JPS58215735A - Optical disc recording method - Google Patents

Abstract

PURPOSE:To increase the amount of recorded information, by using a recording medium capable of changing the depth of pits depending on the amount of exposure for attaining multi-valued digital recording of ternary or more. CONSTITUTION:Laser light from a laser generator 1 is condensed on a recording layer 10 of a disc 9 via a mirror 2, an optical modulator 3, a mirror 5, a lens 6, a mirror 7, and an objective lens 8. The depth of pits is changed for the recording layer with the amount of exposure, allowing to record multi-valued digital signals of ternary or more. Thus, the amount of recorded information is increased in comparison with the recording of binary digital signals.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an optical disc recording method that performs digital multilevel recording.

Conventionally, when recording a digital signal on a recording medium made of photoresist using a laser beam, the digital signal is recorded at a low level (θ) and a high level (1) as shown in FIG. 1A. Was. This invention 1a,
0. It is possible to record a 3-value digital signal of /, 2 (Figure 1B), a + value digital signal (Figure 1C), and a 3-value digital signal (Figure 1D). .

In this way, in contrast to the case where the Aog, n value is recorded by recording the n value of three or more values, (Aog, n
) can transmit twice the amount of information. In the case of 3 values, i, sg times, in the case of da value, 1 time, in the case of S value, 2.3
It is possible to transmit twice the amount of information.

Generally, in order to record and reproduce high-quality digital video signals on an optical disc, a data transfer rate of 30 to 100 sq. dollars is required. Conventional optical discs on which analog video signals are recorded are rotated at 1 goorpm, but in this case it is difficult to achieve the above-mentioned data transfer rate.

Therefore, it is conceivable to form multi-tracks to substantially lower the transfer rate. However, in this case, it is unavoidable that the recording/reproducing time becomes shorter. The present invention is suitable for use in recording digital video signals since it is possible to increase the amount of recorded information as described above.

FIG. 2 shows an example of a recording device in which the present invention is implemented. The light is supplied to an optical modulator 3 using an acousto-optic effect. A recording signal is supplied to this optical modulator 3 from a terminal 4 . The optical path of the output light from the optical modulator 3 is changed by a mirror 5, the optical path is changed by a lens 6, the optical path is changed by a mirror 7, and the output light is irradiated onto a recording layer 10 of a disk 9 via an objective lens 8. Ru.

The disk 9 is rotated by a spindle motor 12 at a predetermined angular velocity. Further, the recording layer 10 is coated on a glass substrate 11, and pits are formed in the recording layer 10 with a depth corresponding to the amount of exposure. For example, a positive photoresist is used as the recording layer 10, and pits can be formed by developing after exposure.

FIG. 3 shows the relationship between the exposure level L of this recording layer (photoresist) 10 and the depth D of the pits formed, t
is the coating thickness of the recording layer 10. The exposure level L means the energy given to the recording layer 10 at the linear velocity of the disk 9/mm km.

As an example, when a triangular wave recording signal as shown in FIG. A laser beam whose exposure energy changes in a slightly rounded manner is generated. In FIG.
In LZ, pits formed in the recording layer 10 are formed on the glass substrate 1.
It shows the exposure energy that reaches the depth up to the 10th plane K.

Therefore, as shown in FIG.
Finally, an inclined portion having a width approximately equal to the diameter of the recording beam spot is formed, and a hole with a depth reaching the surface of the glass substrate 11 is formed in a range where the exposure energy is 2 or more. . Figure C shows the plane and cross section of this pit consisting of the slope and the hole.

The coating thickness t of the recording layer 10 is selected based on the value of the reproduction laser. This is also true when a disk with an aluminum reflective film on the surface is produced using this disk 9 as a master disk. In this way, the depth of the pit is selected, so when reading the pit, the laser beam reflected by the pit,
The surrounding lands cancel each other out, and no playback output is generated. Furthermore, when all the spots of the laser beam for reproduction are irradiated onto the land, the reflected light is not an in-phase component and a reproduction output is generated. Therefore, when a disk having pits in the shape shown in Figure C are formed on the reflective surface is reproduced, a reproduced signal having a waveform as shown in Figure I) is obtained.

As described above, when a triangular wave signal is recorded and reproduced, a reproduced signal having a slope similar to that of the recorded signal is obtained. This slope is caused by the presence of a slope between the land and the pit and by the change in the width of the pit. By utilizing this fact, multi-value recording can be performed.

- For example, when performing ternary recording, in the characteristics shown in Fig. 3, the center Lb of the region where the exposure energy and the depth D of the formed pit are approximately proportional is set as the bias center of the exposure energy, and this is the bias center of the exposure energy. This generates exposure energy that can form deep pits and lands. FIG. sA shows an example of a ternary recording signal. The above-mentioned exposure energy L corresponds to the center value V of this recording signal.
b A laser beam is generated and the level is low. Correspondingly, generation of the laser beam is stopped, or a laser beam is generated with exposure energy that does not reach the threshold L1 (see Figure q, B), and LZ (Qth
(See Figure B) A laser beam with an exposure energy of more than 100% is generated. Therefore, the recording layer 10 of the disc 9 has a recording signal . A land is formed in the section , an intermediate pit is formed in the section vl of the recording signal, and a deep pit is formed in the section v2 of the recording signal. Further, although not shown in the drawings, since the photoresistor has a good S/N ratio, it is possible to record a digital signal of the S value by precisely controlling the exposure energy and process.

As understood from the above explanation, according to this invention,
Multivalued digital signals of three or more values can be recorded on an optical disc. Therefore, there is an advantage that the amount of recorded information can be increased compared to the conventional method of recording a digital signal of 0.

Note that the present invention may be applied to a case where Y signal tracks are simultaneously formed using Y recording laser beams.

[Brief explanation of the drawing]

FIG. 1 is a waveform diagram of a digital signal from A value to S value, FIG. 2 is a route diagram showing the configuration of an optical system of a recording device to which this invention can be applied, and FIG. 3 is a diagram of a recording layer to which this invention can be applied. A route map showing an example of the characteristics, Figure Q and Figure S are route maps used to explain the present invention. 1... Laser generator, 3...
・・・・・・・・・Light modulator, 8・・・・・・・・・・・・
...Objective lens, 9........Disc, 10........Recording layer, 11...
......Glass substrate. Agent Tadashi Sugiura Tomo 3rd Plan 4th t→- Figure 5

Claims (1)

[Claims] An optical disc recording method characterized by performing digital multi-value recording of three or more values using a recording medium in which the depth of a pit can be changed depending on the amount of exposure.