An optimized demodulation method and system for a sapphire method of a pap cavity pressure sensor

Abstract

The application discloses an optimal demodulation method and system for a sapphire Fabry-Perot cavity pressure sensor, and comprises the following steps: S101, obtaining a sensor spectrum signal; S102, performing a smoothing filtering operation and a cubic spline interpolation operation; S103, performing Fourier transform, band pass filtering and inverse Fourier transform to obtain an air cavity spectrum signal; S104, obtaining an initial air cavity length, constructing a template spectrum signal and performing normalization processing; S105, performing mean square error calculation to obtain a minimum value of the mean square error and a minimum value position; S106, judging whether the first effective air cavity length is calculated; if yes, entering S107; otherwise, entering S108; S107, taking the minimum value of the mean square error as a comparison air cavity length, outputting the first effective air cavity length according to an average value of 10 signals, and entering S109; S108, judging whether mode jump occurs; if yes, taking the air cavity length closest to the effective air cavity length of the previous moment as the effective air cavity length, and entering S110; otherwise, entering S109; S109, taking the minimum value of the mean square error as the effective air cavity length; and S110, judging whether demodulation is stopped. The application eliminates the influence of mode jump, effectively reduces signal processing errors and noise interference, and improves precision.

Description

Technical Field

[0001] This invention relates to a method for demodulating the air cavity length of a Fabry-Perot cavity sensor, and more particularly to an optimized demodulation method and system for a sapphire Fabry-Perot cavity pressure sensor. Background Technology

[0002] Fiber Fabry-Perot (FP) cavity sensors with wavelength demodulation have extremely high sensitivity and accuracy, thus playing a crucial role in the research of wavelength demodulation technology for achieving high accuracy, high resolution, and large dynamic range absolute measurement of sensors. Minimum mean square error (MME) is a commonly used demodulation method, but it has several serious drawbacks: (1) Nonlinearity: The MME demodulation algorithm assumes that the sensor response is linear, which is not always the case in reality. Therefore, errors may occur during the demodulation process, leading to inaccurate pressure measurements; (2) Temperature dependence: The MME demodulation algorithm is very sensitive to temperature changes. Temperature changes affect the cavity length and refractive index of sapphire, which will also introduce errors during the demodulation process; (3) Limited dynamic range: The MME demodulation algorithm has a limited dynamic range, so it cannot be applied to high-precision applications under a wide range of pressures; (4) Mode hopping problem: During the measurement process, the MME demodulation algorithm is susceptible to signal interference, such as changes in ambient temperature, nonlinear changes in the sensor response structure, and electromagnetic noise, which will seriously affect the demodulation results, leading to mode hopping in the MME results and causing serious measurement errors. Summary of the Invention

[0003] The purpose of this invention is to solve the problems in the prior art.

[0004] The technical solution adopted by this invention to solve its technical problem is: to provide an optimized demodulation method for a sapphire Fabry-Perot cavity pressure sensor, comprising the following steps:

[0005] S101, acquire the sensor spectral signal of the sapphire Fabry-Perot cavity pressure sensor, and proceed to S102;

[0006] S102 performs smoothing filtering and cubic spline interpolation on the sensor spectral signal, outputs the processed spectral signal, and enters S103;

[0007] S103, Perform Fourier transform on the processed spectral signal to obtain the frequency domain signal, use a bandpass filter in the frequency domain to obtain the air cavity frequency domain signal, and then perform inverse Fourier transform to obtain the air cavity spectral signal, and proceed to S104.

[0008] S104: Obtain the initial air cavity length using the bimodal method, construct the template spectral signal, normalize the template spectral signal and the air cavity spectral signal, and proceed to S105.

[0009] S105, calculate the mean square error of the normalized air cavity spectral signal and the normalized template spectral signal respectively, obtain the minimum value and the location of the minimum value of the mean square error, and proceed to S106.

[0010] S106, determine whether to calculate the length of the first effective air cavity; if yes, proceed to S107, otherwise proceed to S108.

[0011] S107, take the minimum value of the mean square error calculated in S105 as the length of the comparison air cavity, collect 9 more comparison air cavity spectral signals according to steps S101 to S105, output the first effective air cavity length based on the average value of the 10 comparison air cavity lengths, and proceed to S109.

[0012] S108, determine whether a mode jump has occurred. If yes, iterate through all the cavity lengths corresponding to the minimum positions at the current time, find the cavity length that is closest to the effective air cavity length obtained at the previous time, and proceed to S110; otherwise, proceed to S109.

