A method and system for dynamic demodulation of fiber F-P cavity length based on cross-restriction

Abstract

The present application relates to the technical field of optical fiber sensing signal processing, in particular to a fiber F-P cavity length dynamic demodulation method and system based on cross constraint, the method collects the interference spectrum signal reflected by the fiber F-P cavity, extracts multiple effective characteristic wavelengths and constructs a characteristic wavelength sequence; a plurality of wavelength calculation pairs are constructed according to the characteristic wavelength sequence, and a candidate interference order set is calculated; whether the current interference spectrum is abnormal is judged by the dispersion index of the candidate interference order set, and the candidate interference order set is subjected to anti-interference correction processing to determine the effective absolute interference order; then the actual cavity length of the fiber F-P cavity is calculated according to the effective absolute interference order, and the cavity length change information is obtained based on the actual cavity length at different sampling times. The present application also provides a fiber F-P cavity length dynamic demodulation system based on cross constraint. The present application can reduce the interference order misjudgment, and improve the stability and accuracy of the cavity length dynamic demodulation.

Description

Technical Field

[0001] This invention relates to the field of fiber optic sensing signal processing technology, specifically to a method and system for dynamic demodulation of fiber optic FP cavity length based on cross-constraints. Background Technology

[0002] Pipeline transportation, with its low cost, low loss, and high safety, has become the primary mode of oil and gas transportation worldwide. However, natural gas is prone to violent explosions when exposed to open flames or static electricity, which can destroy buildings, cause casualties, and damage roads, bridges, and other pipelines with the shockwave. Fiber optic FP-cavity acoustic pressure sensors possess advantages such as resistance to electromagnetic interference, high sensitivity, intrinsic safety, and suitability for long-distance transmission, making them core sensing devices for pipeline leak monitoring and other scenarios. Demodulation technology, the core step in extracting cavity length changes and reconstructing the acoustic pressure signal from interference signals, directly determines the sensor's detection accuracy and stability. Dynamic acoustic pressure signals are characterized by wide frequency bands, large amplitude fluctuations, and strong on-site interference, placing extremely high demands on the real-time performance, accuracy, anti-interference capabilities, and dynamic range of demodulation technology.

[0003] Comparison and analysis of the shortcomings of existing mainstream demodulation technologies: 1. Intensity demodulation is based on the correspondence between the intensity amplitude of FP interference light and the cavity length. The real-time fluctuation of light intensity is captured by a photodetector, and then the dynamic changes of the cavity length are demodulated in reverse.

[0004] It is commonly used in ultra-high frequency acoustic emission detection scenarios. The system has a simple structure and fast response speed, but it has weak anti-interference ability, narrow dynamic measurement range, poor long-term stability, and cannot achieve absolute cavity length measurement, making it difficult to adapt to long-term online monitoring scenarios.

[0005] 2. Phase demodulation is based on the principle of linear correlation between the phase difference of fiber FP interference and the cavity length. The interference phase change is extracted through optical modulation and signal processing to restore the cavity length change and the measured sound pressure signal.

[0006] Phase demodulation is widely used in fields such as ultrasonic detection of partial discharge. It has the advantages of high demodulation sensitivity, good linearity, wide dynamic range, and strong anti-interference ability. However, the demodulation system is relatively complex and is prone to phase entanglement problems over a large dynamic range.

[0007] 3. Wavelength demodulation is based on the linear mapping relationship between the wavelength drift of the characteristic peak of the fiber FP cavity interference spectrum and the cavity length. By tracking the change in the wavelength position of the characteristic peak, the dynamic change of the cavity length is demodulated.

[0008] It is commonly used in structural health monitoring, long-term online leakage monitoring of long-distance pipelines, and multi-parameter synchronous sensing testing scenarios. It has strong resistance to strong light interference, supports absolute cavity length measurement, has good long-term stability, and facilitates temperature compensation and multi-parameter decoupling. However, the algorithm has a large computational load, the hardware cost is relatively high, and some solutions have problems such as hierarchical ambiguity and large demodulation error.

[0009] In the field of fiber optic FP cavity acoustic pressure signal demodulation, wavelength demodulation technology has attracted much attention due to its advantages such as strong resistance to strong optical interference and support for absolute cavity length measurement. However, existing demodulation algorithms still have significant limitations when dealing with complex dynamic conditions such as natural gas pipeline leak monitoring.

