A method and apparatus for phase analysis of interference fringes

Abstract

The application discloses an interference fringe phase analysis method and device, which can improve the demodulation precision of a traditional frequency spectrum conversion method, suppresses the demodulation error caused by inaccurate main frequency estimation, and has a larger demodulation range; the method comprises the following steps: obtaining an interference spectrum of an interference optical fiber sensor; performing frequency spectrum analysis on the positive order spectrum to obtain a bispectrum of the positive order spectrum; inverting the positive order spectrum to obtain a reverse order spectrum; performing frequency spectrum analysis on the reverse order spectrum to obtain a bispectrum of the reverse order spectrum; obtaining a center frequency estimation value according to the amplitude spectrum of the positive order spectrum and the reverse order spectrum respectively, and taking the center frequency estimation value corresponding to the spectrum peak as an index; monitoring the corresponding initial phase change amount in the phase spectrum of the positive order spectrum and the reverse order spectrum respectively according to the real-time updated index; and performing differential operation on the initial phase change amounts of the positive order spectrum and the reverse order spectrum to obtain an optical path change of the interference optical fiber sensor.

Description

Technical Field

[0001] This invention relates to the field of fiber optic sensing technology, and in particular to a method and apparatus for phase analysis of interference fringes. Background Technology

[0002] The working principle of interferometric fiber optic sensors is based on the principle of light interference. When external physical quantities (such as temperature, strain, pressure, vibration, etc.) act on the interferometric fiber optic sensor, they cause changes in the interference fringes. By monitoring these changes, information about the measured physical quantity can be obtained. Currently, commonly used interference fringe analysis methods can generally be divided into two categories: intensity demodulation and phase demodulation. Intensity demodulation methods generally have a simpler system structure, but are easily affected by environmental fluctuations and cannot meet the requirements of high-precision measurement. Phase demodulation methods can usually accurately capture smaller changes in optical path and are a common solution for high-precision fiber optic interferometric sensing.

[0003] In existing technologies, commonly used phase demodulation methods mainly include spectrum transformation, fringe counting, and single-peak demodulation. Traditional spectrum transformation is usually limited by a finite spectral range, has low frequency resolution, and exhibits significant spectral leakage, resulting in poor resolution of the demodulated output. Fringe counting is susceptible to instability in the number and wavelength of spectral peaks, which may lead to large demodulation errors. Single-peak demodulation requires ensuring that the fringe order of the spectral peaks or valleys does not change during the transformation process; otherwise, the demodulation result will have a large error, and its demodulation range is very limited.

[0004] In summary, existing demodulation methods generally suffer from problems such as limited demodulation accuracy, poor anti-interference ability, and limited dynamic range, which restrict the application of interferometric fiber optic sensors in the field of high-precision monitoring. Summary of the Invention

[0005] One of the objectives of this invention is, at least, to provide a phase analysis method and apparatus for interference fringes to overcome the problems existing in the prior art, thereby improving the demodulation accuracy of the traditional spectrum transformation method, suppressing demodulation errors caused by inaccurate estimation of the dominant frequency, and also having a larger demodulation range.

[0006] To achieve the above objectives, the technical solution adopted by the present invention includes the following aspects.

[0007] This invention provides a phase analysis method for interference fringes, comprising:

[0008] Obtain the interference spectrum of an interferometric fiber optic sensor;

[0009] Spectral analysis was performed on the positive-sequence spectrum to obtain the bispectral data of the positive-sequence spectrum;

[0010] Reversing the forward-order spectrum yields the reverse-order spectrum;

[0011] Spectral analysis was performed on the reverse-order spectrum to obtain the bispectral data of the reverse-order spectrum;

[0012] The center frequency estimates are obtained from the amplitude spectra of the forward and reverse spectra, respectively, and the center frequency estimates corresponding to the spectral peaks are used as indexes.

[0013] The corresponding initial phase change was obtained by monitoring the phase spectra of the forward and reverse sequences based on the real-time updated index.

