A microcavity photonic thermometry system and method

Abstract

The present application relates to a kind of microcavity photonic temperature measurement system and method, belong to sensor technical field, solve the problems that the temperature measurement range and temperature measurement accuracy of existing microcavity photonic thermometer are very low.The system includes: current drive circuit generates drive current, including: FPGA generates digital waveform signal under the action of control signal received from microcontroller;Digital-analog converter converts digital waveform signal into adjustable voltage waveform;Series feedback circuit generates linear adjustable drive current based on adjustable voltage waveform;Laser diode generates wavelength linearly changed emission light under linear adjustable drive current drive;Optical microcavity sensor forms regular change output light signal after wavelength linearly changed emission light passes through temperature changed optical microcavity sensor when emission light is incident to optical microcavity sensor, and microcontroller obtains temperature value according to regular change output light signal.The temperature measurement range can be adjusted by generating linear adjustable drive current.

Description

Technical Field

[0001] This invention relates to the field of sensor technology, and in particular to a microcavity photonic temperature measurement system and method. Background Technology

[0002] Traditional electronic sensors, such as platinum resistance thermometers, are greatly affected by the external environment. Vibration, oxidation, contamination, and electromagnetic interference can all affect their measurement accuracy, causing their stability and accuracy to depend on frequent calibration, making them difficult to apply to high-accuracy measurements. In contrast, optical microcavity sensors have the advantage of electromagnetic immunity, making them suitable for extreme working environments. Their high performance determines that they will bring breakthroughs to the Internet of Things in the fields of high-precision measurement and special extreme applications.

[0003] Currently, whispering-gallery mode optical microcavities are widely used in single-nanoscale particle detection and various microcavity environmental physical parameter sensing, such as temperature, magnetic field, stress, and gyroscopes. Whispering-gallery mode microcavities can be made into high-sensitivity temperature sensors with IoT control capabilities and used in aerial surveying, resource exploration, petrochemical fields, and more.

[0004] like Figure 1 As shown, the existing system includes a distributed laser (DBR), a laser diode (LD) driver, a thermoelectric cooler (TEC) driver, a photodetector, and a self-made transimpedance amplifier (TIA) circuit. The DBR laser includes a TEC, a thermistor, and a monitoring photodiode. The laser current driver and TEC driver are used to stabilize the laser frequency; both can be used to modulate or scan the laser wavelength. With a fixed TEC temperature, the sensor applies a sawtooth wave with an amplitude of 40 mA to the laser near the center current for frequency scanning, causing the laser wavelength to exhibit a linear sawtooth wave variation. However, the system has a very low temperature measurement range and accuracy, with a temperature measurement range of around 10°C and an accuracy on the order of 0.5°C.

[0005] The temperature sensor directly uses the STM32's internal digital-to-analog converter (with a low bit depth, up to a maximum of 12 bits). The bit depth and stability of the DAC directly affect the stability and resolution of the sawtooth wave drive current, which in turn affects the stability and resolution of the laser wavelength. Besides the DAC, the current drive module in this system uses a pre-integrated driver chip. While this reduces the size, the stability, accuracy, and linearity of the current are only average.

[0006] Furthermore, applying a sawtooth wave current causes abrupt changes in current at the end of one waveform cycle and the beginning of the next, which is detrimental to wavelength stability and affects the accuracy of temperature measurement. The acquisition circuit uses only a single operational amplifier to convert the weak current output from the photodetector into a voltage with appropriate gain. This excessive amplification factor results in large waveform fluctuations and distortion, further impacting the accuracy of temperature measurement. The amplified voltage is directly connected to the STM32's ADC interface. However, the STM32's internal ADC is only 12 bits, leading to a significant difference in accuracy compared to an external high-precision ADC.

[0007] In summary, although this design reduces the size, it has the following problems: 1. Directly use the low-bit DAC inside the STM32; 2. Directly using integrated current drive chips generally results in mediocre current performance; 3. A sawtooth wave with a sudden change in current is used, and the amplitude of the sawtooth wave is too small; 4. The single-pass amplification factor of the acquisition circuit is too large, resulting in large waveform fluctuations; 5. Directly use the STM32's internal low-bit ADC; 6. The microcontroller achieves synchronization between laser transmission and transmission spectrum reception, but there is still room for improvement in the processing and calibration of the one-to-one time correspondence.

[0008] The above technical issues will result in poor temperature measurement accuracy of this technical solution. Summary of the Invention

[0009] Based on the above analysis, the present invention aims to provide a microcavity photonic temperature measurement system and method to solve the problem that the temperature measurement range and accuracy of existing microcavity photonic thermometers are very low.

[0010] On one hand, embodiments of the present invention provide a microcavity photonic temperature measurement system comprising: a microcontroller, a current driving circuit, a laser diode, and an optical microcavity sensor. The current driving circuit generates a driving current and includes: an FPGA for generating a digital waveform signal under the action of a control signal received from the microcontroller; a digital-to-analog converter for converting the digital waveform signal into a voltage waveform with adjustable amplitude, phase, and frequency; a series feedback circuit for generating a linearly adjustable driving current based on the voltage waveform; the laser diode for generating emitted light with linearly changing wavelength under the drive of the linearly adjustable driving current; and the optical microcavity sensor, wherein the emitted light is incident on the optical microcavity sensor, causing the linearly changing emitted light to form a regularly changing output light signal after passing through the temperature-changing optical microcavity sensor. The microcontroller obtains a temperature value based on the regularly changing output light signal.

