Dynamic information storage or retrieval – Control of storage or retrieval operation by a control... – Mechanism control by the control signal
Reexamination Certificate
2001-10-24
2004-04-27
Korzuch, William (Department: 2653)
Dynamic information storage or retrieval
Control of storage or retrieval operation by a control...
Mechanism control by the control signal
C369S116000, C369S047490
Reexamination Certificate
active
06728178
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method and a device for controlling the recording power of a semiconductor laser emitted to record marks onto an optical disc according to a data signal.
2. Description of Related Art
FIG. 8
shows the configuration of a semiconductor laser control device according to the prior art.
Light emitted by the semiconductor laser
1
is sensed by a photodetector
2
for monitoring the emission level, converted to a photoelectric current, and then converted to a voltage by a current-voltage convertor
3
.
The sample-hold circuit
5
is set to a sample state by a command from write gate
8
during playback. Playback power current controller
6
compares the read power setting
7
with the detected output in the sample state and outputs the result in a feedback control loop adjusting light output from the semiconductor laser
1
to the read power setting
7
.
During recording, the write gate
8
sets the sample-hold circuit
5
to the hold state, and the peak switch
10
switches between a peak value and the held read power setting to current drive the semiconductor laser
1
.
The pulse beam emitted from the semiconductor laser
1
is sensed by the photodetector
2
, voltage-current converted, and the envelope of the output wave peaks is detected by peak detector
4
. Peak current controller
11
compares the output from peak detector
4
with peak power setting
12
and outputs to the peak switch
10
in a feedback control loop adjusting the peak value of the pulse beam from the semiconductor laser
1
to the peak power setting.
The signals from major parts of the prior art semiconductor laser control circuit are described next with reference to FIGS.
9
(
a
)-
9
(
d
).
FIG.
9
(
a
) shows the output from write gate
8
, which goes from a playback level to a record level at time
13
. FIG.
9
(
b
) shows the output from peak detector
4
, that is, detecting the peak envelope of the pulse wave sensed in the record state. FIG.
9
(
c
) shows the waveform of the light pulses feedback-controlled by the peak current controller
11
. FIG.
9
(
d
) shows the envelope of the playback wave reproduced after this feedback controlled light pulse train is recorded to a track of the optical disc.
The optical disc referred to here is an optical disc such as DVD-R or DVD-RW media, that is, media that can preferably be recorded in multiple sessions with the signals written continuously to the recorded tracks in the same way that signals are recorded to DVD-ROM media. More specifically, the start of recording to an incremental data recording area and the end of the previously recorded data recording area are preferably recorded so that the envelope of the playback signal is continuous. The present invention is therefore applicable to optical disc media such as DVD-R and DVD-RW, and is not applicable to DVD-RAM media.
A problem with the configuration described above is that due to feedback control response, there is a response time delay as shown at bracket
14
in FIG.
9
(
c
) until the peak of the emitted waveform rises to the peak power setting. When the optical disc is recorded with an emission wave as shown at bracket
14
in FIG.
9
(
c
), the amplitude of the reproduced playback wave is degraded according to the response of the emitted waveform as shown in
FIG. 9
(
d
).
A problem with the configuration of a prior art semiconductor laser control device as described above, therefore, is that the amplitude of the playback signal at the beginning of a data recording area appended to the disc deteriorates, and continuity of the playback signal amplitude is thus degraded when incrementally writing to DVD-R or DVD-RW optical disc media.
The present invention is directed to a solution for this problem, and an object of the invention is to provide a method and device for controlling a semiconductor laser in order to prevent playback signal deterioration when incrementally writing to DVD-R or DVD-RW optical disc media by quickly controlling and setting recording pulse power to a desirable recording power level.
SUMMARY OF THE INVENTION
To achieve this object, a method according to the present invention for controlling the optical power of light pulses obtained by modulating a semiconductor laser to at least two optical power levels according to a data signal for recording a mark area to an optical disc according to the data signal modulates light pulses with a test signal in a test emission area provided immediately before the data signal recording area for recording a data signal to an optical disc as light pulses modulated according to the data signal, obtains the difference between a reference level equivalent to a target pulse power level and a photodetection signal obtained by sensing and converting the light pulses to an electrical photodetection signal, and applies feed-forward control so that the difference converges to a specified value and current flowing to the semiconductor laser is controlled to a value equivalent to a target power level. Next, it senses the light pulses modulated according to the data signal in the data signal recording area, converts the sensed light pulses to an electrical photodetection signal, obtains a difference between a reference level equivalent to a target pulse power level and sample values obtained by sequentially sampling the photodetection signal at a specific sampling period, and applies feedback control so that the difference converges to a specified value and current flowing to the semiconductor laser is controlled to a value equivalent to a target power level.
The test emission area and data signal recording area are preferably provided in the area traced within one revolution of the optical disc by the optical head from the time at which the optical disc recording operation starts.
Further preferably, the test emissions in the test emission area include pulse emissions and continuous emissions at a constant level.
Yet further preferably, the test emissions in the test emission area include at least two of the following: pulse emissions modulated between the peak and bottom levels of recording pulses emitted at recording marks in the data signal recording area, constant emission at the pulse bottom level, and constant emission at the space level emitted at recording symbol spaces.
Yet further preferably, recording pulses in the recording mark area of the data signal recording area include a start pulse and plural multipulse trains. Feedback control controlling current flowing to the semiconductor laser to a value equivalent to a target power level is achieved by sequentially sampling at a specific sampling interval and step-by-step comparing with a reference level equivalent to a light pulse target power level only the average of the plural multipulse trains, or the average and bottom level of the multipulse trains in the photodetection signal obtained by sensing and converting to an electrical signal the recording pulses in the recording mark period, and the space level of the photodetection signal obtained by sensing and converting to an electrical signal the recording pulses in the recording symbol space part.
Yet further preferably, the data signal for recording to the optical disc is temporarily stored to buffer memory in the test emission area from the timing at which the optical disc recording operation starts to the beginning of the data signal recording area.
A further method according to the present invention for controlling the optical power of light pulses obtained by modulating a semiconductor laser to at least two optical power levels according to a data signal for recording a mark area to an optical disc according to the data signal modulates light pulses with a first test signal in a first test emission area provided immediately before the data signal recording area for recording a data signal to an optical disc as light pulses modulated according to the data signal, obtains a difference between a reference level equivalent to a target pulse power leve
Fujimoto Toru
Koishi Kenji
Konno Kohjyu
Miyabata Yoshiyuki
Osada Yutaka
Chu Kim-Kwok
Korzuch William
Matsushita Electric - Industrial Co., Ltd.
Wenderoth , Lind & Ponack, L.L.P.
LandOfFree
Semiconductor laser control method and semiconductor laser... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Semiconductor laser control method and semiconductor laser..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Semiconductor laser control method and semiconductor laser... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3260341