JP3497207B2 - Laser drive - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laser driving device having a light output control function. 2. Description of the Related Art Conventionally, as a laser driving device having an optical output control function, a laser driving device disclosed in Japanese Patent Application Laid-Open No. 63-184934 is known. FIG. 3 shows a schematic configuration of such a laser driving device, wherein 1 is a semiconductor laser (LD), 2 is a photodiode (PD), 3 is an amplifier for converting an optical signal into an electric signal, 4 is an amplifier, and 5 is an amplifier. A holding circuit including an amplifier, a resistor, and a capacitor for holding the electric signal, 6 a current source for setting an operating point so that the amplifier 3 does not saturate during recording, and 7 driving the semiconductor laser 1 with the recording signal. A variable amplifier, 8 a comparator, 9 a gate circuit, 10 a counting circuit, a a recording signal, b a test signal, c a reset signal for resetting the counting circuit, d
Is a recording gate signal, e is a reproduction gate signal, SW2,
SW3, SW4, and SW5 are switches that are opened and closed by the gate signal. [0003] In the laser driving apparatus thus constructed, during the reproducing operation, the reproducing gate signal e is given, and the switches SW3 and SW4 are closed to keep the optical output of the semiconductor laser 1 constant. Such an APC (automatic light output control) circuit is configured. in this case,
The semiconductor laser 1 has the current and current of the semiconductor laser 1 shown in FIG.
Biased to the current value I _B1 as shown in C ₁ optical characteristics,
Its light output is emitted by the reproducing light output P _R, the holding circuit 5 operates to hold the bias value. During a recording operation, a recording gate signal d is applied, and switches SW3 and SW4 are opened, and switches SW2 and SW5 are closed. As a result, the semiconductor laser 1 is biased to the bias current value I _B1 , and when the recording signal a is input, the current is amplified by the variable amplifier 7, the pulse current I _P1 is superimposed, and the recording light output P _W It emits light. Here, the threshold current value of the semiconductor laser 1 changes from I _th1 to I _th2 due to the influence of temperature fluctuation.
When the current-optical characteristic shown in is assumed to change as curve C _2, by the action of APC circuit described above, the bias current is changed to I _B2, reproduction optical output P _R becomes constant, also during recording By the operation of the holding circuit 5, the pulse current _IP1 is superimposed on the bias current value _IB2 , and the recording light output _PW is obtained. Further, the recording current is corrected by detecting the deterioration of the differential quantum efficiency of the semiconductor laser before operating the semiconductor laser 1 with the recording light output when turning on the power of the optical disk device or replacing the recording medium, etc. The compensation is performed by controlling the drive current. On the other hand, the test operation of the semiconductor laser 1 is executed by switching the switch SW1 to the lower side (the input side of the test-time signal b). In this case, the counting circuit 10 is reset by the reset signal c, and the gain of the variable amplifier 7 is set to the minimum initial state. The state reproduction gate signal e is given, when the switches SW3, SW4 are closed, the semiconductor laser 1, by the function of the APC circuit, to emit the reproduction light output P _R as indicated by the characteristic C ₂ in FIG. 4 _Is biased by the current _IB2 . When the test signal b is turned on from this state, the gate signal d becomes effective in conjunction with this, the switches SW2 and SW5 are closed, and the state where the current value _IB2 is biased by the holding circuit 5 is maintained. The pulse current I _P1 is superimposed by the signal b, and the semiconductor laser 1 emits light at the output P _Wa . The light output of the semiconductor laser 1 is detected by a photodiode 2, taken out as a photocurrent proportional to the light output, and compared with a reference voltage ref for an appropriate light output by a comparator 8. Here, if the voltage does not reach the reference voltage ref, the output of the comparator 8 becomes H level, and the gate circuit 9
As a result, while the test signal b is being output, the counting circuit 1
0 can be counted, and the falling edge at which the test signal b is turned off is counted. As a result, the gain of the variable amplifier 7 for the signal current is set large, and the pulse current increases by ΔI _P. [0009] Then, the test signal b is turned off, closing switches SW3 and SW4 are, APC circuit to the reproduced light output and P _R is operated. Next, when the test signal b is turned on, the pulse current increases by ΔI _P and is superimposed on the bias current. Such an operation is repeated, and when the light emission output by the test signal b reaches the recording light output P _W , the output of the comparator 8 becomes L level, and the counting of the counting circuit 10 is stopped. When the output of the comparator 8 is at the L level when the test signal is input, the end of the setting of the compensation operation for the deterioration of the external differential quantum efficiency of the semiconductor laser 1 is detected, the test operation is completed, and the switch SW1 is turned on. a
