JP2000200941A - Semiconductor laser drive circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a semiconductor laser driving circuit, in which high-speed and stable modulation responsibility is obtained even with extremely small quantity of light, near zero. SOLUTION: In a semiconductor laser drive circuit which drives/controls a semiconductor laser LD by feeding back negatively a detecting signal for the quantity of light emission of the semiconductor laser and comparing it with a quantity-of-light command signal, a double-negative feedback loop of a linear circuit 2 outputting a linear drive current to the semiconductor laser LD and nonlinear circuits 3 and 4 outputting a nonlinear drive current is constituted, by inputting a difference signal between the detecting signal for the quantity of light emission and the light quantity command signal, and further the light quantity command signal is clipped at a prescribed value, and the signal is added on the way of the signal line of the nonlinear circuits 3 and 4.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a drive circuit for driving a semiconductor laser used in an optical scanning recording apparatus or an optical communication apparatus, and more particularly to a drive circuit for negatively feedbacking a light emission amount of a semiconductor laser and comparing the light emission amount with a light amount command signal. The present invention relates to a semiconductor laser drive circuit whose amount is controlled.

[0002]

2. Description of the Related Art Hitherto, for example, in an optical scanning recording apparatus, an apparatus for scanning a light beam generated from a semiconductor laser on a photosensitive recording material and recording data on the recording material has been put to practical use. Also, in optical communication devices,
2. Description of the Related Art Devices that transmit 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 such an optical scanning recording apparatus or an optical communication apparatus can directly modulate an optical output generated from the semiconductor laser by changing a driving current. The circuit that controls this drive current is:
Normally, an APC (Auto-PC) is used so that a desired optical output set by a light intensity command signal is accurately generated from a semiconductor laser.
matic power control) circuit is often used to stabilize the optical output. The conventional APC circuit is
The amount of monitor light obtained by branching a part of the forward emission light or the backward emission light of the semiconductor laser is detected, and the drive current of the semiconductor laser is adjusted in a direction to eliminate the difference between the emission amount and the set light amount indicated by the light amount command signal. Is configured to perform negative feedback control.

FIG. 13 is a diagram showing a relationship between a current level and a light output when a DC current is supplied as a drive current of a semiconductor laser. If the level of the drive current is smaller than Ith, the power of the optical output increases nonlinearly and gently with an increase in the amount of drive current, and the level of the drive current becomes Ith.
Is exceeded, the power of the optical output increases substantially linearly with an increase in the amount of drive current. 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.

FIG. 14 is a diagram showing the relationship between the drive current of the semiconductor laser and the differential quantum efficiency. The relationship between the drive current of the semiconductor laser and the optical output is a linear relationship when the drive current exceeds Ith, that is, when the drive current exceeds Ith, the differential quantum efficiency is a constant value regardless of the level of the drive current of the semiconductor laser. Take. On the other hand, when the driving current is lower than Ith, the differential quantum efficiency increases as the driving current increases.

As described above, in the semiconductor laser, the rate of increase in light output with respect to the amount of drive current is different between the spontaneous emission region below the threshold and the laser emission region above the threshold. 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, the change in the light output with respect to the change in the driving current is small, so that the light modulation response 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.

In order to cope with this problem, a compensation signal is generated by inputting a light quantity command signal 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, and the compensation signal is supplied to the light quantity command. A technique for improving the modulation response in a low light quantity region by adding to a signal (Japanese Patent Application Laid-Open No. H2-211683), an APC
A technique for improving the modulation response in a low light quantity region by controlling the loop gain of a closed loop circuit in the circuit to be constant based on the light quantity command signal (Japanese Patent Laid-Open No. Sho 6)
3-204522) has been proposed.

However, in the former case, the compensation signal is set to AP
Since the signal is superimposed and added to the light amount command signal from outside the loop of the C circuit, correction is performed in an open loop, and there has been a problem that the modulation responsiveness fluctuates due to a characteristic change due to the temperature of the semiconductor laser. This appears as a change in image sharpness when an image is formed on a photosensitive material by a semiconductor laser.

On the other hand, in the latter case, when the light amount command signal includes a signal component in the natural light emission region and a signal component in the laser light emission region at the same time, for example, when a step-like light amount command signal is input, the loop gain is actually reduced. It is not possible to control the gain to an appropriate value for the amount of light emission, and there is a possibility that oscillation or responsiveness degradation may occur.

[0010] Therefore, the present inventor has proposed a method for realizing high-speed and stable light modulation over the entire region from the natural light-emitting region to the laser light-emitting region, as shown in FIG. A linear gain fitting circuit 101 for dividing into a linear laser emission region and a non-linear spontaneous emission region and 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 Nonlinear Gain Fitting Circuit 1 for Obtaining
02 and the gain fitting circuit 100
Since the laser light is included in the closed loop of the PC circuit, a part of the laser light emitted from the semiconductor laser LD is received by the photodiode PD, and the voltage is converted by the current / voltage conversion circuit 200 to the error calculation unit 300 as a light emission amount detection signal. The error calculation unit 300 processes the difference signal between the light amount command signal and the light emission amount detection signal by the linear gain fitting circuit 101 and the non-linear gain fitting circuit 102, respectively. , 112 to provide a drive current added to the semiconductor laser LD as a drive current added to the semiconductor laser LD, thereby striving to improve the response characteristics over the entire region (see FIG. JP-A-10-2
No. 00179). In the drawing, reference numeral 400 denotes a temperature compensation circuit for creating a temperature compensation signal for compensating the temperature characteristics of the semiconductor laser LD and outputting the signal to the gain fitting circuit 100.

