Narrow linewidth laser module

Abstract

This invention discloses a narrow-linewidth laser module, belonging to the field of narrow-linewidth lasers. It reduces the phase noise of the narrow-linewidth laser module from three aspects: temperature control circuit, power supply fluctuation, and heat dissipation, enabling it to be better applied in fields with high phase noise requirements, such as marine acoustic detection and modern naval anti-submarine warfare. It mainly includes a lower housing and an upper housing. A circuit board is installed inside the lower housing, and the laser is mounted on the circuit board. The circuit board is mounted on several heat dissipation platforms on the lower housing via a thermally conductive layer. Both the lower and upper housings have laser mounting slots, and the laser is fixedly mounted in the laser mounting slots via the thermally conductive layer. The circuit board includes a temperature control circuit, which includes a load drive circuit and an instrumentation amplifier U1. The instrumentation amplifier U1 is connected to a digital-to-analog converter (DAC) via a Wheatstone bridge. The load drive circuit is connected to both the instrumentation amplifier U1 and the DAC. This invention is mainly used for narrow-linewidth laser modules.

Description

Technical Field

[0001] This invention relates to the field of narrow linewidth lasers, and more particularly to a narrow linewidth laser module. Background Technology

[0002] Narrow-linewidth laser modules are generally used in civilian fields such as lidar and optical communication, where phase noise is not a primary concern. However, when they are fabricated into fiber optic hydrophones for research or military applications such as marine acoustic detection and modern naval anti-submarine warfare, phase noise (especially low-frequency phase noise) becomes one of the most important performance indicators. The quality of phase noise in a narrow-linewidth laser module depends primarily on its internal temperature control circuitry, power supply, and heat dissipation.

[0003] Similar narrow-linewidth laser products generally use mature TEC driver chips (such as MAX1978, ADN8835, LT8722, etc.) for temperature control. These chips are designed primarily for temperature control accuracy and energy conversion efficiency, neglecting phase noise. Therefore, narrow-linewidth laser modules made with these TEC driver chips tend to have high phase noise, as illustrated in the temperature control method and system for a narrow-linewidth laser (publication number CN119070131A). Furthermore, power supply fluctuations interfering with the laser driver circuit and component heating further deteriorate the phase noise, making the modules unsuitable for applications such as marine acoustic detection and modern naval anti-submarine warfare. Summary of the Invention

[0004] The purpose of this invention is to provide a narrow linewidth laser module that reduces the phase noise of the narrow linewidth laser module from three aspects: temperature control circuit, power fluctuation and heat dissipation, so that it can be better applied to fields with high requirements for phase noise, such as marine acoustic detection and modern naval anti-submarine warfare.

[0005] This invention is achieved through the following technical solution:

[0006] A narrow linewidth laser module includes a lower housing and an upper housing. A circuit board is installed inside the lower housing, and a laser and connectors are mounted on the circuit board. The circuit board is mounted on several heat dissipation platforms on the lower housing via a thermally conductive layer. Both the lower and upper housings have laser mounting slots, and the laser is fixedly mounted in the laser mounting slots via the thermally conductive layer. The circuit board includes a temperature control circuit, which includes a load drive circuit and an instrumentation amplifier U1. The instrumentation amplifier U1 is connected to a digital-to-analog converter (DAC) via a Wheatstone bridge. The load drive circuit is connected to the instrumentation amplifier U1 and the DAC. The laser is a narrow linewidth laser, and all four sides of the laser are heat dissipation surfaces, allowing the laser to reach thermal equilibrium more quickly and providing better shock resistance.

[0007] Furthermore, the Wheatstone bridge includes fixed resistors R2, R3, and R4, and a thermistor RT. The digital-to-analog converter (DAC) is connected between fixed resistors R2 and R4 via a current-limiting resistor R1. The current-limiting resistor R1 is also connected to the negative input terminal of the instrumentation amplifier U1. The positive input terminal of the instrumentation amplifier U1 is connected between fixed resistor R3 and the thermistor RT. The output terminal of the instrumentation amplifier U1 is connected to the load drive circuit.