Side. This setting is maintained until the power is turned off or the medium is replaced and the next setting operation is started. However, in general, a semiconductor laser can obtain a larger peak power at the time of pulsed light emission (light emission with a pulse width of a recording signal level) than continuous light emission. In the laser driving device, at the time of test emission, the semiconductor laser emits light with a pulse width longer than the recording signal, so that APC by test emission can be performed only up to the upper limit power of continuous emission, and as a result, the peak during pulse emission The power is limited by the upper limit power of continuous light emission. This necessitates the use of a semiconductor laser having a large output, which leads to an increase in cost.In addition, in the conventional laser driving apparatus, if the test pulse width of the test light emission is shortened, the processing circuit is correspondingly reduced. It is necessary to increase the speed, which also leads to an increase in cost. The present invention has been made in view of the above circumstances, and can shorten the pulse width of test light emission without requiring a high-speed processing circuit, and furthermore, has a peak power at the time of pulse light emission of continuous light emission. An object of the present invention is to provide a laser driving device that is not limited by an upper limit power. According to the present invention, there is provided a semiconductor laser for generating an optical output, drive current control means for controlling a drive current of the semiconductor laser in accordance with a recording signal, and light emission of the semiconductor laser. A light-receiving element for receiving light; integrating means for integrating the output of the light-receiving element; and comparing means for comparing the output of the integrating means with a preset reference value. A test signal having a pulse width smaller than the pulse width of the recording signal is input to the drive current control unit instead of the recording signal, and the output of the integrating unit according to the output of the light receiving element accompanying the emission output of the semiconductor laser Is compared with the reference value by the comparison means, and the drive current control means is controlled based on the comparison result to determine the drive current of the semiconductor laser. It is configured to: As a result, according to the present invention, at the time of test light emission of the semiconductor laser, the semiconductor laser is supplied with a test signal having a pulse width equal to or smaller than the pulse width of the recording signal instead of the recording signal. The monitor signal of the optical output of the semiconductor laser is integrated by the integrating means, and the drive current source is controlled so that the integrated value becomes a predetermined reference value to be compared by the comparing means. The drive current is obtained. This eliminates the need for a high-speed processing circuit that was required by setting the pulse width of the test signal to be smaller than the pulse width of the recording signal. In addition, the peak power during pulse emission is reduced to the upper limit power for continuous emission. A large value that is not limited by this can be secured. An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows a schematic configuration of the embodiment, and the same parts as those in FIG. 3 described above are denoted by the same reference numerals. In this case, an integrating circuit 11 is connected to an output terminal of the amplifier 3 that converts an optical signal into an electric signal, and an output terminal of the integrating circuit 11 is connected to one input terminal of the gate circuit 9. Reference numeral 12 denotes a transmitter, and this oscillator 12
Generates a clock for operating the counting circuit 10. In this case, the oscillator 12 operates according to the test mode signal f. The test mode signal f is supplied to the switch S
W1 is operated, and the gate circuit 9 is operated to the active side. Here, the pulse width of the test signal b used at the time of the test light emission is set to be substantially the same as the pulse width of the recording signal a, or the pulse width of the test signal b is set to be smaller than the pulse width of the recording signal a. The allowable peak power can ensure a large value. The pulse width of the recording signal a here is the smallest pulse width given as the recording signal a by the recording data. The other points are the same as those in FIG. 3, and the description is omitted here. Thus, in the laser driving device thus configured, at the time of reproduction, the gate signal e at the time of reproduction is provided, and the switches SW3 and SW4 are closed. On the other hand, at the time of recording, the gate signal d at the time of recording is provided. , Switches SW3 and SW4 open, and conversely, switches SW2 and SW5
Are closed, and the operations at the time of reproduction and at the time of recording are performed in the same manner as described with reference to FIG. Next, the test operation of the semiconductor laser 1 will be described with reference to a time chart shown in FIG. 2 in the case where the pulse width of the test signal is shortened, which cannot be solved conventionally. In this case, during the test emission of the semiconductor laser 1, the test mode signal f becomes H level as shown in FIG. 2A, and the switch SW1 is switched to the lower side (the input side of the test-time signal b). In addition, the gate circuit 9 is operated to the active side, and the oscillator 12 is operated. Then, the reset signal c shown in FIG.