[0011] The beneficial effects of the above technical solution are as follows: the digital waveform signal is converted into an amplitude- and phase-adjustable voltage waveform by a digital-to-analog converter, and a linearly adjustable driving current is generated based on the amplitude- and phase-adjustable voltage waveform by a series feedback circuit, so that the laser diode generates emitted light with a linearly changing wavelength. Therefore, the optical microcavity sensor receives emitted light with a linearly changing wavelength, thereby making the temperature measurement range adjustable.

[0012] Based on further improvements to the above system, the microcontroller is used to send control signal instructions to the FPGA, so that the FPGA generates and sends a waveform digital waveform signal according to the control signal instructions; or the microcontroller is also used to send variable parameters to the FPGA, so that the FPGA generates a digital waveform signal with a certain amplitude and phase according to the variable parameters, wherein the variable parameters include frequency, amplitude and phase.

[0013] Based on further improvements to the above system, the larger the linearly adjustable range of the driving current, the larger the wavelength range of the emitted light, resulting in a larger wavelength range received by the optical microcavity sensor, and thus a larger temperature measurement range; and / or the temperature measurement range can be changed by adjusting the temperature of the laser diode itself.

[0014] Based on a further improvement of the above system, the series feedback circuit includes: a follower, a comparator, a MOS transistor, a sampling resistor, and a laser diode, wherein the follower is used to follow the amplitude-phase adjustable voltage waveform; the comparator is used to compare the amplitude-phase adjustable voltage waveform with the feedback voltage of the sampling resistor to generate a control signal for the MOS transistor; and the MOS transistor has its gate receiving the control signal to control the current output of the MOS transistor, its source being grounded via the sampling resistor, and its drain being connected to the laser diode.

[0015] Based on further improvements to the above system, the microcavity photonic temperature measurement system also includes a signal acquisition circuit, wherein the signal acquisition circuit includes: a photodiode, a current-to-voltage converter, a secondary amplifier, and a first analog-to-digital converter. The photodiode is used to convert the output optical signal into a weak current signal; the amplifier is used to convert and amplify the weak current signal in two stages to generate a secondary amplified voltage signal; and the first analog-to-digital converter is used to perform analog-to-digital conversion on the secondary amplified voltage signal to provide a digital voltage signal to the microcontroller.

[0016] Based on further improvements to the above system, the amplifier includes: a first-stage amplifier and a second-stage amplifier, wherein the first-stage amplifier is used to convert the weak current signal into a first-stage amplified voltage signal using a T-network operational amplification method; and the second-stage amplifier is used to amplify the first-stage amplified voltage signal to generate a second-stage amplified voltage signal.

[0017] Based on further improvements to the above system, the microcavity photonic temperature measurement system also includes a temperature control circuit. This temperature control circuit includes a thermistor, a second analog-to-digital converter, a thermoelectric cooler driver chip, and a thermoelectric cooler. The thermistor is used to detect changes in ambient temperature to generate a differential voltage. The second analog-to-digital converter is used to convert the differential voltage into a differential voltage digital signal and provide the differential voltage digital signal to the microcontroller. The microcontroller is used to obtain the current ambient temperature based on the differential voltage digital signal, calculate the temperature difference between the target temperature and the current ambient temperature, and then provide a PWM signal based on the temperature difference. The thermoelectric cooler driver chip is used to provide a drive current based on the PWM signal. The thermoelectric cooler is used to generate heat or cool under the control of the drive current.

[0018] On the other hand, embodiments of the present invention provide a microcavity photonic temperature measurement method, comprising: generating a driving current, wherein generating the driving current includes: generating a digital waveform signal by an FPGA under the control of a microcontroller; converting the digital waveform signal into a voltage waveform with adjustable amplitude, phase, and frequency; generating a linearly adjustable driving current based on the voltage waveform with adjustable amplitude, phase, and frequency; generating emitted light with linearly changing wavelength through a laser diode under the drive of the linearly adjustable driving current; and incident the emitted light onto an optical microcavity sensor, such that the emitted light with linearly changing wavelength forms a regularly changing output light signal after passing through the temperature-changing optical microcavity sensor, wherein the microcontroller obtains a temperature value based on the regularly changing output light signal.

[0019] Based on a further improvement of the above method, a control signal instruction is sent to the FPGA, causing the FPGA to generate and send a waveform digital signal according to the control signal instruction; or variable parameters are sent to the FPGA, causing the FPGA to generate a triangular wave with a certain amplitude and phase according to the variable parameters, wherein the variable parameters include frequency, amplitude and phase.

[0020] Based on further improvements to the above method, the larger the linearly adjustable range of the driving current, the larger the wavelength range of the emitted light, resulting in a larger wavelength range received by the optical microcavity sensor, and thus a larger temperature measurement range; and / or the temperature measurement range can be changed by adjusting the temperature of the laser diode itself.

[0021] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects: 1. A digital waveform signal is converted into a voltage waveform with adjustable amplitude, phase, and frequency by a digital-to-analog converter. A linearly adjustable drive current is generated based on this voltage waveform via a series feedback circuit. This causes the laser diode to emit light with a linearly changing wavelength. Therefore, the optical microcavity sensor receives this linearly changing emitted light, making the temperature measurement range adjustable. Changing the temperature of the laser diode itself changes the initial wavelength, thus changing the corresponding temperature. Therefore, the temperature measurement range of the sensor can be adjusted by changing the temperature of the laser diode itself.

