Semiconductor laser double-layer temperature control system

Abstract

The invention discloses a semiconductor laser double-layer temperature control system, which is characterized in that firstly, digital PID temperature control is carried out on an external heat sink of a laser, the set voltage of an outer thermistor and an outer slide rheostat is converted by an ADC conversion circuit and then is sent to an STM32, and control information is sent to a DAC conversion circuit after digital PID operation; and the DAC conversion circuit outputs a control signal to a CTLI pin of the MAX1978 after analog-to-digital conversion, and generates a driving current to control an outer TEC, thereby realizing coarse stabilization of the external temperature of the laser. The inner layer adopts a simulation PID control mode, an inner layer MAX1978 chip reads voltage values of a thermistor and a slide rheostat in the laser and then carries out simulation PID network operation, current is output to drive a TEC in the laser, and therefore high-stability temperature control of the laser is achieved.

Description

Technical Field

[0001] The present invention relates to the technical fields of laser technology and quantum precision measurement laser frequency technology, and particularly relates to a double-layer temperature control system for a semiconductor laser. Background Art

[0002] In recent years, quantum technology has played an important role in more and more fields. Especially in quantum precision measurement, instruments such as atomic clocks, atomic magnetometers, and atomic spin inertial measurement instruments have developed very rapidly, providing strong support for the development of the national economy and national defense construction. As an important component for optical pumping of atomic ensembles and high-precision signal detection in quantum precision measurement instruments, the performance of semiconductor lasers is closely related to the precision performance of the measurement system. And the temperature control system of semiconductor lasers determines the accuracy and stability of the output wavelength of the lasers, which is the key to developing high-performance lasers.

[0003] In previous laser temperature control research, most have adopted single-layer analog or digital control, that is, only the laser itself is temperature-controlled. The temperature of the laser chip can be achieved within a short time under laboratory conditions, but the long-term stability is poor, and it is easily interfered by external environmental temperature fluctuations, and long-term stable operation cannot be achieved. When using analog control, the temperature control accuracy is high, and high-stability temperature control can be achieved when the external environmental temperature changes little, but the disadvantage is that the PID parameters are not easy to adjust. The PID parameters of digital control are easy to adjust but are prone to generating large noise and are not suitable for high-precision temperature control. Most commercially available lasers on the market only involve single-layer temperature control of the lasers. The volume of the controller is large, which is not conducive to the miniaturization and integration of the control system, and the cost is relatively high. Summary of the Invention

[0004] The purpose of the present invention is to design a double-layer temperature control system for a semiconductor laser to solve the problems raised in the background art. First, use digital PID to control the heat sink outside the laser to achieve rough temperature stability, create a stable ambient temperature for the laser, and then use analog PID to control the TEC inside the semiconductor laser to achieve precise temperature stability of the laser chip, thereby improving the accuracy and stability of the output wavelength of the laser. To support the requirements for high-precision and high-stability wavelengths output by semiconductor lasers in quantum precision measurement fields such as SERF atomic gyroscopes and magnetometers.

[0005] The specific technical solution of the present invention is as follows: A double-layer temperature control system for a semiconductor laser, including an inner-layer temperature control circuit and an outer-layer temperature control circuit. The inner-layer temperature control circuit is used to achieve precise and stable temperature of the laser chip inside the laser, and the outer-layer temperature control circuit is used to roughly stabilize the temperature of the heat sink outside the laser. The inner-layer temperature control circuit includes a semiconductor laser, an inner-layer sliding rheostat, and an inner-layer MAX1978 chip. The semiconductor laser includes an inner-layer thermistor, a laser chip, and an inner-layer semiconductor refrigeration chip TEC. The inner-layer MAX1978 chip is connected to the inner-layer thermistor and the inner-layer sliding rheostat, and then forms an analog PID compensation network with resistor-capacitor components and outputs a control voltage to the inner-layer TEC to achieve inner-layer temperature control. At the same time, the inner-layer MAX1978 chip is sequentially connected to an ADC conversion circuit, a microcontroller STM32, and a host computer to achieve inner-layer measurement and set temperature. The outer-layer temperature control circuit includes the heat sink outside the laser, an outer-layer thermistor, an outer-layer semiconductor refrigeration chip TEC, an outer-layer sliding rheostat, and an outer-layer MAX1978 chip. First, the outer-layer MAX1978 chip is connected to the outer-layer thermistor and the outer-layer sliding rheostat, and then sequentially connected to an ADC conversion circuit, a microcontroller STM32, and a host computer to achieve outer-layer measurement and set temperature. After digital PID operation in the microcontroller STM32, a control signal is output to a DAC conversion circuit, the outer-layer MAX1978 chip, and the outer-layer TEC in sequence to achieve outer-layer temperature control.

