JP2000216487A - Apparatus and method for drive of semiconductor laser - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an apparatus and a method for the drive of a semiconductor laser, in which an optical output can be controlled automatically up to a region used to saturate the output of a current/voltage converter by expanding the dynamic range of the current/voltage converter, in which the undefined width of a driving current can be reduced and in which the stabilization accuracy of the optical output can be enhanced. SOLUTION: A changeover-type constant current source 8 which changes over the output bias of a current/voltage converter 6 by turning on (closing) and off (opening) a switch means 8A according to a prescribed control signal is provided. In addition, a changeover control circuit 7 which judges whether the peak value of a changed-over voltage signal to be outputted by the current/ voltage converter 6 exceeds at least one kind out of a switch-opening changeover setting threshold value Va and a switch-opening changeover setting threshold value Vb and which generates and outputs a control signal used to control the switch means so as to be closed and opened is provided.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an automatic optical power control (APC).
In particular, the present invention relates to a semiconductor laser driving technique of the (roll) type, in which the dynamic range of the current / voltage converter is expanded to enable automatic optical output control up to a region where the output of the current / voltage converter is saturated, and the drive current has an undefined width The present invention relates to a semiconductor laser driving device and a semiconductor laser driving method capable of reducing the power consumption and improving the stability accuracy of the optical output.

[0002]

2. Description of the Related Art As a conventional gain switching method of a current / voltage (I / V) converter, for example, Japanese Unexamined Patent Publication No.
And Japanese Patent Application Laid-Open No. 10-190369. FIG. 7 is a configuration diagram in the case where a conventional digital APC type semiconductor laser driving circuit is combined with a conventional current / voltage (I / V) converter gain switching method. The description of each component is shown below.

The semiconductor laser driving device shown in FIG. 7 comprises a semiconductor laser P1, a driving circuit (denoted as LDD in the drawing) P2, a communication control unit P3, a comparison amplifier P4, a monitoring light receiving element P5,
A current / voltage converter (denoted as an I / V converter in the figure) P6;
The switching control circuit P7 is mainly configured. The semiconductor laser P1 has the anode terminal connected to the power supply, the cathode terminal is connected to a drive circuit (LDD) P2, is a device which emits light from a drive circuit (LDD) P2 supplied with drive current I _op. The drive circuit (LDD) P2 has the cathode terminal of the semiconductor laser P1 connected to the output terminal, and according to an electric signal from the communication control unit P3, the semiconductor laser P1.
_Is a functional block for supplying a drive current _Iop to the power supply. The communication control unit P3 is a functional block that is connected to an input terminal of the drive circuit (LDD) P2 and outputs an electric signal to the drive circuit (LDD) P2. The comparison amplifier P4 compares the output of the current / voltage converter (I / V converter) P6 with the automatic optical output control convergence voltage, and the optical output power converges to a set value based on the comparison result. As shown in the drive circuit (LDD)
Drive circuit a signal for controlling the driving current _{I op} of P2 (LD
D) Function block for outputting to P2. The monitor light receiving element (PD) P5 has a cathode terminal connected to a power supply,
The anode terminal is a current / voltage converter (I / V converter) P6
And receives the back light of the semiconductor laser P1, and monitors the monitor current I according to the amount of received light.
_This is a functional block for converting to _mon . The current / voltage converter (I / V converter) P6 converts the monitor current I _mon generated and output by the monitoring light receiving element P5 into a voltage (current / current
Voltage conversion), and the gain is switched under the control of the switching control circuit P7. The switching control circuit P7 determines whether the peak value of the output of the current / voltage converter (I / V converter) P6 exceeds the set threshold value or not. Control to switch the gain.

FIG. 8 shows the relationship between the peak value of the input current and the peak value of the output of the current / voltage converter of FIG. The switch closing switching threshold Va or the switch opening switching threshold Vb on the vertical axis is a threshold set when performing gain switching. In the conventional semiconductor laser driving method, the dynamic range is expanded by switching the gain of an operating current / voltage converter (I / V converter) P6 for gain switching.

[0005]

However, the semiconductor laser driving device shown in FIG. 7 expands the dynamic range by switching the gain of the operating current / voltage converter (I / V converter) P6 for gain switching. are therefore, the gain is reduced, the slope of the output V of the current / voltage converter P6 for monitoring current I _{m on} as shown in FIG. 8 is reduced, the following problems arise.

[0006] Figure 9 shows a prior art semiconductor laser driving device current / voltage converter with respect to the drive current I _op in (I / V converter) P6 of relationship between the output V of FIG. As shown in FIG. 9, an input offset occurs in the comparison amplifier P4, and is shown as an indefinite width of the comparison amplifier P4 in FIG. Along with this, also the drive current I _op has a problem that the driving current indefinite width occurs. Further, since the drive current undefined width depends on the magnitude of the gain of the current / voltage converter (I / V converter) P6, as shown in FIG.
By lowering the gain of the voltage converter (I / V converter) P6, there is a problem that the drive current uncertainty width becomes large and the stability of the optical output is deteriorated.

The present invention has been made in view of such a problem, and an object of the present invention is to expand the dynamic range of a current / voltage converter and saturate the output of the current / voltage converter. It is an object of the present invention to provide a semiconductor laser driving device and a semiconductor laser driving method capable of performing automatic light output control up to an area, reducing an indefinite width of a drive current, and improving the stability accuracy of light output.

