JPH0512771B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a semiconductor laser used in an optical information recording/reproducing apparatus for recording information on an optical disk that can be optically recorded and reproduced and for reproducing the recorded information from the optical disk. This relates to control circuits.

Prior Art FIG. 3 is a block diagram of a conventional semiconductor laser control circuit. The output light of the semiconductor laser 1 is received by a photodetector 2, the photodetector output current is subjected to current-voltage conversion by an operational amplifier 3, and is inputted to a control operational amplifier 4 as a control error signal. SW ₁ (5) records the reference voltage that sets the output light level of semiconductor laser 1 (R side),
This is a switch to switch to playback (P side). The operational amplifier 4 compares and outputs the reference voltage 6 or 7 with a control error signal to control the output light of the semiconductor laser to be constant. During recording, the output light of the semiconductor laser 1 is pulse-modulated by the recording signal 8. The recording signal is level-shifted 9, and a variable resistor 10 sets the pulse amplitude value of the output light. SW ² (11) is turned on during recording and is electrostatically coupled to the operational amplifier 4 output voltage by the capacitor 12. Therefore, during recording, the average level of the pulse-modulated output light serves as a control error signal, and the average level is controlled to be constant. The output light of the semiconductor laser 1 is pulse-modulated around this average value by the electrostatically coupled recording signal.

Problems to be Solved by the Invention However, in the above configuration, when the optical output-current characteristic of the semiconductor laser 1 changes due to temperature change or aging, the peak value or bottom value of the pulse-modulated output light becomes large. This has caused a problem in that the recording and reproducing characteristics of the optical disk deteriorate. FIG. 4 is a diagram showing an optical output waveform of a conventional example to explain this problem. Semiconductor laser 1
In the diagram showing the relationship between the optical output-current characteristics and the pulse-modulated output optical waveform, the curve at I ₀ shows the characteristics at temperature T ₀ . When recording on an optical disk, it is necessary to accurately control not only the peak value P _R but also the bottom value P _B of the pulse-modulated output light. For example, for optical discs made of non-erasable materials, the bottom value during recording
Recording may be performed with the optical power of the peak value _PR while performing preheating with the optical power of P _B. Depending on the characteristics of the material, it may be necessary to precisely control the peak value P _R and bottom value P _B . In addition, in an optical disc made of another erasing material, recording may be performed with the optical power of the peak value _PR while erasing is performed with the optical power of the light of the bottom value P _B. Even with such erasing materials, the peak value P _R and bottom value of the optical output waveform
If P _B is not precisely controlled, the necessary recording characteristics
Erasing characteristics may not be obtained. For example, suppose that when the temperature of the semiconductor laser 1 changes from T ₀ to T ₁ , the characteristics change from I ₀ to I ₁ . The recording signal 8 is applied to the semiconductor laser 1 after being converted into a constant current amplitude _IP , and is pulse-modulated around a controlled average value level _PM . Therefore, the average value at temperature T ₁ is controlled so that P _M remains constant even if the characteristics change to I ₁ . However, even when the slope of the optical output-current characteristic curve changes like I ₁ , the current amplitude I _P of the recording signal remains constant, so the peak value of the pulse-modulated optical output is
P _R ′, the bottom value changes significantly to P _B ′. Here, we have described the change in optical output due to the change in temperature characteristics T ₀ →T ₁ , but when the semiconductor laser 1 deteriorates over time, a similar characteristic deterioration occurs as I ₀ →I ₁ .

As described above, the conventional configuration shown in FIG. 3 has the problem that the peak value and bottom value of the pulse-modulated optical output waveform change greatly due to the temperature characteristics of the semiconductor laser 1 and deterioration over time. Ta. Furthermore, when measuring the optical power of a pulse-modulated optical output waveform having such peak and bottom values, a normal optical power meter can only measure the average value P _M.
The peak value P _R and bottom value P _B must be set by waveform observation. It is difficult to accurately measure optical power setting by observing such waveforms. Furthermore, when the current amplitude value I _P is changed by the variable resistor 10, both the peak value P _R and the bottom value P _B change, and P _R ,
It is difficult to set P _B independently. The second problem is that it is difficult to set the optical power precisely in this way.
It also had some drawbacks.

