JP2744045B2 - Semiconductor laser controller - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor laser control device for controlling a light output of a semiconductor laser used as a light source in a laser printer, an optical disk device, an optical communication device and the like.

[Conventional technology]

2. Description of the Related Art Semiconductor lasers are extremely small and can be directly modulated at high speed by a drive current. Therefore, semiconductor lasers have recently been widely used as light sources for optical disk devices, laser printers and the like.

However, the drive current / light output characteristics of the semiconductor laser vary significantly with temperature, which is a problem when the light intensity of the semiconductor laser is set to a desired value. Various APC (Automatic Power Control) circuits have been proposed to solve this problem and utilize the advantages of semiconductor lasers.

 This APC circuit is divided into the following three systems.

(1) The light output of a semiconductor laser is monitored by a light receiving element, and a signal proportional to a light receiving current (proportional to the light output of the semiconductor laser) generated in the light receiving element is always set to be equal to a light emission level command signal. A method in which an optical / electrical negative feedback loop for controlling a forward current of a semiconductor laser is provided, and the optical output of the semiconductor laser is controlled to a desired value by the optical / electrical negative feedback loop.

(2) During the power setting period, the light output of the semiconductor laser is monitored by the light receiving element, and a signal proportional to a light receiving current (proportional to the light output of the semiconductor laser) generated in the light receiving element and a light emission level command signal are output. The forward current of the semiconductor laser is controlled to be equal, and the optical output of the semiconductor laser is controlled to a desired value by holding the value of the forward current of the semiconductor laser set in the power setting period outside the power setting period. I do. Then, outside the power setting period, information is loaded on the optical output of the semiconductor laser by modulating the forward current of the semiconductor laser with the information based on the value of the forward current of the semiconductor laser set in the power setting period.

(3) The temperature of the semiconductor laser is measured, and the forward current of the semiconductor laser is controlled based on the measured temperature, or the temperature of the semiconductor laser is controlled to be constant so that the optical output of the semiconductor laser is desired. Control method to the value of

[Problems to be solved by the invention]

The method (1) is desirable in order to set the optical output of the semiconductor laser to a desired value.
The control speed is limited by the limitation of the operation speed of the amplification element constituting the electric negative feedback loop. For example the step response characteristic of the optical output of the semiconductor laser when the crossover frequency when considering the crossover frequency is f ₀ in the open loop optoelectronic negative feedback loop as a measure of the control speed can be approximated as follows.

Pout = P ₀ {1−exp (−2πf ₀ t)} Pout: light output of the semiconductor laser P ₀ : set light intensity of the semiconductor laser t: time In many applications of the semiconductor laser, the light output of the semiconductor laser is Immediately after the change, until the set time τ ₀ elapses, it is necessary that the total light amount (integral value of light output ∫Pout) be a predetermined value, Becomes Assuming that τ ₀ = 50 ns and the allowable range of error is 0.4%, f ₀ > 800 MHz must be satisfied, which is extremely difficult.

The method (2) does not have the above-mentioned problem of the method (1), and can modulate a semiconductor laser at high speed. However, since the light output of the semiconductor laser is not always controlled in the method (2), the light quantity of the semiconductor laser easily fluctuates due to disturbance or the like. The disturbance includes, for example, a droop characteristic of a semiconductor laser, and the light amount of the semiconductor laser easily causes an error of about several percent due to the droop characteristic. As an attempt to suppress the droop loop characteristic of a semiconductor laser, there has been proposed a method of compensating the thermal time constant of the semiconductor laser by adjusting the frequency characteristic of the semiconductor laser drive current.The thermal time constant of the semiconductor laser is different for each semiconductor laser. There are problems such as individual variations and differences depending on the surrounding environment of the semiconductor laser.

In addition, there is a problem such as a change in the amount of light due to the influence of the return light of the semiconductor laser, which is a problem in an optical disk device or the like.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a high-speed, high-precision, high-resolution semiconductor laser control device which solves the above-mentioned drawbacks.

