JP3304589B2 - Information recording method and information reproducing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for optically recording and reproducing information, and more particularly to a method for rotating a disk-shaped medium and relatively moving a recording and reproducing means in a rotating circumferential direction. The present invention relates to a method for recording and reproducing information using a phase change of a material to be used.

[0002]

2. Description of the Related Art Conventionally, there has been proposed a method of recording information in the form of a circular hole in a previously formed concave and convex pit using a phase change medium. In this method, the temperature distribution at the time of recording or erasing is sharpened by the effect of the shape of the concave and convex pits, and it is possible to record a minute mark. By this method, the position of the recording mark is determined and the density is improved by making it a minute mark. I have to. However, in this method, even though the mark shape is reduced, the size of the read spot is not different from that of the recording spot, so that the density is ultimately limited by the size of the read spot, and a significant increase in density cannot be realized. There was a problem.

[0003]

SUMMARY OF THE INVENTION An object of the present invention is to provide a method capable of achieving a higher density than a conventional recording / reproducing method by using a phase change medium.

[0004]

According to the method of the present invention, a prerecorded concave / convex mark array is provided, information is superimposed and recorded thereon, and the difference in the physical configuration (phase depth, shape) of the mark array is obtained. Recording phase change mark and complex reflectivity at erasure,
By recording and reproducing by changing the shape of the recording mark and the superposition state between the marks, information is recorded corresponding to the positional relationship between the plurality of phase change marks and the concave and convex marks, and the intensity of the reflected or transmitted light is reduced. To detect.

[0005]

According to the method of the present invention, a plurality of levels of reflected or transmitted light can be obtained depending on the difference between the physical configuration of the prerecorded mark arrangement, the optical characteristics of the recording phase change mark, and the superimposed state of the marks. Can be provided. Information can be reproduced by associating the positional relationship between the plurality of marks and the concave and convex marks and the detection level.

[0006]

FIG. 1 shows a mark arrangement according to the present invention. The previously recorded concavo-convex mark arrays 1, 2, 3, 4, and 5 have an elliptical shape having a phase depth of 1/4 of the reproduction wavelength and a width of 0.3 μm and a length of 0.15 μm. I have. These marks are arranged in a line in the traveling direction of the light spot at a repetition period of 0.6 μ. The reflectance of the recording phase change mark 6 is set to 0.2, and the optical phase amount is set to 1/4 of the reproduction wavelength. The reflectance in an unrecorded state is 1, and the phase amount is zero.

[0007] The complex reflectance of the phase change medium is n (1-jκ),
When the thickness of the medium is represented by d, n and κ depend on the reproduction wavelength. Assuming that light is perpendicularly incident on the medium from the air for simplicity, the following relationship exists between the reflectance R and the phase difference θ.

[0008]

R = [(n−1) ² + κ ² ] / [(n + 1) ² + κ ² ] (Equation 1)

[0009]

## EQU2 ## From these equations, it can be seen that the reflectance and the phase difference can be independently controlled in the phase change medium.

When the positional relationship between the recording mark and the concavo-convex mark is changed and the total amount of the reflected light transmitted through the objective lens is received by one detector, the detection signal corresponds to the movement of the spot, and the detection signal shown in FIG. To change.

First, when there is no phase change mark 6, that is, the signal of only the concave and convex marks takes a certain level as shown in FIG. When the recording mark is placed at the position of the coordinate 0 in this state, the mark 1 and the mark 6 overlap, and the waveform at that time becomes as shown in FIG. 3B, and a signal having a peak at the origin appears.

When the mark 6 is shifted by 0.15 μm, the waveform becomes (c) and the level does not change. This is presumably because the effect of the phase change and the effect of the reflectance were canceled. When the mark 6 is shifted by 0.3 μ, a downwardly convex unimodal waveform (d) having a peak at 0.3 μ is obtained. When the mark 6 is shifted by 0.45 μm, the waveform becomes (e), and the level does not change similarly to the waveform (c). When the mark 6 is shifted by 0.6 μm, the mark 3 and the mark 6 overlap, and the detected waveform becomes 0.6 as shown in FIG.
The waveform has a single peak with a peak at μ. When the mark is shifted by −0.15 and −0.3 μm, (g) and
(h), which is symmetrical with respect to the waveforms (c) and (d) and the origin.

From this embodiment, it is possible to shift the signal level to a ternary value and to shift the peak position of the signal corresponding to the mark position, at least according to the mark position. Further, information can be recorded not only by the position of the mark 6 but also by a combination of a plurality of recording marks as shown in FIG.

