Large-range Michelson displacement control system based on fully automatic digital phase-locked feedback

Abstract

This invention discloses a large-range Michelson displacement control system based on fully automatic digital phase-locked feedback, comprising a Michelson laser system and a fully automatic digital phase-locked system. The Michelson laser system includes a reference arm with a fixed cavity length, a movable measuring arm driven by a displacement actuator, and a detector. The photodetector generates a beat frequency signal based on the light output from the reference arm and the movable measuring arm and inputs it into the fully automatic digital phase-locked system. The fully automatic digital phase-locked system generates a phase detection error signal based on the beat frequency signal and the reference signal, and converts it into a feedback signal to drive the displacement actuator, thereby achieving phase-locking of the laser mode within the reference arm and the movable measuring arm. This invention can effectively extend the range of continuous high-precision displacement control from the sub-micrometer level to the centimeter level and above.

Description

Technical Field

[0001] This invention belongs to the field of laser technology, specifically relating to a large-range Michelson displacement control system based on fully automatic digital phase-locked feedback. Background Technology

[0002] With the development of cutting-edge technologies such as ultra-precision machining, micro-nano manufacturing, and high-precision metrology, modern industrial and scientific research equipment has placed stringent demands on the resolution, accuracy, and dynamic response speed of displacement control. In recent years, closed-loop feedback displacement control technology based on laser interferometers and grating rulers has made significant progress. However, existing solutions face technical bottlenecks when dealing with control requirements with resolutions exceeding picometer levels. On the one hand, at the measurement feedback end, due to the non-ideal characteristics of optical components (such as periodic nonlinear errors), electronic noise in photoelectric conversion and signal processing, and the physical limits of analog-to-digital subdivision, current solutions struggle to measure picometer-level displacement signals. On the other hand, at the execution and control end, mechanical vibration, environmental interference, and the nonlinear hysteresis and creep effects of the driving actuators can cause strong interference under complex dynamic conditions, affecting the positioning and control accuracy of the system.

[0003] The Michelson laser proposed in patent CN202210393703.X is based on the core idea of ​​establishing a physical mapping between displacement and frequency change. Utilizing frequency, currently the most precise physical quantity to measure, it theoretically achieves sub-picometer-level displacement measurement resolution. Patent CN202610001019.0 further proposes an atomic frequency stabilization and optical phase-locked Michelson laser displacement measurement system. Leveraging the inherent resolution advantage of the Michelson laser, it combines phase-locked loop technology to correlate the phase of the measuring arm and the reference arm, effectively suppressing mechanical vibration and environmental thermal noise interference, and improving the stability and robustness of system control. However, the above solutions have significant limitations in practical applications: due to the laser cavity mode mechanism, when the frequency change caused by displacement exceeds the range of a single free spectrum, it triggers a laser mode jump, causing phase-locking interruption. This deficiency limits the system's continuous high-precision control range to the sub-micrometer level, making it difficult to meet the practical engineering requirements of modern precision equipment that balance "large range" and "sub-picometer-level ultra-high resolution." Summary of the Invention

[0004] To address the above challenges, this invention aims to develop a large-range Michelson displacement control system based on fully automatic digital phase-locked feedback, comprising a Michelson laser system and a fully automatic digital phase-locked system. The Michelson laser system includes a reference arm with a fixed cavity length and a movable measuring arm pulled by a displacement actuator. The beat frequency of the laser modes within the two arms is detected and captured by the fully automatic digital phase-locked system, and digitally phase-detected and loop-filtered with the reference signal output from a numerically controlled oscillator (NCO). In the continuous tuning region where the laser modes are stable, the system converts the phase detection error into a feedback signal to drive the displacement actuator, achieving phase-locking of the laser modes within the two arms. By actively adjusting the NCO reference frequency to change the phase-locked loop operating frequency in real time, the displacement actuator is driven to generate displacement, achieving sub-picometer level displacement control. During this process, the controller dynamically optimizes the PID parameters in real time to ensure locking accuracy and stability at each phase-locked loop operating frequency. For large stroke requirements, the system automatically executes coordinated control of feedback interruption, state reset, and cross-modal relocking by real-time monitoring of beat frequency fluctuations and phase-locked loop error signal identification mode transitions. The total displacement is calculated by using frequency data before and after multiple phase-locking segments, thereby breaking through the limitation of a single free spectral range and achieving high-resolution continuous displacement control exceeding the centimeter level.