[0022] 2. The triangular wave current scanning range can vary from 0mA to 500mA, with a driving current stability of approximately 500mA±10uA. The linearity of the triangular wave current is good. The PID temperature control accuracy is around 1mK. Using a triangular wave current to scan the laser, the laser wavelength also varies in a triangular wave pattern with good linearity. Therefore, the microcavity photonic temperature measurement system has high precision and a large temperature measurement range.

[0023] 3. Using a current source and temperature control module to drive the laser, the wavelength stability was found to be good when both current and temperature were kept constant.

[0024] In this invention, the above-described technical solutions can be combined with each other to achieve more preferred combinations. Other features and advantages of this invention will be set forth in the following description, and some advantages may become apparent from the description or be learned by practicing the invention. The objects and other advantages of this invention can be realized and obtained from what is particularly pointed out in the description and drawings. Attached Figure Description

[0025] The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Throughout the drawings, the same reference numerals denote the same parts.

[0026] Figure 1 A schematic diagram of an existing temperature sensor. Figure 2 A diagram illustrating how fluctuations in ambient temperature can cause a shift in the resonant wavelength of the resonant mode. Figure 3 This is a block diagram of a microcavity photonic temperature measurement system according to an embodiment of the present invention; Figure 4 This is a framework diagram of a microcavity photonic temperature measurement system according to an embodiment of the present invention; Figure 5 This is a block diagram of the current driving circuit in a microcavity photonic temperature measurement system according to an embodiment of the present invention; Figure 6 This is a block diagram of the temperature control circuit in a microcavity photonic temperature measurement system according to an embodiment of the present invention; Figure 7 This is a block diagram of the signal acquisition circuit in a microcavity photonic temperature measurement system according to an embodiment of the present invention; Figure 8 This is an overall structural diagram of the microcavity photonic temperature measurement system according to an embodiment of the present invention; Figure 9 A graph of an amplitude- and phase-adjustable voltage triangular wave according to an embodiment of the present invention; Figure 10 This is a detailed structural diagram of a two-stage amplifier according to an embodiment of the present invention; Figure 11 The graph shows the linear relationship between the driving current and the emitted light wavelength when the laser temperature is maintained at 20℃. Figure 12 This is a flowchart of a microcavity photon thermometry method according to an embodiment of the present invention; Figure 13 This is a diagram of the driving current and transmitted harmonic signals according to an embodiment of the present invention. Detailed Implementation

[0027] Preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, which form part of this application and are used together with the embodiments of the present invention to illustrate the principles of the present invention, but are not intended to limit the scope of the present invention.

[0028] A specific embodiment of the present invention discloses a microcavity photonic temperature measurement system, such as... Figure 3 As shown, the microcavity photonic temperature measurement system includes a microcontroller 302, a current drive circuit 304, a laser diode 306, and an optical microcavity sensor 308. The current drive circuit 304 generates a drive current and includes: an FPGA 310 that generates a digital waveform signal under the control of a control signal received from the microcontroller; a digital-to-analog converter 312 that converts the digital waveform signal into a voltage waveform with adjustable amplitude, phase, and frequency; and a series feedback circuit 314 that generates a linearly adjustable drive current based on the voltage waveform with adjustable amplitude, phase, and frequency. The laser diode 306 generates emitted light with linearly changing wavelength under the drive of the linearly adjustable drive current. When the emitted light is incident on the optical microcavity sensor, the linearly changing emitted light passes through the temperature-changing optical microcavity sensor to form a regularly changing output light signal. The microcontroller obtains the temperature value based on the regularly changing output light signal; specifically, the microcontroller obtains the temperature value by capturing the peak position of the regularly changing output light signal.

[0029] Compared with the prior art, the microcavity photonic temperature measurement system provided in this embodiment converts digital waveform signals into voltage waveforms with adjustable amplitude and phase through a digital-to-analog converter, and generates linearly adjustable driving current based on the voltage waveform with adjustable amplitude and phase through a series feedback circuit, so that the laser diode generates emitted light with linearly changing wavelength. Therefore, the optical microcavity sensor receives emitted light with linearly changing wavelength, making the temperature measurement range adjustable.

[0030] The following text will refer to Figures 3 to 8 The microcavity photonic temperature measurement system according to an embodiment of the present invention will be described in detail below. The microcavity photonic temperature measurement system includes: a microcontroller 302, a current driving circuit 304, a laser diode 306, an optical microcavity sensor 308, a signal acquisition circuit, and a temperature control circuit.

[0031] The microcontroller 302 is used to control the FPGA 310. Specifically, the microcontroller is used to send control signal instructions to the FPGA, so that the FPGA generates and sends a waveform digital waveform signal according to the control signal instructions; or the microcontroller is also used to send variable parameters to the FPGA, so that the FPGA generates a digital waveform signal with a certain amplitude and phase according to the variable parameters, wherein the variable parameters include frequency, amplitude and phase.

