JPH03181021A - Optical disk and its recording and reproducing method - Google Patents

Abstract

PURPOSE:To perform accurate tracking by condensing and throwing third laser light and using the reflected light from an optical disk of this third laser light to perform the focus control or the tracking control. CONSTITUTION:Not only two laser spots 1 and 2 from first and second light sources 11 and 12 but also a third laser spot 3 from a third light source 10 is condensed on an optical disk 15. The interval between centers of laser spots 1 and 2 in the radial direction of the disk is set to a half of the interval of bottoms of V grooves, and the laser spot 3 is arranged in the middle between laser spots 1 and 2 in the radial direction of the disk. Tracking is so performed that the far field pattern of the reflected light of the laser spot 3 is symmetrical with respect to the bottom or the peak of the V groove. Thus, tracking of two laser spots is accurately performed along two adjacent slopes.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application This invention relates to an optical disc capable of recording or reproducing high-quality information at high density and a method for recording and reproducing the same. Even though "optical video discs" for reproducing signals are commercially available, FM-modulated television signals are recorded on discs with a diameter of 30 cm at a track pitch of 1.67 μm, rotated at 1800 revolutions per minute, and the playback time is limited to one side. In just 30 minutes, a method was developed for recording and reproducing signals in the same way as video tapes by providing a thin film of recording material (e.g. tellurium low oxide thin film T e Ox, x < 2) on the surface of an optical disc. It is also desired to record and play back high-quality signals such as digital video on optical discs in real time, and the inventors of the present invention previously filed a patent application for one method. Showa 57-1471
33, the outline of which is given below, forms a V-shaped groove on the surface of an optical disk as shown in Figure 5.
The entire slope of the groove is used as a signal recording surface, and the interval between the crests of the V-shaped groove is made equal to, for example, the track pitch of the tracks of video discs currently on the market.

Using at least two laser light sources, laser spots 1 and 2 are irradiated at the center of each of two adjacent slopes, such as A and C in FIG. 5 or C and D, as shown in FIG. 6. are driven independently of each other, and the adjacent 2
Using the method of JP-A-57-105828, which simultaneously records different signals on the slopes, ■ When reproducing the signal on one slope of the groove, the crosstalk from the adjacent slope can be made sufficiently small. Lasers from different light sources do not interfere with each other, so two adjacent grooves
Although the signal on the slope can be reproduced independently by two lasers, the two slopes are combined into a set, and by recording one piece of information separately on the two slopes, it is possible to record and play back high-quality information such as digital video. Let's consider a case where an NTSC color television signal is digitized using a composite method.The sampling frequency is set to 10. If you set it to 74MHz and quantize it with 8 bits, it will be 86.
However, excluding the blanking period, error correction can be performed.Using the correlation between adjacent pixels in the field, it is possible to compress the bandwidth to 40-50% with predictive coding. With current technology, NTSC color television signals can be expressed at 35 to 43 Mbit/sec.
By rotating it, an analog signal of about 10 MHz can be recorded and played back at a position with a radius of 50 cm, and this means that a digital signal of about 20 Mbit/sec can be recorded and played back using the MFM modulation method. It cannot handle digital video signals.As mentioned above, if you put two slopes of the V-groove into one set, it will be about 40 Mbit.
/sec digital signals can be recorded and played back, and NT
It is possible to record and play back the digital signals of an SC color TV in real time.The distance between the peaks of the V-groove; It should be short L
Xo Therefore, it is possible to record and play back digital video for 2 hours on both sides at constant angular speed and 2 hours on both sides at constant angular speed using a disk with a diameter of 30 cm.The problem to be solved by the invention is thus: The invention discloses a principle that can significantly increase the recording and reproducing rate.In applying this principle to actual equipment: Accurately track two laser spots along two adjacent slopes. In view of this, we have proposed a recording and reproducing method for an optical disc that can accurately track two laser spots along two adjacent slopes, and a method that can be used together with this recording and reproducing method. Means for solving the problem 311, two laser spots 1 from a second light source,
In addition to 2, a third laser spot 3 from a third light source is also apertured onto the optical disc.Laser spot! , 2, the distance between the centers in the radial direction of the disk is set to half the distance between the valleys of the V-groove, and the laser spot 3 is placed between laser spots 1 and 2 in the radial direction of the disk.Then, the reflected light of laser spot 3 The active laser spot 1. can also be tracked using a method of tracking the far-field image of the V-groove so that it is symmetrical to the valley or peak of the V-groove. The distance between the centers in the radial direction of the disc 2 is half the distance between the valleys of the V grooves, and the laser spot 3 is placed between laser spots 1 and 2 in the radial direction of the disc. Tracking the peaks or valleys of the groove ζL Laser spot 1. 2 is able to track the two adjacent slopes of the V-groove. In the example shown in FIG. The configuration of the example used is shown. Here, even if the diodes 11 and 12 are constructed on one chip, for example, λ1=780nrrx λ
2 = 840nm Figure 1 (b), (c〉1) Figure 1 (a)
) in the X-arrow view @Y-arrow view shows the light from the laser diodes 11 and 12 for recording and reproducing (objective lens 1
3-1, is reflected by the mirror 41, passes through the quarter-wave plate 23, is reflected by the polarizing beam splitter 24, passes through the quarter-wave plate 25, and is focused by the objective lens 14. Even when the center of the slopes C and D is irradiated, the optical filter 22 passes the light of wavelength λ1 and transmits the light of wavelength λ2.
The light is reflected by the two quarter-wave plates 21 and 2.
Step 3 rotates the polarization direction of the laser beam by 90 degrees so that it is reflected as an S wave by the polarizing beam splitter 24.
Although each optical element is configured, the light from the laser diode lO for tracking (9) is collected by the objective lens 13-2, passes through the polarizing beam splitter 24 as a P wave, passes through the quarter-wave plate 23, and is transmitted to the optical It is reflected by the filter 22 and passes through the quarter wave plate 2 again.
3 and is reflected as an S wave by the polarizing beam splitter 24.Then, it passes through the quarter wavelength plate 25, is focused by the objective lens 14, and is irradiated onto the peaks or valleys of the groove. At the time of playback or during playback, the light from the first to third light sources (above) is irradiated onto the optical disc 15 in the positional relationship shown in FIG. is the optical power t from the laser diode 10 Spots 1 and 2 on the slope are the light from the laser diode 11512, respectively. The process is carried out as follows by detecting the reflected light from the optical disc 15. First, the reflected light Gi from the optical disk 15. Both the light with the wavelength λl and the wavelength λ2 are detected by the objective lens 14.4.
It passes through the wavelength plate 25 and the polarizing beam splitter 24 as a P wave, and is collected by the convex lens 31 and sent to the half mirror 3.
Head to 8.