[0011]

However, even if a double negative feedback loop is formed in the driving circuit of the semiconductor laser LD as described above, the gain characteristic of the nonlinear gain fitting circuit 102 and the It has been found that the gain characteristics of the laser are hardly matched, and that the modulation response is deteriorated.

Further, since the characteristics of the differential quantum efficiency of each type of semiconductor laser LD differ, it is necessary to change the gain fitting circuit 100 to a circuit configuration corresponding to each type of semiconductor laser LD or adjust the circuit constant. There is. Also, it takes much time and effort to realize the characteristics of the new semiconductor laser LD,
Some are very difficult to match depending on the characteristics of the differential quantum efficiency. If the inverse characteristics of the differential quantum efficiency of the semiconductor laser LD do not match, the optical modulation response becomes poor, resulting in deterioration of modulation performance.

On the other hand, it is known that such a semiconductor laser causes a laser emission end surface destruction (deterioration) due to excessive light emission or the like and causes a failure. For this reason, conventionally, by monitoring the driving current of the semiconductor laser, an abnormality is determined when an excessive current occurs, and the inflow of the excessive current is limited so as to prevent a failure, or in a state where the semiconductor laser is driven at a constant current. The outgoing light is monitored, and it is checked whether or not a light emission amount equal to or larger than a standard value (initial value) is obtained, thereby detecting the occurrence of a failure in the semiconductor laser.

However, since this end face break occurs at both the front end face and the rear end face of the semiconductor laser, the APC
If the end face on the opposite side to the emission end face of the semiconductor laser whose light emission amount is detected by the APC circuit during control by the circuit deteriorates, even if the emission light quantity is controlled to a constant value by the APC circuit, The failure state cannot be detected and the failure state progresses. In this situation, when the emission end face of the semiconductor laser whose light emission amount is detected by the APC circuit is deteriorated, control is performed so that the emission light does not decrease due to the operation of the APC circuit. This leads to a situation where the breakdown proceeds.

The present invention has been made in view of the above-described circumstances of the semiconductor laser drive circuit, and a first object of the present invention is to provide a high-speed and stable modulation response even at an extremely low light amount near zero light amount. To provide a semiconductor laser drive circuit that can realize the above.

A second object of the present invention is to provide a semiconductor laser drive circuit which is excellent in light quantity stability and modulation response over the entire region from the natural light emission region to the laser light emission region of the semiconductor laser. .

A third object of the present invention is to provide a semiconductor laser drive circuit capable of detecting a failure of a semiconductor laser early and reliably with a simple configuration.

[0018]

According to a first aspect of the present invention, there is provided a semiconductor laser device comprising the steps of: negatively feeding back a detection signal of a light emission amount of a semiconductor laser and comparing the signal with a light amount command signal; A linear circuit that inputs a difference signal between the light emission amount detection signal and the light amount command signal and outputs a linear drive current to the semiconductor laser, and a non-linear circuit that outputs a non-linear drive current And a double feedback loop is formed, the light amount command signal is clipped at a predetermined value, and the signal is added to the middle of the signal line of the nonlinear circuit.

The invention according to claim 2 is the semiconductor laser drive circuit according to claim 1, wherein the predetermined value is a light amount level corresponding to a threshold value of the semiconductor laser at the lowest use temperature.

Further, according to a third aspect of the present invention for solving the above-mentioned problem, the semiconductor laser is driven and controlled by negatively feeding back a detection signal of a light emission amount of the semiconductor laser and comparing the signal with a light amount command signal. In a semiconductor laser drive circuit, a dual circuit including a linear circuit that inputs a difference signal between the light emission amount detection signal and the light amount command signal and outputs a linear drive current to the semiconductor laser and a nonlinear circuit that outputs a non-linear drive current is provided. And the light amount command signal is clipped at a predetermined value, the signal is added to the middle of the signal line of the nonlinear circuit, and the light amount command is issued so that the negative feedback does not work up to the predetermined value. A semiconductor laser drive circuit characterized by adding a compensation voltage to a signal.

The invention according to claim 4 is the semiconductor laser drive circuit according to claim 3, wherein the linear circuit and the non-linear circuit in the negative feedback loop are non-negative.

The invention according to claim 5 is the semiconductor laser drive circuit according to claim 3 or 4, wherein the predetermined value is a light amount level corresponding to a threshold value of the semiconductor laser at the lowest use temperature. .

A sixth aspect of the present invention for solving the second problem.
The described invention is a semiconductor laser drive circuit for controlling the driving of the semiconductor laser by negatively feedbacking a detection signal of the light emission amount of the semiconductor laser and comparing the signal with a light amount command signal, wherein the light emission amount of the semiconductor laser and the light amount command signal are compared. Forming a difference signal and obtaining a signal for driving the semiconductor laser by inputting the difference signal to a circuit having the inverse characteristic of the differential quantum efficiency of the semiconductor laser configured using a look-up table. Semiconductor laser drive circuit.

According to a seventh aspect of the present invention, in the inverse characteristic of the differential quantum efficiency, a linear region is configured using a linear gain fitting circuit, and a non-linear region is configured using a lookup table. Item 7. A semiconductor laser drive circuit according to item 6.

The invention according to claim 8 is the semiconductor laser drive circuit according to claim 6, wherein a digital signal is input as the light amount command signal.

According to a ninth aspect of the present invention, there is provided a means for measuring a temperature of a semiconductor laser for compensating a temperature characteristic of the semiconductor laser, and a temperature compensation signal for compensating the temperature characteristic of the semiconductor laser in accordance with the measured temperature. 9. The semiconductor laser driving circuit according to claim 6, further comprising means for performing temperature compensation of the semiconductor laser by the temperature compensation signal.

