CN215221265U

CN215221265U - Automatic current control system for single-wavelength semiconductor laser

Info

Publication number: CN215221265U
Application number: CN202121216214.4U
Authority: CN
Inventors: 赵番; 司俊; 朱旭晨; 李晓军
Original assignee: Shanghai Special Equipment Supervision and Inspection Technology Institute
Current assignee: Shanghai Special Equipment Supervision and Inspection Technology Institute
Priority date: 2021-06-01
Filing date: 2021-06-01
Publication date: 2021-12-17
Anticipated expiration: 2031-06-01

Abstract

The utility model provides a single wavelength semiconductor laser automatic current control system, single wavelength semiconductor laser has laser LD and photodetector PD dorsad, the negative pole pin of laser LD and the positive pole pin ground connection of photodetector PD dorsad, the positive pole pin LD + of laser LD and the negative pole pin PD-of photodetector PD dorsad connect the positive voltage, a serial communication port, automatic current control system includes mirror current source circuit, reference voltage supply circuit, N passageway MOSFET Q7 and resistance R2. The utility model discloses a current feedback control return circuit carries out closed-loop control to semiconductor laser's injection current to reach the stable purpose of output optical power. Compared with the prior art, the utility model discloses following beneficial effect has: the circuit has the advantages of simple structure, high reliability and low power consumption, and solves the problems of complex circuit, high cost and poor stability in the conventional system.

Description

Automatic current control system for single-wavelength semiconductor laser

Technical Field

The utility model relates to a semiconductor laser automatic current control system forms the negative feedback with the electric current of detector dorsad and controls laser instrument drive current to reach constant current control's purpose, belong to the automated control field.

Background

Semiconductor lasers are widely used in various fields as an important light source. In practical application, the semiconductor laser is affected by the external power supply voltage and temperature variation, resulting in fluctuation of the output power of the laser. At this time, if the driving current of the laser is changed, the driving threshold current of the laser may be exceeded, so that the performance of the laser may be drastically reduced to damage and fail. Therefore, the stability and modulation accuracy of the semiconductor laser driving circuit are required to be high.

The conventional semiconductor laser is designed with a voltage limiting and current limiting module to ensure that the laser LD works within the range of limit voltage and current. The design generally uses a singlechip to control a high-precision digital-to-analog converter, and a discrete device is additionally arranged to ensure the stability of output power, and the circuit has the advantages of complex structure, high cost and poor stability.

Disclosure of Invention

The utility model aims at: the safe and reliable operation of the semiconductor laser is ensured.

In order to achieve the above object, the present invention provides an automatic current control system for a single-wavelength semiconductor laser, the single-wavelength semiconductor laser has a laser LD and a back light detector PD, a cathode pin of the laser LD and an anode pin of the back light detector PD are grounded, an anode pin LD + of the laser LD and a cathode pin PD-of the back light detector PD are connected to a positive voltage, and the automatic current control system includes a mirror current source circuit, a reference voltage supply circuit, an N-channel MOSFET Q7 and a resistor R2, wherein:

the input end of the mirror current source circuit is connected with the constant voltage source DVDD and is provided with two output ends, and currents output by the two output ends of the mirror current source circuit are in a mirror image relation; one output end of the mirror current source circuit is connected with an anode pin LD + of the laser LD, and the other output end of the mirror current source circuit is connected with the drain electrode of an N-channel MOSFET Q7;

the reference voltage provided by the reference voltage supply circuit and the voltage difference formed after the photocurrent coupled to the cathode pin PD — facing away from the photodetector PD flows through the resistor R2 are applied to the gate of the N-channel MOSFET Q7, and the source of the N-channel MOSFET Q7 is grounded.

Preferably, the mirror current source circuit comprises a PNP transistor Q5, a PNP transistor Q6, a resistor R3 and a resistor R4; the emitter of the PNP triode Q5 and the emitter of the PNP triode Q6 are connected with a constant voltage source DVDD; the base electrode of the PNP triode Q5 is connected with the base electrode of the PNP triode Q6; an anode pin LD + of the laser LD is connected with a collector of a PNP triode Q5 through a resistor R3; the base electrode of the PNP triode Q6 is connected with the collector electrode, and the drain electrode of the N-channel MOSFET Q7 is connected with the collector electrode of the PNP triode Q6 through a resistor R4; the current I1 of the collector of the PNP triode Q5 and the PNP triode Q6 is in mirror image relation with the current I2.

