Dynamic information storage or retrieval – Binary pulse train information signal – Binary signal processing for controlling recording light...
Reexamination Certificate
2000-01-28
2003-01-21
Davis, David (Department: 2652)
Dynamic information storage or retrieval
Binary pulse train information signal
Binary signal processing for controlling recording light...
C369S047530
Reexamination Certificate
active
06510116
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical information recording/reproducing method and an optical information recording/reproducing apparatus for recording data on an erasable type optical disk by a mark edge recording method, and more particularly to recording compensation for accurately controlling an edge position of a recording mark.
2. Description of the Related Art
The development of an optical information recording medium which can record and reproduce such information signals as video and audio signals, particularly optical disks, is active. One optical disk media which can record information at high density is a phase change type optical disk. Data is recorded on a phase change type optical disk by emitting a laser beam narrowed down to a 1 &mgr;m or less diameter on a rotating disk, so as to heat and fuse the recording film. Depending on the strength of the recording light beam, the temperature on the recording film when the beam reaches the disk and the cooling process differ, and a phase change of the recording film occurs between the crystal state and amorphous state.
When the light beam is strong (called “peak power level”), the recording film becomes amorphous since the recording film is heated beyond the fusing point, fuses, then rapidly cools down. When the light beam is at medium strength (called “bias power level”), the recording film is crystallized since the recording film is maintained at a temperature higher than the crystallization temperature but is lower than the fusing point. The amorphous part is called a “mark”, and the crystallized part is called a “space”. The method of recording data by assigning information to the length of the mark and space is called the “mark edge recording method”. Since a phase change optical disk can create marks by fusing the recording film at a peak power level, whether the recording film is in an amorphous state or crystal state, simultaneously erasing old data and recording new data using one light beam, that is, direct overwriting, is possible.
However, when a long mark is recorded by mark edge recording, if a light beam at peak power level is emitted to the mark part at a predetermined intensity, the width of the mark becomes gradually wider toward the end of the mark, since heat accumulates on the recording film. This causes signal quality deterioration, such as incomplete erasure, during direct overwriting. To prevent this, recording marks by a light beam which switches alternately between peak power level and bias power level at high-speed between mark blocks, that is, multi-pulse recording, is effective. By this method, the heat accumulating effect at the latter half of a mark subsides, and a mark with a predetermined width from start to end can be created.
For reproducing, a light beam which is weak enough not to cause a phase change of the recording film is emitted, and the intensity of the reflected light is detected by a photo-detector. Since the reflectance of the mark part, which is amorphous, can be significantly different from the reflectance of the space part, which is crystallized, by choosing the material of the recording film and the configuration of the recording film and the protective layer, reproducing signals of the recorded data can be obtained by detecting the difference of the reflected light intensity between the mark part and the space part.
A possible way to improve the recording density of the phase change type optical disk is to decrease the length of the mark and the space to be recorded. If a space length is short, however, the heat at the end edge of the recorded mark conducts through the space part and affects the temperature rising at the start edge of the next mark, or the heat at the start edge of the mark recorded next affects the cooling process at the end edge of the previous mark, that is, thermal interference occurs. As a result, the edge position of the mark changes, and the data error rate at reproduction increases. This phenomena will be described with reference to FIGS.
9
(
a
) to (
e
). FIG.
9
(
a
) is a waveform diagram where the recording data is shown in binary, (b) is a waveform diagram indicating the intensity of laser beam emission in binary, where one mark corresponds to a plurality of short pulses, as mentioned above. (c) is an illustration of recording marks created on the disk, (d) is a waveform diagram of the reproducing signals of the recording mark in (c), and (e) is a waveform diagram when the reproducing signals are binarized. In FIGS.
9
(
a
) to (
e
), a case where a short space is before and after a long mark is shown as a characteristic example of the influence of thermal interference. If the start and end edges of the emission pulses in (b) are placed at the same positional relationship as the start and end edges of the recording data in (a), the start and end edges of the recording mark extend as shown in (c), regardless of the length of spaces before and after. In FIGS.
9
(
a
) to (
e
), the amount of shift at the front edge and rear edge of the mark at the center are denoted by Es
1
and Es
2
. As a result, the mark block becomes longer than the desired length, as shown in FIG.
9
(
d
), and an edge shift occurs when the waveform is binarized, as shown in FIG.
9
(
e
).
The amount of fluctuation of the edge position due to the thermal interference differs depending on the length of the space before and after the target mark. Therefore, to solve this problem, Japanese Patent Application Laid-Open No. S63-48617 discloses a technology to compensate for the fluctuation of the edge position due to thermal interference by changing the start edge position of the recording pulse of the mark part in advance according to the length of the space before the mark. The amount of change of the start edge position is determined by recording a test pattern comprised of a plurality of combinations of marks and spaces of different lengths in advance, reproducing the test pattern, and measuring the deviation between the edge positions of the reproducing signals and the target values.
FIG. 10
shows an example of a test pattern. The pattern of the test pattern is different depending on the data modulation system, but includes at least the shortest mark and space and the longest mark and space which become the references for measuring edge positions. If it is assumed that the channel bit length to be the unit of length of marks and spaces is T, then the shortest channel bit length of recording data is 3T, and the longest is 11T in the case of 8-16 modulation. For example, the edge interval from the reference mark (11T) in the reproducing signal is different between a case where the length of the subsequent space of the 3T target mark is 3T and a case where the length is 11T. A method of compensating for the edge shift with a deviation amount determined by recording such test pattern will be described with reference to FIGS.
11
(
a
) to (
e
). FIGS.
11
(
a
) to (
e
) show the recording data, laser emission signal, recording marks, reproducing signal and binary signal respectively, just like FIG.
10
. Edge compensation is executed by shifting the front edge pulse and rear edge pulse of the laser emission signal by Es
1
′ and Es
2
′ corresponding to the above mentioned shift amounts Es
1
and Es
2
, as shown in FIG.
11
(
b
). In this way, a desired length of marks can be recorded as shown in FIGS.
11
(
c
) to (
e
), which can prevent data reproducing errors.
With such a conventional optical information recording/reproducing method and optical information recording/reproducing apparatus, however, the fluctuation of the edge position of reproducing data can be decreased when reproducing data with the same apparatus as the apparatus which recorded the data, but if the data is reproduced with an apparatus which is different from the apparatus which recorded the data, the fluctuation of the edge position increases, influenced by the laser spot shapes of recording and reproducing, the characteristic ir
Furumiya Shigeru
Ishida Takashi
Koishi Kenji
Minamino Jun-ichi
Miyagawa Naoyasu
Davis David
Dolan Jennifer M
Matsushita Electric - Industrial Co., Ltd.
Wenderoth , Lind & Ponack, L.L.P.
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