Is given, the counting circuit 10 is reset, and the gain of the variable amplifier 7 is set to the minimum initial state. In this state, the reproduction gate signal e is supplied, and the switch SW
3, when SW4 is closed, the semiconductor laser 1, by the function of the APC circuit is biased with a current I _B2 to emit the reproducing optical output P _R as indicated by the characteristic C ₂ in FIG. Then, when the test signal b shown in FIG. 2C is input, the gate signal d at the time of recording becomes effective in conjunction with this, and SW2 and SW5 are closed this time, and the holding circuit 5 biases the current value _IB2 to the current value IB2. In this state, the pulse current I _P1 is superimposed by the test signal b, and the semiconductor laser 1 emits light at the output P _{Wa as} shown in FIG. The light output of the semiconductor laser 1 is taken out by the photodiode 2 as a photocurrent proportional to the light output, converted into a voltage signal by the amplifier 3, and converted into a voltage signal as shown in FIG. Given to. In the integrating circuit 11, the output from the amplifier 3 is integrated as shown in FIG. 2 (f), and this integrated output is given to the comparator 8, where the reference voltage ref with respect to the appropriate light output is obtained. Is compared to Here, if the integration circuit 11 does not reach the reference voltage ref, the output of the comparator 8 goes high and the output of the gate circuit 9 goes high as shown in FIG. . As a result, the counting circuit 10 is kept in a countable state, and the falling edge of the output waveform of the oscillator 12 shown in FIG. . As a result, the gain of the variable amplifier 7 for the signal current is set large, and the pulse current increases by ΔI _P. By repeating such operations, the light output of the semiconductor laser 1 is gradually increased, and the output from the amplifier 3 corresponding to the recording light output P _W and the integrated output of the integrating circuit 11 are also sequentially increased. Thereafter, when the integrated output of the integrating circuit 11 reaches the reference voltage ref, the output of the comparator 8 goes low, the output of the gate circuit 9 goes low, and the counting circuit 10 outputs the output waveform of the oscillator output 12. It will not count even when it is turned off. When the output of the comparator 8 is L
When the level is at the L level, the completion of the setting of the compensation operation for the change in the differential efficiency of the semiconductor laser 1 is detected, the test mode signal f is set to the L level, the switch SW1 is switched to the recording signal a side, and the oscillator is set. The test operation is terminated by stopping the operation of step S12. Accordingly, in this case, the semiconductor laser 1 is caused to emit light by the test signal b at the time of the test light emission, and the monitor signal of the optical output of the semiconductor laser 1 is integrated by the integrating circuit 11, and the integrated value is compared with the comparator 8. The drive current of the semiconductor laser 1 is obtained by controlling the drive current source so as to be a predetermined reference value to be compared with the above. a is almost equal to the pulse width of a, or the test signal b
Is set smaller than the pulse width of the recording signal a, a high-speed processing circuit including the comparator 8, the gate circuit 9, and the counting circuit 10, which is required, can be eliminated, and the cost of the circuit can be reduced. In addition, since the pulse width of the test signal b can be reduced, the peak power at the time of pulse emission can be secured to a large value which is not limited by the upper limit power of the continuous emission, so that a semiconductor laser having a small output can be used. From this point, the cost can be reduced. The present invention is not limited to the above-described embodiment, but can be implemented with appropriate modifications without changing the gist.
For example, in the above-described embodiment, the comparator 8, the gate circuit 9, the counting circuit 10, and the like are used. However, these operations can be realized by software using a microcomputer. According to the present invention, at the time of test emission of a semiconductor laser, the semiconductor laser is controlled by a test signal having a pulse width equal to or smaller than the pulse width of the recording signal instead of the recording signal. The semiconductor laser is driven by emitting light, integrating a monitor signal of the optical output of the semiconductor laser by an integrating means, and controlling a driving current source so that the integrated value becomes a predetermined reference value to be compared by a comparing means. Since the current is obtained, the high-speed processing circuit required by setting the pulse width of the test signal smaller than the pulse width of the recording signal can be eliminated, and the cost of the circuit can be reduced. In addition, since the peak power at the time of pulse emission can secure a large value which is not limited by the upper limit power of continuous emission, a semiconductor laser having a small output can be secured. A user can also be used, and cost reduction can be achieved from this point.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagram showing a schematic configuration of an embodiment of the present invention. FIG. 2 is a time chart for explaining the operation of one embodiment. FIG. 3 is a diagram showing an example of a conventional laser driving device. FIG. 4 is a characteristic diagram for explaining the operation of a conventional laser driving device. [Explanation of Symbols] 1. Semiconductor laser (LD) 2. Photodiode (P
D) 3, amplifier, 4 amplifier, 5 holding circuit, 6 current source, 7 variable amplifier, 8 comparator, 9 gate circuit,
10: counting circuit, 11: integrating circuit, 12: oscillator.

Claims (1)

(57) [Claim 1] A semiconductor laser for generating an optical output, drive current control means for controlling a drive current of the semiconductor laser in accordance with a recording signal, and receiving light emission of the semiconductor laser A light receiving element; integrating means for integrating the output of the light receiving element; and comparing means for comparing the output of the integrating means with a preset reference value. A test signal having a pulse width smaller than the pulse width of the recording signal is input to the drive current control means instead of the recording signal, and the output of the integration means according to the output of the light receiving element accompanying the light emission output of the semiconductor laser is The drive current of the semiconductor laser is obtained by comparing the drive current control means with the comparison result by comparing the drive current with the reference value by comparison means. Laser driving apparatus.