[0005] The technical solution of this invention is as follows: A large-range Michelson displacement control system based on fully automatic digital phase-locked feedback, characterized in that it includes a Michelson laser system and a fully automatic digital phase-locked system; The Michelson laser system includes a reference arm with a fixed cavity length, a movable measuring arm pulled by a displacement actuator, and a detector; the photodetector is used to generate a beat frequency signal based on the light output from the reference arm and the movable measuring arm and input it into the fully automatic digital phase-locked system. The fully automatic digital phase-locked loop system is used to generate a phase detection error signal based on the beat frequency signal and the reference signal, and convert it into a feedback signal to drive the displacement actuator, thereby realizing phase locking of the laser mode in the reference arm and the movable measuring arm.

[0006] Preferably, the phase-locked loop operating frequency is changed in real time by actively adjusting the frequency of the reference signal, thereby driving the displacement actuator to generate displacement and achieving sub-picometer level displacement control.

[0007] Preferably, the Michelson laser system includes an antireflective coated laser diode, a beam splitter module, a first frequency selection element, a reference arm cavity mirror, a piezoelectric ceramic actuator, a frequency locking module, a second frequency selection element, a measuring arm cavity mirror, a displacement actuator, and a photodetector; wherein, the antireflective coated laser diode, beam splitter module, first frequency selection element, reference arm cavity mirror, and piezoelectric ceramic actuator together constitute the reference arm, and the antireflective coated laser diode, beam splitter module, second frequency selection element, measuring arm cavity mirror, and displacement actuator together constitute the movable measuring arm; the photodetector receives the light output from the reference arm and the movable measuring arm via the beam splitter module and generates a beat frequency signal, which is input to the fully automatic digital phase-locked loop system; the fully automatic digital phase-locked loop system includes an analog-to-digital converter, a digital... The system comprises a phase detector, a digital filter, a numerically controlled oscillator, a controller, and a digital-to-analog converter. The analog-to-digital converter receives the beat frequency signal and converts it into a digital beat frequency signal, which is then transmitted to the digital phase detector. The digital phase detector generates a digital error signal based on the phase difference between the digital beat frequency signal and the digital reference signal generated by the numerically controlled oscillator, which is then transmitted to the digital filter. The digital filter performs low-pass filtering on the digital error signal to output a low-frequency phase error signal. The numerically controlled oscillator, controlled by the controller, generates a digital reference signal of a set frequency, which is then transmitted to the digital phase detector as a phase detection reference. The controller generates a digital servo signal based on the low-frequency phase error signal, which is fed back to the displacement actuator via the digital-to-analog converter, thereby achieving phase-locked control of the measuring arm displacement.

[0008] Preferably, the first frequency selection element is used to determine the wavelength of the laser within the reference arm; the first frequency selection element is a grating, an interference filter, or an atomic filter.

[0009] Preferably, the reference arm endoscope is a plane mirror, a corner cone, or a corner cone array.

[0010] Preferably, the frequency locking module is used to receive the laser transmitted through the reference arm cavity mirror, and uses the internal frequency reference to generate an error signal to perform feedback control on the piezoelectric ceramic actuator, thereby locking the laser frequency in the reference arm cavity. Preferably, the frequency stabilization method of the frequency locking module is atomic spectrum frequency stabilization or supercavity frequency stabilization.

[0011] Preferably, the second frequency selection element is used to determine the wavelength of the laser within the movable measuring arm; the second frequency selection element is a grating, an interference filter, or an atomic filter.

[0012] Preferably, the measuring arm endoscope is a plane mirror, a corner cone, or a corner cone array.

