Dynamic information storage or retrieval – Binary pulse train information signal – Format arrangement processing for auxiliary information
Reexamination Certificate
2001-09-14
2003-02-18
Tran, Thang V. (Department: 2653)
Dynamic information storage or retrieval
Binary pulse train information signal
Format arrangement processing for auxiliary information
C369S047230
Reexamination Certificate
active
06522612
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a method and an apparatus for recording information on an information recording medium by directing an energy beam to the medium to melt its recording film, and to the information recording medium used by the method. More particularly, the present invention relates to a method and an apparatus for recording information on phase change disks such as a DVD-RAM and a DVD-RW, and to an information recording medium used for the method.
In the description of the present invention, the information recording medium described above is mentioned as a phase change optical disk or simply as an optical disk. However, the present invention applies to any information recording medium on which information is recorded by directing an energy beam to the medium to heat and melt its recording film in order to change the atomic arrangement. Therefore, regardless of the shape of an information recording medium, the present invention is applicable also to a method and an apparatus for recording information on non-circular information recording media such as an optical card, and to an information recording medium used for the method.
In addition, the energy beam described above is sometimes mentioned simply as a laser beam or as a light. However, any energy beam capable of generating heat on an information recording medium to melt its recording medium may be used in the present invention as described above. Furthermore, although a red laser (645 nm to 660 nm of wave-length) is used in the method and the apparatus according to the present invention, the present invention is applicable also to a high-density optical disk using a relatively shorter wavelength laser, such as a blue laser and a purple laser.
Recently, phase change optical disks such as a 2.6 GB DVD-RAM, capable of reproducing information from reproduction-only optical disks such as a DVD-ROM or DVD-Video, have been placed on the market. However, the 2.6 GB DVD-RAM does not respond sufficiently to the consumer's needs in the recording capacity. This raises expectations for a 4.7 GB DVD-RAM or a 4.7 GB DVD-RW. That is, these phase change optical disks, equivalent to a DVD-Video in recording capacity, are available for use as video recording optical disks that will replace VTRs.
However, it has been pointed out that the recording by the phase-change recording method, if repeated several thousands to scores of thousands times, would degrade the reproduced signal and prevent information from being reproduced correctly (see JP-A-10-49872 disclosed on Feb. 20, 1998). The phase change recording method melts the recording film during information recording. This means that the viscosity of the melted area of the recording film decreases and that the recording film flows in some direction. This also changes the thickness in some areas in the recording film. The central level of the reproduced signal and the amplitude depend largely on the thickness of the recording film. As a result, a degradation that depends upon the thickness of the recording film occurs in the reproduced signal, causing jitters.
To solve this problem, two information recording methods have been devised (Both are described in JP-A-10-49872 described above).
One method is to shift the information recording start position by about eight bytes randomly each time information is recorded in each sector. This method shifts each two consecutive melting parts by at least eight bytes even if the same pattern information is recorded and therefore minimizes the amount of recording film flow described above. The other method is to reverse the polarity of recorded information each time information is recorded in each sector. The optical disk system described above employs the mark edge recording method. This mark edge recording method records marks (parts melted by a high-power pulse train), each having its own length, and spaces (parts created by directing a relatively low-power energy to mark-recorded parts to change them to crystallized parts) and associates the edge positions (both ends) of each mark with information. Unless the relative positions of the edges change, this method retains information even if marks and spaces are reversed. Therefore, even if the polarity is changed alternately, no problem is generated. The method repeats the cycle in which melted parts are crystallized the next time information is recorded, thus minimizing the deterioration in the reproduced signal caused by the recording film flow.
The two methods described above, which are very excellent technologies, are employed as the standard of the 2.6 GB DVD-RAM and the 4.7 GB DVD-RAM.
SUMMARY OF THE INVENTION
The prior art methods described above are very excellent. As a matter of fact, recording the same pattern of information on a 2.6 GB DVD-RAM in the method described above, if repeated about 100,000 times, gives the practically usable reproduced-signal quality. However, recording the same pattern of information on a 4.7 GB DVD-RAM in the method described above, if repeated several thousand times, results in 15% or higher jitters in the reproduced signal, possibly giving practical inconvenience. The investigation made by the inventor and the colleagues reveals at least two causes for this problem. One cause is that the amplitude of the signal reproduced from the shortest mark on the 4.7 GB DVD-RAM is 10 dB or lower than that of the 2.6 GB DVD-RAM. This is because the shortest mark of the 2.6 GB DVD-RAM is about 0.6 microns and the shortest mark of the 4.7 GB DVD-RAM is about 0.42 microns, about ⅔ times shorter than that of the 2.6 GB DVD-RAM. As a result, when the thickness of the recording film changes as described above, the central amplitude level of the reproduced signal and the variation in the amplitude largely exceed the allowable range on a relative basis.
Another cause is that, even if one of the above two methods is used, one sector may include a part which is thicker or thinner than the allowable range. A careful study indicates that the flow direction of the recording film depends on the length of a recorded mark. That is, in part A, which is a part of the mark strings of a recording pattern (mark-space arrangement in one sector) in a sector, where there are many 3T marks, the recording film flows in the beginning-to-end direction of the sector. On the other hand, in part B where there are many 4T-14T marks, the recording film flows in the end-to-beginning direction in contract to the part where there are many 3T marks. As a result, depending upon the positional relation between part A and part B, the thickness of the recording film exceeds the allowable range (becomes thick or thin) in the boundary between part A and part B.
Therefore, it is a first object of the present invention to provide an information recording method and an information recording apparatus, as well as an information recording medium, that do not generate an area where the thickness of the recording film does not exceed the allowable range and that minimizes the change in the central amplitude level of the reproduced signal and in the amplitude of the reproduced signal even if information is re-written more than tens of thousands times.
In addition, even if the above problem is solved, the thickness of the recording film may exceed the allowable range in the beginning and end of a sector and that part of the sector may largely degrade the reproduced signal. This condition occurs when the recording film flow may be suppressed partially but not in the whole sector. That is, when there is an average recording film flow in the whole sector (the amount of beginning-to-end direction flow of a sector does not match that of the opposite direction flow), the thickness of the recording film exceeds the allowable range in a part near the beginning or the end of the sector.
Therefore, it is a second object of the present invention to provide an information recording method and an information recording apparatus, as well as an information recording medium, that do not
Ikeda Tetsuya
Minemura Hiroyuki
Miyamoto Harukazu
Miyamoto Makoto
Shigematsu Kazuo
Hitachi , Ltd.
Mattingly Stanger & Malur, P.C.
Tran Thang V.
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