JPH07147446A - Ld driving circuit of optical fiber module - Google Patents

Abstract

PURPOSE:To hold the level of light output constant by controlling the bias current of a semiconductor laser element. CONSTITUTION:A light receiving power detection means 4 detects the detection output of a photodetector element 1B which detects the light output of a semiconductor laser element 1A. A bias current control means 7 controls a bias current 1b for laser oscillation of the semiconductor laser element 1A. Two or more points of values of the bias current 1b of the semiconductor laser element 1A are changed, light emission power of the semiconductor laser element 1A is detected by a light receiving power detection means 4, and change, etc., of quantum efficiency and a threshold current value of the semiconductor laser element 1A are detected. Thereby, the d.c. bias current 1b of the semiconductor laser element 1A is set to a bias current control means 7. Thereby, the level of light output can be held constant.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor laser driving circuit for an optical fiber module used in the field of optical fiber communication.

[0002]

2. Description of the Related Art As shown in FIG. 8, the current-light output characteristic of a semiconductor laser device is such that the semiconductor laser device does not emit light below a threshold flow value Ith. Therefore, in the conventional semiconductor laser drive circuit, the threshold current value Ith is usually applied to the semiconductor laser device.
The semiconductor laser device is made to emit light by causing the DC bias current Ib to flow to a value in the vicinity thereof and causing the pulse current Ip to flow in the form of being superimposed on this DC bias current Ib.

Further, automatic output adjusting means (hereinafter referred to as an APC circuit) is used as a means for making the light output of the semiconductor laser device constant. A conventional APC circuit is shown in FIG. In FIG. 7, 1 is a semiconductor laser, 1A is a semiconductor laser element of the semiconductor laser 1, and 1B is a light receiving element, and detects the optical output level of the semiconductor laser element 1A of the semiconductor laser 1. Reference numeral 2 denotes an APC circuit, which feeds back using the output of the light receiving element 1B in order to make the optical output of the semiconductor laser element 1A constant. Reference numeral 3 denotes a pulse current modulation means, which is a circuit for pulse-driving the semiconductor laser element 1A. That is,
The output light of the semiconductor laser device 1A is configured to change the DC bias current Ib of the light receiving device 1B to obtain a constant light output. Further, since the semiconductor laser device 1A and the light receiving device 1B have individual variations, it is necessary to initially adjust the DC bias current Ib and the pulse current Ip for each semiconductor laser 1 with variable resistance.

[0004]

However, in the semiconductor laser drive circuit having the conventional APC circuit as described above, when the threshold current value Ith of the semiconductor laser element changes due to temperature, aging, etc. It operates so that the DC bias current Ib changes according to the change. That is, when the conversion efficiency of the semiconductor laser device is lowered, the DC bias current is increased to make the optical output level constant. Therefore, as shown in FIG. 7, even when the pulse-modulated signal input to the semiconductor laser element is at the level of logic 0, light may be emitted by the amount corresponding to ΔP, which causes deterioration of the extinction ratio and reduces signal quality. There is a problem of decreasing the life and a problem of decreasing the life of the semiconductor laser device by increasing the peak power. Also,
Since the semiconductor laser element and the light receiving element have individual variations, it is necessary to adjust the DC bias current Ib and the pulse current Ip for each semiconductor laser 1 in the initial stage with a variable resistor or the like, which requires adjustment work. Therefore, there is a problem that it becomes expensive.

The present invention solves the above problems and it is necessary to control the bias current and the pulse current and adjust the DC bias current and the pulse current in order to keep the optical output level constant. It is an object of the present invention to provide an LD drive circuit for an optical fiber module that does not have the above.

[0006]

In order to achieve the above object, the first to fourth inventions of the present invention provide a semiconductor laser drive circuit having a circuit for adjusting the optical output of a semiconductor laser device to a constant level. A light receiving element for detecting a light output of the semiconductor laser element, a pulse current modulating means for supplying a pulse current to the semiconductor laser element, a pulse current controlling means for controlling a pulse current value of the pulse current modulating means, and a light receiving element detection The semiconductor laser device has a light-receiving power detection unit for detecting an output and a bias current control unit for controlling a bias current for emitting light from the semiconductor laser device, and changes the bias current value of the semiconductor laser device by two or more points to emit light from the semiconductor laser device. The power is detected by the received light power detection means,
By detecting changes in the threshold current value and quantum efficiency of the semiconductor laser element, the DC bias current of the semiconductor laser element is set in the bias current control means, and the pulse current corresponding to the change in quantum efficiency is set as the pulse current. The control means is set.

