Fabry-Perot cavity driving method based on adaptive PID control algorithm

Abstract

The present invention discloses a Fabry-Perot cavity driving method based on an adaptive PID control algorithm, which relates to the design and application fields of Fabry-Perot cavities. The method uses the adaptive PID control method to adjust PID control parameters in real time to adjust the value of the DC voltage, thereby achieving closed-loop control of the Fabry-Perot cavity length and continuously and stably locking the Fabry-Perot cavity to a frequency-stabilized laser beam that has been locked at the atomic energy level. The present invention provides a Fabry-Perot cavity driving method based on an adaptive PID control algorithm. The method adjusts controller parameter settings based on changes in transmitted light power as a feedback signal, and uses a controller parameter design algorithm to achieve adaptive control adjustment of the cavity length. Ultimately, closed-loop control of the Fabry-Perot cavity length is achieved, improving the speed, accuracy, and stability of the Fabry-Perot cavity driving circuit, achieving long-term, highly stable locking of the Fabry-Perot cavity, and meeting the needs of some application scenarios requiring cavity locking.

Description

Technical Field

[0001] The invention relates to a Fabry-Perot cavity driving method based on an adaptive PID control algorithm, and belongs to the technical field of laser frequency stabilization. Background Art

[0002] Narrow-linewidth lasers are widely used in various fields, including medicine, measurement, and military, due to their high energy conversion efficiency, simple structure, and ease of modulation. However, some applications place high demands on the frequency stability of lasers, such as fiber-optic communications, precision spectral analysis, lidar, and quantum optics experiments. Therefore, a range of frequency stabilization methods are required to ensure that the laser's output frequency remains constant. Common frequency stabilization methods fall into two categories: passive and active. Passive frequency stabilization primarily achieves frequency stability by optimizing the design and material selection of the resonant cavity, but its stabilization effect is relatively limited. Active frequency stabilization, on the other hand, achieves frequency stability by introducing an external frequency reference, comparing the laser's output frequency with the reference frequency, and performing feedback control on the laser based on the comparison result. These active frequency stabilization methods require a suitable frequency reference, such as an atomic transition frequency or a molecular absorption line, to ensure the accuracy and reliability of frequency stabilization.

[0003] Among them, the frequency stabilization method based on the Fabry-Perot cavity is widely used in the field of laser frequency stabilization due to its advantages such as simple structure, easy implementation and adjustment. As a high-precision optical resonant cavity, the Fabry-Perot cavity can select the laser wavelength through multiple reflections and interference of the input light, thereby improving the monochromaticity and frequency stability of the laser. Therefore, the Fabry-Perot cavity has broad application prospects in some occasions where laser frequency stabilization is required. For example, in the measurement of magnetic field without spin exchange relaxation, the laser needs to be detuned and stabilized to avoid the resonance between the laser and alkali metal atoms affecting the measurement results. The Fabry-Perot cavity lock technology can obtain a stable free spectral range and provide a frequency reference for the stabilized laser.

[0004] However, the existing Fabry-Perot cavity locking technology still has some shortcomings, such as slow cavity locking speed, low accuracy and poor stability, which will lead to a decrease in the speed and stability of the above-mentioned laser detuning frequency stabilization. Part of the reason is that the control method used by the cavity locking has limitations. For example, the parameter tuning of the commonly used traditional PID control usually depends on the mathematical model of the controlled object, and once the tuning is completed, the parameters tend to remain unchanged during the control process. However, the controlled process has certain nonlinearity, time-varying uncertainty and pure hysteresis characteristics, which leads to poor parameter tuning effect and is not suitable for long-term locking of laser frequency. Therefore, in order to meet the higher requirements for laser frequency stability in practical applications, it is necessary to improve the speed, accuracy and stability of the cavity locking, which can further enhance the effect of Fabry-Perot cavity frequency stabilization. Summary of the Invention

[0005] The technical problem to be solved by the present invention is that the existing Fabry-Perot cavity locking technology has problems such as slow cavity locking speed, low accuracy and poor stability, resulting in insufficient response speed of laser frequency stabilization and easy frequency unlocking due to external interference. The present invention provides a Fabry-Perot cavity driving method based on an adaptive PID control algorithm. The method can meet the basic requirements of laser frequency stabilization using a Fabry-Perot cavity, including outputting a DC voltage signal required to drive the Fabry-Perot cavity, outputting a modulation signal for modulating the cavity length of the Fabry-Perot cavity, and collecting an optical power signal. On this basis, adaptive PID control is added. By introducing an adaptive algorithm, automatic recognition is achieved according to the changing characteristics of the parameters to be controlled, and the PID controller parameters are adjusted in real time according to the recognition results, so as to better meet the control requirements of changes in the cavity locking environment and detuning frequency stabilization of the laser, thereby improving the speed, accuracy and stability of cavity length control.

[0006] The technical solutions of the present invention are as follows:

[0007] A Fabry-Perot cavity driving method based on an adaptive PID control algorithm, characterized by comprising the following steps:

[0008] Step 1: Initialize the adaptive PID control parameter K(k) in the Fabry-Perot cavity driving device including the adaptive PID control algorithm connected to the piezoelectric ceramic end and the laser transmission end of the Fabry-Perot cavity, where K(k)=[K P (k), K I (k), K D (k)], k is the sequence number, K P (k) is the scale parameter, K I (k) is the integration parameter, k D(k) is a differential parameter that defines the deterministic linear model parameters a1, a2, b0, and b1 of the Fabry-Perot cavity-lock system;

[0009] Step 2: In the Fabry-Perot cavity driver, the triangle wave signal path in the adder circuit is closed, the PID control signal path, the modulation wave signal path, and the DC bias voltage signal path are opened, and the locking mode of the Fabry-Perot cavity driver is opened through the host computer, so that the Fabry-Perot cavity locking system enters the control cycle;

[0010] Step 3: Determine whether the Fabry-Perot cavity lock system has entered a control cycle. If so, the Fabry-Perot cavity drive device enters a lock mode and proceeds to step 4. If not, wait for the host computer to send an instruction to enter a control cycle.