[0008] Furthermore, the load drive circuit includes a PID circuit and an inverting amplifier circuit. The output terminal of the instrumentation amplifier U1 is connected to the PID circuit, the output terminal of the PID circuit is connected to the input terminal of the inverting amplifier circuit, the output terminal of the PID circuit is connected to the positive terminal of the TEC, and the output terminal of the inverting amplifier circuit is connected to the negative terminal of the TEC.

[0009] Furthermore, the load drive circuit includes a PID circuit and an inverting amplifier circuit. The output terminal of the instrumentation amplifier U1 is connected to the PID circuit, the output terminal of the PID circuit is connected to the input terminal of the inverting amplifier circuit, the output terminal of the PID circuit is connected to the positive terminal of the TEC through several emitter followers and a ballast resistor, and the output terminal of the inverting amplifier circuit is connected to the negative terminal of the TEC through several emitter follower circuits.

[0010] Furthermore, the PID circuit includes an operational amplifier U2, with a resistor R10 connected to the negative input terminal of operational amplifier U2, a capacitor C1 connected in parallel with the resistor R10, a resistor R9 and a capacitor C2 connected between the negative input terminal and the output terminal of operational amplifier U2, a resistor R10 connected to the output terminal of instrumentation amplifier U1, a ballast resistor R5 connected to the output terminal of operational amplifier U2, and the ballast resistor R5 connected to the positive terminal of TEC; the inverting amplifier circuit includes an operational amplifier U3, with the output terminal of operational amplifier U2 connected to the negative input terminal of operational amplifier U3 through a resistor R12, a resistor R11 connected between the negative input terminal and the output terminal of operational amplifier U3, a ballast resistor R7 connected to the output terminal of operational amplifier U3, and the ballast resistor R7 connected to the negative terminal of TEC.

[0011] Furthermore, the PID circuit includes an operational amplifier U2, with a resistor R10 connected to the negative input terminal of operational amplifier U2, a capacitor C1 connected in parallel with the resistor R10, a resistor R9 and a capacitor C2 connected between the negative input terminal and the output terminal of operational amplifier U2, an instrumentation amplifier U1 with a resistor R10 connected to the output terminal, an operational amplifier U2 with an input terminal connected to several emitter follower circuits I, and a ballast resistor R5 connected to the output terminal of operational amplifier U2. Both the ballast resistor R5 and the output terminal of emitter follower circuits I are connected to the positive terminal of the TEC. The inverting amplifier circuit includes an operational amplifier U3, with the output terminal of operational amplifier U2 connected to the negative input terminal of operational amplifier U3 via a resistor R12, a resistor R11 connected between the negative input terminal and the output terminal of operational amplifier U3, a ballast resistor R7 connected to the output terminal of operational amplifier U3, and the output terminal of operational amplifier U3 connected to the input terminal of several emitter follower circuits II. Both the ballast resistor R7 and the output terminal of emitter follower circuits II are connected to the negative terminal of the TEC.

[0012] Furthermore, the emitter follower circuit I includes an emitter follower I and a ballast resistor R6. The output terminal of operational amplifier U2 is connected to the positive input terminal of emitter follower I, and the output terminal of emitter follower I is connected to the ballast resistor R6. The ballast resistor R6 is connected to the positive terminal of TEC. The emitter follower circuit II includes an emitter follower II and a ballast resistor R8. The output terminal of operational amplifier U3 is connected to the positive input terminal of emitter follower II, and the output terminal of emitter follower II is connected to the ballast resistor R8. The ballast resistor R8 is connected to the negative terminal of TEC.

[0013] Furthermore, it also includes a laser driving circuit, which includes a transistor Q1 and a rectifier filter circuit. The laser is connected to the collector of the transistor Q1 through the rectifier filter circuit. The base of the transistor Q1 is connected to the output terminal of the operational amplifier U21 through a resistor R22. The positive input terminal of the operational amplifier U21 is connected to a current control signal. The negative input terminal of the operational amplifier U21 is connected to a sampling resistor R23. The emitter of the transistor Q1 is connected to the sampling resistor R23.