According to a tenth aspect of the present invention for solving the above second problem, the semiconductor laser is driven and controlled by negatively feedbacking a detection signal of a light emission amount of the semiconductor laser and comparing the signal with a light intensity command signal. In a semiconductor laser driving circuit, a difference signal between a light emission amount of the semiconductor laser and a light amount command signal is formed, and a reverse characteristic of a differential quantum efficiency of the semiconductor laser constituted by a semiconductor chip of the same type as the semiconductor laser and a dividing circuit. A semiconductor laser driving circuit characterized in that a signal for driving a semiconductor laser is obtained by inputting the difference signal to a circuit having the following.

Claim 1 for solving the above third problem.
According to a first aspect of the present invention, there is provided a semiconductor laser driving circuit for controlling the driving of the semiconductor laser by negatively feeding back a detection signal of a light emitting amount of the semiconductor laser and comparing the signal with a light amount command signal, the semiconductor laser for detecting the light emitting amount. The amount of emitted light emitted from the end face opposite to the emission end face is also detected, and the difference or ratio between the emitted light detection signals at both end faces of the semiconductor laser is calculated. If the result is out of the set range, the abnormality determination signal is output. Output from the semiconductor laser driving circuit.

According to a twelfth aspect of the present invention, there is provided a semiconductor laser according to the eleventh aspect, further comprising a circuit for limiting a drive current to the semiconductor laser so as not to exceed a predetermined value by outputting the abnormality determination signal. It is a drive circuit.

Further, according to a thirteenth aspect of the present invention for solving the above third problem, the semiconductor laser is driven and controlled by negatively feeding back a detection signal of a light emission amount of the semiconductor laser and comparing the signal with a light intensity command signal. In the semiconductor laser drive circuit, the amount of emitted light emitted from the end surface opposite to the emission end surface of the semiconductor laser for detecting the amount of emitted light is also detected, and the emission amount detection signals of both end surfaces of the semiconductor laser are respectively detected. A semiconductor laser drive circuit that compares a drive current of a semiconductor laser and outputs an abnormality determination signal when the result is out of a set range.

According to a fourteenth aspect of the present invention, there is provided a semiconductor laser according to the thirteenth aspect, further comprising a circuit for limiting a driving current to the semiconductor laser so as not to exceed a predetermined value by outputting the abnormality determination signal. It is a drive circuit.

[0032]

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

(Claims 1 to 5) FIG. 1 shows claims 1 and 2
1 is a configuration block diagram illustrating an example of an embodiment of a semiconductor laser drive circuit according to the present invention.

As shown in FIG. 3, a part of the laser light emitted from the semiconductor laser LD is received by a photodiode PD for detecting the amount of emitted light, and is converted into a voltage through a current / voltage conversion circuit 1 to emit light. It is input to the error calculation unit 2 as an amount detection signal. The error calculation unit 2 extracts a difference signal from a light amount command signal set in advance based on the standard value of the semiconductor laser LD, and inputs the difference signal to the linear circuit 3 and the nonlinear circuit 4 constituting a gain fitting circuit. .

The linear circuit 3 is responsible for driving the area of the semiconductor laser LD which is equal to or larger than the threshold value (the current amount Ith) shown in the relationship between the current level of the semiconductor laser and the optical output in FIG. Is a circuit that outputs a linear drive current in response to the above, and includes a linear amplifier 3a and a voltage / current conversion circuit 3b.

The nonlinear circuit 4 has a threshold value (current amount Ith) indicating the relationship between the current level and the optical output of the semiconductor laser shown in FIG.
This is a circuit mainly responsible for driving in the following region and outputting a non-linear driving current in response to the input of the difference signal. The first non-linear amplifier 4a and the output of the first non-linear amplifier 4a And a voltage / current conversion circuit 4c at the output side of the second nonlinear amplifier 4b.
And is configured.

The first non-linear amplifier 4a provides a differential gain of the semiconductor laser LD in a region lower than the threshold value (FIG. 14).
, And obtains the inverse characteristic, and functions to decrease the gain relatively slowly.

The second non-linear amplifier 4b obtains the inverse characteristic of the differential gain (FIG. 14) of the semiconductor laser LD near the threshold (but not exceeding the threshold). Since the linear amplifier 3 is responsible for driving in the region equal to or larger than the threshold, the second non-linear amplifier 4b functions to sharply decrease the gain toward the threshold and drop to zero.

The nonlinear circuit 4 uses the first and second nonlinear amplifiers 4a and 4b to provide a circuit having an inverse characteristic of the differential gain in a region below the threshold value of the semiconductor laser LD and the maximum driving current of the semiconductor laser LD. An operation clipped to the threshold current is performed.

The temperature compensating circuit 5 has means (not shown) for measuring the temperature of the semiconductor laser LD in order to compensate the temperature characteristics of the semiconductor laser LD. Create a signal that compensates for the characteristic,
The first nonlinear amplifier 4a and the second nonlinear amplifier 4
b. The semiconductor laser LD functions to change the maximum drive current corresponding to the threshold of the nonlinear circuit 4 in response to the change in the threshold current depending on the temperature. Thus, the output of the nonlinear circuit 4 is controlled according to the difference signal from the error calculator 2 and the temperature of the semiconductor laser LD.