[0013] S109, output the minimum value of the mean square error calculated by S105 as the effective air cavity length, and enter S110;

[0014] S110: Determine whether to stop demodulation. If yes, end; otherwise, return to S101.

[0015] Preferably, the formula for the bimodal method described in S104 is as follows:

[0016]

[0017] Where λ1 and λ2 are the wavelengths corresponding to the positions of two adjacent peaks in the air cavity spectrum, and L is the initial air cavity length calculated by the bimodal method.

[0018] Preferably, the method for constructing the template spectrum in S104 is as follows: The template spectrum is constructed with the initial air cavity length as the center, and the template spectrum formula is as follows:

[0019]

[0020] Among them, I M Here, R is the template spectrum, R is the reflectance of the sapphire wafer, and L is the... M Let λ be the template cavity length, λ be the wavelength, and I0 be the incident light intensity.

[0021] Preferably, the normalization processing of the air cavity spectral signal in step S104 is as follows:

[0022]

[0023] Among them, I Air(λ) represents the air cavity spectral signal, S up (λ) represents the envelope signal in the air cavity spectrum, S down (λ) represents the envelope signal under the air cavity spectrum, I AirNor (λ) is the normalized air cavity spectral signal;

[0024] The template spectral signal is normalized using the same method as described above, and the normalized template spectral signal is I. MN .

[0025] Preferably, the mean square error calculation method described in S105 is as follows:

[0026]

[0027] Where MSE(λ) is the mean square error calculation result, N represents the number of sampling points, n represents the number of template spectra, and I MN (λ) represents the normalized template spectrum, I AirNor (λ) represents the normalized air cavity spectrum.

[0028] Preferably, the S107 output of the effective air cavity length specifically involves: counting the number of cavity lengths less than the average and greater than the average among the 10 comparative air cavity lengths; if the number of cavity lengths less than the average is large, then the first comparative air cavity length less than the average is output as the effective air cavity length; otherwise, the first comparative air cavity length greater than the average is output as the effective air cavity length.

[0029] Preferably, the determination of whether a mode jump has occurred in S108 is specifically as follows: the jump step size is set to 200nm, and the difference between the minimum mean square error value and the air cavity length at the previous moment cannot exceed the jump step size. If it exceeds the jump step size, it is determined that the air cavity length obtained at the current moment has experienced a mode jump.

[0030] This invention also provides a mean square error optimization demodulation system for a sapphire Fabry-Perot cavity pressure sensor, used to implement any of the above-mentioned mean square error optimization demodulation methods for sapphire Fabry-Perot cavity pressure sensors. The system is characterized by comprising: a light source, an optical circulator, a sapphire Fabry-Perot cavity pressure sensor, a spectrometer, and a host computer. The light source illuminates the sapphire Fabry-Perot cavity pressure sensor through the optical circulator. The reflected light from the sapphire Fabry-Perot cavity pressure sensor is emitted from the optical circulator and enters the spectrometer. The spectrometer sends the optical signal to the host computer, which calculates the cavity length and displays the calculation result.

[0031] Preferably, the light source is a supercontinuum broadband light source with a spectral range of 1520nm-1570nm and a center wavelength of 1545nm.

[0032] Preferably, the core of the sapphire Fabry-Perot cavity pressure sensor is composed of a sapphire optical fiber, a base cavity, an air cavity, and a pressure-sensing diaphragm. The sapphire optical fiber is in perpendicular contact with the base cavity, the base cavity has a thickness of about 600 μm, and the air cavity and pressure-sensing diaphragm have a thickness of about 200 μm.

[0033] The present invention has the following beneficial effects:

[0034] 1. Strong robustness: It has a certain degree of robustness and can resist the effects of noise and interference to a certain extent, thereby improving the accuracy and stability of the sensor.

[0035] 2. High accuracy: By estimating the mean square error of the sensor signal, the influence of mode skipping is eliminated, which can effectively reduce the influence of signal processing errors and noise interference, and improve the accuracy of the sensor.

[0036] 3. Good real-time performance: It has a fast computing speed and low computational complexity, enabling real-time signal processing and meeting the requirements for sensor response speed.

[0037] 4. Fewer adjustable parameters: Setting only a small number of adjustable parameters can effectively simplify the debugging and optimization process of the sensor, and reduce the manufacturing cost and maintenance difficulty of the sensor.

[0038] 5. High adaptability: It can adaptively adjust its parameters to adapt to different sensor working conditions and environments, which improves the application range and flexibility of the sensor.