[0006] The present invention has the following beneficial effects:

[0007] Through the combination of digital PID control in the outer layer and analog PID control in the inner layer, high-precision temperature control of the semiconductor laser can be achieved. The outer-layer temperature control circuit can quickly respond to changes in the ambient temperature and provide a relatively stable external environment for the laser; the inner-layer temperature control circuit further precisely controls the temperature inside the laser to ensure the stability of the output wavelength of the laser, meeting the requirements for the wavelength stability of the laser light source in high-precision application scenarios such as atomic spin inertia measurement instruments. Description of the Drawings

[0008] Figure 1 It is the block diagram of the outer-layer temperature control;

[0009] Figure 2 It is the block diagram of the inner-layer temperature control;

[0010] Figure 3 It is the schematic diagram of the temperature measurement and setting circuit;

[0011] Figure 4 It is the schematic diagram of the inner-layer analog PID control network circuit;

[0012] Figure 5 It is the schematic diagram of the peripheral circuit of the inner-layer / outer-layer MAX1978 chip;

[0013] Figure 6 It is the schematic diagram of the peripheral circuit of the microcontroller STM32F103C8T6;

[0014] Figure 7 It is the schematic diagram of the analog-to-digital conversion circuit of ADS7067;

[0015] Figure 8 It is the schematic diagram of the digital-to-analog conversion circuit of AD5541;

[0016] Figure 9 It is the schematic diagram of the power supply and reference voltage circuit;

[0017] Figure 10 It is the block diagram of the double-layer temperature control system. Specific implementation manners

[0018] In order to make the objectives, technical solutions and advantages of the present invention clearer and more understandable, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0019] The present invention provides a double-layer temperature control system for a semiconductor laser. First, the digital PID is used to control the heat sink outside the laser to achieve coarse temperature stability, creating a stable ambient temperature for the laser. Then, the analog PID is used to control the TEC inside the semiconductor laser to achieve fine temperature stability of the laser chip, thereby improving the accuracy and stability of the output wavelength of the laser. To support the requirements for high-precision and high-stability wavelengths of semiconductor lasers in quantum precision measurement fields such as SERF atomic gyroscopes and magnetometers.

[0020] The present invention discloses a double-layer temperature control system for a semiconductor laser. In this system, the target temperatures of the inner and outer layers of the laser are set through two sliding rheostats. Thermistors are used as temperature sensors to collect temperatures in both the inner and outer layers. The temperatures are read by the STM32 chip after being converted by the ADC. The actuators for temperature control in both the inner and outer layers are semiconductor refrigeration chips TEC. First, the digital PID is used to control the temperature of the heat sink outside the laser. The voltage set by the outer-layer thermistor and the outer-layer sliding rheostat is sent to the STM32 chip after being converted by the ADC. After digital PID operation, control information is sent to the DAC. The DAC outputs a control signal to the CTLI pin of the MAX1978 chip after analog-to-digital conversion, generating a driving current to control the outer-layer TEC, thereby achieving coarse stability of the temperature outside the laser. The inner layer adopts the analog PID control method. After the inner-layer MAX1978 chip reads the voltage values of the thermistor and the sliding rheostat inside the laser, it performs analog PID network operation and outputs a current to drive the inner-layer TEC inside the laser, thereby achieving high-stability temperature control of the laser.