[0011] Step 4: collecting feedback signal data y(k) from the lock-in amplifier in the Fabry-Perot cavity driving device and setting the reference input w(k);

[0012] Step 5: Define the data vector and the controller parameter vector θ;

[0013] Step 6: Estimate parameters using recursive least squares method and

[0014] Step 7: Establish the closed-loop characteristic polynomial T(z -1 );

[0015] Step 8, solve the new controller parameter u(k);

[0016] Step 9: Based on u(k), the PID controller converts the error signal into a control signal to control the piezoelectric ceramic, corrects the cavity length of the Fabry-Perot cavity, and then returns to step 3.

[0017] The Fabry-Perot cavity driving device in step 1 includes a Fabry-Perot cavity driving circuit unit respectively connected to a controller parameter design unit, a controller unit and a piezoelectric ceramic end of the Fabry-Perot cavity, wherein the controller parameter design unit is connected to the controller unit, and the Fabry-Perot cavity driving circuit unit is connected to the piezoelectric ceramic. The Fabry-Perot cavity driving circuit unit transmits the collected locking cavity feedback data and controller parameter data to the controller parameter design unit. The controller parameter design unit calculates new controller parameters and transmits them to the controller unit. The controller unit adjusts the control signal according to the new parameters and the reference input, returns the control signal to the Fabry-Perot cavity driving circuit unit, and then acts on the Fabry-Perot cavity to realize locking cavity.

[0018] The Fabry-Perot cavity driving device in step 1 includes a photodetector, a host computer unit, a single-chip microcomputer main control unit, a digital-to-analog converter, an adder circuit, a DC bias circuit, a lock-in amplifier and an analog-to-digital converter. The single-chip microcomputer main control unit is respectively connected to the host computer unit, the analog-to-digital converter, the digital-to-analog converter and the adder circuit. The analog-to-digital converter is respectively connected to the photodetector and the lock-in amplifier. The adder circuit is respectively connected to the DC bias circuit, the digital-to-analog converter and the piezoelectric ceramic. The digital-to-analog converter is connected to the lock-in amplifier. The photodetector is connected to a frequency-stabilized laser through the Fabry-Perot cavity. The single-chip microcomputer main control unit sends instructions to the digital-to-analog converter to control the waveform, amplitude and period of the voltage signal output by it. The digital-to-analog converter outputs two voltage signals, one of which is a triangular wave signal, which is output to the adder circuit for scanning the Fabry-Perot cavity. -Perot cavity, the other is a sinusoidal modulation signal, which is output to the adder for modulating the cavity length of the Fabry-Perot cavity, and is output to the phase-locked amplifier for demodulation. The phase-locked amplifier has two input signals, one is the voltage signal output by the photodetector, and the other is the sinusoidal modulation signal output by the digital-to-analog converter. The phase-locked amplifier demodulates the voltage signal according to the sinusoidal modulation signal to obtain an error signal of the frequency deviation between the resonant frequency of the Fabry-Perot cavity and the frequency of the incident laser, and inputs the signal to the analog-to-digital converter. The analog-to-digital converter collects two voltage signals, one is the voltage signal output by the photodetector, and the converted digital signal is sent to the single-chip microcomputer main control unit, and the single-chip microcomputer main control unit transmits it to the upper computer unit to display the waveform, and the other is the voltage signal output by the phase-locked amplifier, which is sent to the adaptive PID controller of the single-chip microcomputer main control unit to calculate the control signal.

[0019] The piezoelectric ceramic of the Fabry-Perot cavity in step 1 is connected to the output end of the adder circuit, the second input end of the adder circuit is connected to the sinusoidal modulation signal, the first input end of the adder circuit is connected to the output end of the voltage amplifier circuit, the input end of the voltage amplifier circuit is respectively connected to the first output end of the comparator and the output end of the PID parameter design unit through the PID controller, the PID parameter design unit is connected to the second output end of the comparator, the first input end of the comparator is connected to the reference input, and the second input end of the comparator is connected to the piezoelectric ceramic through the phase-locked amplifier and the photodetector in sequence. The adder circuit realizes the superposition of four voltage signals, namely, the triangular wave signal, the PID control signal, the DC bias voltage and the modulation wave signal, and the four signal paths have corresponding switches to control conduction or shutdown.

[0020] Step 1 includes the following relational expressions:

[0021] A(z -1 )y(k)=z -1 B(z -1 )u(k),

[0022] A(z -1 )=1+a1z -1 +a2z -2 ,

[0023] B(z -1 )=b0+b1z -1 ,

[0024] Where A(z -1 ) is the setting polynomial, y(k) is the feedback signal data, z is the z-axis coordinate, which represents the cavity length of the Fabry-Perot cavity, B(z -1 ) is the setting polynomial, and u(k) is the controller parameter.

[0025] Step 4 includes w(k)=0, and step 5 includes the following relational expression:

[0026]

[0027] θ=[a1,a2,b0,b1] T .

[0028] Step 6 includes the following relational expressions:

[0029]

[0030] where I is the identity matrix, is the estimated controller parameter vector, k is the sequence number, P(k) is the recursive parameter, and the exponent T is the transpose operation.

[0031] Step 7 includes the following relational expressions:

[0032] A(z -1 )H(z -1 )+z -1 B(z -1 )G(z -1 )=T(z -1 ),

[0033] H(z -1 )=(1-z -1 )(1+h1z -1 ),

[0034] G(z -1 )=g0+g1z -1 +g2z -2 ,

[0035] g0=K P +K I +K D ,

[0036] g1=-KP -2K D ,

[0037] g2=K D ,

[0038] T(z -1 )=t0+t1z -1 +…+t n z -n ,

[0039] Where n≤4, t is a coefficient, g0, g1 and g2 are intermediate quantities, K P is the scale parameter, K I is the integration parameter, K D is the differential parameter, H(z -1 ) is the intermediate quantity, G(z -1 ) is the intermediate quantity and h1 is the coefficient.

[0040] Step 8 includes the following relational expressions:

[0041] (1-z -1 )(1+h1z -1 )u(k)=(g0+g1z -1 +g2z -2 )e(k),

[0042] e(k)=w(k)-y(k),

[0043] Δu(k)=-h1u(k-1)+h1u(k-2)+(g0+g1z -1 +g2z -2 )e(k),

[0044] Where e(k) is the error, Δu(k) is the control signal increment, and the new control signal can be obtained by adding the original control signal to the control signal increment, which is then used to correct the cavity length.

