Optical fiber Fabry-Perot sensor demodulation method and device

Abstract

The invention discloses an optical fiber Fabry-Perot sensor demodulation method and device, and the method comprises the steps: obtaining the prior parameters of an optical fiber Fabry-Perot sensor for the optical fiber Fabry-Perot sensor to be used at present, the prior parameters are calculated based on two paths of sampled static interference signals under the condition of no external to-be-measured signals; in the process of using the optical fiber Fabry-Perot sensor for measurement, two paths of dynamic interference signals containing external signals to be measured are sampled, and two paths of orthogonal signals are constructed after direct current components are removed from the two paths of dynamic interference signals based on prior parameters of the optical fiber Fabry-Perot sensor; and based on the two paths of orthogonal signals, the cavity length variation caused by an external to-be-measured signal is obtained through demodulation. According to the invention, the application range of the demodulation system is widened, and weak signals can be effectively detected.

Description

Technical Field

[0001] This invention relates to the field of fiber optic sensing technology, specifically to a fiber optic Fabry-Perot sensor demodulation method and apparatus. Background Technology

[0002] Unlike electroacoustic wave sensors, fiber optic ultrasonic sensors offer advantages such as high sensitivity, small size, resistance to electromagnetic interference, intrinsic safety, and remote measurement capabilities. They play an irreplaceable role in special scenarios such as high-voltage power equipment condition monitoring, biomedical imaging, and audio monitoring in flammable and explosive environments.

[0003] The superior sensing performance of fiber optic Fabry-Perot sensors heavily relies on efficient and reliable signal demodulation techniques. Current mainstream demodulation schemes, such as intensity demodulation, while offering fast response times, suffer from signal distortion due to the susceptibility of their orthogonal operating points to environmental interference. Furthermore, their dynamic range is limited. In contrast, dual-wavelength phase demodulation technology is favored for its high sensitivity and wide dynamic range, but it still faces significant bottlenecks in practical applications.

[0004] Traditional dual-wavelength orthogonal phase demodulation methods require strict matching of the cavity length of the Fabry-Perot sensor and the wavelength of the light source to construct orthogonal signals, resulting in poor flexibility and a narrow range of applications for the demodulation system. Furthermore, dual-wavelength demodulation algorithms based on elliptic fitting also have inherent limitations. They require a sufficiently large amplitude of the measured signal to form a complete ellipse or at least a quarter-elliptic arc in the Lissajous figure for accurate parameter fitting. Therefore, this method struggles to accurately extract AC and DC components from weak measured signals, leading to degraded demodulation performance and rendering it unsuitable for detecting weak signals.

[0005] Therefore, how to demodulate fiber optic Fabry-Perot sensors to broaden their application range and effectively detect weak signals is a problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0006] To address the shortcomings of the existing technologies, this invention provides a fiber optic Fabry-Perot sensor demodulation method and apparatus. Based on the static signal collected under conditions of no external signal to be measured, the DC component and AC amplitude are stably calculated, thus broadening the applicability and practicality of the demodulation system and improving the detection capability of weak signals.

[0007] In a first aspect, the present invention provides a method for demodulating an optical fiber Fabry-Perot sensor, comprising: For the fiber optic Fabry-Perot sensor to be used, the prior parameters of the fiber optic Fabry-Perot sensor are obtained. The prior parameters include the DC component and the AC amplitude. The prior parameters are calculated based on the sampled two static interference signals under the condition of no external test signal. During the measurement process using the fiber optic Fabry-Perot sensor, two dynamic interference signals containing external signals to be measured are sampled. Based on the prior parameters of the fiber optic Fabry-Perot sensor, the DC component is removed from the two dynamic interference signals to construct two orthogonal signals. Based on two orthogonal signals, the change in cavity length caused by the external signal to be measured is obtained by demodulation.

[0008] Furthermore, the prior parameters of the fiber optic Fabry-Perot sensor are obtained, including: Determine whether the fiber optic Fabry-Perot sensor is a newly added or replaced sensor; If the judgment result is yes, under the condition of no external signal to be measured, the DC component and AC amplitude are calculated based on the initial cavity length of the fiber optic Fabry-Perot sensor and the two sampled static interference signals, and stored as the prior parameters of the fiber optic Fabry-Perot sensor. If the judgment result is negative, the prior parameters of the fiber optic Fabry-Perot sensor are directly read from the stored information.

[0009] Furthermore, based on the initial cavity length of the fiber optic Fabry-Perot sensor and the sampled two static interference signals, the DC component and AC amplitude are calculated, including: Obtain the initial cavity length of the fiber optic Fabry-Perot sensor and the sampled values ​​of the two static interference signals; Calculate the DC component and AC amplitude using the following formula:

[0010] in, A Represents the DC component. B Indicates the amplitude of alternating current. F 1 represents the sampled value of the first interference signal in the two static interference signals. F 2 represents the sampled value of the second interference signal in the two static interference signals. n The refractive index of the Fabry-Perot cavity is indicated. d 0 indicates the initial cavity length of the sensor. λ 1 represents the wavelength of the first interference signal. λ 2 represents the wavelength of the second interference signal.