[0013] A displacement measurement method based on the aforementioned fully automatic digital phase-locked feedback large-range Michelson displacement control system includes the following steps: Real-time monitoring of beat frequency signal; the controller traverses the reference signal frequency, and sends the beat frequency signal and the reference signal to the digital phase detector to generate an error signal; The system continuously checks whether the error signal is less than the set threshold. If not, it continues to adjust the reference signal frequency. If so, it enters a stable phase-locked state and outputs the feedback signal to the displacement actuator, recording the reference frequency at this time as the starting frequency. In closed-loop mode, the phase-locked loop operating point is changed by actively adjusting the frequency of the reference signal; During the displacement drive process, the instantaneous frequency fluctuation of the beat frequency signal is monitored in real time to determine whether it is less than the set mode jump warning threshold; if so, the phase-locked state is maintained; otherwise, the phase-locked feedback output to the measuring arm displacement actuator is turned off and the reference signal frequency at this time is recorded as the cutoff frequency of the current phase-locked segment. A pre-built and predetermined bias voltage is input to the measuring arm displacement actuator to force the measuring arm laser to complete mode skipping and enter the next resonant mode; After applying a bias voltage to the displacement actuator, it is determined again whether the instantaneous frequency fluctuation of the beat frequency signal is less than the mode skipping warning threshold. If not, the built-in bias voltage is continued to be input to the displacement actuator. If so, the controller traverses the reference signal frequency to find and lock a new operating point and starts the next stage of continuous phase-locked control. The controller calculates the total displacement based on the reference signal frequency data recorded before and after multiple feedback interruptions, as well as the displacement generated during each mode jump reset.

[0014] The innovative points and beneficial effects of the technical solution provided by this invention are as follows: 1. Solved the laser mode hopping problem and achieved large-range continuous control: Introduced an active mode hopping identification and cross-modal collaborative control mechanism. By monitoring the frequency fluctuation of the beat frequency signal in real time to capture the mode hopping critical point, automatically execute feedback interruption, state reset and cross-modal relocking, and use seamless splicing of multi-segment phase-locked frequency data to accurately calculate the total displacement, effectively extending the range of continuous high-precision displacement control from the submicron level to the centimeter level and above; 2. Dynamic optimization of PID parameters enhances system stability under complex operating conditions: This system, under a fully digital control architecture, achieves adaptive adjustment of closed-loop control parameters. When the displacement actuator undergoes long-stroke continuous tuning or faces complex dynamic conditions such as environmental vibration, the controller can dynamically optimize the PID (proportional-integral-derivative) parameters in real time. This mechanism overcomes the shortcomings of traditional analog phase-locked loops where fixed parameters are difficult to adapt to changes in the system's nonlinear state, ensuring the system's phase-locking accuracy, dynamic response speed, and anti-interference robustness at different operating points and under different operating states. 3. Digital operation and fully automatic control: The traditional analog phase detection and filtering are transformed into digital domain processing, realizing full-process automation from phase lock point capture, mode skipping warning to reset and relock, eliminating tedious manual debugging, and improving the system's ease of use, operational reliability and intelligent integration level. 4. An active frequency-driven mechanism is proposed to achieve sub-picometer-level ultra-high resolution in large-range measurements: By actively adjusting the reference frequency of the internal numerically controlled oscillator (NCO), the phase-locked loop operating point is changed in real time, thereby "driving position with frequency" and precisely driving the displacement actuator to generate displacement. This invention fully utilizes "frequency," currently the physical quantity with the highest measurement accuracy, effectively avoiding the periodic nonlinearity error and modulus subdivision limit of traditional optical elements, and still ensuring that the displacement control resolution reaches the sub-picometer level within a large-range framework. Attached Figure Description

[0015] Figure 1 This is a system block diagram of the present invention.

[0016] Figure 2 This is a schematic diagram of the structure of the large-range Michelson displacement control system based on fully automatic digital phase-locked feedback proposed in this invention.

[0017] Figure 3 This is a flowchart of the method of the present invention.

[0018] Figure 4 This is a flowchart illustrating the fully automatic digital phase-locked loop feedback mechanism proposed in this invention.

