JPS61162827A - Controller of semiconductor laser - Google Patents

Abstract

PURPOSE:To obtain a device which stabilizes a peak output in a short time by providing a means which performs forward control over the amplitude of the modulating pulse current of a semiconductor laser after the start of pulse modulation. CONSTITUTION:The peak output side and bottom output side of the output voltage of a preamplifier 3 when pulse modulation is imposed upon the semiconductor laser are sampled and held by the 1st and the 2nd sample holding circuits 7 and 8 in a period of two starting pulses and the amplitude of the modulating pulse current is varied thereafter according to their held vales. At this time, the starting time of the pulse modulation of a modulating signal is detected and a reset signal is sent to a semiconductor laser driving circuit 11 in the period of two pulses. The semiconductor laser driving circuit 11 receives the reset signal from a timing circuit 12 and superposes such a modulating pulse current that the peak output monitor voltage of the semiconductor laser is a peak output monitor voltage VP upon a bottom output driving current at the start of the pulse modulation. Consequently, the peak output when the semiconductor laser is pulse-modulated is controlled and stabilized in a short time.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a semiconductor laser control device, particularly to stabilization of peak output when the semiconductor laser is pulsed xy, s-4.

[Conventional technology]

As a conventional semiconductor laser illilJm device, a semiconductor laser control device is used in a write-once optical disk device that performs recording by directly modulating the semiconductor laser with a recording signal and drilling holes in a rotating circular recording medium. I'm worried.

A typical example of this is an application by a person who has appeared (special issue i1s).
57-34903). In this conventional example, the output of the semiconductor laser is constantly monitored using a photodetector installed in the same pancake as the semiconductor laser.
##i Without pulse modulation, when pulse modulating the output as it is, extract the bottom output monitor voltage using a pinpoint detection circuit or sample hold circuit and compare it with the reference voltage (VB) corresponding to the specified bottom output. The configuration is such that the drive current of the semiconductor laser is feedback-controlled.

However, with the above groove/formation, when performing pulse modulation,
Since only the bottom output side is controlled, the peak output fluctuates depending on the temperature pj of the semiconductor laser characteristics or the influence of aging*.

The oscillation threshold and quantization efficiency of semiconductor lasers change significantly due to temperature and aging changes. Thus, the purpose of the above-mentioned conventional example is to minimize the total change in the output of the semiconductor laser due to aging.

FIG. 8 is a laser output characteristic diagram illustrating a previous work of a conventional semiconductor laser control device, and shows the semiconductor laser drive current versus semiconductor laser output characteristic. In the figure, arrow (9) indicates that the semiconductor laser output characteristic has changed from curve (4) to curve ψ) due to a change in the oscillation threshold. Also, the arrow @ indicates that due to changes in quantization efficiency, the above characteristics change from the curve ■) to the song # (C) shown by the broken line.
show. vBtit bottom output monitor voltage, ■ is the peak output monitor voltage when pulse modulated, VR is the modulation pulse voltage amplitude, and RL is the load resistance of the semiconductor laser.

Therefore, the modulation pulse current tll1m (R) is = VR
/RL becomes.

In the conventional semiconductor laser' control device described above, when the semiconductor laser output characteristic changes from track 1i (2) to track 1i (B), the drive current of the semiconductor laser is changed from (a) to (b) by $
When it is disturbed, the bottom output is stabilized by the seventh, and the eighth
As shown in the figure, the modulation pulse voltage swing +tu (VR)
As long as the quantization efficiency does not change even if
Taking advantage of the fact that the change in output power is also suppressed by small eyes,
Peak output was also indirectly stabilized.

[Problem that the invention seeks to solve]

However, if the quantization efficiency changes, the peak output will change by a corresponding amount.

Therefore, when trying to control the peak output of a semiconductor laser using 7-order pack control, a pull-in operation is required every time pulse modulation is started, and the settling time cannot be ignored compared to the pulse modulation period. It gets bigger. (9) If you try to shorten the settling time, the peak output will fluctuate greatly at the start of modulation. (9) If you try to shorten the settling time, the peak output will fluctuate greatly at the start of modulation. For example, if it is used in an optical disc device, problems such as poor recording and playback will occur. Just in case you can't block time.

This invention was made in order to solve the above-mentioned problems of the conventional ones, and it minimizes the change in peak output due to temperature and aging changes due to the quantization Rh of semiconductor lasers, and moreover, it can be done in a short time. The purpose is to obtain a device that can stabilize the peak output.