[0008]

The gist of the present invention resides in that the dynamic range of the current / voltage converter is expanded and the automatic optical output is extended to a region where the output of the current / voltage converter is saturated. A semiconductor laser drive device capable of controlling, reducing an indefinite width of a drive current, and improving the stability accuracy of the optical output of a semiconductor laser, wherein a constant current is supplied to a light receiving element for monitoring the optical output of the semiconductor laser. At least one or more current sources for flowing current, and at least one or more switch means interposed in series between each of the monitoring light receiving elements and each of the current sources, and according to a predetermined control signal, A switchable constant current source for switching the output bias of the current / voltage converter by closing / opening a switch means, and a peak value of a converted voltage signal output from the current / voltage converter having a predetermined small value. And whether or not each of the switch means provided in the switch-type constant current source is closed / opened in accordance with the determination result. And a switching control circuit for generating and outputting a control signal for performing the above control. According to another aspect of the present invention, the switching control circuit includes a switch for fixing a closed / open state of each of the switch means provided in the switching constant current source. The semiconductor laser driving device according to claim 1. According to another aspect of the present invention, the switching control circuit executes the control of closing / opening each of the switch means provided in the switching-type constant current source at least at the time of setting an optical output. A semiconductor laser driving device according to claim 1 or 2, wherein The gist of claim 4 of the present invention is that the switching control circuit controls the closing / opening of each of the switch means provided in the switching type constant current source by at least an automatic optical output control convergence voltage. The semiconductor laser driving device according to claim 1 or 2, wherein the operation is performed at the time of setting. According to another aspect of the present invention, the current / voltage converter converts the monitor current generated and output by the monitor light receiving element into a voltage, and controls the voltage signal after the conversion. The semiconductor laser driving device according to claim 1, wherein the semiconductor laser driving device is configured to output a signal to the switching control circuit. The gist of claim 6 of the present invention is that the monitor light receiving element has one end of each of the switch means, wherein a cathode terminal is connected to a power supply, and an anode terminal is provided in the switching constant current source. It is connected to an input terminal of the current / voltage converter, receives the back light of the semiconductor laser, and converts the monitor light into the monitor current according to the received light amount and outputs the monitor current to the current / voltage converter. The semiconductor laser driving device according to claim 5, wherein The gist of claim 7 of the present invention is that the switchable constant current source includes a first switch close switch setting threshold and a second switch close switch set threshold as the predetermined at least one or more types of switch open switch setting thresholds. A switch closing switch setting threshold value, wherein when the switch means is in the open state, the switch means is turned off when the peak value of the output of the current / voltage converter exceeds the first switch closing switch setting threshold value. Switch to closed state,
In the closed state of the switch, the switch is opened when the peak value of the output of the current / voltage converter does not exceed the second switch open switching setting threshold. A semiconductor laser driving device according to claim 3 or claim 4. The gist of claim 8 of the present invention is that the dynamic range of the current / voltage converter is expanded to enable automatic optical output control up to a region where the output of the current / voltage converter is saturated, and A semiconductor laser driving device capable of reducing the indefinite width and improving the stability accuracy of the optical output of a semiconductor laser, and is a current source for supplying a constant current to a light receiving element for monitoring the optical output of the semiconductor laser. A variable current source capable of controlling the amount of current supplied to the monitoring light-receiving element in accordance with a control signal; and a peak value of a converted voltage signal output from the current / voltage converter is at least one or more of a predetermined value. In addition to determining whether or not exceeds the switch open switching setting threshold of, according to the determination result,
A switching control circuit for generating and outputting a control signal for specifying an amount of current supplied to the monitor light-receiving element flowing through the variable current source. The gist of the ninth aspect of the present invention is that the switching control circuit includes a switch for fixing an amount of current supplied by the switching-type constant current source. Exists in the device. The gist of claim 10 of the present invention is that the switching control circuit executes the control of the amount of current of the switching type constant current source at least at the time of setting the optical output. The present invention resides in the semiconductor laser driving device described above. According to another aspect of the present invention, the switching control circuit executes the control of the amount of current of the switching-type constant current source at least at the time of setting an automatic optical output control convergence voltage. The semiconductor laser driving device according to 8 or 9 above. According to a twelfth aspect of the present invention, the current / voltage converter converts the monitor current generated and output by the monitor light receiving element into a voltage, and controls the converted voltage signal. 12. The semiconductor laser drive device according to claim 8, wherein the semiconductor laser drive device is configured to output the signal to the switching control circuit. According to a thirteenth aspect of the present invention, in the monitor light receiving element, a cathode terminal is connected to a power supply, and an anode terminal is connected to one end of the switching type constant current source and the current / current source.
Connected to the input end of the voltage converter, configured to receive the back light of the semiconductor laser, convert the monitor current into the monitor current corresponding to the amount of received light, and output the monitor current to the current / voltage converter. A semiconductor laser driving device according to claim 12. Claim 14 of the present invention
The gist of the invention is that the dynamic range of the current / voltage conversion process is expanded to enable automatic optical output control up to the region where the output of the current / voltage converter is saturated, to reduce the indefinite width of the drive current, What is claimed is: 1. A method of driving a semiconductor laser capable of improving the accuracy of stabilizing the optical output of a laser, wherein a peak value of a converted voltage signal output from the current / voltage conversion step is at least one or more types of switch open switching. Determines whether the threshold is exceeded,
According to the determination result, a control signal for controlling a current flowing through at least one current source for flowing a constant current to the light receiving element that monitors the optical output of the semiconductor laser is generated.
A semiconductor laser driving method comprising: a current source control step of outputting; and a bias control step of switching an output bias of the current / voltage conversion step according to the control signal. The gist of claim 15 of the present invention is characterized in that the current source control step includes a step of fixing a closed / open state of each of the switch means provided in the bias control step. A semiconductor laser driving method according to claim 14. According to another aspect of the present invention, in the current source control step, the control of closing / opening of each of the switch means provided in the bias control step is performed at least at the time of setting an optical output. A semiconductor laser driving method according to claim 14 or 15, wherein The gist of claim 17 of the present invention is that the current source control step includes controlling at least one of the switch means provided in the bias control step to close and open at least automatic light output control convergence voltage setting. The method according to claim 14 or 15, wherein the method is executed at any time. The gist of claim 18 of the present invention is to convert the monitor current generated and output by the monitoring light receiving element into a voltage, and to use the converted voltage signal as the control signal in the current source control step. The method according to any one of claims 14 to 17, further comprising a current / voltage conversion step of outputting.