In view of the above, the present invention has been developed to provide a peak value of a pulse-modulated optical output waveform, even if the output light-current characteristics of a semiconductor laser change due to temperature characteristics or aging deterioration.
To provide a semiconductor laser control circuit that can control the bottom value to a constant optical power level and further precisely set the peak value and bottom value of a pulse-modulated optical output waveform using an ordinary optical power meter. The purpose is to

Means for Solving the Problems The present invention provides a first closed-loop system control means for receiving the output light of a semiconductor laser with a photodetector, obtaining an optical power control error signal, and controlling the optical power to a first optical power value. ,
a first open-loop system control means that samples and holds the control voltage of the first closed-loop system and controls the optical power to a first optical power value using the hold voltage; and a second closed-loop system that controls the optical power to a second optical power value. a control means; a second open-loop system control means that samples and holds the control voltage of the second closed-loop system and controls the optical power to a second optical power value using the hold voltage; and a first open-loop system control means. Optical pulse modulation means for modulating the first optical power value into the bottom value of the optical pulse waveform and the second optical power value controlled by the second open-loop system control means into the peak value of the optical pulse waveform; This is a semiconductor laser control circuit equipped with.

Effects According to the present invention, with the above-described configuration, the first and second optical power values are independently and accurately controlled by the closed loop control means. During pulse modulation, the first and second optical power values controlled by the closed-loop control means are maintained independently by the open-loop control means using the held first and second control voltages. This first optical power value becomes the bottom value of the optical pulse waveform, and the second optical power value becomes the peak value of the optical pulse waveform. Therefore, the peak value and bottom value of the optical pulse waveform can be set independently. In this way, first, before pulse-modulating the optical output of the semiconductor laser, DC light is emitted with optical power corresponding to the peak value and bottom value of the optical pulse waveform, and the closed-loop system control means precisely controls the optical power to a set value. In this way, even if the optical output-current characteristics of the semiconductor laser change due to temperature characteristics or aging, the peak value and bottom value of the optical pulse waveform can be independently and precisely controlled. Furthermore, since the optical power control is not performed by directly sampling and holding the peak value and bottom value of the optical pulse waveform, the accuracy of optical power control does not deteriorate even if the modulation frequency becomes higher.
Furthermore, before optical pulse modulation, the optical power values corresponding to the peak value and bottom value can be measured using DC light. Therefore, without using an expensive optical power meter for pulsed light, it is possible to accurately measure the peak and bottom values of the optical pulse waveform using a normal optical power meter for DC light.

