JP3747670B2 - Semiconductor laser drive circuit - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
In the present invention, a driving circuit for driving a semiconductor laser used in an optical scanning recording apparatus or an optical communication apparatus, particularly, the light emission amount of the semiconductor laser is negatively fed back and compared with a light amount command signal to control the light emission amount. The present invention relates to a semiconductor laser driving circuit.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, for example, in an optical scanning recording apparatus, an apparatus that scans a photosensitive recording material with a light beam generated from a semiconductor laser and records data on the recording material has been put to practical use. Also in the apparatus, an apparatus that transmits an optical signal obtained by modulating the optical output of the semiconductor laser via an optical fiber is widely used.
[0003]
Semiconductor lasers used in these optical scanning recording apparatuses, optical communication apparatuses, and the like can directly modulate the optical output generated from the semiconductor lasers by changing the drive current. This circuit for controlling the drive current is usually provided with an APC (Automatic Power Control) circuit so that the desired optical output set by the light quantity command signal is accurately generated from the semiconductor laser, thereby stabilizing the optical output. Control is often performed. A conventional APC circuit detects a light amount of monitor light obtained by branching a part of a front emitted light or a rear emitted light of a semiconductor laser, and cancels a difference between the emitted light amount and a set light amount indicated by the light amount command signal. In addition, negative feedback control is performed on the driving current of the semiconductor laser.
[0004]
FIG. 13 is a diagram showing the relationship between the current level and the optical output when a direct current is passed as the drive current of the semiconductor laser. If the drive current level is smaller than Ith, the power of the optical output increases non-linearly and slowly as the drive current amount increases. If the drive current level exceeds Ith, the optical output power increases as the drive current amount increases. The power of increases substantially linearly. The injection current amount and the optical output of the semiconductor laser have a substantially linear relationship in the laser emission region and a non-linear relationship in the spontaneous emission region, and the current amount Ith is a threshold value.
[0005]
FIG. 14 is a diagram showing the relationship between the driving current of the semiconductor laser and the differential quantum efficiency. The relationship between the driving current of the semiconductor laser and the optical output is linear when the driving current exceeds Ith. That is, when the driving current exceeds Ith, the differential quantum efficiency is a constant value regardless of the level of the driving current of the semiconductor laser. Take. On the other hand, when the drive current is lower than Ith, the differential quantum efficiency increases as the drive current increases.
[0006]
As described above, in the semiconductor laser, the increase rate of the optical output with respect to the drive current amount is different between the spontaneous emission region below the threshold and the laser emission region above the threshold. In order to use a 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 light output characteristic with respect to the drive current is linear, but also in the spontaneous emission region. However, the light output change with respect to the change of the drive current is small, so that the light modulation responsiveness in this region is deteriorated. For example, when an image is formed on a photosensitive material by a semiconductor laser, the image sharpness is deteriorated.
[0007]
In order to cope with such a problem, a compensation signal is created by inputting a light quantity command signal into a signal limiting circuit that suppresses signals exceeding a predetermined value and a high-pass filter that extracts a high frequency component of the signal, and the compensation signal is added to the light quantity command signal. Thus, a technique for improving the modulation response in a low light quantity region (Japanese Patent Laid-Open No. 2-211683) and the loop gain of the closed loop circuit in the APC circuit are controlled to be constant based on the light quantity command signal. Has proposed a technique (Japanese Patent Laid-Open No. 63-204522) for improving the modulation response in a low light quantity region.
[0008]
However, in the former, since the compensation signal is superimposed on the light amount command signal from outside the loop of the APC circuit, the correction is made in an open loop, and the modulation responsiveness fluctuates due to the characteristic change due to the temperature of the semiconductor laser. was there. This appears as a fluctuation in image sharpness when an image is formed on a photosensitive material by a semiconductor laser.
[0009]
On the other hand, in the latter case, when the light intensity command signal includes the signal component of the spontaneous emission region and the signal component of the laser emission region at the same time, for example, when a stepped light amount command signal is input, the loop gain is the actual light emission amount. Therefore, there is a possibility that oscillation or response degradation may occur without being controlled to an appropriate gain.
[0010]
For this reason, the present inventor, in order to realize high-speed and stable light modulation over the entire region from the natural light emitting region to the laser light emitting region, the light emitting region of the semiconductor laser LD is linear laser as shown in FIG. A linear gain fitting circuit 101 for obtaining an inverse characteristic of the differential quantum efficiency corresponding to the laser emission region, and an inverse characteristic of the differential quantum efficiency corresponding to the spontaneous emission region, which are divided into a light emission region and a non-linear spontaneous emission region. By providing the gain fitting circuit 100 composed of the non-linear gain fitting circuit 102 in the closed loop of the APC circuit, a part of the laser light emitted from the semiconductor laser LD is received by the photodiode PD, and the current / voltage conversion circuit 200 is received. Is converted into a voltage and input to the error calculation unit 300 as a light emission amount detection signal. The difference signal between the amount command signal and the light emission amount detection signal is processed by the linear gain fitting circuit 101 and the non-linear gain fitting circuit 102, respectively, and is added through the voltage / current conversion circuits 111 and 112, and the driving current is added. A drive circuit formed by a double negative feedback loop for supplying to a semiconductor laser LD is proposed, and an attempt is made to improve the response characteristics over the entire region (Japanese Patent Laid-Open No. 10-200179). In the figure, reference numeral 400 denotes a temperature compensation circuit for creating a temperature compensation signal for compensating the temperature characteristic of the semiconductor laser LD and outputting it to the gain fitting circuit 100.
