All-fiber liquid level measurement system and method based on dual-optical comb phase decoupling and adaptive compensation

Abstract

The invention discloses an all-optical-fiber liquid level measuring system and method based on double-optical-comb phase decoupling and self-adaptive compensation, and the system comprises a double-optical-comb light source module, an optical fiber coupling module, a signal collection and processing system, a self-adaptive compensation module, a measuring arm and a reference arm. The optical fiber coupling module comprises a polarization-maintaining optical fiber beam splitter and a polarization-maintaining optical fiber beam combiner; the signal acquisition and processing system comprises a balance detector, a lock-in amplifier and an upper computer which are sequentially connected from front to back, and the lock-in amplifier is connected with a self-adaptive compensation module; the double-optical-comb light source module is connected with the measuring arm and the reference arm through the polarization-maintaining optical fiber beam splitter, and the measuring arm and the reference arm are connected with the balance detector through the polarization-maintaining optical fiber beam combiner. According to the invention, interference signal intensity and phase information are combined, the problem of reflectivity difference between transparent liquid and opaque liquid is solved, phase noise caused by environmental disturbance is eliminated, and the measurement stability is improved. According to the invention, non-contact, real-time and high-resolution measurement of the height of the liquid level is realized, especially measurement in a high-pressure, high-temperature or corrosive environment is realized, and the application range is expanded.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of optical fiber liquid level measurement, and particularly relates to a full-optical-fiber liquid level measurement system and method based on double-optical-comb phase decoupling and adaptive compensation. BACKGROUND

[0002] Liquid level measurement technology plays a vital role in industrial control, energy storage, fuel loading and other fields. Liquid level measurement technology includes contact liquid level measurement and non-contact measurement. For example, in the prior art, contact liquid level measurement mainly uses float type and capacitive type sensors, which need to directly contact the liquid, are easily affected by medium conditions, have high maintenance costs, and are not suitable for measuring high-temperature, high-pressure or corrosive media. Non-contact optical measurement mainly uses laser radar and laser triangulation, which relies on single-wavelength laser, is easily disturbed by changes in liquid surface reflectivity, has limited resolution, and is sensitive to air turbulence, vibration and other environments, and needs complex vibration isolation design and calibration. The microwave / ultrasonic wave sensor will enlarge the error due to changes in the dielectric constant or sound velocity of the medium, and cannot meet the measurement demand of sub-millimeter level, and it is difficult to detect in the gas-liquid mixed interface.

[0003] At present, optical frequency comb has become a new tool for precise ranging due to its wide spectrum and high frequency stability. However, for liquid level measurement, the optical frequency comb is easily disturbed by the environment (temperature, vibration), which causes the light path of the measurement light to fluctuate, introduces phase noise, and thus overwhelms the liquid level signal. At the same time, the traditional double-optical-comb needs independent light sources and spatial light paths, which introduces multiple discrete devices and is not conducive to on-site deployment. When the liquid surface of the measured liquid fluctuates and the refractive index changes, it will also cause the phase change carrying the liquid level information to be unable to be stably tracked. SUMMARY

[0004] The purpose of the present application is to provide a full-optical-fiber liquid level measurement system and method based on double-optical-comb phase decoupling and adaptive compensation, which aims to solve the above problems.

[0005] The present application is mainly realized by the following technical solutions:

[0006] A full-optical-fiber liquid level measurement system based on double-optical-comb phase decoupling and adaptive compensation, comprising a double-optical-comb light source module, a fiber coupling module, a signal acquisition and processing system, an adaptive compensation module, a measurement arm and a reference arm, wherein the fiber coupling module comprises a polarization maintaining fiber beam splitter and a polarization maintaining fiber beam combiner; the signal acquisition and processing system comprises a balanced detector, a lock-in amplifier and an upper computer connected in sequence from front to back, and the lock-in amplifier is connected with the adaptive compensation module; the double-optical-comb light source module is connected with the measurement arm and the reference arm through the polarization maintaining fiber beam splitter, and the measurement arm and the reference arm are connected with the balanced detector through the polarization maintaining fiber beam combiner.

[0007] The dual-comb light source module is used for emitting dual-comb laser, and the polarization maintaining optical fiber beam splitter is used for splitting the dual-comb laser to form reference light and measurement light and inputting the reference light and the measurement light into a reference arm and a measurement arm respectively.