[0032] The current drive circuit 304 is used to generate the drive current. (Reference) Figure 5 and Figure 8 The current drive circuit 304 includes: an FPGA 310 for generating a digital waveform signal under the action of a control signal received from a microcontroller, wherein the microcontroller (e.g., STM32) is the master and the FPGA is the slave, and the master and slave communicate via SPI; a digital-to-analog converter 312 for converting the digital waveform signal into a voltage waveform with adjustable amplitude, phase, and frequency; and a series feedback circuit 314 for generating a linearly adjustable drive current based on the voltage waveform with adjustable amplitude, phase, and frequency. The series feedback circuit 314 includes: a follower, a comparator, a MOS transistor, a sampling resistor, and a laser diode. The follower is used to follow the voltage waveform with adjustable amplitude and phase; the comparator is used to compare the voltage waveform with adjustable amplitude and phase with the feedback voltage of the sampling resistor to generate a control signal for the MOS transistor; and the MOS transistor has its gate receiving the control signal to control the current output of the MOS transistor, its source grounded via the sampling resistor, and its drain connected to the laser diode.

[0033] The laser diode 306 is used to generate emitted light with a linearly varying wavelength when driven by a linearly adjustable drive current.

[0034] The optical microcavity sensor 308 emits light, causing the emitted light, with its wavelength changing linearly, to pass through the temperature-changing optical microcavity sensor and form a regularly changing output light signal. The microcontroller then obtains the temperature value based on this regularly changing output light signal. A larger linearly adjustable range of the drive current results in a wider range of emitted light wavelengths, thus a wider range of wavelengths received by the optical microcavity sensor, and consequently a wider temperature measurement range; and / or the temperature measurement range can be changed by adjusting the temperature of the laser diode itself.

[0035] refer to Figure 7 and Figure 8 The signal acquisition circuit includes a photodiode, a current-to-voltage converter, a secondary amplifier, and a first analog-to-digital converter. The photodiode converts the output optical signal (i.e., a weak output optical signal) into a weak current signal; the amplifier converts and amplifies the weak current signal in two stages to generate a secondary amplified voltage signal; and the first analog-to-digital converter performs analog-to-digital conversion on the secondary amplified voltage signal to provide a digital voltage signal to the microcontroller. Specifically, the amplifier includes a primary amplifier and a secondary amplifier, wherein the primary amplifier converts the weak current signal into a primary amplified voltage signal using a T-network operational amplification method; and the secondary amplifier amplifies the primary amplified voltage signal to generate a secondary amplified voltage signal.

[0036] refer to Figure 6 and Figure 8 The temperature control circuit includes a thermistor, a second analog-to-digital converter (ADC), a thermoelectric cooler driver chip, and a thermoelectric cooler. The thermistor detects changes in ambient temperature to generate a differential voltage. The second ADC converts the differential voltage into a digital differential voltage signal and provides this signal to a microcontroller. The microcontroller obtains the current ambient temperature based on the digital differential voltage signal, calculates the temperature difference between the target temperature and the current ambient temperature, and then provides a PWM signal based on this temperature difference. The thermoelectric cooler driver chip (TEC) provides a drive current based on the PWM signal. The thermoelectric cooler heats or cools under the control of the drive current. In an optional embodiment, heating or cooling can also be achieved by changing the current direction of the TEC.

[0037] Another specific embodiment of the present invention discloses a microcavity photon thermometry method, referring to... Figure 12 The microcavity photonic temperature measurement method includes: in step S1202, generating a driving current through a current driving circuit. Specifically, generating the driving current includes: generating a digital waveform signal by an FPGA under the action of a control signal received from a microcontroller; converting the digital waveform signal into a voltage waveform with adjustable amplitude, phase, and frequency; generating a linearly adjustable driving current based on the voltage waveform with adjustable amplitude, phase, and frequency; in step S1204, generating emitted light with linearly changing wavelength through a laser diode under the driving of the linearly adjustable driving current; and in step S1206, incident the emitted light onto an optical microcavity sensor, so that the emitted light with linearly changing wavelength forms a regularly changing output light signal after passing through the temperature-changing optical microcavity sensor, wherein the microcontroller obtains the temperature value based on the regularly changing output light signal. Specifically, the microcontroller obtains the temperature value by capturing the peak position of the regularly changing output light signal, for example, by obtaining the temperature value based on the lowest point of the electrical signal peak converted from the regularly changing output light signal.

[0038] Microcontroller control of FPGA includes sending control signal commands to FPGA, causing FPGA to generate and send waveform digital signals according to the control signal commands; or sending variable parameters to FPGA, causing FPGA to generate a triangular wave with a certain amplitude and phase according to the variable parameters, where the variable parameters include frequency, amplitude and phase.

[0039] The temperature measurement range can be increased by expanding the linearly adjustable range of the drive current. Specifically, the larger the linearly adjustable range of the drive current, the wider the wavelength range of the emitted light, resulting in a wider wavelength range received by the optical microcavity sensor, and thus a wider temperature measurement range. Because the laser has a maximum and minimum operating current, the wavelength range is adjusted by varying the drive current between the minimum and maximum operating currents. Typically, the current range can be set to the maximum operating current. The temperature measurement range can also be changed by adjusting the temperature of the laser diode itself. Changing the temperature of the laser diode changes the initial value of the wavelength, which in turn changes the corresponding temperature, thus making the sensor's temperature measurement range adjustable by changing the laser's own temperature.