[0045] The technical effects of the present invention are as follows: a Fabry-Perot cavity driving method based on an adaptive PID control algorithm can more conveniently perform scanning and locking of the Fabry-Perot cavity. The use of an adder in conjunction with an input path switch can more conveniently switch between scanning mode and locking mode. A DC bias function can shift the position of the optical power signal displayed on the oscilloscope to facilitate finding the transmission peak. The designed analog-to-digital converter and digital-to-analog converter both have high precision, ensuring the accuracy of signal output and data acquisition. The use of the adaptive PID controller designed by the present invention can enhance the control feedback capability of the Fabry-Perot cavity locking system. Before locking the cavity, the output DC voltage can be quickly adjusted to lock the cavity length of the Fabry-Perot cavity to a preset transmission peak position. After locking the cavity, the system can accelerate the process of suppressing errors and interferences, continuously correcting the cavity length to keep the output transmitted laser light power at the peak value. The use of the adaptive PID control method can shorten the time for PID parameter calibration, increase the speed of the locking system, and eliminate the need to recalibrate the PID parameters when system parameters change or the environment changes, thereby reducing the impact of errors and interference on the locking results and enhancing the robustness of the locking system. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 The present invention is a schematic diagram of the components of a Fabry-Perot cavity driving device involved in implementing a Fabry-Perot cavity driving method based on an adaptive PID control algorithm.

[0047] Figure 2 The present invention is a schematic diagram of a circuit involved in a Fabry-Perot cavity driving method based on an adaptive PID control algorithm. Figure 2 The portion included in the dot-dash line is the circuit structure involved in the present invention, and the portion outside the dot-dash line is the optical path structure required for the embodiment.

[0048] Figure 3 The invention provides a control block diagram of an adaptive PID closed-loop control loop involved in implementing a Fabry-Perot cavity driving method based on an adaptive PID control algorithm.

[0049] Figure 4 The present invention is a flowchart of a Fabry-Perot cavity driving method based on an adaptive PID control algorithm. Figure 4 The process includes step 1, initializing the adaptive PID control parameters (PID, Proportion, Integral, Differential), including K(k)=[K P (k), K I (k), K D (k)], K(k) is the PID control parameter, k is the sequence number, K P(k) is the scale parameter, K I (k) is the integration parameter, K D (k) is a differential parameter, defining the deterministic linear model parameters a1, a2, b0, and b1 of the Fabry-Perot cavity lock system; Step 2, close the triangle wave signal path in the adder circuit, open the PID control signal path, the modulation wave signal path, and the DC bias voltage signal path, open the lock mode of the Fabry-Perot cavity drive device through the host computer, and let the Fabry-Perot cavity lock system enter the control cycle; Step 3, determine whether the Fabry-Perot cavity lock system enters the control cycle, if so, the Fabry-Perot cavity drive device enters the lock mode and enters step 4, if not, the system repeats step 3 and waits for the host computer to send an instruction to enter the control cycle; Step 4, collect the feedback signal data y(k) of the phase-locked amplifier and set the reference input w(k); Step 5, define the data vector and controller parameter vector θ; Step 6, use recursive least squares method to estimate the parameters and Step 7: Establish the closed-loop characteristic polynomial T(z -1 ), and calculate H(z -1 ) and G(z -1 ); Step 8, solve the new controller parameter u(k); Step 9, calculate the output voltage to control the piezoelectric ceramic, and return to step 3.

[0050] The accompanying drawings are marked as follows: 101-Fabry-Perot cavity driving circuit unit; 102-controller parameter design unit; 103-controller unit; 104-Fabry-Perot cavity; 201-frequency-stabilized laser; 202-piezoelectric ceramic; 203-Fabry-Perot cavity; 204-photodetector; 205-host computer unit; 206-single-chip microcomputer main control unit; 207-digital-to-analog converter; 208-adder circuit; 209-DC bias circuit; 210-phase-locked amplifier; 211-analog-to-digital converter; 212-Fabry-Perot cavity driving device; 301-reference input; 302-PID parameter design unit; 303-PID controller; 304-voltage amplifier circuit; 305-adder circuit; 306-sinusoidal modulation signal; 307-piezoelectric ceramic; 308-photodetector; 309-phase-locked amplifier. DETAILED DESCRIPTION

[0051] Below is the attached figure ( Figures 1-4 ) and Examples illustrate the present invention.

[0052] Figure 1 The present invention is a schematic diagram of the components of a Fabry-Perot cavity driving device involved in implementing a Fabry-Perot cavity driving method based on an adaptive PID control algorithm. Figure 2 The present invention is a schematic diagram of a circuit involved in a Fabry-Perot cavity driving method based on an adaptive PID control algorithm. Figure 3 The invention provides a control block diagram of an adaptive PID closed-loop control loop involved in implementing a Fabry-Perot cavity driving method based on an adaptive PID control algorithm. Figure 4 This is a flow chart of a Fabry-Perot cavity driving method based on an adaptive PID control algorithm according to the present invention. Figures 1 to 4 As shown, a Fabry-Perot cavity driving method based on an adaptive PID control algorithm comprises the following steps: Step 1, initializing an adaptive PID control parameter K(k) in a Fabry-Perot cavity driving device including an adaptive PID control algorithm connected to a piezoelectric ceramic end and a laser transmission end of the Fabry-Perot cavity, wherein K(k)=[K P (k), K I (k), K D (k)], k is the sequence number, K P (k) is the scale parameter, K I (k) is the integration parameter, K D (k) is a differential parameter that defines the deterministic linear model parameters a1, a2, b0, and b1 of the Fabry-Perot cavity lock system. Step 2: In the Fabry-Perot cavity driver, the triangle wave signal path in the adder circuit is closed, and the PID control signal path, the modulation wave signal path, and the DC bias voltage signal path are opened. The lock mode of the Fabry-Perot cavity driver is opened through the host computer, and the Fabry-Perot cavity lock system enters a control cycle.