In the figure, reference numeral 6 denotes a clipping circuit, which is also inputted to the clipping circuit 6 via the amplifier 7 before the light quantity command signal is inputted to the error calculating section 2. Generally, in a semiconductor laser LD, as shown in FIG. 2, a current-light amount characteristic (IP characteristic) changes depending on a temperature state.
The P characteristic has substantially the same characteristics (region A) even in a natural light emission region where the amount of light is low, even if the temperature state changes, in contrast to the characteristics that greatly change in response to a change in the temperature state in the laser emission region (region B). ), And the relationship between the current and the light amount is almost one-to-one in many cases because linear characteristics are maintained. Therefore, in the low light amount region such as the region A, the drive current is controlled in an open loop rather than the drive current of the semiconductor laser LD is controlled by applying the light amount command signal to the negative feedback loop including the linear circuit 3 and the nonlinear circuit 4. This can realize a high-speed response.

For this reason, the clip circuit 6 sets the light amount level (the maximum light amount of the region A) corresponding to the threshold value between the spontaneous light emission region and the laser light emission region of the semiconductor laser LD at the predetermined value, specifically, the lowest use temperature. (Equal level), 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 applied from the open loop to the non-linear circuit 4 to drive in parallel with the signal in the negative feedback loop, but acts dominantly on the signal in the negative feedback loop, The drive current of the semiconductor laser LD is controlled via the voltage / current conversion circuit 4c.

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 response is deteriorated even at a considerably low light quantity, for example, near zero light quantity. Therefore, the modulation response can be improved. Further, with respect to the laser emission region larger than the threshold value, negative feedback control is performed as in the related art, so that stable and high-speed drive control is possible.

The output of the clip circuit 6 is added to the signal line of the nonlinear circuit 4 as described above. As a mode for adding the signal to the middle of the signal line of the nonlinear circuit 4, a mode for adding the signal to the input side of the first nonlinear amplifier 4a, a mode for adding the signal between the first nonlinear amplifier 4a and the second nonlinear amplifier 4b, There is a mode in which the current is added to the output side of the second nonlinear amplifier 4b. However, when the current is added to the output side of the second nonlinear amplifier 4b, there is a possibility that a current equal to or larger than the threshold value is generated from the nonlinear circuit 4; It is preferable to add to the input side of one nonlinear amplifier 4a or to add between the first nonlinear amplifier 4a and the second nonlinear amplifier 4b.
Of these two aspects, the gain of the first nonlinear amplifier 4a is very large, and therefore, from the viewpoint of increasing the S / N ratio, the gain is added to the input side of the first nonlinear amplifier 4a.
As shown in the figure, the mode of adding between the first non-linear amplifier 4a and the second non-linear amplifier 4b is the most preferable because more accurate control can be realized.

FIG. 3 is a block diagram showing an example of the embodiment of the semiconductor laser drive circuit according to the third to fifth aspects. The same reference numerals as in the configuration block diagram shown in FIG. 1 indicate the same configuration.

In this embodiment, in the region A, the driving of the semiconductor laser LD is controlled only by the signal clipped by the clipping circuit 7 at the predetermined value. In this example, a compensation voltage for disabling negative feedback at a low light quantity is added to a light quantity command signal so that negative feedback does not work.

According to this embodiment, as compared with the configuration shown in FIG. 1, a stable high-speed response characteristic can be obtained with a simple circuit adjustment even with an extremely small light amount near 0.

At this time, the linear circuit and the non-linear circuit in the negative feedback loop perform non-negative processing. As a result, in the region A, the value becomes 0 when the negative feedback loop is invalid, and the drive of the semiconductor laser LD is controlled by the output added in the open state. Therefore, the signal does not move to the minus side, so that a high-speed rising becomes possible.

(Claims 6 to 10) FIG. 4 is a configuration block diagram showing an example of an embodiment of a semiconductor laser drive circuit according to the invention of claim 6. In the following description, the same reference numerals as in the configuration block diagram shown in FIG. 15 indicate the same configuration.

In this embodiment, the gain fitting circuit 100 of the semiconductor laser drive circuit shown in FIG.
A / D conversion circuit 10 and LUT (lookup table)
11 and D / A conversion circuit 12 and voltage / current conversion circuit 13
It is characterized by comprising.

The A / D conversion circuit 10 includes an error calculation unit 300
Is converted into a digital signal and output to the LUT 11.

The LUT 11 has a semiconductor laser L to be used.
Data of input / output characteristics having the inverse characteristic of the differential quantum efficiency of D is written, and the difference signal digitally converted by the A / D conversion circuit 10 is input as an address signal, and corresponds to the address signal on a one-to-one basis. Output a digital signal having an output characteristic.

The D / A conversion circuit 12 converts the digital signal of the output characteristic 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.

According to this embodiment, data of input / output characteristics having the inverse characteristic of the differential quantum efficiency of the semiconductor laser LD can be easily and accurately written digitally using the LUT 11. Thereby, the open loop gain characteristic in the negative feedback loop can be easily linearized, and the semiconductor laser LD has excellent light quantity stability and light modulation response characteristics over the entire natural light emitting region to the laser light emitting region. A laser drive circuit can be obtained. There is also an advantage that even if the characteristics are different for each semiconductor laser LD, there is no need to change the circuit configuration.

FIG. 5 is a configuration block diagram showing an example of an embodiment of a semiconductor laser drive circuit according to claim 7.

In this embodiment, in the gain fitting circuit 100 of the semiconductor laser drive circuit shown in FIG. 15, in the laser emission region of the semiconductor laser LD, a linear gain fitting circuit 10 as an analog circuit is used.
1 in the spontaneous light emission region, and the A / D conversion circuit 14, the LUT 15, and the D / A conversion circuit 1
6.