[0011]
[Problems to be solved by the invention]
However, even if a double negative feedback loop is formed in the drive circuit of the semiconductor laser LD as described above, the gain characteristics of the nonlinear gain fitting circuit 102 and the gain characteristics of the semiconductor laser are difficult to match at a considerably low light quantity. After all, it was found that there was a problem that the modulation response deteriorated.
[0012]
Further, since the characteristics of the differential quantum efficiency of each semiconductor laser LD are different, it is necessary to change the gain fitting circuit 100 to a circuit configuration corresponding to each type of semiconductor laser LD or to adjust circuit constants. In addition, it takes a lot of time to realize the characteristics of the novel semiconductor laser LD, and there are some that are very difficult to match depending on the characteristics of the differential quantum efficiency of the semiconductor laser LD. If the inverse characteristics of the differential quantum efficiencies of the semiconductor laser LD do not match, the light modulation response will deteriorate, resulting in a deterioration in modulation performance.
[0013]
On the other hand, such a semiconductor laser is known to cause a failure due to destruction (deterioration) of the laser emission end face due to excessive light emission or the like. For this reason, conventionally, by monitoring the drive current of the semiconductor laser, an abnormality is determined when an overcurrent is generated, and the inflow of the overcurrent is limited to prevent failure, or the semiconductor laser is driven at a constant current. The emitted light is monitored and the occurrence of a semiconductor laser failure is detected by checking whether or not a light emission amount equal to or greater than a standard value (initial value) is obtained.
[0014]
However, since this end face breakage occurs in both the front end face and the rear end face of the semiconductor laser, the end face on the opposite side opposite to the emission end face of the semiconductor laser whose light emission amount is detected by the APC circuit when controlled by the APC circuit. When it deteriorates, even if the emitted light quantity is controlled to a constant value by the APC circuit, the deterioration of the end face facing it cannot be detected and the failure state proceeds. Under this circumstance, when the emission end face of the semiconductor laser whose light emission amount is detected by the APC circuit deteriorates, control is performed so that the emitted light does not decrease by the operation of the APC circuit, and an excessive current flows and the semiconductor laser rapidly It causes a situation where the failure proceeds.
[0015]
The present invention has been made in view of various circumstances found in the above-described semiconductor laser drive circuit, and the first object of the present invention is to realize a high-speed and stable modulation response even at an extremely low light amount near zero. Another object of the present invention is to provide a semiconductor laser driving circuit.
[0016]
A second object of the present invention is to provide a semiconductor laser driving circuit that is excellent in light quantity stability and modulation response over the entire region from the spontaneous emission region to the laser emission region of the semiconductor laser.
[0017]
A third object of the present invention is to provide a semiconductor laser driving circuit capable of detecting a failure of a semiconductor laser early and reliably with a simple configuration.
[0018]
[Means for Solving the Problems]
According to a first aspect of the present invention, there is provided a semiconductor laser driving circuit for driving and controlling the semiconductor laser by negatively feeding back a detection signal of the light emission amount of the semiconductor laser and comparing it with a light amount command signal. The difference signal between the light emission detection signal and the light intensity command signal is input. By the signal formed based on the difference signal, A linear circuit that outputs linear drive current to a semiconductor laser and a nonlinear drive current are output. Has two nonlinear amplifiers A double negative feedback loop with a non-linear circuit is formed, and the light quantity command signal is This is a voltage that outputs a light level corresponding to the threshold of the semiconductor laser at the lowest operating temperature. Clip at the specified value, Signal line provided on the input side of the first nonlinear amplifier, between the first nonlinear amplifier and the second nonlinear amplifier, or on the output side of the second nonlinear amplifier The semiconductor laser drive circuit is characterized by adding to.
[0020]
Further, a claim for solving the first problem 2 In the semiconductor laser driving circuit for driving and controlling the semiconductor laser by negatively feeding back a detection signal of the light emission amount of the semiconductor laser and comparing the detection signal with the light amount command signal, the light emission amount detection signal and the light amount command signal are Input the difference signal By the signal formed based on the difference signal, A linear circuit that outputs linear drive current to a semiconductor laser and a nonlinear drive current are output. Has two nonlinear amplifiers A double negative feedback loop with a non-linear circuit is formed, and the light quantity command signal is This is a voltage that outputs a light level corresponding to the threshold of the semiconductor laser at the lowest operating temperature. Clip at the specified value, Signal line provided on the input side of the first nonlinear amplifier, between the first nonlinear amplifier and the second nonlinear amplifier, or on the output side of the second nonlinear amplifier And a compensation voltage is added to the light quantity command signal so that negative feedback does not work up to the predetermined value.
[0021]
Claim 3 The invention described in claim 1 is characterized in that the linear circuit and the non-linear circuit in the negative feedback loop perform non-negative processing that is set to 0 when the negative feedback loop is invalid. 2 It is a semiconductor laser drive circuit of description.
[0022]
According to a fifth aspect of the present invention, in the semiconductor laser drive circuit according to the third or fourth aspect, the predetermined value is a light amount level corresponding to a threshold value of the semiconductor laser at the lowest usable temperature.
[0032]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0033]
(Claims 1-5)
FIG. 1 is a configuration block diagram showing an example of an embodiment of a semiconductor laser driving circuit according to claims 1 and 2.