[0007]

According to the present invention, the bias current value of the semiconductor laser device is changed by two or more points, and the light emission power of the semiconductor laser device is detected by the light receiving power detection means. And a change in quantum efficiency, the DC bias current of the semiconductor laser device is set in the bias current control means, and the pulse current corresponding to the change in quantum efficiency is set in the pulse current control means. It is possible to keep the optical output level constant.

[0008]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a configuration diagram of an LD drive circuit of an optical fiber module according to a first embodiment of the present invention. In FIG. 1, 1 is a semiconductor laser, 1A is a semiconductor laser element of the semiconductor laser 1, and 1B is a light receiving element, and detects the optical output level of the semiconductor laser element 1A. Reference numeral 4 denotes a power monitor circuit as a received light power detecting means, which detects the output of the light receiving element 1B which detects the optical output of the semiconductor laser element 1A. An A / D converter 5 converts an analog signal of the power monitor circuit 4 into a digital signal. Reference numeral 6 denotes a microcomputer (hereinafter referred to as a microcomputer), which controls the entire system and calculates a threshold current of the semiconductor laser device 1A described later. 7
Is a bias current control means, which is a circuit for supplying a bias current Ib to the semiconductor laser device 1A. 8 is a D / A converter A
Then, the current value of the bias current Ib of the bias current control circuit 7 is converted into a digital signal of the command value of the microcomputer 6 into an analog signal. Reference numeral 9 denotes a pulse current modulation means, which is a circuit for pulse-driving the semiconductor laser element 1A by causing the pulse modulation Ip to flow in the semiconductor laser element 1A in the form of being superimposed on the DC bias current Ib. Reference numeral 10 is a pulse current control means, which is a circuit for controlling ON / OFF of the operation of the pulse current modulation circuit 9 and the pulse current. A signal select circuit 11 selects an input signal for modulating the semiconductor laser element 1A according to the command of the ACTIVE signal which is the command of the microcomputer 6.

In the normal operation of modulating the semiconductor laser device 1A, the microcomputer 6 turns on the ACTIVE signal, turns off the DISABLE signal which is the operation mode for the host system, sets the pulse current control circuit 10 to the operation mode and the bias current. By setting the value of Ib in the D / A converter A8, the semiconductor laser element 1A is modulated by performing pulse driving according to the input signal.

Next, regarding the method of setting the bias current,
This will be described with reference to FIGS. 1 and 2. FIG. 2 is a diagram showing the relationship between the bias current Ib flowing through the semiconductor laser device 1A and the light receiving power detected by the light receiving device 1B. The relationship between the bias current I for driving the semiconductor laser device 1A and the received light power is in a proportional relationship in the region of the threshold current value Ith or more, and is represented by a linear expression of the relationship of the expression (1).

P = AI + Z (I> th) ... Formula (1) Further, the threshold current value Ith is calculated from the value of the received light power P = 0.
It can be obtained from the equation (2). Ith = -Z / A (2) When the power is turned on, the microcomputer 6 turns off the ACTIVE signal of the signal select circuit 11 when a constant cycle or a system error occurs. The DISABLE signal, which is the non-operation mode, is turned on to the higher-level system, and the pulse current control circuit 10 is set to the non-operation mode to set the pulse current modulation circuit 9 of the semiconductor laser element 1A to the non-operation mode and stop the pulse driving. Next, the microcomputer 6
The semiconductor laser element 1A is caused to emit DC light by setting the D / A converter A8 to a value corresponding to the bias current Ib equal to or more than the threshold current value Ith corresponding to I1 in the D / A converter A8.