[Means for solving the problem]

In order to achieve the above object, the invention according to claim 1 detects a light output of a driven semiconductor laser by a light receiving unit, and receives a light receiving signal and a light emitting level command signal proportional to the light output of the semiconductor laser obtained from the light receiving unit. An optical / electrical negative feedback loop for controlling the forward current of the semiconductor laser so as to make equal, a detecting means for detecting a control current of the optical / electrical negative feedback loop, and an optical output / forward current of the semiconductor laser. The light receiving signal and the light emission level command signal are set to be equal based on the characteristics, the coupling coefficient between the light receiving unit and the semiconductor laser, and the light input / light receiving signal characteristics of the light receiving unit. Converting means for converting a light emission level command signal into a forward current of the semiconductor laser; a control current for the optical / electrical negative feedback loop; The semiconductor laser is controlled by a current that is a sum or a difference from the applied current, and the invention according to claim 2 is the semiconductor laser control device according to claim 1, wherein the light output of the semiconductor laser is received by a light receiving unit. And a light emitting level command signal obtained by converting the first light emitting level command signal into a current is made equal to a light receiving current proportional to the light output of the semiconductor laser obtained from the light receiving unit. A first optical / electrical negative feedback loop for controlling a direction current, and the first light emission level command signal is controlled so that a voltage proportional to the light receiving current is equal to the light emission level command signal according to claim 1. The second light
According to a third aspect of the present invention, in the semiconductor laser control device according to the first aspect, the conversion unit includes the light emitting device. The level command signal is converted into a current proportional to the light emission level command signal by approximating a light output / forward current characteristic of the semiconductor laser as a straight line as an analog signal voltage. 3. The semiconductor laser control device according to claim 2, wherein the conversion unit approximates a light output / forward current characteristic of the semiconductor laser to a straight line by using the light emission level command signal as an analog signal voltage and is proportional to the light emission level command signal. According to a fifth aspect of the present invention, in the semiconductor laser control device according to the first aspect, the conversion means includes a light emitting level. The command signal is converted into a current corresponding to the light emission level command signal by approximating a light output / forward current characteristic of the semiconductor laser to a polygonal line as an analog signal voltage. Item 3. The semiconductor laser control device according to Item 2, wherein the conversion means uses the light emission level command signal as an analog signal voltage and approximates the light output / forward current characteristic of the semiconductor laser to a polygonal line to obtain a current corresponding to the light emission level command signal. According to a seventh aspect of the present invention, in the semiconductor laser control device according to the first aspect, the light emission level command signal is a digital signal, and the conversion unit converts the light emission level command signal into the semiconductor laser. A conversion table for converting the signal into a signal corrected based on the optical output / forward current characteristics of the And a digital / analog converting means for converting the signal into a forward current of the semiconductor laser. The invention according to claim 8, wherein the light emission level command signal is transmitted to the semiconductor laser control device according to claim 2. A digital signal, the conversion means converts the light emission level command signal into a signal corrected based on the light output / forward current characteristics of the semiconductor laser, and converts the signal converted by the conversion table into the semiconductor signal. Digital / analog converting means for converting the current into a forward current of the laser.

(Operation)

In the first aspect of the present invention, the optical / electrical negative feedback loop detects the light output of the semiconductor laser by the light receiving unit, and the light receiving signal proportional to the light output of the semiconductor laser obtained from the light receiving unit becomes equal to the light emission level command signal. Control the forward current of the semiconductor laser in such a way that the conversion means
The light emission level command signal is converted to the light reception signal and the light emission level command according to a conversion rule set in advance based on a forward current characteristic, a coupling coefficient between the light receiving unit and the semiconductor laser, and a light input / light receiving signal characteristic of the light receiving unit. The signal is converted into a photocurrent of the semiconductor laser so that the signal becomes equal. The semiconductor laser is controlled by a sum or difference current between the control current of the optical / electrical negative feedback loop and the current generated by the converter, and the control current of the optical / electrical negative feedback loop is detected by the detector. .

According to the second aspect of the present invention, the first optical / electrical negative feedback loop detects the optical output of the semiconductor laser by a light receiving unit, and a light receiving current proportional to the optical output of the semiconductor laser obtained from the light receiving unit; The forward current of the semiconductor laser is controlled so that the light emission level command signal obtained by converting the light emission level command signal into a current is equal to the light emission level command signal. The first light emission level command signal is controlled so that the light emission level command signal described in the item 1 is equal.

