Optical disk device using a recording medium structurally...

Details Optical disk device using a recording medium structurally... Optical disk device using a recording medium structurally...

2002-02-25

2003-04-08

Dinh, Tan (Department: 2653)

Dynamic information storage or retrieval

Storage or retrieval by simultaneous application of diverse...

Magnetic field and light beam

C369S047530

Reexamination Certificate

active

06545954

ABSTRACT:

TECHNICAL FIELD
The present invention relates to an information recording/reproducing apparatus for recording or reproducing information on or from an optical recording medium, and more particularly to a method and an apparatus for realizing high density recording/reproducing by applying a magnetic field modulation magnetooptical recording method to an optical disk.
BACKGROUND ART
A magnetic field modulation magnetooptical recording/reproducing method has been known conventionally as a technique of making an optical disk highly dense.
As one example of conventional techniques, a consecutive light pulse irradiation and magnetic field modulation method described in JP-A-1-292603 and applied to an optical disk drive will be described. With this disk drive, clock signals are obtained from a preformatted clock pit train on an optical disk of a sample-servo format.
As shown in
FIG. 8
, while high output light pulses
802
synchronizing with clock signals
801
are irradiated, modulation magnetic fields
808
corresponding to data
803
are applied synchronously with the light pulses
802
to form magnetic domains
804
. During the reproduction, the data
803
is detected by using the same clock signals
801
. The characteristic feature of this method resides in that the edge distance
807
of the magnetic domain
805
recorded with too large a power is the same as the edge distance
807
of the magnetic domain
804
recorded with too small a power, irrespective of their different recording powers. It is therefore possible to record/reproduce always at a constant edge distance
807
and is suitable for high bit density recording/reproducing.
A second conventional example as a means for solving a recording medium sensitivity fluctuation problem associated with light modulation edge recording will be described with reference to JP-A-4-61028. According to the second conventional example, a recording medium is provided with a trial writing area at a predetermined position and a trial writing pattern is actually recorded in this trial writing area. By evaluating a signal reproduced from this trial area, optimization of a recording power level is performed.
FIG. 7
shows an example of the structure necessary for evaluating a reproduction signal for the optimization of recording conditions according to the second conventional example.
As shown in
FIG. 7
at (a), a combination of two shortest/longest recording mark/gap repetition patterns determined from a recording modulation method is used as a trial writing pattern. If a (1,7) modulation method is used as a coding method, the lengths of shortest/longest recording mark/gap are 2 Tw and 8 Tw respectively (Tw is a channel bit length, i.e., a shortest change length of a recording mark, i.e., a detection window width). If the bit length of the recording code train is 0.53 microns, the longest mark/gap length is 3.0 microns. If the laser wavelength is 780 nm and the lens NA is 0.55, the amplitude of a signal reproduced from the repetition pattern (hereinafter called “coarsest pattern”) of the longest recording mark/gap (each 8 Tw long) is generally determined only by the width of the recording mark, and the positions of leading and trailing edges of a signal correspond to the edge positions. On the other hand, the amplitude of a signal reproduced from the repetition pattern (hereinafter called “densest pattern”) of the shortest recording mark/gap (each 2 Tw long) is smaller than the coarsest pattern because the recording mark/gap length is generally equal to a half the diameter of the reproduction light spot. The center level of the reproduction signal amplitude shifts toward the recording mark because of optical interference of the preceding and succeeding recording marks. This shift amount is influenced by both the length and width of the recording mark. The longer and wider the recording mark, the larger the shift amount. From the above consideration, the recording control has been performed so that the width of the recording mark becomes generally constant irrespective of the recording mark length, and the recording power level has been optimized by making the amplitude center level determined by the recording mark/gap (e.g., coarsest pattern) sufficiently longer than the diameter of the reproduction light spot become coincident with the reproduction signal center level of the densest pattern.
In the structure shown in
FIG. 7
at (d) and disclosed in the above-cited publication, the center level of the amplitude of a signal reproduced from the densest/coarsest pattern is obtained as an average value of signal levels representative of the upper and lower envelopes. The peak and bottom levels of the reproduction signal
701
of the densest pattern are held by peak and bottom holding circuits
704
and
705
, and the average level of the peak and bottom levels is held by a sample-hold circuit
707
by using a densest pattern detection gate
702
as a trigger. Similarly, the average level of a reproduction signal of the coarsest pattern is held by a sample-hold circuit
706
by using a coarsest pattern detection gate
703
as a trigger. A difference (V
1
−V
2
) between the two average levels is calculated by a differential amplifier circuit
708
to obtain a reproduction signal evaluation result signal
713
(&Dgr;V signal: &Dgr;V=V
1
−V
2
). The center level of a signal reproduced from the coarsest pattern changes scarcely even if the recording conditions shift more or less from the optimum conditions and recording mark/gap lengths are unbalanced more or less.
The structure shown in
FIG. 7
at (e) is also disclosed in the above-cited publication as a method of evaluating the recording conditions from a reproduction signal. By using a low-pass filter
709
having a cut-off frequency lower than the frequency of a reproduction signal of the coarsest pattern, signal levels of the densest/coarsest patterns are sampled and held to form a reproduction signal evaluation result signal
714
(&Dgr;V signal). The recording power has been optimized by setting the recording power level so that &Dgr;V becomes 0. In this manner, recording can be performed always with generally a constant magnetic domain width.
FIG. 9
is a flow chart illustrating a basic sequence of the recording condition optimizing operation of the second conventional example. In this example, it is assumed that the recording medium is an optical disk and the trial writing pattern is a densest/coarsest pattern. When the recording condition optimizing operation starts, a trial writing area provided on a recording medium at a predetermined position is erased to prepare for the next writing operation. As the writing operation starts, a predetermined writing pattern is recorded on the recording medium under different recording conditions for each recording area (e.g., sector) which is the unit of recording management of the recording medium. After the recording operation is finished, the reproduction signal of each recording area is evaluated to determine the recording conditions most suitable for the optimum recording conditions. Since the recording conditions are different in the radial direction of the recording medium, the above recording operation is performed at proper radial positions of the recording medium (e.g., inner circumferential area, middle circumferential area, outer circumferential area, or each recording zone) to complete the trial writing operation.
DISCLOSURE OF INVENTION
High speed and high integration of external storage devices or the like of computers have been long desired. As described with the related art, the magnetic field modulation magnetooptic recording method with light pulse irradiation is expected greatly because it allows overwrite and a bit density is high. Furthermore, this method has the characteristics that an edge distance of a magnetic domain does not change and the reproduction signal waveform is not affected, even if a recording power changes.
This method is, however, associated with the problem that it is difficult to detect

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