The light emission power of the semiconductor laser element 1A at that time is received by the light receiving element 1B, and the power monitor circuit 4,
The microcomputer 6 detects the received light power P1 via the A / D converter 5. Further, the microcomputer 6 uses the D / A converter A8
Then, the semiconductor laser device 1A is caused to emit DC light by setting the value corresponding to the value of the bias current Ib equal to or higher than I1 to I2 in the D / A converter A8. The light emitting power of the semiconductor laser element 1A at that time is received by the light receiving element 1B, and the microcomputer 6 detects the light receiving power P2 via the power monitor circuit 4 and the D / A converter 5. Detected received light power P1 and P
2 and the values of the bias currents I1 and I2 at that time are given by the formula (1)
The light receiving sensitivity A and the offset Z are calculated. Next, the calculated values of A and Z are calculated by the equation (2).
By substituting into, the threshold current value Ith can be detected.
When the semiconductor laser element 1A is pulse-driven including the threshold current value Ith or less, the response speed becomes slow. Therefore, a bias current Ib slightly higher than the detected threshold current value Ith is set in the D / A converter A8, The operation mode of is executed.

Next, when the threshold current value Ith of the semiconductor laser device 1A changes due to temperature change or the like, similarly,
The microcomputer 6 turns off the ACTIVE signal of the signal select circuit 11, and the host system is in the non-operation mode D.
The ISABLE signal is turned on, and the pulse current control circuit 10
Is set to the non-operation mode, the pulse current modulation circuit 9 of the semiconductor laser device 1A is set to the non-operation mode, and the pulse driving is stopped. Next, the microcomputer 6 causes the D / A converter A8 to
The semiconductor laser element 1A is caused to emit DC light by setting a value corresponding to I1 of the bias current Ib equal to or more than the threshold current value Ith in the D / A converter A8. The light emitting power of the semiconductor laser element 1A at that time is received by the light receiving element 1B,
The microcomputer 6 detects the received light power P1 ′ via the power monitor circuit 4 and the A / D converter 5. Further, the microcomputer 6 causes the D / A converter A8 to apply a bias current I of I1 or more.
The semiconductor laser element 1A is caused to emit DC light by setting the value corresponding to the value of b to I2 in the D / A converter A8. The light emission power of the semiconductor laser element 1A at that time is determined by the light receiving element 1
Light is received at B, power monitor circuit 4, A / D converter 5
The microcomputer 6 detects the received light power P2 'via the. The detected light receiving powers P1 ′ and P2 ′ and the values of the bias currents I1 and I2 at that time are substituted into the equation (1) and calculated to calculate the light receiving sensitivity A ′ and the offset Z ′. Next, by substituting the calculated values of A ′ and Z ′ into the equation (2), the threshold current value Ith ′ can be detected. When the semiconductor laser element 1A is pulse-driven including a threshold current value Ith ′ or less, the response speed becomes slower, so that the bias current Ib ′ slightly higher than the detected threshold current value Ith ′ is D /
By setting the A converter A8 and performing the normal operation mode, the optimum bias current can be automatically set even when the threshold current value Ith changes due to a factor such as temperature.

Next, a second embodiment of the present invention will be described with reference to FIG. FIG. 3 is a configuration diagram of an LD drive circuit of an optical fiber module according to a second embodiment of the present invention. In FIG. 3, the same numbers as those in FIG. 1 indicate the same functions. In FIG. 3, reference numeral 12 denotes a D / A converter B for converting a digital signal, which is a command value of the microcomputer 6, into an analog signal from the current value of the pulse current Ip of the pulse current control circuit 10. The pulse current Ip of the pulse current modulation circuit 9 is controlled through pulse modulation in the form of being superimposed on the direct current bias current Ib in the semiconductor laser device 1A.

In the normal operation of modulating the semiconductor laser device 1A, the microcomputer 6 turns on the ACTIVE signal, turns off the DISABLE signal which is the operation mode of the host system, and sets the value of the pulse current Ip to the D / A converter. B12
And the value of the bias current Ib is set in the D / A converter A8, the semiconductor laser element 1A is modulated by performing pulse driving according to the input signal.

Similar to the first embodiment, the microcomputer 6 turns off the ACTIVE signal of the signal select circuit 11 when the power is turned on, a fixed period, or when a system error occurs, and the microcomputer 6 does not notify the host system. The operating mode, DIS
The pulse current modulation circuit 9 of the semiconductor laser device 1A is set to the non-operation mode by turning on the ABLE signal, instructing the D / A converter B12 to a zero-level signal, and setting the pulse current control circuit 10 to the non-operation mode. Stop pulse driving. Next, the microcomputer 6 sets the D / A converter A8 to the D / A converter A8 by setting a value corresponding to the bias current Ib of the threshold current value Ith or more corresponding to I1 to the semiconductor laser device 1A. DC light is emitted.