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 composed of an analog circuit in a linear laser light emission region, and the voltage / current is processed. Output to the conversion circuit 111 to drive the semiconductor laser LD,
In the non-linear spontaneous light emission region, the data is converted into a digital signal by the A / D conversion circuit 14 and output to the LUT 15. This LU
Data of input / output characteristics having the inverse characteristic of the differential quantum efficiency in the nonlinear region of the semiconductor laser LD to be used is written in T15, and the difference signal digitally converted by the A / D conversion circuit 14 is input as an address signal. Then, a digital signal having an output characteristic corresponding to the address signal on a one-to-one basis is output, converted into an analog signal 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.

According to this embodiment, it is possible to set the output characteristics of a non-linear region in which a region which cannot be matched by a conventional analog circuit is set with high precision, and as a whole, the natural light emission of the semiconductor laser LD is achieved. A semiconductor laser drive circuit having excellent light quantity stability and light modulation response characteristics over the entire region from the region to the laser emission region can be provided. Moreover, by configuring only the linear region with an analog circuit, it is possible to increase the modulation speed in the laser emission region.

FIG. 6 is a block diagram showing an example of an embodiment of the semiconductor laser drive circuit according to the present invention.

In this embodiment, a digital adder / subtractor 17 is used instead of the error calculator 300 in the semiconductor laser drive circuit shown in FIG. 15, and an LUT 18, a D / A converter 19 and a voltage / current It is configured using a conversion circuit 20.

Accordingly, the light quantity command signal is input to the digital adder / subtracter 17 as a digital signal, and the light quantity detection signal obtained by converting the light receiving signal of the photodiode PD into a voltage by the current / voltage conversion circuit 20 is A / A. D
The digital signal is converted by the converter 21 and input to the digital adder / subtracter 17 as a digital signal. The digital adder / subtracter 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.

The LUT 18 has a semiconductor laser LD to be used.
The input / output characteristic data having the inverse characteristic of the differential quantum efficiency is written, and the digital signal output from the digital adder / subtractor 17 is used as an address signal, and a digital signal having an output characteristic corresponding to the address signal on a one-to-one basis. Is output to the D / A conversion circuit 19, and is output to the voltage / current conversion circuit 22 to drive and control the semiconductor laser LD.

According to this embodiment, the input / output characteristics data having the inverse characteristic of the differential quantum efficiency of the semiconductor laser LD can be easily and accurately written digitally using the LUT 18. A semiconductor laser driving circuit that can easily make the open loop gain characteristic in the feedback loop linear, and has excellent light intensity stability and light modulation response characteristics over the entire natural light emitting region to the laser light emitting region of the semiconductor laser LD; And a semiconductor laser LD
Even if the characteristics are different every time, in addition to the effect that there is no need to change the circuit configuration, there is an advantage that direct modulation can be performed using a digital signal as the light amount command signal.

FIG. 7 shows the semiconductor laser drive circuit shown in FIG. 6 in which the digital adder / subtracter 17 is omitted and the LUT 18a
It is characterized in that a matrix having a function equivalent to that of the digital adder / subtractor 17 is created above.

Therefore, the LUT 18a is directly input with two digital signals, that is, a light emission amount detection signal and a digital signal of a light intensity command signal, which are digitally converted by the A / D conversion circuit 21. In the LUT 18a, the input of the light emission amount detection signal is used as an address signal, and for example, a table in which data of input / output characteristics having inverse characteristics of the differential quantum efficiency of the semiconductor laser LD to be used is written is determined. ,
Next, a one-to-one output characteristic corresponding to the light quantity command signal is determined and output from the determined table using the light quantity command signal as an address signal.

According to the present embodiment, the structure can be further simplified as compared with the semiconductor laser drive circuit shown in FIG.

FIG. 8 is a block diagram showing an example of an embodiment of a semiconductor laser drive circuit according to claim 9.
5 shows 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.

The temperature compensating 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. A temperature compensation signal for compensating for temperature characteristics is created, and the temperature compensation signal is output as an analog voltage signal.

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.

According to this embodiment, the semiconductor laser L
It is possible to prevent the light quantity stability and the modulation response from deteriorating due to the temperature change of D.

FIG. 9 shows another embodiment in which a temperature compensation circuit is added to the semiconductor laser drive circuit shown in FIG.

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, creates a temperature compensation signal for compensating the temperature characteristics of the semiconductor laser LD according to the measured temperature, and converts the temperature compensation signal to A. / D conversion and output as a digital signal.

The temperature compensation signal which is the digital signal is L
It is input to the UT 11a. In the LUT 11a, a function equivalent to digital addition / subtraction is arranged in a matrix, and a temperature-compensated digital signal having output characteristics is output using the temperature compensation signal as an address signal.

According to this embodiment, the structure can be simplified and the temperature compensation accuracy can be improved.

The temperature compensation circuits 30, 30a
It is needless to say that the present invention is not limited to the semiconductor laser drive circuit shown in FIG. 4 but can be similarly applied to the semiconductor laser drive circuits shown in FIGS. 5, 6, and 7.

FIG. 10 is a block diagram showing an embodiment of a semiconductor laser drive circuit according to the present invention.

In this embodiment, in order to obtain the inverse characteristic of the differential quantum efficiency of the semiconductor laser LD, the gain fitting circuit 1 of the conventional semiconductor laser drive circuit shown in FIG.
Instead of 00, a semiconductor laser LDa of the same type as the semiconductor laser LD is used to obtain a current-light amount characteristic which is a characteristic of the differential quantum efficiency of the semiconductor laser LDa, and create an inverse characteristic of the current-light amount characteristic. As a result, the semiconductor laser L
The inverse characteristic of the differential quantum efficiency of D is obtained.