[0021] As Figure 10As shown, in the embodiment of the present disclosure, the double-layer temperature control system of the semiconductor laser includes an inner-layer temperature control circuit and an outer-layer temperature control circuit. The inner-layer temperature control circuit is used to achieve precise and stable temperature of the laser chip, and the outer-layer temperature control circuit is used to achieve coarse and stable temperature of the external heat sink of the laser. The inner-layer temperature control circuit includes a semiconductor laser, an inner-layer sliding rheostat, and an inner-layer MAX1978 chip. The semiconductor laser includes an inner-layer thermistor, a laser chip, and an inner-layer TEC. First, the inner-layer MAX1978 chip is connected to the inner-layer thermistor and the inner-layer sliding rheostat, and then forms an analog PID compensation network with resistor-capacitor components and outputs a control voltage to the inner-layer TEC to achieve inner-layer temperature control. At the same time, the inner-layer MAX1978 chip is sequentially connected to an ADC chip, a microcontroller STM32, and a host computer to achieve inner-layer measurement and set temperature. The outer-layer temperature control circuit includes the external heat sink of the laser, an outer-layer thermistor, an outer-layer TEC, an outer-layer sliding rheostat, and an outer-layer MAX1978 chip. First, the outer-layer MAX1978 chip is connected to the outer-layer thermistor and the outer-layer sliding rheostat, and then is sequentially connected to an ADC conversion circuit, a microcontroller STM32, and a host computer to achieve outer-layer measurement and set temperature. After digital PID operation in the microcontroller STM32, a control signal is output to a DAC conversion circuit, the outer-layer MAX1978 chip, and the outer-layer TEC in sequence to achieve outer-layer temperature control.

[0022] The specific control flow block diagram of the outer-layer temperature control circuit is as Figure 1 shown. The outer-layer temperature control circuit adopts digital PID control to achieve coarse temperature stability through the microcontroller STM32. The outer-layer temperature control circuit includes an outer-layer thermistor, an outer-layer sliding rheostat, an outer-layer TEC, an outer-layer MAX1978 chip, and a DAC conversion circuit. The outer-layer thermistor is used to measure the temperature of the laser and the external heat sink. The outer-layer sliding rheostat is used to set the target temperature of the external heat sink. The outer-layer TEC is used as a temperature control actuator for heating or cooling the external heat sink. The ADC conversion circuit is used to collect the temperature of the external heat sink and the set temperature of the outer-layer sliding rheostat. After digital PID operation by the STM32 chip, a control signal is output to the DAC conversion circuit. The DAC conversion circuit converts it into a control voltage and provides it to the outer-layer MAX1978 chip. The outer-layer MAX1978 chip, as the core temperature control component, provides a high-precision and low-noise control current to the outer-layer TEC to achieve heating or cooling of the external heat sink of the laser.

[0023] The specific control flow block diagram of the temperature of the inner-layer temperature control circuit is as Figure 2As shown in the figure, the inner layer temperature control circuit adopts analog PID control, and realizes precise temperature stabilization through an analog PID compensation network. The inner layer temperature control circuit mainly includes an inner layer thermistor in the semiconductor laser, a laser chip, an inner layer TEC, an inner layer sliding rheostat, and a MAX1978 chip. The inner layer thermistor is used to measure the temperature of the laser chip, the inner layer sliding rheostat is used to set the target temperature of the laser chip, and the inner layer TEC is used as a temperature control actuator for heating or cooling the laser chip. The inner layer MAX1978 chip is used as the core temperature control component, and together with external resistor-capacitor components, it forms an analog PID compensation network. The specific process is that the inner layer thermistor and the inner layer sliding rheostat are connected to the inner layer MAX1978 chip and then output a differential voltage, which is then output as a control voltage through the analog PID network and returned to the inner layer MAX1978 chip. The inner layer MAX1978 chip outputs a high-precision and low-noise control current to the inner layer TEC to achieve heating or cooling of the laser chip.

[0024] The temperature measurement and setting circuit is as Figure 3 shown. The temperature measurement and setting circuit is used to set the inner layer temperature, the outer layer temperature, the actual temperature of the laser chip, and the actual temperature of the heat sink. The outer layer and the inner layer temperature measurement and setting circuits adopt the same circuit design. The inner layer thermistor and the outer layer thermistor are respectively used to detect the actual temperatures of the laser chip inside the laser and its external heat sink. The inner layer thermistor has been encapsulated inside the semiconductor laser as a temperature sensor to measure the temperature of the laser chip, and its temperature coefficient is 3892. The outer layer thermistor used between the external heat sink of the laser and the semiconductor laser housing has a resistance value of 10 kΩ at 25 °C, and the temperature coefficient is 3380. The formulas for the inner layer and the outer layer thermistors are the same, but the values are different. The calculation formula for the thermistor is as follows:

[0025] ,

[0026] where is the resistance value of the inner layer or outer layer thermistor at the actual temperature of (in units of K); is its resistance value at (usually 298.15 K (25 °C)), is the temperature coefficient of the inner layer or outer layer thermistor material;