[0008] The adaptive compensation module is used for controlling the reference arm based on the phase difference of the phase-locked amplifier feedback and adjusting the dynamic compensation of the optical path of the reference light.

[0009] The measurement arm is used for liquid level measurement and outputs the measurement light reflected by the liquid surface to the polarization maintaining optical fiber beam combiner.

[0010] The balanced photodetector is used for receiving the interference signal output by the polarization maintaining optical fiber beam combiner and outputting the beat frequency signal f beat to the phase-locked amplifier. beat The phase-locked amplifier is used for extracting the phase difference of the beat frequency signal f .

[0011] In order to better realize the present application, further, the adaptive compensation module comprises a PID controller and a PZT driver connected with each other, the reference arm comprises an optical fiber circulator 1, a PZT fiber stretcher and an optical fiber reflector connected in sequence from front to back, the PZT driver is connected with the PZT fiber stretcher, and the optical fiber circulator 1 is connected with the dual-comb light source module and the polarization maintaining optical fiber beam combiner respectively, so as to realize that the reference light enters the optical fiber reflector through the optical fiber circulator 1 and the PZT fiber stretcher, the optical path of the reference light is fixed, and the reference light enters the polarization maintaining optical fiber beam combiner through the end surface of the optical fiber reflector after being reflected.

[0012] In order to better realize the present application, further, the measurement arm comprises an optical fiber circulator 2 and an optical fiber collimator connected with each other, the optical fiber circulator 2 is connected with the polarization maintaining optical fiber beam splitter and the polarization maintaining optical fiber beam combiner respectively, so as to realize that the measurement light enters the optical fiber collimator through the optical fiber circulator 2, is collimated, emits spatial light to the liquid surface to be measured, and returns to the optical fiber collimator, the optical fiber circulator 2 and the polarization maintaining optical fiber beam combiner in sequence after being reflected by the liquid surface.

[0013] In order to better realize the present application, further, the optical fiber circulator 1 and the optical fiber circulator 2 are both polarization maintaining optical fiber circulators.

[0014] In order to better realize the present application, further, the dual-comb light source module is connected with the polarization maintaining optical fiber beam splitter through an optical fiber isolator.

[0015] In order to better realize the present application, further, the splitting ratio of the polarization maintaining optical fiber beam splitter and the polarization maintaining optical fiber beam combiner is 50:50.

[0016] The present application is mainly realized through the following technical solutions:

[0017] A full-optical liquid level measurement method based on dual-comb phase decoupling and adaptive compensation, comprising the following steps:

[0018] Step S1: Emitting dual-comb and splitting to form reference light and measurement light;

[0019] Step S2: Emitting measurement light to the liquid surface to be measured, and returning to the polarization maintaining fiber combiner after reflection by the liquid surface;

[0020] Step S3: The polarization maintaining fiber combiner combines the received reference light and measurement light, and then the balanced photodetector receives the interference signal and outputs the beat frequency signal

[0021] Wherein: N is the mode number of the optical comb;

[0022] Δf r is the repetition frequency difference of the dual-comb;

[0023] is the phase difference caused by the change of the liquid level;

[0024] t is time;

[0025] Step S4: Fourier transform is performed on the beat frequency signal f beat , and the phase difference

[0026] Step S5: If , then the dynamic compensation of the optical path of the reference light is adjusted based on the phase difference ; the compensated reference light is output to the polarization maintaining fiber combiner and enters step S3; if , then step S6 is entered;

[0027] Wherein: is the calibrated value of the phase difference;

[0028] ε is a set threshold value;

[0029] Step S6: Calculating the liquid level height change value:

[0030]

[0031] Wherein: λ is the center wavelength of the optical comb;

[0032] n is the refractive index of the liquid.

[0033] In order to better realize the present application, further, in step S5, the output signal V(t) drives the PZT fiber stretcher, and the axial extension amount ΔLz=βV(t), wherein β is the extension ratio coefficient; the reference light path change ΔL ref =2ΔLz, so as to offset the ΔL introduced by the environmental disturbance.nosie .

[0034] To better realize the present application, further, record each compensation ΔL ref and output signal V(t), and the best PID parameter of the environmental parameter of different temperature and refractive index, optimize the PID parameter by machine learning method, establish the lookup table to realize the self-optimization of the PID control parameter. For example, the prior art CN105973544B can be used to optimize the PID parameter.