According to a third aspect of the present invention, the conversion means converts the light emission level command signal into an analog signal voltage, approximates the light output / forward current characteristic of the semiconductor laser to a straight line, and converts the current into a current proportional to the light emission level command signal.

According to a fourth aspect of the present invention, the conversion means converts the light emission level command signal into an analog signal voltage by approximating the light output / forward current characteristic of the semiconductor laser to a straight line, and converts it into a current proportional to the light emission level command signal.

According to a fifth aspect of the present invention, the converting means converts the light emission level command signal into an analog signal voltage by approximating a light output / forward current characteristic of the semiconductor laser to a polygonal line to convert the current into a current corresponding to the light emission level command signal.

According to a sixth aspect of the present invention, the conversion means converts the light emission level command signal into an analog signal voltage by approximating a light output / forward current characteristic of the semiconductor laser to a polygonal line, and converts it into a current corresponding to the light emission level command signal.

In the invention of claim 7, the light emission level command signal is converted by a conversion means into a signal corrected based on the light output / forward current characteristics of the semiconductor laser by a conversion table, and the digital / analog conversion means converts the light emission level command signal into a signal of the semiconductor laser. Direction current.

Also in the invention of claim 8, the light emission level command signal is converted by a conversion table into a signal corrected based on the light output / forward current characteristics of the semiconductor laser by a conversion table, and the digital / analog converter converts the light emission level command signal into a signal of the semiconductor laser. Direction current.

〔Example〕

 FIG. 2 shows an embodiment of the invention.

The light emission level command signal is supplied to the comparison amplifier 1 and the current converter 2
And a part of the optical output of the driven semiconductor laser 3 is monitored by the light receiving element 4. The comparison amplifier 1, the semiconductor laser 3, the light receiving element 4, and the differential amplifier 9 form an optical / electrical negative feedback loop, and the comparison amplifier 1 generates a photovoltaic current induced in the light receiving element 4 (proportional to the optical output of the semiconductor laser 3). And a light-emission level command signal, and the result is used to determine the forward current of the semiconductor laser 3 via the differential amplifier 9 including the transistors 5 and 6, the current source 7 and the voltage source 8. Control is performed so that the light reception signal and the light emission level command signal are equal. Also, the current converter 2 sets a current (light output / forward current characteristic of the semiconductor laser 3 and the light-receiving element 4 and the semiconductor laser 3) in accordance with the light-emitting level command signal so that the light-receiving signal and the light-emitting level command signal become equal. And a current which is set in advance based on the coupling coefficient of the light receiving element 3 and the light input / light receiving signal characteristics of the light receiving element 3. The sum of the output current of the current converter 2 and the control current output from the comparison amplifier 1 via the differential amplifier 9 is the current of the semiconductor laser 3.
Of the forward current.

Here, the crossover frequency of the open loop of the optical and electrical negative feedback loop and f _0, if set to 10000 DC gain, step response characteristics of the optical output Pout of the semiconductor laser 3 can be approximated as follows.

Pout = PL + (PS−PL) exp (−2πf ₀ t) PL: Light output at t = ∞ PS: Light amount set by current converter 2 DC gain in open loop of light / electric negative feedback loop is 1000
Since it is set to 0, if the allowable range of the setting error is set to 0.1% or less, it is considered that PL is equal to the set light amount.

Therefore, if the light amount PS set by the current converter 2 is equal to PL, the light output of the semiconductor laser 3 instantaneously becomes equal to PL. That is, since the current flowing through the resistor 10 does not change, the output of the comparison amplifier 1 does not change. However, when PS varies due to disturbance or the like, the excess or deficiency current by the current converter 2 is caused to flow in the forward direction of the semiconductor laser 3 by the comparison amplifier 1. This current value is a current obtained by subtracting the current flowing through the resistor 10 from the current set by the current source 7. Therefore, by measuring the voltage between both ends of the resistor 10, the current value corresponding to the conversion error of the current converter 2 can be detected.

In this embodiment, the output current of the current converter 2 is
It is a configuration that adds to the control current of the electric negative feedback loop,
With the configuration in which the current converter 2 is connected in parallel with the semiconductor laser 3, a configuration in which the semiconductor laser 3 is controlled by the difference between the output current of the current converter 2 and the control current of the optical / electrical negative feedback loop can be realized. .