[0027] As Figure 3, for the MAX1978 chip shown, the FB- and FB+ pins respectively correspond to the measured temperature voltage and the set temperature voltage. These two voltages are respectively connected to the inverting and non-inverting inputs of the differential gain circuit. The temperature setting is achieved by the series voltage division formed by the reference voltage VREF and the sliding rheostat. Adjusting the sliding rheostat can change the target temperature; the temperature measurement is achieved by the series voltage division of the reference voltage VREF, the voltage dividing resistor, and the thermistor. The temperature causes the resistance value of the thermistor to change, thereby changing its voltage division. One end of the VREF pin of the MAX1978 chip is connected to the NTC thermistor after passing through the voltage dividing resistor, and the other end is connected to the FB- pin of the MAX1978 chip. The voltage division of the thermistor can measure the actual temperature; the VREF pin of the MAX1978 chip is also connected to the sliding rheostat, and the variable end of the sliding rheostat is connected to the FB+ pin of the MAX1978 chip after passing through a resistor. The variable voltage of the sliding rheostat can set the target temperature. The specific calculation formula is as follows:

[0028] The voltage division of the thermistor for both the inner layer and the outer layer calculations is this formula:

[0029] ,

[0030] The voltage division of the temperature setting resistor:

[0031] ,

[0032] Among them, is the reference voltage (generated internally by the MAX1978 chip, which is 1.5 V), is the resistance value of the inner layer or outer layer thermistor, is the resistance value of the inner layer or outer layer sliding rheostat, is the resistance value of the voltage dividing resistor.

[0033] The actual temperature measured by the inner layer or outer layer thermistor:

[0034] ,

[0035] The inner layer temperature control circuit adopts the analog temperature control method, and the outer layer temperature control circuit adopts the digital temperature control method. The principle of analog temperature control of the inner layer temperature control circuit is as follows, and its circuit schematic diagram is shown in Figure 4: Figure 3The signals of the DIFOUT pins of the middle and inner layer thermistors and the inner layer sliding rheostat enter the differential gain circuit after voltage division to generate an error signal, which is output to the DIFOUT pin of the inner layer MAX1978 chip. The error signal is connected to the INT- pin of the inner layer MAX1978 chip as the reverse input terminal of the PID network integrator. The VREF pin of the MAX1978 chip provides an internal reference voltage as the forward input terminal, and together with external resistor-capacitor components, it forms an analog PID compensation network. The PID network outputs a control voltage to the INTOUT pin of the MAX1978 chip, and after passing through a resistor, it is then connected to the CTLI pin. This voltage is compared with the internal reference voltage again to control the direction and magnitude of the current output by the PWM controller inside the MAX1978 chip to drive the H-bridge circuit. If the output voltage is greater than the reference voltage, a positive current is output; if the output voltage is less than the reference voltage, a reverse current is output. In addition, the magnitude of the voltage on the CTLI pin can control the magnitude of the output current.

[0036] The difference in the digital temperature control principle between the outer layer temperature control circuit and the inner layer temperature control circuit lies in that the voltages of the outer layer thermistor and the set temperature resistor enter the microcontroller STM32 after analog-to-digital conversion by the ADC chip. After digital PID operation inside the microcontroller STM32, a digital control quantity is output, and after digital-to-analog conversion by the DAC chip, a control voltage is output to the CTLI pin of the outer layer MAX1978 chip. The voltage on the CTLI pin is compared with the internal reference voltage of the outer layer MAX1978 chip again to control the direction and magnitude of the current output by the PWM controller inside the chip to drive the H-bridge circuit. If the output voltage is greater than the reference voltage, a positive current is output; if the output voltage is less than the reference voltage, a reverse current is output. In addition, the magnitude of the voltage on the CTLI pin can control the magnitude of the output current. The core device for outputting the control current in both the inner and outer layer temperature control circuits is the MAX1978 chip, and its peripheral circuit is as Figure 5 shown. The main pins used are as follows: FB- is the voltage acquisition pin for the inner or outer layer thermistor, FB+ is the voltage acquisition pin for the inner or outer layer sliding rheostat, BFB- and BFB+ are the voltage monitoring pins for FB- and FB+ respectively, used to connect to the ADC chip, OT and UT pins are the high temperature / low temperature warning pins (the LED lights up when the temperature difference is too large), MAXIP, MAXIN, MAXV are the pins for setting the maximum positive current, negative current, and the maximum voltage of the inner / outer layer TEC, the VREF pin provides the reference voltage, LX1 and LX2 are connected to the inner / outer layer TEC to output the control current, and the CTLI pin controls the magnitude and direction of the output current.