[0034]
As shown in the figure, a part of the laser light emitted from the semiconductor laser LD is received by a photodiode PD for detecting a light emission amount, converted into a voltage through a current / voltage conversion circuit 1, and a light emission amount detection signal. Is input to the error calculator 2. In the error calculation unit 2, a difference signal from a light quantity command signal set in advance based on the standard value of the semiconductor laser LD is extracted and input to the linear circuit 3 and the nonlinear circuit 4 constituting the gain fitting circuit. .
[0035]
The linear circuit 3 is responsible for driving a region that is equal to or greater than the threshold value (value at the current amount Ith) of the semiconductor laser LD shown in the relationship between the current level of the semiconductor laser and the optical output in FIG. The circuit outputs a linear drive current, and includes a linear amplifier 3a and a voltage / current conversion circuit 3b.
[0036]
The non-linear circuit 4 is mainly responsible for driving the region below the threshold value (value at the current amount Ith) shown in the relationship between the current level and the optical output of the semiconductor laser in FIG. 13, and is non-linear corresponding to the input of the difference signal. A circuit that outputs a drive current, a first nonlinear amplifier 4a, a second nonlinear amplifier 4b on the output side of the first nonlinear amplifier 4a, and a voltage / current on the output side of the second nonlinear amplifier 4b. And a conversion circuit 4c.
[0037]
The first nonlinear amplifier 4a obtains the inverse characteristic corresponding to the change in the differential gain (FIG. 14) of the semiconductor laser LD in the region lower than the threshold value, and reduces the gain relatively slowly. Function.
[0038]
The second nonlinear amplifier 4b obtains the inverse characteristic of the differential gain (FIG. 14) of the semiconductor laser LD near the threshold value (but not exceeding the threshold value). Since the linear amplifier 3 is responsible for driving the region above the threshold, the second nonlinear amplifier 4b functions to sharply decrease the gain toward the threshold and drop to zero gain.
[0039]
The non-linear circuit 4 is a circuit having a reverse characteristic of the differential gain in the region below the threshold of the semiconductor laser LD by the first and second non-linear amplifiers 4a and 4b, and the maximum drive current becomes the threshold current of the semiconductor laser LD. Perform clipped motion.
[0040]
The temperature compensation circuit 5 has means (not shown) for measuring the temperature of the semiconductor laser LD in order to compensate for the temperature characteristics of the semiconductor laser LD, and compensates the temperature characteristics of the semiconductor laser LD according to the measured temperature. Are generated and output to the first nonlinear amplifier 4a and the second nonlinear amplifier 4b. The semiconductor laser LD functions to change the maximum drive current amount corresponding to the threshold value of the non-linear circuit 4 in response to the change of the threshold current amount depending on the temperature. Thereby, the output of the nonlinear circuit 4 is controlled in accordance with the difference signal from the error calculation unit 2 and the temperature of the semiconductor laser LD.
[0041]
In the figure, reference numeral 6 denotes a clipping circuit, which is also input to the clipping circuit 6 via the amplifier 7 before the light quantity command signal is input to the error calculation unit 2. In general, as shown in FIG. 2, the semiconductor laser LD has a current-light quantity characteristic (IP characteristic) that changes depending on the temperature state, and the IP characteristic varies greatly according to the temperature state change in the laser emission region. In the spontaneous emission region where the amount of light is low compared to (region B), the characteristics are substantially the same (region A) even if the temperature changes, and many maintain linear characteristics, so the relationship between current and light amount Are in a one-to-one relationship. Therefore, in the low light amount region such as region A, the drive current is controlled in an open loop rather than in the case where the light amount command signal is applied to the negative feedback loop composed of the linear circuit 3 and the nonlinear circuit 4 to control the drive current of the semiconductor laser LD. This makes it possible to achieve faster responsiveness.
[0042]
For this reason, the clipping circuit 6 has a light amount level corresponding to a threshold value between the natural light emitting region and the laser light emitting region of the semiconductor laser LD at a predetermined value, specifically, the lowest usable temperature (a level equal to the maximum light amount in the region A). And the signal is added in the middle of the signal line of the nonlinear circuit 4. The signal clipped by the clip circuit 6 is added to the nonlinear circuit 4 from the open loop, so that it is driven in parallel with the signal in the negative feedback loop, but it works dominantly on the signal in the negative feedback loop, The drive current of the semiconductor laser LD is controlled through the voltage / current conversion circuit 4c.
[0043]
As a result, in the semiconductor laser drive circuit having a double negative feedback loop composed of the linear circuit 3 and the nonlinear circuit 4, the modulation can be performed without causing deterioration of responsiveness even in the case of a considerably low light amount, for example, near 0 light amount. Responsiveness can be improved. Further, since a negative feedback control is performed on the laser emission region larger than the threshold value as in the conventional case, stable and high-speed drive control is possible.
[0044]
The output of the clip circuit 6 is added in the middle of the signal line of the nonlinear circuit 4 as described above. As an aspect of adding in the middle of the signal line of the nonlinear circuit 4, an aspect of adding to the input side of the first nonlinear amplifier 4a, an aspect of adding between the first nonlinear amplifier 4a and the second nonlinear amplifier 4b, and There is a mode of adding to the output side of the second nonlinear amplifier 4b. However, when adding to the output side of the second nonlinear amplifier 4b, there is a possibility that a current exceeding the threshold value is generated from the nonlinear circuit 4. A mode of adding to the input side of one non-linear amplifier 4a or a mode of adding between the first non-linear amplifier 4a and the second non-linear amplifier 4b is preferable. Of these two modes, the gain of the first non-linear amplifier 4a is very large. From the viewpoint of increasing the S / N ratio, as shown in the figure, the gain is added to the input side of the first non-linear amplifier 4a. The mode of adding between the first nonlinear amplifier 4a and the second nonlinear amplifier 4b is most preferable because more accurate control can be realized.