Thus, according to this embodiment, a high-speed, high-precision, high-resolution semiconductor laser control device can be realized.

 FIG. 1 shows another embodiment of the present invention.

In this embodiment, the power supplies Vcc and Vss are reversed in the above embodiment, and NPN transistors 5 and 6 are used. Further, the voltage between both ends of the resistor 10 is taken out via the differential amplifier 11.

 FIG. 3 shows another embodiment of the present invention.

This embodiment differs from the embodiment shown in FIG. 1 in that the differential amplifier 9 is omitted and the output current of the comparison amplifier 2 is supplied to the semiconductor laser 3 via a resistor 10.

 FIG. 4 shows another embodiment of the invention.

The light emission level command signal is supplied to the comparison amplifier 12 and the current converter 2
And a part of the optical output of the driven semiconductor laser 3 is monitored by the light receiving element 4. The high frequency component of the photovoltaic current Is (which is proportional to the optical output of the semiconductor laser 3) induced in the light receiving element 4 flows into the capacitor C and is input to the impedance converter 13, and the low frequency component of the photovoltaic current Is Flows through the resistor R and is converted into a voltage. The voltage generated at the resistor R is input to the comparison amplifier 12 and the voltage / current converter 14, and the voltage / current converter 14 converts the voltage generated at the resistor R into a current. The output current of the voltage-current converter 14 are added by the output current and the adder 15 of the impedance converter 13, a current I ₀ equal to the photovoltaic current Is generated in the light receiving element 4. On the other hand, the comparison amplifier 12 compares the voltage generated at the resistor R with the light emission level command signal and amplifies the difference voltage, and the output voltage of the comparison amplifier 12 is converted to a current by the voltage / current converter 16 and The light emission level command signal current becomes 1. The subtractor 17 subtracts the current I ₀ from the adder 15 from the first light emission level command signal current IL from the voltage / current converter 16 and outputs the difference current, and the difference current is amplified by the current amplifier 18. Then, it is output as a control current of the semiconductor laser 3 via the differential amplifier 9. Accordingly, the light receiving element 4, the capacitance C, the resistance R, the impedance converter 13, the voltage / current converter 14, the adder 15, the subtractor 17, the current amplifier 18, and the differential amplifier 9 are proportional to the optical output of the semiconductor laser 3. Photoelectromotive current Is of light receiving element 4 and first light emission level command signal current from voltage / current converter 16
A first optical / electrical negative feedback loop for controlling the forward current of the semiconductor laser 3 so that IL becomes equal to the reference current is formed. The comparison amplifier 12 and the voltage / current converter 16 are provided with a photoelectromotive current Is of the light receiving element 4.
The first light emission level command signal current IL so that the voltage proportional to the second light emission level command signal and the external second light emission level command signal become equal.
Is configured as a second optical / electrical negative feedback loop for controlling

The current converter 2, the differential amplifier 9, the resistor 10, and the differential amplifier 11 operate in the same manner as in the above embodiment, and the output current of the current converter 2 and the control current output by the differential amplifier 9 Is the forward current of the semiconductor laser 3.

Here, the crossover frequency of the open loop of the first optoelectronic negative feedback loop and f _0, with the 30 DC gain, 1000 DC gain of the second optical-electrical negative feedback loop
When 0, the step response characteristic of the optical output Pout of the semiconductor laser 3 can be approximated as follows.

Pout = PL + (PS−PL) exp (−2πf ₀ t) Since the DC gain of the second optical / electrical negative feedback loop is 10,000, if the allowable range of the setting error is 0.1% or less, PL is It is considered to be equal to the set light amount. Further, since the DC gain of the first optical / electrical negative feedback loop is set to 30, the steady-state error in the first optical / electrical negative feedback loop is about (PS-PL) / 30. Therefore, if the light amount PS set by the current converter 2 is equal to PL, the light output of the semiconductor laser 3 instantaneously becomes equal to PL. In this case, Pout = PL, so that the output of the comparison amplifier 12 becomes It does not change. That is, since the value of the current flowing through the resistor 10 does not change, the voltage between both ends of the resistor 10 does not change. However,
If Ps fluctuates due to disturbance or the like, the excess or deficiency current by the current converter 2 is compared with the semiconductor laser 3 by the comparison amplifier 12.
Flow in the forward direction. This current value is a value obtained by subtracting the current flowing through the resistor 10 from the current set by the current source 7. Therefore, by measuring the voltage between both ends of the resistor 10, the current value corresponding to the conversion error of the current converter 2 can be detected.

