JPH0547898B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION FIELD OF INDUSTRIAL APPLICATION The present invention relates to an apparatus for reproducing information by focusing and irradiating laser light onto an optical disk.

Conventional configuration and its problems In recent years, "digital audio disks (compact disks)" and analog signal "video disks" have been commercially available. On these disks, laser spots are arranged as shown in FIG. The information pit 10 has an optical depth of about one-fourth of the laser wavelength, and is formed in the shape of a track on the same plane. 1 is a reproduction spot, and 2 and 3 are tracking spots.

It is also desired to digitize video signals, and the method for doing so is disclosed in Japanese Patent Application No. 57-147133 and Japanese Patent Application No. 58
- Proposed in No. 175259. As shown in FIG. 2, a V-shaped groove is formed on the surface of the optical disk, and each slope of the groove is used as a signal surface. Signals are recorded using two adjacent slopes such as A and B or C and D in FIG. 2 as one set. The laser spot on the disk is the third
By arranging them as shown in Figures 11 and 12, signals on two slopes (for example, C and D) can be read out simultaneously, thereby doubling the transfer rate.

Note that the inclination angle of the slope of the V-groove is set so that the reflected light from the slope falls within the aperture of the lens.
This point is also described in, for example, Japanese Unexamined Patent Publication No. 105828/1983, which recommends an angle of about 7.1° to 10.5°, for example.

Laser light with a wavelength of 780 nm has a numerical aperture (NA) of 0.5
By narrowing down the aperture with an objective lens, pits with a minimum length of 0.55 μm can be reproduced. This allows the disk to run at 1800 speeds per minute.
If you rotate it and read out the signals of two adjacent slopes at the same time at a radius of 55 mm, you can obtain the recording density coefficient (DR).
This means that information at approximately 56.5 Mbit/sec can be reproduced using a modulation method of 1.5.

NTSC TV signal with color subcarrier frequency 2
Multiply sub-Nyquist sampling and 8-bit quantization,
The amount obtained by removing the blanking period and adding approximately 20% redundancy can be expressed by the transfer rate mentioned above (approximately 56.5 Mbps).

By using the method disclosed in JP-A-57-105828 and reading out the reflected light on the objective lens 14 in the area M or N as shown in Figure 4, crosstalk from signals on the adjacent slope can be reduced. . The distance between the peaks of the V groove (2P) in Figure 2 can be made equal to the track pitch of a commercially available video disc, and the diameter is 30 cm.
With this disc, digital video signals can be played for one hour on both sides when rotated at a constant angular speed, and for two questions on both sides when rotated at a constant speed.

It is desirable to have a device that can play not only the above-mentioned two-slope simultaneous playback disc (so-called digital video disc) but also single-track playback discs such as commercially available compact discs and analog signal video discs. In this case, the laser spot on the disk must be arranged as shown in FIG. 3a, which is similar to FIG. 1. However, in the method disclosed in Japanese Patent Application No. 58-175259, the laser spots 11, 12 and 13 each focus light from different semiconductor lasers, and the optical system is complicated. It is desirable to have an optical system that focuses the light from a single semiconductor laser through a diffraction grating into three laser spots, like a commercially available disc playback device, and plays back a dual-slope simultaneous playback disc (digital video disc).

OBJECTS OF THE INVENTION It is an object of the present invention to provide an optical playback device with a simple configuration and excellent reliability, which is capable of playing both commercially available single-track playback discs such as compact discs and dual-slope simultaneous playback discs. The purpose is to

Structure of the Invention Light from one semiconductor laser is divided into three diffracted lights, 0th order, +1st order and -1st order, by a diffraction grating, focused on three laser spots on a disk, and each diffracted light is reflected. It has a photodetector that separates and receives the light, each photodetector that receives the ±1st order reflected diffraction light is divided into two, and there are also 4 photodetectors that receive the 0th order reflected diffraction light. By dividing the disc into two parts, it can be played back as a single-track playback disc such as a compact disc or an analog video disc, or as a two-slope simultaneous playback disc.

DESCRIPTION OF EMBODIMENTS FIG. 5 shows an embodiment of the optical system of the present invention. 21
2 is a semiconductor laser, 22 is a diffraction grating, 23 is a polarizing beam splitter, and 24 is a quarter wavelength plate. The incident light a emitted from the semiconductor laser 21 passes through these and is focused onto the disk 26 by the objective lens 25. The incident light a is divided into three parts, a 0th-order diffracted light and a ±1st-order diffracted light, by the diffraction grating 22, and is distributed on the disk 26 at spots 11, 12, and 13 in FIG. 3a.
However, to avoid complexity, the diffracted light is shown without being separated in Figure 5. The reflected light b from the disk is separated from the incident optical path by a polarizing beam splitter 23, passes through a cylindrical lens 27, and is received by a photodetector 28. FIG. 6 shows the shape of the photodetector 28. 41, 42 and 43 are +1
It represents the reflected beams of diffracted light of order, -1st and 0th order. Further, the photodetector 28 is divided into eight parts 31 to 38.