[0014] The optical path change of the interferometric fiber optic sensor is obtained by performing differential calculations on the initial phase changes of the forward and reverse sequences.

[0015] Preferably, the number of sampling points in the interference spectrum is N, and the starting frequency of the interference spectrum is v1, and the ending frequency of the interference spectrum is v. N Given a refractive index of n0, a speed of light of c, and an initial arm length difference of d, the interference fringe function f is expressed as: ;

[0016] In the formula, A represents the DC component of the interference signal, B represents the amplitude of the AC component of the interference signal, and v represents the optical frequency of the interference spectrum.

[0017] Preferably, the spectrum analysis is performed using the Fast Fourier Transform (FFT) or the Z-spectrum transform (Z-transform) method.

[0018] Preferably, the initial phase change ΔΦ1 of the positive sequence spectrum is expressed as: ;

[0019] The initial phase change ΔΦ2 of the reverse-order spectrum is expressed as: ;

[0020] In the formula, v1 represents the starting frequency of the interference spectrum, v N The frequency of the terminating light in the interference spectrum is represented by n, n0 represents the refractive index, and c represents the speed of light. This indicates the change in the difference in arm length.

[0021] Preferably, the step of performing a differential operation on the initial phase changes of the forward-order and reverse-order spectra to obtain the optical path change of the interferometric fiber optic sensor includes:

[0022] according to The wavelength λ1 when the starting frequency of the interference spectrum is v1 and the ending frequency of the interference spectrum are obtained. N wavelength λ at that time N Substituting the initial phase change ΔΦ1 of the forward-sequence spectrum and the initial phase change ΔΦ2 of the reverse-sequence spectrum, we obtain the initial phase change of the forward-sequence spectrum. :

[0023] The initial phase change ΔΦ2 of the reversed-sequence spectrum: ;

[0024] Perform a difference operation on the initial phase change ΔΦ1 of the forward-sequence spectrum and the initial phase change ΔΦ2 of the reverse-sequence spectrum: ;

[0025] The optical path change of the interferometric fiber optic sensor was obtained by summarizing the data. ;

[0026] In the formula, λ represents the change in arm length difference, λ1 represents the wavelength of the initial light in the interference spectrum at frequency v1, and λ N The frequency of the termination light in the interference spectrum is v. N The wavelength at which n0 is measured is given by the refractive index. , Represents the speed of light. This represents the optical frequency of the interference spectrum.

[0027] The present invention also provides a phase analysis device for interference fringes, comprising a laser source, a circulator or coupler, an interferometric fiber optic sensor, a multi-channel spectral detection module, and a calculation module;

[0028] The laser beam emitted from the laser source is coupled into the interferometric fiber optic sensor after passing through a circulator or coupler. After the interferometric fiber optic sensor performs sensing measurements, the interferometric light signal carrying information returns to the circulator or coupler and then enters the multi-channel spectral detection module. The interferometric spectrum of the interferometric fiber optic sensor is obtained through the multi-channel spectral detection module. The interferometric spectrum is input into the calculation module, which is configured to perform the aforementioned phase analysis method of the interference fringes to obtain the optical path change of the interferometric fiber optic sensor.

[0029] Preferably, the laser source is a broadband light source or a wavelength-tunable light source.

[0030] Preferably, the interferometric fiber optic sensor includes a Fabry-Perot interferometer, a Mach-Zehnder interferometer, or a Michelson interferometer.

[0031] In summary, by adopting the above technical solution, the present invention has at least the following beneficial effects:

[0032] The center frequency estimate is obtained from the amplitude spectra of the forward and reverse sequences. The center frequency estimate corresponding to the spectral peak is used as an index, and the corresponding initial phase change is monitored in the phase spectra of the forward and reverse sequences based on the real-time updated index. By performing differential operations on the initial phase changes of the forward and reverse sequences, the optical path change of the interferometric fiber optic sensor is inferred. This fully utilizes the initial phase information of the spectrum, suppresses demodulation errors caused by inaccurate main frequency estimation, and improves spectral demodulation accuracy. Compared to the traditional spectral demodulation method that locks a frequency point to monitor a single initial phase, the phase analysis method of the interference fringes in this invention has stronger anti-interference capabilities, higher demodulation accuracy, and a larger demodulation range. Attached Figure Description

[0033] Figure 1 This is a flowchart of a phase analysis method for interference fringes according to an exemplary embodiment of the present invention.

