Fabry-Perot cavity driving method based on adaptive PID (Proportion Integration Differentiation) control algorithm

Abstract

The invention discloses a Fabry-Perot cavity driving method based on an adaptive PID (Proportion Integration Differentiation) control algorithm, which relates to the field of design and application of a Fabry-Perot cavity and realizes closed-loop control on the cavity length of the Fabry-Perot cavity by setting PID control parameters through the adaptive PID control method and adjusting the value of direct-current voltage in real time. And the Fabry-Perot cavity is continuously and stably locked to a beam of frequency-stabilized laser subjected to atomic energy level locking. According to the Fabry-Perot cavity driving method based on the adaptive PID control algorithm provided by the invention, the transmission light power change is used as a feedback signal, the controller parameter setting is adjusted, the adaptive control adjustment of the cavity length is realized by using the controller parameter design algorithm, and finally the closed-loop control of the cavity length of the Fabry-Perot cavity is realized. The rapidity, the accuracy and the stability of the Fabry-Perot cavity driving circuit are improved, long-time high-stability locking of the Fabry-Perot cavity is achieved, and some application scenes needing cavity locking are met.

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 such as medicine, measurement, and military industry because of their high energy conversion efficiency, simple structure, and easy modulation. In some applications, high requirements are placed on the frequency stability of lasers, such as fiber-optic communications, precision spectral analysis, lidar, and quantum optics experiments. Therefore, a series of frequency stabilization methods are needed to ensure that the output frequency of the laser remains constant. Common frequency stabilization methods include passive frequency stabilization and active frequency stabilization. Passive frequency stabilization mainly achieves frequency stability by optimizing the design of the resonant cavity and the selection of materials, but its frequency stabilization effect is relatively limited. Active frequency stabilization introduces an external frequency reference, compares the output frequency of the laser with the reference frequency, and performs feedback control on the laser based on the comparison result, thereby achieving frequency stability. These active frequency stabilization methods require a suitable frequency reference, such as atomic transition frequency, molecular absorption line, etc., 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 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 interferences 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 spectrum range and provide a frequency reference for the stabilized laser.

[0004] However, the existing Fabry-Perot cavity lock technology still has some shortcomings, such as slow cavity lock speed, low accuracy and poor stability, which will lead to the above-mentioned laser detuning frequency stabilization. The rapidity and stability of the lock are reduced. One of the reasons is that the control method used by the lock cavity has limitations. For example, the parameter setting of the commonly used traditional PID control usually depends on the mathematical model of the controlled object, and once the setting is completed, the parameters tend to remain unchanged during the control process, but the controlled process has certain nonlinearity, time-varying uncertainty and pure hysteresis characteristics, which leads to poor parameter setting 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 rapidity, accuracy and stability of the lock cavity, which can further improve 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 lock technology has the problems of slow cavity lock 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, which 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 an optical power signal acquisition function, and on this basis, an adaptive PID control is added, and an adaptive algorithm is introduced to realize automatic identification according to the change characteristics of the parameters to be controlled, and the PID controller parameters are adjusted in real time according to the identification results, so as to better meet the changes in the cavity lock environment and the control requirements of laser detuning frequency stabilization, thereby improving the rapidity, accuracy and stability of cavity length control.

[0006] The technical solution of the present invention is 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, initializing an adaptive PID control parameter K(k) in a Fabry-Perot cavity driving device including an adaptive PID control algorithm connected to the piezoelectric ceramic end and the laser transmission end of the Fabry-Perot cavity, 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, defining 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 driving device, 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 driving device 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 enters the control cycle, if yes, the Fabry-Perot cavity drive device enters the lock mode, and enters step 4, if no, wait for the host computer to send an instruction to enter the control cycle;

[0011] Step 4, collecting feedback signal data y(k) of 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 controller parameter vector θ;

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

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

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

[0016] Step 9: According to 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 Fabry-Perot cavity piezoelectric ceramic end, 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 cavity locking feedback data and controller parameter data to the controller parameter design unit, and 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 cavity locking.

