Laser control device

Details Laser control device Laser control device

2001-12-05

2004-01-27

Hindi, Nabil (Department: 2655)

Dynamic information storage or retrieval

Condition indicating, monitoring, or testing

Including radiation storage or retrieval

C369S116000, C369S047530

Reexamination Certificate

active

06683836

ABSTRACT:

TECHNICAL FIELD
The present invention relates to a laser control apparatus, more particularly, an apparatus which carries out power control of a semiconductor laser employed for an optical recording/reproducing apparatus, and can control the optical power stably even when an output light is modulated at high speed at the high-speed recording.
BACKGROUND ART
A semiconductor laser is generally employed as an optical pick up and the like in an optical recording/reproducing apparatus such as a CD player, a writable CD-R drive, an erasable CD-RW drive and the like. The power of a semiconductor laser varies greatly in accordance with a temperature change or changes with passage of time(lifetime), and therefore, it is necessary to carry out power control for stabilizing the power when employing a semiconductor laser as a light source in an apparatus for performing recording/reproduction into/from an optical recording medium such as an optical disk and the like.
Such prior art semiconductor laser power control apparatus is disclosed in Japanese Published Patent Application No. Hei. 1-204224 in detail.
FIG. 9
is a block diagram for illustrating a prior art semiconductor laser power control apparatus. In figure, numeral
10
denotes a semiconductor laser for radiating laser light to an optical disk; numeral
1
denotes a photodiode for receiving the irradiation light of the semiconductor laser
10
; numeral
2
denotes a monitor circuit for monitoring the output of the photodiode
1
; numeral
20
denotes a bottom hold circuit for holding a bottom level of the output from the monitor circuit
2
; numeral
21
denotes a sample-hold circuit for sample-holding the output from the monitor circuit
2
; numeral
22
denotes a peak hold circuit for holding a peak level of the output from the monitor circuit
2
; numeral
19
denotes a control circuit for outputting a first, a second and a third digital signals corresponding to a bias reference voltage, an erase power reference voltage and a peak power reference voltage, respectively; numeral
26
denotes a D/A converter for converting the first digital signal outputted by the control circuit
19
to a bias reference voltage; numeral
27
denotes a D/A converter for converting the second digital signal outputted by the control circuit
19
to an erase reference voltage; numeral
28
denotes a D/A converter for converting the third digital signal outputted by the control circuit
19
to a peak power reference voltage; numeral
23
denotes a servo amplifier for comparing the bias reference voltage outputted by the D/A converter
26
with the bottom level which is held in the bottom hold circuit
20
to amplify the error; numeral
24
denotes a servo amplifier for comparing the erase reference voltage outputted by the D/A converter
27
with a sample-hold level which is held in the sample-hold circuit
21
to amplify the error; numeral
25
denotes a servo amplifier for comparing the peak power reference voltage outputted by the D/A converter
28
with the peak hold level which is held in the peak hold circuit
22
to amplify the error; numerals
7
,
8
and
9
denote current sources for generating the currents corresponding to the outputs of the servo amplifiers
23
,
24
and
25
, respectively; numeral
11
denotes a switch means for disconnecting the current source
8
with the semiconductor laser
10
in accordance with data EFM
1
; numeral
12
denotes a switch means for disconnecting the current source
9
with the semiconductor laser
10
in accordance with data EFM
2
.
Next, the operation will be described. A portion of the output light from the semiconductor laser
10
is received by the photodiode
1
and the generated photoelectric current is converted to a voltage in the monitor circuit
2
.
At reproduction from the optical disk, the reproduction power reference voltage VR which is outputted by the D/A (Read/Bias) converter
26
serving as a reference voltage source and a voltage which is obtained by the bottom hold circuit
20
by sample-holding the output of the monitor circuit
2
are compared by the servo amplifier
23
and a current is passed through the semiconductor laser
10
by the current source
7
which is controlled by the comparison result of servo amplifier
23
so that a reproduction power PR corresponding to the reproduction power reference voltage VR is constantly outputted.
At recording into an optical disk, as shown in
FIG. 2
, the power of the semiconductor laser
10
is modulated into the three values of bias power PB, erase power PE, and peak power PP, thereby recording is performed into the optical disk. Then, a portion of the output light from the semiconductor laser
10
is received by the photodiode
1
, and a signal corresponding to the optical output is outputted from the monitor circuit
2
. The signal from the monitor circuit
2
is held by the bottom hold circuit
20
, the sample-hold circuit
21
, and the peak hold circuit
22
respectively, and the bottom level, the erase level and the peak level of the optical output are detected respectively. Initially, the bias power PB can be obtained by switching the output of the D/A (Read/Bias) converter
26
serving as a reference voltage source in
FIG. 9
to switch over from the VR to the bias power reference voltage VB corresponding to the bias power PB. The bias power reference voltage VB and the voltage which is held in the bottom hold circuit
20
are compared by the servo amplifier
23
, and a current is passed through the semiconductor laser
10
by the current source
7
which is controlled by the comparison result of servo amplifier
23
so that the bias power PB corresponding to the bias power reference voltage VB is constantly outputted.
Next, the erase power PE is obtained by comparing the erase power reference voltage VE outputted by the D/A(Erase) converter
27
serving as a reference voltage source and the output from the sample-hold circuit
21
by the servo amplifier
24
and by passing an erase power current through the semiconductor laser
10
with the erase power current superposed on the bias power current by the current source
8
which is controlled by the comparison result of servo amplifier
24
.
Further, the peak power PP is obtained by comparing the peak power reference voltage VP outputted by the D/A(Peak) converter
28
serving as a reference voltage source and the output from the peak hold circuit
22
by the servo amplifier
25
and by passing a peak power current through the semiconductor laser
10
with the peak power current further superposed on the erase power current by the current source
9
which is controlled by the comparison result of servo amplifier
25
.
Meanwhile, the erase power PE and the peak power PP are turned on and off by the switch means
11
and
12
which are switched by data EFM
1
and EFM
2
, respectively, and therefore the power of the semiconductor laser is modulated between the bias power PB, the erase power PE and the peak power PP. As shown in
FIG. 3
, the interval at which the modulation is performed between the bias power PB and the peak power PP is the interval at which pits are formed on the track, and when the switch means
11
and
12
are in the state of on and off, respectively, the intervals at which the value of the erase power PE is maintained are the intervals where the space between pits are erased and spaces are formed. The three power values (the value of the bias power PB, the value of the erase power PE, and the value of the peak power PP) can obtain the desired power values by changing the respective reference voltages of D/A converters
26
,
27
and
28
serving as the reference voltage sources.
The conventional semiconductor laser power control apparatus is constructed as above, and it can perform such a control that the powers of peak and bottom of the semiconductor laser should be predetermined by detecting the powers of peak and bottom of the semiconductor laser.
By the way, in a CD-R drive, a CD-RW drive or the like, the recording of data into an optical disk is performe

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