[0019] Among them, 01-Michelson laser system; 011-reference arm; 012-measuring arm; 013-detector; 02-fully automatic digital phase-locked system; A-Michelson laser system; B-fully automatic digital phase-locked system; 1-laser diode with antireflection coating; 2-beam splitting module; 3-first frequency selection element; 4-reference arm cavity mirror; 5-piezoelectric ceramic actuator; 6-frequency locking module; 7-second frequency selection element; 8-measuring arm cavity mirror; 9-displacement actuator; 10-photodetector; 11-analog-to-digital converter (ADC); 12-digital phase detector; 13-digital filter; 14-numerically controlled oscillator (NCO); 15-digital signal processing and control module (hereinafter referred to as controller); 16-digital-to-analog converter (DAC). Detailed Implementation

[0020] To make the objectives, contents, and advantages of the present invention clearer, the specific embodiments of the present invention will be described in further detail below with reference to the accompanying drawings.

[0021] like Figure 1As shown, an optional embodiment of the present invention provides a large-range Michelson displacement control system based on fully automatic digital phase-locked feedback, characterized in that it includes a Michelson laser system and a fully automatic digital phase-locked system; The Michelson laser system includes a reference arm with a fixed cavity length, a movable measuring arm pulled by a displacement actuator, and a detector; the photodetector is used to generate a beat frequency signal based on the light output from the reference arm and the movable measuring arm and input it into the fully automatic digital phase-locked system. The fully automatic digital phase-locked loop system is used to generate a phase detection error signal based on the beat frequency signal and the reference signal, and convert it into a feedback signal to drive the displacement actuator, thereby realizing phase locking of the laser mode in the reference arm and the movable measuring arm.

[0022] like Figure 2 As shown, one embodiment of the present invention includes: a Michelson laser system A and a fully automatic digital phase-locked loop system B.

[0023] The Michelson laser system A includes an antireflection coated laser diode 1, a beam splitter module 2, a first frequency selection element 3, a reference arm cavity mirror 4, a piezoelectric ceramic actuator 5, a frequency locking module 6, a second frequency selection element 7, a measuring arm cavity mirror 8, a displacement actuator 9, and a photodetector 10; the fully automatic digital phase-locked loop system B includes an analog-to-digital converter (ADC) 11, a digital phase detector 12, a digital filter 13, a numerically controlled oscillator (NCO) 14, a digital signal processing and control module (hereinafter referred to as the controller) 15, and a digital-to-analog converter (DAC) 16.

[0024] The laser diode 1 with antireflection coating, the beam splitter module 2, the first frequency selection element 3, the reference arm cavity mirror 4, and the piezoelectric ceramic actuator 5 together constitute the reference arm of the Michelson laser system. The laser diode 1 with antireflection coating, the beam splitter module 2, the second frequency selection element 7, the measuring arm cavity mirror 8, and the displacement actuator 9 together constitute the measuring arm of the Michelson laser system.

[0025] The laser diode 1 with the antireflection coating outputs a wide-spectrum fluorescence signal, providing gain for the Michelson laser system; the antireflection coating on its front end is used to eliminate the oscillation of the internal cavity mode, ensuring the dominance of the external resonant cavity.

[0026] The beam splitting module 2 splits the emitted light from the antireflection coated laser diode 1 into two paths: transmitted light and reflected light, which enter the measurement arm and reference arm systems, respectively. At the same time, the beam splitting module 2 further splits the light returned from the reference arm cavity mirror 4 and the measurement arm cavity mirror 8, transmitting the light from the reference arm cavity mirror 4 and reflecting the light from the measurement arm cavity mirror 8 into the photodetector 10, and transmitting the light reflected from the reference arm cavity mirror 4 and the light transmitted from the measurement arm cavity mirror 8 to the antireflection coated laser diode 1.

[0027] The first frequency selection element 3 is a frequency selection element within the reference arm, which determines the wavelength of the laser within the reference arm; the first frequency selection element 3 can be a macroscopic frequency selection element such as a grating or an interference filter, or a microscopic frequency selection element such as an atomic filter.