Further, even if the PS fluctuates by 5% due to disturbance or the like, the steady-state error of the first optical / electrical negative feedback loop is about 0.2%, so that f ₀ = about 40 MHz and the first optical / electrical negative feedback loop If the DC gain is about 30, the semiconductor laser 3
In the light output of, the error with respect to the set value becomes 0.4% or less.

In addition, the optical / electrical negative feedback for the error of the total light amount (integral value of optical output ∫Pout) to become 0.4% or less from immediately after changing the optical output of the semiconductor laser 3 until the set time τ ₀ elapses. The crossover frequency of the loop is 40 when τ ₀ = 50 ns
MHZ or higher, and DC of the optical / electrical negative feedback loop
The gain only needs to be about 30 times, and if the crossover frequency and the DC gain are at such a level, it can be easily realized.

 FIG. 5 shows another embodiment of the present invention.

This embodiment differs from the embodiment shown in FIG. 4 in that the output voltage of the comparison amplifier 12 is input to the current converter 19 instead of the second light emission level command signal. A current (light output / forward current characteristic of the semiconductor laser 3 and a coupling coefficient between the light receiving element 4 and the semiconductor laser 3) preset according to the output voltage of the comparison amplifier 12 so that the light receiving signal and the light emission level command signal become equal. Light receiving element 3
(A current set based on the light input / light receiving signal characteristics). That is, the current converter 19 outputs the current I ₀ from the adder 15 for the high frequency component of the light emission level command signal.
And the first light emission level command signal current IL are equalized in accordance with the output voltage of the comparison amplifier 12 (the light output / forward current characteristic of the semiconductor laser 3 and the current between the light receiving element 4 and the semiconductor laser 3). A current preset based on the coupling coefficient and the light input / light receiving signal characteristics of the light receiving element 3)
And a current set in advance according to the output voltage of the comparison amplifier 12 so that the voltage between both ends of the resistor R and the first light emission level command signal become equal for the low frequency component of the second light emission level command signal. (A light output / forward current characteristic of the semiconductor laser 3, a coupling coefficient between the light receiving element 4 and the semiconductor laser 3, and a current preset based on the light input / light receiving signal characteristic of the light receiving element 3).

 FIG. 6 shows another embodiment of the present invention.

In this embodiment, a current converter 20 composed of a differential amplifier 21, a transistor 22 and a resistor _R0 is used as a current converter in the embodiment of FIG. 1, and the differential amplifier 11 is omitted. The current converter 20 sets a current (light output / forward current characteristic of the semiconductor laser 3 and the light-receiving element 4 and the semiconductor laser 3) set in advance according to the light-emitting level command signal Vs so that the light-receiving signal and the light-emitting level command signal become equal.
(A current set in advance based on the coupling coefficient of the light receiving element 3 and the light input / light receiving signal characteristics of the light receiving element 3). That light emission level instruction signal Vs is input to the differential amplifier 21, it is converted by the transistor 22 and the resistor R ₀ in current Vs / R _0. The Vs / R ₀ of the current and the current Vs / R ₀ + AΔV the sum of the output currents EiderutaV of the differential amplifier 9 becomes forward current of the semiconductor laser 3, the semiconductor laser 3 is determined by the forward current Vs / R ₀ + AΔV and outputs the light output P _0. As described above, the resistor 10 converts the control current of the optical / electrical negative feedback loop into a voltage, detects the voltage, and outputs the voltage.

In general, a semiconductor laser can approximate the relationship between the light output and the forward current with a straight line of the differential quantum efficiency η for a forward current equal to or larger than the threshold current Ith. In this case the optical output P ₀ can be expressed as follows.