[0009]

BRIEF DESCRIPTION OF THE DRAWINGS FIG.
The laser driving device has an automatic optical output control (APC: Autom
atic Power Control) type semiconductor
It is a laser drive device.
Photocurrent (monitor current) generated by (PD) 5
I_mon) Current / voltage converter (I / V converter)
6 dynamic range, and at that time
Semiconductor laser driving method. Current / voltage converter (I
/ V converter) 6 to increase the dynamic range
In the prior art, the forward of the semiconductor laser (LD) 1
For sample variation and monitoring of coupling efficiency in load light
Due to sample variation in conversion efficiency of light receiving element (PD) 5
The output of the current / voltage converter (I / V converter) 6 is saturated
Automatic light output control can be performed up to the region where the light is output. Off
As an alternative, a conventional semiconductor laser driving method is used.
Switching the gain of the current / voltage converter (I / V converter)
When using the method (Fig. 7), the gain is switched to the smaller one.
The drive current due to the offset of the comparator amplifier
I_opOf the optical output becomes large, and the stability of the optical output is degraded.
Problems arise. The semiconductor laser of each embodiment described below
The driving device and the semiconductor laser driving method have a current / voltage conversion
The switching type constant current source 8 is arranged in parallel with the converter (I / V converter) 6.
Connected to a column and switched according to a control signal from the switching control circuit 7.
Switch means 8A (or switch means 81A)₁,…,
81A_N), Or using the variable current source 82
Flow control is performed (FIG. 1). As mentioned above, half of the prior art
The semiconductor laser driving device is used to drive the semiconductor laser (LD) P1.
Sample variation and monitoring of coupling efficiency in forward light
Variation in conversion efficiency of photo detector for photo detector (PD) P5
Output of the current / voltage converter (I / V converter) P6
That the power is saturated and automatic light output control is not possible
is there. To solve this problem, a current / voltage converter (I
/ V converter) Widen the dynamic range of P6
No. However, in this case, the conventional gain switching technology is used.
Then, because of the offset of the comparison amplifier P4, the drive power
Style I _opThe optical output stability is inferior
Problems arise. This offset constitutes the circuit
Is caused by the characteristic variation of the
Can not. New switching means that can solve this problem
It is an invention. Hereinafter, embodiments of the present invention will be described with reference to the drawings.
This will be described in detail.

(First Embodiment) FIG. 1 is a functional block diagram for explaining a first embodiment of a semiconductor laser driving device according to the present invention. Referring to FIG. 1, a semiconductor laser driving device according to a first embodiment includes a semiconductor laser (LD in the drawing).
1, a drive circuit (denoted as LDD in the figure) 2, a communication control unit 3, a comparison amplifier 4, a light receiving element for monitoring (P in the figure).
D) 5, a current / voltage converter (denoted as an I / V converter in the figure) 6, a switching control circuit 7, and a switching constant current source 8.

The semiconductor laser (LD) 1 has an anode terminal connected to a power supply and a cathode terminal connected to a drive circuit (LDD).
2 and drive current I from drive circuit (LDD) 2
_This is a device that emits light upon receiving the supply of _op . Drive circuit (LDD) 2, a cathode terminal of the semiconductor laser (LD) 1 is connected to the output terminal, in accordance with an electric signal from the communication control unit 3, a semiconductor laser (LD) functional block supplies a drive current I _op 1 It is. The communication control unit 3 is connected to an input terminal of the drive circuit (LDD) 2 and controls the drive circuit (LDD).
2 is a functional block that outputs an electric signal to the control unit 2. The comparison amplifier 4 compares the output of the current / voltage converter (I / V converter) 6 with the automatic optical output control convergence voltage, and the optical output power converges to the set value based on the comparison result. as a functional block for outputting a signal for controlling the driving current _{I op} drive circuit (LDD) 2 to the drive circuit (LDD) 2. The monitoring light receiving element (PD) 5 has a cathode terminal connected to a power supply, and an anode terminal connected to one end of a switch means 8A provided in the switching constant current source 8 and a current / voltage converter (I / V converter). 6 is a functional block that receives the back light of the semiconductor laser (LD) 1 and converts the back light into a monitor current I _mon according to the amount of received light. The current / voltage converter (I / V converter) 6 converts the monitor current I _mon generated and output by the monitoring light receiving element (PD) 5 into a voltage (current / voltage conversion), and a converted voltage signal. Is output to the comparison amplifier 4 and the switching control circuit 7.

The switching control circuit 7 of the present embodiment determines whether the peak value of the converted voltage signal output from the current / voltage converter (I / V converter) 6 is equal to the switch closing switch setting threshold Va or the switch open switching. It is determined whether or not the voltage exceeds a set threshold value Vb, and according to the determination result, the ON / OFF state of a switch means 8A provided in the switch-type constant current source 8 is determined.
A function block for generating and outputting a control signal for controlling (closed) / OFF (open) control.
(Closed) / OF of switch means 8A provided in
Switch to fix the state of F (open) (fixing switch)
And that ON (close) and OFF (open) control of the switch means 8A provided in the switching constant current source 8 is performed only when the optical output is set (when the automatic optical output control convergence voltage is set). Has features.

The switching type constant current source 8 according to the present embodiment is a current source 8 for supplying a constant current to the monitoring light receiving element (PD) 5.
B, a switch means 8A interposed in series between the monitoring light receiving element (PD) 5 and the current source 8B, and the switch means 8A is turned on in accordance with a control signal from the switching control circuit 7.
This is a functional block for switching the output bias of the current / voltage converter (I / V converter) 6 by opening (closing) and OFF (opening).

FIG. 2 shows the current / voltage converter (I / V) of FIG.
The relationship between the peak value of the input current (monitor current I _mon ) of the converter 6 and the peak value of the output V is shown. The horizontal axis is the peak value of the input current (monitor current I _mon ), and the vertical axis is the peak value of the output V. In the semiconductor laser drive device of the present embodiment, as shown in FIG. 2, the dynamic range of the current / voltage converter (I / V converter) 6 can be expanded, and furthermore, the stability of the optical output deteriorates. This has the effect of not occurring.