[0028] The reference arm cavity mirror 4 is used to reflect part of the light passing through the first frequency selection element 3 back to the laser diode 1 coated with antireflection film to achieve laser oscillation, while part of the light is transmitted through and enters the frequency locking module 6; the cavity length of the reference arm is the physical length from the rear end face of the laser diode 1 coated with antireflection film to the reference arm cavity mirror 4; the reference arm cavity mirror 4 can be a plane mirror, a corner pyramid, a corner pyramid array, or other elements.

[0029] The piezoelectric ceramic actuator 5 is glued to the reference arm cavity mirror 4 and driven by a bias voltage, which can push the reference arm cavity mirror 4 to move along the optical axis of the reference arm, so as to cooperate with the frequency stabilization feedback of the frequency locking module 6 to perform cavity length fine adjustment.

[0030] The frequency locking module 6 is used to receive the laser transmitted through the reference arm cavity mirror 4, generate an error signal in combination with the internal highly stable frequency reference, and feed the signal back to the piezoelectric ceramic actuator 5, thereby locking the laser frequency in the reference arm cavity; its frequency stabilization method can be atomic spectrum stabilization such as saturated absorption spectrum or modulation transfer spectrum, or ultracavity frequency stabilization based on PDH technology.

[0031] The second frequency-selective element 7 is a frequency-selective element within the measurement arm, determining the lasing wavelength of the laser within the measurement arm. Similar to the first frequency-selective element 3, it can be a macroscopic element such as a grating or interference filter, or a microscopic element such as an atomic filter. To ensure the stable and independent operation of the laser modes of the two arms, the lasing wavelength of the second frequency-selective element 7 must be spectrally offset from that of the first frequency-selective element 3, and both must fall strictly within the effective gain bandwidth of the laser diode 1 coated with an antireflection film.

[0032] The measuring arm cavity mirror 8 is used to reflect the light passing through the second frequency selection element 7 back to the antireflection coated laser diode 1 to achieve laser oscillation. The cavity length of the measuring arm is the physical length from the rear end face of the antireflection coated laser diode 1 to the measuring arm cavity mirror 8. The measuring arm cavity mirror 8 can be composed of elements such as a plane mirror, a pyramid, or a pyramid array.

[0033] The displacement actuator 9 is glued to the measuring arm cavity mirror 8 and driven by a bias voltage, which can push the measuring arm cavity mirror 8 to generate displacement along the optical axis of the measuring arm; the change in the length of the measuring arm cavity is the displacement ∆L generated by the system.

[0034] The photodetector 10 receives transmitted light from the reference arm endoscope 4 and reflected light from the measuring arm endoscope 8, causing optical heterodyne beat frequency to occur on the photosensitive surface of the detector, thereby generating an analog microwave beat frequency signal containing relative phase information, and inputting it into the fully automatic digital phase-locked system B.

[0035] The analog-to-digital converter (ADC) 11 is used to receive the analog beat frequency signal from the photodetector 10, discretize it at high speed and convert it into a digital beat frequency signal, and then transmit it to the digital phase detector 12.

[0036] The digital phase detector 12 is used to perform real-time phase comparison between the digital beat frequency signal output by the ADC 11 and the digital reference signal generated by the internal numerically controlled oscillator (NCO) 14, accurately extract the transient phase difference between the two, and generate a digital error signal to be transmitted to the digital filter 13.

[0037] The digital filter 13 is used to perform low-pass filtering and shaping on the received digital error signal, filtering out the accompanying high-frequency noise, electronic interference and aliasing spectral components, and outputting a smooth low-frequency phase error signal with a high signal-to-noise ratio.

[0038] The numerically controlled oscillator (NCO) 14 is controlled by the digital signal processing and control module 15 to generate a digital reference signal of a specific frequency and send it to the digital phase detector 12 as a phase detection reference.

[0039] The digital signal processing and control module (hereinafter referred to as the controller) 15 is the core computing unit of the entire system. It receives the filtered low-frequency error signal and performs proportional-integral-derivative (PID) calculations based on the built-in algorithm to generate a digital servo signal. On the one hand, this servo signal is fed back to the displacement actuator 9 via the digital-to-analog converter (DAC) 16 to achieve closed-loop phase-locked control of the measuring arm displacement. On the other hand, the controller 15 maintains high-speed communication with the NCO 14 and actively modifies the output frequency parameters of the NCO 14 to offset the phase-locked operating point in real time, thereby generating the target displacement by "frequency-driven position". At the same time, the controller 15 is also responsible for performing adaptive real-time optimization of PID parameters under complex dynamic conditions, as well as active monitoring, early warning and coordinated reset control of mode skipping state.