The same type here means a semiconductor laser LD chip of the same manufacturer and the same model number.

The driving 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 calculator 300 is converted into a current by the voltage / current conversion circuit 40, The LDa is driven. The outgoing light from the semiconductor laser LDa is received by the photodiode PDa, and the current / voltage conversion circuit 41
To convert the detection signal (current-light amount characteristic) into a voltage. The voltage-converted detection signal is input to a divider 42,
In the divider 42, an inverse characteristic of the current-light amount characteristic of the semiconductor laser LDa is created, and this is converted into a voltage / current conversion circuit 43.
Is supplied to the semiconductor laser LD as a drive control signal for the semiconductor laser LD.

Therefore, 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 the semiconductor laser LD itself. By realizing this in a negative feedback loop, the open loop gain characteristic can be made linear, and excellent light quantity modulation performance can be realized.

(Claims 11 to 14) FIG.
FIG. 3 is a configuration block diagram illustrating an example of an embodiment of a semiconductor laser drive circuit according to the inventions described in 1 and 12.

A part of the forward light emitted from the forward emission end face of the semiconductor laser LD in the right direction in the figure is branched via the sampling mirror M and enters the photodiode PD1 for receiving the forward light. The PD 1 converts the received light signal into a current signal and outputs it to the front light receiving circuit 50.

The forward light receiving circuit 50 receives the current signal output from the photodiode PD1, detects the amount of forward light emitted from the semiconductor laser LD, and outputs the emitted light amount detection signal.

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 set value set in advance based on the standard value of the semiconductor laser LD, and emits the amount of forward light input from the front light receiving circuit 1. The difference between the detection signal and the light amount command signal is calculated, and the two are compared.

Numeral 52 denotes a current drive circuit which, based on the difference between the forward light emission amount detection signal and the light amount command signal calculated by the APC control circuit 51, eliminates the difference between them, that is, emits the forward light. A drive current is supplied to the semiconductor laser LD so that the value of the amount detection signal becomes equal to the value of the light amount command signal, and the light emission amount of the semiconductor laser LD is controlled.

Then, these photodiodes PD1,
The forward light receiving circuit 50, the APC control circuit 51, and the current drive circuit 52 detect the amount of light emitted from the semiconductor laser LD and perform negative feedback to form a negative feedback loop for controlling the amount of light emitted from the semiconductor laser LD. are doing.

In the semiconductor laser drive circuit according to 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 semiconductor laser LD is provided on the rear side of the semiconductor laser LD opposite to the emission end face of the forward light. The photodiode PD2 is provided, and is configured to be able to simultaneously receive rear light emitted from the rear end face of the semiconductor laser LD.

The photodiode PD2 receives the rear light emitted from the rear end face of the semiconductor laser LD,
The current signal is output to the rear light receiving circuit 53.

The rear light receiving circuit 53 converts the current signal input from the photodiode PD2 into a semiconductor laser L.
The light emission amount of the rear light of D is detected, and the light emission amount detection signal is output. Therefore, the emitted light from the semiconductor laser LD receives front light emitted from the front emission end face and rear light emitted from the opposite rear emission end face by the photodiodes PD1 and PD2, respectively. The front light receiving circuit 50 and the rear light receiving circuit 53 detect the amount of light emitted from both emission end faces of the semiconductor laser LD.

The light emission amount detection signals respectively detected by the front light receiving circuit 50 and the rear light receiving circuit 53 are:
Both are input to the calculation circuit 54.

The calculation circuit 54 is provided with the front light receiving circuit 50
In response to the light emission amount detection signal detected by the rear light receiving circuit 53, the difference or ratio between the two detection signals is calculated, and the calculated value is output to the abnormality determination circuit 55.

In the abnormality determination circuit 55, a reference value range for determining an abnormality of the semiconductor laser LD based on the calculated value is set in advance, and the difference between the two detection signals calculated by the calculation circuit 54 or the difference between the two detection signals is calculated. The ratio is monitored and compared with the above set range. If a failure due to an end face break has occurred in either the front or rear emission end face of the semiconductor laser LD, the semiconductor laser LD detected by the front light receiving circuit 50 and the rear light receiving circuit 53, respectively.
The relationship between the respective light emission amounts of the front light and the rear light deviates from the initial value (reference value). Therefore, by calculating the difference in the light emission amount as a difference or a ratio by the calculation circuit 54 and comparing the difference with a preset range in the abnormality determination circuit 55, it is possible to detect a failure due to the end face destruction of the semiconductor laser LD. it can.

When it is determined that the semiconductor laser LD has a failure due to end face destruction as described above, the abnormality determination circuit 55 outputs an abnormality determination signal, and the alarm means such as an alarm or an alarm lamp outputs the abnormality of the semiconductor laser LD. Alarm for abnormalities.

Therefore, according to this embodiment, even if a failure due to end face breakage occurs in either the front emission end face or the rear emission end face of the semiconductor laser LD, the semiconductor laser LD can be quickly and reliably assembled. It is possible to detect a failure.

When the abnormality is determined, for example, when the amount of forward light emission / the amount of rear light emission> set range, it is determined that the rear light is abnormal, and the amount of forward light emission / the amount of rear light emission <set range. In this case, by determining that the forward light is abnormal, it is possible to separately detect which emission 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 abnormalities of the forward light include not only the destruction of the end face of the semiconductor laser LD but also the optical axis of the optical system for sampling the forward light. Situation such as displacement and component deterioration is also assumed. In such a case, it is possible to return to a normal state by maintenance of the sampling optical system of the apparatus.

