JPH01266776A - Dc bias control circuit of semiconductor laser - Google Patents

Abstract

PURPOSE:To kept the ratio of the threshold current of a semiconductor laser to a DC bias current applied to the semiconductor laser approximately constant by providing a differential amplifier which inputs a reference signal from a reference signal generator and a bias control signal from an inverse-logarithmic amplifier and loads the semiconductor laser with DC. CONSTITUTION:One of the inputs of a differential amplifier 6 is a reference signal from a reference signal generator 1 which is an output voltage without an ambient temperature dependence and the other input is a bias control signal from an inverse-logarithmic amplifier 4 which is an output voltage whose value is increased exponentially in accordance with the decrease of an ambient temperature detection signal voltage from an ambient temperature detector 3 along with the rise of the ambient temperature. Therefore, when the threshold current of a semiconductor laser is increased exponentially with the rise of the ambient temperature, a DC bias current applied to the semiconductor laser is increased exponentially with the rise of the ambient temperature. With this constitution, the ratio of the threshold current of the semiconductor laser to the DC bias current applied to the semiconductor laser can be kept approximately constant.

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention provides a direct current bias current for a semiconductor laser.
Even if the threshold 1a current of the semiconductor laser has an ambient temperature dependence, the ratio of the threshold current of the semiconductor laser to the DC bias current for the semiconductor laser is controlled to maintain a substantially constant relationship. Related to DC bias control circuit.

[Conventional technology]

Conventionally, in a semiconductor laser drive circuit that obtains light emission from the semiconductor laser according to the modulation signal current by supplying N currents of modulation signals to the semiconductor laser at a DC bias current of m, the output light from the semiconductor laser is The intensity of the output light from the semiconductor laser is detected by a photoelectric conversion element, and the detection output controls the DC bias current for the semiconductor laser. Since the threshold current of the laser has a dependency on the ambient temperature, the DC bias of the semiconductor laser is designed to compensate for the change in the ratio of the threshold current of the semiconductor laser and the DC bias current for the semiconductor laser due to the ambient humidity. A control circuit is proposed.

Problem to be Solved by the Invention 1 However, in the case of the conventional DC bias control circuit for a semiconductor laser described above, the dependence of the threshold current of the semiconductor laser on the ambient temperature becomes an exponential function as the ambient temperature increases. However, the external temperature dependence of the intensity of the output light from a semiconductor laser does not increase exponentially as the ambient temperature increases. Even if the change in the ratio between the tJ l+ff current of the laser and the DC bias current for the semiconductor laser is compensated to some extent, the ratio between the threshold current of the semiconductor laser and the DC bias current for the semiconductor laser remains approximately constant. It had the disadvantage that it could not be done. Therefore, the present invention aims to propose a novel DC bias control circuit for a semiconductor laser, which does not have the above-mentioned drawbacks. [Means for Solving the Problems] A DC bias control circuit for a semiconductor laser according to the present invention has the following features:
A reference signal generation circuit that outputs an output voltage that has no dependence on ambient temperature as a reference signal, and a temperature-sensitive semiconductor element that outputs an output voltage that is independent of ambient temperature as a reference signal, and an output voltage that decreases as the ambient temperature increases. An ambient temperature detection circuit outputs as a detection signal, and an ambient temperature detection signal from the ambient temperature detection circuit is input, and increases exponentially as the voltage of the ambient temperature detection signal decreases. an antilogarithmic amplifier circuit that outputs an output voltage as a bias control signal, a reference signal from the reference signal generation circuit, and a bias control signal from the antilogarithmic amplifier circuit; It has a differential amplifier circuit which uses as a DC load.