[0034] Figure 2 This is a schematic diagram of a phase analysis device for interference fringes according to an exemplary embodiment of the present invention.

[0035] Figure 3 This is a schematic diagram of the orthogonal spectrum of an exemplary embodiment of the present invention.

[0036] Figure 4 This is a schematic diagram of the reverse-order spectrum of an exemplary embodiment of the present invention.

[0037] Figure 5 This is a schematic diagram of the amplitude and phase spectra of the positive-sequence spectrum according to an exemplary embodiment of the present invention. Figure 5 The upper part shows the amplitude spectrum, and the lower part shows the phase spectrum.

[0038] Figure 6 This is a schematic diagram of the amplitude and phase spectra of the reverse-order spectrum according to an exemplary embodiment of the present invention. Figure 6 The upper part shows the amplitude spectrum, and the lower part shows the phase spectrum. Detailed Implementation

[0039] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments, so that the objectives, technical solutions, and advantages of the present invention will be clearer. It should be understood that the specific embodiments described herein are only for explaining the present invention and are not intended to limit the present invention.

[0040] like Figure 1 As shown, the phase analysis method for interference fringes in an exemplary embodiment of the present invention includes the following steps:

[0041] S1. Obtain the interference spectrum of the interferometric fiber optic sensor;

[0042] In this embodiment, the interferometric fiber optic sensor can be a Fabry-Perot interferometer, a Mach-Zehnder interferometer, or a Michelson interferometer, etc. For ease of description, the interference spectrum of the acquired interferometric sensor is denoted as the positive sequence spectrum.

[0043] Taking an interference spectrum with N sampling points as an example, let the starting frequency of the interference spectrum be v1 and the ending frequency be v. N Given a refractive index of n0, a speed of light of c, and an initial arm length difference of d, the interference fringe function f can be expressed as: ;

[0044] In the formula, A represents the DC component of the interference signal, B represents the amplitude of the AC component of the interference signal, and v represents the optical frequency of the interference spectrum; for example, the obtained interference spectrum is as follows: Figure 3 As shown.

[0045] S2. Spectral analysis methods such as Fast Fourier Transform and Z-spectrum Transform are used to perform spectral analysis on the positive sequence spectrum to obtain the bispectral spectrum (amplitude spectrum and phase spectrum). Figure 3 The amplitude and phase spectra of the middle positive sequence spectrum are as follows: Figure 5 As shown.

[0046] S3. Reverse the forward-order spectrum to obtain the reverse-order spectrum; Figure 3 Taking the forward-order spectrum as an example, the inversion process involves reversing the wavelength axes of the forward-order spectrum. The wavelength axis representing increasing wavelengths (1525nm→1565nm) is reversed to a wavelength axis representing decreasing wavelengths (1565nm→1525nm). During this reversal, the mapping relationship between each wavelength and its corresponding intensity value remains unchanged. The final result is a horizontally mirrored inverted forward-order spectrum. (Refer to...) Figure 4 .

[0047] S4. Spectral analysis methods such as Fast Fourier Transform and Z-spectrum Transform are used to perform spectral analysis on the reverse-order spectrum to obtain the bispectral spectrum (amplitude spectrum and phase spectrum), such as... Figure 6 As shown, the amplitude spectrum of the reverse-order spectrum is the same as that of the forward-order spectrum.

[0048] S5. Obtain the center frequency estimate based on the amplitude spectra of the forward and reverse spectra respectively, and use the center frequency estimate corresponding to the spectral peak as the index.