ΔV = Vs / R1−αSP ₀ Vs is V ₀ (the optical output of the semiconductor laser 3 corresponding to V ₀ is the light intensity when the current of the semiconductor laser is equal to or higher than the threshold current)
The response characteristics when changed to Vi are the same as in the embodiment of FIG. Can be approximated.

Therefore, if the setting is made so that R = αSηR ₀ , an effect equivalent to that of the embodiment of FIG. 4 can be obtained with a simple configuration.

The current converter 20 in this embodiment may have a configuration as shown in FIG. 9 and FIG.

The current converter shown in FIG. 9 includes transistors 23 to 26, a current source 27, a voltage source 28, and resistors 29 to 33. The current converter shown in FIG. 10 includes transistors 34 to 37, a current source 38, and a voltage source. 39, comprised of resistors 40-44. These current converters are, like the current converter 20, a current (light output / forward current characteristic of the semiconductor laser 3) set in advance according to the light emission level command signal so that the light receiving signal and the light emission level command signal become equal. And a coupling coefficient between the light receiving element 4 and the semiconductor laser 3 and a current preset based on the light input / light receiving signal characteristics of the light receiving element 3). The directional current characteristic is approximated to a straight line and converted into a current proportional to the light emission level command signal.

 FIG. 7 shows another embodiment of the present invention.

This embodiment differs from the embodiment of FIG. 4 in that the current converter 20 is used as a current converter and the differential amplifier 11 is omitted.

Generally to semiconductor lasers can be approximated the relationship between a light output, a forward current in the linear differential quantum efficiency η relative to the threshold current Ith or more forward current, the optical output P ₀ of the semiconductor laser 3 of the following Can be expressed as

Vs is from V ₀ (the optical output of the semiconductor laser 3 corresponding to V ₀ is the light intensity when the current of the semiconductor laser is equal to or higher than the threshold current)
The response characteristics when changed to Vi are the same as in the embodiment of FIG. Can be approximated.

Therefore, if the setting is made so that R = αSηR ₀ , an effect equivalent to that of the embodiment of FIG. 4 can be obtained with a simple configuration.

 FIG. 8 shows another embodiment of the present invention.

This embodiment is different from the embodiment of FIG. 7 in that the output voltage of the comparison amplifier 12 is input to the current converter 19 instead of the second light emission level command signal.

In the embodiment described above, a general current converter and a current converter approximated to a straight line are used. However, a current converter approximated to a broken line may be used. 11 to 13 show examples of the current converter based on the polygonal line approximation used as the current converter in the above embodiment.

The current converter shown in FIG. 11 includes a differential amplifier 45, a transistor 46, a diode 47, a voltage source 48, and resistors 49 to 51. The break point is determined by the voltage of the voltage source 48. The current converter shown in FIG. 12 includes transistors 52 to 55, a current source 56, diodes 57 and 58, voltage sources 59 to 61, and resistors 62 to 69, and the break point is determined by the voltages of the voltage sources 59 and 60. The current converter shown in FIG. 13 has transistors 70 to 75 and current sources 76 to 7
9. It is composed of voltage sources 80 and 81 and resistors 82 to 85, and the break point is determined by the voltage of the voltage sources 80 and 81.

In order to optimize the above current converter, it is effective to correct the light output / forward current characteristics of the semiconductor laser by a conversion table using the light emission level command signal as a digital signal. Is shown in FIG.

In this embodiment, in the above embodiment, the light emission level command signal composed of a digital signal is subjected to data conversion by the conversion table 86 so as to correct the light output / forward current characteristics of the semiconductor laser, and is converted into digital / analog (D / A) conversion. Container 8
7, D / A conversion is performed, and transistors 88 to 91, a current source 92,
The current is converted into a current by a current conversion unit including a voltage source 93 and resistors 94 to 98 and supplied to the semiconductor laser 3. Also, the light emission level command signal is delayed for a predetermined time by the data delay circuit 99,
The signal is D / A converted by the D / A converter 100 and input to the comparison amplifier 12.