[Means for Solving Problems J] A semiconductor laser control device according to the present invention includes a photodetecting means for detecting the output of the semiconductor laser, a bottom output of the semiconductor laser is detected by the photodetecting means, and the semiconductor laser is driven. l A first means for controlling the current flow, a first detection and hold circuit that detects and holds the peak output when the semiconductor laser is pulse modulated at the start of pulse modulation, a bottom output when the semiconductor laser is pulse modulated; detects force,
The present invention includes a second detection and hold circuit for holding, and a second means for feedforward controlling the amplitude of the modulated pulse current of the semiconductor laser after the start of pulse modulation according to the outputs of these detection and hold circuits.

- [Operation] The semiconductor laser control device according to the present invention samples and holds the peak output and bottom output of the semiconductor laser at the start of pulse modulation, detects changes in quantization efficiency, and uses the values to control the modulation of the semiconductor laser. Control pulse vibration and obtain stable peak output.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings. 1st
The figure is a block diagram showing a control device for a semiconductor laser according to an embodiment of the present invention. (3) is a preamplifier that converts the output of the photodetector to a predetermined voltage level;
) and (3) constitute a photodetection means for detecting the output of the semiconductor laser. (4) is a peak detection circuit that detects the peak of the bottom output side of the output of the preamplifier (3); (5)
ti peak detected output to the specified bottom output reference voltage (
(6) is an amplifier circuit that amplifies the output of the comparison circuit (5), and (7) is a semiconductor laser pulsed f1.VB). Peak output of preamplifier (3) when tuned <11! I t-, at the start of pulse modulation, for example,
The first sample and hold time M detects the sample and hold for 2 pulses immediately after the start of pulse modulation (al is the bottom output of the preamplifier (3) when pulse modulating the semiconductor laser, a second sample-and-hold circuit that detects sample-and-hold, (
9) is the output (give) of the first sample and hold circuit (7) and the output (VB') of the second sample and hold circuit (8)
, an arithmetic circuit that calculates the amplitude of the modulated pulse after the start of the pulse modulation H, (lυ) is an amplifier circuit that amplifies the output of the arithmetic circuit (9), and (11) always follows the output of the amplification circuit (6). , the bottom output drive current of the semiconductor laser is controlled, and immediately after the start of pulse modulation, a constant modulation pulse current is applied, and after the start of pulse modulation, the modulation pulse current according to the output of the amplifier circuit (10) and the above-mentioned bottom output are controlled. The semiconductor laser drive circuit (12), which is superimposed on the drive current, detects the start of pulse modulation, outputs a sample pulse for sampling, for example, two pulses only at the start of pulse modulation, and outputs a sample pulse for sampling only at the start of pulse modulation, and controls the semiconductor laser for that period. It is a timing circuit that informs the drive circuit, and according to (4) (5) (6) and (11), the first means for detecting the bottom output of the semiconductor laser and controlling the drive current of the semiconductor laser is (7) ( 1
2) The first detection and hold circuit detects the peak output when the semiconductor laser is pulse-modulated from K at the start of modulation, and holds it with the peak output when the semiconductor laser is pulse-modulated using (8) (12). Detects bottom output,
The second test hold circuit to hold is (9) (1
0XlIX12) constitutes a second means for feedforward controlling the modulation pulse current amplitude of the semiconductor laser after the start of pulse modulation according to the outputs of the first and second detection and hold circuits.

Next, the operation will be explained based on the drawings.

%1 In the figure, the output of the semiconductor laser (1) is always
Light detection 11! (2) and is monitored by the preamplifier (3).
is converted into a voltage at a predetermined level. The bottom output side of the semiconductor laser of the output voltage of this preamplifier is monitored by the peak detection circuit (4) K by detecting the busy peak, and compared with the reference voltage (VB) corresponding to the standard bottom output by the comparison circuit (5). The difference is amplified by the amplifier circuit (6) and provided as negative feedback to the semiconductor laser drive circuit (11). As a result, the bottom output monitor voltage of the semiconductor laser is always maintained at the standard bottom output (VB), and the bottom output of the semiconductor laser becomes the specified bottom output. In the absence of modulation, the playback output is maintained equal to the reference bottom output.

The configuration up to this point corresponds to a conventional semiconductor laser control device. FIG. 2 is a waveform diagram illustrating the operation of a semiconductor laser control device according to one embodiment of the present invention.
In addition to the above conventional fRK, when the semiconductor laser is pulse-modulated, the peak output side and bottom output side of the output voltage of the preamplifier (3) can be adjusted immediately after the start of pulse modulation, for example, 11.11 and 11.11 of the first two pulses. 542 sample and hold circuits (7) and (8) detect the sample and hold, and thereafter, according to these hold values, the modulated pulse current machine -
Width f: Vary. At this time, the start of pulse modulation is detected for the modulation signal as shown in FIG. 2(a), and a reset signal as shown in FIG. 2(d) is sent to the semiconductor laser for a predetermined number of pulses, for example between two pulses. In addition to sending the sample pulse to the drive circuit (11), it also samples the peak output side of the two pulses as shown in Figure 2(b), and the bottom output side of the two pulses as shown in Figure 2(c). A timing circuit (12) generates a sample pulse to be sampled.