Next, the operation of the semiconductor laser driving device of the present embodiment and the operation of the semiconductor laser driving method executed by the semiconductor laser driving device of the present embodiment will be described with reference to the drawings. First, the basic operation of the semiconductor laser driving device according to the present embodiment will be described. Referring to FIG. 1, a drive circuit (LDD) 2 that has received an electric signal from a communication control unit 3 generates a drive current I
_The electric signal is converted into an optical signal by supplying the _op and causing the semiconductor laser (LD) 1 to emit light. The light from the semiconductor laser (LD) 1 is transmitted to a monitor light receiving element (PD) 5.
And is converted into a monitor current I _mon .
This monitor current I _mon is converted into a voltage signal by a current / voltage converter (I / V converter) 6. The voltage signal output from the current / voltage converter (I / V converter) 6 is input to the comparison amplifier 4. The comparison amplifier 4 compares the voltage signal output from the current / voltage converter (I / V converter) 6 with a preset automatic optical output control convergence voltage, and based on the comparison result, Drive circuit (LD
D) The semiconductor laser (L) is controlled by controlling the drive current I _{op of} 2
D) Make the light output from 1 constant.

Next, the operation of the switching type constant current source 8 of the present embodiment will be described. In the present embodiment, ON (closed) and OFF of the switch means 8A provided in the switching constant current source 8
It is characterized in that (open) control is performed only when the light output is set (when the automatic light output control convergence voltage is set). FIG. 2 (FIG. 1)
(A graph showing the relationship between the peak value of the input current (monitor current I _mon ) of the current / voltage converter (I / V converter) 6 and the peak value of the output V), as shown in FIG. The output bias differs depending on the ON (closed) and OFF (open) of the switch means 8A of FIG.
(N: solid line). The relationship between the switch closing switching setting threshold Va or the switch opening switching setting threshold Vb and the output V of the current / voltage converter (I / V converter) 6 in the switching control circuit 7 will be described below. When the switching means 8A of the switching type constant current source 8 is OFF (open),
When the peak value of the output V of the voltage converter (I / V converter) 6 exceeds the switch closing switching setting threshold value Va, the switch means 8A switches to ON (closed). Switching type constant current source 8
When the peak value of the output V of the current / voltage converter (I / V converter) 6 does not exceed the switch open switching setting threshold Vb in the ON (closed) state of the switch unit 8A, the switch unit 8A Switches to OFF (open).

The O of the switching means 8A of the switching type constant current source 8
By N (closed) and OFF (open), the input current (monitor current I _mon ) of the current / voltage converter (I / V converter) 6
Does not change. Therefore, the dynamic range of the current / voltage converter (I / V converter) 6 can be expanded without causing the problem of the conventional technology that the stability of the optical output is deteriorated due to the conventional technology (gain switching type). Can be.

At the time of operation after the optical output power setting (automatic optical output control convergence voltage setting), the setting level of the optical output power setting (automatic optical output control convergence voltage setting) is set using the fixing switch of the switching control circuit 7. Is fixed when the switch means 8A of the switching constant current source 8 is ON (closed) or OFF (open). Further, even when the automatic optical output control convergence voltage matches the switch closing switching setting threshold Va or the switch opening switching setting threshold Vb, the operation is fixed to one of ON (closed) and OFF (open). The switch closing switch setting threshold Va or the switch opening switch setting threshold Vb is set so that the fluctuation range of the monitor current I _mon falls within the dynamic range of the current / voltage converter (I / V converter) 6. (Figure 2
reference).

In this embodiment, as shown in FIG. 2, the switching means of the switch-type constant current source 8 has a switch closing switch setting threshold Va or a switch open switch setting threshold Vb of the switch-type constant current source 8. 8A ON (closed) / OFF
The monitor current I _{mon at the} switching point for (open) matches. At this time, for example, when the automatic optical output control convergence voltage matches the switch closing switching setting threshold Va or the switch opening switching setting threshold Vb, it turns ON (closed).
-There is a possibility that the state will be OFF (open) and the circuit operation will be unstable. FIG. 3 shows the peak value of the input current (monitor current I _mon ) and the output V of the current / voltage converter (I / V converter) 6 shown in FIG. 1 when the switching in the switching control circuit 7 has a hysteresis characteristic. Shows the relationship with the peak value. In the semiconductor laser driving device and the semiconductor laser driving method of the present embodiment, the switching control in the switching control circuit 7 has a hysteresis characteristic to prevent the above-described phenomenon in which the circuit operation becomes unstable.

The present embodiment is configured as described above, and has the following effects. First, by increasing the dynamic range of the current / voltage converter (I / V converter) 6, a semiconductor laser (LD) is
1 to the region where the output of the current / voltage converter (I / V converter) 6 is saturated due to the sample variation of the coupling efficiency in the forward light and the sample variation of the conversion efficiency of the monitoring light receiving element (PD) 5. Automatic light output control becomes possible. Second, it is possible to cope with a wide range of optical output power settings. Third, when the dynamic range of the current / voltage converter (I / V converter) 6 is widened, unlike the conventional semiconductor laser driving method (gain switching), the indefinite width of the driving current _Iop can be reduced. The stability of light output can be improved.

(Second Embodiment) FIG. 4 is a functional block diagram for explaining a second embodiment of a semiconductor laser driving apparatus according to the present invention, and is a switching circuit provided with N constant current sources and switch means. The figure shows a constant current source 81 and its peripheral parts. In the semiconductor laser driving device according to the first embodiment described above, a single constant current source is used as the switching constant current source 8, but the switching constant current source 8 is replaced with the second embodiment. In the semiconductor laser driving device of (1), as shown in FIG.
It is characterized in that a configuration is used in which a plurality of _N (current sources 81B ₁ ,..., 81B _N ) constant current sources are connected in parallel. In other words, the N switch means 81A ₁ ,.
And a switched constant current source 81 having a 1A _N.

Referring to FIG. 4, a semiconductor laser driving device according to a second embodiment includes a semiconductor laser (LD) 1, a driving circuit (LDD) 2, a communication control unit 3, a comparison amplifier 4, and a monitoring light receiving element (PD). 5, a current / voltage converter (I / V converter) 6, a switching control circuit 71, and a switching type constant current source 81. Switch means _81A 1, ..., 8
1A is between each end and the ground potential GND of _N, ON (closed) · OF in response to a control signal from the switching control circuit 71
F (open) Possible N current sources _81B 1, ..., are connected 81B _N. Switch means _81A 1, ..., _{81A N}
A current / voltage converter (I / V converter) is connected to the node between the other end of the device and the anode terminal of the monitoring light receiving element (PD) 5.
6 input terminals are connected.