[0040] In the following text, refer to Figure 2 , Figures 4 to 11 The microcavity photon thermometry according to embodiments of the present invention will be described in detail by way of specific examples.

[0041] The basic principle of temperature sensing by optical microcavity sensors is that when the ambient temperature of the microcavity changes, the refractive index and the size of the microcavity change due to the thermal refraction or thermal expansion of the optical microcavity material itself, which in turn change the resonant wavelength of the resonant mode.

[0042] When the probe light is coupled into the optical microcavity through the fiber taper, the optical microcavity exhibits a Lorentz line shape in the transmission spectrum. The wavelength of light that satisfies the resonance condition will show an absorption peak in the transmission spectrum (which is represented by the lowest point in the transmission spectrum). For a specific optical microcavity, there is a specific absorption peak under each temperature condition.

[0043] The temperature measurement system is based on mode shifting in a microcavity sensing mechanism. In mode shifting, the resonant wavelength is easily affected by thermal effects. Temperature fluctuations in the environment surrounding the optical microcavity can cause a shift in the resonant wavelength of the resonant mode, such as... Figure 2 As shown. Therefore, by measuring the magnitude of the resonant wavelength shift, the temperature change can be calculated.

[0044] like Figure 4 As shown, the whispering-gallery mode microcavity photonic thermometer consists of two parts: an optical system and a circuit system. This technical solution focuses on the design of the circuit system. The overall circuit includes a drive circuit (containing two modules: LD current drive and TEC temperature control) and a signal acquisition circuit. The microprocessor simultaneously controls the laser drive current and temperature, as well as processes the acquired voltage signal. The optical system consists of a waveguide and a resonant cavity.

[0045] 1. Design of the drive circuit (including current drive and temperature control) Large, high-precision laser source devices can be replaced with smaller, current-driven laser diodes. For example... Figure 5 and Figure 8 As shown, the FPGA sends the required digital waveform signal, which is then converted into an amplitude- and phase-adjustable voltage waveform via a digital-to-analog converter (high-bit DAC). Figure 9 As shown in the figure, the voltage triangular wave serves as the reference voltage for the feedback-type constant current source circuit, ultimately generating a linearly adjustable current triangular wave that can drive the laser diode, thereby achieving the purpose of precisely controlling the linear change of the emitted light wavelength of the laser diode.

[0046] The FPGA is controlled by an STM32 microcontroller; see [link / reference]. Figure 4 The STM32 is the system's CPU. The STM32 sends instructions to the FPGA, allowing the FPGA to begin sending waveforms. The STM32 can also send parameters such as frequency, amplitude, and phase to the FPGA. The FPGA receives these parameters from the STM32 and then generates the required triangular wave with the specified amplitude and phase.

[0047] Frequency adjustment methods: 1) Modify the DAC_CLK speed. A faster CLK speed increases the digital-to-analog conversion speed and the output waveform frequency. 2) Without changing the DAC_CLK, adjust the frequency by changing the amount of digital data read from a waveform. Reducing the amount of digital data read, although slightly reducing the resolution, shortens the time to output a complete waveform, thus increasing the frequency.

[0048] Amplitude adjustment method: A triangular wave is generated by incrementing the minimum digital value (corresponding to the lowest voltage point) by 1 for one DAC_CLK cycle until reaching the maximum digital value (corresponding to the highest voltage point). Then, the maximum digital value (corresponding to the highest amplitude point) is decremented by 1 for one DAC_CLK cycle until reaching the minimum digital value (corresponding to the lowest amplitude point). To adjust the amplitude, the values ​​of the maximum and minimum digital values ​​are changed.

[0049] Phase adjustment method: Set a phase control variable. That is, add an offset digital value to the starting digital value to adjust the initial phase.

[0050] Simultaneously, a PID temperature control circuit was built to monitor and maintain the temperature of the laser itself, such as... Figure 6 and Figure 8 As shown, it uses an STM32 as the main control unit, selects a high-precision thermistor to detect temperature changes, and uses a thermoelectric cooler to regulate the temperature of the laser.

[0051] The PID temperature control module consists of two parts: temperature measurement and temperature control.

[0052] The temperature measurement section is as follows: When the ambient temperature changes, the resistance of the NTC changes, which in turn causes the voltage across the NTC to change. A high-precision ADC is used to collect the voltage across the NTC (when the current is constant, the voltage represents the resistance). The ambient temperature corresponding to the resistance value is obtained from the resistance-temperature fitting curve.

[0053] The voltage signals at both ends of the NTC are converted into digital quantities by the ADC, and the conversion results are output through the four-wire SPI interface (clock signal SCLK, data input line DIN, data output line DOUT, and chip select line CS).

[0054] The DIN pin sends the STM32's serial data to the input shift register on the ADC for control and configuration. DOUT is a multiplexed pin for serial and data output; the ADC uses this pin to transmit the acquired voltage data to the STM32. SCLK is the serial clock pin with an internal Schmitt trigger.

[0055] The temperature control section is as follows: After reading the actual temperature value, the deviation between the target temperature and the actual temperature is used to form a control quantity by proportional and integral linear combination. This control quantity is output as a PWM wave through pins A and B of the STM32.

[0056] The output PWM wave triggers the DRV (TEC driver chip). When the PWM is high, the DRV outputs current to drive the TEC to work; when the PWM is low, the DRV has no output current and the TEC does not work.

