An automatic current control system for single-wavelength semiconductor lasers

Abstract

The present invention provides a single-wavelength semiconductor laser automatic current control system, wherein the single-wavelength semiconductor laser has a laser LD and a back-light detector PD, the cathode pin of the laser LD and the anode pin of the back-light detector PD are grounded, the anode pin LD+ of the laser LD and the 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. The present invention performs closed-loop control on the injection current of the semiconductor laser through a current feedback control loop to achieve the purpose of stabilizing the output optical power. Compared with the prior art, the present invention has the following beneficial effects: simple circuit structure, high reliability, low power consumption, and solves the problems of complex circuits, high costs, and poor stability in the existing system.

Description

Technical Field

[0001] The invention relates to a semiconductor laser automatic current control system, which uses the current of the back detector to form negative feedback to control the laser driving current to achieve the purpose of constant current control, and belongs to the field of automatic control. Background Art

[0002] As an important light source, semiconductor lasers are widely used in many fields. In practical applications, semiconductor lasers are affected by external power supply voltage and temperature changes, resulting in fluctuations in the output power of the device. At this time, if the driving current of the laser is changed blindly, it may exceed the driving threshold current of the laser, causing the laser performance to drop sharply and become damaged and ineffective. Therefore, the stability and modulation accuracy of the semiconductor laser driving circuit are very high.

[0003] Conventional semiconductor laser designs have voltage limiting and current limiting modules to ensure that the laser LD operates within the limit voltage and current range. This design is generally controlled by a single-chip microcomputer to control a high-precision digital / analog converter, and external discrete devices to ensure the stability of the output power. The circuit structure is complex, the cost is high, and the stability is poor. Summary of the invention

[0004] The purpose of the present invention is to ensure the safe and reliable operation of the semiconductor laser.

[0005] In order to achieve the above object, the technical solution of the present invention is to provide a single-wavelength semiconductor laser automatic current control system, wherein the single-wavelength semiconductor laser has a laser LD and a back-light detector PD, the cathode pin of the laser LD and the anode pin of the back-light detector PD are grounded, the anode pin LD+ of the laser LD and the cathode pin PD- of the back-light detector PD are connected to a positive voltage, characterized in that 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:

[0006] The input end of the mirror current source circuit is connected to the constant voltage source DVDD, and has two output ends, and the currents outputted by the two output ends of the mirror current source circuit are in a mirror relationship; one output end of the mirror current source circuit is connected to the anode pin LD+ of the laser LD, and the other output end is connected to the drain of the N-channel MOSFET Q7;

[0007] The reference voltage provided by the reference voltage supply circuit and the voltage difference formed by the photocurrent coupled to the cathode pin PD- of the back-facing photodetector PD flowing through the resistor R2 are jointly loaded to the gate of the N-channel MOSFET Q7. The source of the N-channel MOSFET Q7 is grounded. Then, the opening between the drain and the source of the N-channel MOSFET Q7 is jointly affected by the voltage difference on the resistor R2 and the reference voltage:

[0008] When the external power supply voltage increases suddenly, the forward voltage of the semiconductor laser on its PN junction increases, the injection current of the laser LD increases, and the output laser power of the laser LD increases suddenly; when the ambient temperature decreases, the output power of the laser LD also increases suddenly; the sudden increase in the output power of the laser LD causes the photocurrent coupled to the cathode pin PD- of the back-to-back photodetector PD to increase proportionally, then the opening between the drain and source of the N-channel MOSFET Q7 decreases, so that the current on the anode pin LD+ of the laser LD decreases, the drive current of the laser LD decreases, and the output power of the laser LD decreases; when the external power supply voltage decreases suddenly, the forward voltage of the semiconductor laser on its PN junction decreases, the injection current of the laser LD decreases, and the output laser power of the laser LD suddenly decreases; when the ambient temperature increases, the output power of the laser LD also decreases suddenly; the sudden decrease in the output power of the laser LD causes the photocurrent coupled to the cathode pin PD- of the back-to-back photodetector PD to decrease proportionally, then the N-channel MOSFET The opening between the drain and source of Q7 increases, so that the current on the anode pin LD+ of the laser LD increases, the driving current of the laser LD increases, and the output power of the laser LD increases.