[0035] The beneficial effects of the present application are as follows:

[0036] (1) The present application realizes non-contact, real-time and high-resolution measurement of liquid level height based on the repetition frequency difference and phase decoupling algorithm of double optical comb combined with adaptive optical path compensation, and is suitable for liquid level monitoring of transparent and non-transparent liquids, especially for measurement in high-pressure, high-temperature or corrosive environment; the present application combines interference signal intensity and phase information to solve the reflectivity difference problem of transparent and non-transparent liquids, and expands the application range. Specifically, the present application solves the phase noise caused by environmental disturbance in traditional single optical comb measurement by jointly solving the repetition frequency difference (Δf r ) of double optical comb and the phase difference caused by liquid level change, and improves the stability of measurement.

[0037] (2) The present application uses a piezoelectric ceramic driven adjustable optical path delay device to compensate the additional optical path difference caused by temperature or liquid refractive index change in real time, and ensures that the measurement accuracy is not affected by environmental parameters. The core optical path of the present application uses a polarization maintaining optical fiber and a polarization maintaining optical fiber coupler, which avoids the problem that the spatial optical path is sensitive to vibration, and enhances the industrial environment applicability. BRIEF DESCRIPTION OF DRAWINGS

[0038] Figure 1 is the principle block diagram of the all-fiber liquid level measurement system based on double optical comb phase decoupling and adaptive compensation of the present application;

[0039] Figure 2 is the flow chart of adaptive compensation in embodiment 3. DETAILED DESCRIPTION

[0040] Embodiment 1:

[0041] An all-fiber liquid level measurement system based on double optical comb phase decoupling and adaptive compensation, as shown in Figure 1 , includes a double optical comb light source module, a fiber isolator, a polarization maintaining optical fiber beam splitter, a polarization maintaining optical fiber beam combiner, a fiber collimator, a fiber mirror, a fiber ring 1, a fiber ring 2, an adaptive compensation module, a balanced photodetector, a lock-in amplifier, an upper computer, a temperature sensor, and a refractive index sensor.

[0042] The fiber circulator 1, the PZT fiber stretcher and the fiber mirror constitute a reference arm of the measurement system;

[0043] The fiber circulator 2, the fiber collimator and the liquid surface to be measured constitute a measurement arm of the measurement system;

[0044] The balanced photodetector, the lock-in amplifier and the host computer constitute a signal acquisition and signal processing system of the measurement system,

[0045] The PID controller, the PZT driver and the PZT fiber stretcher constitute an adaptive compensation module.

[0046] The dual-comb light source module outputs dual-comb laser through a polarization maintaining optical fiber, the polarization maintaining optical fiber is connected with an input end of a polarization maintaining optical fiber isolator, and an output end of the fiber isolator is connected with an input end of a polarization maintaining optical fiber beam splitter.

[0047] The output port 2 of the polarization maintaining optical fiber beam splitter is connected with the reference arm, specifically, in the reference arm, the output port 1 of the polarization maintaining optical fiber beam splitter is connected with the port (1) of the fiber circulator 1, the port (2) of the fiber circulator 1 is connected with the PZT fiber stretcher, the other end of the PZT fiber stretcher is connected with the fiber mirror, and the port (3) of the fiber circulator 1 is connected with the input port 1 of the polarization maintaining optical fiber beam combiner.

[0048] The output port 1 of the polarization maintaining optical fiber beam splitter is connected with the measurement arm, specifically, in the measurement arm, the output port 1 of the polarization maintaining optical fiber beam splitter is connected with the port (1) of the fiber circulator 2, the port (2) of the fiber circulator 2 is connected with the fiber collimator, the fiber collimator is installed above the liquid surface to be measured, and the port (3) of the fiber circulator 2 is connected with the input port 2 of the polarization maintaining optical fiber beam combiner.

[0049] The output end of the polarization maintaining optical fiber beam combiner is connected with the input end of the balanced photodetector, the output end of the balanced photodetector is connected with the input end of the lock-in amplifier, the lock-in amplifier is further connected with the host computer and the PID controller respectively, the PID controller is connected with the PZT driver, and finally the PZT controller is connected with the PZT fiber stretcher.