[0057] When the control input is positive, the TEC needs to heat up. At this time, pin A outputs a PWM wave, while pin B does not output a PWM wave. The DRV provides forward current to the TEC, causing the TEC to heat up. The magnitude of the control input determines the duty cycle of the PWM wave; the larger the duty cycle, the larger the forward current, and the more heat is generated.

[0058] When the control input is negative, the TEC (Transformer Control Unit) needs cooling. In this case, pin B outputs a PWM wave, while pin A does not. The DRV (Dual Current Regulator) provides reverse current to the TEC, causing it to cool. The magnitude of the control input determines the duty cycle of the PWM wave; a larger duty cycle results in a larger reverse current and increased cooling capacity.

[0059] The software part adjusts the scaling factor. K P Integral time T i This ultimately enables the entire system to achieve good temperature stability, ensuring the stability of the emitted laser wavelength so that the emitted wavelength only changes with the current.

[0060] The system starts running and collects the current ambient temperature at regular intervals. S v For the target temperature, X k For ambient temperature, E k = S v - X k .

[0061] E k When the temperature is >0, we need to heat it. E k Cooling starts when the temperature is below 0. The degree of heating and cooling depends on... E k The magnitude of the absolute value.

[0062]

[0063] K p This represents the proportionality coefficient, the magnitude of which directly affects the system's response speed.

[0064] if K p It's very large, so what a small difference is? E k This will also result in a larger value. Pout The system will experience violent fluctuations and will be difficult to stabilize. K p If the value is too small, the system's response speed will be too slow, even with a large difference. E k Only a small value can be obtained. Pout Therefore, the system needs a long time to reach a stable state.

[0065] Based on the above calculations, the difference was obtained. E k Under continuous temperature data acquisition, some difference samples are obtained, and these differences are accumulated. S E This is the sum of the difference samples.

[0066] for S E >0 will provide positive current to control TEC heating. S E When the current is less than 0, reverse current control will be provided for TEC cooling. The degree of heating and cooling depends on... S E The magnitude of the absolute value.

[0067]

[0068] T i This represents the integration time, and its magnitude will affect... Iout The size. When T i When the value is large, it takes a long time for the ambient temperature to return to the set value. T i When the temperature is low, the ambient temperature will fluctuate more significantly.

[0069] 2. Design of signal acquisition circuit The light emitted by the laser diode is coupled to the optical microcavity sensor through an optical fiber taper. Light of different wavelengths can form a regularly changing optical signal after passing through the microcavity.

[0070] like Figure 7 and Figure 8 As shown, the optical signal can be converted into a weak current signal by a photodiode. This weak current signal is amplified into a small voltage signal by a T-network operational amplifier circuit, and then further amplified by a three-op-amp instrumentation amplifier. (Reference) Figure 10 An instrumentation amplifier composed of three operational amplifiers is used as a secondary amplifier, which has the characteristics of high common-mode rejection ratio.

[0071] R G1 =R G2 R1=R3, R2=R4, R5=R6 Vout=(V IN2 -V IN1 (1+R1 / R) G1 (R5 / R2) Based on the formula above, set the resistor R... G1 =R G2 R1=R3, R2=R4, R5=R6, and the voltage amplification factor is adjusted by changing the value of R5.

[0072] A high-precision ADC is used to convert the voltage into a digital signal and transmit it to the microcontroller. The microcontroller determines whether the received digital signal is a spike signal and determines the current driving current and the wavelength value corresponding to that current (when the laser itself is at a constant temperature, each different driving current corresponds to a specific wavelength), and finally achieves temperature measurement.

[0073] 3. Technical details: To obtain the triangular wave voltage signal, a direct digital synthesis method is adopted. This method achieves waveform output through a phase accumulator, a phase modulator, real-time waveform data modification, and a DA converter. It has advantages such as low cost, low power consumption, high resolution, and fast conversion time.

[0074] like Figure 5 As shown on the right, to meet the laser's current parameter requirements, a series feedback circuit based on a field-effect transistor and an operational amplifier is designed to ensure current stability and high accuracy. This series feedback circuit specifically includes a follower, a comparator, a MOSFET, a sampling resistor, and the laser load. In the comparator module, the current output of the field-effect transistor is controlled by comparing a reference voltage (a voltage triangular wave generated by the FPGA) with the feedback voltage of the sampling resistor, thereby adjusting the feedback voltage until it equals the reference voltage to ensure the stability of the constant current source.

[0075] The laser is a current-driven device with a threshold current of 50mA and a maximum operating current of 500mA. Therefore, the driving current source is designed to meet the requirement of 50-500mA, and the reference voltage is 2.5V. Thus, the sampling resistor is selected to have a resistance of about 5 ohms to ensure that a current of 2.5V / 5Ω = 500mA can be generated.

[0076] refer to Figure 11 Simultaneously, a precision wavelength meter was used to accurately calibrate the linear relationship between the driving current and the emitted light wavelength. For every 1 mA increase in current, the emitted light wavelength increases by approximately 5 pm, and this relationship is linear.

[0077] A low-cost, high-precision instrumentation amplifier with a wide gain range is selected to amplify the voltage signal, and an external resistor is used to set the gain. The amplification circuit is divided into two stages. If the single amplification factor is too large, the waveform will fluctuate greatly and be prone to distortion.