[0053] Step 3: Determine whether the Fabry-Perot cavity lock system enters the control cycle. If so, the Fabry-Perot cavity drive device enters the lock mode and enters step 4. If not, wait for the host computer to send an instruction to enter the control cycle; Step 4: Collect the feedback signal data y(k) of the phase-locked amplifier in the Fabry-Perot cavity drive device and set the reference input w(k); Step 5: Define the data vector φ(k) and the controller parameter vector θ; Step 6: Use the recursive least squares method to estimate the parameters and Step 7: Establish the closed-loop characteristic polynomial T(z -1 ); Step 8, solve the new controller parameter u(k); Step 9, based on u(k), the PID controller converts the error signal into a control signal to control the piezoelectric ceramic, corrects the cavity length of the Fabry-Perot cavity, and then returns to Step 3.

[0054] The Fabry-Perot cavity driving device in step 1 includes a Fabry-Perot cavity driving circuit unit 101 respectively connected to a controller parameter design unit 102, a controller unit 103 and a piezoelectric ceramic end of the Fabry-Perot cavity, wherein the controller parameter design unit 102 is connected to the controller unit 103, and the Fabry-Perot cavity driving circuit unit 101 is connected to the piezoelectric ceramic. The Fabry-Perot cavity driving circuit unit 101 transmits the collected locking cavity feedback data and controller parameter data to the controller parameter design unit 102. The controller parameter design unit 102 calculates new controller parameters and transmits them to the controller unit 103. The controller unit 103 adjusts the control signal according to the new parameters and the reference input, returns the control signal to the Fabry-Perot cavity driving circuit unit 101, and then acts on the Fabry-Perot cavity 104 to realize the locking cavity.

[0055] The Fabry-Perot cavity driving device 212 in step 1 includes a photodetector 204, a host computer unit 205, a single-chip microcomputer main control unit 206, a digital-to-analog converter 207, an adder circuit 208, a DC bias circuit 209, a lock-in amplifier 210 and an analog-to-digital converter 211, wherein the single-chip microcomputer main control unit 206 is connected to the host computer unit 205, the analog-to-digital converter 211, the digital-to-analog converter 207 and the adder circuit 208, and the analog-to-digital converter 211 is connected to the photodetector 204 and the lock-in amplifier. The adder circuit 208 is connected to the DC bias circuit 209, the digital-to-analog converter 207 and the piezoelectric ceramic 202 respectively. The digital-to-analog converter 207 is connected to the phase-locked amplifier 210. The photodetector 204 is connected to the frequency-stabilized laser 201 through the Fabry-Perot cavity 203. The single-chip main control unit 206 sends instructions to the digital-to-analog converter 207 to control the waveform, amplitude and period of the voltage signal output by it. The digital-to-analog converter 207 outputs two voltage signals, one of which is a triangle. The first circuit is a sine wave signal, which is output to the adder circuit 208 for scanning the Fabry-Perot cavity. The other circuit is a sinusoidal modulation signal, which is output to the adder circuit 208 for modulating the cavity length of the Fabry-Perot cavity and output to the phase-locked amplifier 210 for demodulation. The phase-locked amplifier 210 has two input signals, one is the voltage signal output by the photodetector 204, and the other is the sinusoidal modulation signal output by the digital-to-analog converter 207. The phase-locked amplifier 210 demodulates the voltage signal according to the sinusoidal modulation signal to obtain the resonant frequency of the Fabry-Perot cavity 203. The error signal of the frequency deviation between the laser frequency and the incident laser frequency is obtained, and the signal is input to the analog-to-digital converter 211. The analog-to-digital converter 211 collects two voltage signals. One is the voltage signal output by the photodetector 204. The converted digital signal is sent to the single-chip microcomputer main control unit 206, and is transmitted by the single-chip microcomputer main control unit 206 to the host computer unit 205 to display the waveform. The other is the voltage signal output by the phase-locked amplifier 210, which is sent to the adaptive PID controller of the single-chip microcomputer main control unit 206 to calculate the control signal.

[0056] The piezoelectric ceramic 307 of the Fabry-Perot cavity in step 1 is connected to the output end of the adder circuit 305, the second input end of the adder circuit 305 is connected to the sinusoidal modulation signal 306, the first input end of the adder circuit 305 is connected to the output end of the voltage amplifier circuit 304, the input end of the voltage amplifier circuit 304 is respectively connected to the first output end of the comparator and the output end of the PID parameter design unit 302 through the PID controller 303, the PID parameter design unit 302 is connected to the second output end of the comparator, the first input end of the comparator is connected to the reference input 301, and the second input end of the comparator is connected to the piezoelectric ceramic 307 through the lock-in amplifier 309 and the photodetector 308 in sequence. The adder circuit 305 realizes the superposition of four voltage signals, namely the triangular wave signal, the PID control signal, the DC bias voltage and the modulation wave signal, and the four signal paths have corresponding switches to control conduction or shutdown.

[0057] Step 1 includes the following relational expressions:

[0058] A(z -1 )y(k)=z -1 B(z -1 )u(k),

[0059] A(z -1 )=1+a1z -1 +a2z -2 ,

[0060] B(z -1 )=b0+b1z -1 ,

[0061] Where A(z -1 ) is the setting polynomial, y(k) is the feedback signal data, z is the z-axis coordinate, which represents the cavity length of the Fabry-Perot cavity, B(z -1 ) is the setting polynomial, and u(k) is the controller parameter.

[0062] Step 4 includes w(k)=0, and step 5 includes the following relational expression:

[0063]

[0064] θ=[a1,a2,b0,b1] T .

[0065] Step 6 includes the following relational expressions:

[0066]

[0067] where I is the identity matrix, is the estimated controller parameter vector, k is the sequence number, P(k) is the recursive parameter, and the exponent T is the transpose operation.

[0068] Step 7 includes the following relational expressions:

[0069] A(z -1 )H(z -1 )+z -1 B(z -1 )G(z -1 )=T(z -1 ),

[0070] H(z -1 )=(1-z -1 )(1+h1z -1 ),

[0071] G(z -1 )=g0+g1z -1 +g2z -2 ,

[0072] g0=K P +K I +K D ,

[0073] g1=-K P -2K D ,

[0074] g2=K D ,

[0075] T(z -1 )=t0+t1z -1 +…+t n z -n ,

[0076] Where n≤4, t is a coefficient, g0, g1 and g2 are intermediate quantities, K P is the scale parameter, K I is the integration parameter, K D is the differential parameter, H(z -1 ) is the intermediate quantity, G(z -1 ) is the intermediate quantity and h1 is the coefficient.

