JPH0419613B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an information recording and reproducing method for a recordable and reproducible optical disc.

Traditionally, the disk is pre-filled with a depth of λ/8.
A DC track groove is formed, and when the optical spot deviates from the center of the track, a tracking signal is detected using the fact that asymmetry occurs in the diffracted light due to the edges of the track groove, and this tracking signal is used to perform track tracking. A device is known in which information is recorded on a DC track groove using a laser beam modulated by an information signal during the recording. In this device, two photodetectors placed parallel to the track receive the diffracted light beam from the track groove, and a tracking signal is detected by taking the difference in output between the two photodetectors. Such a device is disclosed in Japanese Unexamined Patent Application Publication No. 1973-
No. 60702.

In this device, when the optical spot is moved by, for example, a galvanic mirror for tracking control, a tracking offset occurs in the tracking signal.
Also, when the disk is tilted, coma aberration occurs,
This coma aberration particularly disrupts the balance of the two photodetectors arranged parallel to the track, causing more track offsets to occur. This results in the disadvantage that normal track tracking cannot be performed. This tracking signal determines the structure of the DC groove on the disk, i.e. the depth, width,
It is expressed as a function of the wavelength of the light source, its distribution, and the numerical aperture of the lens.

Figure 8 shows that in the conventional device, the light spot
FIG. 7 is a diagram showing a tracking signal obtained when the DC groove is deviated from the center.

The parameters of the disk and optical system are wavelength λ =
0.82 μm, groove depth λ/8, width 0.45 μm, track pitch 1.6 μm, lens numerical aperture 0.5, distribution coefficient r ² =4, and θ=0.5°. As is clear from Figure 8, in this case the tracking offset is
It becomes 0.08 μm. Experimentally, stable tracking cannot be performed if there is an offset of 0.08 μm.

Furthermore, when reproducing a disc on which information is recorded in the DC groove at a high density, there is a drawback that tracking sensitivity is reduced and tracking offset becomes large. Moreover, in the case of the conventional recording material having DC grooves having a depth of λ/8, the selection is narrow and the range of applications is narrowed. That is, there is a drawback that the tracking signal becomes unstable due to differences in reflectance, unevenness, and refractive index of the disk.

The present invention has been made in view of these points, and solves all the problems of the above-mentioned prior art,
It is an object of the present invention to provide an information recording and reproducing method that can perform stable tracking control regardless of the recording material of a disk, and can also perform stable information recording and reproduction.

In order to achieve such an object, the present invention records synchronization pits for tracking on a disk in advance, detects a tracking signal from these synchronization pits, and uses this signal to track between the synchronization pits. It is characterized by recording an information signal on.

Embodiments of the present invention will be described below with reference to the drawings. Figure 1-a is a diagram showing the configuration of an optical system for recording and reproducing information on an optical disc.
Figure b is a diagram for explaining the principle of driving a semiconductor laser. By pulse modulating the drive current level (horizontal axis) from x ₁ to x ₂ , semiconductor lasers
It is possible to directly modulate the output level (vertical axis) of the amount of laser light from y ₁ to y ₂ . During playback, the laser light output level is set to _y1 , and during recording, the laser light output level is set to _y2 . In FIG. 1-a, 3 is a drive circuit for the semiconductor laser 4. In FIG. The light beam emitted from the laser 4 passes through a coupling lens 5, a beam splitter 6, a galver mirror 7, 1/
A disk 10 is formed by a four-wavelength plate 8 and an objective lens 9.
A light spot 11 is irradiated onto the information groove 12 of. The reflected light diffracted by the information groove 12 returns to the above-mentioned optical system again, is reflected by the beam splitter 6 due to the polarization effect of the 1/4 wavelength plate 8, and is transmitted to the 4-split photodetector 1.
The light is received at 3. FIG. 2 shows the structure of a photodetector for obtaining a tracking signal from the photodetector 13 and its signal processing circuit. In the second step, the origin of the photodetector is aligned with the optical axis of the optical system (Figure 1-a),
The X axis is set parallel to the track direction and the Y axis is set in the direction across the track, and output signals I ₁₄ ,
Take out I ₁₆ , I ₁₅ , and I ₁₇ and add the signals DF=(I ₁₄ + I ₁₅ )−(I ₁₆ +I ₁₇ ) to the addition circuits 18 and 19 and the subtraction circuit 21
A signal of RF=(I ₁₄ +I ₁₅ )−(I ₁₆ +I ₁₇ ) is created by adding circuits 18, 19, and 20.