[0049] S6. Based on the real-time updated index, the corresponding initial phase change is monitored in the phase spectra of the forward-order and reverse-order spectra, respectively, such as... Figure 5 , Figure 6 As shown;

[0050] The initial phase change ΔΦ1 of the positive sequence spectrum can be expressed as: ;

[0051] The initial phase change ΔΦ2 of the reverse-order spectrum can be expressed as: ;

[0052] In the formula, v1 represents the starting frequency of the interference spectrum, v N The frequency of the terminating light in the interference spectrum is represented by n, n0 represents the refractive index, and c represents the speed of light. This indicates the change in the difference in arm length.

[0053] S7. Perform a difference operation on the initial phase change of the forward-order spectrum and the initial phase change of the reverse-order spectrum to obtain the optical path change of the interferometric fiber optic sensor.

[0054] according to ( , Represents the speed of light. (representing the optical frequency of the interference spectrum) to obtain the wavelength λ1 when the starting optical frequency of the interference spectrum is v1, and the wavelength λ1 when the ending optical frequency of the interference spectrum is v1. N wavelength λ at that time N Substituting the initial phase change ΔΦ1 of the forward-sequence spectrum and the initial phase change ΔΦ2 of the reverse-sequence spectrum into S6, we obtain the initial phase change ΔΦ1 of the forward-sequence spectrum: ;

[0055] The initial phase change ΔΦ2 of the reversed-sequence spectrum: ;

[0056] Perform a difference operation on the initial phase change ΔΦ1 of the forward-sequence spectrum and the initial phase change ΔΦ2 of the reverse-sequence spectrum: ;

[0057] The optical path change of the interferometric fiber optic sensor was obtained by summarizing the data. ;

[0058] In the formula, λ represents the change in arm length difference, λ1 represents the wavelength of the initial light in the interference spectrum at frequency v1, and λ N The frequency of the termination light in the interference spectrum is v. N The wavelength at which n0 is measured is given, and n0 represents the refractive index.

[0059] Through the above process, differential calculation of the initial phase change of the forward and reverse spectra can make full use of the initial phase information of the forward and reverse spectra, suppress the influence of inaccurate center frequency estimation, increase the dynamic range and improve demodulation accuracy. At this time, the differential value of the initial phase change can be used to obtain the optical path change of the interferometric fiber optic sensor, realizing the sensing of external physical quantities.

[0060] The present invention also discloses a phase analysis device for interference fringes, with reference to Figure 2The device includes a laser source, a circulator (or coupler), an interferometric fiber optic sensor, a multi-channel spectral detection module, and a computing module. The laser beam emitted from the laser source passes through the circulator (or coupler) and is coupled into the interferometric fiber optic sensor. After sensing and measuring, the interferometric fiber optic sensor returns to the circulator (or coupler) and then passes through the circulator (or coupler) into the multi-channel spectral detection module. The multi-channel spectral detection module obtains the interference spectrum of the interferometric fiber optic sensor, which is then input into the computing module. The computing module calculates the optical path change of the interferometric fiber optic sensor. During implementation, the computing module is configured to perform the phase analysis method of the interference fringes described in S1 to S7 to obtain the optical path change of the interferometric fiber optic sensor. The computing module includes, but is not limited to, a computer, a microcontroller, or an FPGA.

[0061] In the phase analysis device for interference fringes of the present invention, the laser source can be a broadband light source or a wavelength-tunable light source, or a laser source with multiple wavelengths.

[0062] The above description is merely a detailed illustration of specific embodiments of the present invention and is not intended to limit the invention. Various substitutions, modifications, and improvements made by those skilled in the art without departing from the principles and scope of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for phase analysis of interference fringes, characterized in that, include: Obtain the interference spectrum of an interferometric fiber optic sensor; Spectral analysis was performed on the positive-sequence spectrum to obtain the bispectral data of the positive-sequence spectrum; Reversing the forward-order spectrum yields the reverse-order spectrum; Spectral analysis was performed on the reverse-order spectrum to obtain the bispectral data of the reverse-order spectrum; The center frequency estimates are obtained from the amplitude spectra of the forward and reverse spectra, respectively, and the center frequency estimates corresponding to the spectral peaks are used as indexes. The corresponding initial phase change was obtained by monitoring the phase spectra of the forward and reverse sequences based on the real-time updated index. The optical path change of the interferometric fiber optic sensor is obtained by performing differential calculations on the initial phase changes of the forward and reverse sequences.