〔The invention's effect〕

As described above, according to the first aspect of the present invention, the light output of the driven semiconductor laser is detected by the light receiving unit, and the light receiving signal proportional to the light output of the semiconductor laser obtained from the light receiving unit and the light emission level command signal are output. An optical / electrical negative feedback loop for controlling the forward current of the semiconductor laser to be equal;
Detecting means for detecting the control current of the optical / electrical negative feedback loop; light output / forward current characteristics of the semiconductor laser; coupling coefficient between the light receiving unit and the semiconductor laser; light input / light receiving signal of the light receiving unit A conversion unit that converts the light emission level command signal into a photocurrent of the semiconductor laser according to a preset conversion rule so that the light reception signal and the light emission level command signal are equal based on characteristics,
Since the semiconductor laser is controlled by the sum or difference current of the control current of the optical / electrical negative feedback loop and the current generated by the conversion means, the semiconductor laser is controlled at high speed, high accuracy, high resolution and is not affected by disturbances. A strong semiconductor laser control device can be realized.

According to a second aspect of the present invention, there is provided the semiconductor laser control device according to the first aspect, wherein the light output of the semiconductor laser is detected by a light receiving portion and the light receiving current is proportional to the light output of the semiconductor laser obtained from the light receiving portion. And a first optical / electrical negative feedback loop for controlling a forward current of the semiconductor laser so that a light emission level command signal current obtained by converting the first light emission level command signal into a current is equal. 2. The optical / electrical negative feedback loop according to claim 1, wherein said second optical / electrical negative feedback loop controls said first optical emission level command signal so that the proportional voltage becomes equal to said optical emission level command signal. Since the feedback loop is formed, an effect equivalent to that of the semiconductor laser control device according to the first aspect can be obtained even if the open loop gain of the high-frequency optical / electrical negative feedback loop is not very large.

According to a third aspect of the present invention, in the semiconductor laser control device according to the first aspect, the conversion means approximates the light output / forward current characteristic of the semiconductor laser to a straight line by using the light emission level command signal as an analog signal voltage. Since the current is converted into a current proportional to the light emission level command signal, an effect equivalent to that of the semiconductor laser control device according to the first aspect can be obtained with a simple circuit configuration.

According to a fourth aspect of the present invention, in the semiconductor laser control device according to the second aspect, the conversion means approximates the light output / forward current characteristic of the semiconductor laser to a straight line by using the light emission level command signal as an analog signal voltage. Since the current is converted into a current proportional to the light emission level command signal, an effect equivalent to that of the semiconductor laser control device according to the second aspect can be obtained with a simple circuit configuration.

According to a fifth aspect of the present invention, in the semiconductor laser control device according to the first aspect, the conversion means approximates the light output / forward current characteristic of the semiconductor laser to a polygonal line using the light emission level command signal as an analog signal voltage. Since the current is converted into a current corresponding to the light emission level command signal, an effect equivalent to that of the semiconductor laser control device according to claim 1 can be obtained with a simple circuit configuration and higher accuracy than in the case of linear approximation.

According to a sixth aspect of the present invention, in the semiconductor laser control device according to the second aspect, the converting means approximates the light output / forward current characteristic of the semiconductor laser to a polygonal line using the light emission level command signal as an analog signal voltage. Since the current is converted into a current corresponding to the light emission level command signal, an effect equivalent to that of the semiconductor laser control device according to claim 2 can be obtained with a simple circuit configuration and higher accuracy than in the case of linear approximation.

According to a seventh aspect of the present invention, in the semiconductor laser control device according to the first aspect, the light emission level command signal is a digital signal, and the converting means converts the light emission level command signal into a light output / forward current characteristic of the semiconductor laser. 2. A current conversion unit according to claim 1, further comprising a conversion table for converting the signal converted based on the conversion table, and a digital / analog converter for converting the signal converted by the conversion table into a forward current of the semiconductor laser. 2. The method according to claim 1, wherein the accuracy is assured in order to guarantee the non-linearity by using a conversion table.
The same effects as those of the described semiconductor laser control device can be obtained.

According to an eighth aspect of the present invention, in the semiconductor laser control device according to the second aspect, the light emission level command signal is a digital signal, and the converting means converts the light emission level command signal into a light output / forward current characteristic of the semiconductor laser. 3. A current conversion means according to claim 2, further comprising a conversion table for converting a signal converted based on the conversion table, and a digital / analog converter for converting the signal converted by the conversion table into a forward current of the semiconductor laser. Claim 2 has high accuracy in order to assure non-linearity by sides or tables.
The same effects as those of the described semiconductor laser control device can be obtained.