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 semiconductor laser LD so that a drive current of a certain value or more does not flow to the semiconductor laser LD.
To control the amount of drive current supplied to the motor. Therefore, the current drive circuit 52 is provided with a circuit that receives the abnormality determination signal from the abnormality determination circuit 55 and limits the supply of the drive current to the semiconductor laser LD. By adding a circuit for limiting the drive current to the semiconductor laser LD when an abnormal state of the semiconductor laser LD is detected in this way, if a failure occurs in the semiconductor laser LD, the failure state is advanced. It is possible to emit light without causing an increase in the life of the semiconductor laser LD.

FIG. 12 is a configuration block diagram showing an example of an embodiment of a semiconductor laser drive circuit according to claims 13 and 14. The same reference numerals as those in the configuration block diagram shown in FIG. 11 denote the same components, and a detailed description thereof will be omitted.

In this embodiment, a front light abnormality detection circuit 56 and a rear light abnormality detection circuit 57 are provided instead of the calculation circuit 54 shown in FIG.

The forward light abnormality detection circuit 56 detects the amount of forward 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 output from the current drive circuit 52. By inputting the drive current supplied to the LD, the drive current is compared with a specified light emission amount. For example, forward light emission amount / drive current <
By performing the determination of the constant (Equation 1), it is possible to detect a state in which the prescribed amount of forward light is not obtained despite the flow of current.

The rear light abnormality detection circuit 57 outputs the 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 current drive circuit 52. By inputting the drive current supplied to the semiconductor laser LD, the drive current is similarly compared with a prescribed light emission amount. For example, by determining the amount of backward light emission / drive current <constant (Equation 2), it is possible to detect a state in which the specified amount of backward light is not obtained despite the current flowing.

The detection results from the front light abnormality detection circuit 56 and the rear light abnormality detection circuit 57 are input to an abnormality determination circuit 58, respectively. The abnormality determination circuit 58 determines that the semiconductor laser LD is abnormal 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. Has become. Therefore, if a failure due to the end face destruction has occurred in the front emission end face of the semiconductor laser LD, a state in which the prescribed light emission amount is not obtained with respect to the drive current is detected, and the forward light abnormality detection circuit 56 determines 1 is true, and the abnormality determination circuit 58 can determine that the semiconductor laser LD is in a failure state.

In this abnormality determination, when the above equation 1 is true and the above equation 2 is false, it is determined that the forward light is abnormal, and the above equation 1 is false and the above equation 2 is false. Is true, it is determined that the rear light is abnormal.
Is true and the above equation 2 is also true, it is determined whether the semiconductor laser LD is completely in a failure state to determine whether the front or rear emission end face of the semiconductor laser LD is in an abnormal state. Can be separated. Therefore, 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 and deterioration of parts is assumed. It is possible to return to a normal state by maintenance of the sampling optical system of the apparatus.

Therefore, according to the present embodiment, similarly, even if a failure due to the end face breakage occurs in either the front emission end face or the rear emission end face of the semiconductor laser LD, the semiconductor laser LD can be quickly and reliably achieved. Can be detected.

When the abnormality of the semiconductor laser LD is determined in this way, the abnormality determination circuit 58 outputs an abnormality determination signal,
An abnormality of the semiconductor laser LD is alarmed by alarm means such as an alarm and an alarm lamp.

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. The current drive circuit 52 receives the abnormality determination signal and controls the supply amount of the drive current to the semiconductor laser LD so that the 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 limits the supply of the drive current to the semiconductor laser LD. By adding a circuit for limiting the drive current to the semiconductor laser LD when an abnormal state of the semiconductor laser LD is detected in this way, if a failure occurs in the semiconductor laser LD, the failure state is advanced. It is possible to emit light without causing an increase in the life of the semiconductor laser LD.

[0106]

According to the first to fifth aspects of the present invention, the light amount is zero.
It is possible to provide a semiconductor laser drive circuit capable of realizing high-speed and stable modulation response even in the vicinity of low light quantity.

According to the sixth to tenth aspects of the present invention, it is possible to provide a semiconductor laser driving circuit which is excellent in light quantity stability and modulation response over the entire region from the natural light emitting region to the laser light emitting region of the semiconductor laser.

According to the present invention, it is possible to provide a semiconductor laser drive circuit capable of detecting a failure of a semiconductor laser quickly and reliably with a simple configuration.

[Brief description of the drawings]

FIG. 1 is a configuration block diagram illustrating an embodiment of a semiconductor laser drive circuit.

FIG. 2 is a current-light amount characteristic diagram of a semiconductor laser drive circuit.

FIG. 3 is a configuration block diagram showing another embodiment of the semiconductor laser drive circuit.

FIG. 4 is a configuration block diagram showing a gain fitting circuit in the embodiment of the semiconductor laser drive circuit.

FIG. 5 is a block diagram showing a configuration of a gain fitting circuit according to another embodiment of the semiconductor laser drive circuit.

FIG. 6 is a block diagram showing a configuration of a gain fitting circuit according to still another embodiment of the semiconductor laser drive circuit.

FIG. 7 is a block diagram showing a configuration of a gain fitting circuit according to still another embodiment of the semiconductor laser drive 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 in which 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 drive circuit.

FIG. 11 is a block diagram showing a configuration of an embodiment of a semiconductor laser drive circuit for performing abnormality determination of a semiconductor laser.