[0014] Furthermore, the rectifier filter circuit includes a switching diode D1 and an inductor L1. The laser is connected in parallel with a switching diode D1 and a capacitor C22. One end of the laser is connected to an inductor L1, and the other end of the laser is connected to an RC filter circuit composed of a resistor R21 and a capacitor C21. Both the inductor L1 and the RC filter circuit are connected to the collector of the transistor Q1.

[0015] Furthermore, the thermally conductive layer is a thermally conductive silicone pad and / or thermally conductive grease. The back of the operational amplifier in the circuit board temperature control circuit is a restricted area. The restricted area is placed on a heat sink through a thermally conductive silicone pad and / or thermally conductive grease to conduct away the heat generated by the operational amplifier during operation and reduce the thermal noise of the operational amplifier. The surface of the operational amplifier is coated with conformal coating for protection, while the restricted area is not coated with conformal coating to protect the circuit from damage under vibration, humidity, salt spray, and high temperature conditions.

[0016] Compared with the prior art, the beneficial effects of the present invention are:

[0017] 1. A low-noise temperature control circuit based on an operational amplifier (especially phase noise in the low-frequency band) is provided, which solves the problem of high phase noise in commonly used TEC driver chips; to address the deficiency of insufficient driving capability of operational amplifiers, double or even multiple times the driving capability can be obtained by adding an RF follower.

[0018] 2. The interference of power supply fluctuations on the laser driver circuit is suppressed by the rectifier and filter circuit.

[0019] 3. The circuit board is mounted on the heat sink via a thermally conductive layer. This allows the heat generated by the operational amplifier during operation to be dissipated without affecting the application of conformal adhesive to the components, thereby reducing the thermal noise of the operational amplifier.

[0020] 4. The laser is installed in the laser mounting slot. Its heat dissipation and fixing method allows the laser to reach thermal equilibrium more quickly and has better shock resistance. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the structure of the present invention;

[0022] Figure 2 This is a schematic diagram of the structure of the present invention;

[0023] Figure 3 This is a schematic diagram of the circuit principle of Embodiment 2 of the present invention;

[0024] Figure 4 This is a schematic diagram of the circuit principle of a set of emitter follower circuits in Embodiment 3 of the present invention;

[0025] Figure 5 This is a detailed circuit diagram of an emitter follower circuit in Embodiment 3 of the present invention;

[0026] Figure 6 This is a schematic diagram of the circuit principle of two sets of emitter follower circuits in Embodiment 3 of the present invention;

[0027] Figure 7 This is a circuit diagram of the laser driving circuit of the present invention.

[0028] In the diagram: 1. Upper housing; 2. Circuit board; 3. Laser; 4. Connector; 5. Laser mounting slot; 6. Heat sink; 7. Lower housing. Detailed Implementation

[0029] The present invention will now be further described in conjunction with the accompanying drawings.

[0030] Example 1

[0031] like Figure 1 – Figure 2 As shown, a narrow linewidth laser module includes a lower housing 7 and an upper housing 1. A circuit board 2 is installed inside the lower housing 7. The circuit board 2 houses a laser 3 and connectors 4 (existing technology). The circuit board 2 is mounted on several heat sinks 6 on the lower housing 7 via a thermally conductive layer. Both the lower housing 7 and the upper housing 1 have laser mounting slots 5. The laser 3 is fixedly mounted in the laser mounting slots 5 via the thermally conductive layer. The circuit board 2 includes a temperature control circuit, which includes a load drive circuit and an instrumentation amplifier U1. The instrumentation amplifier U1 is connected to a digital-to-analog converter (DAC) via a Wheatstone bridge. The load drive circuit is connected to both the instrumentation amplifier U1 and the DAC. The laser 3 is a narrow linewidth laser, with all four sides serving as heat dissipation surfaces, allowing the laser to reach thermal equilibrium more quickly and providing better shock resistance. The Wheatstone bridge includes fixed resistors R2, R3, and R4. The thermistor RT and the digital-to-analog converter (DAC) are connected between fixed resistors R2 and R4 via a current-limiting resistor R1. The current-limiting resistor R1 is also connected to the negative input terminal of the instrumentation amplifier U1. The positive input terminal of the instrumentation amplifier U1 is connected between a fixed resistor R3 and the thermistor RT. The output terminal of the instrumentation amplifier U1 is connected to the load drive circuit. The thermal conductive layer is a thermally conductive silicone pad and / or thermally conductive grease. The back of the operational amplifier in the temperature control circuit of circuit board 2 is a restricted area (the restricted area refers to the area where no components are placed). The restricted area is placed on the heat sink 6 with a thermally conductive silicone pad and / or thermally conductive grease to conduct away the heat generated by the operational amplifier during operation and reduce the thermal noise of the operational amplifier. The operational amplifier and other components are protected with conformal coating. The restricted area is not coated with conformal coating to protect the circuit from damage under conditions such as vibration, humidity, salt spray, and high temperature.