[0040] The digital-to-analog converter (DAC) 16 is connected to the output of the controller 15 and is used to convert the received digital servo signal into a continuous analog control voltage.

[0041] like Figure 3 As shown, an optional embodiment of the present invention provides a displacement measurement method for a large-range Michelson displacement control system based on fully automatic digital phase-locked feedback, the steps of which include: Real-time monitoring of beat frequency signal; the controller traverses the reference signal frequency, and sends the beat frequency signal and the reference signal to the digital phase detector to generate an error signal; The system continuously checks whether the error signal is less than the set threshold. If not, it continues to adjust the reference signal frequency. If so, it enters a stable phase-locked state and outputs the feedback signal to the displacement actuator, recording the reference frequency at this time as the starting frequency. In closed-loop mode, the phase-locked loop operating point is changed by actively adjusting the frequency of the reference signal; During the displacement drive process, the instantaneous frequency fluctuation of the beat frequency signal is monitored in real time to determine whether it is less than the set mode jump warning threshold; if so, the phase-locked state is maintained; otherwise, the phase-locked feedback output to the measuring arm displacement actuator is turned off and the reference signal frequency at this time is recorded as the cutoff frequency of the current phase-locked segment. A pre-built and predetermined bias voltage is input to the measuring arm displacement actuator to force the measuring arm laser to complete mode skipping and enter the next resonant mode; After applying a bias voltage to the displacement actuator, it is determined again whether the instantaneous frequency fluctuation of the beat frequency signal is less than the mode skipping warning threshold. If not, the built-in bias voltage is continued to be input to the displacement actuator. If so, the controller traverses the reference signal frequency to find and lock a new operating point and starts the next stage of continuous phase-locked control. The controller calculates the total displacement based on the reference signal frequency data recorded before and after multiple feedback interruptions, as well as the displacement generated during each mode jump reset.

