Method and device for high-precision in-situ calibration and high-speed real-time demodulation of the cavity length of optical fiber Fabry-Perot sensor

Abstract

The present invention discloses a method and device for high-precision in-situ calibration and high-speed real-time demodulation of the cavity length of an optical fiber Fabry-Perot sensor, the device comprising a broadband light source, an optical circulator, a coupler, n tunable filters, n photodetectors, a signal amplification and conditioning module, a signal acquisition module, and a calculation and demodulation module; the method steps are: 1) in-situ calibration of the optical fiber Fabry-Perot pressure optical fiber Fabry-Perot sensor to obtain the optical fiber Fabry-Perot sensor cavity length-spectral intensity relationship; 2) the calculation and demodulation module determines the optical fiber Fabry-Perot sensor cavity length corresponding to the current light intensity signal according to the optical fiber Fabry-Perot sensor cavity length-spectral intensity relationship. The present invention overcomes the problem that the traditional light intensity method relies on the experimental environment for calibration, resulting in a conflict with the actual test environment.

Description

Technical Field

[0001] The invention relates to the field of optical fiber sensing technology, and in particular to a method and device for high-precision in-situ calibration and high-speed real-time demodulation of the cavity length of an optical fiber Fabry-Perot sensor. Background Art

[0002] The fiber optic Fabry-Perot sensor is an optical detection device with the advantages of simple structure, small size, no electrical leads, and resistance to electromagnetic interference. It has good application prospects in physical quantity testing in extreme environments of high temperature, high pressure, strong chemical corrosion and strong electromagnetic interference.

[0003] The basic principle of its sensing is that when external physical quantities such as pressure, temperature, strain, etc. act on the Fabry-Perot structure, the Fabry-Perot structure will deform, change the length of its Fabry-Perot cavity, and modulate the signal of multi-beam interference in this structure. By demodulating the interference signal carrying the cavity length information, the information of the physical quantity to be measured can be obtained.

[0004] The fiber Fabry-Perot sensing system generally consists of a hardware system for collecting and processing signals and an algorithm software for calculating and demodulating the Fabry-Perot cavity length. The quality of the cavity length demodulation method determines the accuracy and speed of the system in obtaining the physical quantity to be measured. An important research direction in the field of fiber Fabry-Perot sensing is to continuously improve the demodulation method to meet different engineering measurement needs.

[0005] The phase demodulation method is commonly used at present. It uses various mathematical transformation tools such as Fourier transform and correlation calculation to transform the interference spectrum signal into the spectrum domain, find the peak of the transform spectrum in the spectrum domain, and then calculate the sensor cavity length. This method has high demodulation accuracy. However, in some measurements with extremely fast signal change frequency, the system needs to sample and calculate thousands of complete spectrum data, which inevitably brings about the problem of slow demodulation speed due to the large amount of data, restricting the application of such sensors in measurements with high requirements for demodulation speed.

[0006] The intensity demodulation method reacts to the change of cavity length by detecting the change of output light intensity of a single wavelength (or several wavelengths). It has the advantages of simple principle and fast response speed. This method can realize high-speed real-time demodulation of cavity length. The intensity demodulation method requires the calibration of the cavity length-intensity relationship in advance. The existing technical means need to calibrate by building a simulation test system in an experimental environment. The cavity length-intensity calibration relationship obtained by this method has high reliability. However, in reality, there are great differences between the test environment and the constructed simulation test system and the laboratory environment and the real system. For example, in different temperature and humidity environments, the reflectivity of the same structure is different, resulting in different intensity values. This phenomenon makes the calibration results obtained in the experimental environment not necessarily applicable to field tests, which will bring errors to the demodulation results. Summary of the invention

[0007] The purpose of the present invention is to provide a high-precision in-situ calibration and high-speed real-time demodulation device for the cavity length of an optical fiber Fabry-Perot sensor, comprising a broadband light source, an optical circulator, a coupler, n tunable filters, n photodetectors, a signal amplification and conditioning module, a signal acquisition module, and a calculation demodulation module;

[0008] The broadband light source provides a wide spectrum input light source signal to the optical circulator through an optical fiber;

[0009] The optical circulator transmits the broadband light source signal to the optical fiber Fabry-Perot sensor through the optical fiber, and receives the reflected light interference signal returned by the optical fiber Fabry-Perot sensor;