[0010] Limitations of single-peak demodulation algorithms: These algorithms primarily invert cavity length variations by tracking the wavelength shift of a single characteristic peak in the interference spectrum. While single-peak demodulation offers high resolution, it is a relative measurement method and suffers from a severe "interference order ambiguity" problem. The inability to lock onto the absolute interference order limits the dynamic measurement range, and environmental disturbances causing signal fluctuations easily lead to nonlinear demodulation errors, failing to meet the stability requirements of long-distance online monitoring.

[0011] The drawbacks of dual-peak / multi-peak demodulation algorithms: These algorithms calculate the absolute cavity length using the wavelength differences of multiple characteristic peaks. However, in practical applications, their demodulation accuracy is significantly inversely proportional to the selected order difference. Limited by hardware bandwidth and signal-to-noise ratio, their demodulation error is typically several orders of magnitude higher than that of single-peak algorithms, making it difficult to achieve nanometer-level high-sensitivity sound pressure detection standards and hindering the high-precision extraction of weak leakage signals.

[0012] Limitations of the multi-peak-single-peak joint demodulation algorithm: While the multi-peak-single-peak joint demodulation scheme can balance large range and high accuracy, its reliability is poor in complex engineering environments. During dynamic sound pressure measurement, environmental noise and "phase jumps" caused by transient pressure pulses can lead to errors in the algorithm's logical determination of interference levels. The cumulative effect of this error can cause "level jumps," resulting in a step distortion in the demodulated cavity length signal, completely losing the ability to stably monitor dynamic sound pressure signals.

[0013] Existing fiber optic FP cavity acoustic pressure dynamic demodulation schemes struggle to simultaneously achieve a large dynamic measurement range, nanometer-level demodulation accuracy, resistance to order jumps, and strong anti-interference capabilities. Therefore, this invention provides a cross-constraint-based fiber optic FP cavity length dynamic demodulation method and system to address the problems in the prior art. Summary of the Invention

[0014] To address the shortcomings of current technologies, this invention provides a dynamic demodulation method for fiber optic FP cavity length that is engineerable, has strong anti-interference capabilities, and is adaptable to complex field conditions. It meets the requirements for long-term online dynamic sound pressure detection and can solve the problem that existing wavelength demodulation algorithms cannot simultaneously handle large dynamic measurement range and high-precision demodulation. It also addresses the problems of existing multi-peak-single-peak joint demodulation algorithms in dynamic measurement, such as the accumulation of interference order errors, order jumps, and distortion of demodulation results caused by noise and phase jumps.

[0015] The technical solution of the present invention is as follows: A dynamic demodulation method for fiber FP cavity length based on cross-constraint includes the following steps: S1: Acquire the interference spectrum signal reflected by the fiber FP cavity, extract the effective characteristic wavelength values ​​from the interference spectrum signal, and construct the characteristic wavelength sequence; S2, construct multiple wavelength calculation pairs based on the characteristic wavelength sequence, calculate the candidate interference order corresponding to each wavelength calculation pair, and obtain the candidate interference order set; S3, calculate the dispersion index of the candidate interference order set, and determine whether there are any abnormal phenomena in the interference spectrum at the current time due to external environmental noise interference based on the dispersion index. S4. Based on the judgment result of S3, perform anti-interference correction processing on the candidate interference level set to determine the effective absolute interference level at the current sampling time; S5, calculate the actual cavity length of the fiber FP cavity based on the effective absolute interference order; obtain cavity length variation information based on the actual cavity length at different sampling times.

[0016] Based on the above demodulation method, the present invention also provides a cross-constraint-based fiber FP cavity length dynamic demodulation system, including a signal demodulator module, a data acquisition module, a processor module, and a sensing module; the sensing module includes a fiber FP cavity acoustic pressure sensor, a standard sensor, and a sound source module. The signal demodulator module is connected to the fiber optic FP cavity acoustic pressure sensor. The signal demodulator module includes a demodulator, which is used to output a swept laser to the fiber optic FP cavity acoustic pressure sensor, receive the interference light signal returned by the fiber optic FP cavity acoustic pressure sensor, and convert the interference light signal into a first electrical signal. The sound source module is used to apply sound pressure signals to the standard sensor and the fiber optic FP cavity sound pressure sensor, causing the standard sensor to generate a second electrical signal and causing the interference light signal returned by the fiber optic FP cavity sound pressure sensor to change with the sound pressure signal. The data acquisition module is connected to a standard sensor to acquire the second electrical signal generated by the standard sensor. The processor module is connected to the signal demodulator module and the data acquisition module respectively, and is used to receive and process the first electrical signal and the second electrical signal.

