Dynamic information storage or retrieval – Binary pulse train information signal – Having specific code or form generation or regeneration...
Reexamination Certificate
1998-12-08
2001-07-03
Huber, Paul W. (Department: 2651)
Dynamic information storage or retrieval
Binary pulse train information signal
Having specific code or form generation or regeneration...
C369S047510
Reexamination Certificate
active
06256277
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an information recording apparatus for injecting an energy beam into a recording medium to form a mark different in physical properties from a non-mark portion to thereby record information and particularly to an optical disk device.
Currently, generally available optical disks may be roughly classified into magneto-optical disks of the type in which a recording film is heated to form marks by means of inversion magnetic domains on the recording film, and phase-change disks of the type in which the quantity of given energy beam at the time of heating is controlled to thereby change the cooling speed of a recording film to form marks by means of amorphous regions on the recording film. In order to attain improvement in information transfer speed of these optical disks at the time of recording/reproducing operation, there are a method of increasing recording linear density and a method of increasing the scanning speed of the recording medium scanned by a light spot. Examples of the method of increasing recording linear density may include a method of shrinking/shortening mark/space length and a method of shortening the time pitch of the change of mark/space length to thereby reduce the time span for detecting the mark edge position. In such a method of increasing recording linear density, however, the signal-to-noise ratio in a reproduced signal becomes a problem. Accordingly, in the present situation, it is impossible to expect great increase of the recording linear density.
For the purpose of forming minute marks accurately on an optical disk as a first prior art, JP-A-5-298737 (laid-open on Nov. 12, 1993) discloses a method in which a recording waveform corresponding to a mark forming period is constituted by a sequence of pulses corresponding to the mark length of a recording data sequence and the number and amplitude of pulses are controlled in accordance with the length of the recording data sequence. The recording waveform of the mark forming period is divided into two parts, namely, a heat part and a tail part. The two parts are generally different in pulse height from each other. Further, in a mark non-forming period of the recording waveform, a pause part is pre-positioned to thereby generate recording auxiliary pulses. In the above first prior art, it is said that heat diffusion from a preceding mark forming portion to a mark front edge position just after the mark forming portion can be compensated by the method of the first prior art regardless of the space length so that the mark width and the mark edge position can be controlled accurately. Here, the mark forming period is representative of or corresponds to a mark length in a recording data sequence, and is defined as a period from the leading edge of the first one of pulses having an energy level for supplying recording energy required for formation of a single mark, that is, pulses having such an energy level that any mark cannot be formed if the energy level is not generated, to the trailing edge of the last pulse, as shown in FIG.
3
. Further, the mark non-forming period is representative of or corresponds to a space length in a recording data sequence, and is defined as a period except the mark forming period. The above definition is common to the whole description in this specification.
Further, as a second prior art, JP-A-8-7277 (laid-open on Jan. 12, 1996) discloses a method in which each recording data is decomposed into a plurality of basic elements different in length from each other so that one recording pulse corresponds to one element, and each recording data is formed as a series of independent recording marks recorded by corresponding element pulses. In the second prior art, it is said that not only the lowering of the reproduced signal level can be prevented but also recording can be performed stably also in a modulation system including long marks even if independent marks are recorded by the disclosed method. Further, it is said that increase of jitter in a reproduced signal after repetition of rewriting can be suppressed in a rewritable type recording medium.
Further, as a third prior art, JP-A-9-134525 (laid-open on Oct. 22, 1986) discloses a method in which the pulse width of succeeding heating pulses and succeeding cooling pulses is selected to be substantially equal to a recording channel clock period in the case where an even-number or odd-number mark length with respect to the recording channel clock period is recorded in a multi-pulse recording system using a head heating pulse, succeeding heating pulses, succeeding cooling pulses and a tail cooling pulse. In the third prior art reference, it is said that the cooling time of the recording medium can be secured sufficiently so that accurate edge position control can be made by the disclosed method.
As other prior art references as for waveform control, there are JP-A-55-139693 (laid-open on Oct. 31, 1980), JP-A-61-237233 (laid-open on Oct. 22, 1986), etc.
SUMMARY OF THE INVENTION
In the first prior art, one recording pulse corresponds to an extension of marks corresponding to the detection window width. Accordingly, when the detection window width is shortened, the semiconductor laser diode which is a recording energy generating source is required to be driven at a higher speed than the conventional speed. For example, when a general (1, 7) modulation system is used to achieve a burst transfer rate of 10 MBytes/sec equivalent to that of a magnetic disk device, the detection window width in a reproduced signal becomes about 8.3 ns and, accordingly, the shortest recording current pulse width becomes about 4.2 ns which is about half the detection window width. It is, however, difficult to generate recording light pulses accurately because the time of the order of several nano seconds is required for starting of the semiconductor laser. Even if recording light pulses can be generated accurately, normal mark formation cannot be made because the next light pulse is radiated while the heated portion is not yet cooled sufficiently in the case where multi-pulse recording is applied to a medium such as a phase-change disk in which mark formation is controlled on the basis of the cooling speed of the heated portion. For example, when a (1, 7) modulation system is used to achieve a burst transfer rate of 10 MBytes/sec as described above, marks cannot be formed correctly in accordance with the characteristic of the recording medium because the cooling time of the recording medium becomes about 4.2 ns which is equal to the shortest recording current pulse width.
In the second prior art, there is disclosed a method in which each recording data is decomposed into a plurality of basic elements different in length from each other so that one recording pulse corresponds to one element, and each recording data is formed as a series of independent recording marks recorded by means of recording pulses. In the second prior art, however, thermal balance between recording pulses corresponding to elements is not taken into consideration, so that a problem arises in mark edge position control as recording linear density increases. That is, when marks corresponding to one recording data are to be formed, the recording mark width varies in accordance with the position so that accurate edge recording cannot be performed because the quantity of heat accumulated in the recording film in the head part of the recording data is different from the quantity of heat accumulated in the recording film in the tail part of the recording data.
In the third prior art, there is a case where a considerably shorter pulse than the detection window width is inserted into the recording waveform in the vicinity of the intermediate part of the mark forming period so that the mark width varies in the vicinity of the intermediate part of the mark forming period more greatly than in the other parts. In the description of the third prior art reference, it is said that the variation of the signal amplitude in the intermediate part
Saga Hideki
Sukeda Hirofumi
Antonelli Terry Stout & Kraus LLP
Htiachi Ltd.
Huber Paul W.
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