2. The phase analysis method for interference fringes according to claim 1, characterized in that, The number of sampling points in the interference spectrum is N. Let the starting frequency of the interference spectrum be v1 and the ending frequency be v. N Given a refractive index of n0, a speed of light of c, and an initial arm length difference of d, the interference fringe function f is expressed as: ; In the formula, A represents the DC component of the interference signal, B represents the amplitude of the AC component of the interference signal, and v represents the optical frequency of the interference spectrum.

3. The phase analysis method for interference fringes according to claim 1, characterized in that, The spectrum analysis is performed using either the Fast Fourier Transform (FFT) or the Z-spectrum transform (Z-transform) method.

4. The phase analysis method for interference fringes according to claim 2, characterized in that, The initial phase change ΔΦ1 of the positive sequence spectrum is expressed as: ; The initial phase change ΔΦ2 of the reverse-order spectrum is expressed as: ; In the formula, v1 represents the starting frequency of the interference spectrum, v N The frequency of the terminating light in the interference spectrum is represented by n, n0 represents the refractive index, and c represents the speed of light. This indicates the change in the difference in arm length.

5. The phase analysis method for interference fringes according to claim 4, characterized in that, The differential operation on the initial phase changes of the forward-order and reverse-order spectra to obtain the optical path change of the interferometric fiber optic sensor includes: according to The wavelength λ1 when the starting frequency of the interference spectrum is v1 and the ending frequency of the interference spectrum are obtained. N wavelength λ at that time N Substituting the initial phase change ΔΦ1 of the forward-sequence spectrum and the initial phase change ΔΦ2 of the reverse-sequence spectrum, we obtain the initial phase change of the forward-sequence spectrum. : ; The initial phase change ΔΦ2 of the reversed-sequence spectrum: ; Perform a difference operation on the initial phase change ΔΦ1 of the forward-sequence spectrum and the initial phase change ΔΦ2 of the reverse-sequence spectrum: ; The optical path change of the interferometric fiber optic sensor was obtained by summarizing the data. ; In the formula, λ represents the change in arm length difference, λ1 represents the wavelength of the initial light in the interference spectrum at frequency v1, and λ N The frequency of the termination light in the interference spectrum is v. N The wavelength at which n0 is measured is given by the refractive index. , Represents the speed of light. This represents the optical frequency of the interference spectrum.

6. A phase analysis device for interference fringes, characterized in that, It includes a laser source, a circulator or coupler, an interferometric fiber optic sensor, a multi-channel spectral detection module, and a computing module; The laser beam emitted by the laser source is coupled into the interferometric fiber optic sensor after passing through a circulator or coupler. After the interferometric fiber optic sensor performs sensing measurements, the interferometric light signal carrying information returns to the circulator or coupler and enters the multi-channel spectral detection module through the circulator or coupler. The interferometric spectrum of the interferometric fiber optic sensor is obtained through the multi-channel spectral detection module. The interferometric spectrum is input into the calculation module, which is configured to execute the phase analysis method of the interference fringes according to any one of claims 1 to 5 to obtain the optical path change of the interferometric fiber optic sensor.

7. The phase analysis device for interference fringes according to claim 6, characterized in that, The laser source is a broadband light source or a wavelength-tunable light source.

8. The phase analysis apparatus for interference fringes according to claim 6 or 7, characterized in that, The interferometric fiber optic sensor includes a Fabry-Perot interferometer, a Mach-Zehnder interferometer, or a Michelson interferometer.

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