[0032] Example 2

[0033] like Figure 3As shown, a narrow linewidth laser module includes a load drive circuit comprising a PID circuit and an inverting amplifier circuit. The output of an instrumentation amplifier U1 is connected to the PID circuit, the output of the PID circuit is connected to the input of the inverting amplifier circuit, the output of the PID circuit is connected to the positive terminal of a TEC, and the output of the inverting amplifier circuit is connected to the negative terminal of the TEC. The PID circuit includes an operational amplifier U2, the negative input of which is connected to a resistor R10, and a capacitor C1 is connected in parallel with the resistor R10. A connection is also established between the negative input and the output of the operational amplifier U2. The circuit includes a resistor R9 and a capacitor C2. The output of instrumentation amplifier U1 is connected to resistor R10, and the output of operational amplifier U2 is also connected to a ballast resistor R5, which is connected to the positive terminal of the TEC. The inverting amplifier circuit includes operational amplifier U3. The output of operational amplifier U2 is connected to the negative input of operational amplifier U3 via resistor R12. A resistor R11 is connected between the negative input and output of operational amplifier U3. The output of operational amplifier U3 is connected to a ballast resistor R7, which is connected to the negative terminal of the TEC. Other aspects are the same as in Example 1. In practical applications, if the required drive current is less than the maximum output current of an operational amplifier, the emitter follower can be removed (and ballast resistors R5 and R8 can be removed simultaneously).

[0034] Example 3

[0035] like Figure 4 – Figure 6As shown, a narrow linewidth laser module includes a load drive circuit comprising a PID circuit and an inverting amplifier circuit. The output of an instrumentation amplifier U1 is connected to the PID circuit, and the output of the PID circuit is connected to the input of the inverting amplifier circuit. The output of the PID circuit is connected to the positive terminal of a TEC via several emitter followers and a ballast resistor. The output of the inverting amplifier circuit is connected to the negative terminal of the TEC via several emitter follower circuits. The PID circuit includes an operational amplifier U2. A resistor R10 is connected to the negative input of operational amplifier U2, and a capacitor C1 is connected in parallel with the resistor R10. A resistor R9 and a capacitor C2 are also connected between the negative input and the output of operational amplifier U2. The output of instrumentation amplifier U1 is connected to the resistor R10. The output of operational amplifier U2 is connected to the input of several emitter follower circuits I, and a ballast resistor R5 is also connected to the output of operational amplifier U2. Both the ballast resistor R5 and the output of emitter follower circuits I are connected to the positive terminal of the TEC. The inverting amplifier... The circuit includes an operational amplifier U3. The output of operational amplifier U2 is connected to the negative input of operational amplifier U3 through resistor R12. Resistor R11 is connected between the negative input and output of operational amplifier U3. Ballast resistor R7 is connected to the output of operational amplifier U3. The output of operational amplifier U3 is connected to the input of several emitter follower circuits II. Ballast resistor R7 and the output of emitter follower circuits II are both connected to the negative terminal of TEC. The emitter follower circuit I includes an emitter follower I and a ballast resistor R6. The output of operational amplifier U2 is connected to the positive input of emitter follower I. The output of emitter follower I is connected to the ballast resistor R6. Ballast resistor R6 is connected to the positive terminal of TEC. The emitter follower circuit II includes an emitter follower II and a ballast resistor R8. The output of operational amplifier U3 is connected to the positive input of emitter follower II. The output of emitter follower II is connected to the ballast resistor R8. Ballast resistor R8 is connected to the negative terminal of TEC. Other aspects are the same as in Embodiment 1. Figure 4 and Figure 5 The diagram shows the output of operational amplifier U2 connected to an emitter follower circuit I, and the output of operational amplifier U3 connected to an emitter follower circuit II. If a large drive current is required... Figure 6 The given circuit connects two sets of emitter followers (with a ballast resistor added to the output of each emitter follower), which provides three times the driving capability without emitter followers; the same principle applies to connecting three or more sets.