[Action/effect]

According to the DC bias control circuit for a semiconductor laser according to the present invention, the reference signal from the reference signal generation circuit, which is one input of the differential amplifier circuit, is an output voltage having no dependence on the ambient temperature. In addition, the bias control signal from the antilogarithmic amplifier circuit, which is the other input of the differential amplifier circuit, increases exponentially as the voltage of the ambient temperature detection signal from the ambient temperature detection circuit decreases. On the other hand, since the ambient temperature detection signal from the ambient temperature detection circuit is an output voltage that decreases as the ambient humidity increases, the other input of the differential amplifier circuit One bias control signal is an output voltage that increases exponentially as the ambient temperature increases. Therefore, when the threshold 1+fi TFi current of the semiconductor laser increases exponentially as the ambient temperature increases, the DC bias current for the semiconductor laser increases exponentially as the ambient temperature increases. Therefore, the ratio between the threshold current of the semiconductor laser and the DC bias current for the semiconductor laser can be kept approximately constant.

[Actual drop example]

Next, an embodiment of a semiconductor DC bias control circuit according to the present invention will be described with reference to FIG. The DC bias control circuit for a semiconductor laser according to the present invention shown in FIG. 1 has the configuration described below. That is, the reference signal generation circuit 1 is changed to the right. This reference signal generation circuit 1 uses, for example, an npn type transistor 14 whose collector and base are connected to each other between a power supply line 11 and a power supply line 12 that is connected to the ground. The pn junction element 13 is the constant current circuit 1
5 and a resistor 16 in that order, and
In parallel with the series circuit of the resistor 16 and the pn junction element 13, a resistor 17 and an npn type transistor 18 whose base is connected to the midpoint of the connection between the resistor 16 and the pn junction element 13;
A series circuit in which the resistor 19 and the resistor 19 are connected in series in that order is connected with the resistor 19 on the power supply line 12 side, and the base is connected to the midpoint between the resistor 17 and the collector of the transistor 18. An npn type transistor 20 is connected tf1 with its emitter facing the power supply line 12, and the collector of the transistor 20 is connected to the output line 2.
1 is derived, which itself has a known configuration. It also has an ambient temperature detection circuit 3. In addition to this, the thirst detection circuit 3 includes a plurality of pn junction elements 32 using a plurality of npn type transistors 31 whose bases and collectors are connected to each other between the power supply lines 11 and 12 described above. A series circuit is connected through the resistor 33, and the base is connected to the midpoint of the connection between the resistor 33 and the series circuit of the plurality of pn junction cables 32.
An n-type I transistor 34 has a resistor 35 at its emitter.
are connected in series, and the output line 3 is connected from the midpoint of the connection between the emitter of the transistor 34 and the resistor 35.
6 has been derived, which itself is a known configuration. Furthermore, it has an anti-logarithm amplifier circuit 4. This anti-logarithm amplifier circuit 4 has one input terminal 41a (negative polarity) connected through a resistor 42 to the other end (positive polarity) of a reference voltage source 43 whose one end is connected to ground, and the other input terminal 41a (negative polarity).
b (positive polarity) is connected to the ground, the output end 41c is connected to the input end 41a through the capacitive element 44, a resistor 45, and an npn type transistor 46 whose base is connected to the ground through the resistor 47. The operational amplifier 41 is connected to the input < 41a through a series circuit of
An operational amplifier 51 is connected to the output terminal 41c of the circuit, the other input terminal 51b (positive polarity) is connected to ground, and the output terminal 51c is connected to the input terminal 51a through a parallel circuit of a capacitive element 54 and a resistor 55. The above-described ambient temperature is detected from the midpoint between the base of the transistor 44 and the resistor 47, which is connected between the output end 41c and the input end 41a of the operational amplifier 41 through the resistor 45, through the resistor 48. An input line 49 connected to the output line 36 of the circuit 3 is led out, and an output line 56 is led out from the output terminal 5C of the operational amplifier 51.
It has a structure that is known per se. Further, the differential amplifier circuit 6 is shown on the right. This differential amplifier circuit 6 has a collector connected to the above-mentioned power supply F1111 through a semiconductor laser 61 as a DC load, and an emitter connected to the above-mentioned power supply line 12 through a resistor 62 and a constant current circuit 63 in that order. npn
An npn type transistor 64 whose collector is connected to the above-mentioned power supply line 11 through a resistor 71 and whose emitter is connected to the above-mentioned power supply line 12 through a resistor 72 and the above-mentioned constant current circuit 63 in that order. transistor 74
An input line 65 connected to the output line 56 of the anti-logarithmic amplifier circuit 4 described above is led out from the base of the transistor 64, and an input line 65 connected to the output line 56 of the above-mentioned anti-logarithmic amplifier circuit 4 is led out from the base of the transistor 74. The input line 75 connected to the output line 21 is led out, which has a configuration known per se. The above is the configuration of the embodiment of the DC bias control circuit for a semiconductor laser according to the present invention. The reference signal generation circuit 1 of the DC bias control circuit for a semiconductor laser having such a configuration is well known in itself, so a detailed explanation will be omitted! However, the resistor 16.
If you select the values of 17 and 19 appropriately and add J3, the output line 21