[0010] The optical circulator transmits the reflected light interference signal to the coupler;

[0011] The coupler transmits the reflected light interference signal in multiple paths to n tunable filters respectively;

[0012] The i-th tunable filter filters the reflected light interference signal and retains the wavelength λ i The reflected light interference signal under the condition is transmitted to the corresponding photodetector; i = 1, 2, ..., n;

[0013] The photoelectric detector converts the reflected light interference signal into an analog electrical signal and transmits it to the signal amplification and conditioning module;

[0014] The signal amplification and conditioning module amplifies and filters the analog electrical signal and transmits it to the signal acquisition module;

[0015] The signal acquisition module transmits the amplified and filtered multi-channel analog signals to the calculation and demodulation module;

[0016] The calculation and demodulation module selects one or more light intensity signals corresponding to wavelengths from multiple light signals, and processes the light intensity signals according to the optical fiber Fabry-Perot sensor cavity length-light intensity relationship to obtain the optical fiber Fabry-Perot sensor cavity length corresponding to the current light intensity signal.

[0017] Furthermore, the broadband light source is a wide spectrum light source, including ASE and SLD, which has a flat spectrum and adjustable power within the signal demodulation range.

[0018] The demodulation method based on the high-precision in-situ calibration of the cavity length of the optical fiber Fabry-Perot sensor and the high-speed real-time demodulation device comprises the following steps:

[0019] 1) Calibrate the fiber Fabry-Perot sensor in situ to obtain the relationship between the cavity length and spectral intensity of the fiber Fabry-Perot sensor;

[0020] 2) The broadband light source provides a wide spectrum input light source signal to the optical circulator through the optical fiber;

[0021] 3) The optical circulator transmits the broadband light source signal to the fiber Fabry-Perot sensor through the optical fiber, and receives the reflected light interference signal returned by the fiber Fabry-Perot sensor;

[0022] 4) Use the coupler, tunable filter, photodetector, signal amplification and conditioning module, and signal acquisition module in sequence to obtain the signal at wavelength λ i The sparse spectrum under the condition is transmitted to the calculation demodulation module;

[0023] 5) The calculation and demodulation module selects a wavelength from the multiple optical signals, and processes the light intensity signal corresponding to the wavelength according to the optical fiber Fabry-Perot sensor cavity length-light intensity relationship to obtain the optical fiber Fabry-Perot sensor cavity length corresponding to the current light intensity signal.

[0024] Further, the steps of in-situ calibration of the optical fiber Fabry-Perot sensor include:

[0025] 1.1) A broadband light source provides a wide spectrum input light source signal to the optical circulator through an optical fiber;

[0026] 1.2) The optical circulator transmits the broadband light source signal to the fiber Fabry-Perot sensor through the optical fiber, and receives the reflected light interference signal returned by the fiber Fabry-Perot sensor;

[0027] 1.3) Using the tunable filter of channel 1 to scan the wavelength, a complete reflection spectrum under the environmental state E0 is obtained;

[0028] 1.4) Using the coupler, tunable filter, photodetector, signal amplification and conditioning module, and signal acquisition module in sequence to obtain the light intensity signal, and transmit it to the calculation and demodulation module;

[0029] 1.5) The calculation demodulation module demodulates the interference spectrum signal to obtain the fiber Fabry-Perot cavity length L under the environmental state E0. i ;The initial value of i is 0;

[0030] 1.6) Change the environmental state and return to step 1) until a cavity length sequence L = {L0, L1…L N}, and the spectrum intensity sequence P = {P0, P1...P N};

[0031] 1.7) For the cavity length sequence L = {L0, L1…L N} and the spectral intensity sequence P = {P0, P1...P N} is fitted to obtain the relationship between the cavity length and spectral intensity of the optical fiber Fabry-Perot sensor at a single wavelength point λ0.

[0032] Furthermore, the device for loading the optical fiber Fabry-Perot sensor includes a micro-displacement stage and a pressure generator.

[0033] Furthermore, during demodulation, the cavity length L fluctuates within the linear range of demodulation. At this time, the cavity length L is related to the received light intensity I R The linear range of demodulation is the wavelength range of the λ / 4 monochromatic light source centered at the Q point with the largest slope.