[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 the digital-to-analog converter. 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, 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 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, 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 contains the following relational expression:

[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 contains 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: the present invention is a Fabry-Perot cavity driving method based on an adaptive PID control algorithm, which can more conveniently scan and lock the Fabry-Perot cavity, and can more conveniently switch between the scanning mode and the locking mode by using an adder in combination with an input path switch; the DC bias function can move the position of the optical power signal displayed on the oscilloscope, which is convenient for finding the transmission peak; the designed analog-to-digital converter and digital-to-analog converter have high precision, which can ensure the accuracy of signal output and data acquisition. The adaptive PID controller designed by the present invention can enhance the control feedback capability of the Fabry-Perot cavity locking system, and can quickly adjust the output DC voltage before locking the cavity, so that the cavity length of the Fabry-Perot cavity is locked to the preset transmission peak position; after locking the cavity, the system can speed up the process of suppressing errors and interferences, and continuously correct the cavity length to keep the output transmission laser optical power always at the peak value; the adaptive PID control method can shorten the time of correcting PID parameters, increase the rapidity of the locking system, and do not need to re-correct the PID parameters when the system parameters change or the environment changes, reduce the influence of errors and interferences on the locking results, and enhance the robustness of the locking system. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0047] Figure 2 The invention discloses a circuit diagram of 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 discloses a control block diagram of an adaptive PID closed-loop control loop involved in 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, which defines 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, and open the lock mode of the Fabry-Perot cavity drive device through the host computer to allow the Fabry-Perot cavity lock system to enter the control cycle; Step 3, determine whether the Fabry-Perot cavity lock system has entered 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 a 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 execute step 3.

[0050] The reference numerals are 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 ceramics; 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 ceramics; 308-photodetector; 309-phase-locked amplifier. DETAILED DESCRIPTION

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

[0052] Figure 1 It is a schematic diagram of component units of a Fabry-Perot cavity driving device involved in implementing a Fabry-Perot cavity driving method based on an adaptive PID control algorithm of the present invention. Figure 2 The invention discloses a circuit diagram of a Fabry-Perot cavity driving method based on an adaptive PID control algorithm. Figure 3 The invention discloses a control block diagram of an adaptive PID closed-loop control loop involved in 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, defining the deterministic linear model parameters a1, a2, b0, and b1 of the Fabry-Perot cavity lock system; Step 2, in the Fabry-Perot cavity drive device, 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 lock mode of the Fabry-Perot cavity drive device is opened through the host computer, so that the Fabry-Perot cavity lock system enters the control cycle;

[0053] Step 3, determine whether the Fabry-Perot cavity lock system enters the control cycle. If yes, the Fabry-Perot cavity drive device enters the lock mode and enters step 4. If no, 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 a closed-loop characteristic polynomial T(z -1 ); Step 8, solve the new controller parameter u(k); Step 9, according to 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 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 Fabry-Perot cavity piezoelectric ceramic end, 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 cavity locking feedback data and controller parameter data to the controller parameter design unit 102, and 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 cavity locking.

[0055] The Fabry-Perot cavity driving device 212 in step 1 includes 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 phase-locked amplifier 210 and an analog-to-digital converter 211, wherein the single-chip computer main control unit 206 is respectively 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 respectively connected to the photodetector 204 and the phase-locked amplifier The adder circuit 208 is connected to the DC bias circuit 209, the D / A converter 207 and the piezoelectric ceramic 202 respectively, the D / A 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 D / A converter 207 to control the waveform, amplitude and period of the voltage signal output by it, and the D / A converter 207 outputs two voltage signals, one of which is a triangle The first circuit is a wave signal, which is output to the adder circuit 208 for scanning the Fabry-Perot cavity, and the second 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 is 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 resonance frequency of the Fabry-Perot cavity 203. The error signal of the frequency deviation between the frequency and the incident laser frequency is obtained, and the signal is input into 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 the single-chip microcomputer main control unit 206 transmits it to the host computer unit 205 to display the waveform. The other is the voltage signal output by the phase-locked amplifier 210, and the signal 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 phase-locked 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 contains the following relational expression:

[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 contains 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 driving system based on an adaptive PID control algorithm, and relates to the design and application field of the Fabry-Perot cavity. The present invention realizes outputting a DC voltage applied to both ends of a piezoelectric ceramic, adjusting the value of the DC voltage in real time by setting the PID control parameters through an adaptive PID control method, realizing closed-loop control of the cavity length of the Fabry-Perot cavity, and continuously and stably locking the Fabry-Perot cavity to a beam of frequency-stabilized laser after atomic energy level locking. The present invention provides a Fabry-Perot cavity driving system based on an adaptive PID control algorithm, which adjusts the controller parameter settings according to the change in the transmitted light power as a feedback signal, and uses the controller parameter design algorithm to realize adaptive control adjustment of the cavity length, and finally realizes closed-loop control of the cavity length of the Fabry-Perot cavity, improves the rapidity, accuracy and stability of the Fabry-Perot cavity driving circuit, realizes long-term high-stability locking of the Fabry-Perot cavity, and meets some application scenarios that require 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 phase-locked 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, and is used to realize 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 the digital-to-analog converter.

[0085] The digital-to-analog converter is implemented by chip AD5689R; the digital-to-analog converter involved in the present invention can output two voltage signals, one is a triangle 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 phase-locked 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 output voltage signal of the adder circuit, 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 realize 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 switch controls to turn on or off; the front stage of the input end of the adder circuit is a voltage amplifier circuit, which can amplify the voltage of the triangular wave signal and the PID control signal.