[0042] Figure 4 The following is a flowchart illustrating the fully automatic digital phase-locked loop feedback mechanism according to an embodiment of the present invention. The specific control and execution steps are as follows: S1. Initial Monitoring and Frequency Traversal: After the system starts up, the laser frequency inside the measuring arm is monitored and measured in real time. Laser frequency within the movable reference arm The generated beat frequency Subsequently, the controller iterates through the reference signal frequencies output by the numerically controlled oscillator (NCO). , beat frequency signal With reference signal The signal is fed into a digital phase detector for digital phase detection and loop filtering to generate an error signal. ; S2. Phase-locked acquisition: Real-time judgment of error signals Is it less than the set threshold? . if not ( If the frequency of the reference signal is adjusted, the loop will return to continue adjusting the frequency of the reference signal. ;if( If ), then the system is determined to have entered a lockable range. The system then enters a stable phase-locked state and outputs a feedback signal to the measuring arm displacement actuator. Simultaneously, the reference frequency at this point is recorded as the starting frequency. ; S3. Displacement Drive and PID Parameter Optimization: In closed-loop mode, the system actively adjusts the reference signal frequency. To change the phase-locked loop operating point and beat frequency Consequently, it changes synchronously under the influence of the servo system. Let the change in the reference signal frequency be denoted as... Due to the reference arm frequency The frequency is kept constant under the control of the frequency locking module, and the synchronous change of the beat frequency is... Essentially stemming from the laser frequency within the movable measuring arm Change All three satisfy an equal tracking relationship in phase-locked state. This frequency change, through the physical mapping relationship of the optical resonant cavity, directly reflects the displacement of the movable measuring arm actuator. (Where L is the length of the measuring arm cavity). Simultaneously, during phase-locked operation, the controller optimizes the PID control parameters in real time based on the current frequency response and system dynamic state; S4. Mode Jump Warning and Feedback Interruption: During the displacement driving process, the system continuously monitors the instantaneous frequency fluctuation of the beat frequency signal in real time. Determine whether it is less than the set mode skipping warning threshold. .like This indicates that the laser is currently in the continuous tuning region, and the system maintains a phase-locked state; if This indicates that the laser has reached the critical mode-hopping state, and the system immediately shuts off the phase-locked feedback output to the measuring arm displacement actuator. The physical basis of this judgment mechanism is that when the laser is in the critical mode-hopping state, the intracavity lasing mode becomes extremely unstable, which macroscopically manifests as instantaneous frequency fluctuations in the beat frequency signal. The frequency increases significantly. At the instant the feedback output is turned off, the system extracts and records the reference signal frequency at this moment (i.e., the instant before the feedback interruption), and records it as the cutoff frequency of this phase-locked loop. ; S5. State Reset: The system inputs a pre-built and predetermined bias voltage to the measuring arm displacement actuator, forcing the measuring arm laser to complete mode skipping and enter the next resonant mode. The displacement of the measuring arm displacement actuator under this bias voltage is... The displacement can be obtained in the following ways: by consulting the product manual of the measuring arm displacement actuator; by linear extrapolation based on the measured data of "frequency-feedback voltage" in the non-mode skipping continuous tuning range (this extrapolation is based on the physical premise that the actuator displacement changes strictly linearly with the driving voltage and the response has a high degree of consistency); or by calibration using external displacement measuring equipment such as a high-precision laser interferometer. S6. Reset Decision and Relock Cycle: After applying a bias voltage to the displacement actuator, the system again determines the instantaneous frequency fluctuation of the beat frequency signal. Is it less than the threshold? If not, the built-in bias voltage is continued to be input to the displacement actuator; if yes, it indicates that the state reset was successful and the laser has entered the stable tuning range of the next longitudinal mode. The system then jumps back to the "traversing the reference signal frequency output by the numerically controlled oscillator (NCO)" step in S1, finds and locks the new operating point again, thereby starting the next stage of continuous phase-locked control; S7. Data Processing: The controller extracts and summarizes the reference signal frequency data recorded before and after each (N times in total) feedback interruption (i.e., the starting frequency of each relocking). and cutoff frequency (where i = 1, 2, 3, ..., N). The system accurately converts and accumulates the effective frequency changes within multiple continuous tuning intervals, and then compares these values ​​with the displacement generated during each mode jump reset. Seamless splicing is achieved. Total displacement. The precise solution formula is: in, The cavity length of the arm is measured at the beginning of the i-th continuous tuning segment, and the cavity length iteration relationship is satisfied. = , During the phase-locked loop process of the i-th continuous tuning segment, the displacement generated by adjusting the signal generator to drive the measuring arm movement is calculated. The system then calculates the total displacement. Then, the output is displayed in real time.

[0043] The above description is only a preferred embodiment of the present invention. For those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A large-range Michelson displacement control system based on fully automatic digital phase-locked feedback, characterized in that, Including the Michelson laser system and the fully automated digital phase-locked loop system; The Michelson laser system includes a reference arm with a fixed cavity length, a movable measuring arm pulled by a displacement actuator, and a detector; the photodetector is used to generate a beat frequency signal based on the light output from the reference arm and the movable measuring arm and input it into the fully automatic digital phase-locked system. The fully automatic digital phase-locked loop system is used to generate a phase detection error signal based on the beat frequency signal and the reference signal, and convert it into a feedback signal to drive the displacement actuator, thereby realizing phase locking of the laser mode in the reference arm and the movable measuring arm.

2. The system according to claim 1, characterized in that, By actively adjusting the frequency of the reference signal to change the phase-locked loop operating frequency in real time, the displacement actuator is driven to generate displacement, thereby achieving sub-picometer level displacement control.