[0034] The approximate linear relationship is as follows:

[0035] I R =αI0L(1)

[0036] In the formula, I R is the light intensity signal; α is the proportional coefficient; L is the cavity length; I0 is the incident light intensity.

[0037] Furthermore, the light intensity signal I R As shown below:

[0038]

[0039] Where L is the cavity length; I0 is the incident light intensity; R is the end reflectivity, and λ is the wavelength of the light.

[0040] Further, the step of selecting the single wavelength point λ0 includes:

[0041] Taking the variation range of the cavity length L, that is, the initial cavity length determined when designing the optical fiber Fabry-Perot sensor and the cavity length value when the maximum deformation is reached as variables, the characteristics of the reflection spectrum curves at the single wavelength points of N sparse spectra are compared in turn, and the wavelength value corresponding to a curve that is monotonic, has the highest linearity and the highest sensitivity within the cavity length range is selected as the single wavelength point λ0.

[0042] The technical effect of the present invention is unquestionable. The present invention proposes a fiber optic Fabry-Perot sensor testing system based on the intensity method with a high-precision in-situ calibration function for the cavity length, which overcomes the problem that the traditional light intensity method relies on the experimental environment for calibration, resulting in a conflict with the actual test environment. At the same time, the system can realize high-speed real-time demodulation of the cavity length.

[0043] The present invention uses a set of systems to complete calibration and measurement. When calibrating the light intensity-cavity length relationship, the required data does not need to be obtained by adding separate light source and data acquisition modules, thus achieving system reuse.

[0044] The present invention can realize cavity length demodulation based on different principles by flexibly changing the hardware arrangement of the system, thereby improving the demodulation accuracy and application range of the system. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 This is a diagram of the optical fiber Fabry-Perot pressure measurement system;

[0046] Figure 2 (a)-(b) are the relationship curves between FP cavity length and output light intensity and the principle diagram of cavity length demodulation based on light intensity method

[0047] Figure 3 The schematic diagram of the relationship between cavity length and light intensity at different single wavelengths;

[0048] Figure 4 Run a flowchart for the system; DETAILED DESCRIPTION

[0049] The present invention is further described below in conjunction with the embodiments, but it should not be understood that the above subject matter of the present invention is limited to the following embodiments. Without departing from the above technical ideas of the present invention, various substitutions and changes are made according to the common technical knowledge and customary means in the art, which should all be included in the protection scope of the present invention.

[0050] Embodiment 1:

[0051] See also Figures 1 to 4 , a high-precision in-situ calibration and high-speed real-time demodulation device for the cavity length of an optical fiber Fabry-Perot sensor, including a broadband light source, an optical circulator, a coupler, n tunable filters, n photodetectors, a signal amplification and conditioning module, a signal acquisition module, and a computational demodulation module;

[0052] The broadband light source provides a wide spectrum input light source signal to the optical circulator through an optical fiber;

[0053] The optical circulator transmits the broadband light source signal to the optical fiber Fabry-Perot sensor through the optical fiber, and receives the reflected light interference signal returned by the optical fiber Fabry-Perot sensor;

[0054] The optical circulator transmits the reflected light interference signal to the coupler;

[0055] The coupler transmits the reflected light interference signal in multiple paths to n tunable filters respectively;

[0056] The i-th tunable filter filters the reflected light interference signal and retains the wavelength λ i The reflected light interference signal under the condition is transmitted to the corresponding photodetector; i = 1, 2, ..., n;

[0057] The photoelectric detector converts the reflected light interference signal into an analog electrical signal and transmits it to the signal amplification and conditioning module;

[0058] The signal amplification and conditioning module amplifies and filters the analog electrical signal and transmits it to the signal acquisition module;

[0059] The signal acquisition module transmits the amplified and filtered multi-channel analog signals to the calculation and demodulation module;

[0060] The calculation and demodulation module selects one or more light intensity signals corresponding to wavelengths from multiple light signals, and processes the light intensity signals according to the optical fiber Fabry-Perot sensor cavity length-light intensity relationship to obtain the optical fiber Fabry-Perot sensor cavity length corresponding to the current light intensity signal.