[0045]
FIG. 3 is a configuration block diagram showing an example of an embodiment of a semiconductor laser driving circuit according to claims 3 to 5. The same reference numerals as those in the configuration block diagram shown in FIG.
[0046]
In this embodiment, in the region A, the semiconductor laser LD is driven and controlled only by the signal clipped at the predetermined value by the clip circuit 7, so that the negative feedback is performed at a low light amount smaller than the predetermined value. Therefore, a compensation voltage that invalidates the negative feedback with a low light amount is added to the light amount command signal.
[0047]
According to this embodiment, a stable high-speed response characteristic can be obtained even with a very small amount of light in the vicinity of light amount 0 by simple circuit adjustment as compared with the configuration of FIG.
[0048]
At this time, the linear circuit and the nonlinear circuit in the negative feedback loop are non-negatively processed. As a result, in the region A, when the negative feedback loop is invalid, it becomes 0, and the semiconductor laser LD is driven and controlled by the output added in the open state. Therefore, since no signal is applied to the minus side, high-speed rising is possible.
[0049]
Figure 4 Half It is a block diagram which shows an example of embodiment of a conductor laser drive circuit. In the following description, the same reference numerals as those in the configuration block diagram shown in FIG. 15 denote the same configurations.
[0050]
In this embodiment, the gain fitting circuit 100 of the semiconductor laser driving circuit shown in FIG. 15 includes an A / D conversion circuit 10, an LUT (lookup table) 11, a D / A conversion circuit 12, and a voltage / current conversion circuit 13. It is characterized by comprising.
[0051]
The A / D conversion circuit 10 digitally converts the difference signal input from the error calculation unit 300 and outputs it to the LUT 11.
[0052]
In the LUT 11, input / output characteristic data having the inverse characteristic of the differential quantum efficiency of the semiconductor laser LD to be used is written, and the difference signal digitally converted by the A / D conversion circuit 10 is input as an address signal. A digital signal having an output characteristic corresponding to the address signal on a one-to-one basis is output.
[0053]
The D / A conversion circuit 12 converts the digital signal having the output characteristics output from the LUT 11 into an analog signal and outputs the analog signal to the voltage / current conversion circuit 13. The voltage / current conversion circuit 13 converts the signal from the D / A conversion circuit 12 into a current and supplies a drive current to the semiconductor laser LD.
[0054]
According to this embodiment, it is possible to easily write data of input / output characteristics having the inverse characteristic of the differential quantum efficiency of the semiconductor laser LD with high accuracy and digitally using the LUT 11. As a result, the open-loop gain characteristic in the negative feedback loop can be easily made linear, and the semiconductor is excellent in light quantity stability and light modulation response characteristics from the natural light emitting region to the entire laser light emitting region of the semiconductor laser LD. A laser driving circuit can be obtained. Further, there is an advantage that it is not necessary to change the circuit configuration even if the characteristics are different for each semiconductor laser LD.
[0055]
FIG. Half It is a block diagram which shows an example of embodiment of a conductor laser drive circuit.
[0056]
In this embodiment, the gain fitting circuit 100 of the semiconductor laser driving circuit shown in FIG. 15 is configured using the linear gain fitting circuit 101 that is an analog circuit as it is in the laser emission region of the semiconductor laser LD, and in the spontaneous emission region. Similarly to the above, the A / D conversion circuit 14, the LUT 15, and the D / A conversion circuit 16 are configured.
[0057]
Therefore, the difference signal between the light amount command signal and the light emission amount detection signal output from the error calculation unit 300 is processed by the linear gain fitting circuit 101 formed of an analog circuit in the linear laser light emission region, and the voltage / current conversion circuit 111 is processed. In the non-linear spontaneous emission region, the A / D conversion circuit 14 performs digital conversion to output to the LUT 15. In this LUT 15, input / output characteristic data having the inverse characteristic of the differential quantum efficiency in the nonlinear region of the semiconductor laser LD to be used is written, and the difference signal digitally converted by the A / D conversion circuit 14 is used as an address signal. The digital signal having an output characteristic corresponding to the address signal is output in analog form by the D / A conversion circuit 16 and output to the voltage / current conversion circuit 112. The currents output from the voltage / current conversion circuits 111 and 112 are added and supplied to the semiconductor laser LD.
[0058]
According to this embodiment, it becomes possible to set the output characteristics of the non-linear region where there is a region that cannot be matched by the conventional analog circuit with high accuracy, and the laser from the spontaneous emission region of the semiconductor laser LD as a whole. A semiconductor laser drive circuit having excellent light quantity stability and light modulation response characteristics over the entire light emitting region can be obtained. In addition, it is possible to increase the modulation speed in the laser emission region by configuring only the linear region with an analog circuit.
[0059]
FIG. Half It is a block diagram which shows an example of embodiment of a conductor laser drive circuit.
[0060]
In this embodiment, a digital adder / subtractor 17 is used in place of the error calculator 300 in the semiconductor laser driving circuit shown in FIG. 15, and the LUT 18, the D / A converter 19, and the voltage / current converter 20 are added to the gain fitting circuit 100. It is configured using.