[0088] 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 incident laser frequency, and inputs the 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 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; the other is the voltage signal output by the phase-locked 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 cavity lock feedback data and controller parameter data to the controller parameter design unit, and then 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 the cavity lock. 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 present invention. Figure 2 Further explanation, the specific implementation of the controller parameter design unit and the controller unit will be combined with 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 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), an analog-to-digital converter (211), and a Fabry-Perot cavity driving device (212), wherein the portion included in the dot-dashed line is the Fabry-Perot cavity driving circuit structure of the present invention, and the portion outside the dot-dashed line is the optical path structure necessary for 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 single-chip main control unit, and the single-chip 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.

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

[0095] Fourth, the single-chip microcomputer 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 single-chip microcomputer main control unit. The digital-to-analog converter outputs a sinusoidal modulation 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 of 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, the PID control signal, the DC bias voltage and the modulation wave signal, and the four signal paths have corresponding switch controls to turn on or off; and, the triangular wave signal and the 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 lock 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 light power signal. After adjusting to a suitable resistance position, the output end of the photodetector is connected to the phase-locked 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 the single-chip microcomputer main control unit transmits it to the host computer unit to display the waveform; 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.

[0102] Figure 3The invention relates to an adaptive PID closed-loop control circuit involved in 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 is passed through the PID controller to obtain the PID control signal, which is amplified by the voltage amplifier circuit and superimposed with the modulation signal in the adder circuit to obtain the driving signal, and then acts on 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 the feedback signal, which 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 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, and 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 discloses an algorithm flow of an adaptive PID control method for implementing a Fabry-Perot cavity driving device based on an adaptive PID control method of the present invention. 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 yes, 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 a 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 execute 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, open the lock cavity mode of the Fabry-Perot cavity drive device through the host computer, and let the Fabry-Perot cavity lock cavity system enter the control cycle;

[0107] Step 3, determine whether the Fabry-Perot cavity lock system enters the control cycle. If yes, the Fabry-Perot cavity drive device enters the lock mode and enters step 4. If no, the system repeats step 3 and waits for the host computer to send an instruction to enter the control cycle.

[0108] Step 4, collecting feedback signal data y(k) of the lock-in amplifier and setting 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 a closed-loop characteristic polynomial T(z -1 ), and calculate H(z -1 ) and G(z -1 );

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

[0113] Step 9, calculating the output voltage to control the piezoelectric ceramic, and returning 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 an analog-to-digital converter (211), and the reference input w(k) is 0;

[0121] Step 5 includes the following relational expressions:

[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 can be obtained by adding the original control signal to the control signal increment, and then used to correct the cavity length.

[0145] The device can lock the cavity length of the Fabry-Perot cavity at the transmission peak of the incident laser, and the adder and the input path switch can be used to more conveniently switch between the scanning mode and the cavity lock mode; the DC bias function can move 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 have high precision, which can ensure the accuracy of signal output and data acquisition. The adaptive PID controller designed by the present invention can enhance the control feedback capability of the Fabry-Perot cavity lock system, can quickly lock the cavity length to the position where the transmission peak appears, and has a certain anti-interference ability, which increases the rapidity, accuracy and stability of the cavity lock system.

[0146] The contents not described in detail in the specification of the present invention belong to the prior art known to the professional and technical personnel in the field. It is pointed out here that the above description helps those skilled in the art to understand the invention, but does not limit the protection scope of the invention. Any equivalent replacement, modification and / or simplification of the above description without departing from the essence of the invention falls within the protection scope of the 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, initializing an adaptive PID control parameter K(k) in a Fabry-Perot cavity driving device including an adaptive PID control algorithm connected to the piezoelectric ceramic end and the laser transmission end of the Fabry-Perot cavity, 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, defining the deterministic linear model parameters a1, a2, b0, and b1 of the Fabry-Perot cavity-lock system; Step 2: in the Fabry-Perot cavity driving device, 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 driving device 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 enters the control cycle, if yes, the Fabry-Perot cavity drive device enters the lock mode, and enters step 4, if no, wait for the host computer to send an instruction to enter the control cycle; Step 4, collecting feedback signal data y(k) of 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 a closed-loop characteristic polynomial T(z -1 ); Step 8, solving the new controller parameter u(k); Step 9: According to 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 Fabry-Perot cavity piezoelectric ceramic end, 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 cavity locking feedback data and controller parameter data to the controller parameter design unit, and 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 cavity locking.

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 the digital-to-analog converter. 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, 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 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, 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 contains the following relational expression: 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 contains 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.

Images