Further, the semiconductor laser drive circuit (11) receives a reset signal from the timing circuit (12), and when the pulse adjustment is started, the peak output monitor voltage of the semiconductor laser is set to the specified peak output monitor voltage (VP/ It is assumed that the modulation pulse current (E, =vR/RL) is adjusted so as to be superimposed on the t-bottom output drive current.

FIG. 3 is a laser output characteristic diagram illustrating the cutting of a semiconductor laser control device according to an embodiment of the present invention.

How the peak output of the semiconductor laser is controlled by using the semiconductor laser control device configured as described above will be explained with reference to FIGS. 1, 2, and 3.

Now, in Fig. 3, the semiconductor laser drive current versus semiconductor laser output characteristic during room temperature adjustment is curve '4! Suppose that the characteristic is as shown in (4). As long as the driving current vs. laser output characteristic of the semiconductor laser does not change from curve (4), the peak output monitor voltage (V (A) of the semiconductor laser at the start of pulse modulation
) becomes vP, and the peak output of the semiconductor laser becomes the specified peak output. However, if the characteristics of the semiconductor laser change from curve (4) to curve (B) due to changes in temperature over time, the peak output monitor voltage of the semiconductor laser at the start of pulse modulation will be VPIJ3), The peak output of the laser ends up being smaller than the specified peak output.

Therefore, the sample and hold value (VP') of the peak output monitor voltage of the half-quadruple laser immediately after the start of pulse modulation is
and bottom output monitor voltage sample hold value (VB
As can be seen from FIG. The pressure becomes vP, and the peak output of the semiconductor laser becomes the specified peak output.

In FIG. 1, the arithmetic circuit (9) performs the following division operation. Therefore, it is necessary to adjust the number of amplifier circuits (10) to increase. At this time, I took a break from teaching.
In the drive assist circuit (11), the above vR1 is connected to the amplifier circuit (10).
) is sent from. Then, as shown in Fig. 2(d), when the reset signal is released, the modulation /47L/
Sumie flow surface width t-VR/RL (=I,) to vR'/R
LC=x, change to one. As a result, the output monitor voltage of the semiconductor laser becomes as shown in FIG.
) changes to vP=maP(4), and the peak output of the semiconductor laser becomes the specified peak output.

As the semiconductor laser drive circuit (11) of the main culprit embodiment, circuits such as those shown in FIGS. 4, 5, and 6 can be considered, for example.

FIG. 4, FIG. 5, and FIG. 6 are circuit diagrams each showing a specific example of a semiconductor laser drive circuit according to an embodiment of the present invention.

In FIG. 4, % (13) is an analog switch, which switches to the vR side when the reset signal is H and to the vRl side when it is L, as shown in FIG. 2(d). Analog switch, output of Tsuchi (13) to V. shall be.

(14) is a multiplier, and the output is the input with amplitude V0=1
The modulation pulse has a width v0.

Further, in this circuit type, a divider is used in place of the multiplier (14), so that the division operation of the arithmetic circuit (9) can be changed to a subtraction operation.

In this case, the arithmetic circuit (9) has vA'=VP1-vB'
It is assumed that l/vR is input in place of vR and 1/VR' is input in place of vRl to the annular and negative switch (13). Therefore, an amplification factor of 2 is sent from the amplifier circuit (10) to the amplifier circuit (lO).

In these cases, the modulated pulse voltage amplitude is controlled by inputting the modulated pulse directly to the multiplier/divider (14) and performing a final division operation with vo. Although the structure is simple,
This requires a multiplier/divider with good characteristics that does not distort the pulse waveform, which poses problems in terms of accuracy and cost.

The modulated pulse, whose amplitude is controlled to be equal to or vRl by the calculator (14), is output from the bottom output of the semiconductor laser by a clamp circuit composed of a capacitor (15) and a diode (16). Department #
superimposed on the voltage. The drive of mixed semiconductor lasers! II
The IJ pressure is added to the pace of the semiconductor laser m auxiliary transistor (17), and the semiconductor laser is current-driven by passing the semiconductor laser drive current through the semiconductor laser's load resistor (18).