3. The system according to claim 1, characterized in that, The Michelson laser system comprises an antireflective coated laser diode, a beam splitter module, a first frequency selection element, a reference arm cavity mirror, a piezoelectric ceramic actuator, a frequency locking module, a second frequency selection element, a measuring arm cavity mirror, a displacement actuator, and a photodetector. The antireflective coated laser diode, beam splitter module, first frequency selection element, reference arm cavity mirror, and piezoelectric ceramic actuator together constitute the reference arm, while the antireflective coated laser diode, beam splitter module, second frequency selection element, measuring arm cavity mirror, and displacement actuator together constitute the movable measuring arm. The photodetector receives light from the reference arm and the movable measuring arm output by the beam splitter module and generates a beat frequency signal, which is input to the fully automatic digital phase-locked loop system. The fully automatic digital phase-locked loop system includes an analog-to-digital converter and a digital phase detector. The device comprises a sensor, a digital filter, a numerically controlled oscillator, a controller, and a digital-to-analog converter. The analog-to-digital converter receives the beat frequency signal and converts it into a digital beat frequency signal, which is then transmitted to a digital phase detector. The digital phase detector generates a digital error signal based on the phase difference between the digital beat frequency signal and the digital reference signal generated by the numerically controlled oscillator, which is then transmitted to the digital filter. The digital filter performs low-pass filtering on the digital error signal to output a low-frequency phase error signal. The numerically controlled oscillator, controlled by the controller, generates a digital reference signal of a set frequency, which is then transmitted to the digital phase detector as a phase detection reference. The controller generates a digital servo signal based on the low-frequency phase error signal, which is fed back to the displacement actuator via the digital-to-analog converter to achieve phase-locked control of the measuring arm displacement.

4. The system according to claim 3, characterized in that, The first frequency selection element is used to determine the wavelength of the laser within the reference arm; the first frequency selection element is a grating, an interference filter, or an atomic filter.

5. The system according to claim 3, characterized in that, The reference arm endoscope is a plane mirror, a pyramid, or an array of pyramids.

6. The system according to claim 3, characterized in that, The frequency locking module is used to receive the laser light transmitted through the reference arm cavity mirror, and uses the internal frequency reference to generate an error signal to perform feedback control on the piezoelectric ceramic actuator, thereby locking the laser frequency inside the reference arm cavity.

7. The system according to claim 6, characterized in that, The frequency locking module stabilizes the frequency using either atomic spectrum stabilization or supercavity stabilization.

8. The system according to claim 3, characterized in that, The second frequency selection element is used to determine the wavelength of the laser within the movable measuring arm; the second frequency selection element is a grating, an interference filter, or an atomic filter.

9. The system according to claim 3, characterized in that, The measuring arm endoscope is a plane mirror, a pyramid, or an array of pyramids.

10. A displacement measurement method based on the fully automatic digital phase-locked feedback large-range Michelson displacement control system of claim 1, comprising the following steps: Real-time monitoring of beat frequency signals; The controller iterates through the reference signal frequencies and sends the beat frequency signal and the reference signal into the digital phase detector to generate an error signal; The system continuously checks whether the error signal is less than the set threshold. If not, it continues to adjust the reference signal frequency. If so, it enters a stable phase-locked state and outputs the feedback signal to the displacement actuator, recording the reference frequency at this time as the starting frequency. In closed-loop mode, the phase-locked loop operating point is changed by actively adjusting the frequency of the reference signal; During the displacement drive process, the instantaneous frequency fluctuation of the beat frequency signal is monitored in real time to determine whether it is less than the set mode jump warning threshold; if so, the phase-locked state is maintained; otherwise, the phase-locked feedback output to the measuring arm displacement actuator is turned off and the reference signal frequency at this time is recorded as the cutoff frequency of the current phase-locked segment. A pre-built and predetermined bias voltage is input to the measuring arm displacement actuator to force the measuring arm laser to complete mode skipping and enter the next resonant mode; After applying a bias voltage to the displacement actuator, it is determined again whether the instantaneous frequency fluctuation of the beat frequency signal is less than the mode skipping warning threshold. If not, the built-in bias voltage is continued to be input to the displacement actuator. If so, the controller traverses the reference signal frequency to find and lock a new operating point and starts the next stage of continuous phase-locked control. The controller calculates the total displacement based on the reference signal frequency data recorded before and after multiple feedback interruptions, as well as the displacement generated during each mode jump reset.

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