[0050] In the whole measurement system during use, the dual-comb light source module provides dual-comb output, the reference arm provides a stable phase reference, a fixed optical path design is adopted, the armored optical fiber and the shockproof packaging are used to reduce the influence of temperature and vibration environment on the fixed optical path. The adaptive compensation module is introduced into the reference arm, the phase difference fed back by the lock-in amplifier is input into the PID control PZT fiber stretcher to realize dynamic compensation of the optical path, offset the phase noise caused by environmental interference, the adaptive algorithm is introduced to realize fast dynamic compensation of the optical path. The phase of the reference arm is adjustable and can be used for system calibration and temperature drift correction. The measurement arm is used for direct liquid level measurement.

[0051] Embodiment 2:

[0052] A kind of all-optical fiber liquid level measurement system based on dual optical comb phase decoupling and adaptive compensation, for measuring the liquid level of fuel tank.The measurement system is modularized, as shown in Figure 1 Mainly includes dual optical comb light source module, reference arm, measurement arm, fiber coupling module, signal acquisition and processing system, adaptive compensation module, as shown in the figure.The fiber coupling module includes polarization maintaining optical fiber beam splitter and polarization maintaining optical fiber combiner.Each module is encapsulated in a case, and fiber collimator is used as measurement probe, and fiber collimator is connected with system case by pigtail, which can adapt to different installation scenes, so that the application can adapt to various harsh measurement scenes.

[0053] Preferably, the fiber circulator 1, PZT fiber stretcher and fiber mirror constitute the reference arm of the measurement system;

[0054] The fiber circulator 2, fiber collimator and the liquid surface to be measured constitute the measurement arm of the measurement system;

[0055] The balanced photodetector, lock-in amplifier and host computer constitute the signal acquisition and signal processing system of the measurement system,

[0056] The PID controller, PZT driver and PZT fiber stretcher constitute the adaptive compensation module.

[0057] The dual optical comb light source module outputs dual optical comb laser through polarization maintaining optical fiber, the polarization maintaining optical fiber is connected with the input end of polarization maintaining optical fiber isolator, and the output end of the fiber isolator is connected with the input end of the polarization maintaining optical fiber beam splitter.

[0058] Preferably, in the embodiment, the case of the measurement system can be placed in a more balanced environment, the fiber collimator is connected with the measurement system by fiber, and the fiber collimator can be designed as a through-wall sealed joint and directly inserted into the matched access window above the oil tank.For transparent liquid, the collimator is installed vertically to the liquid surface, and for non-transparent liquid level, the collimator is installed obliquely to obtain stronger liquid surface reflection.

[0059] In use, the dual optical comb light source module emits a dual optical comb, which enters a polarization maintaining fiber beam splitter through a fiber isolator (to avoid the harm of reflected light to the light source). After beam splitting, reference light and measurement light are formed. The reference light enters a fiber mirror through a fiber circulator 1 and a PZT fiber stretcher. The optical path of the reference light is fixed, and after reflection by the end face of the fiber mirror, the reference light enters the polarization maintaining fiber combiner through the fiber circulator 1. The measurement light enters a fiber collimator through a fiber circulator 2. After collimation, spatial light is emitted to the liquid surface to be measured. After reflection by the liquid surface, the light returns to the fiber collimator, the fiber circulator 2 and the polarization maintaining fiber combiner in turn. After the reference light and the measurement light are combined by the polarization maintaining fiber combiner, the interference signal is received by a balanced photodetector, and a beat frequency signal is output wherein N is the mode number of the optical comb, is the phase difference caused by the change in the liquid level, and Δf r is the repetition frequency difference of the dual optical comb. The phase information in the beat frequency signal f beat is extracted by a lock-in amplifier, and signal processing and liquid level settlement are performed by an upper computer. If the adaptive compensation module is triggered.

[0060] Preferably, the adaptive compensation module is used to compensate the optical path of the reference light. A piezoelectric ceramic (PZT) drive is adopted, a PID controller outputs a signal V(t) to drive a PZT driver, so that the axial expansion and contraction amount ΔLz of the PZT fiber stretcher is βV(t), wherein β is a stretching and contraction coefficient; at this time, the reference arm optical path change ΔL ref = 2ΔLz, so as to offset the ΔL nosie introduced by the environmental disturbance.

[0061] After compensation, the is detected again. If the compensation is successful, otherwise the PID controller is iteratively executed for adjustment until convergence. The ΔLz and V(t) of each compensation, and the optimal PID parameters under different working conditions (environmental parameters provided by a temperature sensor and a refractive index sensor) are recorded. Through machine learning, the PID parameters are optimized, a lookup table is established, the self-optimization of the control parameters is realized, and further improvement is achieved.