Next, in the specific example shown in FIG. 5, (19) is a transistor, (20) is a resistor, the transistor (19) and the resistor (20) constitute a switching circuit, and the ground and Tc are connected in response to the modulation pulse. Switching is performed between.

As a result, the modulation pulse table is V.

It is converted from Vc to K. The following is the same as FIG. 4. In this case, the multiplier/divider (14) is not required, but the arithmetic circuit (9) is 1, and there are 6 bonitos that are completed before changing from H to L.

This division operation is a so-called DC-like operation and does not directly handle the modulation pulse, so the pulse waveform k of the modulation pulse
Since frequency characteristics at a level that does not cause noise are not required, it is possible to use an inexpensive and highly accurate circuit.

It also becomes possible to use monolithic ICs.

Next, in the specific example of Fig. 6, (21), (22)
, (23) is a transistor, (24)% (25),
(26) is the resistance. As a result of the modulation pulse #CI6, the collector-emitter of the transistor (21) performs an on-off switching operation. When the transistor (21) is off, the current flowing through the semiconductor laser (L) becomes as follows, the semiconductor laser is driven only by the bottom output drive current, and the output of the semiconductor laser is maintained at the specified bottom output. . When the transistor (21) is on, the current flowing through the semiconductor laser (L) becomes "R=IB+f" from IL=, and the semiconductor laser is driven by the current that is the sum of the bottom output drive current and the modulation pulse current. The output of the laser becomes a specified peak output.

Here, the expression is ignored as the base-emitter voltage vBE of the transistor (22), but in reality, it is realized by adding VBIi to the voltage of Vc by a considerable amount. As the first and second sample and hold circuits (7) and (8), a circuit as shown in FIG. 7 can be considered. In Figure 7, (27) is a voltage level conversion layer, (28) is a field effect transistor, (29) is a hold capacitor, (3υ) is FIX' input I input 1A
F amp. The TTL level sample pulse is converted to +v0° and -vDD levels by voltage level conversion l (27) and input to the gate of the field effect transistor (28). Gate voltage is +1°. 10 Va at the time of
The source (S) input voltage below c -Vth is turned on,
When the dart voltage is -vDD, the source (S) input voltage above -vDI) is turned off. Here, vth is the source (S)-gate (G) voltage required to conduct the source (S) and drain (9) of the field effect transistor. In addition, the preamp (3
+v0° and -vDDt-Z shall be determined according to the range of the output monitor voltages of the semiconductors S to D which are the outputs of ). At this time, the sample pulse is as shown in Fig. 2(b).
When going from L to H, the gate voltage of the field effect transistor (28) is +7° from -VDD. So, the sauce (8
) and drain (2) are conductive, and the output monitor voltage of the semiconductor laser is charged to the Holt capacitor (29) and outputted via the voltage-lock type x and f using the OP amplifier (30). Ru. Then, when the sample pulse returns from ■ to B, the voltage at the gate (9) of the field effect transistor (28) changes from +v0° to -vD.
D, the source (S) and drain (2) become non-conductive, and the output monitor voltage of the semiconductor laser immediately before this is held in the hold capacitor (29) and outputted via the buffer mentioned above. Again. In the above example, the peak detection circuit J@ (4) is used as the first means to detect the bottom output of the semiconductor laser and control the drive current of the semiconductor laser, but the sample hold circuit (7J , (using a circuit similar to 8J,
During the pulse modulation period, a method may be considered in which the bottom output monitor voltage of the semiconductor laser immediately before is held, and a method in which the bottom output side of the semiconductor laser is always sampled and held also during the pulse modulation period. These methods can also share the second sample and hold circuit (8). In this case, the second sample-and-hold circuit (the 8th sample pulse is sent from the timing % (12) at the timing of sampling the bottom output for the entire pulse modulation period before the start of pulse modulation, During the period when pulse modulation is not performed, the sample pulse must always be at H level.

Further, in the above embodiment, as the second detection hold circuit,
We used a @2 number hold circuit (8) and a timing circuit (12) that sample and hold the bottom output when pulse modulating a semiconductor laser immediately after the start of pulse modulation. Sample and hold the bottom output side during the entire pulse modulation period, such as immediately before the start of modulation or the bottom period of the pulse modulation period □
The sample and hold circuit (8) and timing circuit (12) may be configured so as to do so.

In addition, in the explanation so far, when the pulse modulation starts, the sample and hold voltage tm is set using two pulses. If the temperature and rise are stabilized within one pulse, only one pulse is sufficient.Also, with an appropriate range for the pulse modulation period, two
You may use more than a pulse.