The reproducing wavelength used is 680 nm, and the numerical aperture of the objective lens is 0.55. According to the present invention, possible signal levels are multi-valued. As another method, information can be made to correspond not to the level but to a position shift (phase shift on a time axis) of a peak point of a detection signal from a specific position. Furthermore, regularity can be taken such that both the multilevel level and the phase change on the signal waveform. The signal recording form is as shown in FIG. FIG. 3A shows the relationship between the recording mark and the spot 100, and FIG. 3B is a cross-sectional view of the mark along the track traveling direction.

In general, a method called multi-level phase shift keying is known as a modulation method capable of maximally utilizing the information capacity that can be transmitted in a communication path having a limited band. That is, this is a method of transmitting transmission information as a change in amplitude and phase on a signal waveform. The characteristics of a normal transmission path have a large dynamic range of signal amplitude and have linear characteristics, so that a transmission waveform can be transmitted as it is.

However, the recording / reproducing characteristics of the optical disk except for the phase change medium are limited to only one type in which the recording mark changes optically, and the change width has a nonlinear response to the recording operation. Therefore, the concept of the communication channel could not be applied as it is. On the other hand, in the phase change medium, since the recording mark has a form in which the complex reflectance is changed as an optical characteristic, both the reflectance and the phase amount can be changed. According to the present invention, by controlling the phase depth of a previously recorded concavo-convex pattern, the reflectivity of a recording mark, and the amount of phase, it is possible to perform multi-level recording that cannot be realized with other optical disk media.

As a conventional multi-valued optical disc, a method using waveform interference has been mainly used. This is because the medium state has strong nonlinearity as described above, and the intermediate state cannot be stably recorded. Therefore,
The multi-value is applied to the detected waveform using the interference at the time of reproduction between the recording marks indicating one state. For this reason, the number of levels of the multi-value quantization is also about three values, and the possible dynamic range is determined by the reflectance at the time of non-recording.
N also had a limit.

However, in the present invention, first, in the phase change medium, multi-values can be formed on the detected waveform by the reflectance of the recorded mark and the shape of the recorded mark. Further, by combining the phase depth of the previously recorded concavo-convex mark and the phase amount of the phase-change recording mark, multi-leveling can be performed on the detected waveform. In addition, a multi-valued operation that cannot be realized by a conventional optical disk can be realized by a synergistic effect of the two. That is, by increasing the reflectivity of the phase change mark, the dynamic range that the signal can take can be expanded, and the S / N
Can be improved.

In order to form a recording mark on a concave / convex mark, some timing information synchronized with the concave / convex mark is required. As a method of producing this, a method of arranging pits discretely and producing a clock for recording tracking information and data from the pits can be used. A phase change mark array is recorded using a clock to be created from now on, and a recording pulse train corresponding to recording information is also created using this clock when reproducing an information mark.

[0020]

According to the present invention, compared with the conventional phase-change optical disk recording method, the S / N is not reduced,
The detection signal can be multi-valued, and the recording density can be increased without minimizing the characteristics of the detection system and the mark shape.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing a relationship between a concave and convex mark and a recording mark according to the present invention.

FIG. 2 is an explanatory diagram of a signal waveform detected from the mark arrangement of FIG. 1;

FIG. 3 is an explanatory diagram of another arrangement of recording marks and concave and convex marks according to the present invention.

────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Motoyasu Terao 1-280 Higashi Koigakubo, Kokubunji-shi, Tokyo Inside the Central Research Laboratory, Hitachi, Ltd. (56) References JP-A-5-109084 (JP, A) JP-A-4 −141828 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G11B ^7/ 00-7/013

Claims (3)

(57) [Claims] An information recording method for recording information by forming a fine light spot on a disc-shaped recording medium by using light from a light source via an optical system, comprising: an uneven mark having a repetition period recorded in advance ; Having a recording film on the irregular mark
Using a medium, write the above-mentioned mark from concave to convex
Information recording method and recording the information so that the recording mark Rokumaku are recorded superimposed. 2. A recording medium comprising: a phase change recording medium, wherein a phase depth of the concave / convex mark and a recording mark arrangement are provided.
2. The information recording method according to claim 1, wherein the information is additionally recorded so as to take a plurality of levels by changing a reflectance and a phase amount of the information. 3. A medium having a concave / convex mark having a repetition cycle recorded in advance on a disc-shaped recording medium through an optical system through a light source , and a recording film on the concave / convex mark.
The recording film from the concave to the convex of the concave and convex mark
An information reproducing method comprising: reproducing information from a medium on which information is recorded by forming a minute light spot so that the recording mark is superimposed and recorded .