[Brief description of the drawings]

1 to 8 are circuit diagrams showing each embodiment of the present invention, FIGS. 9 to 13 are circuit diagrams showing a current converter in another embodiment of the present invention, and FIG. FIG. 9 is a circuit diagram showing a part of another embodiment. 1,12 ... Comparison amplifier, 2,19,20 ... Current converter, 3 ...
Semiconductor laser, 4 ... light receiving element, 9 ... differential amplifier, 10
... resistance, 13 ... impedance converter, 14, 16 ... voltage-current converter, 15 ... adder, 17 ... subtractor, 18 ...
Current amplifier, C: capacitance, R: resistance, 86: conversion table, 87: D / A converter.

Claims (8)

(57) [Claims] An optical output of a driven semiconductor laser is detected by a light-receiving section, and the light-emitting level command signal is made equal to a light-receiving signal proportional to the light output of the semiconductor laser obtained from the light-receiving section. An optical / electrical negative feedback loop for controlling the forward current of the semiconductor laser; detecting means for detecting a control current of the optical / electrical negative feedback loop; an optical output / forward current characteristic of the semiconductor laser; The light emitting level command signal is converted into the semiconductor laser according to a preset conversion rule so that the light receiving signal and the light emitting level command signal become equal based on a coupling coefficient with a laser and a light input / light receiving signal characteristic of the light receiving unit. And a conversion means for converting the control current of the optical / electrical negative feedback loop and the current generated by the conversion means. The semiconductor laser control apparatus and controls the semiconductor laser by the flow. 2. The semiconductor laser control device according to claim 1, wherein the light output of said semiconductor laser is detected by a light receiving portion, and a light receiving current proportional to the light output of said semiconductor laser obtained from said light receiving portion; A first light source for controlling a forward current of the semiconductor laser so that a light emission level command signal current obtained by converting the light emission level command signal into a current becomes equal.
An electric negative feedback loop; and a second optical / electrical negative feedback loop that controls the first light emission level command signal so that a voltage proportional to the light receiving current is equal to the light emission level command signal according to claim 1. 3. A semiconductor laser control device comprising the optical / electrical negative feedback loop according to claim 1. 3. The semiconductor laser control device according to claim 1, wherein said conversion means uses said light emission level command signal as an analog signal voltage and approximates a light output / forward current characteristic of said semiconductor laser to a straight line to obtain said light emission level. A semiconductor laser control device for converting a current into a current proportional to a command signal. 4. The semiconductor laser control device according to claim 2, wherein said conversion means uses said light emission level command signal as an analog signal voltage and approximates a light output / forward current characteristic of said semiconductor laser to a straight line to obtain said light emission level. A semiconductor laser control device for converting a current into a current proportional to a command signal. 5. The semiconductor laser control device according to claim 1, wherein said conversion means uses said light emission level command signal as an analog signal voltage and approximates a light output / forward current characteristic of said semiconductor laser to a polygonal line to obtain said light emission level. A semiconductor laser control device for converting a current into a current corresponding to a command signal. 6. The semiconductor laser control device according to claim 2, wherein said conversion means uses said light emission level command signal as an analog signal voltage to approximate the light output / forward current characteristic of said semiconductor laser to a polygonal line. A semiconductor laser control device for converting a current into a current corresponding to a command signal. 7. The semiconductor laser control device according to claim 1, wherein the light emission level command signal is a digital signal,
A conversion table for converting the emission level command signal into a signal corrected based on the light output / forward current characteristics of the semiconductor laser by the conversion means; and converting the signal converted by the conversion table into a forward current of the semiconductor laser. And a digital / analog converting means for converting the data into digital data. 8. The semiconductor laser control device according to claim 2, wherein the light emission level command signal is a digital signal,
A conversion table for converting the emission level command signal into a signal corrected based on the light output / forward current characteristics of the semiconductor laser by the conversion means; and converting the signal converted by the conversion table into a forward current of the semiconductor laser. And a digital / analog converting means for converting the data into digital data.