[0009] Preferably, the mirror current source circuit includes a PNP transistor Q5, a PNP transistor Q6, a resistor R3 and a resistor R4; the emitter of the PNP transistor Q5 and the emitter of the PNP transistor Q6 are connected to a constant voltage source DVDD; the base of the PNP transistor Q5 is connected to the base of the PNP transistor Q6; the anode pin LD+ of the laser LD is connected to the collector of the PNP transistor Q5 through the resistor R3; the base and collector of the PNP transistor Q6 are connected, and the drain of the N-channel MOSFET Q7 is connected to the collector of the PNP transistor Q6 through the resistor R4; the collector current I1 of the PNP transistor Q5 and the PNP transistor Q6 is in a mirror relationship with the current I2.

[0010] Preferably, the reference voltage supply circuit includes a resistor R6 and a voltage reference chip U4, one end of the resistor R6 is connected to a constant voltage source DVDD, and the other end is connected to a 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 to a gate of the N-channel MOSFET Q7, and the gate of the N-channel MOSFET Q7 is also connected to a cathode pin PD- of the back-facing light detector PD.

[0011] The present invention performs closed-loop control on the injection current of the semiconductor laser through a current feedback control loop to achieve the purpose of stabilizing the output optical power. Compared with the prior art, the present invention has the following beneficial effects: simple circuit structure, high reliability, low power consumption, and solves the problems of complex circuits, high costs, and poor stability in the prior art. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 The internal structure diagram of the laser selected for use in a semiconductor laser automatic current control system of the present invention;

[0013] Figure 2 The present invention discloses a control circuit diagram of a semiconductor laser automatic current control system. DETAILED DESCRIPTION

[0014] The present invention will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and are not intended to limit the scope of the present invention. In addition, it should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms fall within the scope limited by the appended claims of the application equally.

[0015] like Figure 1 As shown, the laser selected in the present invention comprises a laser LD and a backlight detector PD, wherein the laser LD is used to emit laser light, and the backlight detector PD is used to detect the intensity of the laser light emitted by the laser LD. The backlight detector PD converts part of the received optical power into a monitoring current, which is proportional to the laser power received by the backlight detector PD, thereby controlling the output optical power of the laser LD.

[0016] 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-facing photodetector PD is grounded, the cathode pin of the back-facing photodetector PD is connected to a positive voltage, forming a reverse bias, thereby achieving the purpose of driving the laser diode forward.

[0017] Under normal conditions, the laser LD operates at a set drive current, and the drive 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 end of the back-light detector PD also increases proportionally. When the output optical power of the laser LD decreases, the photocurrent coupled to the feedback end of the back-light detector PD also decreases accordingly.

[0018] The present invention designs a circuit, which converts the photocurrent at the feedback end of the back-to-back photodetector PD into a voltage through a series resistor, and controls the driving current of the laser LD through the voltage change to achieve the purpose of automatic current control. When the output photocurrent of the laser LD decreases, the injection current of the laser LD is increased through 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 is reduced.

[0019] like Figure 2 As shown, a semiconductor laser automatic current control system provided by the present invention includes: PNP transistors Q5, Q6, resistors R3, R4, R2, R6, a voltage reference chip U4, and an N-channel MOSFET Q7.

[0020] The cathode pin PD- of the back-facing 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 the 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.

[0021] PNP transistors Q5, Q6 and resistors R3, R4 form a mirror current source circuit. The anode pin LD+ of the laser LD is connected to the collector (pin 3) of the PNP transistor Q5 through the resistor R3, and the drain (pin 3) of the N-channel MOSFET Q7 is connected to the collector (pin 3) of the PNP transistor Q6 through the resistor R4. The design of the PNP transistor makes the collector currents I1 and I2 of the PNP transistors Q5 and Q6 in a mirror relationship.

[0022] When the external power supply voltage increases suddenly, the forward voltage of the semiconductor laser on its PN junction increases, the injection current of the laser LD increases, and the output laser power of the laser LD increases suddenly. When the ambient temperature decreases, the output power of the laser LD will also increase suddenly. The sudden increase in the output power of the laser LD causes the photocurrent coupled to the cathode pin PD- of the back-facing photodetector PD to increase proportionally. The photocurrent coupled to the cathode pin PD- of the back-facing photodetector PD passes through the resistor R2, and the voltage difference formed across the resistor R2 increases. Since the reference voltage output by the voltage reference chip U4 remains unchanged, the gate (pin 1) voltage of the N-channel MOSFET Q7 decreases, and the opening between the drain (pin 3) and the source (pin 2) of the N-channel MOSFET Q7 decreases, and the drain current decreases. The other end of the mirror current source circuit is connected to the anode pin LD+ of the laser LD, and the current on the anode pin LD+ of the laser LD decreases, the driving current of the laser LD decreases, the power of the laser LD decreases, the light emission weakens, and it returns to the previous light emission intensity.