Embodiment FIG. 1 shows a configuration diagram of a semiconductor laser control circuit in a first embodiment of the present invention. The output light of the semiconductor laser 1 is received by a photodetector 2, and the light receiving current of the photodetector is converted into a current voltage by an operational amplifier 3. This operational amplifier output becomes the optical power control error voltage 14. Reference numeral 13 indicates optical power control error voltage generating means. Reference numeral 15 indicates a first closed loop system control means. Reference numeral 15 controls the output light of the semiconductor laser to a first optical power value, that is, the bottom value of the optical pulse waveform when pulse modulated. Reference numeral 15 is composed of an operational amplifier 4, which compares the optical power control error voltage (PDER) 14 with a first reference voltage 16 and outputs the result. 27 is a first reference voltage generating means. Reference numeral 17 denotes a switch, which is turned on when controlling the closed loop system control means 15 to the first optical power value. A switch 18 is turned on when the closed-loop system control means is not setting power during pulse modulation, that is, during reproduction in the optical recording/reproducing apparatus, and switches the first reference voltage to the reference voltage 19 during reproduction. During reproduction, it is sufficient to simply cause the semiconductor laser to emit DC light, so 15 maintains closed loop system control. BSGT is a bias gate and remains at H level during periods other than playback, turning on switch 17.
Turn on switch 18. The first control voltage 2 comparatively outputted by the first closed loop system control means 15
0, the optical power control of the first closed-loop system control means is switched to the setting of the first optical power value from the time of reproduction, and the switch 21 is turned off when the optical power control becomes stable. 22 is a first sample and hold means that holds the first control voltage value 20 inputted by the operational amplifier 23 and the capacitor 24 and outputs the first hold voltage 25. By turning off the switch 21, the switch 15 interrupts the closed loop system control, and the output light of the semiconductor laser 1 is set to the first hold voltage 25.
This results in open-loop system control, and the first optical power value is maintained. A control voltage or a hold voltage is input to the base of the transistor 26 to drive the semiconductor laser with current. WTGT is a light gate, and when the optical power control of the first closed loop system control means 15 becomes stable, it becomes H level and the switch 21 is turned on.
is turned off and the first control voltage is held. 28
is the second closed loop system control means. The operational amplifier 29 outputs a second control voltage 31 by comparing the optical power control error voltage 14 and the second reference voltage 30 . The second closed-loop system control means controls the optical power to a second optical power value, that is, the optical power corresponding to the peak value of the optical pulse waveform during pulse modulation. 32 is a second reference voltage generating means;
When the write gate WTGT becomes H level, the switch 33 is turned on, the switch 34 is turned off, and a second reference voltage 30 is generated to set the second optical power value. When the optical power control by this second closed-loop system control means is stabilized, the peak hold gate
Set PKHD to H level and turn off switch 35. As a result, the second sample hold means 36
holds the second control voltage 31 and outputs the second hold voltage 37. When the peak hole gate reaches the H level, 28 interrupts the closed loop system control, and the output light of the semiconductor laser 1 is changed to the second hold voltage 37.
This results in open-loop system control and maintains the second optical power value. 38 is a transistor that drives the semiconductor laser with current using a second control voltage or a second hold voltage. 39 is a light pulse modulation means. When an open loop control state is entered in which the transistors 26 and 28 are driven by the first and second hold voltages, a modulation signal is input to the write data WTDT. Transistors 40 and 41 perform differential switching according to write data 8, and transistor 38
The current flowing through the device is turned on and off according to the modulation signal.
Therefore, the current driven by the transistor 26 always flows through the semiconductor laser 1, and the current driven by the transistor 38 is turned on and off. That is, during pulse modulation, the bottom value of the pulse waveform is controlled to the first optical power value, and the peak value is controlled to the second optical power value.

FIG. 2 is an operational waveform diagram in the configuration of FIG. 1. The bias gate BSGT is at H level from the time of reproduction until a series of power settings and pulse modulation are completed. The period from the rise of the bias gate BSGT to the stop of the light gate WTGT is the period in which the first closed loop system control 15, which sets the first optical power value, that is, the bottom value of the optical pulse waveform, is operating. The period from the rise of the light gate WTGT to the rise of the peak hold gate PKHD is the second
This is the section in which the second closed-loop system control 28, which sets the optical power value of , that is, the peak value of the optical pulse waveform, is operating. SV1 indicates the waveform of the first control voltage 20, and _SV2 indicates the waveform of the second control voltage 31. HD1 is the first peak hold voltage 25
HD2 shows the waveform of the second peak hold voltage 37. LD indicates the optical output waveform of semiconductor laser 1, PWR0 indicates the reproduction power,
PWR1 indicates the bottom value of the optical pulse waveform, and PWR2 indicates the level of the peak value of the optical pulse waveform.
PDER is an optical power control error voltage 14 obtained from light received from the photodetector 2. As shown in SV1, at a time point 42 when the first closed-loop system control operates and the optical power control becomes stable, the light gate WTGT is raised to the H level and the first control voltage is held (43). The held voltage is maintained until the end of pulse modulation and the next reproduction. Next, when the WTGT turns on, the second closed-loop system control operates as shown in SV2, and the optical power control becomes stable at the point 4
4, raise the peak hold gate PKHD to H level and hold the second control voltage (4
5). The held voltage is maintained until the end of pulse modulation and the next reproduction. As shown in Fig. 2, the output light of the semiconductor laser 1 is subjected to independent closed-loop optical control in the DC emission state in the first and second closed-loop control sections, and the first and second control in the pulse modulation section. While holding the voltage, pulse modulation is performed between the levels of the first optical power value and the second optical power value.