and ground, an output voltage that does not have dependence on the ambient temperature (similar to the ambient temperature of the semiconductor laser 61 in the differential amplifier circuit 6) is output as the reference signal SO. Further, according to the ambient temperature detection circuit 3 having the above-mentioned configuration, which is known per se and will not be described in detail, the plurality of pn junction elements 32 detect the ambient temperature (semiconductor Since it acts as a temperature-sensitive semiconductor device whose equivalent resistance decreases as the ambient temperature (similar to the ambient temperature of the laser 61) increases, there is a connection between the output line 36 and ground as the ambient temperature increases. The output voltage that decreases according to the temperature is outputted as an ambient temperature dependence of ¥331. Furthermore, according to the inverse logarithm amplifier circuit 4 having the above-mentioned configuration, since it is known per se, a detailed explanation will be omitted, but v
Four camphor amplifiers 41 and 51 are connected in cascade via a transistor 53, and a transistor 44 connected to an output terminal 41c and an input terminal 41a of the operational amplifier 41 via a resistor 45 outputs an output from the ambient temperature detection circuit 3. Since it is controlled by the ambient temperature detection signal S1, the output ?
156 and ground, an output voltage that increases exponentially as the voltage of the ambient temperature detection signal S1 from the ambient temperature detection circuit 3 decreases, and therefore the ambient temperature (differential amplification) The output voltage that increases exponentially as the output voltage of the semiconductor laser 61 in the circuit 6 increases is outputted as the bias control signal S2. Further, according to the differential amplifier circuit 6 having the above-described configuration,
Although the detailed explanation will be omitted since it is well known per se, one input line 75 is supplied with a reference signal SO which indicates an output voltage having no dependence on ambient temperature from the reference signal generation circuit 1.
Since the other input 1fj65 is supplied with the bias control signal 82 from the antilogarithmic amplifier circuit 4, which has an output voltage that increases exponentially as the ambient temperature rises,
A DC bias current that increases exponentially as the ambient temperature increases is supplied to the semiconductor laser 61. Therefore, according to the DC bias control circuit for a semiconductor laser according to the present invention shown in FIG. The DC bias current to the laser 61 rises exponentially as the ambient temperature increases, and therefore the ratio between the threshold current of the semiconductor laser 61 and the DC bias current to the semiconductor laser 61 is kept almost constant. can be kept. Note that in this case, the semiconductor laser 61 is 1 (superimposed on the DC bias ff DC, detailed illustration rJ'c is omitted, but by supplying the modulation signal current, light emission corresponding to the modulation signal current)] is output. . Furthermore, according to the DC bias control circuit for a semiconductor laser according to the present invention shown in FIG. The relationship between the DC bias current flowing through the 1' conductor relay 1161 and the current flowing through the constant current circuit 15 in the reference signal generation circuit and the resistor 4B in the anti-logarithm amplifier circuit 4 is as follows.
By using the resistance value as a parameter, the resistance value is obtained as shown by lines A, [3, and C in FIG. Therefore, if the constant current circuit 15 in the reference signal generation circuit 1 is made variable and the current flowing therein is adjusted, ul! The characteristic temperature T of the semiconductor radar 61 can be determined by adjusting the resistance value of the EJ7CJII11 female type. In addition, by adjusting the current flowing through the constant current circuit 15 in the reference signal generation circuit 1 while keeping the resistance value of the resistor 48 in the anti-logarithm amplifier circuit 4 constant, the output of the semiconductor laser 61 can be adjusted. Characteristic temperature T. With constant j, the threshold 1j'T of the half-solid laser 61 is
The coefficient value of temperature characteristics related to current can be adjusted,
Therefore, the coefficient of the temperature characteristic of the semiconductor laser 61 regarding the threshold 1ifIfi current and the characteristic temperature T of the semiconductor laser 61. Even if there are variations in the semiconductor laser 6
1, the DC bias current can be supplied so that the ratio between the threshold current and the -If61 threshold current is approximately constant. Note that lines A, B, and C in FIG. 2 indicate that the current of the constant current circuit 15 is 15 mA, 7 mA, and 2.7 mA, respectively, and the resistance value of the resistor 48 is 17.5 Ω, 15 Ω, and 13 Ω, respectively. The side love conduit of the tuyere which was set to Ω is also mofushi, haori, ■90
Output roughness 8 and D are both resistor 1 of resistor 48 to 13 Ω.
In this state, the measured viscosity is shown when the 'Ki current of the constant current circuit 15 is set to 2.7 mA and 6 mA, respectively. Furthermore, according to the present invention shown in FIG. 1, although detailed explanation is omitted, the resistors 62 and 72 connected to the -I emitters of the transistors 4 and 74 in the differential amplifier circuit 6 are of variable type. By adjusting the resistance value of
Furthermore, by making the resistors 33 and 35 in the ambient temperature detection circuit 3 variable and adjusting their resistance values, the number of the plurality of pn junction elements 32 in the ambient temperature detection circuit 3 can be selected in advance. By doing so, the excellent effects described above can be obtained over a wide temperature range of the ambient temperature. Note that the above description merely shows one embodiment of the DC bias control circuit for a semiconductor laser according to the present invention.
Each of the reference signal generation circuit 1, ambient temperature detection circuit 3, anti-logarithmic amplifier circuit 4, and differential amplifier circuit 6 may be replaced with the above-mentioned configurations, and may be changed to various configurations that are known per se. , various modifications and changes may be made without departing from the spirit of the invention.