[0061] Broadband light sources are wide spectrum light sources, including ASE (Amplified spontaneous emission) and SLD (Super-Luminescent Diodes), which have flat spectrum and adjustable power within the signal demodulation range.

[0062] The demodulation method based on the high-precision in-situ calibration of the cavity length of the optical fiber Fabry-Perot sensor and the high-speed real-time demodulation device comprises the following steps:

[0063] 1) Calibrate the fiber Fabry-Perot sensor in situ to obtain the relationship between the cavity length and spectral intensity of the fiber Fabry-Perot sensor;

[0064] 2) The broadband light source provides a wide spectrum input light source signal to the optical circulator through the optical fiber;

[0065] 3) The optical circulator transmits the broadband light source signal to the fiber Fabry-Perot sensor through the optical fiber, and receives the reflected light interference signal returned by the fiber Fabry-Perot sensor;

[0066] 4) Use the coupler, tunable filter, photodetector, signal amplification and conditioning module, and signal acquisition module in sequence to obtain the signal at wavelength λ i The sparse spectrum under the condition is transmitted to the calculation demodulation module;

[0067] 5) The calculation and demodulation module selects a wavelength from the multiple optical signals, and processes the light intensity signal corresponding to the wavelength according to the optical fiber Fabry-Perot sensor cavity length-light intensity relationship to obtain the optical fiber Fabry-Perot sensor cavity length corresponding to the current light intensity signal.

[0068] The steps for in-situ calibration of the fiber optic Fabry-Perot sensor include:

[0069] 1.1) A broadband light source provides a wide spectrum input light source signal to the optical circulator through an optical fiber;

[0070] 1.2) The optical circulator transmits the broadband light source signal to the fiber Fabry-Perot sensor through the optical fiber, and receives the reflected light interference signal returned by the fiber Fabry-Perot sensor;

[0071] 1.3) Using the tunable filter of channel 1 to scan the wavelength, a complete reflection spectrum under the environmental state E0 is obtained;

[0072] 1.4) Using the coupler, tunable filter, photodetector, signal amplification and conditioning module, and signal acquisition module in sequence to obtain the light intensity signal, and transmit it to the calculation and demodulation module;

[0073] 1.5) The calculation demodulation module demodulates the interference spectrum signal to obtain the fiber Fabry-Perot cavity length L under the environmental state E0. i ;The initial value of i is 0;

[0074] 1.6) Change the environmental state and return to step 1) until a cavity length sequence L = {L0, L1…L N}, and the spectrum intensity sequence P = {P0, P1...P N};

[0075] 1.7) For the cavity length sequence L = {L0, L1…L N} and the spectral intensity sequence P = {P0, P1...P N} is fitted to obtain the relationship between the cavity length and spectral intensity of the optical fiber Fabry-Perot sensor at a single wavelength point λ0.

[0076] The device for loading the optical fiber Fabry-Perot sensor comprises a micro-displacement stage and a pressure generator.

[0077] During demodulation, the cavity length L fluctuates within the linear range of demodulation. At this time, the cavity length L is related to the received light intensity I R The linear range of demodulation is the wavelength range of the λ / 4 monochromatic light source centered at the Q point with the largest slope.

[0078] The approximate linear relationship is as follows:

[0079] I R =αI0L(1)

[0080] In the formula, I R is the light intensity signal; α is the proportional coefficient; L is the cavity length; I0 is the incident light intensity.

[0081] Light intensity signal I R As shown below:

[0082]

[0083] Where L is the cavity length; I0 is the incident light intensity; R is the end reflectivity, and λ is the wavelength of the light.

[0084] The steps of selecting a single wavelength point λ0 include:

[0085] Taking the variation range of the cavity length L, that is, the initial cavity length determined when designing the optical fiber Fabry-Perot sensor and the cavity length value when the maximum deformation is reached as variables, the characteristics of the reflection spectrum curves at the single wavelength points of N sparse spectra are compared in turn, and the wavelength value corresponding to a curve that is monotonic, has the highest linearity and the highest sensitivity within the cavity length range is selected as the single wavelength point λ0.

