JPH11238932A - Semiconductor laser device and laser-light receiver - Google Patents

Abstract

PROBLEM TO BE SOLVED: To perform modulating operation adequately in the broad range of a laser light emitting region from a natural light emitting region, by forming a semiconductor laser driving signal in correspondence with the deviation between a light-amount command signal and a feedback signal, and overlapping a driving current in correspondence with the signal in linear and nonlinear patterns. SOLUTION: A light-amount command signal S for driving a semiconductor laser LD is inputted into a terminal 11. A monitoring circuit 400 receives the light from the laser LD with a photodiode PD, outputs a light-amount monitoring voltage signal M, negatively feedbacks the signal to a driving control circuit 200, and performs control. A linear driving-current output circuit 300 amplifies the laser driving signal outputted from the driving control circuit 200. A nonlinear driving-current output circuit 500 outputs the signal in correspondence with the nonlinear pattern with the increase and the decrease of the laser driving signal and controls the gain of the laser light emitting region from the natural light emitting region. At the rising-up time of the driving current, the driving current, which is in proportion to the inverse number of the emitted light amount for the injected light of the laser LD, flows and is overlapped on the output current of the linear output circuit 300.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a driving circuit for driving a semiconductor laser used in an optical scanning recording apparatus or an optical communication apparatus, and more particularly, to an improvement in responsiveness when an optical output of the semiconductor laser is analog-modulated. The present invention relates to a semiconductor laser device and a laser light receiving device that receives a laser beam and outputs a monitor signal.

[0002]

2. Description of the Related Art Conventionally, for example, in an optical scanning recording apparatus, an apparatus which scans a light beam generated from a semiconductor laser on a photosensitive recording material and records data on the recording material has been put into practical use. In optical communication devices, devices for transmitting an optical signal obtained by modulating the optical output of a semiconductor laser via an optical fiber are widely used.

A semiconductor laser used in a semiconductor laser device such as an optical scanning recording device or an optical communication device can directly modulate an optical output generated from the semiconductor laser by changing a driving current. A circuit for controlling the drive current usually has an APC (Automatic Power Co.) so that a desired optical output set by the light intensity command signal is accurately generated from the semiconductor laser.
In many cases, control is performed to stabilize the optical output by providing an (control) circuit. A conventional APC circuit detects a light amount of a monitor light obtained by branching a part of a forward emission light or a backward emission light of a semiconductor laser, and cancels a difference between the light amount and a set light amount indicated by the light amount command signal. Is configured to control the drive current of the semiconductor laser. However, in the semiconductor laser, as shown in FIG. 2, the light output characteristics with respect to the drive current significantly change between the spontaneous light emitting region (LED region) and the laser light emitting region. In order to use the semiconductor laser by changing the light output over a wide range, it is necessary to use the semiconductor laser not only in the laser emission region where the optical output characteristic with respect to the driving current is linear, but also in the natural emission region. In this case, there is a problem that a change in optical output with respect to a change in drive current is small, and therefore, modulation responsiveness is deteriorated.

Therefore, various means for solving the above-mentioned problems have been proposed.

For example, in a semiconductor laser driving circuit known in Japanese Patent Application Laid-Open No. Hei 2-21683, a light amount command signal is inputted to a signal limiting circuit for suppressing a signal of a predetermined value or more and a high-pass filter for extracting a high frequency component of the signal. By generating a compensation signal by adding the compensation signal to the light amount command signal, the modulation response in a low light amount region is improved. That is, the compensation signal is not added to the light amount command signal with respect to the loop transmission characteristic 61 before feedback in the natural light emission region and the loop transmission characteristic 62 before feedback in the laser emission region shown in FIG. As shown by the solid line 71 in FIG. 17A, the closed-loop characteristic in this case is such that the characteristic of the spontaneous light emission region has a low high-speed response. Therefore, a light amount command signal is input to a signal limiting circuit and a high-pass filter to generate a compensation signal, and the compensation signal is added to the light amount command signal.
When the semiconductor laser is driven using a signal as indicated by the broken line in FIG. 17B, the closed-loop characteristic in the spontaneous light emission region is changed to a characteristic 71 'indicated by the broken line in FIG.
This is improved to a characteristic equivalent to the characteristic 72 'of the laser emission region shown by the solid line in FIG. Note that the curve of the characteristic 72 'is a virtual characteristic curve, and is a curve in a state where the high-frequency characteristics in the natural light emission region are improved to be equal to those in the laser light emission region.

Further, for example, Japanese Patent Application Laid-Open No. Sho 63-204522
In a known laser recording apparatus, the modulation response in a low light quantity region is improved by controlling a loop gain of a feedback circuit in an APC circuit to be constant based on a light quantity command signal. That is, for the loop transfer characteristics 61 and 62 of the feedback before compensation shown in FIG. 16 described above, compensation for controlling the loop gain to be constant as shown in FIG. 17 is performed on the characteristic 61, and as shown in FIG. Loop transfer characteristics 81 and 8 after feedback correction
By setting the value to 2, a constant transfer characteristic is obtained for the entire amount of light from the natural light emission region to the laser light emission region.

[0007]

However, in the above-described semiconductor laser driving circuit disclosed in Japanese Patent Laid-Open Publication No. Hei 2-21683, compensation is made from a light quantity command signal before a signal corresponding to a change in the light quantity of the semiconductor laser is fed back. Since the signal is generated and the compensation signal is superimposed on the light amount command signal and added, the compensation signal is an open-loop compensation that does not correspond to a change in the light amount of the semiconductor laser. Therefore, Japanese Patent Application Laid-Open
The semiconductor laser driving circuit disclosed in Japanese Patent No. 21683 has a problem that precise compensation cannot be performed when the actual light amount fluctuates with respect to the light amount command signal. For example, there is a problem that when the optical output characteristic with respect to the drive current of the semiconductor laser changes due to a temperature change, the modulation response greatly fluctuates.