[0017] Furthermore, the processor module is used to obtain a reference sound pressure value based on the second electrical signal and the preset sensitivity of the standard sensor.

[0018] Furthermore, the processor module is also used to acquire the interference spectrum signal reflected by the fiber FP cavity based on the first electrical signal, and to perform the above-mentioned dynamic demodulation method for fiber FP cavity length based on cross constraints on the interference spectrum signal.

[0019] The beneficial effects of this invention are as follows: 1. Balancing demodulation accuracy and dynamic range. By combining the absolute cavity length measurement capability of multi-peak demodulation with the high precision advantage of single-peak demodulation, the problem of the inability to simultaneously achieve dynamic range and demodulation accuracy in traditional algorithms is solved, enabling precise demodulation of nanometer-scale cavity lengths over a large dynamic range.

[0020] 2. Strong resistance to single-point noise interference and anti-jump capability. This invention uses internal cross-constraints instead of traditional unidirectional numerical comparison. Transient noise often has randomness; by calculating the discreteness of the candidate interference level set and combining it with a majority voting algorithm, the influence of outlier levels on the determination result of the effective absolute interference level is reduced.

[0021] 3. Strong anti-interference capability and wide adaptability. Based on the wavelength demodulation principle, it has strong resistance to light intensity fluctuations and environmental disturbances, and is suitable for long-term online detection needs in complex working conditions such as field pipeline monitoring. At the same time, the algorithm has strong compatibility and can be adapted to various diaphragm fiber optic FP cavity acoustic pressure sensors. Attached Figure Description

[0022] Figure 1 This is a flowchart illustrating the dynamic demodulation method for fiber FP cavity length based on cross-constraints according to the present invention. Figure 2 This is a structural block diagram of the fiber optic FP cavity length dynamic demodulation system based on cross-constraint of the present invention; Figure 3 This is a schematic diagram illustrating the variation of fiber optic FP cavity length with the signal acquisition time of the demodulator under existing demodulation techniques. Figure 4 This is a comparison chart of the cavity length demodulation results between existing demodulation methods and the demodulation algorithm of this invention. Detailed Implementation

[0023] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0024] Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0025] refer to Figure 1 This embodiment employs a cross-constraint-based fiber FP cavity length dynamic demodulation method, which can balance large dynamic range and high-precision demodulation. It can reduce order misjudgments caused by noise, spectral distortion, or phase jumps, suppress demodulation distortion, and improve the stability and accuracy of long-term online detection of sound pressure signals under complex operating conditions. The specific steps are as follows: S1. Construct a multi-characteristic wavelength sequence for the interference spectrum. The interference spectrum signal reflected from the fiber optic FP cavity is acquired. Unlike the traditional approach of selecting only the first and last characteristic peaks, a peak-finding algorithm is used to extract the effective characteristic wavelength values ​​from the interference spectrum, constructing a characteristic wavelength sequence. The effective characteristic wavelength values ​​are either troughs or peaks; this embodiment selects troughs. The characteristic wavelength sequence is Λ={ λ 1, λ 2, ..., λ N},in N The total number of effective characteristic wavelengths in the current spectrum ( N ≥4); S2, construct wavelength pairs and calculate the candidate interference order set. Traverse the characteristic wavelength sequence Λ and select different interval numbers. q wavelength pairs, such as intervals q ={ N -1, N -2, N -3……}, forming multiple wavelength calculation pairs ( λ i , λ j Substitute each wavelength pair into the multi-peak order calculation formula for parallel calculation: In the formula, wavelength λ i and λ j Number of characteristic peak intervals between them Round This is the rounding function. To calculate the pair based on wavelength ( λ i , λ j The candidate interferometric orders are calculated. One candidate interferometric order is calculated for each wavelength pair, and these are summed to obtain the set of candidate interferometric orders at the current sampling time. ={m 1, m 2, ..., m K},in K The total number of wavelength pairs used in the calculation is calculated.