The semiconductor laser (LD) 1 has an anode terminal connected to a power supply and a cathode terminal connected to a drive circuit (LDD).
2 and drive current I from drive circuit (LDD) 2
_This is a device that emits light upon receiving the supply of _op . Drive circuit (LDD) 2, a cathode terminal of the semiconductor laser (LD) 1 is connected to the output terminal, in accordance with an electric signal from the communication control unit 3, a semiconductor laser (LD) functional block supplies a drive current I _op 1 It is. The communication control unit 3 is connected to an input terminal of the drive circuit (LDD) 2 and controls the drive circuit (LDD).
2 is a functional block that outputs an electric signal to the control unit 2. The comparison amplifier 4 compares the output of the current / voltage converter (I / V converter) 6 with the automatic optical output control convergence voltage, and the optical output power converges to the set value based on the comparison result. as a functional block for outputting a signal for controlling the driving current _{I op} drive circuit (LDD) 2 to the drive circuit (LDD) 2. Monitoring light receiving element (PD) 5, a cathode terminal is connected to a power source, switch means 81A 1 whose anode terminal is provided on a switched constant current source 81, _..., the one end and the current / voltage conversion of each of 81A _N Is connected to the input terminal of a converter (I / V converter) 6, receives the back light of the semiconductor laser (LD) 1, and monitors the monitor current I according to the amount of received light.
_This is a functional block for converting to _mon . The current / voltage converter (I / V converter) 6 is a monitoring light receiving element (PD) 5
Is a functional block that converts the monitor current I _mon generated and output into a voltage (current / voltage conversion), and outputs the converted voltage signal to the comparison amplifier 4 and the switching control circuit 71.

FIG. 6 shows the relationship between the peak value of the peak value and the output V of the input current (monitor current I _{m on)} in FIG. 4 of the current / voltage converter (I / V converter). The horizontal axis is the peak value of the input current (monitor current I _mon ), and the vertical axis is the peak value of the output V. In the semiconductor laser driving device according to the present embodiment, a switching type constant current source 81 having N constant current sources and switch means is provided, so that a current / voltage converter (I / V converter) as shown in FIG. 6) The dynamic range of 6 can be further expanded as compared with the first embodiment.
This has the effect that the problem of deteriorating the stability accuracy of the optical output does not occur.

The switching control circuit 71 of the present embodiment has a
It is determined whether or not the peak value of the converted voltage signal output from the voltage converter (I / V converter) 6 exceeds the switch closing switching setting threshold Va or the switch opening switching setting threshold Vb. According to the determination result, the switch means 81A ₁ , provided in the switching type constant current source 81,
..., a functional block for generating and outputting a control signal for controlling the respective ON of 81A _N (closed), OFF (open), switch means 81A ₁ provided in the switched constant current source 81 the current , ..., each of ON of 81A _N (closed) · O
Provided with a switch (fixed switch) for fixing the state of the FF (open), switch means _81A 1 provided in the switched constant current source 81, ..., each of 81A _N O
It is characterized in that the control of N (closed) and OFF (open) is performed only when the light output is set (when the automatic light output control converging voltage is set).

The switched constant current source 81 of this embodiment, current source _81B 1 for supplying a constant current to the monitor light-receiving element (PD) 5, ..., and each of 81B _N, monitor light-receiving element (PD) 5 and the current source _81B 1, ..., switch means _81A 1 are interposed in series between each of 81B _N, ..., 81
Provided each of A _N, switch means _81A 1 under the control of the switching control circuit 71, ..., ON each of 81A _N (closed)
・ By turning OFF (open), the current / voltage converter (I / V
The function block switches the output bias of the converter 6.

Next, the operation of the semiconductor laser driving device of this embodiment and the operation of the semiconductor laser driving method executed by the semiconductor laser driving device of this embodiment will be described with reference to FIGS.

First, the basic operation of the semiconductor laser driving device according to the present embodiment will be described. Referring to FIG. 4, the drive circuit (LDD) 2 which receives the electric signal from the communication control unit 3, by causing the semiconductor laser to emit light (LD) 1 supplies a drive current I _op, the electrical signal to an optical signal Convert. Light from the semiconductor laser (LD) 1 is detected by a monitoring light receiving element (PD) 5 and converted into a monitoring current I _mon . This monitor current I _mon is converted into a voltage signal by a current / voltage converter (I / V converter) 6. The voltage signal output from the current / voltage converter (I / V converter) 6 is input to the comparison amplifier 4. The comparison amplifier 4 compares the voltage signal output from the current / voltage converter (I / V converter) 6 with a preset automatic optical output control convergence voltage, and based on the comparison result, by controlling the drive current _{I op} drive circuit (LDD) 2 to a constant light output from the semiconductor laser (LD) 1.

Next, the operation of the switching type constant current source 81 of the present embodiment will be described. In this embodiment, switch means _81A 1 provided in the switched constant current source 81, ..., the control of each of the ON of 81A _N (closed) · OFF (open), the optical output setting time (automatic optical power control It is characterized in that only the convergence voltage is set). FIG. 6 (the current / voltage converter (I / V
As shown in a graph showing the relationship between the peak value of the input current (monitor current I _mon ) of the converter 6 and the peak value of the output V), the switch means 81A ₁ ,
..., the difference in the output of the biased by respective ON of 81A _N (closed) · OFF (open) (specifically, shown in the previous figure,
A broken line occurs when the switch is off, and a solid line occurs when the switch is on. The switch closing switching threshold V in the switching control circuit 71 is described below.
The relationship between a or the switch open switching setting threshold Vb and the output V of the current / voltage converter (I / V converter) 6 will be described. The switch means 81A ₁ ,..., Of the switchable constant current source 81
In the state of 81A _N each OFF (open), when the peak value of the output V of the current / voltage converter (I / V converter) 6 exceeds the set threshold Va exchange switch閉切, switching means 8
1A _1, ..., each of 81A _N is switched to ON (closed). The switch means 81A ₁ ,..., Of the switchable constant current source 81
In the state of 81A _N of each ON (closed), when the peak value of the output V of the current / voltage converter (I / V converter) 6 no longer exceeds the switch open switch setting threshold Vb, the switch means 81A _1, ..., each of 81A _N is switched to OFF (open).