The light emission power of the semiconductor laser element 1A at that time is received by the light receiving element 1B, and the power monitor circuit 4,
The microcomputer 6 detects the received light power P1 via the A / D converter 5. Further, the microcomputer 6 uses the D / A converter A8
In addition, the semiconductor laser element 1A is caused to emit DC light by setting the value of the bias current Ib equal to or greater than I1 corresponding to I2 in the D / A converter A8. The light emission power of the semiconductor laser element 1A at that time is received by the light receiving element 1B, and the microcomputer 6 detects the light reception power P2 via the power monitor circuit 4 and the A / D converter 5. Detected received light power P1 and P
2 and the values of the bias currents I1 and I2 at that time are given by the formula (1)
The light receiving sensitivity A and the offset Z are calculated. Next, the calculated values of A and Z are calculated by the equation (2).
By substituting into, the threshold current value Ith can be detected.
When the semiconductor laser element 1A is pulse-driven including the threshold current value Ith or less, the response speed becomes slow. Therefore, a bias current Ib slightly higher than the detected threshold current value Ith is set in the D / A converter A8, The operation mode of is executed. Further, when the threshold current value Ith changes due to temperature or the like, it can be realized by the same method as the contents described in the first embodiment, and therefore the description thereof is omitted.

Next, the conversion efficiency of the semiconductor laser element 1A changes, the sensitivity of the light receiving element 1B and the characteristics of the circuit, and the power supply and the like change, so that the driving current and the light receiving power of the semiconductor laser element 1A are changed. The case where the sensitivity of No. 1 is changed will be described with reference to FIGS. 3, 4, 5, and 6. When the power is turned on, a fixed period, or when a system error occurs, the microcomputer 6 operates the AC of the signal select circuit 11.
By turning off the TIVE signal, turning on the DISABLE signal which is the non-operation mode to the upper system, commanding the zero level signal to the D / A converter B12, and setting the pulse current control circuit 10 to the non-operation mode, the semiconductor Laser element 1
The pulse current modulation circuit 9 of A is set to the non-operation mode, and the pulse driving is stopped. Next, the microcomputer 6 uses the D / A converter A
8, the semiconductor laser device 1A is caused to emit DC light by setting the value corresponding to the bias current Ib equal to or more than the threshold current value Ith to I1 in the D / A converter A8. The light emitting power of the semiconductor laser element 1A at that time is received by the light receiving element 1B, and the microcomputer 6 detects the light receiving power P1 ′ via the power monitor circuit 4 and the A / D converter 5. further,
The microcomputer 6 sends to the D / A converter A8 a value corresponding to the bias current Ib of I1 or more corresponding to I2.
The semiconductor laser device 1A is caused to emit DC light by setting to 1. The light emission power of the semiconductor laser element 1A at that time is received by the light receiving element 1B, and the power monitor circuit 4, A / D
The microcomputer 6 detects the received light power P2 ′ via the converter 5. The detected light receiving powers P1 ′ and P2 ′ and the values of the bias currents I1 and I2 at that time are substituted into the equation (1) and calculated to calculate the light receiving sensitivity A ′ and the offset Z ′. Next, the threshold current value Ith can be detected by substituting the calculated values of A ′ and Z ′ into the equation (2). Also,
Previously calculated light receiving efficiency A and newly detected light receiving efficiency A '
Therefore, in order to keep the light emission power of the semiconductor laser device 1A constant, the relational expression of Expression (3) is established.

Ip ′ = A ′ / A * Ip Equation (3) Then, by substituting in Equation (3), the pulse drive current I
p'can be set, a digital signal corresponding to the pulse drive current Ip 'is set in the D / A converter B12, the pulse current control circuit 10 is controlled, and the semiconductor laser element 1A is pulse-driven by Ip'. Therefore, it becomes possible to obtain a constant emission power of the semiconductor laser device 1A.