[0062] Embodiment 3:

[0063] A full-fiber liquid level measurement method based on dual optical comb phase decoupling and adaptive compensation, comprising the following steps:

[0064] (1) When there is no change in the liquid level, the initial phase difference between the reference arm and the measurement arm is recorded The optical path of the reference arm is adjusted by a PZT fiber stretcher, so that tends to zero, eliminating the static error of the system;

[0065] (2) Real-time adaptive compensation of reference arm optical path according to environmental temperature changes, to ensure Only caused by liquid level changes.

[0066] (3) Liquid level height change Δh leads to measurement arm optical path change ΔL = 2nΔh, causing phase difference The balanced photodetector output signal is Fourier transformed, and the phase difference is extracted Combined with the real-time monitored liquid refractive index n (through auxiliary temperature sensor or refractometer), the liquid level height is calculated as:

[0067]

[0068] Where: λ is the center wavelength of the optical comb;

[0069] Δf r is the repetition frequency difference of the dual optical comb;

[0070] is the phase difference caused by liquid level change;

[0071] n is the liquid refractive index;

[0072] t is time.

[0073] Preferably, as Figure 2 shown, the adaptive compensation of the reference arm optical path includes the following steps:

[0074] A1: Environmental parameter monitoring (temperature, refractive index): Real-time acquisition of environmental temperature T, liquid refractive index n, etc. through temperature sensor and refractive index sensor in the system, to provide prior parameters for optical path compensation. Temperature change ΔT will cause fiber expansion ΔL1 = α·L·ΔT; Refractive index change causes optical path change ΔL2 = LΔn.

[0075] Where: α is the thermal expansion coefficient;

[0076] L is the fiber length.

[0077] A2: Phase difference detection: balanced photodetector output interference signal, real-time phase difference is extracted through digital phase-locked amplifier

[0078] A3: Detect whether there is a phase disturbance, i.e. if it is determined that environmental disturbance leads to additional phase noise, triggering compensation Step A4 is entered. Otherwise, maintain the current optical path and enter step (3) to further calculate the liquid level height information.

[0079] Where: is the initial phase difference between the reference arm and the measurement arm when there is no change in liquid level; βV(t) = ΔLz = ΔL1 + ΔL2 is the optical path adjusted by the PID compensation.

[0080] ε can be dynamically adjusted according to the type of liquid (transparent / opaque).

[0081] A4: generate a control signal V(t), and the optical path adjustment is ΔLz = βV(t), the reference arm optical path change ΔL ref = 2ΔLz to offset the ΔL introduced by environmental disturbances nosie . Enter step A2.

[0082] wherein β is the scaling coefficient.

[0083] The above is only a preferred embodiment of the present application, not any form of limitation on the present application, any simple modification, equivalent change of the above embodiment according to the technical essence of the present application, falls within the protection scope of the present application.

Claims

1. An all-fiber liquid level measurement system based on dual-comb phase decoupling and adaptive compensation, characterized in that: It includes a dual-comb light source module, a fiber coupling module, a signal acquisition and processing system, an adaptive compensation module, a measuring arm, and a reference arm. The fiber coupling module includes a polarization-maintaining fiber beam splitter and a polarization-maintaining fiber combiner. The signal acquisition and processing system includes a balanced detector, a phase-locked amplifier, and a host computer connected in sequence from front to back. The phase-locked amplifier is connected to the adaptive compensation module. The dual-comb light source module is connected to the measuring arm and the reference arm respectively through the polarization-maintaining fiber beam splitter. The measuring arm and the reference arm are respectively connected to the balanced detector through the polarization-maintaining fiber combiner. The dual-comb light source module is used to emit dual-comb laser light, and the polarization-maintaining fiber beam splitter is used to split the dual-comb laser light into reference light and measurement light, and input them into the reference arm and the measurement arm respectively; The adaptive compensation module is used to control the reference arm based on the phase difference feedback from the lock-in amplifier to adjust the dynamic compensation of the reference light path; the reference arm is used to output the compensated reference light to the polarization-maintaining fiber combiner; The measuring arm is used for liquid level measurement and outputs the measuring light reflected by the liquid surface to the polarization-maintaining fiber combiner; The balanced photoelectric detector is used to receive the interference signal output by the polarization-maintaining fiber combiner and output the beat frequency signal f beat to a lock-in amplifier, which is used to extract the beat frequency signal f beat phase difference.