Furthermore, the difference signal DEF=(I ₁₄ +I ₁₇ )−(I ₁₅ +I ₁₆ ) is added to the addition circuits 50 and 51 and the subtraction circuit 5.
Make it with 2.

A tracking signal is obtained by supplying the RF signal, DEF signal, and DF signal to the circuit shown in FIG.

FIG. 3 shows an example of a track recorded by the present invention. The track 12 is composed of a combination of two types of blocks A and B. Block A is a SYNC pit 24 for applying a phase lock, and a SYNC pit for determining the origin of data block B.
PATTERN Consists of 25 pits. this
SYNC pit 24 and SYNC PATTERN pit 2
5, a timing pulse train 26 is created, and using this timing pulse and the synchronization pit 27 recorded in data block B, the synchronization pit 2
7, the information pit 28 is accurately recorded. Similarly, playback is done using SYNC Pit 24 and SYNC
The origin of the timing pulse 26 and the data block B is determined by the PATTERN pit 25, and the information pit 28 and the synchronization pit 27 are distinguished and reproduced.

FIG. 4 is a circuit block diagram for obtaining a tracking signal by a synchronization pit, and FIG. 5 is a diagram for explaining its operation, and is a diagram showing the output waveforms of each block in FIG. 4. When the laser spot 11 irradiates the synchronization pit 27 on the track 12 in time series, the four-divided photodetector 14,1
Sum of signals generated from 5, 16, and 17 respectively RF=
(I ₁₄ + I ₁₅ ) + (I ₁₆ + I ₁₇ ) and difference signal DEF = (I ₁₄ + I ₁₇
)
−(I ₁₅ + I ₁₆ ) and difference signal DF = (I ₁₄ + I ₁₅ ) − (I ₁₆ +
The waveform of the RF signal 22 (I ₁₇ ) is as shown in FIG.
At the synchronization pit 27, the signal level decreases due to diffraction. DEF signal 62 is synchronized pit 2
The signal waveform has peaks at both ends of 7, and is like a differentiated RF signal. The DF signal 23 is 180 degrees depending on the direction in which the optical spot 11 is shifted from the center of the track.
A signal whose phase is inverted is obtained, and has a waveform that is zero at the center of the synchronization pit 27 and has peaks at both ends of the pit. The DEF signal 62 is differentiated by a differentiating circuit 60 to obtain an output 60'. Further, this differential output 60' is used to detect zero points 61 ⁽¹⁾ , 61 ⁽²⁾ . . . by a zero point detection circuit 61. Furthermore, the zero points 61 ⁽¹⁾ , 61 are set by the pulse circuits 31 and 32.
⁽²⁾ ..., (that is, create edge pulses 31' and 32' indicating the edge position of the synchronization pit 27, sample and hold the level of the DF signal 23 at that time in sample and hold circuits 36 and 37, and output the respective outputs 36' , 37' is generated by a subtracter 38 to obtain a tracking signal 39. This tracking signal 39 drives the galver mirror shown in FIG. On the other hand, in order to record the information pit 28 between the synchronization pits 27 with the information modulation pulse 28', the synchronization pit 27
The edge pulse 32' generated at one end of the information write timing pulse 2 is generated by the one-shot multi 35, and the information modulation pulse 2 is generated.
A timing time T ₁ to T ₂ for recording 8' is created. Furthermore, this information write timing time T ₁ −T ₂
An information modulation pulse 28' is included in the tracking signal 3.
In order to prevent disturbances from occurring in the synchronization pit 27, the sample and hold outputs 36' and 37 are held at the synchronization pit 27. For this purpose, the outputs of the sample and hold control drivers 33 and 34 are made to be zero with the write timing pulse 2, and the sample output is held.