[0026] S3, Order jump determination based on discreteness. In dynamic sound pressure measurement, if the spectrum is not affected by distortion, the calculation results in the set should be highly consistent; if the local characteristic wavelength is shifted due to transient noise, it will cause the calculation pair containing that characteristic wavelength to produce an incorrect order.

[0027] Calculate the candidate interference order set The dispersion index can be a set of candidate interference levels. Statistical variance Or standard deviation; in this embodiment, variance is selected. , ,in, K is The total number of elements in the candidate interference order set, i.e., the total number of candidate interference orders participating in this variance calculation. The first in the candidate interference level set k The value of each element. It is the arithmetic mean of all elements in the candidate interference level set; typically, under ideal conditions... .

[0028] Set the dispersion threshold .like The current interference spectrum is determined to be normal, with no order jumps or severe interference; if The current interference spectrum is determined to be abnormal, indicating that the current spectrum is subject to transient interference, interference order ambiguity, or phase jump.

[0029] S4, based on the judgment result of S3, determine the effective absolute interference level at the current moment. If the interference spectrum is normal, then average and round down. ,in, K is The total number of elements in the candidate interference level set. The first in the candidate interference level set k The value of each element. The result represents the average level of candidate interference orders obtained from multi-wavelength demodulation; the calculation result needs to be rounded. Alternatively, it can be rounded to the nearest integer. The mode as the effective absolute interference level If the interference spectrum is abnormal, anti-interference processing is performed. Since high-frequency noise or local spectral distortion usually only contaminates a few characteristic peaks, most unaffected characteristic wavelength pairs can still be used to calculate the true interference order. Therefore, the effective absolute interference order is calculated using a voting algorithm. ,in, For the set of candidate interference levels, Mode This is the mode function.

[0030] S5, single-peak high-precision cavity length demodulation. This converts the effective absolute interference order obtained through the cross-constraints of S2-S4. Substituting into the single-peak demodulation algorithm formula, the high-precision actual cavity length of the fiber FP cavity is calculated. d , ,in n Let be the refractive index of the medium inside the FP cavity. The center wavelength, the center wavelength For any effective characteristic wavelength selected from the characteristic wavelength sequence Λ in S1, To achieve an effective absolute interference order, the cavity length variation information of the fiber FP cavity is obtained based on the actual cavity length at different sampling times.

[0031] This embodiment determines the effective absolute interference order through multi-wavelength cross-constraint and calculates the actual cavity length by combining it with a single-peak demodulation algorithm. This reduces the impact of misjudgment of interference order and cavity length jump on the demodulation results of the sound pressure signal, and obtains high-precision information on the cavity length variation of the fiber FP cavity, thereby demodulating a high-precision and stable fiber FP cavity sound pressure signal.

[0032] Based on the above method, the present invention also provides an optical fiber FP cavity acoustic pressure signal demodulation system that is engineerable, has strong anti-interference ability, and is adaptable to complex field conditions, thus meeting the requirements for long-term online dynamic acoustic pressure detection.

[0033] like Figure 2 As shown, a cross-constraint-based fiber FP cavity length dynamic demodulation system includes a signal demodulator module, a data acquisition module, a processor module, and a sensing module. The sensing module includes a fiber FP cavity acoustic pressure sensor, a standard sensor, and a sound source module. The fiber FP cavity acoustic pressure sensor is the sensor under test. The standard sensor, the sensor under test, and the loudspeaker are placed together in an acoustic soundproof box to form a relatively stable acoustic testing environment.

[0034] The signal demodulator module is connected to the fiber optic FP cavity acoustic pressure sensor. The module outputs a swept-frequency laser to the sensor, receives the interference light signal returned by the sensor, and converts the interference light signal into a first electrical signal. In this embodiment, the FAZ-I4G signal demodulator is selected, which integrates a tunable scanning laser and a photodetector. It is suitable for both static and dynamic measurements. The swept-frequency laser offers multiple scanning frequencies and can be connected to a host computer via an Ethernet interface for high-speed data acquisition and real-time display.