Preferably, the reference voltage supply circuit comprises a resistor R6 and a voltage reference chip U4, one end of the resistor R6 is connected to a constant voltage source DVDD, the other end is connected to the cathode of the voltage reference chip U4 and one end of the resistor R2, and the anode of the voltage reference chip U4 is grounded; the other end of the resistor R2 is connected with the gate of the N-channel MOSFET Q7, and the gate of the N-channel MOSFET Q7 is also connected with the cathode pin PD-which faces away from the light detector PD.

The utility model discloses a current feedback control return circuit carries out closed-loop control to semiconductor laser's injection current to reach the stable purpose of output optical power. Compared with the prior art, the utility model discloses following beneficial effect has: the circuit has the advantages of simple structure, high reliability and low power consumption, and solves the problems of complex circuit, high cost and poor stability in the conventional system.

Drawings

FIG. 1 is a schematic diagram of an internal structure of a semiconductor laser for use in an automatic current control system for the semiconductor laser;

fig. 2 is a circuit diagram of an automatic current control system for a semiconductor laser.

Detailed Description

The present invention will be further described with reference to the following specific examples. It should be understood that these examples are for illustrative purposes only and are not intended to limit the scope of the present invention. Furthermore, it should be understood that various changes and modifications of the present invention may be made by those skilled in the art after reading the teachings of the present invention, and these equivalents also fall within the scope of the appended claims.

As shown in fig. 1, the utility model discloses the laser of chooseing for use has laser LD and back photodetector PD, and laser LD is used for sending laser, and back photodetector PD is used for detecting the laser intensity that laser LD sent. The back light detector PD converts a portion of the received optical power into a monitoring current, which is proportional to the laser power received by the back light detector PD, thereby controlling the output optical power of the laser LD.

In this embodiment, when the cathode pin of the laser LD is grounded, the anode pin of the laser LD is connected to a positive voltage. When the anode pin of the back light detector PD is grounded, the cathode pin of the back light detector PD is connected with a positive voltage to form reverse bias, so that the aim of forward driving the laser diode is fulfilled.

In a normal state, the laser LD operates at a set driving current, and the driving current I is proportional to the output optical power of the laser. When the output power of the laser LD increases, the photocurrent coupled to the feedback terminal facing away from the photodetector PD also increases proportionally. When the output optical power of the laser LD decreases, the photocurrent coupled to the feedback terminal of the back photodetector PD decreases accordingly.

The utility model discloses a circuit converts the photocurrent that will be dorsad light detector PD feedback end into voltage through series resistance, controls laser LD's drive current through voltage change to reach current automatic control's purpose. When the output photocurrent of the laser LD is reduced, the injection current of the laser LD is increased by the N-channel MOSFET to maintain the stability of the output power. On the contrary, if the output photocurrent of the laser LD increases, the injection current of the laser LD decreases.

As shown in fig. 2, the present invention provides an automatic current control system for a semiconductor laser, comprising: PNP triodes Q5, Q6, resistors R3, R4, R2, R6, a voltage reference chip U4 and an N-channel MOSFET Q7.

The cathode pin PD-of the back photodetector PD is connected to the gate (pin 1) of the N-channel MOSFET Q7 and is electrically connected to the cathode of the voltage reference chip U4 through a resistor R2. The opening of the gate of the N-channel MOSFET Q7 is affected by the cathode pin PD-voltage and the reference voltage output by the voltage reference chip U4.

The PNP triodes Q5 and Q6 and the resistors R3 and R4 form a mirror current source circuit. The anode pin LD + of the laser LD is connected with the collector (pin 3) of the PNP triode Q5 through a resistor R3, and the drain (pin 3) of the N-channel MOSFET Q7 is connected with the collector (pin 3) of the PNP triode Q6 through a resistor R4. The PNP triode is designed so that currents I1 and I2 of collectors of the PNP triodes Q5 and Q6 are in a mirror image relation.

