Dynamic information storage or retrieval – Specific detail of information handling portion of system – Radiation beam modification of or by storage medium
Reexamination Certificate
1998-12-16
2002-06-04
Hudspeth, David (Department: 2651)
Dynamic information storage or retrieval
Specific detail of information handling portion of system
Radiation beam modification of or by storage medium
C369S059110, C369S053260
Reexamination Certificate
active
06400673
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical disk drive in which recording and erasing of information, and initialization are performed on an optical disk as a result of light having a waveform of pulse series emitted from a light source being applied on the optical disk. The frequency of the pulse series is higher than the frequency of an information code (recording code) which is recorded on the optical disk. In particular, the present invention relates to a laser-power control device for controlling light-emitting power of a semiconductor laser (laser diode) or the like which is the light source of the optical disk drive.
2. Description of the Related Art
Phase-change-type optical disks such as CD-RW (Compact Disks ReWriteable) are disks on which high-density recording can be performed, and recording and erasing of information and initialization are performed on such disks.
Various methods for recording information on such phase-change-type optical disks have been proposed.
For example, as a recording method which is suitable for use in which overwriting of data is performed on a disk, a recording method (disclosed in Japanese Laid-Open Patent Application No. 63-266632) in which a laser beam having a waveform of a single or a plurality of pulses is applied on a disk so that an amorphous mark is formed on the disk, a recording method (disclosed in Japanese Laid-Open Patent Application No. 1-119921) in which a laser beam having a waveform of high-frequency pulse series is applied on a disk so that an amorphous mark is formed on the disk and a portion of the disk is crystallized, and so forth, have been known.
A recording method for phase-change-type optical disks will now be simply described.
FIGS. 1A and 1B
illustrate a principle of the recording method for phase-change-type optical disks.
FIG. 1A
shows relation between an information code and laser power, and
FIG. 1B
shows a recorded condition, corresponding to the information code, on a track of the disk. In
FIG. 1A
, Pp represents a amorphous-phase forming level, Pe represents a crystallizing level and Pr represents a reading level.
In a case where such a phase-change-type optical disk is used, when information is recorded on the disk, a laser spot is applied on the disk, and laser power of a laser beam is changed in accordance with an information code. Thereby, crystallized areas and amorphous marks are formed on a recording film of the disk. Thus, information is recorded on the disk.
Specifically, with reference to
FIG. 1A
, for a ‘0’ level of the information code, the laser power is caused to be in the crystallizing level Pe. Thereby, portions of the recording film of the disk are crystallized, and, thus, the crystallized areas are formed.
In contrast to this, for a ‘1’ level of the information code, the laser power is changed between the amorphous-phase forming level Pp and the reading level Pr so as to have a waveform of pulse series. Thereby, portions of the recording film of the disk enter an amorphous phase, and, thus, amorphous marks are formed there.
Through such a recording operation, as shown in
FIG. 1B
, amorphous marks are formed for the ‘1’ level of the information code on the track.
As shown in
FIG. 1A
, Pp (amorphous-phase forming level)>Pe (crystallizing level)>Pr (reading level).
Thus, on the phase-change-type optical disk, the crystallized areas for the ‘0’ level of the information code and the amorphous marks for the ‘1’ level of the information code are formed.
For this purpose, the laser power is controlled to have the three levels, that is, the (middle) crystallizing level Pe for the ‘0’ level of the information code, and the (highest) amorphous-phase forming level Pp and the (lowest) recording level Pr for forming the amorphous marks for the ‘1’ level of the information code.
In an optical disk drive, for phase-change-type optical disks such as CD-RW, in which a laser spot having a waveform of high-frequency pulse series is applied on an optical disk, and thus, recording and erasing of information and initialization are performed on the disk, laser power changes at a high frequency.
Therefore, when an emitted-light-intensity detector having a relatively narrow detection frequency band is used, it is difficult to precisely detect emitted-light intensity.
When emitted-light intensity is adjusted by using such imprecisely detected emitted-light intensity, it is difficult to precisely adjust light intensity, and, thereby, it is difficult to stabilize light intensity.
As a result, there is a case where recording or erasing of information, or initialization is performed incompletely.
When using an emitted-light-intensity detector having a wide detection frequency band, expensive light-receiving device and amplifier are needed, and, thereby, the cost of the optical disk drive increases.
In order to eliminate such problems, the inventor of the present invention proposed (in Japanese Laid-Open Patent Application No. 9-171631) an optical disk drive in which emitted-light intensity of a laser diode is stabilized by using an inexpensive and simple arrangement, and, thereby, information recorded on a disk has high reliability.
A laser-power control device in this optical disk drive provides a period during which a laser diode is driven to emit light which does not have a waveform of pulse series. During the period, emitted-light power is detected, and, by using the detected emitted-light power, emitted-light power is controlled.
As a result of emitted-light power being controlled as mentioned above, it is possible to precisely detect emitted-light intensity even by using an emitted-light-intensity detector having a relatively narrow detection frequency band.
However, in detection of emitted-light intensity of the laser diode, the laser diode emits light of recording power (the above-mentioned amorphous-phase forming level Pp) during the period during which the laser diode is driven to emit light which does not have a waveform of pulse series. When light of such high power is applied to an optical disk and emitted-light power is controlled, the optical disk is degraded. When light of the recording power not having a waveform of pulse series is applied on a phase-change-type optical disk, characteristics of the optical disk are remarkably degraded. As a result, recording, reproducing and erasing of information cannot be performed with high reliability.
In order to eliminate this problem, the inventor of the present invention proposed (in Japanese Laid-Open Patent Application No. 9-288840) a laser-power control device in an optical disk drive. In this laser-power control device, setting of laser power having the crystallizing level (middle level) Pe is performed during a period during which an information code has a ‘0’ level and light not having a waveform of pulse series is applied on an optical disk. Thereby, an optimum additional current Ie for the crystallizing level Pe is obtained. An optimum additional current Ip for the amorphous-phase forming level Pp is obtained as a result of the additional current Ie, detected in the period during which the applied light does not have a waveform of a pulse series, being multiplied by a certain coefficient. A base current Ir for the reading level Pr is obtained as a result of a detection output smoothed through a low-pass filter being used, and, thus, an average power level between the highest amorphous-phase forming level Pp and the lowest reading level Pr being detected.
Thus, emitted-light power is controlled by using the output of the low-pass filter during a period during which light has a waveform of pulse series. Thereby, even by using an emitted-light-intensity detector having a relatively narrow detection frequency band and therefore being inexpensive, precise power control can be performed.
As described above, the laser-power control devices in the optical disk drives, by which, even by using an emitted-light-intensity detector having a relatively narrow detection frequency band and therefor
Chu Kim-Kwok
Dickstein , Shapiro, Morin & Oshinsky, LLP
Hudspeth David
Ricoh & Company, Ltd.
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