[0035] The sound source module includes a signal generator and a speaker. The speaker is connected to the signal generator using a BNC interface signal cable. The sound source module is used to apply sound pressure signals to a standard sensor and a fiber optic FP cavity acoustic pressure sensor, causing the standard sensor to generate a second electrical signal and causing the interference light signal returned by the fiber optic FP cavity acoustic pressure sensor to change with the sound pressure signal.

[0036] The data acquisition module connects to a standard sensor to acquire the second electrical signal generated by the standard sensor. In this embodiment, the data acquisition module is a data acquisition card, and a data acquisition card from National Instruments (NI) can be selected.

[0037] The processor module is connected to both the signal demodulator module and the data acquisition module. The data acquisition module transmits the second electrical signal to the processor module, which then obtains the measurement reference sound pressure value based on the second electrical signal and the preset sensitivity of the standard sensor. In this embodiment, the processor module can be a host computer. After receiving the first electrical signal, the host computer obtains the interference spectrum signal corresponding to the reflected interference light from the fiber FP cavity based on the first electrical signal and the frequency sweep wavelength correspondence of the signal demodulator module. It then performs the aforementioned dynamic demodulation method for the fiber FP cavity length based on cross-constraints on the interference spectrum signal to obtain the actual cavity length and cavity length variation information of the fiber FP cavity, and obtains the sound pressure signal of the fiber FP cavity based on the cavity length variation information.

[0038] Figure 3 This diagram illustrates the demodulation results of a current multi-peak / single-peak joint demodulation algorithm, showing the change in fiber optic FP cavity length under 40Hz sound pressure level. (Reference) Figure 3 The horizontal axis represents the signal acquisition time of the demodulator, in ms; the vertical axis represents the fiber FP cavity length obtained by demodulation using the existing multi-peak-single-peak joint demodulation algorithm, in nm; in the figure, the curve represents the change in FP cavity length under the action of sound waves, and the peak represents the erroneous cavity length jump point caused by the interference order jump due to the influence of external environmental noise.

[0039] Figure 4 This is a comparison chart of the demodulation results between the algorithm of this invention and existing algorithms. The horizontal axis represents the signal acquisition time of the demodulator, in milliseconds (ms); the left and right vertical axes represent the cavity lengths of the fiber FP cavity obtained by demodulation using the existing multi-peak-single-peak joint demodulation algorithm and the algorithm of this invention, respectively, in nm. The black curve represents the cavity length demodulation result without using the algorithm of this invention, and the red curve represents the cavity length demodulation result after using the algorithm of this invention.

[0040] Depend on Figure 4As can be seen, without using the algorithm of this invention, obvious spikes appear in the demodulation results around 30ms, 50ms, 75ms, and 95ms, indicating that existing demodulation methods are easily affected by external environmental noise, phase jumps, and other factors, resulting in misjudgment of interference order and cavity length jumps, leading to distortion of the demodulation results. In contrast, after using the algorithm of this invention, the red curve shows a continuous and stable periodic change without abnormal spikes, which can better reflect the true change of the FP cavity length under the action of sound waves. Therefore, this invention determines the effective absolute interference order through multi-wavelength cross-constraint and combines it with single-peak high-precision demodulation, which can effectively suppress order jumps and erroneous cavity length jump points, solve the problems of interference order error accumulation, order jumps, and demodulation result distortion caused by environmental noise in the prior art, and improve the stability and accuracy of dynamic cavity length demodulation results, thereby improving the stability and accuracy of dynamic sound pressure signal demodulation.

[0041] The above are merely embodiments of the present invention and are not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principle of the present invention should be included within the scope of the claims of the present invention.