[0077] Step 8 includes the following relational expressions:

[0078] (1-z -1 )(1+h1z -1 )u(k)=(g0+g1z -1 +g2z -2 )e(k),

[0079] e(k)=w(k)-y(k),

[0080] Δy(k)=-h1u(k-1)+h1u(k-2)+(g0+g1z -1 +g2z -2 )e(k),

[0081] Where e(k) is the error, Δu(k) is the control signal increment, and the new control signal can be obtained by adding the original control signal to the control signal increment, which is then used to correct the cavity length.

[0082] The present invention discloses a Fabry-Perot cavity drive system based on an adaptive PID control algorithm, and relates to the design and application fields of Fabry-Perot cavities. The present invention outputs a DC voltage applied to both ends of a piezoelectric ceramic, adjusts the DC voltage value in real time by adjusting the PID control parameters using an adaptive PID control method, implements closed-loop control of the Fabry-Perot cavity length, and continuously and stably locks the Fabry-Perot cavity to a frequency-stabilized laser beam that has been locked to the atomic energy level. The present invention provides a Fabry-Perot cavity drive system based on an adaptive PID control algorithm. The controller parameter settings are adjusted based on the change in transmitted light power as a feedback signal, and the controller parameter design algorithm is used to implement adaptive control adjustment of the cavity length, ultimately achieving closed-loop control of the Fabry-Perot cavity length, improving the speed, accuracy, and stability of the Fabry-Perot cavity drive circuit, and achieving long-term, highly stable locking of the Fabry-Perot cavity, meeting some application scenarios requiring cavity locking.

[0083] A Fabry-Perot cavity driving system based on an adaptive PID control algorithm comprises the following structures: a frequency-stabilized laser (201), a piezoelectric ceramic (202), a Fabry-Perot cavity (203), a photodetector (204), a host computer unit (205), a single-chip computer main control unit (206), a digital-to-analog converter (207), an adder circuit (208), a DC bias circuit (209), a lock-in amplifier (210), and an analog-to-digital converter (211); and the device relates to an adaptive PID control algorithm used in a Fabry-Perot cavity driving device, for realizing a cavity locking function.

[0084] The chip model used by the single-chip microcomputer main control unit is STM32F407ZET6. The single-chip microcomputer main control unit sends instructions to the digital-to-analog converter through SPI communication to control the waveform, amplitude and period of the voltage signal output by it.

[0085] The digital-to-analog converter is implemented using the chip AD5689R; the digital-to-analog converter involved in the present invention can output two voltage signals, one is a triangular wave signal, which is output to the adder circuit for scanning the Fabry-Perot cavity, and the other is a sinusoidal modulation signal, which is output to the adder for modulating the cavity length of the Fabry-Perot cavity and output to the lock-in amplifier for demodulation.

[0086] The DC bias circuit can generate a DC voltage of 0V to +15V and output it to the adder circuit. By adjusting the variable resistor to change the DC bias of the adder circuit output voltage signal, it is easy to find the peak position of the optical power signal of the transmitted laser.

[0087] The main function of the adder circuit is to achieve the superposition of four voltage signals: a triangular wave signal, a PID control signal, a DC bias voltage, and a modulation wave signal. Each of the four signal paths has a corresponding switch control to turn on or off. The input end of the adder circuit is preceded by a voltage amplifier circuit, which can amplify the voltage of the triangular wave signal and the PID control signal.

[0088] The lock-in amplifier has two input signals, one is the voltage signal output by the photodetector, and the other is the sinusoidal modulation signal output by the digital-to-analog converter; the lock-in amplifier demodulates the voltage signal according to the sinusoidal modulation signal to obtain an error signal of the frequency deviation between the resonant frequency of the Fabry-Perot cavity and the incident laser frequency, and inputs this signal into the analog-to-digital converter.

[0089] The analog-to-digital converter is implemented using the chip AD7190; the function of the analog-to-digital converter involved in the present invention is to collect two voltage signals, one of which is the voltage signal output by the photodetector, and send the converted digital signal to the single-chip microcomputer main control unit, and then transmit it from the single-chip microcomputer main control unit to the host computer unit for waveform display; the other is the voltage signal output by the lock-in amplifier, and the signal is sent to the adaptive PID controller of the single-chip microcomputer main control unit to calculate the control signal.

[0090] Figure 1 The present invention is a driving device component unit involved in the implementation of the Fabry-Perot cavity driving device based on the adaptive PID control method of the present invention, including a Fabry-Perot cavity driving circuit unit (101), a controller parameter design unit (102), a controller unit (103), and a Fabry-Perot cavity (104). The Fabry-Perot cavity driving circuit unit transmits the collected lock cavity feedback data and controller parameter data to the controller parameter design unit, and then the controller parameter design unit calculates the new controller parameters and transmits them to the controller unit. The controller unit adjusts the control signal according to the new parameters and the reference input, returns the control signal to the Fabry-Perot cavity driving circuit unit, and then acts on the Fabry-Perot cavity to realize the lock cavity. Among them, the Fabry-Perot cavity driving circuit unit, the controller parameter design unit and the controller unit constitute the Fabry-Perot cavity driving device designed by the present invention. The specific implementation method of the Fabry-Perot cavity driving circuit unit will be combined with the Figure 2 Further explanation, the specific implementation of the controller parameter design unit and the controller unit will be combined Figure 3 and Figure 4 Further explanation.

[0091] Figure 2 The invention discloses a circuit in an embodiment of a Fabry-Perot cavity driving device based on an adaptive PID control method of the present invention, comprising a frequency-stabilized laser (201), a piezoelectric ceramic (202), a Fabry-Perot cavity (203), a photodetector (204), a host computer unit (205), a single-chip microcomputer main control unit (206), a digital-to-analog converter (207), an adder circuit (208), a DC bias circuit (209), a lock-in amplifier (210), an analog-to-digital converter (211), and a Fabry-Perot cavity driving device (212). The portion enclosed by the dot-dashed line is the structure of the Fabry-Perot cavity driving circuit of the present invention, and the portion outside the dot-dashed line is the optical path structure required by the embodiment. The designed Fabry-Perot cavity driving circuit performs the following functions in sequence:

[0092] First, the host computer displays the optical power signal waveform of the laser transmitted from the Fabry-Perot cavity, and the Fabry-Perot cavity is locked on a certain transmission peak on the host computer.

