Dynamic information storage or retrieval – Storage medium structure – Optical track structure
Reexamination Certificate
1997-09-08
2001-06-26
Hindi, Nabil (Department: 2651)
Dynamic information storage or retrieval
Storage medium structure
Optical track structure
C369S053330
Reexamination Certificate
active
06252844
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to an optical recording medium capable of recording data thereinto or reproducing data therefrom, and more particularly to an optical recording medium suitable for carrying out so-called “simultaneous recording and verification” where confirmation as to whether data is properly recorded is carried out concurrently with recording data into a medium. The invention also relates to a method of optically recording data into an optical recording medium and reproducing data therefrom.
2. Description of the Related Art
As one of optical disc mediums capable of recording data thereinto and reproducing data therefrom both by radiating laser beam spot thereto is known a phase-change type optical disc. The phase-change type optical disc is capable of carrying out over-recording by a single beam, which is difficult to carry out by a magneto-optical (MO) disc. An optical head system for the phase-change optical disc is simpler than that for the MO disc.
A method of carrying out simultaneous recording and verification in such a phase-change type recording medium has been suggested in Japanese Unexamined Patent Publications Nos. 60-145537, 63-183624, and 6-349067. According to these Publications, when pulse beams are radiated onto the phase-change type recording medium, an intensity of reflected beams is varied almost at the same with the radiation. The suggested methods make it possible to confirm whether data is properly recorded by detecting the variation in the reflected beams by means of either the reflected beams itself or RF signals.
Roughly speaking, data is recorded into a phase-change type optical disc medium by the following steps: radiating laser beams onto a non-recorded region, which is in crystal condition, to thereby heat a recording layer; a temperature of the recording layer being raised; melting of the recording layer; and cooling down the recording layer to thereby reduce the recording layer amorphous. Hence, non-recorded and recorded regions have different phase conditions, and as a result, non-recorded and recorded regions have different reflectivity. Accordingly, an intensity of reflected laser beams is varied in accordance with the phase condition. A phase-change type optical disc medium utilizes such variation in an intensity of reflected laser beams for recording data thereinto.
It is known that a recording layer becomes as illustrated in
FIG. 1
, when a recording layer is molten by a laser beam spot. Thus, all regions of a recording layer are not always molten in a beam spot, even if a laser beam is radiated onto the recording layer. Herein, the molten region
60
corresponds to a region in which data is recorded, and the non-molten region
62
corresponds to a region in which data is not recorded yet. As mentioned earlier, the molten region
60
becomes amorphous when cooled down, whereas the non-molten region
62
remains crystal. If a recording layer is not molten, the recording layer is not reduced amorphous. In the beam spot, reflectivity of the recorded or amorphous region
60
coexists together with reflectivity of the non-recorded or crystal region
62
, and hence it would be quite difficult to clearly distinguish the recorded region
60
from the non-recorded region
62
. As a result, it would be difficult to accurately carry out simultaneous recording and verification only based on variation in the reflectivity. Hence, verification has to be carried out again after data has been recorded into a phase-change type optical disc medium in the above mentioned conventional mediums. As a result, it is substantially impossible to carry out simultaneous recording and verification in the conventional mediums.
In addition, in the conventional mediums where the recorded region has to have reflectivity quite different from that of the non-recorded region, there would be generated a large fluctuation in RF signals in over-recording, resulting in unstable verification together with reduction in reliability.
SUMMARY OF THE INVENTION
In view of the foregoing problems of the conventional recording mediums, it is an object of the present invention to provide a phase-change type optical recording medium which is capable of accurately carrying out simultaneous recording and verification, specifically carrying out verification by which it is confirmed whether data is properly recorded both in initial recording and over-recording.
Another object of the present invention is to provide a phase-change type optical recording medium which is capable of carrying out verification with high accuracy in smaller period of time to thereby make it possible to record data with higher reliability.
It is also an object of the present invention to provide a method of optically recording data by employing the above mentioned phase-change type optical recording medium.
In one aspect, there is provided a phase-change type optical recording medium, including (a) a substrate, (b) a recording layer formed on the substrate, phase condition of the recording layer being changed when a laser beam is radiated thereonto, to thereby record, erase or reproduce data into or from the recording layer, and (c) a reflection layer formed on the recording layer for reflecting a laser beam having been radiated onto the recording layer. The recording layer is formed so that the following equation (A) is established:
Rc>Rm>Ra (A)
wherein Rc indicates a reflectivity to be obtained when the recording layer is in crystal condition, Ra indicates a reflectivity to be obtained when the recording layer is in amorphous condition, and Rm indicates a reflectivity to be obtained when the recording layer is in mixed condition of molten condition and crystal or amorphous condition.
By arranging the recording layer to have a thickness such that the above mentioned equation (A) is established, it is possible to have recording sensitivity suitable for recording data into and reproduce data from an optical recording medium, and accomplish simultaneous recording and verification. In addition, the phase-change type optical recording medium is capable of providing high reproducing output, being accessible at a higher speed, and recording data at a higher density.
There is further provided a phase-change type optical recording medium, including (a) a substrate, (b) a recording layer formed on the substrate, phase condition of the recording layer being changed when a laser beam is radiated thereonto, to thereby record, erase or reproduce data into or from the recording layer, and (c) a reflection layer formed on the recording layer for reflecting a laser beam having been radiated onto the recording layer. The recording layer is formed so that the following equation (B) is established:
|
Rc−Ra|≦
5%
Rc>Rm, Ra>Rm (B)
wherein Rc indicates a reflectivity to be obtained when the recording layer is in crystal condition, Ra indicates a reflectivity to be obtained when the recording layer is in amorphous condition, and Rm indicates a reflectivity to be obtained when the recording layer is in mixed condition of molten condition and crystal or amorphous condition.
Since the above mentioned equation (B) includes reflectivity in the laser beam spot as one of standards for judgement, it is surely confirmed as to whether the recording layer has a molten or recorded region in the laser beam spot by means of the phase-change type optical recording medium meeting the equation (B). Thus, it is possible to carry out verification while data is being recorded into the phase-change type optical recording medium.
For instance, if verification is to be carried out by employing RF signals obtained from reflected laser beams, it would be possible to obtain clearly distinguishable RF waveforms between when data is properly recorded and when data is not properly recorded. In addition, since RF waveforms obtained when data is properly recorded is stable, precise verification can be carried out. Furthermore, since a difference between
Hayes Soloway Hennessey Grossman & Hage PC
Hindi Nabil
NEC Corporation
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