[0078] The circuit exhibits input and output offset voltages. To eliminate the bias, an external zero-adjustment circuit is added. This zero-adjustment circuit is connected after the second-stage amplifier circuit. It adds a DC offset to the transmission spectrum signal via a subtractor. By simply adjusting the value of the variable resistor that acts as a voltage divider, the voltage applied to the inverting input can be adjusted to a suitable range for the output signal.

[0079] The signal has a low frequency and a large amount of low-frequency noise. A chopper-stabilized operational amplifier is selected to give the measurement signal certain characteristics. It can be modulated with a sine wave, then amplified, and the signal is demodulated after the noise is separated.

[0080] High-bit ADCs are used for voltage acquisition, which have advantages such as low noise, strong anti-interference ability, fast sampling speed and high sampling accuracy.

[0081] By adjusting the software to synchronize the microcontroller's transmission and reception, it is ensured that the relationship between the peak wavelength of the laser's emitted light and time, and the relationship between the transmission spectrum peak and time, can correspond one-to-one.

[0082] The key points of the embodiments of this application are as follows: 1. Using a microcontroller as the core for intelligent detection and control, the functions of other instruments and equipment in the laboratory temperature measurement device are realized on miniaturized functional modules. All the required devices are integrated into a small embedded system, achieving freedom and portability.

[0083] 2. The core microprocessor controls the laser drive and performs matching measurements based on the acquired output light signal. To ensure that the wavelength-time relationship of the laser emitted light corresponds one-to-one with the wavelength-time relationship in the transmission spectrum, the microcontroller's transmission and reception must be synchronized.

[0084] During the programming process, the time from when the microcontroller sends data to when it receives data is fixed. If there is a certain delay in the response of the laser's emitted light, this delay will be eliminated or calibrated in subsequent data processing.

[0085] 3. In order to achieve the tuning of the microcavity sensor (which is equivalent to a process of searching for the resonant wavelength. When the ambient temperature changes, the refractive index of the surface material of the microcavity will change, and the wavelength that satisfies its resonance condition will change. In order to find this resonant wavelength, a large wavelength range needs to be generated to lock this resonant wavelength (i.e., the resonant frequency)), the wavelength of the laser needs to change linearly.

[0086] The wavelength of light emitted by a laser is affected by both the driving current and temperature. However, it is difficult to make the temperature change in a gradient or linear manner. The only way is to keep the temperature constant and make the current change linearly.

[0087] 4. The wavelength of the laser emitted by the laser is affected by two factors: the laser driving current and the laser's own temperature. The larger the range of the driving current, the larger the range of wavelengths emitted by the laser, and the larger the range of wavelengths received by the microcavity. Therefore, the temperature measurement range is also larger. The temperature measurement range can be changed by adjusting the temperature of the laser diode (i.e., the laser) itself.

[0088] The temperature measurement range is affected by the threshold current and maximum current of the laser driver, as well as the current range of the driving circuit. However, the temperature measurement range can be changed by altering the initial value of the laser wavelength, thereby changing the wavelength range of the laser scan.

[0089] Therefore, our drive circuit design not only enables adjustable current, but the PID temperature control circuit also enables adjustable laser temperature. Temperature and peak wavelength calibration (refer to Table 1 below).

[0090]

[0091]

[0092] For example, by controlling the laser temperature at 20℃ and applying a drive current of 50mA-450mA, the temperature range for the wavelengths that meet the microcavity resonance condition is -42℃ to -1℃. However, by controlling the laser temperature at 25℃ and still applying a drive current of 50mA-450mA, the temperature range for the wavelengths that meet the microcavity resonance condition changes to -33.1℃ to 8.66℃.

[0093] 5. Within the maximum driving current range that the laser can withstand, the amplitude, frequency, and phase of the triangular wave current are adjustable. After detecting the approximate range of the resonant wavelength corresponding to a certain temperature, the frequency sweep range can be quickly narrowed, and frequency sweeping can be performed near the resonant wavelength to find the resonant peak, thereby improving the accuracy and speed of temperature measurement.

[0094] The beneficial effects of the embodiments of this application are as follows: The drive circuit of this invention has been designed and tested. The triangular wave current scanning range can vary from 50mA to 450mA, the drive current stability is approximately 500mA±10uA, and the linearity of the triangular wave current is good. The PID temperature control accuracy is approximately 1mK.

[0095] By using a current source and a temperature control module to drive our laser, we found that the wavelength stability was good when both the current and temperature were kept constant.

[0096] By scanning our laser with a triangular wave current, the laser wavelength also changes in a triangular wave pattern, exhibiting good linearity. (Reference) Figure 13 According to the signal acquisition circuit of the present invention, the transmission spectrum can be clearly observed and the resonance peak at the time of resonance is obvious.

[0097] Based on the above experimental results, the microcavity photon temperature measurement system under this technical solution will have advantages such as high precision, large temperature measurement range, and adjustable temperature measurement interval.

[0098] Those skilled in the art will understand that all or part of the processes of the methods described in the above embodiments can be implemented by a computer program instructing related hardware, and the program can be stored in a computer-readable storage medium. The computer-readable storage medium may be a disk, optical disk, read-only memory, or random access memory, etc.