[0011] Furthermore, based on the prior parameters of the fiber optic Fabry-Perot sensor, after removing the DC component from the two dynamic interference signals, two orthogonal signals are constructed, including: Calculate the phase difference between the two dynamic interference signals; Subtract the DC component from the prior parameters from the two dynamic interference signals to obtain the two signals after removing the DC component; Based on the phase difference and the two signals after removing the DC component, two orthogonal signals are constructed.

[0012] Furthermore, the phase difference between the two dynamic interference signals is calculated using the following formula:

[0013] in, β This represents the phase difference between the two dynamic interference signals. λ 1 represents the wavelength of the first interference signal. λ 2 represents the wavelength of the second interference signal. n The refractive index of the Fabry-Perot cavity is indicated. d 0 indicates the initial cavity length of the fiber optic Fabry-Perot sensor.

[0014] Furthermore, construct two orthogonal signals according to the following formula:

[0015] in, S 1 represents the Q signal in the two quadrature signals. S 2 represents the two orthogonal signals. I road signal, I 1 represents the signal obtained after removing the DC component from the first interference signal of the two dynamic interference signals. I 2 represents the signal obtained after removing the DC component from the second interference signal of the two dynamic interference signals. a The cosine of the phase difference between the two dynamic interference signals is given. b It is the sine value of the phase difference between the two dynamic interference signals.

[0016] Furthermore, based on the two orthogonal signals, the cavity length change caused by the external signal under test is obtained by demodulation, including: For two orthogonal signals Q Road signals and I The ratio of the signal to the signal is arctangented to obtain the phase related to the external signal to be measured. The change in cavity length caused by the external signal to be measured is calculated using the following formula:

[0017] in, This represents the change in cavity length caused by the external signal to be measured. λ 1 This represents the wavelength of the first interference signal. n The refractive index of the Fabry-Perot cavity is indicated. d 0 This indicates the initial cavity length of the fiber optic Fabry-Perot sensor.

[0018] Furthermore, the aforementioned fiber optic Fabry-Perot sensor demodulation method also includes: During the measurement process using this fiber optic Fabry-Perot sensor, it is necessary to determine whether there is a signal intermittent period. If it is during a signal interval, sample two static interference signals that do not currently contain external signals to be measured in order to update the prior parameters of the fiber optic Fabry-Perot sensor; The determination of whether it is in a signal intermittent period includes: Obtain the sampled value and mean value of any dynamic interference signal within the sliding window; Calculate the sample variance within the sliding window based on the sampled values ​​and mean. Compare the sample variance with a preset threshold; If continuous M If the variance of all samples within a sliding window is less than a preset threshold, it is determined that the signal is in an intermittent period.

[0019] Furthermore, the prior parameters of the fiber optic Fabry-Perot sensor are updated, including: Based on the initial cavity length of the sensor and the two currently sampled static interference signals, the current DC component and AC amplitude are calculated. The DC component and AC amplitude of the fiber optic Fabry-Perot sensor are updated according to the following formula:

[0020] in, A new This represents the updated DC component. B new This indicates the updated AC amplitude. A old This represents the DC component before the update. B old This indicates the AC amplitude before the update. A current Indicates the current DC component. B current This indicates the current AC amplitude. This represents the filtering smoothing factor.

[0021] Secondly, the present invention also provides an apparatus for implementing any of the fiber optic Fabry-Perot sensor demodulation methods described above, comprising: The acquisition module is used to acquire the prior parameters of the fiber optic Fabry-Perot sensor to be used. The prior parameters include the DC component and the AC amplitude. The prior parameters are calculated based on the sampled two static interference signals under the condition of no external signal to be measured. The processing module is used to sample two dynamic interference signals containing external signals to be measured during the measurement process using the fiber optic Fabry-Perot sensor. Based on the prior parameters of the fiber optic Fabry-Perot sensor, the DC component is removed from the two dynamic interference signals to construct two orthogonal signals. The demodulation module is used to demodulate the cavity length change caused by the external signal to be measured based on two orthogonal signals.

[0022] The fiber optic Fabry-Perot sensor demodulation method and apparatus provided by this invention have at least the following beneficial effects: (1) For any fiber optic Fabry-Perot sensor, two interference signals are sampled under the condition of no external interference from the signal to be measured, and prior parameters (i.e. DC component and AC amplitude) are established for the fiber optic Fabry-Perot sensor. Demodulation is performed based on these prior parameters during measurement. There is no need for precise matching between the sensor cavity length and the light source wavelength. Fiber optic Fabry-Perot sensors with different cavity lengths can be demodulated. There is no need to recalibrate or adjust the optical path, which improves the flexibility of demodulation and greatly expands the applicability and practicality of the demodulation system.