[0093] Second, the host computer unit sends a lock cavity instruction to the MCU main control unit, and the MCU main control unit sends an instruction to the digital-to-analog converter through SPI communication to control the waveform, amplitude and period of the voltage signal output by it.

[0094] Third, the main control unit of the single-chip microcomputer outputs the PID control signal through the digital-to-analog conversion pin of the chip, and the signal is output to the adder circuit.

[0095] Fourth, the MCU main control unit sends instructions to the analog-to-digital converter through SPI communication to control it to send the detected electrical signal data to the MCU main control unit. The digital-to-analog converter outputs a sinusoidal modulated signal, which is output to the adder for modulating the cavity length of the Fabry-Perot cavity and to the phase-locked amplifier for demodulation.

[0096] Fifth, the DC bias circuit generates a DC voltage from 0V to +15V and outputs it to the adder circuit. The voltage value is changed by adjusting the variable resistor. The function of this DC voltage is to shift the waveform image displayed by the host computer left and right.

[0097] Sixth, the adder circuit realizes the superposition of the triangular wave signal, PID control signal, DC bias voltage and modulation wave signal, and the four signal paths have corresponding switch control on or off; and the triangular wave signal and PID control signal first pass through the voltage amplifier circuit and then are connected to the input end of the adder circuit to amplify the 0-5V voltage signal to 0-30V.

[0098] Seventh, in the scanning mode, only the triangle wave signal path and the DC bias voltage path are opened; in the locked cavity mode, only the PID control signal path, the DC bias voltage path and the sinusoidal modulation signal path are opened.

[0099] Eighth, the photodetector converts the detected Fabry-Perot cavity transmitted laser light power signal into a current signal, and then converts the current signal into a voltage signal through an internal transimpedance amplifier, and has 11 resistance positions, including 5kΩ, 10kΩ, 20kΩ, 30kΩ, 50kΩ, 100kΩ, 200kΩ, 300kΩ, 500kΩ, 1MΩ, and 2MΩ, to increase the detection range of the optical power signal. After adjusting to the appropriate resistance position, the output end of the photodetector is connected to the lock-in amplifier.

[0100] Ninth, the phase-locked amplifier has two input signals, one is the voltage signal output by the photodetector, and the other is the sinusoidal modulation signal output by the digital-to-analog converter; the phase-locked amplifier demodulates the voltage signal according to the sinusoidal modulation signal to obtain an error signal describing the frequency deviation between the resonant frequency of the Fabry-Perot cavity and the incident laser frequency, and inputs the signal into the analog-to-digital converter.

[0101] Tenth, the analog-to-digital converter collects two voltage signals, one is the voltage signal output by the photodetector, and the converted digital signal is sent to the single-chip microcomputer main control unit, and then transmitted by the single-chip microcomputer main control unit to the host computer unit to display the waveform; the other is the voltage signal output by the lock-in amplifier, which is sent to the adaptive PID controller of the single-chip microcomputer main control unit to calculate the control signal.

[0102] Figure 3The invention relates to an adaptive PID closed-loop control circuit for implementing a Fabry-Perot cavity driving device based on an adaptive PID control method of the present invention, comprising a reference input (301), a PID parameter design unit (302), a PID controller (303), a voltage amplifier circuit (304), an adder circuit (305), a sinusoidal modulation signal (306), a piezoelectric ceramic (307), a photodetector (308), and a lock-in amplifier (309). After the system is initialized, the reference signal passes through the PID controller to obtain a PID control signal, which is amplified by the voltage amplifier circuit and superimposed with the modulation signal in the adder circuit to obtain a driving signal. The driving signal is then applied to the piezoelectric ceramic to control the cavity length of the Fabry-Perot cavity. The optical power signal is detected by the photodetector and demodulated by the phase-locked amplifier to obtain a feedback signal. This signal describes the difference between the resonant frequency of the Fabry-Perot cavity and the resonant frequency of the incident laser. The error signal is obtained by subtracting the reference input from the feedback signal. The error signal is transmitted to the PID parameter design unit and the adjustable PID controller. The PID parameter design unit adjusts the new PID controller parameters. The PID controller converts the error signal into a control signal to correct the cavity length of the Fabry-Perot cavity.

[0103] Figure 4 The invention provides an algorithm flow for implementing the adaptive PID control method of the Fabry-Perot cavity driving device based on the adaptive PID control method. Figure 4 The process includes step 1, initializing the adaptive PID control parameters, including K(k)=[K P (k), K I (k), K D (k)], define the deterministic linear model parameters a1, a2, b0, b1 of the Fabry-Perot cavity lock system; Step 2, close the triangle wave signal path in the adder circuit, open the PID control signal path, the modulation wave signal path and the DC bias voltage signal path, open the lock mode of the Fabry-Perot cavity drive device through the host computer, and let the Fabry-Perot cavity lock system enter the control cycle; Step 3, determine whether the Fabry-Perot cavity lock system enters the control cycle, if so, the Fabry-Perot cavity drive device enters the lock mode and enters step 4, if not, the system repeats step 3 and waits for the host computer to send an instruction to enter the control cycle; Step 4, collect the feedback signal data y(k) of the phase-locked amplifier and set the reference input w(k); Step 5, define the data vector φ(k) and the controller parameter vector θ; Step 6, use the recursive least squares method to estimate the parameters and Step 7: Establish the closed-loop characteristic polynomial T(z -1 ), and calculate H(z -1 ) and G(z -1); Step 8, solve the new controller parameter u(k); Step 9, calculate the output voltage to control the piezoelectric ceramic, and return to step 3.

