the product of the refractive index and depth of the medium through which light passes. A track signal output from the photodetector is guided from a servo circuit 13 to a galvano mirror 4 via a differential amplifier 11, and the deflection angle of the galvano mirror is controlled to perform tracking. On the other hand, the video output signal is similarly output from the differential amplifier 1.
2, the signal is guided to a signal demodulation circuit 14 and a TV monitor 15.

Figure 2 shows the principle of track signal detection. The information track is recorded as a concave and convex stamp whose cross section is substantially square. 16 stamps like this
When the spot 17 illuminates the edge 16-1, the intensity distribution of the reflected and diffracted light on the photodetectors 9 and 10 becomes 20, and in the case of the marking 16-2, the intensity distribution becomes 21. In this way, a left-right imbalance of reflected diffracted light occurs in response to the irradiation of the left and right edges of the marking. This occurs when the marking depth is not an integral multiple of λ/4 for the laser wavelength λ (6328 Å). When it is an integral multiple of λ/4, the left and right sides are symmetrical as shown by the dotted line 25, and no imbalance occurs. Therefore, even if the differential outputs of the photodetectors 9 and 10 are used, no tracking signal can be detected. FIG. 3 shows the principle of video signal detection. Spot 1 with engraving 16
7 sequentially illuminates in the direction of the arrow. The cross section of the engraving has a roughly rectangular unevenness as shown in 22, and only when the optical depth of the engraving is not an even multiple of λ/4 for the laser wavelength λ (6328 Å), A video signal 23 is detected. When it is an even multiple of λ/4, the output becomes constant as shown by the dotted line 24, and no video signal is detected. This is λ/4
In the case of an even multiple of λ/2, λ, 3/2λ, etc., the round-trip optical path becomes λ, 2λ, 3λ, etc.,
This is because optically it is the same as if there were no markings (pits). Therefore, in order to detect both the track signal and the video signal, the optical depth of the marking must not be an integral multiple of λ/4. In addition,
When the tracking signal level is an odd multiple of λ/8, the tracking signal level is maximum, but the video signal level becomes small, so it is necessary to prevent the optical depth of the marking from being an odd multiple of λ/8. In order to satisfy this condition, the present invention defines the relationship between the laser wavelength and the depth of marking as described above. Note that the stamp may not be perfectly square due to manufacturing, and the side wall may have a trapezoidal unevenness with a slight slope.A similar phenomenon occurs in this case as well, and depending on the depth of the stamp, the track signal and Of course, since the playback level of the video signal is affected, the principles of the present invention apply. Further, although the above embodiments have been described with respect to reflection type signal detection, it goes without saying that the same principle applies to transmission type signal detection.

In other words, in the case of a transmissive type, the optical depth of the engraving should be twice that of the reflective type, but since this condition is included in the above conditions for the reflective type, the laser should be adjusted to satisfy the above conditions. It is clear that, provided the wavelength and the optical depth of the inscription are defined, both the tracking signal and the video signal can be detected using the same detector even in transmissive disks.

FIG. 4 shows a second embodiment of the present invention, in which the effects of the present invention are most exhibited.
The laser beam from the semiconductor laser 26 passes through the lens 2
7. The light passes through the galvanometer mirror 4 and is focused by the lens 5 onto an information track 7 on the information recording medium 6. The reflected laser beam from the information track is guided by a half mirror 8 to photodetectors 9 and 10. As in the first embodiment, the detection signal is processed as a tracking signal and a video signal. For example, the semiconductor laser used in this example is described in the literature.
Journal of Applied Physics Volume 45
A point-emitting buried hetero laser shown in November 1974 Number 11, pages 4899 to 4906 is suitable. The wavelength λ of a semiconductor laser is usually about 8000 Å. If we use a disc recorded for He-Ne laser reproduction light, the depth of the marking will not be an integral multiple of λ/4, so as shown in the first embodiment,
A single photodetector can detect both track and video signals. This brings about the following great practical advantages. In other words, pick-up using a small and simple semiconductor laser can be applied to all discs recorded using He-Ne lasers without any modification, regardless of the difference in laser wavelength. It will be possible.

Note that FIG. 5 shows changes in the pattern on the photodetector placed at the defocus position. When the depth d of the pit is selected to be 1500 Å, which is about 1/4 of the He-Ne laser wavelength (6328 Å), the optical distribution of the information reproducing light is the same when the spot position changes to ~ in Figure b. Shown in Figure c. In addition, the upper part of the figure is λ=
In the case of 6328 Å, the bottom row is the case of λ = 8300 Å.

MOD is the degree of modulation, and MOD = amount of light entering the lens/amount of light reflected from the disk. The numerical aperture NA of the lens is 0.4. The size of the bit is 2.1 μm in length and 0.7 μm in width.

As can be seen from Figure 5, when the depth d of the pit is λ/4 (in the case of 6328 Å) with respect to the wavelength λ of the laser, the pattern of the reflected diffracted light is is in Figure 5c,
As shown in the upper row of , the tracking signal cannot be detected by two photodetectors because of the vertical and horizontal symmetry. However, if the wavelength λ is set to 8300 Å (if d≒λ/6), then when the spot hits the edge of the marking (pit), the pattern of the reflected diffraction light will be 5th.
As shown in the lower part of Figure c, the top and bottom are asymmetrical. This relationship holds true even when the spot is shifted in the width direction of the track, and the tracking signal can be detected by taking the difference between the outputs of the two photodetectors. At the same time, MOD is 0.331 ~
It becomes 0.522, and a sufficient information signal can be obtained. In the case of a reflective type, by setting the optical depth d to be greater than λ/8 and smaller than λ/4, such as d≈λ/6 in this example, a high information signal level can be achieved in the photodetector for tracking signal detection. At the same time, a sufficiently high tracking signal level can be obtained.

As explained above, by using the information reproducing device of the present invention, it is possible to detect video signals and track signals with two photodetectors, and semiconductor lasers can be smoothly applied to conventional disks. This makes it possible to provide a simple and compact information reproducing device.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing a first embodiment of the present invention. Second
Figure 3 is a supplementary figure to Figure 1. FIG. 4 is a diagram showing a second embodiment of the present invention. FIGS. 5a and 5b are diagrams showing changes in the information reproducing light with respect to the spot position.

Claims (1)

[Scope of Claims] 1. A laser beam, an information recording medium, and an optical means for guiding the laser beam from the laser beam to an information track on the information recording medium as a convergence spot;
at least two that capture the luminous flux from the information track.
In an information reproducing device consisting of a photodetector,
The information track is recorded on the information recording medium with unevenness whose cross section is substantially square, and the optical depth thereof is an odd number of λ/8 with respect to the wavelength λ of the laser beam. λ/4×n (n:
(non-integer), detects a tracking signal based on a difference in the outputs of the photodetectors, and detects an information signal based on the sum of the outputs of the photodetectors.