In general, a rectangular wave, a sawtooth wave or the like can be decomposed into sine wave components having different wavelengths. JP-A-63-2045
In the laser recording device known in Japanese Patent Publication No. 22, when a light amount command signal that suddenly changes in a step-like manner such as a rectangular wave is input, a plurality of sine waves having different wavelengths are input.
There is a problem that oscillation or deterioration of responsiveness may occur. In other words, when the light amount command signal that rapidly changes in a step-like manner includes a signal component in the spontaneous light emission region and a signal component in the laser light emission region, the laser recording device disclosed in Japanese Patent Application Laid-Open No. 63-204522 is suitable for the spontaneous light emission region. It is undefined which of the gain and the gain suitable for the laser emission region is selected. That is, it is impossible to select two different loop gains at the same time even if the loop gain is controlled to be constant, so that an appropriate loop gain is not always selected. For this reason, when a light amount command signal that suddenly changes in a step-like manner is input, the loop gain is too high when the light amount command signal rises, and oscillation occurs, or the loop gain is too low when the light amount command signal falls, so that the drive current does not drop easily. And the operation of the circuit becomes extremely unstable. Accordingly, JP-A-63-204
The laser recording apparatus disclosed in Japanese Patent No. 522 cannot withstand practical use unless the gradation change is a very gentle light quantity command signal, and is difficult to be applied to an optical recording apparatus or an optical communication apparatus that attempts to respond to any light quantity command signal. There's a problem.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and enables stable and precise compensation in a closed loop in a semiconductor laser device, and is compatible with all light quantity command signals including zero light quantity. To compensate for the gain,
It is an object of the present invention to improve modulation response characteristics so as to stably and accurately follow an input signal that is modulated at high speed.

In some cases, these semiconductor laser devices include a photoelectric conversion element that receives a laser beam emitted by a semiconductor laser and outputs a monitor signal according to the amount of received light.
In addition, a laser light receiving device such as an inspection device that performs an inspection using laser light may also include a photoelectric conversion element. In a semiconductor laser device or a laser light receiving device equipped with these photoelectric conversion elements, for example, a device having a photodiode for monitoring in a package of a semiconductor laser chip, either an anode terminal or a cathode terminal of the semiconductor laser. One of them may be electrically connected to one of the anode terminal and the cathode terminal of the photoelectric conversion element.
With this connection, the high-frequency component of the drive current for driving the semiconductor laser passes through the junction capacitance and stray capacitance of the photoelectric conversion element and appears at the terminal of the photoelectric conversion element. The monitor signal is output at an incorrect level with respect to the level of the monitor signal expected from the amount,
There is a problem that the monitor accuracy becomes inaccurate.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and it is an object of the present invention to reduce or eliminate an error component generated in a photoelectric conversion element for light reception and to improve monitoring accuracy.

[0012]

The object of the present invention can be solved by the following semiconductor laser device. That is, a semiconductor laser device according to claim 1, wherein the semiconductor laser device drives a semiconductor laser based on an input light amount command signal and controls the amount of laser light emitted from the semiconductor laser. A light amount monitoring unit that includes a photoelectric conversion element that receives light, monitors a light amount of the laser light that changes according to the input light amount command signal, and outputs a feedback signal corresponding to the light amount; A drive control unit that generates a semiconductor laser drive signal in accordance with a deviation from the feedback signal, a linear drive unit that outputs a drive current that linearly corresponds to the semiconductor laser drive signal, and a drive that nonlinearly supports the semiconductor laser drive signal A non-linear driving unit for outputting a current, wherein the non-linear driving unit is configured to operate the semiconductor laser in response to an increase in the input semiconductor laser driving signal. A first non-linear characteristic stage for non-linearly decreasing the output gain in accordance with a gentle portion of the rate of change of the differential quantum efficiency of the semiconductor laser with an increase in the input output signal of the first non-linear characteristic stage. A second non-linear characteristic stage that reduces the output gain more steeply and non-linearly than the first non-linear characteristic stage in accordance with a steep portion of the rate of change of the differential quantum efficiency; A third nonlinear characteristic stage that outputs the signal output from the second nonlinear characteristic stage as it is when the output signal is equal to or less than the set value, and outputs a constant value signal when the output signal is equal to or greater than the set value. ,
The level of the drive current corresponding to the nonlinearity is controlled by the first to third nonlinear characteristic stages, and the semiconductor laser is driven by the semiconductor laser drive current obtained by superimposing the drive current output from the linear drive unit and the nonlinear drive unit. It is characterized by doing.

According to the semiconductor laser device of the first aspect, it is possible to perform stable and precise compensation in a closed loop, and to perform gain compensation in response to any light quantity command signal including zero light quantity. As a result, the modulation response characteristics could be improved so as to stably and accurately follow an input signal that is modulated at high speed.

According to a ninth aspect of the present invention, there is provided a semiconductor laser device for driving a semiconductor laser based on an input light amount command signal and controlling the amount of laser light emitted from the semiconductor laser. A light amount monitoring unit that includes a photoelectric conversion element that receives a laser light emitted by a laser, monitors a light amount of the laser light that changes according to the input light amount command signal, and outputs a feedback signal corresponding to the light amount; A drive control unit that generates a semiconductor laser drive signal according to a deviation between the light amount command signal and the feedback signal,
A drive unit that outputs a drive current according to the semiconductor laser drive signal; and a high-pass filter having a band characteristic that passes only a high-frequency component of a signal proportional to the drive current, and an anode terminal of the semiconductor laser. , One of the cathode terminals and one of the anode terminal and the cathode terminal of the photoelectric conversion element is electrically connected, and the light amount monitoring unit outputs the output of the photoelectric conversion element and the output of the high-pass filter. An output according to the deviation is output as the feedback signal.