[Brief explanation of the drawing]

FIG. 1 is a line connection diagram showing an embodiment of a DC bias control circuit for a semiconductor laser according to the present invention. FIG. 2 is a diagram illustrating the relationship between the DC bias M current flowing through the semiconductor laser and the ambient temperature for purposes of explanation. 1...Reference signal generation circuit 3...
... Ambient temperature detection circuit 4 ...... Anti-logarithmic amplifier circuit 6 ...... Differential amplifier circuit 11.12 ...... Power line 13...... pn junction element 14.18.20, 31.34.46.53.64.7
4......npn type transistor 15.63......constant current circuit 16.17.19.33.35.42.45.47.4
8.55.62.71.72 ......Resistance 21.36.56 ......Output line 41.51 ......Calculation Amplifier 43...Reference voltage sources 44, 54...Capacitive element 49,65,75...Input line 61... ... Semiconductor laser applicant Nippon Telegraph and Telephone Corporation 1@-NiichiKabe-zu3

Claims (1)

[Claims] A reference signal generation circuit that outputs an output voltage that has no dependence on ambient temperature as a reference signal, and a temperature-sensitive semiconductor element that decreases as the ambient temperature rises. an ambient temperature detection circuit that outputs an output voltage as an ambient temperature detection signal; an ambient temperature detection signal from the ambient temperature detection circuit is input; an antilogarithmic amplifier circuit that outputs an output voltage that increases exponentially as a bias control signal; a reference signal from the reference signal generation circuit and a bias control signal from the antilogarithmic amplifier circuit; A DC bias circuit for a semiconductor laser, further comprising a differential amplifier circuit using the semiconductor laser as a DC load.