The half mirror 38 reflects only the light of wavelength λ2 and reflects the light of wavelength λl.
Although the light of wavelength λ2 is transmitted, a mirror 36 is inserted in the middle where the light of wavelength λ2 is focused, and the focus control is performed on the photodetector placed at the aperture point based on the output of L. By controlling the far-field image of the light of wavelength λ2 symmetrically using the mirrors S and T, information can be reproduced even if the center of the laser spot 3 is tracked along the valley or peak of the V-groove. Transmitted wavelength λ1
The light is received by photodetectors M and N.

Situation G' on photodetectors M and N! ,, As shown in Fig. 3, the light from the laser diodes 11 and 12 is also used for the spots 101 and 102ζ, respectively.The photodetector M1 reproduces the signal of the slope C, and the photodetector N2 reproduces the signal of the slope. The optical system of this embodiment can also play back "optical video discs" currently on the market. The appearance of the disc surface of the "optical video disc" is shown in FIG. Even though image information is recorded as a string of 40 bits, the known 3-beam system is known to be stable in order to track this bit string. It is possible to extract the image signals from M2 and N2 and track them by comparing their envelope signals.
Using the signal of the sum of L, S and T, let's consider a so-called playback-only digital video disk on which digital video is pre-recorded, using two adjacent slopes of the groove as one set.

The shape of the signal on the slope Fl is filled with shading bits and hole-shaped bits with varying reflectance.According to the present invention, as mentioned above, it is compatible with optical video discs currently on the market, and has a high recording and playback rate. According to the present invention, the two adjacent slopes of the V-groove are used as one set of signal recording surfaces, and the recording and reproducing rate is improved compared to the conventional one. This can greatly improve the ability to record and play back high-quality information in real time.

[Brief explanation of drawings]

Fig. 1 shows the arrangement of the laser spot when the present invention is applied to the reproduction of a conventional optical video disc. Fig. 2 shows the arrangement of the laser spot. The explanation of the tracking method of the invention is shown in Fig. 3 (top). Figure 4 ζ Dia The state of the disc surface of an optical video disc is shown in Figure 5 ζ Figure 6 is a perspective view of a notch showing the structure of an optical disc with a V-groove. Figure 6 is a diagram showing the arrangement of laser spots on an optical disc. 10.11,12...Laser diode, 13-
1... Objective lens X 15... Optical disc lens 21.
23, 25... Quarter wave plate 22... Optical filter A-F... Diagonal five M, N... Photo detection plate

Claims (2)

[Claims] (1) A groove whose radial cross section is V-shaped is formed on the optical disk, and a light source that oscillates two laser beams, a first laser beam and a second laser beam, is provided, and the first laser beam is emitted into the first laser beam of the V-shaped groove. The second laser beam is focused on a slope, the second laser beam is focused on a second slope adjacent to the first slope, and the reflected lights of the first and second laser beams from the optical disk are separated and signal detected. When recording, reproducing or erasing information, the V-groove along the peak or valley located between the aperture spot centers of the first and second laser beams focused on the adjacent first and second slopes. Then, a third laser beam is focused and irradiated, and using the reflected light of this third laser beam from the optical disk,
An optical disc recording and reproducing method characterized by performing focus control or tracking control. (2) A groove whose radial cross section is V-shaped is formed on the surface, two adjacent slopes of the V-shaped groove are made into a set, and information is divided into two parts, each of which is transmitted to the adjacent An optical disc recorded on two matching slopes.