According to the semiconductor laser device of the ninth aspect, an error component generated in the photoelectric conversion element for light reception can be reduced or eliminated, and the monitoring accuracy can be improved.

According to a tenth aspect of the present invention, a semiconductor laser is driven based on an input light quantity command signal, and a laser beam emitted from the semiconductor laser is received by a photoelectric conversion element. In a laser light receiving device that outputs a monitor signal according to the amount of light, one of an anode terminal and a cathode terminal of the semiconductor laser and one of an anode terminal and a cathode terminal of the photoelectric conversion element are electrically connected. A driving unit that outputs a driving current according to the light amount command signal; and a high-pass filter having a band characteristic that passes only a high-frequency component of a signal proportional to the driving current. An output corresponding to a deviation between the output of the element and the output of the high-pass filter is output as the monitor signal.

According to the laser light receiving device of the tenth aspect, the error component generated in the light receiving photoelectric conversion element is reduced.
It was able to remove and improve the monitoring accuracy.

[0018]

Embodiments of the present invention will now be described with reference to the drawings.

FIG. 1 is a circuit diagram of a semiconductor laser driving circuit which is a main part of a semiconductor laser device. Note that the semiconductor laser drive circuit is a circuit that is a main part of a semiconductor laser device such as an optical scanning recording device or an optical communication device.

In FIG. 1, an input terminal 11 is a terminal for connection to a control computer (not shown).
The control computer or the like is a modulation signal source, and a light amount command signal S for controlling a drive current of the semiconductor laser LD so that a desired light output is emitted from the semiconductor laser LD is input to the input terminal 11 from the control computer or the like. . The light quantity command signal S has an impedance,
Levels have been adjusted.

The monitor circuit 400 receives a part of the forward or backward emitted light emitted from the semiconductor laser LD and converts the received light into a current signal, and converts the current signal generated from the photodiode PD into a voltage signal. And an operational amplifier A1 for amplifying to a desired voltage level. The operational amplifier A1 converts the current signal generated by the photodiode PD into a current-voltage signal and outputs the converted signal as a light amount monitor signal M as a voltage output.

The drive control circuit 200 includes an addition point 201 and an operational amplifier A2. At the addition point 201, the light intensity command signal S and the light intensity monitor signal M are added. A signal indicating the deviation of M is input. The operational amplifier A2 amplifies the input signal indicating the deviation and outputs a semiconductor laser drive signal.

The linear drive current output circuit 300 includes a linear amplifier 301 and a transistor Tr4 that performs voltage-current conversion. The linear amplification unit 301 is a circuit that outputs a signal linearly corresponding to an increase or a decrease in the semiconductor laser drive signal.
The input terminal of the linear amplifier 301 is connected to the output terminal of the drive control circuit 200, and the output terminal is connected to the base of the transistor Tr4. The transistor Tr4 has a collector connected to the cathode electrode of the semiconductor laser LD, and an emitter grounded via a resistor. Semiconductor laser L
The anode electrode of D is connected to a positive power supply. The semiconductor laser drive signal output from the drive control circuit 200 is amplified by the linear drive current output circuit 300 and
4, a collector current linearly corresponding to the increase or decrease of the semiconductor laser drive signal flows through the transistor Tr4. The collector current of the transistor Tr4 is a drive current of the semiconductor laser LD.

The non-linear drive current output circuit 500 includes an operational amplifier A3 and a transistor Tr3 that performs voltage-current conversion.
And a voltage dividing circuit 510, 520 and a switching circuit 530 for producing nonlinear characteristics, and outputs a signal nonlinearly corresponding to an increase or decrease of the semiconductor laser drive signal.

The voltage dividing circuit 510 is an example of the first nonlinear characteristic stage of the present invention, and includes a resistor R1 and a diode D connected in series.
1 to obtain an output nonlinearly corresponding to the increase or decrease of the semiconductor laser drive signal output from the drive control circuit 200 from between the resistor R1 and the anode of the diode D1. The circuit constant of the voltage dividing circuit 510 is set such that the output gain changes nonlinearly in accordance with the characteristics of the portion where the conversion rate of the differential quantum efficiency of the semiconductor laser LD is gentle.

The operational amplifier A3 amplifies the output of the voltage dividing circuit 510 and outputs it to the voltage dividing circuit 520.

The voltage dividing circuit 520 is an example of the second nonlinear characteristic stage of the present invention, and includes a resistor R2 and a diode D connected in series.
2, an output is provided between the resistor R2 and the anode of the diode D2, the output nonlinearly corresponding to the increase or decrease of the semiconductor laser drive signal output from the drive control circuit 200. The circuit constant of the voltage dividing circuit 520 is set such that the gain changes nonlinearly in accordance with the characteristics of the portion where the conversion rate of the differential quantum efficiency of the semiconductor laser LD is steep.

Although the response output of each of the voltage dividing circuits 510 and 520 nonlinearly responds to the increase of the semiconductor laser drive signal, the gain decreasing tendencies are different from each other.
Also, the ranges in which the response outputs of the voltage dividing circuits 510 and 520 become nonlinear are shifted from each other. The total output gain of the voltage dividing circuit 510, the operational amplifier A3, and the voltage dividing circuit 520 becomes an output gain nonlinearly corresponding to the input semiconductor laser drive signal.

The switching circuit 530 is an example of the third nonlinear characteristic stage of the present invention, and includes two transistors Tr1 and Tr2.
Tr2 is provided. The base of the transistor Tr1 is connected to the output circuit of the voltage dividing circuit 520, the emitter is connected to the transistor Tr2 via a resistor, and the collector is grounded. The collector of the transistor Tr2 is connected to a positive power supply, and the emitter is connected to the transistor T2 via a resistor R4.
The base of the transistor Tr3 is connected to a control substrate (not shown) provided outside the substrate of the semiconductor laser drive circuit, and the control signal C is input thereto. The switching circuit 530 outputs a constant current when the output of the semiconductor laser drive signal is equal to or more than a certain value, and outputs the output of the voltage dividing circuit 520 as it is when the output of the semiconductor laser drive signal is equal to or more than a certain value.

When the output of the voltage dividing circuit 520 exceeds a certain value, the emitter output of the transistor Tr2 is applied to the base of the transistor Tr3 by the switching action of the transistor Tr1, and the emitter output of the transistor Tr1 is not applied to the base of the transistor Tr3. Since the control signal C having a constant voltage is input to the base of the transistor Tr2, the collector current of the transistor Tr3 takes a constant value when the output of the voltage dividing circuit 520 exceeds a constant value.

If the output of the voltage dividing circuit 520 is equal to or less than a predetermined value, the emitter output of the transistor Tr1, that is, the response output nonlinearly corresponding to the increase of the semiconductor laser drive signal is applied to the base of the transistor Tr3, and the transistor Tr3 is driven.

The entire non-linear driving current output circuit 500 has a voltage dividing circuit 510 and a voltage dividing circuit 52 depending on circuit constants.
The gain reduction rate is set to increase in the order of 0, and the switching operation of the switching circuit 530 can be regarded as the gain reduction rate becomes infinitesimal, so that the brightness of the semiconductor laser LD gradually increases from the light-off state. Accordingly, first, the gain of the non-linear driving current output circuit 500 gradually decreases, and then, when the semiconductor laser driving signal further increases, the gain of the non-linear driving current output circuit 500 sharply decreases. When the set value is reached, the gain of the non-linear driving current output circuit 500 is cut, and the non-linear driving current output circuit 500 does not substantially output any more driving current.

The semiconductor laser LD includes a collector current of the transistor Tr4 (drive transistor) of the linear drive current output circuit 300 and a nonlinear drive current output circuit 500.
The transistor Tr3 (drive transistor) emits light when driven by the sum of the collector currents.

The monitor circuit 400 described above outputs a change in the amount of light of the semiconductor laser LD as a light amount monitor signal M, which is an electric signal, and performs negative feedback to the drive control circuit 200 for control. It operates so as to be stable according to the light amount command signal S.

Next, the operation and output gain characteristics of the semiconductor laser drive circuit shown in the embodiment will be described with reference to FIGS.

FIG. 2 is a diagram showing a general relationship between a current level and a light output when a DC current is supplied as a drive current (injection current) of a semiconductor laser. The semiconductor laser switches from spontaneous emission to laser emission when the level of the drive current is increased. However, when the level of the drive current is smaller than Ith, spontaneous emission is dominant. Therefore, the power of the optical output increases nonlinearly. On the other hand, when the level of the drive current exceeds Ith, laser emission occurs, and in this laser emission region, the power of the optical output increases substantially linearly with an increase in the amount of drive current. In a spontaneous light emission region in which the drive current is smaller than the current value Ith, the larger the drive current value, the larger the change in the optical output with respect to the change in the drive current.

FIG. 3 is a diagram showing the relationship between the drive current of the semiconductor laser and the differential quantum efficiency. In FIG. 2, in a region where the relationship between the drive current and the optical output is linear, that is, in a region where the drive current exceeds Ith, the differential quantum efficiency takes a substantially constant value regardless of the level of the drive current of the semiconductor laser LD. In the drawing, the line L indicates the differential quantum efficiency of the semiconductor laser in the laser emission region where the drive current exceeds Ith. When the drive current is lower than Ith, the differential quantum efficiency increases as the drive current increases. The curve N in the figure shows the differential quantum efficiency of the semiconductor laser in the spontaneous emission region where the drive current does not exceed Ith.

Since the differential quantum efficiency can be regarded as the gain of the element of the semiconductor laser alone, it can be seen that the semiconductor laser drive circuit has an element whose gain varies with respect to the input in a closed loop.

FIG. 4 is a diagram showing the relationship between the input value (semiconductor laser drive signal) of the nonlinear drive current output circuit 500 and the output gain. The characteristic curve of the non-linear driving current output circuit 500 is preferably set to a curve that satisfies the reciprocal relationship with respect to the curve N shown in FIG. The relationship between the input value and the output gain of the non-linear driving current output circuit 500 includes the characteristics of the voltage dividing circuit 510 (FIG. 5), the characteristics of the operational amplifier A3 (FIG. 6), the characteristics of the voltage dividing circuit 520 (FIG. 7), and the switching circuit. 530 are realized by combining the respective characteristics of FIG. 8 (FIG. 8). The portion of a1 is approximately the characteristics of the voltage dividing circuit 510 and the operational amplifier A3, the portion of b1 is the characteristic of the voltage dividing circuit 520, and the portion of c1. Depends on the characteristics of the switching circuit 530.

FIG. 5 is a diagram showing the relationship between the input and the output gain (input / output characteristics) of the voltage dividing circuit 510. The portion a2 of this characteristic curve is a part of the characteristic curve of FIG. The rate of change is matched.

FIG. 6 shows the relationship between the input and the output gain (input / output characteristics) of the operational amplifier A3.
No. 3 provides a constant output gain regardless of the level of the input value.

FIG. 7 is a diagram showing the relationship between the input and the output gain (input / output characteristics) of the voltage dividing circuit 520. The portion b2 of the characteristic curve is the same as the portion b1 of the characteristic curve of FIG. Matches.

FIG. 8 shows a switching circuit 53 for an input.
FIG. 4 is a diagram showing a relationship between output gains (input / output characteristics) of 0, where a portion of c2 of the characteristic curve coincides with a portion of c1 which is a part of the characteristic curve of FIG. This characteristic curve is realized by the circuit constant of the transistor Tr1. The drive current is Ith
When the voltage applied to the base of the transistor Tr1 is Vth, the output gain is constant regardless of the input value of the semiconductor laser drive signal and the voltage is Vth when the voltage applied to the base of the transistor Tr1 is Vth or less.
, The output gain decreases extremely sharply due to the switching operation of the transistor Tr1.

The characteristic curve of FIG. 5 can be obtained by the ratio of the voltage division by the resistor R1 and the diode D1, and the characteristic curve of FIG. 7 can be set by the ratio of the voltage division by the resistor R1 and the diode D2. Further, the output gain of the voltage dividing circuit 510 is raised by the operational amplifier A3, thereby realizing the characteristics of the portion a1 in FIG.

As described above, the nonlinear drive current output circuit 5
00 were amplified with high gain corresponding to the differential quantum efficiency when the semiconductor laser LD by the light intensity command signal S is operated in a natural light emission region (hereinafter drive current threshold I _th), closer to the laser emission area from the spontaneous emission region In the laser light emission region where the gain gradually decreases and the differential quantum efficiency takes a constant value, the circuit has an input / output characteristic that outputs a non-linear driving current such that the gain becomes approximately −∞.

As described above, the nonlinear drive current output circuit 500
Is provided with a voltage dividing circuit 510 as a first non-linear characteristic stage and a voltage dividing circuit 520 as a second non-linear characteristic stage, and the level of the semiconductor laser driving signal of the drive control circuit 200 becomes equal to or lower than Ith. If the voltage is smaller than the power voltage, the drive current proportional to the reciprocal of the relationship between the amount of light emission and the injection current of the semiconductor laser LD flows at the rise of the drive current by the nonlinear drive current output circuit 500, and the output of the linear drive current output circuit 300 is output. Superimposed with current.

The semiconductor laser drive circuit of the present embodiment includes the nonlinear drive current output circuit 500 to stabilize the loop gain of the circuit including the element whose gain fluctuates with respect to the input level, and The correction is performed so that the response characteristics of the spontaneous light emission region and the response characteristics of the laser light emission region to the drive current match.

Therefore, according to the above-described semiconductor laser driving circuit, the semiconductor laser LD can be modulated at a high speed with a constant response over a wide range from the natural light emitting region to the laser light emitting region. Also, the nonlinear drive current output circuit 500
Is performed in a closed loop corresponding to the change in the light amount of the semiconductor laser LD in the linear drive current output circuit 300, so that a light amount command signal having a large gradation change width, such as a rectangular wave light amount command signal, is input. However, an appropriate driving current is output, and the light amount tracking performance is improved.

Next, the temperature compensation of the semiconductor laser drive circuit will be described with reference to FIGS.

FIG. 9 is a diagram showing a change in differential quantum efficiency with respect to a drive current (injection current) of a semiconductor laser when a temperature fluctuation occurs. The characteristic curve shows the differential quantum efficiency at an arbitrarily set reference temperature. A characteristic curve Hi indicates a state where the temperature of the semiconductor laser LD is higher than the reference temperature. The characteristic curve Low indicates that the semiconductor laser L is lower than the reference temperature.
This shows a state where the temperature of D has dropped. As is apparent from FIG. 9, when the temperature condition is changed, even when a drive current equal to the semiconductor laser LD is injected, the light emission decreases as the temperature increases, and conversely increases as the ambient temperature decreases. I understand.

FIG. 10 shows an example of a control block diagram of a semiconductor laser drive circuit for performing temperature compensation. In the figure, a drive circuit 10 includes a drive control circuit 20 described with reference to FIG.
0, linear drive current output circuit 300, monitor circuit 400,
A non-linear driving current output circuit 500 is provided. However, the semiconductor laser LD and the photodiode PD shown in FIG. 1 are taken out as described later. The terminal 11 is an input terminal for the light amount command signal S already described with reference to FIG. The terminal 12 is a terminal connected to the terminal 511, the terminal 521, and the terminal 531. The LD chip 13 is a device in which a semiconductor laser LD and a photodiode PD are integrally packaged, and is fixed to a holder 14 made of aluminum.
The connection between the LD chip 13 and the power supply is omitted. Holder 1
4 is made of aluminum, so that the entire temperature is kept substantially uniform. The temperature measurement unit 16 is embedded in the holder 14 and outputs a signal corresponding to the temperature of the holder 14,
For example, a thermistor or the like can be used. The temperature adjusting section 15 is in contact with the holder 14 and cools or heats the holder 14, and for example, a Peltier element or the like can be used. When a Peltier element is used, the surface to be cooled when energized is brought into contact with the holder 14 so that the LD chip 13
The holder 14 that has been overheated by the heat generated is cooled. The LD chip temperature control unit 17 controls the operation of the temperature adjustment unit 15 according to the signal output from the temperature measurement unit 16, and as a result, the temperature of the semiconductor laser LD included in the LD chip 13 is controlled within a certain range. .

On the other hand, the characteristic curves of the nonlinear drive current output circuit 500 (see FIG. 4) are represented by the terminals 511, 521, 531
It can be moved in the horizontal axis direction by the bias voltage and the semiconductor laser drive signal input to (see FIG. 1). In the temperature compensation circuit 600, a reference bias voltage applied to the terminal 12 is set so that an appropriate characteristic curve can be obtained at the reference temperature. From the output of the temperature measuring unit 16, when the temperature of the semiconductor laser LD is high, the bias voltage input to the terminal 12 is higher than the reference bias voltage, and when the temperature of the semiconductor laser LD is low, the bias voltage input to the terminal 12 is Control is performed so as to be lower than the reference bias voltage.
That is, the circuit characteristics can be made to follow the temperature change of the semiconductor laser LD shown in FIG. 9 by the temperature compensation circuit 600, and the semiconductor laser LD responds without being affected by the temperature change of the semiconductor laser LD. It has become possible. A resistance component may be provided between the terminals 12 and 511, between the terminals 12 and 521, and between the terminals 12 and 531 so that the bias voltage differs for each terminal.

When a plurality of LD chips 13 are mounted on the holder 14, or when a plurality of holders 14 each having the LD chip 13 are arranged close to each other, the semiconductor laser driving circuit operates for each LD chip 13. The drive circuit 10 is provided one by one. A plurality of L
When the D chip 13 is provided, the temperature of each LD chip 13 becomes substantially constant due to heat conduction, and when a plurality of holders 14 are arranged close to each other, radiation or convection causes the temperature of each holder 14, and thus the LD chip 13. Since the temperature is substantially constant, each semiconductor laser LD has substantially the same temperature. Accordingly, each drive circuit 10
However, if a common bias voltage is applied, the circuit can be simplified.

Next, a semiconductor laser drive circuit for automatically setting the characteristics of the linear drive current output circuit 300 by automatically following the characteristics of the semiconductor laser LD will be described with reference to FIG.

FIG. 11 is a control block diagram of a semiconductor laser drive circuit for automatically setting the characteristics of the nonlinear drive current output circuit 500. The drive circuit 10 in FIG.
Control circuit 200, linear drive current output circuit 300, monitor circuit 400, nonlinear drive current output circuit 5
00 is provided. However, the semiconductor laser L shown in FIG.
D and the photodiode PD are taken out as described later. The terminal 11 is an input terminal for the light amount command signal S already described with reference to FIG. The terminal 12 is a terminal connected to the terminal 511, the terminal 521, and the terminal 531. LD chip 13
Is a device in which a semiconductor laser LD and a photodiode PD are integrally packaged, and is fixed to a holder 14 made of aluminum. The connection between the LD chip 13 and the power supply is omitted. The light emission waveform analysis unit 18 also serves as a light emission waveform analysis unit and a correction information acquisition unit of the present invention.

The light emission waveform analyzer 18 analyzes the waveform of the light amount monitor signal M and outputs analysis information. As the analysis information, a peak value, a delay amount, and the like of the waveform of the light amount monitor signal M are acquired.

The nonlinear characteristic input unit 610 applies an appropriate bias voltage to the terminal 12 with respect to the analysis information obtained by the emission waveform analysis unit 18.

According to the semiconductor laser drive circuit shown in FIG.
Even when the characteristics of the semiconductor laser LD are unknown, or when the characteristics change due to deterioration over time, it is possible to drive the semiconductor laser LD under operating conditions suitable for the characteristics of the semiconductor laser to be used. Further, even when the semiconductor laser drive circuit is mounted on a system that cannot accurately measure temperature, the semiconductor laser LD can be driven under appropriate operating conditions.

Next, referring to FIGS. 12, 13 and 14, noise generated due to parasitic capacitance when a semiconductor laser LD and a photoelectric conversion element such as a photodiode PD are used in combination is reduced or eliminated. An example of a semiconductor laser drive circuit will be described.

FIG. 12 is a circuit diagram showing the concept when the semiconductor laser LD and the photodiode PD are driven by a common power supply. FIG. 13 is a circuit diagram illustrating an embodiment of a semiconductor laser drive circuit for reducing or removing generated noise. FIG. 14 is a diagram for explaining the noise and the waveform of the light amount monitor signal M of the semiconductor laser drive circuit.

In FIG. 12, the power supply Pw supplies power to the semiconductor laser LD and supplies a reverse bias to the photodiode PD, and connects the anode of the semiconductor laser LD and the cathode of the photodiode PD. The parasitic capacitance Cs is the sum of the stray capacitance between the terminals of the photodiode PD, the junction capacitance of the photodiode PD, and the like, and is shown in parallel with the photodiode PD using a capacitor symbol in the figure. The drive current Id is a drive current for driving the semiconductor laser LD, and the photoelectric conversion current Ipd is an output of the photodiode PD. The transistor Tr10 is a semiconductor laser LD
The drive transistor controls the current value of the drive current Id according to the input signal to the base.

When the semiconductor laser LD emits light in the circuit of FIG. 12, the photodiode PD outputs a photoelectric conversion current Ipd according to the received light waveform. At this time, the noise current I due to the drive current Id of the semiconductor laser according to the capacitance of the parasitic capacitance Cs
n occurs. The noise current In is a noise component in which a high-frequency component of the drive current Id has passed through the parasitic capacitance Cs, and is superimposed on the photoelectric conversion current Ipd via the parasitic capacitance Cs.

That is, one of the input terminal and the output terminal of the semiconductor laser of the semiconductor laser drive circuit and one of the input terminal and the output terminal of the photoelectric conversion element such as the photodiode PD of the monitor circuit 400 are electrically connected. When a circuit configuration that is connected in a serial manner is applied to a semiconductor laser drive circuit that performs negative feedback based on the output of the photoelectric conversion element as shown in FIG. 1, for example, the control of the negative feedback is inaccurate due to the noise current In. Problem.

Next, an embodiment of a semiconductor laser drive circuit for solving this problem will be described with reference to FIG.

In FIG. 13, the drive control circuit 200, the linear drive current output circuit 300, and the non-linear drive current output circuit 500 are the same as those already described in FIG.
However, the transistors Tr4 and Tr3 included in the linear drive current output circuit 300 and the non-linear drive current output circuit 500 are explicitly shown in the figure for convenience.

The semiconductor laser drive circuit shown in FIG. 13 is connected to the anode terminal of the semiconductor laser LD and the operational amplifier A1 via a high-pass filter 700 having a capacitor Ch and a resistor R5.
1 input terminal. As a result, the operational amplifier A11 outputs the photoelectric conversion current Ipd and the high-pass filter 700.
Is different from the operational amplifier A1 in FIG.

Next, the operation of the circuit of FIG. 13 will be described with reference to FIG. When the waveform of the drive current Id is in the state shown in FIG. 14A, if the high-pass filter 700 is not provided, the noise current In is superimposed on the photoelectric conversion current Ipd and then amplified by the operational amplifier A11. Operational amplifier A
The output signal of No. 11 is in the state shown in FIG. The noise current In is pulse-like noise that has passed through the parasitic capacitance Cs, and the high-pass filter 700
14C is output as a signal obtained by cutting out a high-frequency component of a signal proportional to the drive current Id. The cut-off frequency of the high-pass filter 700 is set so that the noise component passes and the signal component is cut off.

In the example shown in FIG. 13, the operational amplifier A11 receives the signal containing the noise component shown in FIG.
Since the difference between the cancel signals Sc shown in FIG. 14C is output, noise components are canceled from the light amount monitor signal M as shown in FIG.

Generally, one of the input terminal and the output terminal of the semiconductor laser of the semiconductor laser drive circuit is electrically connected to one of the input terminal and the output terminal of the photoelectric conversion element such as the photodiode PD. Semiconductor laser L
D and the photodiode PD are connected to a common terminal.
In this case, when connecting the cathodes to a common terminal,
When the anodes are connected to a common terminal, the cathode of the semiconductor laser LD and the anode of the photodiode PD may be connected to a common terminal. In this example, the anode of the semiconductor laser LD and the cathode of the photodiode PD are shared. In the above description, the power supply Pw is connected.

In order to connect either the input terminal or the output terminal of the semiconductor laser to the input terminal or the output terminal of the photoelectric conversion element such as the photodiode PD, components of resistance, inductance, and reactance are connected. May be passed through.

FIG. 15 is a conceptual diagram illustrating a schematic configuration of an optical scanning recording apparatus having a semiconductor laser drive circuit.

The laser light source 1 houses the semiconductor laser drive circuit shown in FIG. The light beam (laser beam) emitted from the laser light source 1 is deflected by the rotation of the polygon mirror 2 and is incident on the fθ lens 3. lens 3 converges the laser beam deflected by polygon mirror 2 and emits the laser beam at a constant speed on the scanning surface. The recording medium P is, for example, a sheet-shaped or roll-shaped photosensitive material, and is exposed to a laser beam to form a latent image.
The recording medium P on which the latent image is formed is developed by a developing device to obtain an output image. The setting input unit 4 includes the temperature compensation circuit 600 shown in FIG. 10 and the nonlinear characteristic input unit 610 shown in FIG.

[0073]

According to the semiconductor laser driving circuit of the present invention, the semiconductor laser LD can be appropriately modulated in a wide range from the natural light emitting region to the laser light emitting region. Further, even when a light amount command signal having a large gradation change width such as a rectangular wave light amount command signal is input, an appropriate drive current is output, and the light amount followability is improved.

Further, according to the laser light receiving device of the present invention, it is possible to reduce / eliminate an error component generated in the photoelectric conversion element for light reception, and to improve monitoring accuracy.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a semiconductor laser drive circuit.

FIG. 2 is a diagram showing a general relationship between a current level and a light output when a DC current is passed as a drive current of a semiconductor laser.

FIG. 3 is a diagram showing a relationship between a driving current of a semiconductor laser and differential quantum efficiency.

FIG. 4 is a diagram illustrating a relationship between an input value and an output gain of a nonlinear drive current output circuit.

FIG. 5 is a diagram showing a relationship between output gains of a voltage dividing circuit 510.

FIG. 6 is a diagram showing an output gain of an operational amplifier A3.

FIG. 7 is a diagram showing a relationship between output gains of a voltage dividing circuit 520.

FIG. 8 is a diagram illustrating an output gain of a switching circuit.

FIG. 9 is a diagram illustrating differential quantum efficiency with respect to a drive current of a semiconductor laser when a temperature fluctuation occurs.

FIG. 10 is a control block diagram of a semiconductor laser drive circuit that performs temperature compensation.

FIG. 11 is a control block diagram of a semiconductor laser drive circuit that automatically sets characteristics of a nonlinear drive current output circuit.

FIG. 12 is a circuit diagram showing a concept when a semiconductor laser and a photodiode are driven by a common power supply.

FIG. 13 is a circuit diagram illustrating a semiconductor laser driving circuit that reduces or eliminates noise generated due to parasitic capacitance of a semiconductor laser.

FIG. 14 is a diagram illustrating waveforms of noise and a light amount monitor signal of a semiconductor laser drive circuit.

FIG. 15 is a conceptual diagram illustrating a schematic configuration of an optical scanning recording device including a semiconductor laser drive circuit.

FIG. 16 is a characteristic diagram of a conventional semiconductor laser drive circuit.

FIG. 17 is a characteristic diagram of a conventional semiconductor laser drive circuit.

FIG. 18 is a characteristic diagram of a conventional semiconductor laser drive circuit.

[Explanation of symbols]

 Reference Signs List 13 LD chip 17 LD chip temperature controller 18 Light emission waveform analyzer 200 Drive control circuit 300 Linear drive current output circuit 400 Monitor circuit 500 Nonlinear drive current output circuit 600 Temperature compensation circuit 700 High pass filter S Light amount command signal M Light amount monitor signal PD Photo Diode LD Semiconductor laser Id Drive current Ipd Photoelectric conversion current In Noise current

Claims (10)

[Claims] 1. A semiconductor laser device for driving a semiconductor laser based on an input light amount command signal and controlling the amount of laser light emitted from the semiconductor laser, wherein the photoelectric conversion element receives the laser light emitted from the semiconductor laser. A light amount monitoring unit that monitors the light amount of the laser light that changes according to the input light amount command signal and outputs a feedback signal corresponding to the light amount, and calculates a deviation between the light amount command signal and the feedback signal. A drive control unit that generates a semiconductor laser drive signal in response thereto; a linear drive unit that outputs a drive current that linearly corresponds to the semiconductor laser drive signal; and a non-linear drive unit that outputs a drive current that nonlinearly corresponds to the semiconductor laser drive signal. The nonlinear drive unit, the change rate of the differential quantum efficiency of the semiconductor laser with the increase of the input semiconductor laser drive signal A first non-linear characteristic stage for non-linearly decreasing the output gain in accordance with a gentle part; and a steep change rate of the differential quantum efficiency of the semiconductor laser with an increase in the input output signal of the first non-linear characteristic stage. A second non-linear characteristic stage that reduces the output gain more steeply and non-linearly than the first non-linear characteristic stage in accordance with the appropriate part, and a case where the input output signal of the second non-linear characteristic stage is equal to or less than a set value. A third nonlinear characteristic stage that outputs the signal output from the second nonlinear characteristic stage as it is, and outputs a signal of a constant value when the signal is equal to or greater than the set value. Controlling the level of the driving current corresponding to the non-linearity by a non-linear characteristic stage; The semiconductor laser device according to claim Rukoto. 2. The first non-linear characteristic stage includes a first voltage dividing circuit including a resistor and a diode. The second non-linear characteristic stage includes a second voltage dividing circuit including a resistor and a diode. 2. The semiconductor laser device according to claim 1, wherein the non-linear characteristic stage includes a switching circuit using a transistor. 3. The semiconductor laser device according to claim 1, wherein the differential quantum efficiency of the semiconductor laser has a difference of about 30 times or more between a laser emission region and a natural emission region. 4. A first setting signal for adjusting a bias of an input / output characteristic of the first nonlinear characteristic stage, and a second setting for adjusting a bias of an input / output characteristic of the second nonlinear characteristic stage. 4. The semiconductor laser device according to claim 1, further comprising a set value input unit that controls a set signal for adjusting a signal and the set value of the third nonlinear characteristic stage. 5. A laser emission control board including the light quantity monitor section, the drive control section, the linear drive section, and the non-linear drive section, and set value input means arranged outside the laser emission control board. The semiconductor laser device according to claim 4, wherein: 6. The semiconductor laser device according to claim 4, wherein said set value input means outputs said set signal corresponding to a temperature condition. 7. A plurality of laser emission control boards are disposed under substantially the same temperature environment inside the semiconductor laser device, and the set value input means inputs a common setting signal to the plurality of laser emission control boards. 7. The semiconductor laser device according to claim 4, 5 or 6, wherein: 8. An emission waveform analyzing means for analyzing an emission waveform of the semiconductor laser, and correction information obtaining means for obtaining a result of the analysis and outputting correction information, wherein the setting value input means obtains the obtained 8. The semiconductor laser device according to claim 4, wherein the setting signal is adjusted and output according to correction information. 9. A semiconductor laser device for driving a semiconductor laser based on an input light amount command signal and controlling the amount of laser light emitted from the semiconductor laser, wherein the photoelectric conversion element receives the laser light emitted from the semiconductor laser. A light amount monitoring unit that monitors the light amount of the laser light that changes according to the input light amount command signal and outputs a feedback signal corresponding to the light amount, and calculates a deviation between the light amount command signal and the feedback signal. A drive control unit that generates a semiconductor laser drive signal in response to the drive control unit, and a drive unit that outputs a drive current in accordance with the semiconductor laser drive signal;
A high-pass filter having a band characteristic of passing only a high-frequency component of a signal proportional to the drive current, and one of an anode terminal of the semiconductor laser and a cathode terminal, and an anode terminal of the photoelectric conversion element, One of the cathode terminals is electrically connected, and the light quantity monitor outputs an output corresponding to a deviation between the output of the photoelectric conversion element and the output of the high-pass filter as the feedback signal. Semiconductor laser device. 10. A laser light receiving device that drives a semiconductor laser based on an input light amount command signal, receives laser light emitted from the semiconductor laser by a photoelectric conversion element, and outputs a monitor signal according to the light amount of the laser light. In the apparatus, one of an anode terminal and a cathode terminal of the semiconductor laser,
One of an anode terminal and a cathode terminal of the photoelectric conversion element is electrically connected, a driving unit that outputs a driving current according to the light amount command signal, and only a high-frequency component of a signal proportional to the driving current. A laser light receiving device, comprising: a high-pass filter having a band characteristic to pass therethrough; and outputting, as the monitor signal, an output corresponding to a deviation between the output of the photoelectric conversion element and the output of the high-pass filter. .