[0099] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A microcavity photonic temperature measurement system, characterized in that, include: Microcontroller, current-driven circuit, laser diode and optical microcavity sensor, among which, The current driving circuit is used to generate a driving current, and the current driving circuit includes: An FPGA is used to generate digital waveform signals under the action of control signals received from the microcontroller. A digital-to-analog converter is used to convert the digital waveform signal into a voltage waveform with adjustable amplitude, phase, and frequency. A series feedback circuit is used to generate a linearly adjustable drive current based on the voltage waveform with adjustable amplitude, phase, and frequency. The laser diode is used to generate emitted light with linearly varying wavelengths under the drive of the linearly adjustable driving current; and The optical microcavity sensor, when the emitted light is incident on the optical microcavity sensor, causes the emitted light with a linearly changing wavelength to form a regularly changing output light signal after passing through the optical microcavity sensor with a temperature change. The microcontroller obtains the temperature value based on the regularly changing output light signal.

2. The microcavity photonic temperature measurement system according to claim 1, characterized in that, The microcontroller is used to send control signal instructions to the FPGA, causing the FPGA to generate and send a waveform digital waveform signal according to the control signal instructions; or The microcontroller is used to send variable parameters to the FPGA, so that the FPGA generates a digital waveform signal with a certain amplitude and phase according to the variable parameters, wherein the variable parameters include frequency, amplitude and phase.

3. The microcavity photonic temperature measurement system according to claim 1, characterized in that, The larger the linearly adjustable range of the driving current, the larger the wavelength range of the emitted light, resulting in a larger wavelength range received by the optical microcavity sensor, and consequently a larger temperature measurement range; and / or The temperature measurement range can be changed by adjusting the temperature of the laser diode itself.

4. The microcavity photonic temperature measurement system according to claim 1, characterized in that, The series feedback circuit includes: a follower, a comparator, a MOS transistor, a sampling resistor, and a laser diode, wherein, The follower is used to follow the amplitude-phase adjustable voltage waveform; The comparator is used to compare the amplitude- and phase-adjustable voltage waveform with the feedback voltage of the sampling resistor to generate a control signal for the MOS transistor; and The MOS transistor has a gate that receives a control signal to control its current output, and its source is grounded via the sampling resistor and its drain is connected to the laser diode.

5. The microcavity photonic temperature measurement system according to claim 2, characterized in that, It also includes a signal acquisition circuit, which comprises: a photodiode, a current-to-voltage converter, a secondary amplifier, and a first analog-to-digital converter. The photodiode is used to convert the output optical signal into a weak current signal; The amplifier is used to convert and amplify the weak current signal in two stages to generate a second-stage amplified voltage signal; and The first analog-to-digital converter is used to perform analog-to-digital conversion on the voltage signal amplified in the second stage to provide a digital voltage signal to the microcontroller.

6. The microcavity photonic temperature measurement system according to claim 5, characterized in that, The amplifier includes: a primary amplifier and a secondary amplifier, wherein, The first-stage amplifier is used to convert the weak current signal into a first-stage amplified voltage signal using a T-network operational amplification method; and The secondary amplifier is used to amplify the voltage signal amplified by the primary amplifier to generate a voltage signal amplified by the secondary amplifier.

7. The microcavity photonic temperature measurement system according to claim 5, characterized in that, It also includes a temperature control circuit, which comprises a thermistor, a second analog-to-digital converter, a thermoelectric cooler driver chip, and a thermoelectric cooler, wherein... The thermistor is used to detect changes in ambient temperature to generate a differential voltage; The second analog-to-digital converter is used to convert the differential voltage into a differential voltage digital signal and provide the differential voltage digital signal to the microcontroller; The microcontroller is configured to obtain the current ambient temperature based on the differential voltage digital signal, calculate the temperature difference between the target temperature and the current ambient temperature, and then provide a PWM signal based on the temperature difference. The thermoelectric cooler driver chip is used to provide drive current according to the PWM signal; The thermoelectric cooler is used to generate heat or cool under the control of the drive current.

8. A microcavity photon thermometry method, characterized in that, include: Generate drive current, wherein generating drive current includes: Digital waveform signals are generated by the FPGA under the control of the microcontroller; The digital waveform signal is converted into a voltage waveform with adjustable amplitude, phase, and frequency; A linearly adjustable drive current is generated based on the voltage waveform with adjustable amplitude, phase, and frequency. Driven by the linearly adjustable driving current, a laser diode generates emitted light with a linearly changing wavelength; and The emitted light is incident on an optical microcavity sensor, so that the emitted light with linearly changing wavelength passes through the optical microcavity sensor with temperature changing to form a regularly changing output light signal, wherein the microcontroller obtains the temperature value based on the regularly changing output light signal.

9. The microcavity photon thermometry method according to claim 8, characterized in that, The control signal command is sent to the FPGA, causing the FPGA to generate and send a waveform digital signal according to the control signal command; or The variable parameters are sent to the FPGA, so that the FPGA generates a triangular wave with a certain amplitude and phase according to the variable parameters, wherein the variable parameters include frequency, amplitude and phase.

10. The microcavity photonic thermometry method according to claim 8, characterized in that, The larger the linearly adjustable range of the driving current, the larger the wavelength range of the emitted light, resulting in a larger wavelength range received by the optical microcavity sensor, and consequently a larger temperature measurement range; and / or The temperature measurement range can be changed by adjusting the temperature of the laser diode itself.

Images