(9) In the above embodiment, the first detection and hold circuit pulse-modulates the semiconductor laser, detects the peak output at 9 o'clock immediately after the start of pulse modulation, and holds it thereafter, and the first detection and hold circuit pulse-modulates the semiconductor laser and detects the peak output at 9 o'clock as a pulse. A second detection and hold circuit detects the peak output and bottom output when the semiconductor laser is pulse modulated, and first and second sample and hold circuits that sample and hold the output immediately after the start of pulse modulation, as a second detection and hold circuit that detects immediately after the start of modulation and holds the remaining period. (7)
, (8) and timing circuit (12) t'' were used,
A peak detection circuit detects the peak output when pulse modulating the semiconductor V-D and the peak immediately after the start of pulse modulation, and a peak detection circuit detects the bottom output immediately before or after the start of pulse modulation or during the bottom period of the pulse modulation period. May be used.

Further, the semiconductor laser control device described above can be used not only in the above-mentioned optical disk device but also in an optical laser card or the like to realize a highly reliable device.

〔Effect of the invention〕

As described above, according to the present invention, there is a photodetecting means for detecting the output of the V-engineered conductor laser, and a first means for detecting the bottom output of the semiconductor laser from the photodetecting means and controlling the drive current of the semiconductor laser. , a first detection and hold circuit that detects and holds the peak output when the semiconductor laser is pulse modulated at the start of pulse modulation, and a second detection and hold circuit that detects and holds the bottom output when the semiconductor laser is pulse modulated. The semiconductor laser control device is configured with a hold circuit and a second arm that performs tweed-forward control of the modulation pulse of the semiconductor laser after the start of pulse modulation according to the outputs of these detection and hold circuits. The peak output when pulse-modulating the laser can be controlled and stabilized with short poem 1#J (for example, 2 pulses of darkness).

[Brief explanation of drawings]

FIG. 1 is a block diagram showing a semiconductor laser control device according to an embodiment of the present invention, and FIGS. 2 and 3 are waveform diagrams illustrating the operation of the semiconductor laser control device according to an embodiment of the present invention, respectively. Laser output characteristic diagrams, FIG. 4, FIG. 5, and FIG. 6 are circuit diagrams each showing a semiconductor laser drive circuit according to an embodiment of the present invention, and FIG. 7 is a circuit diagram showing an embodiment V of the present invention.
FIG. 8 is a circuit diagram showing such a sample and hold circuit, and FIG. 8 is a laser output characteristic diagram illustrating a previous version of a conventional semiconductor laser IJ control device. In the figure, (l) is a semiconductor laser, (2) is a photodetector, (3) is a preamplifier, (4) is a peak detection circuit, (5) is a
) is a comparison circuit, (6) and (10) are each an amplifier circuit, (
7) and (8) are the first and second sample and hold circuits IG, (9) the ld calculation circuit, (11) the semiconductor laser drive circuit, (12) the timing circuit, and (2) (
(4) (5) (6) (n)
(7) (12) for the first detection hold circuit; (8) (12) for the second detection hold circuit; <9) (10XllX12) for the second detection hold circuit.
constitutes the means of In addition, in the figures, the same reference numerals indicate the same or corresponding parts. Agent Masuo Oiwa?・Written amendment to the procedure (voluntary) 1. Indication of the incident Patent application 1988-1988? No. 7 26
Name of the invention: Semiconductor laser control device 3, Representative Hitoshi Katayama of the person making the amendment Section 6, Detailed description of the invention in the specification to be amended 6, Contents of the amendment (1) Specification, page 15, 11 Correct the line "TC" to "VC". (2) "Holt capacitor" in line 5 of page 18 is corrected to "hold capacitor." (3) "Follower type" in line 7 of page 18 is corrected to "follower type." (4) Change “Sample Hold” on page 19, line 18 of the same page to “
Corrected to ``Second Sample Hold.''that's all

Claims (3)

[Claims] (1) a photodetection means for detecting the output of the semiconductor laser; a first means for detecting the bottom output of the semiconductor laser from the photodetection means and controlling the driving current of the semiconductor laser;
A first detection and hold circuit detects and holds the peak output when the semiconductor laser is pulse modulated at the start of pulse modulation, and a second detection and hold circuit detects and holds the bottom output when the semiconductor laser is pulse modulated. ,
and a second means for feedforward controlling the amplitude of the modulated pulse current of the semiconductor laser after the start of the pulse modulation according to the outputs of these detection and hold circuits. (2) The semiconductor laser control device according to claim 1, wherein the second detection and hold circuit detects the bottom output immediately before or after the start of pulse modulation and holds it for the other period. (3) The semiconductor laser control device according to claim 1, wherein the second detection and hold circuit detects the bottom output during the bottom period of the pulse modulation period and holds it for other periods.