[0086] Embodiment 2:

[0087] See also Figures 1 to 4 , high-precision in-situ calibration and high-speed real-time demodulation device for fiber Fabry-Perot sensor cavity length, such as Figure 2 As shown, it includes a broadband light source, an optical circulator, a coupler, a tunable filter, a photodetector, a signal amplification and conditioning module, a signal acquisition module and a calculation demodulation module; the system can obtain the interference spectrum of the optical fiber Fabry-Perot sensor at a single (or several) wavelengths.

[0088] The functions of each part of the hardware system are:

[0089] The broadband light source provides the system with a broadband light source with flat spectrum and stable and adjustable power.

[0090] The optical circulator sends the scanning light signal emitted by the light source to the fiber Fabry-Perot pressure fiber Fabry-Perot sensor through the optical fiber, and transmits the interference signal returned by the fiber Fabry-Perot sensor to the coupler at the same time.

[0091] The coupler transmits one light path in multiple paths.

[0092] The filter allows the interference light reflected from the fiber Fabry-Perot sensor to pass at a specific wavelength λ0, and attenuates the light of other wavelengths. The wavelength allowed to pass by the filter is adjustable to output light of different wavelengths. At the same time, the number of added filters can be reasonably selected according to the requirements of demodulation accuracy to achieve cavity length demodulation of different methods.

[0093] The photoelectric detector is used to receive and convert the reflected light interference signal and output it as an analog electrical signal.

[0094] The signal amplification and conditioning module amplifies and filters the analog signal transmitted from the photoelectric detector.

[0095] The signal acquisition module converts the amplified and conditioned analog information into digital signals, collects and stores them, and transmits them to the subsequent system for calculation and demodulation.

[0096] The calculation and demodulation module calculates the transmitted digital signal to achieve demodulation of the optical fiber Fabry-Perot cavity length.

[0097] Figure 1The system suitable for measuring high-frequency dynamic pressure is demonstrated. The fiber Fabry-Perot sensor can be adapted to high-frequency dynamic pressure change environments by optimizing the structural design, diaphragm material and packaging process, meeting the requirements of high-frequency dynamic pressure response speed and range. The scanning light source in the system can set the scanning wavelength interval. The light source is sent to the fiber Fabry-Perot sensor through an optical circulator, and the circulator then transmits the reflected light to the photoelectric detector, data acquisition and processing module, and calculation demodulation module in sequence to realize the continuous equal-wavelength interval scanning acquisition, storage and demodulation of the reflection spectrum.

[0098] During calibration, the pressure generator is used to load the Fabry-Perot sensor with pressure. The light source continuously scans the light to obtain the interference signal spectrum reflected by the fiber optic Fabry-Perot sensor. The cavity length L is calculated using the phase demodulation method or other methods. i By changing the loading conditions, multiple spectra and corresponding cavity lengths are obtained, forming a cavity length demodulation sequence L = {L0, L1…L N}; Then search for the intensity P at the single wavelength point λ0 corresponding to the spectrum of different cavity lengths i , obtain the light intensity sequence P = {P0, P1...P N}; Fit the cavity length sequence and the light intensity sequence to obtain the cavity length-intensity relationship at this wavelength point λ0.

[0099] In actual testing, the system is set to continuously scan and acquire the reflected signal at the single wavelength point λ0, and the searched intensity change data is used to achieve high-speed real-time demodulation of the cavity length using the cavity length-wavelength relationship.

[0100] This process can be implemented through algorithms on off-the-shelf computers or by developing dedicated high-speed embedded systems.

[0101] Embodiment 3:

[0102] A method for high-precision in-situ calibration of cavity length and high-speed real-time demodulation of cavity length, the specific steps of the method are:

[0103] S1: Detection system, keep the environment of the fiber Fabry-Perot sensor stable. Use the tunable filter of channel 1 to scan the wavelength and obtain the complete reflection spectrum under the environment state E0;

[0104] S2: Use the phase demodulation method to calculate the cavity length L0 under the environmental state E0, repeat steps 1 and 2 to obtain the cavity length sequence L=[L0, L1, ...LN] under different environmental states;

[0105] S3: According to the wavelength selection criteria, the intensity value sequence P = [P0, P1, ..., PN] of λ0 under different environmental conditions is obtained, and the corresponding relationship between intensity (sequence P) and cavity length (sequence L) is established.