As described above, according to this embodiment, first, before pulse-modulating the optical output of the semiconductor laser, the optical power corresponding to the peak value and bottom value of the optical pulse waveform is
The light is emitted and precisely controlled to a set optical power by a closed-loop control means. Next, the control voltage obtained by the closed loop system control means is held and pulse modulated. By doing so, even if the optical output-current characteristics of the semiconductor laser change due to temperature characteristics or aging, the peak value and bottom value of the optical pulse waveform can be independently and precisely controlled. Furthermore, precise optical power control is possible regardless of the modulation frequency of the optical pulse waveform.

Effects of the Invention As explained above, according to the present invention, even if the optical output-current characteristics of a semiconductor laser change due to temperature characteristics or aging, the peak value and bottom value of the optical pulse waveform can be independently and precisely controlled. can do.
Furthermore, since the optical power control is not performed by directly sampling and holding the peak value and bottom value of the optical pulse waveform, the accuracy of optical power control does not deteriorate even if the modulation frequency becomes higher. Furthermore, before optical pulse modulation, optical power values corresponding to the peak value and bottom value of the optical pulse waveform can be measured using DC light. Therefore, without using an expensive optical power meter for pulsed light, the peak value and bottom value of the optical pulse waveform can be precisely measured using an ordinary optical power meter for DC light.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram of a semiconductor laser control circuit according to an embodiment of the present invention, FIG. 2 is an operation waveform diagram of the same embodiment, FIG. 3 is a configuration diagram of a conventional semiconductor laser control circuit, and FIG. 4 is a conventional semiconductor laser control circuit. FIG. 3 is an optical output waveform diagram of the semiconductor laser control circuit of FIG. 1... Semiconductor laser, 2... Photodetector, 15...
...First closed loop system control means, 22...First sample hold means, 27...First reference voltage generation means, 28...Second closed loop system control means, 3
2...Second reference voltage generation means, 36...Second sample and hold means, 39...Pulse modulation means.

Claims (1)

[Claims] 1 Optical power control error voltage generating means for receiving the output light of the semiconductor laser with a photodetector and generating an optical power control error voltage;
a first reference voltage generating means for generating a first reference voltage for setting the optical power value to an optical power value; and a first reference voltage generated by comparing and outputting the optical power control error voltage and the first reference voltage a first closed-loop system control means for controlling the output light of the semiconductor laser to a first optical power value by changing the current flowing through the semiconductor laser with a control voltage; and optical power control by the first closed-loop system control means. holds the first control voltage value at the time when the first control voltage becomes stable;
a first sample and hold means for outputting a hold voltage; and a first sample and hold means for controlling the output light of the semiconductor laser to the first optical power value by changing the current flowing through the semiconductor laser with the first hold voltage.
a second reference voltage generation means for generating a second reference voltage for setting the output light of the semiconductor laser to a second optical power value; and an optical power control error voltage. , the second reference voltage obtained by comparing and outputting the second reference voltage.
a second closed-loop system control means for controlling the output light of the semiconductor laser to the second optical power value by changing the current flowing through the semiconductor laser with a control voltage; and an optical power by the second closed-loop system control means. A second control voltage that holds the second control voltage value at the time when the control is stabilized and outputs the second hold voltage.
sample and hold means; second open-loop system control means for controlling the output light of the semiconductor laser to the second optical power value by changing the current flowing through the semiconductor laser with the second hold voltage; The first optical power value controlled by the first open-loop control means is used as the bottom value of the optical pulse waveform, and the second optical power value controlled by the second open-loop control means is used as the optical pulse waveform. A semiconductor laser control circuit comprising an optical pulse modulation means for modulating optical pulses to a peak value of.