In this way, it becomes possible to write the information pit 28 between the synchronization pits 27 while detecting the tracking signal from the synchronization pits 27.

FIG. 6 shows an example of the circuit configuration and waveforms of the sample and hold control drivers 33, 34, and 43 shown in FIG. 4, and shows a case where a NOR circuit is used.

FIG. 7 is a diagram showing the relationship between a tracking signal and a tracking deviation according to the present invention. According to this, even if the disk is tilted by 0.8 degrees, the offset is less than 0.03 μm, and stable tracking is possible.

FIG. 8 shows data for a conventional DC group with a groove depth of λ/8. Comparing FIGS. 7 and 8, it is clear that the effect of the present invention is remarkable.

As described in detail above, according to the information recording and reproducing method of the present invention, it is possible to record information on a disk at high density and read out the information recorded at high density accurately, and it is possible to This can bring about significant advances in the field of applications such as audio disks. In the present invention, the conventional λ/8 depth DC
This solves the drawback of the method of recording information in the grooves, that is, the large tracking offset when the disk is tilted. Furthermore, when playing back discs with high density information recorded in the DC groove,
It is also possible to solve the problem that tracking offset increases due to decreased tracking sensitivity. In addition, in the conventional method of forming a DC groove with a depth of λ/8, the selection of recording materials is narrow and the range of application is limited, but in the present invention, the synchronization pits are Even when recorded as a difference in refractive index, it is possible to extract a tracking signal, making it possible to select a wide range of materials.

Furthermore, since a highly accurate mechanism is not required, a very inexpensive device can be obtained.

Note that the present invention is not limited to the above-mentioned embodiments,
It goes without saying that various modifications are possible.
For example, the information grooves formed on the disk are not limited to a spiral shape, but may be concentric circles. In addition, not only a semiconductor laser but also a combination of an external modulator and a gas laser may be used to record information on the disk. Furthermore, the method of recording the synchronization detection signal on the disk recording medium is not limited to the method of the above-mentioned embodiment. Another time synchronization pulse is recorded between the synchronization pits, and this time synchronization pulse is used. It is also possible to record information without phase shift while maintaining timing.

[Brief explanation of drawings]

Figure 1-a is a diagram showing an optical system for recording and reproducing information on an optical disk, Figure 1-b is a diagram for explaining the operating principle for modulating and driving a semiconductor laser, and Figure 2 is a diagram showing an optical system for recording and reproducing information on an optical disk. Diagram showing the structure of a photodetector, 3rd
The figure shows an example of a track recorded by the present invention, FIGS. 4 and 5 show an embodiment of the present invention, and FIG. 6 shows an example of a sample and hold control driver used in the present invention. Figure 7 shows
FIG. 8 is a diagram showing the relationship between the tracking deviation and the tracking signal in the present invention and the conventional example, respectively.

Claims (1)

[Claims] 1. A recording medium in which synchronization pits provided in advance in an optically detectable form are arranged in two rows at a predetermined interval along a track, and the area between the synchronization pits is used as a recording area in which information can be recorded. , a light beam is irradiated, and a sample pulse for detecting a tracking signal samplewise is generated from the light beam modulated by the front end and the rear end of the synchronization pit using a differentiating circuit, and the sample pulse is transmitted to the front end of the synchronization pit. The first sample-hold circuit and the second pulse are divided into a first pulse corresponding to the rear end and a second pulse corresponding to the rear end.
The tracking signal is detected from the difference signal between the outputs of both sample and hold circuits by controlling the sample and hold circuits of both sample and hold circuits, and a gate signal indicating the recording area is generated from the light beam modulated by the synchronization pit. An information reproducing method characterized in that the detected tracking signal is held during a period in which a gate signal is generated, and information is recorded and reproduced in the recording area while tracking using the held tracking signal.