Switching means 81A of switching type constant current source 81
_1, ..., by each of the ON of 81A _N (closed) · OFF (open), the slope of the output V with respect to the current / voltage converter (I / V converter) 6 of the input current (monitor current _{I mon)} is unchanged . Therefore, the dynamic range of the current / voltage converter (I / V converter) 6 can be expanded without causing the problem of the conventional technology that the stability of the optical output is deteriorated due to the conventional technology (gain switching type). Can be.

At the time of operation after the optical output power setting (automatic optical output control convergence voltage setting), the setting level of the optical output power setting (automatic optical output control convergence voltage setting) is set using the fixing switch of the switching control circuit 71. According to the switching type constant current source 81
Switch means _81A 1, ..., each is in the ON 81A _N
It is fixed where it is either (closed) or OFF (open). Further, even when the automatic optical output control convergence voltage matches the switch closing switching setting threshold value Va or the switch opening switching setting threshold value Vb, it is ON (closed) / OF.
The switch closing switching threshold is set so that the fluctuation range of the monitor current I _mon falls within the dynamic range of the current / voltage converter (I / V converter) 6 when the operation is fixed to one of F (open). A value Va or a switch open switching setting threshold Vb is set (see FIG. 6).

The switch closed switch setting threshold value Va or the switch open switch set threshold value Vb of the switching type constant current source 81
For, in the present embodiment, as shown in FIG. 6, switch means _81A 1 of switched constant current source 81, ..., each of the ON (closed) of 81A _N · OFF monitor current of the switching point for the (open) _{I mon} Matches. At this time, for example, when the automatic optical output control convergence voltage matches the switch closing switching setting threshold value Va or the switch opening switching setting threshold value Vb, the ON (closed) / OFF (open) state is not reached. Circuit operation may become unstable.
FIG. 3 shows the current / voltage converter (I / V) of FIG. 4 when the switching in the switching control circuit 71 has a hysteresis characteristic.
The relationship between the peak value of the input current (monitor current I _mon ) of the converter 6 and the peak value of the output V is shown. In the semiconductor laser driving device and the semiconductor laser driving method according to the present embodiment, the switching control in the switching control circuit 71 can be provided with a hysteresis characteristic to prevent the above-described phenomenon in which the circuit operation becomes unstable.

The present embodiment is configured as described above, and has the following effects. First, by using a switching type constant current source 81 having N constant current sources and switch means, a current / voltage converter (I / V converter) 6
The dynamic range of the semiconductor laser (LD) 1 can be increased by increasing the dynamic range of the current / voltage converter (I / V converter) 6 in comparison with the first embodiment. Sample variation of coupling efficiency in forward light and monitor photo detector (PD)
Automatic light output control is possible up to a region where the output of the current / voltage converter (I / V converter) 6 is saturated due to the sample variation of the conversion efficiency 5. Second, it is possible to cope with a wide range of optical output power settings. Third, when the dynamic range of the current / voltage converter (I / V converter) 6 is widened, unlike the conventional semiconductor laser driving method (gain switching), the indefinite width of the driving current _Iop can be reduced. The stability of light output can be improved.

(Third Embodiment) FIG. 5 is a functional block diagram for explaining a third embodiment of the semiconductor laser driving apparatus according to the present invention, and shows a variable current source 82 and its peripheral portion. . Referring to FIG. 5, the semiconductor laser driving device according to the third embodiment includes a semiconductor laser (LD) 1, a driving circuit (LDD) 2, a communication control unit 3, a comparison amplifier 4, a monitoring light receiving element (PD) 5, a current / Voltage converter 6, switching control circuit 72, and variable current source 82. Between the anode terminal of the monitoring light receiving element (PD) 5 and the ground potential GND, a variable type that can control the amount of current supplied to the monitoring light receiving element (PD) 5 according to a control signal from the switching control circuit 72 A current source 82 is connected. A node between the anode terminal of the monitoring light receiving element (PD) 5 and the variable current source 82 is connected to a current / voltage converter (I / V
The input terminal of the converter 6 is connected.

The semiconductor laser (LD) 1 has an anode terminal connected to a power supply and a cathode terminal connected to a drive circuit (LDD).
2 and drive current I from drive circuit (LDD) 2
_This is a device that emits light upon receiving the supply of _op . Drive circuit (LDD) 2, a cathode terminal of the semiconductor laser (LD) 1 is connected to the output terminal, in accordance with an electric signal from the communication control unit 3, a semiconductor laser (LD) functional block supplies a drive current I _op 1 It is. The communication control unit 3 is connected to an input terminal of the drive circuit (LDD) 2 and controls the drive circuit (LDD).
2 is a functional block that outputs an electric signal to the control unit 2. The comparison amplifier 4 compares the output of the current / voltage converter (I / V converter) 6 with the automatic optical output control convergence voltage, and the optical output power converges to the set value based on the comparison result. as a functional block for outputting a signal for controlling the driving current _{I op} drive circuit (LDD) 2 to the drive circuit (LDD) 2. The monitoring light receiving element (PD) 5 has a cathode terminal connected to the power supply, an anode terminal connected to the output terminal of the variable current source 82 and the input terminal of the current / voltage converter (I / V converter) 6, While receiving the back light of the semiconductor laser (LD) 1, the monitor current I _mon according to the amount of received light is received.
This is a functional block for converting to. Current / voltage converter (I
/ V converter) 6 converts the monitor current I _mon generated and output by the monitoring light receiving element (PD) 5 into a voltage (current / voltage conversion), and converts the converted voltage signal into the comparison amplifier 4 and the switching control. This is a functional block that outputs to the circuit 72.

FIG. 6 shows the relationship between the peak value of the peak value and the output V of the input current (monitor current I _{m on)} in FIG. 5 of the current / voltage converter (I / V converter). The horizontal axis is the peak value of the input current (monitor current I _mon ), and the vertical axis is the peak value of the output V. In the semiconductor laser driving device according to the present embodiment, by providing the variable current source 82 having N constant current sources and switch means, as shown in FIG.
The dynamic range of the voltage converter (I / V converter) 6 can be further expanded as compared with the first embodiment, and furthermore, there is an effect that the problem of deteriorating the stability accuracy of the optical output does not occur.