Focus control, tracking control, and information of commercially available compact discs, analog video discs, and dual-slope simultaneous playback discs (Fig. 2) are performed by appropriately combining the light reception signals in the photodetectors 31 to 38 shown in Fig. 6. Explain that it can be played.
First, a method of reproducing the dual-slope simultaneous reproducing disk (FIG. 2) will be explained. Since focus control uses the cylindrical lens 27, a known astigmatism method (Japanese Patent Publication No. 53-39123) is used to control the light detection section 35 in FIG.
This can be done by comparing the sum of the amounts of light received at and 38 with the sum of the amounts of light received at 36 and 37. Tracking control can be carried out so that the far-field image of the reflected beam (43 in FIG. 6) of the 0th-order diffracted light is symmetrical with respect to the groove. 36 and 38
Compare the sum of received light amounts. To reproduce information, two adjacent slopes (for example, C and D in FIG. 3) are read out simultaneously. Reference numerals 41 and 42 in FIG. 6 are reflected beams from the laser spots 11 and 12 in FIG. 3a, which include signals from the slopes C and D, respectively. Photodetector 32, 3
3 corresponds to areas N and M in Figure 4, respectively, and 32 corresponds to C.
and the D signal at 33 at the same time.

Next, we will explain how to play commercially available discs (compact discs and analog video discs). Focus control is performed by the photodetectors 35 to 3 as described above.
8 uses the astigmatism method. It is stable to use a known three-beam method for tracking control, and the tracking control is performed by making the sum signal amplitude of photodetectors 31 and 32 equal to the sum signal amplitude of photodetectors 33 and 34. To reproduce information, a laser spot (1 in FIG. 1) of 0th-order diffracted light is irradiated along the row of information pits 10, and the reflected beam 43 in FIG. 6 contains the information. Therefore, it is sufficient to reproduce the signal as the sum of the signals of the photodetectors 35 to 38.

Effects of the Invention As described above, by using a photodetector that separates and receives reflected beams of 0th-order and ±1st-order diffracted light, ±
By dividing the photodetectors that receive the 1st-order diffracted light into two parts, and by dividing the photodetector that receives the 0th-order diffracted light into four parts, commercially available compact discs, analog discs, etc. It has been possible to provide an optical system that can be used as both a video disc and a two-sided simultaneous playback disc (digital video disc).

In addition, the light from one semiconductor laser is divided into three parts: 0th-order diffracted light and ±1st-order diffracted light.In other words, since there is only one light source, these three lights are focused on the disk and formed. The relative position change of the spots can be made sufficiently small, and since tracking is performed using the zero-order diffracted light spots, the slopes of the V-shaped groove can be precisely aligned using the ±1st-order diffracted light spots formed on both sides. It is possible to realize a highly reliable device that can irradiate light, consistently regenerate signals stably, and has excellent reliability.

[Brief explanation of the drawing]

FIG. 1 is a diagram of the laser spot arrangement on a commercially available optical disk, FIG. 2 is a perspective view of an optical disc with a V-groove formed thereon, and FIGS. FIG. 4 is an explanatory diagram of a method for reproducing a V-groove disk, FIG. 5 is a diagram showing an optical system according to an embodiment of the present invention, and FIG. 6 is a diagram showing the configuration of a photodetector according to the present invention. 1, 13... Laser spot of 0th order diffracted light,
2, 11... Laser spot of +1st order diffracted light,
3, 12...-laser spot of first-order diffracted light,
21... Semiconductor laser, 22... Diffraction grating, 2
6... Optical disk, 28... Photodetector, 10...
Information pit.

Claims (1)

[Scope of Claims] 1. A semiconductor laser, a diffraction grating that divides the light from the semiconductor laser into 0th-order, +1st-order, and -1st-order diffraction light, and a diffraction grating that divides the light from the semiconductor laser into 0th-order, +1st-order, and -1st-order diffraction light, and a diffraction grating that divides the light from the semiconductor laser into 0th-order, +1st-order, and −1st-order diffraction lights, and a slanted surface for each diffraction light. A lens capable of concentrating and irradiating a light spot onto an optical disk surface having a V-shaped groove formed thereon and containing the reflected light within its aperture; It has first, second, and third photodetectors that receive light, and the first photodetector is composed of a photodetector divided into four to obtain a signal for tracking control, and the The second and third photodetectors are composed of two divided photodetecting sections in order to obtain a signal for reproducing the signal recorded on the slope of the V-shaped groove, and the second and third photodetectors are composed of a photodetecting section divided into two, and the 0th-order diffracted light is irradiated onto the peaks or valleys of the optical disc, and its reflected light is received by the first photodetector, and the +1st order and -1st order diffracted lights are irradiated onto the adjacent slopes of the optical disc. Along with being
This reflected light is received by the second and third photodetectors, respectively. 2. The optical reproducing device according to claim 1, wherein tracking control is performed so that the far-field image of the reflected light of the 20th order diffracted light is symmetrical with respect to the V-shaped groove.