[0061]
Therefore, the light amount command signal is input as a digital signal to the digital adder / subtractor 17, and the light emission amount detection signal obtained by converting the light reception signal of the photodiode PD by the current / voltage conversion circuit 20 is also an A / D converter. The digital signal is converted by 21 and input to the digital adder / subtractor 17 as a digital signal. The digital adder / subtractor 17 outputs a digital signal of a difference signal between the light emission amount detection signal and the light amount command signal to the LUT 18.
[0062]
The LUT 18 is written with input / output characteristic data having the inverse characteristic of the differential quantum efficiency of the semiconductor laser LD to be used. The digital signal output from the digital adder / subtractor 17 is used as an address signal, one-to-one with the address signal. A digital signal having an output characteristic corresponding to the above is output, analog-converted by the D / A conversion circuit 19 and output to the voltage / current conversion circuit 22, and the semiconductor laser LD is driven and controlled.
[0063]
According to this embodiment, it is possible to easily write the data of the input / output characteristics having the inverse characteristic of the differential quantum efficiency of the semiconductor laser LD using the LUT 18 with high accuracy and easily in the negative feedback loop. The open loop gain characteristic of the semiconductor laser can be easily made linear, and a semiconductor laser driving circuit having excellent light quantity stability and light modulation response characteristics from the spontaneous emission region to the entire laser emission region of the semiconductor laser LD. In addition to the effect that there is no need to change the circuit configuration even if the characteristics are different for each semiconductor laser LD, there is an advantage that it can be directly modulated using a digital signal as a light quantity command signal.
[0064]
FIG. 7 is characterized in that in the semiconductor laser driving circuit shown in FIG. 6, the digital adder / subtracter 17 is omitted and a matrix having the same function as the digital adder / subtractor 17 is created on the LUT 18a.
[0065]
Accordingly, the LUT 18a is directly input with two digital signals, that is, the light emission amount detection signal digitally converted by the A / D conversion circuit 21 and the digital signal of the light amount command signal. In this LUT 18a, an input of the light emission amount detection signal is used as an address signal, and for example, which one of the tables in which input / output characteristic data having the inverse characteristic of the differential quantum efficiency of the semiconductor laser LD to be used is written is used. Then, using the light quantity command signal as an address signal, the one-to-one output characteristic corresponding to the light quantity command signal is determined and output from the determined table.
[0066]
According to this embodiment, the configuration can be further simplified as compared with the semiconductor laser driving circuit shown in FIG.
[0067]
Figure 8 Half FIG. 5 is a configuration block diagram showing an example of an embodiment of a conductor laser drive circuit, showing a configuration in which a temperature compensation circuit is added to the gain fitting circuit 100 of the semiconductor laser drive circuit shown in FIG. 4.
[0068]
The temperature compensation circuit 30 has means (not shown) for measuring the room temperature and the temperature of the semiconductor laser LD in order to compensate for the temperature characteristics of the semiconductor laser LD, and the temperature characteristics of the semiconductor laser LD are adjusted according to the measured temperature. A temperature compensation signal to be compensated is generated, and the temperature compensation signal is output as an analog voltage signal.
[0069]
The temperature compensation signal is added to or subtracted from the drive control signal of the semiconductor laser LD output from the D / A converter 12 to compensate the temperature of the drive control signal of the semiconductor laser LD.
[0070]
According to this embodiment, it is possible to prevent the deterioration of the light quantity stability and the modulation response due to the temperature change of the semiconductor laser LD.
[0071]
FIG. 9 shows another embodiment in which a temperature compensation circuit is added to the semiconductor laser driving circuit shown in FIG.
[0072]
The temperature compensation circuit 30a shown in this embodiment has means (not shown) for measuring the room temperature and the temperature of the semiconductor laser LD, and compensates the temperature characteristics of the semiconductor laser LD according to the measured temperature. The temperature compensation signal is A / D converted and output as a digital signal.
[0073]
The temperature compensation signal, which is the digital signal, is input to the LUT 11a. In this LUT 11a, functions equivalent to digital addition and subtraction are arranged in a matrix, and a digital signal having an output characteristic subjected to temperature compensation is output using the temperature compensation signal as an address signal.
[0074]
According to this embodiment, the configuration can be simplified and the temperature compensation accuracy can be improved.
[0075]
The temperature compensation circuits 30 and 30a are not limited to the semiconductor laser drive circuit shown in FIG. 4, but can be applied to the semiconductor laser drive circuits shown in FIGS. 5, 6, and 7, respectively. .
[0076]
FIG. Half It is a block diagram which shows an example of embodiment of a conductor laser drive circuit.
[0077]
In this embodiment, in order to obtain the inverse characteristic of the differential quantum efficiency of the semiconductor laser LD, a semiconductor laser LDa of the same type as the semiconductor laser LD is used instead of the gain fitting circuit 100 of the conventional semiconductor laser driving circuit shown in FIG. Is used to obtain the current-light quantity characteristic which is the characteristic of the differential quantum efficiency of the semiconductor laser LDa, and the inverse characteristic of the current-light quantity characteristic is created, thereby obtaining the reverse characteristic of the differential quantum efficiency of the semiconductor laser LD. I am doing so.
[0078]
Here, the same type means semiconductor laser LD chips of the same manufacturer and the same model number.