[0039] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments, but the present invention is not limited to the embodiments. Attached Figure Description

[0040] Figure 1 This is a step diagram illustrating an optimized demodulation method for a sapphire Fabry-Perot cavity pressure sensor according to an embodiment of the present invention;

[0041] Figure 2 This is a detailed flowchart of an optimized demodulation method for a sapphire Fabry-Perot cavity pressure sensor according to an embodiment of the present invention;

[0042] Figure 3 This is a sensor spectrum diagram of an optimized demodulation method for a sapphire Fabry-Perot cavity pressure sensor according to an embodiment of the present invention;

[0043] Figure 4 The image shows a sensor spectrum diagram of an optimized demodulation method for a sapphire Fabry-Perot cavity pressure sensor according to an embodiment of the present invention.

[0044] Figure 5 The image shows an air cavity spectrum diagram of an optimized demodulation method for a sapphire Fabry-Perot cavity pressure sensor according to an embodiment of the present invention.

[0045] Figure 6 The image shows an air cavity spectrum of an optimized demodulation method for a sapphire Fabry-Perot cavity pressure sensor according to an embodiment of the present invention.

[0046] Figure 7 The mean square error result is shown in the figure for an optimized demodulation method for a sapphire Fabry-Perot cavity pressure sensor according to an embodiment of the present invention.

[0047] Figure 8 This is a schematic diagram of mode skipping in an optimized demodulation method for a sapphire Fabry-Perot cavity pressure sensor according to an embodiment of the present invention.

[0048] Figure 9 This is a schematic diagram of the mean square error optimization demodulation system for a sapphire Fabry-Perot cavity pressure sensor according to an embodiment of the present invention;

[0049] Figure 10 This is a schematic diagram of the sensor cross-sectional structure of a mean square error optimization demodulation system for a sapphire Fabry-Perot cavity pressure sensor according to an embodiment of the present invention. Figure 11 The length of the air cavity in the demodulated sapphire Fabry-Perot cavity pressure sensor. Detailed Implementation

[0050] See Figure 1 The diagram shown illustrates the steps of an embodiment of the present invention, including the following steps:

[0051] S101, acquire the sensor spectral signal of the sapphire Fabry-Perot cavity pressure sensor, and proceed to S102;

[0052] S102 performs smoothing filtering and cubic spline interpolation on the sensor spectral signal, outputs the processed spectral signal, and enters S103;

[0053] S103, Perform Fourier transform on the processed spectral signal to obtain the frequency domain signal, use a bandpass filter in the frequency domain to obtain the air cavity frequency domain signal, and then perform inverse Fourier transform to obtain the air cavity spectral signal, and proceed to S104.

[0054] S104: Obtain the initial air cavity length using the bimodal method, construct the template spectral signal, normalize the template spectral signal and the air cavity spectral signal, and proceed to S105.

[0055] S105, calculate the mean square error of the normalized air cavity spectral signal and the normalized template spectral signal respectively, obtain the minimum value and the location of the minimum value of the mean square error, and proceed to S106.

[0056] S106, determine whether to calculate the length of the first effective air cavity; if yes, proceed to S107, otherwise proceed to S108.

[0057] S107, take the minimum value of the mean square error calculated in S105 as the length of the comparison air cavity, collect 9 more comparison air cavity spectral signals according to steps S101 to S105, output the first effective air cavity length based on the average value of the 10 comparison air cavity lengths, and proceed to S109.

[0058] S108, determine whether a mode jump has occurred. If yes, iterate through all the cavity lengths corresponding to the minimum positions at the current time, find the cavity length that is closest to the effective air cavity length obtained at the previous time, and proceed to S110; otherwise, proceed to S109.

[0059] S109, output the minimum value of the mean square error calculated by S105 as the effective air cavity length, and enter S110;

[0060] S110: Determine whether to stop demodulation. If yes, end; otherwise, return to S101.

[0061] Specifically, the formula for the bimodal method described in S104 is as follows:

[0062]

[0063] Where λ1 and λ2 are the wavelengths corresponding to the positions of two adjacent peaks in the air cavity spectrum, and L is the initial air cavity length calculated by the bimodal method.

[0064] Specifically, the method for constructing the template spectrum described in S104 is as follows: The template spectrum is constructed with the initial air cavity length as the center, and the template spectrum formula is as follows:

[0065]

[0066] Where IM is the template spectrum, R is the reflectivity of the sapphire wafer, LM is the template cavity length, λ is the wavelength, and I0 is the incident light intensity.

[0067] Specifically, the normalization processing of the air cavity spectral signal described in S104 is as follows:

[0068]

[0069] Where IAir(λ) is the air cavity spectral signal, Sup(λ) is the upper envelope signal of the air cavity spectrum, Sdown(λ) is the lower envelope signal of the air cavity spectrum, and IAirNor(λ) is the normalized air cavity spectral signal.