[0104] The present invention provides an adaptive PID control method for a Fabry-Perot cavity driving device, comprising the following steps:

[0105] Step 1: Initialize the adaptive PID control parameters, including K(k)=[K P (k), K I (k), K D (k)], define the deterministic linear model parameters a1, a2, b0, b1 of the Fabry-Perot cavity lock system;

[0106] Step 2: Close the triangle wave signal path in the adder circuit, open the PID control signal path, the modulation wave signal path, and the DC bias voltage signal path, and open the locked cavity mode of the Fabry-Perot cavity drive device through the host computer to allow the Fabry-Perot cavity locked cavity system to enter the control cycle;

[0107] Step 3: Determine whether the Fabry-Perot cavity lock system has entered a control cycle. If so, the Fabry-Perot cavity drive device enters a lock mode and proceeds to step 4. If not, the system repeats step 3 and waits for the host computer to send an instruction to enter a control cycle.

[0108] Step 4: Collect the feedback signal data y(k) of the lock-in amplifier and set the reference input w(k);

[0109] Step 5, define the data vector φ(k) and the controller parameter vector θ;

[0110] Step 6: Estimate parameters using recursive least squares method and

[0111] Step 7: Establish the closed-loop characteristic polynomial T(z -1 ), and calculate H(z -1 ) and G(z -1 );

[0112] Step 8, solve the new controller parameter u(k);

[0113] Step 9: Calculate the output voltage to control the piezoelectric ceramic, and return to step 3;

[0114] The deterministic linear model parameters a1, a2, b0, and b1 in step 1 are derived from a mathematical model of a Fabry-Perot cavity-lock system, which includes the following relational expressions:

[0115] A(z -1)y(k)=z -1 B(z -1 )u(k)

[0116] in

[0117] A(z -1 )=1+a1z -1 +a2z -2

[0118] B(z -1 )=b0+b1z -1

[0119] As shown in the above expression, a1, a2, b0, b1 are A(z -1 ) and B(z -1 )’s polynomial coefficients;

[0120] The feedback signal data y(k) in step 4 is collected by the analog-to-digital converter (211), and the reference input w(k) is 0;

[0121] Step 5 includes the following relational expression:

[0122]

[0123] θ=[a1,a2,b0,b1] T

[0124] Step 6 contains the following relational expression:

[0125]

[0126]

[0127]

[0128] Where I is the identity matrix;

[0129] Step 7 contains the following relational expression:

[0130] A(z -1 )H(z -1 )+z -1 B(z -1 )G(z -1 )=T(z -1 )

[0131] in

[0132] H(z -1 )=(1-z -1 )(1+h1z -1 )

[0133] G(z-1 )=g0+g1z -1 +g2z -2

[0134] g0=K P +K I +K D

[0135] g1=-K P -2K D

[0136] g2=K D

[0137] T(z -1 )=t0+t1z -1 +…+t n z -n

[0138] Where n≤4, n=2 is generally selected;

[0139] Step 8 contains the following relational expression:

[0140] (1-z -1 )(1+h1z -1 )u(k)=(g0+g1z -1 +g2z -2 )e(k)

[0141] e(k)=w(k)-y(k)

[0142] After solving the above expression, we get

[0143] Δu(k)=-h1u(k-1)+h1u(k-2)+(g0+g1z -1 +g2z -2 )e(k)

[0144] The new control signal is obtained by adding the original control signal and the control signal increment, and then used to correct the cavity length.

[0145] This device can lock the cavity length of a Fabry-Perot cavity at the transmission peak of the incident laser. By combining an adder with an input path switch, it is possible to more easily switch between scanning mode and cavity lock mode. A DC bias function can shift the position of the optical power signal displayed on the oscilloscope, facilitating the identification of the transmission peak. Both the analog-to-digital converter and the digital-to-analog converter are designed to have high precision, ensuring the accuracy of signal output and data acquisition. The adaptive PID controller designed in this invention can enhance the control feedback capability of the Fabry-Perot cavity lock system, quickly locking the cavity length to the position where the transmission peak occurs. It also has a certain degree of anti-interference capability, increasing the speed, accuracy, and stability of the cavity lock system.

[0146] Any content not described in detail in this specification is prior art known to those skilled in the art. It should be noted that the above description is intended to help those skilled in the art understand the present invention, but does not limit the scope of protection of the present invention. Any equivalent substitution, modification, improvement, and / or simplification of the above description that does not depart from the essence of the present invention shall fall within the scope of protection of the present invention.

Claims

1. A Fabry-Perot cavity driving method based on an adaptive PID control algorithm, characterized in that: The following steps are involved: Step 1: Initialize the adaptive PID control parameter K(k) in the Fabry-Perot cavity driving device including the adaptive PID control algorithm connected to the piezoelectric ceramic end and the laser transmission end of the Fabry-Perot cavity, where K(k)=[K P (k), K I (k), K D (k)], k is the sequence number, K P (k) is the scale parameter, K I (k) is the integration parameter, K D (k) is a differential parameter that defines the deterministic linear model parameters a1, a2, b0, and b1 of the Fabry-Perot cavity-lock system; Step 2: In the Fabry-Perot cavity driver, the triangle wave signal path in the adder circuit is closed, the PID control signal path, the modulation wave signal path, and the DC bias voltage signal path are opened, and the locking mode of the Fabry-Perot cavity driver is opened through the host computer, so that the Fabry-Perot cavity locking system enters the control cycle; Step 3: Determine whether the Fabry-Perot cavity lock system has entered a control cycle. If so, the Fabry-Perot cavity drive device enters a lock mode and proceeds to step 4. If not, wait for the host computer to send an instruction to enter a control cycle. Step 4: collecting feedback signal data y(k) from the lock-in amplifier in the Fabry-Perot cavity driving device and setting the reference input w(k); Step 5, define the data vector φ(k) and the controller parameter vector θ; Step 6: Estimate parameters using recursive least squares method and Step 7: Establish the closed-loop characteristic polynomial T(z -1 ); Step 8, solve the new controller parameter u(k); Step 9: Based on u(k), the PID controller converts the error signal into a control signal to control the piezoelectric ceramic, corrects the cavity length of the Fabry-Perot cavity, and then returns to step 3.

