Dynamic information storage or retrieval – Binary pulse train information signal – Binary signal processing for controlling recording light...
Reexamination Certificate
2001-01-30
2002-07-30
Huber, Paul W. (Department: 2653)
Dynamic information storage or retrieval
Binary pulse train information signal
Binary signal processing for controlling recording light...
C369S047280, C369S053340
Reexamination Certificate
active
06426930
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an information recording method for forming a record mark on an optical recording medium by the heat of an optical beam and an information recording apparatus therefor, and in particular, to a method and an apparatus for recording information by a mark edge recording method.
BRIEF SUMMARY OF THE INVENTION
With the demand of increasing the informational density of optical recording media, a mark edge recording method has been used widely as a recording method in recent years. In the mark edge recording method, the edge of a record mark corresponds to “1” of binary informational data. This method is capable of recording information at a higher density than that of a mark position recording method, in which the presence and absence of a record mark correspond to “1” and “0”, respectively.
In order to realize high density recording on an optical recording medium, it is important to secure the precision of the recording control in addition to usage of the mark edge recording method. In Japanese Patent Application Laid-Open No. 3-22223 (1991), the present assignee has proposed a control method and an apparatus therefor in which a signal of laser light irradiation for forming one record mark is pulsed whereby the length and the amplitude of the series of pulses for the next mark is adjusted depending on the length of the mark non-formed portion (space). In this control method, the shape distortion in the trailing edge of a mark due to the influence of the heat of the preceding mark can be corrected. However, there have still been unsolved problems of the shape distortion in the leading edge of the mark and of the shift of edge position.
A method for resolving the problem of the positional shift of a formed mark has been proposed in Japanese Patent Application Laid-Open No. 6-84224 (1994). The method is a multi-pulse recording method in which the power of laser light for forming a mark is pulsed by modulating into three values while the power of laser light for forming spaces is modulated into two values, and in which the length of the series of pulses is adjusted depending on the mark length. In this method, the amount of heat supply of the preceding mark is adjusted depending on the length thereof, whereby the positional shift of the next mark formation is prevented. However, there has been a problem that the influence of heat caused by the length of the preceding space can not be avoided.
Further, a recording method and a recording apparatus for maintaining the constancy of the positional shift quantity of a record mark edge has been proposed in Japanese Patent Application Laid-Open No. 6-76401 (1994). In the method, the shorter preceding space causes the later timing of the next light emission, and the longer record mark causes the earlier timing of the light extinction. However, there has been a problem of incapability of recording compensation corresponding to various combinations of the mark length and the space length of a data signal.
FIG.
1
and
FIG. 2
are timing charts showing a record waveform together with the data to be recorded in accordance with a prior art.
FIG. 1
shows a multi-pulse record waveform in accordance with Japanese Patent Application Laid-Open No. 6-84224 (1994), where the power of laser light for forming marks is modulated into three values of Pa, Pw
1
, and Pw
2
, while the power of laser light for forming spaces is modulated into two values of Pa and Pr. The number of irradiated pulses sequentially increases correspondingly to record marks 2T, 3T, . . . , 8T of (1, 7) RLL modulation coding. The region from the rise point to the fall point of data to be recorded corresponds to a record mark. The timing of pulse termination of each record mark is earlier by “T/2” than the timing of the fall of data to be recorded. This comes from the consideration that the trailing edge of a record mark expands rearward due to the influence of heat.
In a magneto-optical disk having record marks formed by the record waveform shown in
FIG. 1
, the shift quantity was measured for the leading and trailing edges of the record marks. The measurement has shown a large shift quantity for short marks. Further, the measurement of random jitter for leading and trailing edges has shown the jitter of 11.2% for leading edges, 12.1% for trailing edges, and 11.7% in average. Both the jitters of leading and trailing edges exceed the jitter tolerance of 10%. It has been also found that the jitter substantially increases with decreasing shortest length of record marks. Here, in the measurement of random jitter, the standard deviation of the time difference between the edge of a record mark and the edge of a reference clock signal is detected and expressed by the ratio to the reference clock.
FIG. 2
shows a multi-pulse record waveform proposed by the present assignee. In this method, the power of laser light for forming marks is modulated into four values of Pa, Pw
1
, Pw
2
, and Pw
3
, while the power of laser light for forming spaces is modulated into two values of Pa and Pb. The number of pulses sequentially increases correspondingly to each record mark 2T, 3T, . . . , 8T of (1, 7) RLL modulation coding. The timing of pulse termination of each record mark is earlier than the timing of the fall of data to be recorded similarly to FIG.
1
.
In a magneto-optical disk having record marks formed by such a record waveform, the shift quantity was measured for the leading and trailing edges of the record marks. The measurement has shown that the shift quantity is reduced in comparison with that by the record waveform shown in FIG.
1
. That is, the measured random jitter for leading and trailing edges are 11.4% for leading edges, 10.5% for trailing edges, and 11.0% in average. The jitter of trailing edges is decreased in comparison with that by the record waveform shown in
FIG. 1
, however, the jitter values exceed the jitter tolerance.
As such, in the formation of record marks having various lengths such as 2T through 8T, there has been a limit in controlling the edge shift of each record mark only by adjusting the number of pulses and the power of laser. Further, the jitter substantially increases with decreasing shortest length of record marks. In particular, in a magnetic super-resolution medium capable of reproducing record marks having a dimension smaller than the beam spot, for example, a dimension of 0.4 &mgr;m or less, there bas been a problem of a high jitter due to the positional shift of record marks.
The present invention has been devised considering such problems. An object of the invention is to provide an information recording apparatus and an information recording method in which the pulse start timing and/or the pulse termination timing of beam light are adjusted during the recording of those permutational combinations of a space of a predetermined length and a mark of a predetermined length, whereby the positional shift quantity of leading and trailing edges is reduced even for the marks having a dimension of 0.4 &mgr;m or less, whereby the jitter is reduced.
The present assignee has obtained the following findings from the evaluation of edge shift for respective permutational combinations of spaces and marks recorded by the multi-pulse recording method described above (see FIG.
2
). For the evaluation of edge shift, the edge shift quantity was measured for both the marks recorded in a pattern-shift pattern shown in FIG.
3
A and the marks recorded in a thermal shift pattern shown in FIG.
3
B. FIG.
3
A and
FIG. 3B
are diagrams showing the record mark length and the space distance for the measurement of pattern shift and thermal shift. In the pattern-shift pattern, the space distance is kept constant and the record mark length is varied as shown in FIG.
3
A. Using this pattern, the influence of the heat of record mark formation over the trailing edge of the record mark can be observed.
FIG. 4
is a graph showing the shift quantity in the length for each conventional mark recorded in the pattern-shift pat
Kamimura Takuya
Taguchi Masakazu
Tanaka Tsutomu
Greer Burns & Crain
Huber Paul W.
LandOfFree
Information recording method and information recording... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Information recording method and information recording..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Information recording method and information recording... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2829622