The switching control circuit 72 of the present embodiment has a
This is a functional block for controlling the variable current source 82 according to the peak value of the converted voltage signal output from the voltage converter (I / V converter) 6. Switch for fixing the quantity control status (fixing switch)
And the control of the variable current source 82 is performed only when the optical output is set (when the automatic optical output control convergence voltage is set). Further, the variable current source 82 of the present embodiment
Is a functional block for switching the output bias of the current / voltage converter (I / V converter) 6 by controlling the current amount according to the control of the switching control circuit 72.

Next, the operation of the semiconductor laser driving device of the present embodiment and the operation of the semiconductor laser driving method executed by the semiconductor laser driving device of the present embodiment will be described with reference to FIGS. First, the basic operation of the semiconductor laser driving device according to the present embodiment will be described. Referring to FIG. 5, the communication control unit 3
More driving circuit which receives an electrical signal (LDD) 2, by causing the semiconductor laser to emit light (LD) 1 supplies a drive current I _op, and converts an electrical signal into an optical signal. The light from the semiconductor laser (LD) 1 is transmitted to the monitor light receiving element (P
D) Detected by 5 and converted to monitor current I _mon . The monitor current I _mon is a current / voltage converter (I
/ V converter) 6 to convert it into a voltage signal. Current /
The voltage signal output from the voltage converter (I / V converter) 6 is input to the comparison amplifier 4. The comparison amplifier 4 has a current /
The voltage signal output from the voltage converter (I / V converter) 6 is compared with a preset automatic optical output control convergence voltage, and the driving circuit (LDD) 2 is controlled based on the comparison result. by controlling the drive current I _op is a constant light output from the semiconductor laser (LD) 1.

Next, the operation of the variable current source 82 of this embodiment will be described. The present embodiment is characterized in that the control of the variable current source 82 is performed only when the light output is set (when the automatic light output control convergence voltage is set). As in the above embodiments, the current / current control by the variable current source 82
The slope of the output V with respect to the input current (monitor current I _mon ) of the voltage converter (I / V converter) 6 does not change. Therefore, the dynamic range of the current / voltage converter (I / V converter) 6 can be expanded without causing the problem of the conventional technology that the stability of the optical output is deteriorated due to the conventional technology (gain switching type). Can be.

At the time of operation after the optical output power setting (automatic optical output control convergence voltage setting), the setting level of the optical output power setting (automatic optical output control convergence voltage setting) is set using the fixing switch of the switching control circuit 72. , The current amount of the variable current source 82 is fixed.

The present embodiment is configured as described above, and has the following effects. First, by using the variable current source 82, the current / voltage converter (I / V
The dynamic range of the current / voltage converter (I / V converter) 6 can be increased as compared with the first embodiment. An area where the output of the current / voltage converter (I / V converter) 6 is saturated due to the sample variation of the coupling efficiency in the forward light of the LD) 1 and the sample variation of the conversion efficiency of the monitoring light receiving element (PD) 5. Until the above, automatic light output control becomes possible. Second, it is possible to cope with a wide range of optical output power settings. Third, when the dynamic range of the current / voltage converter (I / V converter) 6 is widened, unlike the conventional semiconductor laser driving method (gain switching), the indefinite width of the driving current _Iop can be reduced. The stability of light output can be improved.

It should be noted that the present invention is not limited to the above embodiments, and that each embodiment can be appropriately modified within the scope of the technical idea of the present invention. Further, the number, position, shape, and the like of the constituent members are not limited to the above-described embodiment,
The number, position, shape, and the like suitable for carrying out the present invention can be obtained. In each drawing, the same components are denoted by the same reference numerals.

[0043]

Since the present invention is configured as described above, the following effects can be obtained. First, by widening the dynamic range of the current / voltage converter, conventionally, the variation in the coupling efficiency in the forward light of the semiconductor laser and the variation in the conversion efficiency of the monitoring light-receiving element cause the variation in the current / voltage converter. Automatic light output control is possible up to a region where the output of the device is saturated. Second
In addition, a wide range of optical output power settings can be supported. Third, when expanding the dynamic range of the current / voltage converter, a conventional semiconductor laser driving method (gain switching)
Unlike this, the indeterminate width of the drive current can be reduced, and the accuracy of stabilizing the optical output can be improved.

[Brief description of the drawings]

FIG. 1 is a functional block diagram for explaining a first embodiment of a semiconductor laser driving device according to the present invention.

FIG. 2 shows a relationship between a peak value of an input current (monitor current) and a peak value of an output of the current / voltage converter of FIG.

FIG. 3 shows a relationship between a peak value of an input current (monitor current) and a peak value of an output of the current / voltage converter in FIG. 1 when a hysteresis characteristic is given to switching in the switching control circuit.

FIG. 4 is a functional block diagram for explaining a second embodiment of the semiconductor laser driving device according to the present invention, showing a portion of a switching type constant current source including N constant current sources and switch means. ing.

FIG. 5 is a functional block diagram for explaining a third embodiment of the semiconductor laser driving device according to the present invention, showing a variable current source and a peripheral portion thereof.

FIG. 6 shows a relationship between a peak value of an input current and a peak value of an output of the current / voltage converters of FIGS.

FIG. 7 is a configuration diagram in a case where a conventional digital APC type semiconductor laser driving circuit is combined with a conventional current / voltage (I / V) converter gain switching method.