[0036] Example 4

[0037] like Figure 7As shown, a narrow linewidth laser module further includes a laser driving circuit. The laser driving circuit includes a transistor Q1 and a rectifier-filter circuit. The laser 3 is connected to the collector of transistor Q1 through the rectifier-filter circuit. The base of transistor Q1 is connected to the output of operational amplifier U21 through resistor R22. The positive input of operational amplifier U21 is connected to a current control signal, and the negative input of operational amplifier U21 is connected to a sampling resistor R23. The emitter of transistor Q1 is connected to the sampling resistor R23. The rectifier-filter circuit includes a switching diode D1 and an inductor L1. The laser 3 is connected in parallel with the switching diode D1 and the capacitor C22. One end of the laser 3 is connected to the inductor L1, and the other end of the laser 3 is connected to an RC filter circuit composed of resistor R21 and capacitor C21. Both the inductor L1 and the RC filter circuit are connected to the collector of transistor Q1. The rest is the same as in Embodiment 1. Switching diode D1 and capacitor C22 are used to prevent sudden voltage pulses from damaging laser 3. Inductor L1 further stabilizes the current flowing through laser 3. The RC filter circuit composed of resistor R21 and capacitor C21 can be used to remove interference signals of fixed frequency.

[0038] Working principle (based on) Figure 5 For example:

[0039] 1) The digital-to-analog converter (DAC) outputs a temperature control voltage V1, which corresponds to the target temperature.

[0040] 2) The thermistor RT is located inside the laser. The value of the thermistor RT corresponds to the current temperature, and Vcc is the power supply. A pair of voltages V2 and V3 are obtained using a Wheatstone bridge. According to Kirchhoff's laws, V2 = Vcc*RT / (R3+RT), V3 = (V1*R2*R4+Vcc*R1*R4) / (R1*R2+R2*R4+R1*R4). Since the power supply Vcc and the resistors R1 and R4 are fixed values, voltage V2 can be calculated from the thermistor RT, reflecting the current temperature. Voltage V3 can be calculated from voltage V1, reflecting the target temperature. If the current temperature is higher than the target temperature, then V2 < V3; if the current temperature is equal to the target temperature, then V2 = V3; if the current temperature is lower than the target temperature, then V2 > V3.

[0041] 3) Input voltages V2 and V3 into the positive and negative input terminals of the instrumentation amplifier, respectively, and apply a reference voltage Vref to the instrumentation amplifier to obtain the output voltage V4 = V2 - V3 + Vref. Clearly, voltage V4 reflects the difference between the current temperature and the target temperature. The reference voltage Vref is introduced here to provide a positive bias voltage to voltage V4, ensuring that the value of voltage V4 is always positive.

[0042] 4) Inputting voltage V4 into the PID circuit yields output voltage V5. The PID circuit is a proportional-integral-derivative control circuit, which improves the stability and reliability of temperature control. Capacitors C1 and C2 are known capacitances, and resistors R9 and R10 are known resistances; therefore, the following can be calculated: Since V4 = V2 - V3 + Vref, therefore

[0043] 5) Voltage V5 is amplified by an inverting amplifier to obtain voltage V6, where resistors R11 and R12 are known resistors. Since the PID circuit and the inverting amplifier circuit share a common reference voltage Vref, V6 can be calculated as (Vref - V5) * R11 / R12 + Vref.