FIG. 12 is a block diagram showing a configuration of another embodiment of a semiconductor laser drive circuit for performing abnormality determination of a semiconductor laser.

FIG. 13 is a characteristic diagram showing a relationship between a current and a light amount of a semiconductor laser.

FIG. 14 is a characteristic diagram showing a relationship between current and differential quantum efficiency of a semiconductor laser.

FIG. 15 is a configuration block diagram of a conventional semiconductor laser drive 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 calculation unit 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 determination circuit 56 forward light abnormality detection circuit 57 Back light abnormality detection circuit 100 Gain fitting circuit 101 Linear gain fitting circuit 102 Nonlinear gain fitting circuit 300 Error calculation unit 400 Temperature compensation circuit

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2C362 AA03 AA53 AA55 AA59 AA61 AA72 5F073 BA02 BA07 EA13 EA28 GA12 GA14 GA20 GA33 GA35 GA38

Claims (14)

[Claims] A semiconductor laser driving circuit for controlling the driving of the semiconductor laser by negatively feeding back a detection signal of a light emission amount of the semiconductor laser and comparing the signal with a light amount command signal; A double negative feedback loop including a linear circuit that inputs a difference signal and outputs a linear driving current to the semiconductor laser and a nonlinear circuit that outputs a non-linear driving current is configured, and the light amount command signal is clipped at a predetermined value. And a signal added to the signal line in the signal line of the nonlinear circuit. 2. The semiconductor laser drive circuit according to claim 1, wherein said predetermined value is a light amount level corresponding to a threshold value of the semiconductor laser at the lowest use temperature. 3. A semiconductor laser drive circuit for driving and controlling the semiconductor laser by negatively feeding back a detection signal of a light emission amount of the semiconductor laser and comparing the signal with a light amount command signal. A double negative feedback loop including a linear circuit that inputs a difference signal and outputs a linear driving current to the semiconductor laser and a nonlinear circuit that outputs a non-linear driving current is configured, and the light amount command signal is clipped at a predetermined value. A semiconductor laser drive circuit, wherein the signal is added to the middle of the signal line of the nonlinear circuit, and a compensation voltage is added to the light intensity command signal so that the negative feedback does not work until the predetermined value. 4. The semiconductor laser drive circuit according to claim 3, wherein the linear circuit and the non-linear circuit in the negative feedback loop are non-negative. 5. The semiconductor laser drive circuit according to claim 3, wherein the predetermined value is a light amount level corresponding to a threshold value of the semiconductor laser at the lowest use temperature. 6. A semiconductor laser drive circuit for controlling the driving of the semiconductor laser by negatively feeding back a detection signal of a light emission amount of the semiconductor laser and comparing the signal with a light amount command signal. Forming a difference signal and obtaining a signal for driving the semiconductor laser by inputting the difference signal to a circuit having the inverse characteristic of the differential quantum efficiency of the semiconductor laser configured using a look-up table. Semiconductor laser drive circuit. 7. The semiconductor laser according to claim 6, wherein, of the inverse characteristic of the differential quantum efficiency, a linear region is configured using a linear gain fitting circuit, and a non-linear region is configured using a look-up table. Drive circuit. 8. The semiconductor laser drive circuit according to claim 6, wherein a digital signal is input as said light amount command signal. 9. A device for measuring a temperature of a semiconductor laser for compensating a temperature characteristic of the semiconductor laser, and a unit for generating a temperature compensation signal for compensating a temperature characteristic of the semiconductor laser according to the measured temperature, 9. The semiconductor laser according to claim 6, wherein the temperature of said semiconductor laser is compensated by said temperature compensation signal.
The semiconductor laser drive circuit according to any one of the above. 10. A semiconductor laser drive circuit for controlling the driving of the semiconductor laser by negatively feeding back a detection signal of a light emission amount of the semiconductor laser and comparing the signal with a light amount command signal, wherein the light emission amount of the semiconductor laser and the light amount command signal are compared. A signal for driving the semiconductor laser by forming the difference signal and inputting the difference signal to a circuit having the inverse characteristic of the differential quantum efficiency of the semiconductor laser constituted by a semiconductor chip and a division circuit of the same type as the semiconductor laser. And a semiconductor laser driving circuit. 11. A semiconductor laser driving circuit for controlling the driving of the semiconductor laser by negatively feeding back a detection signal of the light emission amount of the semiconductor laser and comparing the signal with a light amount command signal. It also detects the amount of emitted light emitted from the end face opposite to the end face, calculates the difference or ratio between the emitted light quantity detection signals of both end faces of these semiconductor lasers, and generates an abnormality determination signal when the result is out of the set range. A semiconductor laser drive circuit characterized by outputting. 12. The semiconductor laser drive circuit according to claim 11, further comprising a circuit for limiting a drive current to the semiconductor laser so as not to flow over a predetermined value by outputting the abnormality determination signal. 13. A semiconductor laser drive circuit for controlling the driving of the semiconductor laser by negatively feeding back a detection signal of the light emission amount of the semiconductor laser and comparing the signal with a light amount command signal. The amount of emitted light emitted from the end face opposite to the end face is also detected, and each of the emitted light quantity detection signals at both end faces of the semiconductor laser is compared with the drive current of the semiconductor laser, and when the result is out of the set range. A semiconductor laser drive circuit for outputting an abnormality determination signal to the semiconductor laser. 14. A semiconductor laser drive circuit according to claim 13, further comprising a circuit for limiting a drive current to the semiconductor laser so as not to flow over a predetermined value by outputting the abnormality determination signal.