FIG. 5 is a diagram showing the relationship between the pulse drive current waveform and the light emission power of the semiconductor laser element 1A when the light receiving sensitivity is A. In FIG. 5, the semiconductor laser device 1A
Has a bias current of Ib, a pulse current of Ip, an emission power of Pmin when the input signal is zero, and an input signal of 1
The light emission power Pmax at the time is. Next, FIG. 6 is a diagram showing the relationship between the pulse drive current waveform and the light emission power of the semiconductor laser device 1A when the light receiving sensitivity is A '. In FIG. 6, the semiconductor laser device 1 is manufactured by performing the procedure described above.
The bias current of A is Ib ′, the pulse current is Ip ′, the emission power when the input signal is zero is Pmin, and the emission power when the input signal is 1 is Pmax. It is possible to obtain the light emission output of. That is, even when the threshold current value Ith and the light receiving sensitivity are changed, the optimum bias current and the optimum pulse current can be automatically set.

In this embodiment, the threshold current value Ith
Also, in order to detect the photosensitivity A, the bias current Ib is detected by changing it at two points.
It is needless to say that the threshold current value Ith and the light receiving sensitivity A can be detected by changing the points or more and using, for example, the least square method. Further, even when the threshold current value Ith and the light receiving sensitivity A are changed at the same time, it can be detected by the above method. Further, in the present embodiment, the microcomputer is used for implementation, but it goes without saying that it can be configured by hardware. Further, in the present invention, in order to detect the threshold current value Ith and the light receiving sensitivity A, the pulse driving is stopped, but the pulse driving is performed in a fixed pattern (for example, the duty is constant) to change the bias current. It can be detected even if changed. Further, although the detection is performed at regular time intervals, in the normal operation, the detected threshold current value It
Based on the setting of the bias current Ib by h, the conventional A
There is no problem even if the configuration is switched to the PC circuit.

[0022]

As described above, according to the present invention, the bias current value of the semiconductor laser device is changed by two points or more, and the light emission power of the semiconductor laser device is detected by the light receiving power detecting means, and the threshold value of the semiconductor laser device is detected. By detecting the change in the current value and the quantum efficiency, the DC bias current of the semiconductor laser device is set in the bias current control means, and the pulse current corresponding to the change in the quantum efficiency is set in the pulse current control means. This makes it possible to maintain the optical output level at a constant level, improve reliability, and further control the bias current and pulse current, making it unnecessary to adjust the drive current of the semiconductor laser, making it an inexpensive optical fiber. Modules can be provided.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing a first embodiment of the present invention.

FIG. 2 is an operation explanatory diagram of the first embodiment of the LD drive circuit of the optical fiber module of the present invention.

FIG. 3 is a configuration diagram showing a second embodiment of the present invention.

FIG. 4 is an operation explanatory diagram of a second embodiment of the LD drive circuit of the optical fiber module of the present invention.

FIG. 5 is an operation explanatory diagram of the pulse current of the second embodiment of the LD drive circuit of the optical fiber module of the present invention.

FIG. 6 is another operation explanatory diagram of the pulse current of the second embodiment of the LD drive circuit of the optical fiber module of the present invention.

FIG. 7 is a configuration diagram showing a conventional semiconductor laser drive circuit.

FIG. 8 is a characteristic diagram showing an example of current-light output characteristics of a semiconductor laser device and its input / output relationship.

[Explanation of symbols]

 1 Semiconductor Laser 1A Semiconductor Laser Element 4 Receiving Power Detection Means 5 A / D Converter 6 Microcomputer 7 Bias Current Control Means 8 D / A Converter A 9 Pulse Current Modulation Means 10 Pulse Current Control Means 11 Signal Select Circuits 12 D / A Converter B

Claims (10)