[0044] 6) Connecting emitter follower circuit I below the PID circuit and emitter follower circuit II below the inverting amplifier is to compensate for the shortcomings of the operational amplifier's small output current and insufficient driving capability. These two emitter followers are also made using operational amplifiers, such as... Figure 5 Operational amplifiers U4 and U5 are used in the circuit. Adding an emitter follower at each end approximately doubles the driving capability without the emitter follower. Ballast resistors R5-R8 have equal resistance values, approximately 10% of the equivalent resistance of the TEC. For ease of calculation, we assume the equivalent resistance of the TEC is Rt, then R5 = R6 = R7 = R8 = 10% * Rt. Resistors R5 and R6 balance the output voltage of the PID controller and emitter follower I, while resistors R7 and R8 balance the output voltage of the inverting operational amplifier U3 and emitter follower II. The output voltage of the emitter follower equals the input voltage; therefore, the output voltage of emitter follower I is V5, and the output voltage of emitter follower II is V6. The driving current of the entire temperature control circuit can then be calculated as It = (V5 - V6) / (1.1 * Rt).

[0045] 7) When It > 0, the TEC cools the laser; when It < 0, the TEC heats the laser. The larger the absolute value of It, the greater the heating / cooling power. The driving capability of the entire load drive circuit mainly depends on the maximum output current of operational amplifiers U2-U5. The driving capability for cooling (i.e., the maximum positive current flowing through the TEC) is equal to the sum of the maximum output currents of operational amplifiers U2 and U4, and the driving capability for heating (i.e., the maximum negative current flowing through the TEC) is equal to the sum of the maximum output currents of operational amplifiers U3 and U5.

Claims

1. A narrow linewidth laser module comprising a lower housing (7) and an upper housing (1), characterized in that: The lower shell (7) is provided with a circuit board (2), and the circuit board (2) is provided with a laser (3); the circuit board (2) is installed on a plurality of heat dissipation tables (6) of the lower shell (7) through a heat conduction layer; the lower shell (7) and the upper shell (1) are both provided with a laser mounting groove (5), and the laser (3) is fixedly installed in the laser mounting groove (5) through a heat conduction layer; the circuit board (2) comprises a temperature control circuit, and the temperature control circuit comprises a load driving circuit and an instrument amplifier U1; the instrument amplifier U1 is connected with a digital-analog converter DAC through a Wheatstone bridge; the load driving circuit is connected with the instrument amplifier U1 and a TEC respectively; the laser (3) is a narrow line width laser; the Wheatstone bridge comprises fixed resistors R2, R3 and R4 and a thermistor RT; the digital-analog converter DAC is connected between the fixed resistor R2 and the fixed resistor R4 through a current limiting resistor R1; the current limiting resistor R1 is also connected with a negative input end of the instrument amplifier U1; a positive input end of the instrument amplifier U1 is connected between the fixed resistor R3 and the thermistor RT; an output end of the instrument amplifier U1 is connected with the load driving circuit; the load driving circuit comprises a PID circuit and a reverse amplifier circuit; the output end of the instrument amplifier U1 is connected with the PID circuit; an output end of the PID circuit is connected with an input end of the reverse amplifier circuit; the output end of the PID circuit is connected with a positive electrode of the TEC through a plurality of emitter followers and ballast resistors; an output end of the reverse amplifier circuit is connected with a negative electrode of the TEC through a plurality of emitter follower circuits; the PID circuit comprises an operational amplifier U2; the operational amplifier U2 is connected with a resistor R10; the resistor R10 is connected with a capacitor C1 in parallel; the operational amplifier U2 is also connected with a resistor R9 and a capacitor C2 between the negative input end and the output end of the operational amplifier U2; the output end of the instrument amplifier U1 is connected with the resistor R10; the output end of the operational amplifier U2 is connected with input ends of a plurality of emitter follower circuits I; the output end of the operational amplifier U2 is also connected with a ballast resistor R5; the ballast resistor R5 and output ends of the emitter follower circuits I are both connected with the positive electrode of the TEC; the reverse amplifier circuit comprises an operational amplifier U3; the output end of the operational amplifier U2 is connected with a negative input end of the operational amplifier U3 through a resistor R12; the operational amplifier U3 is connected with a resistor R11 between the negative input end and the output end of the operational amplifier U3; the output end of the operational amplifier U3 is connected with a ballast resistor R7; the output end of the operational amplifier U3 is connected with input ends of a plurality of emitter follower circuits II; the ballast resistor R7 and output ends of the emitter follower circuits II are both connected with the negative electrode of the TEC.