2. The all-fiber liquid level measurement system based on dual-comb phase decoupling and adaptive compensation according to claim 1 is characterized in that: The adaptive compensation module includes a PID controller and a PZT driver connected to each other. The reference arm includes a fiber circulator 1, a PZT fiber stretcher, and a fiber reflector connected in sequence from front to back. The PZT driver is connected to the PZT fiber stretcher. The fiber circulator 1 is respectively connected to the dual-comb light source module and the polarization-maintaining fiber combiner, so as to enable the reference light to enter the fiber reflector through the fiber circulator 1 and the PZT fiber stretcher. The optical path of the reference light is fixed, and after being reflected by the end face of the fiber reflector, it passes through the fiber circulator 1 and enters the polarization-maintaining fiber combiner.

3. The all-fiber liquid level measurement system based on dual-comb phase decoupling and adaptive compensation according to claim 2 is characterized in that: The measuring arm includes an interconnected optical fiber circulator 2 and an optical fiber collimator. The optical fiber circulator 2 is respectively connected to a polarization-maintaining optical fiber splitter and a polarization-maintaining optical fiber combiner, so as to enable the measuring light to enter the optical fiber collimator through the optical fiber circulator 2, and after collimation, emit spatial light to the liquid surface to be measured, and after reflection from the liquid surface, return to the optical fiber collimator, the optical fiber circulator 2 and the polarization-maintaining optical fiber combiner in sequence.

4. The all-fiber liquid level measurement system based on dual-comb phase decoupling and adaptive compensation according to claim 3 is characterized in that: The optical fiber circulator 1 and the optical fiber circulator 2 are both polarization-maintaining optical fiber circulators.

5. The all-fiber liquid level measurement system based on dual-comb phase decoupling and adaptive compensation according to claim 1 is characterized in that: The dual-comb light source module is connected to the polarization-maintaining optical fiber splitter through an optical fiber isolator.

6. The all-fiber liquid level measurement system based on dual-comb phase decoupling and adaptive compensation according to claim 1, characterized in that: The splitting ratio of the polarization-maintaining fiber splitter and the polarization-maintaining fiber combiner is 50:

50.

7. An all-fiber liquid level measurement method based on dual-comb phase decoupling and adaptive compensation, characterized in that: The following steps are involved: Step S1: Launch a dual optical comb and split it into reference light and measurement light; Step S2: transmitting the measuring light to the liquid surface to be measured, and after being reflected by the liquid surface, returning to the polarization-maintaining fiber combiner; Step S3: After the polarization-maintaining fiber combiner combines the received reference light with the measurement light, the balanced photodetector receives the interference signal and outputs the beat frequency signal f beat =NΔf r ±Δφ(t) / 2π; Where: N is the number of optical comb modes; Δf r is the repetition frequency difference of the dual combs; Δφ(t) is the phase difference caused by the liquid level change; t is time; Step S4: The beat frequency signal f beat Perform Fourier transform to extract the phase difference Δφ(t); Step S5: If |Δφ(t)-φ 0 |≥ε, then adjust the dynamic compensation of the reference light path based on the phase difference Δφ(t); output the compensated reference light to the polarization-maintaining fiber combiner and enter step S3; if |Δφ(t)-φ 0 |<ε, then go to step S6; Where: φ 0 is the calibration value of the phase difference; ε is the set threshold; Step S6: Calculate the liquid level change value: Where: λ is the central wavelength of the optical comb; n is the refractive index of the liquid.

8. The all-fiber liquid level measurement method based on dual-comb phase decoupling and adaptive compensation according to claim 7, characterized in that: In step S5, the output signal V(t) drives the PZT fiber stretcher, and its axial expansion and contraction amount ΔLz=βV(t), where β is the expansion and contraction ratio coefficient; the reference light optical path changes ΔL ref =2ΔLz, to offset the ΔL introduced by environmental disturbances nosie .

9. The all-fiber liquid level measurement method based on dual-comb phase decoupling and adaptive compensation according to claim 8, characterized in that: Record the ΔL of each compensation ref The output signal V(t), as well as the optimal PID parameters of environmental parameters with different temperatures and refractive indices, are obtained. The PID parameters are optimized based on the machine learning method, and a lookup table is established to achieve self-optimization of the PID control parameters.

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