[0037] The microcontroller is the core of the outer layer temperature control circuit, and its main functions include: configuring the registers of the ADC and DAC chips and transmitting digital information; converting and reading temperature data and calculating and outputting temperature control algorithms; communicating with the host computer, converting the measured voltage signal into temperature and displaying it in real time on the host computer and storing data. In this invention, the STM32F103C8T6 chip produced by STMicroelectronics is selected as the microcontroller (MCU) of the temperature control circuit system. As Figure 6 Shown is the peripheral circuit of STM32F103C8T6. SPI1 is used to communicate with AD5541, PA4 is connected to DAC_CS as the chip select signal pin, PA5 is connected to DAC_SCLK as the clock frequency pin, and PA7 is connected to DAC_SDIN as the digital-to-analog conversion output pin. SPI2 is used to communicate with ADS7067, PB12 is connected to ADC_CS as the chip select signal pin, PB13 is connected to ADC_SCLK as the clock frequency pin, PB14 is connected to ADC_SDO as the serial data input pin, and PB15 is connected to ADC_SDI as the serial data output pin.

[0038] To ensure the signal acquisition and control accuracy during the temperature control process, the system uses the ADS7067 (ADC) and AD5541 (DAC) conversion circuits. The ADC conversion circuit realizes the real-time monitoring of the set temperature, actual temperature, and TEC current magnitude by connecting to the pins such as BFB+ / BFB–, AOUT, DIFOUT, and ITEC of the MAX1978 chip in the inner and outer layer temperature control circuits; its reference voltage is provided by an independent reference voltage circuit, thus ensuring the conversion accuracy and long-term stability. Its circuit is as Figure 7 Shown. The ADC chip communicates with the microcontroller STM32 through the SPI2 interface, and each signal channel is connected to the corresponding sampling points of the inner and outer layer temperature control circuits. The schematic diagram of the DAC conversion circuit is as Figure 8 Shown. The DAC chip converts the digital control quantity obtained by the STM32 through PID operation into an analog voltage, and this voltage is directly transmitted to the CTLI pin of the outer layer MAX1978, thereby adjusting the control current of the outer layer TEC. The DAC circuit also uses the highly stable voltage provided by the reference voltage circuit as the reference benchmark and is connected to the STM32 through the SPI1 interface to ensure the level consistency between the digital and analog signals.

[0039] To meet the requirements of each module for a stable power supply, this invention designs a perfect power supply and reference voltage circuit as Figure 9As shown. The entire system takes a 5V DC voltage as the input. After preliminary filtering by a magnetic bead and a filter capacitor, it is boosted to 10V through a charge pump to power the reference voltage chip. At the same time, through a buck circuit, 5V is respectively reduced to 3.3V. One path is used for the power output of the MAX1978 chip, and the other path supplies each chip of the STM32 and other digital control parts, so as to ensure that each module works under low-noise and high-stability conditions.

[0040] According to the ADC conversion circuit in this example, the pins of the inner and outer layers of MAX1978 are connected to monitor the set temperature, actual temperature, and TEC current magnitude of the controlled object. The DAC conversion circuit is connected to the STM32 and the outer layer MAX1978 chip, and converts the STM32 digital control quantity into a voltage signal to control the output current of the outer layer MAX1978.

[0041] Furthermore, the reference voltage of the ADC chip is provided by the reference voltage circuit part to achieve high stability of the ADC reference voltage. The 1st channel of the ADC chip is connected to the BFB+ pin of the inner layer MAX1978, the 2nd channel is connected to the BFB- pin, the 3rd channel is connected to the AOUT pin, and the 4th channel is connected to the ITEC pin; the 5th channel and the BFB+ pin of the outer layer MAX1978 chip, the 6th channel and the BFB- pin, the 7th channel and the DIFOUT pin, the 8th channel and the ITEC pin are connected. The CS, SCLK, SDI, and SDO pins are respectively connected to PB12, PB13, PB14, and PB15 of the microcontroller STM32, that is, communication is carried out using SPI2. In the DAC conversion circuit of this example, the reference voltage is also provided by the reference voltage circuit part to achieve high stability of the DAC reference voltage and keep the signal level consistent with that of the ADC. The VOUT pin of the DAC chip is directly connected to the CTLI pin of the outer layer MAX1978 chip, and the DIN, CS, and SCLK pins are respectively connected to PA7, PA4, and PA5 of the microcontroller STM32, that is, communication is carried out using SPI1.