[0023] (2) The DC component and AC amplitude are calculated by using static signal stability, which can effectively overcome the problem that the fitting accuracy is reduced due to the weak signal to be measured, making it difficult to accurately extract the AC and DC components and thus the demodulation fails. This ensures the high stability and high accuracy of the demodulation process under weak signal conditions and improves the weak signal detection capability.

[0024] (3) During the measurement process of the fiber optic Fabry-Perot sensor, the monitoring signal interval is used to dynamically correct the DC component and AC amplitude of the fiber optic Fabry-Perot sensor based on the static signal during the signal interval. This can compensate for parameter changes caused by factors such as ambient temperature and light source fluctuations, realize parameter adaptive update, and more effectively ensure the demodulation accuracy, stability and reliability of the demodulation system in long-term operation. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the fiber optic Fabry-Perot sensor demodulation system provided by the present invention; Figure 2 A flowchart of a fiber optic Fabry-Perot sensor demodulation method provided by the present invention; Figure 3 A schematic diagram of the demodulation process of the fiber optic Fabry-Perot sensor provided by the present invention; Figure 4 A schematic diagram of the Lissajous figure provided by the present invention for constructing two dynamic interference signals; Figure 5 A schematic diagram of the demodulated signal amplitude provided by the present invention; Figure 6 A schematic diagram illustrating the demodulation results under different sound pressure levels provided by this invention; Figure 7 The present invention provides a structural block diagram of a fiber optic Fabry-Perot sensor demodulation device. Detailed Implementation

[0026] To better understand the above technical solutions, a detailed description of the solutions will be provided below in conjunction with the accompanying drawings and specific embodiments. Obviously, the described embodiments are merely some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0027] The terminology used in the embodiments of this invention is for the purpose of describing particular embodiments only and is not intended to limit the invention. The singular forms “a,” “the,” and “the” as used in the embodiments of this invention and the appended claims are also intended to include the plural forms, and “multiple” generally includes at least two unless the context clearly indicates otherwise.

[0028] It should also be noted that the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that an article or device that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such an article or device. Without further limitation, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the article or device that includes said element.

[0029] like Figure 1 The diagram shown is a schematic of the fiber optic Fabry-Perot sensor demodulation system, which includes: a light source module 10, a fiber optic circulator 20, a fiber optic Fabry-Perot sensor 30, a dense wavelength division multiplexer 40, a photodetector 50, a sampling module 60, and a data processing module 70.

[0030] The light source module 10 is used to generate light signals. Specifically, a broadband light source module can be used to generate broadband light signals.

[0031] The fiber optic circulator 20 is connected to the light source module 10, the fiber optic Fabry-Perot sensor 30, and the dense wavelength division multiplexer 40. It is used to guide the optical signal generated by the light source module 10 to the fiber optic Fabry-Perot sensor 30 and to guide the interference optical signal returned by the fiber optic Fabry-Perot sensor 30 to the dense wavelength division multiplexer 40.

[0032] The dense wavelength division multiplexer 40 is used to filter and separate the interfering optical signal, outputting two interference signals with different wavelengths, specifically two narrowband interference signals with different center wavelengths. That is, in this invention, the wavelengths of the two interference signals are fixed and determined by the dense wavelength division multiplexer 40.

[0033] The photodetector 50 and sampling module 60 are used to synchronously sample the two interference signals. There are two photodetectors 50, both connected to a dense wavelength division multiplexer 40. Each photodetector 50 converts the two narrowband interference signals into two electrical signals. The sampling module 60, connected to the photodetectors 50, is used to synchronously acquire and convert the two electrical signals from analog to digital to obtain a digital signal.

[0034] The data processing module 70, connected to the sampling module 60, is used to execute the fiber optic Fabry-Perot sensor demodulation method of the present invention based on the sampled signal. The fiber optic Fabry-Perot sensor demodulation method of the present invention belongs to an improved dual-wavelength demodulation algorithm.

[0035] The continuous optical signal emitted by the light source module 10 (e.g., with a wavelength range of 1535nm to 1565nm and an average output power of approximately 30mW) enters the fiber optic circulator 20 through port 1 of the fiber optic circulator 20, and then enters the fiber optic Fabry-Perot sensor 30 through port 2 of the fiber optic circulator 20, where interference occurs within the Fabry-Perot cavity. The interference optical signal returned by the fiber optic Fabry-Perot sensor 30 enters the dense wavelength division multiplexer 40 through port 3 of the fiber optic circulator 20 (e.g., the optical wavelengths output by its channels 1 and 2 are 1549.32nm and 1557.36nm, respectively). The dense wavelength division multiplexer 40 filters the signal and outputs two narrowband interference signals, which enter two photodetectors 50 respectively, converting the optical signal into an analog electrical signal. The signal is then sampled into a digital signal by the sampling module 60 and finally enters the data processing module 70 for signal demodulation. After processing by the improved dual-wavelength demodulation algorithm, the value of the physical quantity to be measured is obtained, such as the acoustic information to be measured.