[0070] The template spectral signal is normalized using the same method as described above, and the normalized template spectral signal is IMN.

[0071] Specifically, the mean square error calculation method described in S105 is as follows:

[0072]

[0073] Where MSE(λ) is the mean square error calculation result, N represents the number of sampling points, n represents the number of template spectra, IMN(λ) represents the normalized template spectrum, and IAirNor(λ) represents the normalized air cavity spectrum.

[0074] See Figure 7 The diagram shown is a detailed flowchart of an embodiment of the present invention.

[0075] Specifically, S107 counts the number of cavity lengths that are less than or greater than the average among the 10 comparison air cavity lengths; if the number of cavity lengths less than the average is large, the first comparison air cavity length less than the average is output as the effective air cavity length, otherwise the first comparison air cavity length greater than the average is output as the effective air cavity length.

[0076] Specifically, the criterion for determining whether a mode jump has occurred, as described in S108, is as follows: the jump step size is set to 200 nm, meaning that the change in the air cavity length obtained through the minimum mean square error algorithm cannot exceed ±200 nm. If the change in the air cavity length obtained at the current moment exceeds the jump step size, it is determined that a mode jump has occurred in the air cavity length obtained at the current moment. See also... Figure 8 The diagram shown is a schematic representation of an embodiment of the present invention in which no mode hopping occurs.

[0077] See Figure 9 The above is a schematic diagram of the system structure of an embodiment of the present invention, including: a light source, an optical circulator, a sapphire Fabry-Perot cavity pressure sensor, a spectrometer, and a host computer; the light source illuminates the sapphire Fabry-Perot cavity pressure sensor through the optical circulator, the light reflected by the sapphire Fabry-Perot cavity pressure sensor is emitted from the optical circulator and enters the spectrometer, the spectrometer sends the light signal to the host computer, the host computer calculates the cavity length and displays the calculation result.

[0078] Specifically, the light source is a supercontinuum broadband light source with a spectral range of 1520nm-1570nm and a center wavelength of 1545nm.

[0079] For details, see Figure 10 The diagram shown is a cross-sectional structural schematic of a sapphire Fabry-Perot cavity pressure sensor according to an embodiment of the present invention. The core of the sapphire Fabry-Perot cavity pressure sensor consists of a sapphire optical fiber 1, a base cavity 2, an air cavity 3, and a pressure-sensing diaphragm 4. The sapphire optical fiber 1 is in perpendicular contact with the base cavity 2. The thickness of the base cavity 2 is about 600 μm, and the thickness of the air cavity 3 and the pressure-sensing diaphragm 4 is about 200 μm.

[0080] In this embodiment, during continuous pressure testing from 0-10 MPa, the demodulated sapphire Fabry-Perot cavity pressure sensor air chamber length is as follows: Figure 11 As shown, the sensor demodulation accuracy is 0.46%.

[0081] As can be seen, the optimized demodulation method and system for sapphire Fabry-Perot cavity pressure sensors proposed in this invention eliminates the influence of mode hopping by estimating the mean square error of the sensor signal, effectively reducing the impact of signal processing errors and noise interference, and improving the accuracy of the sensor. It features fast processing speed and low computational complexity, enabling real-time signal processing and meeting the requirements for sensor response speed. With only a few adjustable parameters, it effectively simplifies the sensor debugging and optimization process, reducing sensor manufacturing costs and maintenance difficulty. It can adaptively adjust its parameters to adapt to different sensor operating conditions and environments, improving the sensor's application range and flexibility. It also exhibits a certain degree of robustness.