[0042] According to the microcontroller STM32 in this example, STM32 processes the temperature signal collected by the ADC and sends it to the host computer for display through serial communication. STM32 performs PID operation on the set temperature of the outer layer and the collected temperature and then sends control information to the DAC chip. SPI1 of STM32 is used for the DAC, and SPI2 is used for communication with the ADC chip.

[0043] According to the inner MAX1978 chip and the outer MAX1978 chip in this example, the maximum positive and negative currents of the TEC can be set. For both channels, a constant voltage source is provided by the VREF pin inside the MAX1978 chip and grounded after two resistors are connected in series. The voltage division of one of the resistors is connected to MAXIP or MAXIN of the MAX1978 chip to set the maximum positive and negative currents. The inner layer temperature control is through the differential pressure signal of the thermistor and the sliding rheostat, which forms an analog PID control network through resistor-capacitor components and the operational amplifier inside the MAX1978 chip, and the output voltage controls the output current of the inner layer MAX1978 chip to the TEC in the laser.

[0044] In summary, the double-layer temperature control system of the semiconductor laser of the present invention realizes hierarchical and precise control of the laser temperature by adopting a temperature control strategy combining digital PID in the outer layer and analog PID in the inner layer, as well as using high-precision MAX1978 chips, ADC / DAC conversion circuits and a stable power supply system. This system can not only quickly perform rough temperature control when the external environmental temperature changes drastically, but also finely adjust the temperature of the laser chip after the temperature control environment is stable, so as to ensure that the temperature control of the laser reaches the goals of high precision, low noise and long-term stability.

[0045] The content not detailedly described in the specification of the present invention belongs to the prior art well-known to those skilled in the art. It is easy for those skilled in the art to understand that the above is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A semiconductor laser double-layer temperature control system, characterized in that: It includes an inner temperature control circuit and an outer temperature control circuit. The inner temperature control circuit is used to achieve precise stabilization of the temperature of the laser chip inside the laser. The outer temperature control circuit is used to achieve rough stabilization of the temperature of the heat sink outside the laser. The inner temperature control circuit includes a semiconductor laser, an inner sliding rheostat, and an inner MAX1978 chip. The semiconductor laser includes an inner thermistor, a laser chip, and an inner semiconductor refrigeration chip TEC. The inner MAX1978 chip is connected to the inner thermistor and the inner sliding rheostat, and then forms an analog PID compensation network with the resistor and capacitor to output a control voltage to the inner TEC to achieve inner temperature control. At the same time, the inner MAX1978 chip is connected to the ADC in sequence. The conversion circuit, microcontroller STM32, and host computer are used to realize inner layer measurement and temperature setting; the outer layer temperature control circuit includes the laser external heat sink, the outer layer thermistor, the outer layer semiconductor refrigeration chip TEC, the outer layer sliding rheostat, and the outer layer MAX1978 chip. First, the outer layer MAX1978 chip is connected to the outer layer thermistor and the outer layer sliding rheostat, and then connected to the ADC conversion circuit, microcontroller STM32, and host computer in turn to realize outer layer measurement and temperature setting. After digital PID calculation is performed in the microcontroller STM32, the control signal is output to the DAC conversion circuit, the outer layer MAX1978 chip, and the outer layer TEC in turn to realize outer layer temperature control.

2. A semiconductor laser double-layer temperature control system according to claim 1, characterized in that: The thermistor in the outer temperature control circuit is an NTC thermistor, which is used to measure the temperature of the laser and the external heat sink. The two sliding rheostats in the inner and outer layers are used to set the target temperature of the laser chip and the external heat sink respectively. The semiconductor refrigeration chip TEC is a temperature control actuator, which is used to heat or cool the laser chip and the external heat sink.

3. The semiconductor laser double-layer temperature control system according to claim 1, characterized in that: The internal reference voltage of the MAX1978 chip and the NTC thermistor form a voltage divider network to obtain the voltage signals of the laser chip and the outer heat sink respectively to calculate the temperature information; the reference voltage of the MAX1978 chip and the sliding rheostat are used to divide the voltage to set the target voltage of the laser chip and the outer heat sink, which is also the target temperature.