[0036] The data processing module 70 mainly performs the following tasks: initializing pre-calibration to calculate prior parameters, and performing real-time demodulation using prior parameters during dynamic measurement using the fiber optic Fabry-Perot sensor. It can also perform adaptive updates of prior parameters, which will be explained in detail later.

[0037] The demodulation system described above can be connected to different fiber optic Fabry-Perot sensors. Using the demodulation method of this invention, high-precision and high-stability fast demodulation can be achieved for different fiber optic Fabry-Perot sensors.

[0038] like Figure 2 As shown, the present invention provides a fiber optic Fabry-Perot sensor demodulation method, comprising the following steps: S201. For the fiber optic Fabry-Perot sensor to be used, obtain the prior parameters of the fiber optic Fabry-Perot sensor. The prior parameters include the DC component and the AC amplitude. The prior parameters are calculated based on the sampled two static interference signals under the condition of no external signal to be measured. S202, during the measurement process using the fiber optic Fabry-Perot sensor, two dynamic interference signals containing external signals to be measured are sampled. Based on the prior parameters of the fiber optic Fabry-Perot sensor, the DC component is removed from the two dynamic interference signals to construct two orthogonal signals. S203, based on two orthogonal signals, demodulates the cavity length change caused by the external signal to be measured.

[0039] This invention targets any fiber optic Fabry-Perot sensor. Under conditions of no external interference from the target signal (i.e., in a static environment), it samples two interference signals to establish prior parameters (i.e., DC component and AC amplitude) for the fiber optic Fabry-Perot sensor. Demodulation is then performed based on these prior parameters during measurement. This eliminates the need for precise matching between the sensor cavity length and the light source wavelength, and allows for demodulation of fiber optic Fabry-Perot sensors with different cavity lengths. Furthermore, it eliminates the need for recalibration or optical path adjustment, improving demodulation flexibility and significantly expanding the applicability and practicality of the demodulation system. Moreover, by stably calculating the DC component and AC amplitude using static signals, it effectively overcomes the problem of decreased fitting accuracy and difficulty in accurately extracting AC and DC components due to weak target signals, thus ensuring high stability and high accuracy in the demodulation process under weak signal conditions and improving weak signal detection capabilities.

[0040] In one embodiment, obtaining the prior parameters of the fiber optic Fabry-Perot sensor includes: Determine whether the fiber optic Fabry-Perot sensor is a newly added or replaced sensor; If the judgment result is yes, under the condition of no external signal to be measured, the DC component and AC amplitude are calculated based on the initial cavity length of the fiber optic Fabry-Perot sensor and the two sampled static interference signals, and stored as the prior parameters of the fiber optic Fabry-Perot sensor. If the judgment result is negative, the prior parameters of the fiber optic Fabry-Perot sensor are directly read from the stored information.

[0041] This embodiment performs an initial calibration process for newly added or replaced fiber optic Fabry-Perot sensors. Under the condition of no external signal to be measured, the prior parameters of the fiber optic Fabry-Perot sensor are calculated and stored based on the initial cavity length of the fiber optic Fabry-Perot sensor and the two sampled static interference signals for subsequent dynamic demodulation.

[0042] Furthermore, based on the initial cavity length of the fiber optic Fabry-Perot sensor and the sampled two static interference signals, the DC component and AC amplitude are calculated, including: Obtain the initial cavity length of the fiber optic Fabry-Perot sensor and the sampled values ​​of the two static interference signals; Calculate the DC component and AC amplitude using the following formula:

[0043] in, ARepresents the DC component. B Indicates the amplitude of alternating current. F 1 represents the sampled value of the first interference signal in the two static interference signals. F 2 represents the sampled value of the second interference signal in the two static interference signals. n This represents the refractive index of the Fabry-Perot cavity, where the medium is air. n =1, d 0 indicates the initial cavity length of the fiber optic Fabry-Perot sensor. λ 1 represents the wavelength of the first interference signal. λ 2 represents the wavelength of the second interference signal. λ 1 and λ 2 is determined by the dense wavelength division multiplexer.

[0044] This embodiment uses the above formula to stably calculate the DC component and AC amplitude based on the static signal. It does not require precise matching of the fiber optic Fabry-Perot sensor cavity length and the light source wavelength, nor does it require recalibration or adjustment of the optical path. This improves the flexibility of demodulation, greatly expands the applicability and practicality of the demodulation system, and enhances the detection capability of weak signals.

[0045] Specifically, white light interferometry can be used to accurately measure the initial cavity length of the sensor. d 0 :

[0046] in, λ m and λ m+q They represent the first in the interference spectrum. m Level and First m+q The wavelength of light corresponding to the peak of the wave. q It represents the series difference between two peaks in the interference spectrum.

[0047] In one embodiment, based on the prior parameters of the fiber optic Fabry-Perot sensor, two orthogonal signals are constructed by removing the DC component from the two dynamic interference signals, including: Calculate the phase difference between the two dynamic interference signals; Subtract the DC component from the prior parameters of the two dynamic interference signals to obtain two signals after removing the DC component; construct two orthogonal signals based on the phase difference and the two signals after removing the DC component.

[0048] Specifically, based on the prior parameters of the fiber optic Fabry-Perot sensor, the DC component is removed from the two dynamic interference signals, and the expressions for the two signals are as follows:

[0049] in,f 1 This represents the sampled value of the first interference signal in the two dynamic interference signals. f 2 This represents the sampled value of the second interference signal in the two dynamic interference signals. A Represents the DC component. B Indicates the amplitude of alternating current. I 1 This represents the signal obtained after removing the DC component from the first interference signal of the two dynamic interference signals. I 2 This represents the signal obtained after removing the DC component from the second interference signal of the two dynamic interference signals. β This represents the phase difference between the two dynamic interference signals. θ t This indicates the phase that needs to be calculated in relation to the external signal being measured.

[0050] In this embodiment, prior parameters are used to compensate for the dynamic interference signal to obtain the signal after removing the DC component.

[0051] θ t The expression is: ,in, d t This indicates the total cavity length of the fiber optic Fabry-Perot sensor under the influence of an external signal to be measured.

[0052] Phase difference between two dynamic interference signals β The expression should be: .

[0053] Considering that the change in cavity length caused by the external signal to be measured (generally small, such as a few tenths of a micrometer) is much smaller than the initial cavity length of the fiber optic Fabry-Perot sensor (several hundred micrometers), that is... Therefore, the phase difference β between the two dynamic interference signals can be approximated as a fixed value according to the following formula:

[0054] Where β represents the phase difference between the two dynamic interference signals, λ1 represents the wavelength of the first interference signal, and λ2 represents the wavelength of the second interference signal. λ1 and λ2 are determined by the dense wavelength division multiplexer. n The refractive index of the Fabry-Perot cavity is indicated. d 0 This indicates the initial cavity length of the fiber optic Fabry-Perot sensor.

[0055] Specifically, the two orthogonal signals are constructed according to the following formula:

[0056] Where S1 represents the Q-channel signal (i.e., the quadrature component) of the two quadrature signals, and S2 represents the Q-channel signal (i.e., the quadrature component) of the two quadrature signals. I In-phase signal (i.e., in-phase component). I 1 represents the signal obtained after removing the DC component from the first interference signal of the two dynamic interference signals. I 2 This represents the signal obtained after removing the DC component from the second interference signal of the two dynamic interference signals. a The cosine of the phase difference between the two dynamic interference signals is given. b Let be the sine value of the phase difference between the two dynamic interference signals, i.e.: , β This represents the phase difference between two dynamic interference signals.

[0057] In combination with the above I 1 and I The expression for 2 can be obtained S 1 and S The expression for 2 is as follows:

[0058] in, B Indicates the amplitude of alternating current. θ t This represents the phase that needs to be calculated in relation to the external signal being measured. Based on this expression, the following can be obtained: θ t .

[0059] In one embodiment, based on two orthogonal signals, the cavity length change caused by the external signal under test is demodulated, including: For two orthogonal signals Q Road signals and I The ratio of the signal to the external signal is arctangented to obtain the phase related to the external signal under test. θ t The arctangent operation is performed according to the following formula: ; The change in cavity length caused by the external signal to be measured is calculated using the following formula:

[0060] in, This represents the change in cavity length caused by the external signal to be measured. λ 1 represents the wavelength of the first interference signal. n The refractive index of the Fabry-Perot cavity is indicated. d 0 indicates the initial cavity length of the fiber optic Fabry-Perot sensor.

[0061] This embodiment uses arctangent operation to extract data from two orthogonal signals. S1 and S In step 2, the phase information is demodulated, and then the change in cavity length caused directly by the external signal to be measured is calculated based on the phase information. This change is then output as the demodulation result. Based on the correspondence between the change in cavity length and the measured physical quantity, the value of the measured physical quantity can be obtained.

[0062] The present invention can also adaptively update the prior parameters of the fiber optic Fabry-Perot sensor. In one embodiment, the above-mentioned fiber optic Fabry-Perot sensor demodulation method further includes: During the measurement process using this fiber optic Fabry-Perot sensor, it is necessary to determine whether there is a signal intermittent period. If there is a signal interval, sample two static interference signals that do not currently contain external signals to be measured in order to update the prior parameters of the fiber optic Fabry-Perot sensor.

[0063] In this embodiment, during the measurement process of the fiber optic Fabry-Perot sensor, the signal interval is monitored, and the DC component and AC amplitude of the fiber optic Fabry-Perot sensor are dynamically corrected based on the static signal during the signal interval. This can compensate for parameter changes caused by factors such as ambient temperature and light source fluctuations, realize parameter adaptive updates, and more effectively ensure the demodulation accuracy, stability and reliability of the demodulation system in long-term operation.

[0064] Further, determining whether it is in a signal intermittent period includes: Obtain the sampled value and mean value of any dynamic interference signal within the sliding window; Calculate the sample variance within the sliding window based on the sampled values ​​and mean. Compare the sample variance with a preset threshold; If continuous M If the variance of all samples within a sliding window is less than a preset threshold, it is determined that the signal is in an interval. M It can be determined based on the actual situation.

[0065] For example, set a length of N A sliding window is used to buffer the most recently acquired dynamic interference signal. of N Sample values ​​x1, x2, ..., x N Calculate the sample variance σ within the sliding window. 2 :

[0066] in, This represents the mean of the dynamic interference signal within the sliding window. Indicates the first [number]th ... i Each sample value, N This indicates the length of the sliding window.

[0067] The preset threshold can be determined by measuring the background noise variance over a period of time in the initial static environment of the demodulation system.

[0068] This embodiment continuously monitors dynamic signals, calculates the sample variance of the signal within a sliding window, and compares it with a preset threshold. This allows for accurate and reliable determination of whether the external signal to be measured is in a signal interval period, and the prior parameters of the corresponding fiber optic Fabry-Perot sensor can be updated using the signal interval period.

[0069] Furthermore, the prior parameters of the fiber optic Fabry-Perot sensor are updated, including: Based on the initial cavity length of the sensor and the two currently sampled static interference signals, the current DC component and AC amplitude are calculated, and the specific calculation formula is the same as described above. The DC component and AC amplitude of the fiber optic Fabry-Perot sensor are updated according to the following formula:

[0070] in, A new This represents the updated DC component. B new This indicates the updated AC amplitude. A old This represents the DC component before the update. B old This indicates the AC amplitude before the update. A current Indicates the current DC component. B current This indicates the current AC amplitude. The filter smoothing factor is used to control the update rate and can be selected from various values. α =0.01.

[0071] In this embodiment, during signal intervals, a first-order infinite impulse response low-pass filter algorithm is used to dynamically correct the DC component and AC amplitude. The updated parameters will overwrite the stored original parameters and be used for subsequent demodulation, thus achieving adaptive parameter updating.

[0072] like Figure 3 As shown, the demodulation process of the fiber optic Fabry-Perot sensor includes the following steps: S301, Begin.

[0073] S302, start the demodulation system and perform hardware initialization. The two operating wavelengths are respectively... and The wavelength data is loaded into the data processing module.

[0074] S303, the system determines whether the currently used fiber optic Fabry-Perot sensor is a newly added or replaced sensor. If yes, proceed to S304; otherwise, proceed to S307.

[0075] S304, Perform the initial calibration procedure.

[0076] S305 uses white light interferometry to accurately measure the initial cavity length of this fiber optic Fabry-Perot sensor. d 0 For example, the initial cavity length of the sensor was measured to be 194.43 μm in the experiment.

[0077] Under conditions where there is no external signal to be measured (i.e., in a static environment), the output values ​​of the two interference signals are acquired and recorded, which are the static interference signals. and .

[0078] S306, the data processing module calculates the DC component A and AC amplitude B corresponding to the fiber optic Fabry-Perot sensor as prior parameters based on the initial cavity length of the sensor and the two static interference signals, and stores parameters A and B for subsequent dynamic demodulation.

[0079] S307, retrieve the DC component corresponding to the fiber optic Fabry-Perot sensor from the memory. A With AC amplitude B .

[0080] S308, place the fiber optic Fabry-Perot sensor in the environment under test, and simultaneously acquire two dynamic interference signals. and .

[0081] S309, The system continuously monitors the dynamic interference signal, calculates the sample variance of the signal within the sliding window, and compares it with a preset threshold to determine whether it is in a signal interval period. If yes, proceed to S310; otherwise, proceed to S311.

[0082] S310, during the signal interval, acquires the current static interferometric signal. and The DC component A and AC amplitude B of the fiber optic Fabry-Perot sensor are dynamically updated using a first-order infinite impulse response (IIR) low-pass filtering algorithm. The updated parameters will overwrite the stored original parameters and be used for subsequent demodulation.

[0083] S311, using prior parameters A and B DC compensation is performed on the dynamic interference signal to obtain a signal with the DC component removed, and two orthogonal signals are further constructed. S 1 and S 2 .

[0084] S312, employing the arctangent algorithm, extracts data from orthogonal signals. S 1 and S 2 The phase information is demodulated, and the change in cavity length caused by weak external signals is calculated based on the phase information. This is output as the demodulation result.

[0085] S313, End.

[0086] During the measurement process of the fiber optic Fabry-Perot sensor, the above steps S308 to S312 are executed cyclically to continuously perform dynamic signal demodulation and adaptive update loop.

[0087] When the phase amplitude of the external signal to be measured is as low as 0.01 rad, the Lissajous figure formed by the two interfering signals in the traditional dual-wavelength demodulation method is as follows: Figure 4 As shown, the graph fails to form a complete elliptical trajectory, causing the traditional dual-wavelength demodulation algorithm based on ellipse fitting to fail due to its inability to complete effective fitting.

[0088] Under the same weak signal conditions, the results obtained by using the demodulation method of this invention are as follows: Figure 5 As shown, the demodulation method of the present invention can accurately restore the original signal waveform without distortion, demonstrating its effectiveness and reliability under weak signal conditions.

[0089] Figure 6 This paper demonstrates a comparison of the linear response of the demodulation method of this invention with that of the traditional elliptic fitting algorithm under a wide range of sound pressure excitations, thereby comparing the demodulation performance under different sound pressures. Figure 6 It is known that when the sound pressure level is below 2 Pa, the fitting error of the ellipse fitting algorithm increases significantly due to the excessively short arc segment of the Lissajous figure, resulting in a significant deviation in the demodulated phase amplitude, exhibiting an overall nonlinear phenomenon of first rising and then falling. When the sound pressure level further drops below 0.8 Pa, the algorithm completely fails. In contrast, the demodulation method of this invention demonstrates excellent stability throughout the entire test range, maintaining a good linear relationship between the demodulated output and the input sound pressure level, effectively expanding the dynamic range and weak signal detection capability of the demodulation system.

[0090] This invention provides a dual-wavelength demodulation scheme for a fiber optic Fabry-Perot sensor based on pre-calibration and adaptive DC compensation. During the initialization phase, prior parameters (DC component and AC amplitude) are established for the fiber optic Fabry-Perot sensor based on the sensor's initial cavity length and two static interference signals acquired under static conditions, for use in subsequent demodulation. During the dynamic measurement phase, the existing prior parameters are directly used for DC compensation and orthogonal signal construction, and the cavity length change is demodulated through arctangent calculation. During signal intervals in the measurement process, the prior parameters are dynamically corrected based on the two currently acquired static interference signals to compensate for environmental interference and achieve adaptive parameter updates. This invention, by combining pre-calibrated references with online adaptive correction, can easily and reliably extract the DC component, even for weak signals, thus effectively ensuring the demodulation accuracy and stability of the demodulation system during long-term operation.

[0091] like Figure 7 As shown, the present invention also provides an apparatus for implementing any of the fiber optic Fabry-Perot sensor demodulation methods described above, comprising: The acquisition module 701 is used to acquire the prior parameters of the fiber optic Fabry-Perot sensor to be used. The prior parameters include the DC component and the AC amplitude. The prior parameters are calculated based on the sampled two static interference signals under the condition of no external signal to be measured. The processing module 702 is used to sample two dynamic interference signals containing external signals to be measured during the measurement process using the fiber optic Fabry-Perot sensor, and to construct two orthogonal signals after removing the DC component from the two dynamic interference signals based on the prior parameters of the fiber optic Fabry-Perot sensor. The demodulation module 703 is used to demodulate the cavity length change caused by the external signal to be measured based on two orthogonal signals.

[0092] Although preferred embodiments of the invention have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including both the preferred embodiments and all changes and modifications falling within the scope of the invention. Clearly, those skilled in the art can make various alterations and modifications to the invention without departing from its spirit and scope. Thus, if these modifications and modifications of the invention fall within the scope of the claims and their equivalents, the invention is also intended to include these modifications and modifications.

Claims

1. A method for demodulating an optical fiber Fabry-Perot sensor, characterized in that, include: For the fiber optic Fabry-Perot sensor to be used, the prior parameters of the fiber optic Fabry-Perot sensor are obtained. The prior parameters include the DC component and the AC amplitude. The prior parameters are calculated based on the sampled two static interference signals under the condition of no external test signal. During the measurement process using the fiber optic Fabry-Perot sensor, two dynamic interference signals containing external signals to be measured are sampled. Based on the prior parameters of the fiber optic Fabry-Perot sensor, the DC component is removed from the two dynamic interference signals to construct two orthogonal signals. Based on two orthogonal signals, the change in cavity length caused by the external signal to be measured is obtained by demodulation.

2. The method according to claim 1, characterized in that, Obtain the prior parameters of the fiber optic Fabry-Perot sensor, including: Determine whether the fiber optic Fabry-Perot sensor is a newly added or replaced sensor; If the judgment result is yes, under the condition of no external signal to be measured, the DC component and AC amplitude are calculated based on the initial cavity length of the fiber optic Fabry-Perot sensor and the two sampled static interference signals, and stored as the prior parameters of the fiber optic Fabry-Perot sensor. If the judgment result is negative, the prior parameters of the fiber optic Fabry-Perot sensor are directly read from the stored information.

3. The method according to claim 2, characterized in that, Based on the initial cavity length of the fiber optic Fabry-Perot sensor and the sampled two static interference signals, the DC component and AC amplitude are calculated, including: Obtain the initial cavity length of the fiber optic Fabry-Perot sensor and the sampled values ​​of the two static interference signals; Calculate the DC component and AC amplitude using the following formula: ； in, A Represents the DC component. B Indicates the amplitude of alternating current. F 1 This represents the sampled value of the first interference signal in the two static interference signals. F 2 This represents the sampled value of the second interference signal in the two static interference signals. n The refractive index of the Fabry-Perot cavity is indicated. d 0 indicates the initial cavity length of the fiber optic Fabry-Perot sensor. λ 1 represents the wavelength of the first interference signal. λ 2 represents the wavelength of the second interference signal.

4. The method according to claim 1, characterized in that, Based on the prior parameters of the fiber optic Fabry-Perot sensor, after removing the DC component from the two dynamic interference signals, two orthogonal signals are constructed, including: Calculate the phase difference between the two dynamic interference signals; Subtract the DC component from the prior parameters from the two dynamic interference signals to obtain the two signals after removing the DC component; Based on the phase difference and the two signals after removing the DC component, two orthogonal signals are constructed.

5. The method according to claim 4, characterized in that, The phase difference between the two dynamic interference signals is calculated using the following formula: ； in, β This represents the phase difference between the two dynamic interference signals. λ 1 represents the wavelength of the first interference signal. λ 2 represents the wavelength of the second interference signal. n The refractive index of the Fabry-Perot cavity is indicated. d 0 indicates the initial cavity length of the fiber optic Fabry-Perot sensor.

6. The method according to claim 4, characterized in that, Construct two orthogonal signals using the following formula: ； in, S 1 represents the two orthogonal signals. Q road signal, S 2 Indicating two orthogonal signals I road signal, I 1 represents the signal obtained after removing the DC component from the first interference signal of the two dynamic interference signals. I 2 represents the signal obtained after removing the DC component from the second interference signal of the two dynamic interference signals. a The cosine of the phase difference between the two dynamic interference signals is given. b It is the sine value of the phase difference between the two dynamic interference signals.

7. The method according to claim 1, characterized in that, Based on two orthogonal signals, the cavity length change caused by the external signal under test is obtained by demodulation, including: For two orthogonal signals Q Road signals and I The ratio of the signal to the signal is arctangented to obtain the phase related to the external signal to be measured. The change in cavity length caused by the external signal to be measured is calculated using the following formula: ； in, This represents the change in cavity length caused by the external signal to be measured. λ 1 This indicates the wavelength of the first interference signal. n The refractive index of the Fabry-Perot cavity is indicated. d 0 This indicates the initial cavity length of the fiber optic Fabry-Perot sensor.

8. The method according to claim 1, characterized in that, Also includes: During the measurement process using this fiber optic Fabry-Perot sensor, it is necessary to determine whether there is a signal intermittent period. If it is during a signal interval, sample two static interference signals that do not currently contain external signals to be measured in order to update the prior parameters of the fiber optic Fabry-Perot sensor; The determination of whether it is in a signal intermittent period includes: Obtain the sampled value and mean value of any dynamic interference signal within the sliding window; Calculate the sample variance within the sliding window based on the sampled values ​​and mean. Compare the sample variance with the preset threshold; If continuous M If the variance of all samples within a sliding window is less than a preset threshold, it is determined that the signal is in an intermittent period.

9. The method according to claim 8, characterized in that, The prior parameters of the fiber optic Fabry-Perot sensor are updated, including: Based on the initial cavity length of the sensor and the two currently sampled static interference signals, the current DC component and AC amplitude are calculated. The DC component and AC amplitude of the fiber optic Fabry-Perot sensor are updated according to the following formula: ； in, A new This represents the updated DC component. B new This indicates the updated AC amplitude. A old This represents the DC component before the update. B old This indicates the AC amplitude before the update. A current Indicates the current DC component. B current This indicates the current AC amplitude. This represents the filtering smoothing factor.

10. An apparatus for implementing the fiber optic Fabry-Perot sensor demodulation method as described in any one of claims 1 to 9, characterized in that, include: The acquisition module is used to acquire the prior parameters of the fiber optic Fabry-Perot sensor to be used. The prior parameters include the DC component and the AC amplitude. The prior parameters are calculated based on the sampled two static interference signals under the condition of no external signal to be measured. The processing module is used to sample two dynamic interference signals containing external signals to be measured during the measurement process using the fiber optic Fabry-Perot sensor. Based on the prior parameters of the fiber optic Fabry-Perot sensor, the DC component is removed from the two dynamic interference signals to construct two orthogonal signals. The demodulation module is used to demodulate the cavity length change caused by the external signal to be measured based on two orthogonal signals.

Images