[0106] S4: During the test, the system is set to obtain the interference signal at λ0 in real time, and the cavity length is demodulated using the intensity-cavity length relationship.

[0107] The basic principle of intensity-cavity length calibration in step S3 is that after the reflection spectrum passes through the tunable filter, the system obtains an interference signal at one (or several) wavelength points, and the light intensity value of the signal will change with the change of the measured physical quantity, that is, different Fabry-Perot cavity lengths result in different received light intensity values. Generally, the received light intensity signal I R It can be expressed as:

[0108]

[0109] Where: I0 is the incident light intensity, R is the end face reflectivity, λ is the wavelength of the light wave, and L is the length of the Fabry-Perot cavity. When the end face reflectivity of the optical fiber Fabry-Perot sensor is not too high, the above formula can be simplified to:

[0110]

[0111] It can be seen that the received reflected light intensity I R is the single variable cosine function of the cavity length L. The point with the best linearity in the spectrum, i.e. the point with the largest slope, is taken as the initial working point Q. The wavelength range of the λ / 4 monochromatic light source centered on the Q point is taken as the linear interval of demodulation. When the cavity length L fluctuates within this interval, the cavity length L and the received light intensity I R It is approximately linear relationship, that is:

[0112] I R =αI0L(3)

[0113] Among them, α is the proportional coefficient, and the corresponding curve between the intensity value and the Fabry-Perot cavity length is as follows: Figure 2 a, Q point in the figure is the initial working point, Δh is the λ / 4 linear region. The purpose of calibration is to obtain an approximate linear relationship between cavity length and light intensity in this region.

[0114] Since in actual testing, the system uses the reflected light intensity data obtained in real time at a single wavelength point to demodulate the cavity length, when calibrating the cavity length-wavelength relationship in step S3, the wavelength λ0 of the monochromatic light source used in the calibration must be selected in combination with the spectrum corresponding to different wavelength points to achieve a better test effect.

[0115] The specific method is to use numerical simulation to select the single wavelength point λ0. It can be seen from formula (2) that the reflected light intensity signal received by the photodetector is related to the end face reflectivity R, the Fabry-Perot cavity length L, and the incident light wavelength λ0. During numerical simulation, the variation range of the cavity length L, that is, the initial cavity length determined when the optical fiber Fabry-Perot sensor is designed and the cavity length value when the maximum deformation is reached, is used as a variable. The dynamic range, linearity, sensitivity and other characteristics of the reflection spectrum curve at the single wavelength point that constitutes the broadband light source are examined in turn. The end face reflectivity R is determined according to the type of optical fiber Fabry-Perot sensor actually used and is a certain value. The schematic diagram of the principle is shown in the figure. Figure 3 shown.

[0116] However, broadband light sources have an infinite number of single wavelength points to choose from within the bandwidth, and it is impossible to determine the most suitable λ through a limited number of comparisons. 0， Therefore, in actual operation, it is necessary to combine existing engineering experience and make selections around the commonly used wavelength point range.

[0117] The light intensity variation curves of different single wavelength points in a certain cavity length range are different. The purpose of selection is to obtain a curve with monotonicity, good linearity and high sensitivity in the cavity length range and its corresponding wavelength value for calibration and testing.

[0118] In step S4, the single wavelength point λ is fixed at point Q, and the reflected light intensity value I is obtained in real time. R , the cavity length can be calculated in real time by bringing it into the cavity length-light intensity linear relationship obtained in S3. The demodulation principle is as follows: Figure 2 As shown in b.

[0119] Embodiment 4:

[0120] The method of applying the high-precision in-situ calibration and high-speed real-time demodulation device of the fiber Fabry-Perot sensor cavity length to the actual high-frequency dynamic pressure test uses single-wavelength intensity demodulation to achieve high-speed and real-time demodulation of the cavity length. However, in actual applications, the interference factors of the optical path and the test environment are complex, resulting in limited demodulation accuracy and a small demodulation range.

[0121] See also Figure 1 In the system diagram shown, this embodiment can obtain interference spectra at two or more wavelength points by adjusting the number of tunable filters to achieve dual-wavelength demodulation, three-wavelength demodulation, etc. of the system. This embodiment takes the dual-wavelength demodulation method as an example to introduce a method for improving the applicability of the system by adjusting the composition of the system.