4. A semiconductor laser double-layer temperature control system according to claim 3, characterized in that: The VREF pin of the MAX1978 chip passes through a voltage divider resistor The rear end is connected to the NTC thermistor, and one end is connected to the FB- pin of the MAX1978 chip. The voltage division of the thermistor can measure the actual temperature. The VREF pin of the MAX1978 chip is also connected to the sliding rheostat. The variable resistance end of the sliding rheostat is connected to the resistor Then connect the FB+ pin of the MAX1978 chip, and the variable voltage of the sliding rheostat can set the target temperature. The specific calculation formula is as follows: Thermistor voltage division: ， Temperature setting resistor voltage division: ， in, is the reference voltage, is the resistance of the inner or outer thermistor, is the resistance value of the inner or outer sliding rheostat, is the voltage divider resistor value; The thermistor resistance is calculated as follows: ， in, Is the inner or outer thermistor in The resistance value at the actual temperature; It is in The resistance value when is the temperature coefficient of the inner or outer thermistor material; Further get the actual temperature measured by the thermistor: 。 5. The semiconductor laser double-layer temperature control system according to claim 1, characterized in that: The ADC conversion circuit is connected to the pins of the inner and outer MAX1978 chips to monitor the set temperature and actual temperature of the controlled object and the TEC current size. The DAC conversion circuit is connected to the microcontroller STM32 chip and the outer MAX1978 chip to convert the digital control quantity of the microcontroller STM32 chip into a voltage signal to control the output current of the outer MAX1978 chip.

6. A semiconductor laser double-layer temperature control system according to claim 5, characterized in that: The ADC conversion circuit includes an ADC chip. The reference voltage of the ADC chip is provided by the reference voltage circuit part. Channel 1 of the ADC chip is connected to the BFB+ pin of the inner MAX1978, channel 2 is connected to the BFB- pin, channel 3 is connected to the AOUT pin, and channel 4 is connected to the ITEC pin; channel 5 is connected to the BFB+ pin of the outer MAX1978 chip, channel 6 is connected to the BFB- pin, channel 7 is connected to the DIFOUT pin, and channel 8 is connected to the ITEC pin. The CS, SCLK, SDI, and SDO pins are respectively connected to PB12, PB13, PB14, and PB15 of the STM32, that is, SPI2 is used for communication.

7. A semiconductor laser double-layer temperature control system according to claim 5, characterized in that: The reference voltage of the DAC conversion circuit is also provided by the reference voltage circuit part and is consistent with the signal level of the ADC conversion circuit. The DAC conversion circuit includes a DAC chip. The VOUT pin of the DAC chip is directly connected to the CTLI pin of the outer MAX1978 chip. The DIN, CS, and SCLK pins of the DAC chip are respectively connected to PA7, PA4, and PA5 of the STM32 microcontroller, that is, SPI1 is used for communication.

8. The semiconductor laser double-layer temperature control system according to claim 1, characterized in that: The microcontroller STM32 processes the temperature signal collected by the ADC chip and sends it to the host computer for display through serial communication. The microcontroller STM32 performs PID calculation on the outer layer set temperature and the collected temperature and sends control information to the DAC chip.

9. The semiconductor laser double-layer temperature control system according to claim 1, characterized in that: The inner MAX1978 chip and the outer MAX1978 chip control circuit can set the maximum TEC current. The inner setting and target temperature signals pass through the PID control network formed by the resistor and capacitor device and the operational amplifier in the MAX1978 chip, and the output voltage controls the inner MAX1978 chip to output the current to the inner TEC in the laser.

10. The semiconductor laser double-layer temperature control system according to claim 1, characterized in that: The power supply circuit provides power, and the reference voltage circuit provides a high-stability voltage reference for the ADC and DAC.

11. A semiconductor laser double-layer temperature control system according to claim 10, characterized in that: In the power supply circuit, after the 5V voltage is filtered by magnetic beads and capacitors, the first path is boosted to 10V by the charge pump chip as the power supply for the voltage reference chip, the second path is reduced to 3.3V by the step-down chip as the power output power supply for the MAX1978 chip, and the third path is reduced to 3.3V by the step-down chip as the power supply for the microcontroller STM32, ADC chip, and DAC chip.

Images