8 illustrates a relationship between a peak value of an input current and a peak value of an output of the current / voltage converter of FIG. 7;

9 shows the relationship between the drive current and the output of the current / voltage converter in the conventional semiconductor laser drive device of FIG. 7;

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Semiconductor laser (LD) 2 ... Drive circuit (LDD) 3 ... Communication control part 4 ... Comparison amplifier 5 ... Monitoring light receiving element (PD) 6 ... Current / voltage converter (I / V converter) 7 ... Switching control circuit 71 ... switching control circuit 72 ... switching control circuit 8 ... switched constant current sources 8A ... switch means 81 ... switched constant current source 81A _{1, ...,} 81A N ... switch means 81B _{1, ...,} 81B N ... current source 82 ... variable current source I _{mon ...} monitor current Va ... switch閉切exchange set threshold Vb ... open switch switching setting threshold

Claims (18)

[Claims] 1. A semiconductor laser in which the dynamic range of a current / voltage converter is expanded to enable automatic optical output control up to a region where the output of the current / voltage converter is saturated, thereby reducing the indeterminate width of a drive current. A semiconductor laser driving device capable of improving the stability accuracy of the optical output of the semiconductor laser, comprising: at least one current source for supplying a constant current to a light receiving element for monitoring the optical output of the semiconductor laser; At least one or more switch means interposed in series between the element and each of the current sources, and closing / opening the switch means according to a predetermined control signal to output the current / voltage converter A switching type constant current source for switching a bias; and a switch open switching setting threshold value having at least one or more predetermined peak values of the converted voltage signal output from the current / voltage converter. With determining whether or not the example,
A switching control circuit for generating and outputting a control signal for controlling the closing and opening of each of the switch means provided in the switching constant current source in accordance with the determination result. Laser drive. 2. The switching control circuit according to claim 1, wherein the switching control circuit includes a switch for fixing a closed / open state of each of the switching means provided in the switching constant current source. Semiconductor laser drive. 3. The switching control circuit according to claim 1, wherein each of the switching means provided in the switching-type constant current source is controlled to close and open at least when a light output is set. Or the semiconductor laser drive device according to 2. 4. The switching control circuit according to claim 1, wherein each of the switching means provided in the switching constant current source is controlled to close and open at least when an automatic optical output control convergence voltage is set. The semiconductor laser driving device according to claim 1 or 2, wherein: 5. The current / voltage converter converts the monitor current generated and output by the monitor light-receiving element into a voltage, and outputs the converted voltage signal as the control signal to the switching control circuit. The semiconductor laser driving device according to claim 1, wherein the semiconductor laser driving device is configured to perform the following. 6. The monitor light receiving element, wherein a cathode terminal is connected to a power supply, and an anode terminal is connected to one end of each of the switch means provided in the switching constant current source and an input of the current / voltage converter. An end of the semiconductor laser is configured to receive the back light of the semiconductor laser, convert the monitor light into the monitor current according to the amount of received light, and output the monitor current to the current / voltage converter. 6. The semiconductor laser driving device according to 5. 7. The switching constant current source includes a first switch closing switching setting threshold and a second switch closing switching setting threshold as the predetermined at least one type of switch opening switching setting threshold. In the open state of the switch means, when the peak value of the output of the current / voltage converter exceeds the first switch close switching setting threshold value, the switch means is switched to the closed state, In the closed state, the switch means is switched to open when the peak value of the output of the current / voltage converter does not exceed the second switch open switching setting threshold value. The semiconductor laser driving device according to claim 3 or 4, wherein 8. The semiconductor laser according to claim 1, wherein the dynamic range of the current / voltage converter is expanded to enable automatic optical output control up to a region where the output of the current / voltage converter is saturated. A semiconductor laser driving device capable of improving the stability accuracy of the light output of the semiconductor laser, wherein the current source for flowing a constant current to a light receiving element for monitoring the light output of the semiconductor laser, A variable current source capable of controlling the amount of current supplied to the monitoring light receiving element; and a switch open switching setting threshold value having at least one or more predetermined peak values of the converted voltage signal output from the current / voltage converter. And whether or not it exceeds
A switching control circuit that generates and outputs a control signal that specifies an amount of current supplied to the monitoring light-receiving element that flows through the variable current source according to the determination result. 9. The semiconductor laser driving device according to claim 8, wherein the switching control circuit includes a switch for fixing an amount of current supplied by the switching constant current source. 10. The semiconductor laser driving device according to claim 8, wherein the switching control circuit controls the amount of current of the switching type constant current source at least at the time of setting an optical output. 11. The semiconductor laser according to claim 8, wherein the switching control circuit controls the amount of current of the switching constant current source at least at the time of setting an automatic optical output control convergence voltage. Drive. 12. The current / voltage converter converts the monitor current generated and output by the monitoring light receiving element into a voltage, and outputs the converted voltage signal as the control signal to the switching control circuit. The semiconductor laser driving device according to any one of claims 8 to 11, wherein the semiconductor laser driving device is configured to perform the following. 13. The monitoring light-receiving element, wherein a cathode terminal is connected to a power supply, an anode terminal is connected to one end of the switch-type constant current source and an input terminal of the current / voltage converter, and a back light of the semiconductor laser is provided. 13. The semiconductor laser driving device according to claim 12, wherein the semiconductor laser driving device is configured to receive the light, convert the light into the monitor current according to the amount of received light, and output the monitor current to the current / voltage converter. 14. A semiconductor laser in which the dynamic range of the current / voltage conversion step is expanded to enable automatic optical output control up to a region where the output of the current / voltage converter is saturated, thereby reducing the indefinite width of the drive current. A method of driving a semiconductor laser capable of improving the accuracy of stabilization of optical output, wherein a peak value of a converted voltage signal output by the current / voltage conversion step is at least one or more types of switch open switching settings It is determined whether or not the threshold value is exceeded, and at least one of the at least one for flowing a constant current to the light receiving element that monitors the optical output of the semiconductor laser is determined in accordance with the determination result.
A current source control step of generating and outputting a control signal for controlling a current flowing through one or more current sources; and a bias control step of switching an output bias of the current / voltage conversion step according to the control signal. Semiconductor laser driving method. 15. The semiconductor according to claim 14, wherein said current source control step includes a step of fixing a closed / open state of each of said switch means provided in said bias control step. Laser driving method. 16. The method according to claim 14, wherein in the current source control step, the closing / opening control of each of the switch means provided in the bias control step is performed at least at the time of setting an optical output. 16. The method for driving a semiconductor laser according to item 15. 17. The method according to claim 17, wherein the current source control step executes the control of closing / opening each of the switch means provided in the bias control step at least when an automatic light output control convergence voltage is set. A method for driving a semiconductor laser according to claim 14. 18. A current / voltage conversion step of converting the monitor current generated and output by the monitoring light receiving element into a voltage and outputting the converted voltage signal as the control signal to the current source control step. The method for driving a semiconductor laser according to any one of claims 14 to 17, comprising: