Cross-correlation coefficient compensation method, system and device based on EFPI-FBG coupled spectrum

Abstract

The present invention discloses a mutual correlation coefficient compensation method, system and device based on EFPI-FBG coupled spectrum, and belongs to the field of optical fiber sensor demodulation technology. In view of the order jump problem caused by the traditional mutual correlation phase demodulation EFPI-FBG coupled spectrum, the step jump problem of FBG affecting the FP cavity length, and the phase offset and correction problem, the present invention uses the coupled spectrum and the traditional mutual correlation template function to perform mutual correlation operation, determines the mutual correlation compensation coefficient, and compensates the FP cavity length value in combination with the mutual correlation compensation coefficient, thereby improving the accuracy of the mutual correlation operation for the calculation of the EFPI-FBG coupled spectrum. The mutual correlation coefficient compensation method in the present invention has the advantages of high precision, full-band temperature measurement, and no need to decouple the FBG spectrum, and is expected to promote the application of optical fiber sensing technology in industrial production, energy development, environmental monitoring and other fields.

Description

Technical Field

[0001] The invention relates to the technical field of optical fiber sensor demodulation, and in particular to a mutual correlation coefficient compensation method, system and equipment based on EFPI-FBG coupling spectrum. Background Art

[0002] Fiber FP sensor is a sensor commonly used for temperature measurement and strain monitoring in high temperature environments. However, high temperature environments pose a challenge to the performance of FP sensors, because under high temperature conditions, the optical path length in the FP air cavity will be affected by temperature, and its output signal will produce nonlinear changes, reducing the accuracy and stability of temperature measurement. When fiber FP sensors face the challenges of high temperature environments, traditional demodulation methods have certain limitations in solving nonlinear errors. This nonlinear error not only affects the credibility of experimental results, but may also cause damage to the equipment or performance degradation. Therefore, there is an urgent need for a new solution that can effectively meet this challenge. In order to solve this problem, fiber Bragg grating (FBG) is usually used as a means of temperature compensation. Temperature measurement is achieved by monitoring the spectral shift of FBG, and it is jointly demodulated with the signal of the FP sensor.

[0003] For the demodulation method of EFPI-FBG coupling, the common methods currently include spectrum analysis, phase modulation and time domain analysis. For the demodulation of the coupled spectrum, it is necessary to first split the spectrum into the FBG working band and the FP working band for separate demodulation, or decouple the coupled spectrum to obtain the FP spectrum and the FBG spectrum for separate demodulation. However, the existing methods often find it difficult to completely eliminate the error caused by the FBG coupled EFPI sensor spectrum during the demodulation process, and all methods need to process the original spectrum before demodulation. This operation limits and affects the accuracy and reliability of the sensor demodulation system. Summary of the invention

[0004] In view of the above-mentioned problems, the present invention aims to provide a method, system and device for compensating the cross-correlation coefficient based on EFPI-FBG coupling spectrum, which can solve the order jump problem caused by traditional cross-correlation phase demodulation EFPI-FBG coupling spectrum, the step jump problem of FBG affecting FP cavity length, and the phase offset and correction problem.

[0005] In order to achieve the above object, the technical solution adopted by the present invention is as follows:

[0006] The cross-correlation coefficient compensation method based on EFPI-FBG coupling spectrum includes the following steps:

[0007] S1: Establishment of EFPI-FBG coupling spectral model based on reflection spectrum;

[0008] S2: Based on the EFPI-FBG coupled spectral model, determine the basic cross-correlation coefficient of the coupled spectral signal to be processed;

[0009] S3: determining the cross-correlation compensation coefficient of the coupled spectrum signal to be processed according to the standard cross-correlation coefficient;

[0010] S4: Determine the compensated standard correlation coefficient according to the results of step S2 and step S3;

[0011] S5: Demodulate the FP cavity length according to the compensated standard cross-correlation coefficient to complete the compensation demodulation of the sensor.

[0012] Furthermore, the EFPI-FBG coupled spectral model described in step S1 is expressed as In the formula, G is the EFPI-FBG coupled spectral model, FBG is the FBG reflectance spectrum, is the FP reflectance spectrum.

[0013] Furthermore, the basic correlation coefficient of the coupled spectral signal to be processed in step S2 is R 1 is represented by In the formula, is the frequency sweep template function, a and b They represent the lower limit and upper limit of the integral, that is, the lower limit and upper limit of the wavelength of the reflected spectrum after coupling.

[0014] Furthermore, the specific operation of step S3 includes the following steps:

[0015] S301: According to the standard correlation coefficient , the standard correlation coefficient R Further expressed as ;

[0016] S302: Use the variable amplitude threshold function to approximately fit the FBG spectrum, and obtain in, i represents the FBG spectrum signal data point, n Indicates the number of data points, represents the half bandwidth of FBG;

[0017] The standard correlation coefficient R Further expressed as ;

[0018] In the formula, c and d They represent the upper and lower limits of the FBG half-bandwidth respectively;

[0019] S303: Order Cis the cross-correlation compensation coefficient, then .

[0020] Further, the compensated standard correlation coefficient described in step S4 is expressed as In the formula, R 2 is the standard correlation coefficient after compensation.

[0021] Furthermore, the present invention also includes a mutual correlation coefficient compensation system based on EFPI-FBG coupled spectrum, which includes an EFPI-FBG coupled spectrum model establishment module, a mutual correlation coefficient compensation module and a FP cavity length demodulation module;

[0022] The EFPI-FBG coupling spectrum model building module builds the EFPI-FBG coupling spectrum model based on the reflection spectrum;

[0023] The cross-correlation coefficient compensation module is used to calculate the basic cross-correlation coefficient, the cross-correlation compensation coefficient and the compensated standard cross-correlation coefficient of the coupled spectral signal to be processed;

[0024] The FP cavity length demodulation module demodulates the FP cavity length according to the compensated standard cross-correlation coefficient;

[0025] The EFPI-FBG coupled spectrum model building module, the mutual correlation coefficient compensation module and the FP cavity length demodulation module are implemented using the mutual correlation coefficient compensation method based on the EFPI-FBG coupled spectrum as described above.

[0026] Furthermore, the present invention also includes an electronic device, which includes at least one processor; and a memory communicatively connected to the processor; wherein the memory stores instructions executable by the processor, and the instructions are executed by the processor so that the processor can execute the mutual correlation coefficient compensation method based on EFPI-FBG coupling spectrum as described above.

[0027] The beneficial effects of the present invention are:

[0028] 1. The cross-correlation coefficient compensation method of the present invention has high calculation accuracy, high precision and effectiveness, and can be widely used in the field of FP cavity length demodulation.

[0029] 2. The mutual correlation coefficient compensation method of the present invention can measure temperature in the full band without spectrum segmentation and will not affect FP demodulation.

[0030] 3. The cross-correlation coefficient compensation method in the present invention does not require decoupling of the coupled spectrum. If the existing EFPI-FBG demodulation does not want to split the spectrum, it is necessary to remove the influence of FBG from the FP spectrum and restore the original FP spectrum signal. The method in the present invention directly cross-correlates the coupled spectrum and then compensates it, without decoupling the FBG component.

[0031] 4. The mutual correlation coefficient compensation method in the present invention can significantly improve the temperature measurement accuracy and stability of the optical fiber FP sensor under the coupled FBG spectrum. It can not only promote the application of optical fiber sensing technology in industrial production, energy development, environmental monitoring and other fields, but also is expected to provide a new solution for engineering problems in high temperature environments. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 Schematic diagram of calculation of basic mutual correlation coefficients in the present invention.

[0033] Figure 2 Schematic diagram of the calculation of the standard mutual correlation coefficient in the present invention.

[0034] Figure 3 It is a schematic diagram of the FBG spectrum approximate gate function fitting in the present invention.

[0035] Figure 4 It is a schematic diagram of the calculation results of the simulation experiment of the present invention. DETAILED DESCRIPTION

[0036] In order to enable those skilled in the art to better understand the technical solution of the present invention, the technical solution of the present invention is further described below in conjunction with the accompanying drawings and embodiments. Embodiment 1

[0037] Embodiment 1 provides a method for compensating a cross-correlation coefficient based on an EFPI-FBG coupling spectrum, which specifically includes the following steps:

[0038] S1: Establishment of EFPI-FBG coupling spectral model based on reflection spectrum;

[0039] Specifically, the EFPI-FBG coupled spectral model G Expressed as (1)

[0040] In the formula, FBG is the FBG reflectance spectrum, is the FP reflectance spectrum;

[0041] S2: Based on the EFPI-FBG coupled spectral model, determine the basic cross-correlation coefficient of the coupled spectral signal to be processed;

[0042] Specifically, the basic cross-correlation coefficient of the coupled spectral signal to be processed is R 1 is represented by (2)

[0043] In the formula, is the frequency sweep template function, a and bThey represent the lower limit and upper limit of the integral, that is, the lower limit and upper limit of the wavelength of the reflected spectrum after coupling.

[0044] S3: determining the cross-correlation compensation coefficient of the coupled spectrum signal to be processed according to the standard cross-correlation coefficient;

[0045] Specifically, S301: The standard cross-correlation coefficient can be obtained according to the standard cross-correlation formula R for (3)

[0046] In formula (2), Therefore, the standard correlation coefficient R It can be further expressed as (4)

[0047] S302: using a variable amplitude threshold function to approximately fit the FBG spectrum;

[0048] Formula (4) is used to compensate for the error caused by the cross-correlation operation between the EFPI-FBG coupled spectrum and the standard cosine template function, but FBG The term is unknown, and the only information obtained after collecting the spectrum is FBG Therefore, the present invention proposes to use a variable amplitude threshold function to approximate the simplified formula of the FBG spectrum, as shown in formula (5): (5)

[0049] In the formula, i represents the FBG spectrum signal data point, n Indicates the number of data points, represents the half bandwidth of FBG.

[0050] After FBG spectrum fitting, formula (4) can be further expressed as (6)

[0051] S303: Order C is the cross-correlation compensation coefficient, which is the interference term caused by the FBG spectrum to the cross-correlation operation in formula (6). (7)

[0052] In the formula, c and d They represent the upper and lower limits of the FBG half-bandwidth respectively.

[0053] S4: Use the cross-correlation compensation coefficient obtained in step S3 C Determine the standard correlation coefficient after compensation;

[0054] The standard correlation coefficient after compensation R 2 is represented by (8)

[0055] In formula (8) R 2 is close to the standard correlation coefficient R , which can be directly used for the accurate calculation of the FP cavity length value.

[0056] S5: Perform peak location. According to the correction curve (the standard mutual correlation coefficient after compensation), the original peak is shifted to the right to obtain the corrected peak. This corrected peak is the precise FP cavity length value after removing the FBG interference term (that is, the FP cavity length value demodulated according to formula (8)), completing the compensation demodulation of the sensor.

[0057] Simulation experiment:

[0058] The light in the broadband light source is transmitted through the optical fiber channel. When it contacts the FBG in the optical fiber and the FP structure in the sensitive chip and reflects and interferes with the incident light, it is transmitted back through the optical fiber channel and transmitted to the spectrometer through the ring structure in the light source to collect the reflective spectrum data of the optical fiber EFPI-FBG sensor. The spectrum data with wavelength as the horizontal axis and light intensity reflectivity as the vertical axis is collected by the spectrum analyzer. At this time, the power spectrum density diagram of discrete points can be obtained, and the mutual correlation coefficient compensation method of the coupled spectrum is used for demodulation in the subsequent steps. The simulation process in the present invention is as follows:

[0059] S1: Establishment of EFPI-FBG coupling spectral model based on reflection spectrum; Among them, FP spectrum model Includes 2560 data points, Contains phase information with a cavity length of 204000nm, FPG bandwidth of 0.625nm, and a central wavelength of 1550nm;

[0060] S2: Determine the basic cross-correlation coefficient of the coupled spectral signal to be processed In the formula, Generate 10,000 template function signals for the frequency sweep template, with a step size of 2nm and a range of 190,000nm-210,000nm. The basic cross-correlation coefficient calculation diagram is shown in the attached figure. Figure 1 shown.

[0061] S3: determining the cross-correlation compensation coefficient of the coupled spectrum signal to be processed according to the standard cross-correlation coefficient;

[0062] Standardized correlation coefficient The calculation diagram is shown in the attached Figure 2 shown.

[0063] The bandwidth of the simulated FBG signal is 0.625nm, and there are 40 data points. The schematic diagram of the FBG spectrum calculation is as shown in the attached figure. Figure 3As shown, it is expressed as Compensation coefficient C Expressed as .

[0064] S4: Calculate the FP cavity length using the cross-correlation compensation coefficient obtained in step S3;

[0065] Specifically, the calculation formula of the FP cavity length is expressed as

[0066] S5: Perform peak location, shift the original peak to get the corrected peak, which is the precise FP cavity length value after removing the FBG interference term. After calculation, the peak of the cross-correlation curve without cross-correlation coefficient compensation corresponds to the cavity length value of 203992nm. After compensation, the peak moves to the cavity length of 204000nm, which is consistent with the generated cavity length value, completing the compensation algorithm demodulation of the sensor, as shown in the attached figure. Figure 4 shown. Embodiment 2

[0067] Embodiment 2 provides a mutual correlation coefficient compensation system based on EFPI-FBG coupling spectrum, the system comprising an EFPI-FBG coupling spectrum model establishment module, a mutual correlation coefficient compensation module and an FP cavity length demodulation module;

[0068] The EFPI-FBG coupling spectrum model building module builds the EFPI-FBG coupling spectrum model based on the reflection spectrum;

[0069] The cross-correlation coefficient compensation module is used to calculate the basic cross-correlation coefficient, the cross-correlation compensation coefficient and the compensated standard cross-correlation coefficient of the coupled spectral signal to be processed;

[0070] The FP cavity length demodulation module demodulates the FP cavity length according to the compensated standard cross-correlation coefficient;

[0071] The EFPI-FBG coupling spectrum model building module, the mutual correlation coefficient compensation module and the FP cavity length demodulation module are implemented by using the mutual correlation coefficient compensation method based on the EFPI-FBG coupling spectrum described in the first embodiment. Embodiment 3

[0072] Embodiment three provides an electronic device, which includes at least one processor; and a memory communicatively connected to the processor; wherein the memory stores instructions executable by the processor, and the instructions are executed by the processor so that the processor can execute the mutual correlation coefficient compensation method based on EFPI-FBG coupling spectrum described in embodiment one.

[0073] The above shows and describes the basic principles, main features and advantages of the present invention. It should be understood by those skilled in the art that the present invention is not limited to the above embodiments, and the above embodiments and descriptions are only for explaining the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements, which fall within the scope of the present invention to be protected. The scope of protection of the present invention is defined by the attached claims and their equivalents.

Claims

1. A cross-correlation coefficient compensation method based on EFPI-FBG coupled spectrum, characterized in that: The following steps are involved: S1: Establishment of EFPI-FBG coupling spectral model based on reflection spectrum; The EFPI-FBG coupled spectral model is expressed as Where G is the EFPI-FBG coupled spectral model, FBG is the FBG reflection spectrum, is the FP reflectance spectrum; S2: Based on the EFPI-FBG coupled spectral model, determine the basic cross-correlation coefficient of the coupled spectral signal to be processed; The basic correlation coefficient R1 of the coupled spectral signal to be processed is expressed as In the formula, is the frequency sweep template function, a and b represent the lower and upper limits of the integral, i.e. the lower and upper limits of the wavelength of the reflection spectrum after coupling, respectively; S3: determining the cross-correlation compensation coefficient of the coupled spectrum signal to be processed according to the standard cross-correlation coefficient; S4: Determine the compensated standard correlation coefficient according to the results of step S2 and step S3; S5: Demodulate the FP cavity length according to the compensated standard cross-correlation coefficient to complete the compensation demodulation of the sensor; The specific operation of step S3 includes the following steps: S301: According to the standard correlation coefficient The standard correlation coefficient R is further expressed as S302: Use the variable amplitude threshold function to approximately fit the FBG spectrum, and obtain Where i represents the FBG spectrum signal data point, n represents the number of data points, and bandwidth represents the half bandwidth of FBG; The standard correlation coefficient R is further expressed as Where c and d represent the upper and lower limits of the FBG half-bandwidth, respectively; S303: Let C be the cross-correlation compensation coefficient, then The compensated standard correlation coefficient described in step S4 is expressed as R2=R1-C; Where R2 is the standard correlation coefficient after compensation.

2. The cross-correlation coefficient compensation system based on EFPI-FBG coupled spectrum is characterized by: It includes EFPI-FBG coupled spectrum model building module, mutual correlation coefficient compensation module and FP cavity length demodulation module; The EFPI-FBG coupling spectrum model building module builds the EFPI-FBG coupling spectrum model based on the reflection spectrum; The cross-correlation coefficient compensation module is used to calculate the basic cross-correlation coefficient, the cross-correlation compensation coefficient and the compensated standard cross-correlation coefficient of the coupled spectrum signal to be processed; The FP cavity length demodulation module demodulates the FP cavity length according to the compensated standard cross-correlation coefficient; The EFPI-FBG coupling spectrum model building module, the mutual correlation coefficient compensation module and the FP cavity length demodulation module are implemented by using the mutual correlation coefficient compensation method based on the EFPI-FBG coupling spectrum described in claim 1.

3. An electronic device, characterized in that: It comprises at least one processor; and a memory connected to the processor in communication; wherein the memory stores instructions executable by the processor, and the instructions are executed by the processor so that the processor can execute the mutual correlation coefficient compensation method based on EFPI-FBG coupling spectrum described in claim 1.

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