2. The narrow-linewidth laser module of claim 1, wherein: The load driving circuit comprises the PID circuit and the reverse amplifier circuit; the output end of the instrument amplifier U1 is connected with the PID circuit; the output end of the PID circuit is connected with an input end of the reverse amplifier circuit; the output end of the PID circuit is connected with the positive electrode of the TEC; and the output end of the reverse amplifier circuit is connected with the negative electrode of the TEC.

3. The narrow-linewidth laser module of claim 1, wherein: The PID circuit comprises an operational amplifier U2, the negative input end of the operational amplifier U2 is connected with a resistor R10, the resistor R10 is connected in parallel with a capacitor C1, the negative input end of the operational amplifier U2 is also connected with a resistor R9 and a capacitor C2 between the output end of the operational amplifier U2, the output end of the operational amplifier U1 is connected with the resistor R10, the output end of the operational amplifier U2 is also connected with a ballast resistor R5, and the ballast resistor R5 is connected with the positive pole of the TEC; the inverse amplifier circuit comprises an operational amplifier U3, the output end of the operational amplifier U2 is connected with the negative input end of the operational amplifier U3 through a resistor R12, the negative input end of the operational amplifier U3 is connected with a resistor R11 between the output end of the operational amplifier U3, the output end of the operational amplifier U3 is connected with a ballast resistor R7, and the ballast resistor R7 is connected with the negative pole of the TEC.

4. The narrow-linewidth laser module of claim 1, wherein: The emitter follower circuit I comprises an emitter follower I and a ballast resistor R6, the output end of the operational amplifier U2 is connected with the positive input end of the emitter follower I, the output end of the emitter follower I is connected with the ballast resistor R6, and the ballast resistor R6 is connected with the positive pole of the TEC; the emitter follower circuit II comprises an emitter follower II and a ballast resistor R8, the output end of the operational amplifier U3 is connected with the positive input end of the emitter follower II, the output end of the emitter follower II is connected with the ballast resistor R8, and the ballast resistor R8 is connected with the negative pole of the TEC.

5. The narrow-linewidth laser module of claim 1, wherein: The laser driving circuit comprises a transistor Q1 and a rectifier filter circuit, the laser (3) is connected with the collector of the transistor Q1 through the rectifier filter circuit, the base of the transistor Q1 is connected with the output end of an operational amplifier U21 through a resistor R22, the positive input end of the operational amplifier U21 is connected with a current control signal, the negative input end of the operational amplifier U21 is connected with a sampling resistor R23, and the emitter of the transistor Q1 is connected with the sampling resistor R23.

6. The narrow-linewidth laser module of claim 5, wherein: The rectifier filter circuit comprises a switching diode D1 and an inductor L1, the laser (3) is connected in parallel with the switching diode D1 and a capacitor C22 respectively, one end of the laser (3) is connected with the inductor L1, the other end of the laser (3) is connected with an RC filter circuit composed of a resistor R21 and a capacitor C21, and the inductor L1 and the RC filter circuit are both connected with the collector of the transistor Q1.

7. The narrow-linewidth laser module of claim 1, wherein: The heat-conducting layer is a heat-conducting silica gel pad and / or a heat-conducting silicone grease, the back of the operational amplifier in the temperature control circuit of the circuit board (2) is a forbidden cloth area, the forbidden cloth area is placed on the heat-dissipating table (6) through the heat-conducting silica gel pad and / or the heat-conducting silicone grease below, so as to conduct the heat generated by the operational amplifier during operation, reduce the thermal noise of the operational amplifier, and the surface of the operational amplifier is coated with a waterproof glue for protection.

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