[0023] When the external power supply voltage suddenly decreases, the forward voltage of the semiconductor laser on its PN junction 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 will also suddenly decrease. The sudden decrease in the output power of the laser LD causes the photocurrent coupled to the cathode pin PD- of the back-facing photodetector PD to also decrease proportionally. The photocurrent coupled to the cathode pin PD- of the back-facing photodetector PD passes through the resistor R2, and the voltage difference formed across the resistor R2 decreases. Since the reference voltage output by the voltage reference chip U4 remains unchanged, the gate (pin 1) voltage of the N-channel MOSFET Q7 increases, and the opening between the drain (pin 3) and the source (pin 2) of the N-channel MOSFET Q7 becomes larger, and the drain current increases. The other end of the mirror current source circuit is connected to the anode pin LD+ of the laser LD, and the current on the anode pin LD+ of the laser LD increases, the driving current of the laser LD increases, the laser power increases, the light emission is enhanced, and the light emission intensity is restored to the previous level. The driving current of the laser LD is controlled by the current of the back-to-back photodetector PD, thereby achieving the purpose of automatic current control of the semiconductor laser.

Claims

1. A single-wavelength semiconductor laser automatic current control system, wherein the single-wavelength semiconductor laser comprises a laser LD and a back-facing photodetector PD, wherein the cathode pin of the laser LD and the anode pin of the back-facing photodetector PD are grounded, and the anode pin LD+ of the laser LD and the cathode pin PD- of the back-facing photodetector PD are connected to a positive voltage, wherein: 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 to the constant voltage source DVDD, and has two output ends, and the currents outputted by the two output ends of the mirror current source circuit are in a mirror relationship; one output end of the mirror current source circuit is connected to the anode pin LD+ of the laser LD, and the other output end is connected to the drain of the N-channel MOSFET Q7; The reference voltage provided by the reference voltage supply circuit and the voltage difference formed by the photocurrent coupled to the cathode pin PD- of the back-facing photodetector PD flowing through the resistor R2 are jointly loaded to the gate of the N-channel MOSFET Q7. The source of the N-channel MOSFET Q7 is grounded. Then, the opening between the drain and the source of the N-channel MOSFET Q7 is jointly affected by the voltage difference on the resistor R2 and the reference voltage: When the external power supply voltage increases suddenly, the forward voltage of the semiconductor laser on its PN junction increases, the injection current of the laser LD increases, and the output laser power of the laser LD increases suddenly; when the ambient temperature decreases, the output power of the laser LD also increases suddenly; the sudden increase in the output power of the laser LD causes the photocurrent coupled to the cathode pin PD- of the back-to-back photodetector PD to increase proportionally, then the opening between the drain and source of the N-channel MOSFET Q7 decreases, so that the current on the anode pin LD+ of the laser LD decreases, the drive current of the laser LD decreases, and the output power of the laser LD decreases; when the external power supply voltage decreases suddenly, the forward voltage of the semiconductor laser on its PN junction decreases, the injection current of the laser LD decreases, and the output laser power of the laser LD suddenly decreases; when the ambient temperature increases, the output power of the laser LD also decreases suddenly; the sudden decrease in the output power of the laser LD causes the photocurrent coupled to the cathode pin PD- of the back-to-back photodetector PD to decrease proportionally, then the N-channel MOSFET The opening between the drain and source of Q7 increases, so that the current on the anode pin LD+ of the laser LD increases, the driving current of the laser LD increases, and the output power of the laser LD increases; The mirror current source circuit includes a PNP transistor Q5, a PNP transistor Q6, a resistor R3 and a resistor R4; the emitter of the PNP transistor Q5 and the emitter of the PNP transistor Q6 are connected to a constant voltage source DVDD; the base of the PNP transistor Q5 is connected to the base of the PNP transistor Q6; the anode pin LD+ of the laser LD is connected to the collector of the PNP transistor Q5 through the resistor R3; the base and collector of the PNP transistor Q6 are connected, and the drain of the N-channel MOSFET Q7 is connected to the collector of the PNP transistor Q6 through the resistor R4; the current I1 of the collector of the PNP transistor Q5 and the PNP transistor Q6 is in a mirror relationship with the current I2; The reference voltage supply circuit includes a resistor R6 and a voltage reference chip U4. One end of the resistor R6 is connected to a constant voltage source DVDD, and the other end is connected to a 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 to a gate of the N-channel MOSFET Q7, and the gate of the N-channel MOSFET Q7 is also connected to a cathode pin PD- of the back-facing light detector PD.

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