2. The Fabry-Perot cavity driving method based on the adaptive PID control algorithm according to claim 1, characterized in that: The Fabry-Perot cavity driving device in step 1 includes a Fabry-Perot cavity driving circuit unit respectively connected to a controller parameter design unit, a controller unit and a piezoelectric ceramic end of the Fabry-Perot cavity, wherein the controller parameter design unit is connected to the controller unit, and the Fabry-Perot cavity driving circuit unit is connected to the piezoelectric ceramic. The Fabry-Perot cavity driving circuit unit transmits the collected locking cavity feedback data and controller parameter data to the controller parameter design unit. The controller parameter design unit calculates new controller parameters and transmits them to the controller unit. The controller unit adjusts the control signal according to the new parameters and the reference input, returns the control signal to the Fabry-Perot cavity driving circuit unit, and then acts on the Fabry-Perot cavity to realize locking cavity.

3. The Fabry-Perot cavity driving method based on the adaptive PID control algorithm according to claim 1, characterized in that: The Fabry-Perot cavity driving device in step 1 includes a photodetector, a host computer unit, a single-chip microcomputer main control unit, a digital-to-analog converter, an adder circuit, a DC bias circuit, a lock-in amplifier and an analog-to-digital converter. The single-chip microcomputer main control unit is respectively connected to the host computer unit, the analog-to-digital converter, the digital-to-analog converter and the adder circuit. The analog-to-digital converter is respectively connected to the photodetector and the lock-in amplifier. The adder circuit is respectively connected to the DC bias circuit, the digital-to-analog converter and the piezoelectric ceramic. The digital-to-analog converter is connected to the lock-in amplifier. The photodetector is connected to a frequency-stabilized laser through the Fabry-Perot cavity. The single-chip microcomputer main control unit sends instructions to the digital-to-analog converter to control the waveform, amplitude and period of the voltage signal output by it. The digital-to-analog converter outputs two voltage signals, one of which is a triangular wave signal, which is output to the adder circuit for scanning the Fabry-Perot cavity. -Perot cavity, the other is a sinusoidal modulation signal, which is output to the adder for modulating the cavity length of the Fabry-Perot cavity, and is output to the phase-locked amplifier for demodulation. The phase-locked amplifier has two input signals, one is the voltage signal output by the photodetector, and the other is the sinusoidal modulation signal output by the digital-to-analog converter. The phase-locked amplifier demodulates the voltage signal according to the sinusoidal modulation signal to obtain an error signal of the frequency deviation between the resonant frequency of the Fabry-Perot cavity and the frequency of the incident laser, and inputs the signal to the analog-to-digital converter. The analog-to-digital converter collects two voltage signals, one is the voltage signal output by the photodetector, and the converted digital signal is sent to the single-chip microcomputer main control unit, and the single-chip microcomputer main control unit transmits it to the upper computer unit to display the waveform, and the other is the voltage signal output by the phase-locked amplifier, which is sent to the adaptive PID controller of the single-chip microcomputer main control unit to calculate the control signal.

4. The Fabry-Perot cavity driving method based on the adaptive PID control algorithm according to claim 1, characterized in that: The piezoelectric ceramic of the Fabry-Perot cavity in step 1 is connected to the output end of the adder circuit, the second input end of the adder circuit is connected to the sinusoidal modulation signal, the first input end of the adder circuit is connected to the output end of the voltage amplifier circuit, the input end of the voltage amplifier circuit is respectively connected to the first output end of the comparator and the output end of the PID parameter design unit through the PID controller, the PID parameter design unit is connected to the second output end of the comparator, the first input end of the comparator is connected to the reference input, and the second input end of the comparator is connected to the piezoelectric ceramic through the phase-locked amplifier and the photodetector in sequence. The adder circuit realizes the superposition of four voltage signals, namely, the triangular wave signal, the PID control signal, the DC bias voltage and the modulation wave signal, and the four signal paths have corresponding switches to control conduction or shutdown.

5. The Fabry-Perot cavity driving method based on the adaptive PID control algorithm according to claim 1, characterized in that: Step 1 includes the following relational expressions: A(z -1 )y(k)=z -1 B(z -1 )u(k), The -1 )=1+a1z -1 +a2z -2 , B(from -1 )=b0+b1z -1 , Where A(z -1 ) is the setting polynomial, y(k) is the feedback signal data, z is the z-axis coordinate, which represents the cavity length of the Fabry-Perot cavity, B(z -1 ) is the setting polynomial, and u(k) is the controller parameter.

6. The Fabry-Perot cavity driving method based on the adaptive PID control algorithm according to claim 1, characterized in that: Step 4 includes w(k)=0, and step 5 includes the following relational expression: <h2 style=";text-align:left;direction:ltr">θ=[a1, a2, b0, b1]<h2 style=";text-align:left;direction:ltr"> T <h2 style=";text-align:left;direction:ltr"> ; Step 6 includes the following relational expressions: where I is the identity matrix, is the estimated controller parameter vector, k is the sequence number, P(k) is the recursive parameter, and the exponent T is the transpose operation.

7. The Fabry-Perot cavity driving method based on the adaptive PID control algorithm according to claim 1, characterized in that: Step 7 includes the following relational expressions: A(z -1 )H(z -1 )+z -1 B(z -1 )G(z -1 )=T(z -1 ), H(z -1 )=(1-z -1 )(1+h1z -1 ), G(z -1 )=g0+g1z -1 +g2z -2 , g0=K P +K I +K D , g1=-K P -2K D , g2=K D , T(z -1 )=t0+t1z -1 +…+t n z -n , Where n≤4, t is a coefficient, g0, g1 and g2 are intermediate quantities, K P is the scale parameter, K I is the integration parameter, K D is the differential parameter, H(z -1 ) is the intermediate quantity, G(z -1 ) is the intermediate quantity and h1 is the coefficient.

8. The Fabry-Perot cavity driving method based on the adaptive PID control algorithm according to claim 1, characterized in that: Step 8 includes the following relational expressions: (1-z -1 )(1+h1z -1 )u(k)=(g0+g1z -1 +g2z -2 )e(k), e(k)=w(k)-y(k), Δu(k)=-h1u(k-1)+h1u(k-2)+(g0+g1z -1 +g2z -2 )e(k), Where e(k) is the error, Δu(k) is the control signal increment, and the new control signal can be obtained by adding the original control signal to the control signal increment, which is then used to correct the cavity length.

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