[Claims] 1. A semiconductor laser drive circuit comprising a circuit for adjusting the optical output of a semiconductor laser element to a constant value, wherein a light receiving element for detecting the optical output of the semiconductor laser element and a pulse current are supplied to the semiconductor laser element. The bias current value of the semiconductor laser device includes pulse current modulation means, light receiving power detection means for detecting the detection output of the light receiving element, and bias current control means for controlling the bias current for emitting light from the semiconductor laser element. By changing at least two points, the light emission power of the semiconductor laser element is detected by the light receiving power detection means, and the threshold current value of the semiconductor laser element is detected, whereby the DC bias current of the semiconductor laser element is changed to the bias voltage. An LD drive circuit for an optical fiber module, wherein the LD drive circuit is set in a current control means. 2. A semiconductor laser drive circuit comprising a circuit for adjusting the optical output of a semiconductor laser element to a constant value, wherein a light receiving element for detecting the optical output of the semiconductor laser element and a pulse current are supplied to the semiconductor laser element. Pulse current modulating means, pulse current controlling means for controlling the pulse current value of the pulse current modulating means, light receiving power detecting means for detecting the detection output of the light receiving element, and bias current for emitting light from the semiconductor laser element. Bias current control means for changing the bias current value of the semiconductor laser element by two or more points, and the light emission power of the semiconductor laser element is detected by the light reception power detection means, and the threshold current of the semiconductor laser element is detected. The DC bias current of the semiconductor laser device is detected by detecting the change in the value and the quantum efficiency. An LD drive circuit for an optical fiber module, characterized in that it is set in the as-current control means, and a pulse current corresponding to a change in quantum efficiency is set in the pulse current control means. 3. A semiconductor laser drive circuit comprising a circuit for adjusting the optical output of a semiconductor laser element to a constant value, wherein a light receiving element for detecting the optical output of the semiconductor laser element and a pulse current are supplied to the semiconductor laser element. Pulse current modulating means, light receiving power detecting means for detecting a detection output of the light receiving element, bias current control means for controlling a bias current for emitting light from the semiconductor laser element, set bias current value and light receiving power detection. Means for performing feedback control in comparison with the means, and switching means for switching between the bias control means and the automatic output adjusting means, and changing the bias current value of the semiconductor laser element by two or more points, The light emission power of the semiconductor laser device is detected by the light reception power detection means,
An LD of an optical fiber module, which detects a threshold current value of the semiconductor laser element, sets a DC bias current of the semiconductor laser element in the bias current control means, and switches the switching means to the automatic output adjusting means. Drive circuit. 4. A semiconductor laser drive circuit comprising a circuit for adjusting the optical output of a semiconductor laser element to a constant value, wherein a light receiving element for detecting the optical output of the semiconductor laser element and a pulse current are supplied to the semiconductor laser element. Pulse current modulating means, pulse current controlling means for controlling the pulse current value of the pulse current modulating means, light receiving power detecting means for detecting the detection output of the light receiving element, and bias current for emitting light from the semiconductor laser element. Bias current control means, automatic output adjustment means for performing feedback control by comparing the set bias current value with the received light power detection means, and switching means for switching the bias control means and the automatic output adjustment means. By changing the bias current value of the semiconductor laser element by two or more points. The direct-current bias current of the semiconductor laser element is set in the bias current control means by detecting the light emission power of the element by the received light power detection means and detecting changes in the threshold current value and quantum efficiency of the semiconductor laser element. Further, the LD drive circuit of the optical fiber module, wherein the pulse current control means is set to a pulse current corresponding to a change in quantum efficiency, and the switching means is switched to the automatic output adjusting means. 5. In order to detect a change in threshold current value Ith or quantum efficiency of the semiconductor laser device, the pulse current means of the semiconductor laser device is stopped to change the bias current of the semiconductor laser device. L of the optical fiber module according to claim 1, 2, 3 or 4.
D drive circuit. 6. In order to detect a change in the threshold current value Ith or the quantum efficiency of the semiconductor laser device, the pulse current means of the semiconductor laser device is pulse-driven in a fixed pattern to change the bias current of the semiconductor laser device. The LD drive circuit for an optical fiber module according to claim 1, 2, 3, or 4. 7. A bias current equal to or greater than a maximum threshold current value Ith of the semiconductor laser device is changed in order to detect a change in threshold current value Ith or quantum efficiency of the semiconductor laser device. The LD drive circuit of the optical fiber module according to 2, 3, or 4. 8. The optical fiber module according to claim 1, wherein the state is instructed to a host system when the threshold current value Ith or quantum efficiency of the semiconductor laser device is detected. LD drive circuit. 9. A threshold current value Ith of the semiconductor laser device when power is turned on, the system is started up, at regular time intervals, and at least any one of error occurrences occurs.
Alternatively, the LD drive circuit for the optical fiber module according to claim 1, wherein a change in quantum efficiency or the like is detected. 10. The LD drive circuit for an optical fiber module according to claim 1, wherein the bias current of the semiconductor laser device is set to a threshold current value Ith of the detected semiconductor laser device or more.