[0082] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. An optimized demodulation method for a sapphire Fabry-Perot cavity pressure sensor, characterized in that, Includes the following steps: S101, acquire the sensor spectral signal of the sapphire Fabry-Perot cavity pressure sensor, and proceed to S102; S102 performs smoothing filtering and cubic spline interpolation on the sensor spectral signal, outputs the processed spectral signal, and enters S103; S103, Perform Fourier transform on the processed spectral signal to obtain the frequency domain signal, use a bandpass filter in the frequency domain to obtain the air cavity frequency domain signal, and then perform inverse Fourier transform to obtain the air cavity spectral signal, and proceed to S104. S104: Obtain the initial air cavity length using the bimodal method, construct the template spectral signal, normalize the template spectral signal and the air cavity spectral signal, and proceed to S105. S105, calculate the mean square error of the normalized air cavity spectral signal and the normalized template spectral signal respectively, obtain the minimum value and the location of the minimum value of the mean square error, and proceed to S106. S106, determine whether to calculate the length of the first effective air cavity; if yes, proceed to S107, otherwise proceed to S108. S107, take the minimum value of the mean square error calculated in S105 as the length of the comparison air cavity, collect 9 more comparison air cavity spectral signals according to steps S101 to S105, output the first effective air cavity length based on the average value of the 10 comparison air cavity lengths, and proceed to S109. S108, determine whether a mode jump has occurred. If so, iterate through all the cavity lengths corresponding to the minimum positions at the current time, find the cavity length that is closest to the effective air cavity length obtained at the previous time, and enter S110. Otherwise proceed to S109; S109, output the minimum value of the mean square error calculated by S105 as the effective air cavity length, and enter S110; S110: Determine whether to stop demodulation. If yes, end; otherwise, return to S101. The formula for the bimodal method described in S104 is as follows: ； Where λ1 and λ2 are the wavelengths corresponding to the positions of two adjacent peaks in the air cavity spectrum, and L is the initial air cavity length calculated by the bimodal method formula; The method for constructing the template spectrum described in S104 is as follows: The template spectrum is constructed with the initial air cavity length as the center, and the template spectrum formula is as follows: ； Among them, I M Here, R is the template spectrum, R is the reflectance of the sapphire wafer, and L is the... M Where λ is the template cavity length, λ is the wavelength, and I0 is the incident light intensity; The normalization processing of the air cavity spectral signal described in S104 is as follows: ； Among them, I Air (λ) represents the air cavity spectral signal, S up (λ) represents the envelope signal in the air cavity spectrum, S down (λ) represents the envelope signal under the air cavity spectrum, I AirNor (λ) is the normalized air cavity spectral signal; The template spectral signal is normalized using the same method as described above, and the normalized template spectral signal is I. MN .

2. The optimized demodulation method for a sapphire Fabry-Perot cavity pressure sensor according to claim 1, characterized in that, The mean square error calculation method described in S105 is as follows: ； Where MSE(λ) is the mean square error calculation result, N represents the number of sampling points, n represents the number of template spectra, and I MN (λ) represents the normalized template spectrum, I AirNor (λ) represents the normalized air cavity spectrum.

3. The optimized demodulation method for a sapphire Fabry-Perot cavity pressure sensor according to claim 1, characterized in that, The S107 outputs the effective air cavity length by: counting the number of cavity lengths that are less than or greater than the average value among the 10 comparative air cavity lengths; if the number of cavity lengths that are less than the average value is large, then the first comparative air cavity length that is less than the average value is output as the effective air cavity length; otherwise, the first comparative air cavity length that is greater than the average value is output as the effective air cavity length.

4. The optimized demodulation method for a sapphire Fabry-Perot cavity pressure sensor according to claim 1, characterized in that, The determination of whether a mode jump has occurred as described in S108 is as follows: the jump step size is set to 200nm, and the difference between the minimum mean square error value and the air cavity length at the previous moment cannot exceed the jump step size. If it exceeds the jump step size, it is determined that the air cavity length obtained at the current moment has caused a mode jump.

5. A mean square error optimization demodulation system for a sapphire Fabry-Perot cavity pressure sensor, used to implement the optimization demodulation method for a sapphire Fabry-Perot cavity pressure sensor as described in any one of claims 1 to 4, characterized in that, include: The system comprises a light source, an optical circulator, a sapphire Fabry-Perot cavity pressure sensor, a spectrometer, and a host computer. The light source illuminates the sapphire Fabry-Perot cavity pressure sensor through the optical circulator. The light reflected from the sapphire Fabry-Perot cavity pressure sensor is emitted through the optical circulator and enters the spectrometer. The spectrometer sends the light signal to the host computer, which calculates the cavity length and displays the result.

6. The mean square error optimization demodulation system for a sapphire Fabry-Perot cavity pressure sensor according to claim 5, characterized in that, The light source is a supercontinuum broadband light source with a spectral range of 1520nm-1570nm and a center wavelength of 1545nm.

7. The mean square error optimization demodulation system for a sapphire Fabry-Perot cavity pressure sensor according to claim 5, characterized in that, The core of the sapphire Fabry-Perot cavity pressure sensor consists of a sapphire optical fiber, a base cavity, an air cavity, and a pressure-sensing diaphragm. The sapphire optical fiber is in perpendicular contact with the base cavity, which has a thickness of approximately 600 μm, while the air cavity and pressure-sensing diaphragm have a thickness of approximately 200 μm.

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