When the applied power supply voltage suddenly increases, the forward voltage of the semiconductor laser at its PN junction increases, the injection current of the laser LD increases, and the output laser power of the laser LD suddenly increases. When the ambient temperature decreases, the output power of the laser LD also abruptly increases. The sudden increase in the output power of the laser LD causes a proportional increase in the photocurrent coupled to the cathode pin PD-facing away from the photodetector PD. The photocurrent coupled to the cathode pin PD — facing away from the photodetector PD passes through the resistor R2, and the voltage difference formed across the resistor R2 increases. Since the reference voltage outputted by the voltage reference chip U4 is not changed, the gate (pin 1) voltage of the N-channel MOSFET Q7 is decreased, the opening between the drain (pin 3) and the source (pin 2) of the N-channel MOSFET Q7 is decreased, and the drain current is decreased. The other end of the mirror current source circuit is connected with an anode pin LD + of the laser LD, the current on the anode pin LD + of the laser LD is reduced, the driving current of the laser LD is reduced, the power of the laser LD is reduced, the light emission is weakened, and the previous light emission intensity is recovered.

When the external power supply voltage suddenly decreases, the forward voltage of the semiconductor laser at the PN junction thereof decreases, the injection current of the laser LD decreases, and the output laser power of the laser LD suddenly decreases. When the ambient temperature rises, the output power of the laser LD also abruptly decreases. The sudden decrease of the output power of the laser LD causes the photocurrent coupled to the cathode pin PD-facing away from the photo detector PD to also decrease proportionally. The photocurrent coupled to the cathode pin PD — facing away from the photodetector PD passes through the resistor R2, and the voltage difference formed across the resistor R2 decreases. Since the reference voltage outputted from the voltage reference chip U4 is not changed, the voltage of the gate (pin 1) of the N-channel MOSFET Q7 increases, the opening between the drain (pin 3) and the source (pin 2) of the N-channel MOSFET Q7 increases, and the drain current increases. The other end of the mirror current source circuit is connected with an anode pin LD + of the laser LD, so that the current on the anode pin LD + of the laser LD is increased, the driving current of the laser LD is increased, the laser power is increased, the light emission is enhanced, and the previous light emission intensity is recovered. The driving current of the laser LD is controlled by the current back to the photodetector PD, thereby achieving the purpose of automatic current control of the semiconductor laser.

Claims

1. An automatic current control system for a single wavelength semiconductor laser having a laser LD and a photodetector PD facing away from the laser LD, a cathode pin of the laser LD and an anode pin of the photodetector PD facing away from the laser LD being grounded, an anode pin LD + of the laser LD and a cathode pin PD-of the photodetector PD facing away from the laser LD being connected to a positive voltage, the automatic current control system comprising a mirror current source circuit, a reference voltage supply circuit, an N-channel MOSFET Q7 and a resistor R2, wherein:

2. The automatic current control system of a single wavelength semiconductor laser as claimed in claim 1 wherein the mirror current source circuit comprises a PNP transistor Q5, a PNP transistor Q6, a resistor R3, and a resistor R4; the emitter of the PNP triode Q5 and the emitter of the PNP triode Q6 are connected with a constant voltage source DVDD; the base electrode of the PNP triode Q5 is connected with the base electrode of the PNP triode Q6; an anode pin LD + of the laser LD is connected with a collector of a PNP triode Q5 through a resistor R3; the base electrode of the PNP triode Q6 is connected with the collector electrode, and the drain electrode of the N-channel MOSFET Q7 is connected with the collector electrode of the PNP triode Q6 through a resistor R4; the current I1 of the collector of the PNP triode Q5 and the PNP triode Q6 is in mirror image relation with the current I2.

3. The automatic current control system of a single wavelength semiconductor laser as claimed in claim 1 wherein, the reference voltage supply circuit comprises a resistor R6 and a voltage reference chip U4, one end of the resistor R6 is connected to a constant voltage source DVDD, the other end is connected to the cathode of the voltage reference chip U4 and one end of the resistor R2, the anode of the voltage reference chip U4 is grounded; the other end of the resistor R2 is connected with the gate of the N-channel MOSFET Q7, and the gate of the N-channel MOSFET Q7 is also connected with the cathode pin PD-which faces away from the light detector PD.