[0079]
This drive circuit will be further described. The difference signal between the light emission amount detection signal of the semiconductor laser LD and the light amount command signal output from the error calculation unit 300 is converted into a current by the voltage / current conversion circuit 40 to drive the semiconductor laser LDa. Let Light emitted from the semiconductor laser LDa is received by the photodiode PDa, and the current / voltage conversion circuit 41 converts the detection signal (current-light quantity characteristic) into a voltage. The voltage-converted detection signal is input to the divider 42, which generates a reverse characteristic of the current-light quantity characteristic of the semiconductor laser LDa, and drives the semiconductor laser LD through the voltage / current conversion circuit 43. A signal is supplied to the semiconductor laser LD.
[0080]
Therefore, since the semiconductor laser LD is driven and controlled by the inverse characteristic of the differential quantum efficiency created by the semiconductor laser LDa of the same type as itself, the inverse characteristic of the differential quantum efficiency of the semiconductor laser LD can be accurately realized with a simple configuration. Thus, by configuring this in a negative feedback loop, the open loop gain characteristic can be made linear, and excellent light quantity modulation performance can be realized.
[0081]
FIG. Half It is a block diagram which shows an example of embodiment of a conductor laser drive circuit.
[0082]
A part of the forward light emitted from the front emission end face of the semiconductor laser LD in the right direction in the figure is branched through the sampling mirror M and enters the photodiode PD1 for receiving the forward light. The received light signal is converted into a current signal and output to the front light receiving circuit 50.
[0083]
The front light receiving circuit 50 receives the current signal output from the photodiode PD1, detects the light emission amount of the front light of the semiconductor laser LD, and outputs the light emission amount detection signal.
[0084]
Reference numeral 51 denotes an APC control circuit to which a light emission amount detection signal detected by the front light receiving circuit 50 is input. The APC control circuit 51 receives, for example, a light amount command signal corresponding to a light amount setting value set in advance based on the standard value of the semiconductor laser LD, and the light emission amount of the front light input from the front light receiving circuit 1 The difference between the detection signal and the light quantity command signal is calculated and compared.
[0085]
52 is a current drive circuit, and based on the difference between the light emission amount detection signal of the front light calculated by the APC control circuit 51 and the light amount command signal, there is no difference between them, that is, the light emission amount detection signal of the front light. The drive current is supplied to the semiconductor laser LD so that the value of becomes equal to the value of the light quantity command signal, and the light emission amount of the semiconductor laser LD is controlled.
[0086]
The photodiode PD1, the forward light receiving circuit 50, the APC control circuit 51, and the current driving circuit 52 detect the amount of light emitted from the semiconductor laser LD and negatively feed back the amount of light emitted from the semiconductor laser LD. The negative feedback loop to be controlled is configured.
[0087]
In the semiconductor laser driving circuit shown in the present embodiment, in addition to the configuration of the negative feedback loop for controlling the light emission amount of the semiconductor laser LD, the photodiode PD2 is arranged on the rear side of the semiconductor laser LD opposite to the front light emitting end face. The rear light emitted from the rear end face of the semiconductor laser LD can be received simultaneously.
[0088]
The photodiode PD2 receives the backward light emitted from the rear end face of the semiconductor laser LD and outputs the current signal to the backward light receiving circuit 53.
[0089]
The rear light receiving circuit 53 detects the light emission amount of the rear light of the semiconductor laser LD from the current signal input from the photodiode PD2, and outputs the light emission amount detection signal. Therefore, the emitted light from the semiconductor laser LD is received by the photodiodes PD1 and PD2, respectively, the front light emitted from the front emission end face and the rear light emitted from the rear emission end face opposed thereto, respectively. The front light receiving circuit 50 and the rear light receiving circuit 53 respectively detect the emission amounts of the emitted light from both emission end faces of the semiconductor laser LD.
[0090]
Both the light emission amount detection signals detected by the front light receiving circuit 50 and the rear light receiving circuit 53 are input to the calculation circuit 54.
[0091]
The calculation circuit 54 receives the light emission amount detection signals detected by the front light receiving circuit 50 and the rear light receiving circuit 53, calculates the difference or ratio between the two detection signals, and calculates the calculated value as the abnormality determination circuit 55. Output to.
[0092]
The abnormality determination circuit 55 is preset with a reference value range for determining an abnormality of the semiconductor laser LD based on the calculated value, and monitors the difference or ratio between the two detection signals calculated by the calculation circuit 54. Then, the comparison with the set range is performed. If a failure due to end face breakage occurs at either the front or rear emission end face of the semiconductor laser LD, the front light of the semiconductor laser LD detected by the front light receiving circuit 50 and the rear light receiving circuit 53, respectively. The relationship between the amount of emitted light and the amount of backward light deviates from the initial value (reference value). Therefore, the difference in the light emission amount is calculated as a difference or ratio by the calculation circuit 54 and compared with a preset range set in the abnormality determination circuit 55, thereby detecting a failure due to the end face destruction of the semiconductor laser LD. it can.
[0093]
When it is determined that a failure due to end face destruction has occurred in the semiconductor laser LD as described above, the abnormality determination circuit 55 outputs an abnormality determination signal, and an alarm means such as an alarm or an alarm lamp warns the semiconductor laser LD of an abnormality. To do.
[0094]
Therefore, according to this embodiment, even if a failure due to end face destruction occurs on either the front emission end face or the rear emission end face of the semiconductor laser LD, the failure of the semiconductor laser LD is detected early and reliably. Is possible.
[0095]
Further, when determining the abnormality, for example, when the front light emission amount / rear light emission amount> the set range, it is determined that the rear light is abnormal, and the front light emission amount / rear light emission amount <the setting range is satisfied. By determining that the front light is abnormal, it is possible to distinguish and detect which outgoing end face of the semiconductor laser LD is in an abnormal state. For example, when it is determined that only the forward light is abnormal and the backward light is normal, the forward light abnormality is not only the end face destruction of the semiconductor laser LD but also the optical axis of the optical system for sampling the forward light. Situations such as misalignment and component deterioration are also assumed. In such a case, the normal state can be restored by maintenance of the sampling optical system of the apparatus.
[0096]
In this embodiment, when the abnormality determination circuit 55 determines that the semiconductor laser LD is in an abnormal state, the abnormality determination signal is further output to the current drive circuit 52. In response to the abnormality determination signal, the current drive circuit 52 controls the amount of drive current supplied to the semiconductor laser LD so that a drive current of a certain value or more does not flow to the semiconductor laser LD. Therefore, a circuit for limiting the supply of drive current to the semiconductor laser LD in response to the abnormality determination signal from the abnormality determination circuit 55 is added to the current drive circuit 52. When an abnormal state of the semiconductor laser LD is detected in this way, by adding a circuit that limits the drive current to the semiconductor laser LD, the failure state is advanced when a failure occurs in the semiconductor laser LD. Thus, it is possible to emit light without increasing the life of the semiconductor laser LD.
[0097]
FIG. Half It is a block diagram which shows an example of embodiment of a conductor laser drive circuit. The same reference numerals as those in the configuration block diagram shown in FIG. 11 denote the same configurations, and detailed descriptions thereof are omitted.
[0098]
In this embodiment, instead of the calculation circuit 54 shown in FIG. 11, a front light abnormality detection circuit 56 and a rear light abnormality detection circuit 57 are provided.
[0099]
The front light anomaly detection circuit 56 supplies a light emission amount detection signal of the front light emitted from the front emission end face of the semiconductor laser LD output from the front light receiving circuit 50 and the semiconductor laser LD output from the current drive circuit 52. The driving current is compared with the specified light emission amount by inputting the driving current. For example, by determining whether the forward light emission amount / the drive current <the constant (Equation 1), it is possible to detect a state where the prescribed light emission amount of the front light is not obtained despite the current flowing. .
[0100]
The rear light anomaly detection circuit 57 also detects a light emission amount detection signal of the rear light emitted from the rear emission end face of the semiconductor laser LD output from the rear light receiving circuit 53 and the semiconductor laser LD output from the current drive circuit 52. In the same manner, the drive current is compared with the specified light emission amount by inputting the drive current supplied to the. For example, by determining the amount of back light emission / drive current <constant (Equation 2), a state in which a prescribed amount of back light is not obtained despite the current flowing is detected.
[0101]
The detection results in the front light abnormality detection circuit 56 and the rear light abnormality detection circuit 57 are input to the abnormality determination circuit 58, respectively. The abnormality determination circuit 58 determines the abnormality of the semiconductor laser LD when at least one of the detection results of the front light abnormality detection circuit 56 and the rear light abnormality detection circuit 57 is true. It has become. Therefore, if a failure due to end face breakage occurs at the front emission end face of the semiconductor laser LD, a state in which a prescribed light emission amount is not obtained with respect to the drive current is detected, and the front light abnormality detection circuit 56 determines Thus, the result of the above equation 1 becomes true, and the abnormality determination circuit 58 can determine that the semiconductor laser LD is in a failure state.
[0102]
In this abnormality determination, if the above expression 1 is true and the above expression 2 is false, it is determined that the front light is abnormal, the above expression 1 is false, and the above expression 2 is true. In some cases, it is determined that the rear light is abnormal, and further, if the above equation 1 is true and the above equation 2 is also true, it is determined that the semiconductor laser LD is completely in a failure state. It can be discriminated whether the exit end face in front of or behind the LD is in an abnormal state. Accordingly, even in this case, for example, when it is determined that only the front light is abnormal and the rear light is normal, a situation such as an optical axis shift of the optical system for sampling the front light, component deterioration, etc. is assumed. It is possible to return to the normal state by maintenance of the sampling optical system of the apparatus.
[0103]
Therefore, even in this embodiment, even if a failure due to end face breakage occurs on either the front emission end face or the rear emission end face of the semiconductor laser LD, the failure of the semiconductor laser LD can be detected quickly and reliably. It is possible to detect.
[0104]
When the abnormality of the semiconductor laser LD is determined in this way, the abnormality determination circuit 58 outputs an abnormality determination signal and warns the abnormality of the semiconductor laser LD by an alarm means such as an alarm or an alarm lamp.
[0105]
When the abnormality determination circuit 58 determines that the semiconductor laser LD is in an abnormal state, the abnormality determination signal is further output to the current drive circuit 52. In response to the abnormality determination signal, the current drive circuit 52 controls the amount of drive current supplied to the semiconductor laser LD so that a drive current of a certain value or more does not flow to the semiconductor laser LD. Therefore, in this case, the current drive circuit 52 has a circuit that receives the abnormality determination signal from the abnormality determination circuit 58 and restricts the supply of the drive current to the semiconductor laser LD. When an abnormal state of the semiconductor laser LD is detected in this way, by adding a circuit that limits the drive current to the semiconductor laser LD, the failure state is advanced when a failure occurs in the semiconductor laser LD. Thus, it is possible to emit light without increasing the life of the semiconductor laser LD.