Claims

1. A method for dynamic demodulation of fiber FP cavity length based on cross-constraint, characterized in that: Includes the following steps: S1, acquire the interference spectrum signal reflected by the fiber FP cavity, and extract the effective characteristic wavelength values ​​from the interference spectrum signal to construct a characteristic wavelength sequence; S2, construct multiple wavelength calculation pairs based on the characteristic wavelength sequence, calculate the candidate interference order corresponding to each wavelength calculation pair, and obtain a set of candidate interference orders; S3, calculate the dispersion index of the candidate interference order set, and determine whether there are any abnormal phenomena in the interference spectrum at the current time due to external environmental noise interference based on the dispersion index. S4. Based on the judgment result of S3, perform anti-interference correction processing on the candidate interference level set to determine the effective absolute interference level at the current sampling time; S5, calculate the actual cavity length of the fiber FP cavity based on the effective absolute interference order; obtain cavity length variation information based on the actual cavity length at different sampling times; In S2, Traverse the characteristic wavelength sequence Λ and select different interval numbers q Wavelength pairs, forming multiple wavelength calculation pairs ( λ i , λ j The solution is obtained using the multi-peak order calculation formula: In the formula, Calculate pairs for each wavelength group ( λ i , λ j The number of characteristic peak intervals between ) Round This is the rounding function. To calculate the pair based on wavelength ( λ i , λ j The candidate interference orders are calculated; thus, the set of candidate interference orders is obtained. ; The demodulation method is implemented based on a fiber optic FP cavity length dynamic demodulation system, which includes a signal demodulator module, a data acquisition module, a processor module, and a sensing module; the sensing module includes a fiber optic FP cavity acoustic pressure sensor, a standard sensor, and a sound source module. The signal demodulator module is connected to the fiber optic FP cavity acoustic pressure sensor. The signal demodulator module is used to output a swept laser to the fiber optic FP cavity acoustic pressure sensor, receive the interference light signal returned by the fiber optic FP cavity acoustic pressure sensor, and convert the interference light signal into a first electrical signal. The sound source module is used to apply a sound pressure signal to the standard sensor and the fiber optic FP cavity acoustic pressure sensor, so that the standard sensor generates a second electrical signal and the interference light signal returned by the fiber optic FP cavity acoustic pressure sensor changes with the sound pressure signal. The data acquisition module is connected to the standard sensor and is used to acquire the second electrical signal generated by the standard sensor. The processor module is connected to the signal demodulator module and the data acquisition module respectively, and is used to receive and process the first electrical signal and the second electrical signal.

2. The fiber optic FP cavity length dynamic demodulation method based on cross-constraint as described in claim 1, characterized in that: In S1, Effective characteristic wavelength values ​​are extracted using a peak-finding algorithm, and a characteristic wavelength sequence Λ={ λ 1, λ 2, ..., λ N },in N This represents the total number of effective characteristic wavelengths in the current interference spectrum. N ≥4.

3. The fiber optic FP cavity length dynamic demodulation method based on cross-constraint as described in claim 1, characterized in that: S3 specifically refers to... S31, Calculate the statistical variance of the candidate interference order set. As a measure of dispersion: ,in, K is Candidate Interference Level Set The total number of candidate interference levels, The first in the candidate interference level set k The value of each element. It is the arithmetic mean of all elements in the candidate interference level set; S32, Set the dispersion threshold And compare the dispersion index with the dispersion threshold, if If the current interference spectrum is normal, it is determined that the current time is normal; The current time is used to determine the anomaly in the interference spectrum.

4. The fiber optic FP cavity length dynamic demodulation method based on cross-constraint as described in claim 3, characterized in that: In S4, the anti-interference correction process is specifically as follows: Based on the judgment result of S32, the effective absolute interference order after anti-interference correction is obtained. If the interference spectrum is normal, then average and round down the result. ,in, K is The total number of elements in the candidate interference level set. The first in the candidate interference level set k The value of each element. The calculated result is the average level of the candidate interference orders obtained from multi-wavelength demodulation and needs to be rounded. If the interference spectrum is abnormal, anti-interference processing is performed. ,in, For the set of candidate interference levels, Mode This is the mode function.

5. The fiber optic FP cavity length dynamic demodulation method based on cross-constraint as described in claim 1, characterized in that: In S5, The actual cavity length of the fiber FP cavity is calculated using a single-peak demodulation algorithm. d , ,in n Let be the refractive index of the medium inside the FP cavity. The center wavelength, For any effective characteristic wavelength selected from the characteristic wavelength sequence Λ in S1, For effective absolute interference levels.

6. The fiber optic FP cavity length dynamic demodulation method based on cross-constraint as described in claim 1, characterized in that: The processor module is used to obtain a reference sound pressure value based on the second electrical signal and the preset sensitivity of the standard sensor.

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