[0106]
【The invention's effect】
According to the first to fifth aspects of the present invention, it is possible to provide a semiconductor laser driving circuit capable of realizing high-speed and stable modulation responsiveness even with a low light amount near zero.
[Brief description of the drawings]
FIG. 1 is a configuration block diagram showing an embodiment of a semiconductor laser driving circuit.
FIG. 2 is a current-light quantity characteristic diagram of a semiconductor laser driving circuit.
FIG. 3 is a block diagram showing the configuration of another embodiment of a semiconductor laser driving circuit.
FIG. 4 is a configuration block diagram showing a gain fitting circuit in an embodiment of a semiconductor laser driving circuit;
FIG. 5 is a configuration block diagram showing a gain fitting circuit in another embodiment of a semiconductor laser driving circuit;
FIG. 6 is a configuration block diagram showing a gain fitting circuit in still another embodiment of the semiconductor laser driving circuit.
FIG. 7 is a configuration block diagram showing a gain fitting circuit in still another embodiment of the semiconductor laser driving circuit.
8 is a configuration block diagram showing a case where a room temperature compensation circuit is added to the gain fitting circuit shown in FIG.
9 is a configuration block diagram showing another example when a room temperature compensation circuit is added to the gain fitting circuit shown in FIG.
FIG. 10 is a configuration block diagram showing a gain fitting circuit in still another embodiment of the semiconductor laser driving circuit.
FIG. 11 is a block diagram showing the configuration of an embodiment of a semiconductor laser driving circuit for determining an abnormality of a semiconductor laser.
FIG. 12 is a block diagram showing the configuration of another embodiment of a semiconductor laser drive circuit for determining an abnormality of a semiconductor laser.
FIG. 13 is a characteristic diagram showing the relationship between the current and light amount of a semiconductor laser.
FIG. 14 is a characteristic diagram showing the relationship between the current of a semiconductor laser and the differential quantum efficiency.
FIG. 15 is a configuration block diagram of a conventional semiconductor laser driving circuit.
[Explanation of symbols]
LD, LDa Semiconductor laser
PD, PD1, PD2, PDa Photodiode
M Sampling mirror
1, 20, 41 Current / voltage conversion circuit
2 Error calculator
3 Linear circuit
3a linear amplifier
3b Voltage / current conversion circuit
4 Nonlinear circuit
4a First nonlinear amplifier
4b Second nonlinear amplifier
4c Voltage / current conversion circuit
5 Temperature compensation circuit
6 Clip circuit
7 Amplifier
10, 14, 21 A / D conversion circuit
11, 11a, 15, 18, 18a LUT
12, 16, 19 D / A conversion circuit
13, 22, 40, 43, 111, 112 Voltage / current conversion circuit
17 Digital adder
30, 30a Temperature compensation circuit
42 Divider
50 Front light receiving circuit
51 APC control circuit
52 Current drive circuit
53 Back light receiving circuit
54 Calculation circuit
55, 58 Abnormality judgment circuit
56 Front light anomaly detection circuit
57 Backlight anomaly detection circuit
100 gain fitting circuit
101 Linear gain fitting circuit
102 Nonlinear gain fitting circuit
300 Error calculator
400 Temperature compensation circuit

Claims (3)

In a semiconductor laser driving circuit for driving and controlling the semiconductor laser by negatively feeding back a detection signal of the emission amount of the semiconductor laser and comparing it with a light amount command signal, a difference signal between the detection signal of the light emission amount and the light amount command signal is input. Thus, a double negative feedback loop of a linear circuit that outputs a linear driving current to the semiconductor laser and a nonlinear circuit that has two nonlinear amplifiers that output a nonlinear driving current is generated by a signal formed based on the difference signal. The light intensity command signal is clipped with a predetermined value that is a voltage that outputs a light intensity level corresponding to the threshold value of the semiconductor laser at the minimum operating temperature, and the input side of the first nonlinear amplifier or the first nonlinear amplifier is clipped. between the amplifier and the second linear amplifier, or a semiconductor laser driving, characterized in that added to the second signal line provided on the output side of the nonlinear amplifier Road. In a semiconductor laser driving circuit for driving and controlling the semiconductor laser by negatively feeding back a detection signal of the emission amount of the semiconductor laser and comparing it with a light amount command signal, a difference signal between the detection signal of the light emission amount and the light amount command signal is input. Thus, a double negative feedback loop of a linear circuit that outputs a linear driving current to the semiconductor laser and a nonlinear circuit that has two nonlinear amplifiers that output a nonlinear driving current is generated by a signal formed based on the difference signal. The light intensity command signal is clipped with a predetermined value that is a voltage that outputs a light intensity level corresponding to the threshold value of the semiconductor laser at the minimum operating temperature, and the input side of the first nonlinear amplifier or the first nonlinear amplifier is clipped. While adding to the signal line provided between the amplifier and the second nonlinear amplifier or on the output side of the second nonlinear amplifier, and negative feedback up to the predetermined value Semiconductors laser drive circuit characterized that you add the compensation voltage to the light intensity command signal so as not to Ka. 3. The semiconductor laser driving circuit according to claim 2, wherein the linear circuit and the nonlinear circuit in the negative feedback loop perform non-negative processing that is set to 0 when the negative feedback loop is invalid .

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