[0122] Two tunable filters are used in the dual-wavelength demodulation method. The wavelengths of the output light of the tunable filters are set to λ1 and λ2, and their phase and They can be expressed as:

[0123]

[0124]

[0125] In the dual-wavelength demodulation method, the phase difference between the two beams is generally set to 90°, that is, When the pressure changes and the cavity length changes, the intensity of the reflected light received by the system changes accordingly, resulting in a phase The change in cavity length will also produce a corresponding change:

[0126]

[0127] After the initial cavity length L0 is determined, the cavity length can be demodulated by detecting the parameters of two optical signals with different wavelengths.

[0128] Embodiment 5:

[0129] The invention discloses a high-precision in-situ calibration and high-speed real-time demodulation device for the cavity length of an optical fiber Fabry-Perot sensor, comprising a broadband light source, an optical circulator, a coupler, n tunable filters, n photoelectric detectors, a signal amplification and conditioning module, a signal acquisition module and a calculation demodulation module.

[0130] The broadband light source provides a wide spectrum input light source signal to the optical circulator through an optical fiber;

[0131] The optical circulator transmits the broadband light source signal to the optical fiber Fabry-Perot sensor through the optical fiber, and receives the reflected light interference signal returned by the optical fiber Fabry-Perot sensor;

[0132] The optical circulator transmits the reflected light interference signal to the coupler;

[0133] The coupler transmits the reflected light interference signal in multiple paths to n tunable filters respectively;

[0134] The i-th tunable filter filters the reflected light interference signal and retains the wavelength λ i The reflected light interference signal under the condition is transmitted to the corresponding photodetector; i = 1, 2, ..., n;

[0135] The photoelectric detector converts the reflected light interference signal into an analog electrical signal and transmits it to the signal amplification and conditioning module;

[0136] The signal amplification and conditioning module amplifies and filters the analog electrical signal and transmits it to the signal acquisition module;

[0137] The signal acquisition module transmits the amplified and filtered multi-channel analog signals to the calculation and demodulation module;

[0138] The calculation and demodulation module selects one or more light intensity signals corresponding to wavelengths from multiple light signals, and processes the light intensity signals according to the optical fiber Fabry-Perot sensor cavity length-light intensity relationship to obtain the optical fiber Fabry-Perot sensor cavity length corresponding to the current light intensity signal.

[0139] Embodiment 6:

[0140] A high-precision in-situ calibration and high-speed real-time demodulation device for the cavity length of an optical fiber Fabry-Perot sensor, the main contents of which are shown in Example 5, wherein the broadband light source is a wide-spectrum light source, including ASE and SLD, which has a flat spectrum and adjustable power within the signal demodulation range.

[0141] Embodiment 7:

[0142] The demodulation method of the high-precision in-situ calibration of the cavity length of the optical fiber Fabry-Perot sensor and the high-speed real-time demodulation device comprises the following steps:

[0143] 1) Calibrate the fiber Fabry-Perot sensor in situ to obtain the relationship between the cavity length and spectral intensity of the fiber Fabry-Perot sensor;

[0144] 2) The broadband light source provides a wide spectrum input light source signal to the optical circulator through the optical fiber;

[0145] 3) The optical circulator transmits the broadband light source signal to the fiber Fabry-Perot sensor through the optical fiber, and receives the reflected light interference signal returned by the fiber Fabry-Perot sensor;

[0146] 4) Use the coupler, tunable filter, photodetector, signal amplification and conditioning module, and signal acquisition module in sequence to obtain the signal at wavelength λ i The sparse spectrum under the condition is transmitted to the calculation demodulation module;

[0147] 5) The calculation and demodulation module selects a wavelength from the multiple optical signals, and processes the light intensity signal corresponding to the wavelength according to the optical fiber Fabry-Perot sensor cavity length-light intensity relationship to obtain the optical fiber Fabry-Perot sensor cavity length corresponding to the current light intensity signal.

[0148] Embodiment 8:

[0149] The demodulation method of the high-precision in-situ calibration and high-speed real-time demodulation device of the optical fiber Fabry-Perot sensor cavity length is shown in Example 7. The steps of in-situ calibration of the optical fiber Fabry-Perot sensor include:

[0150] 1) The broadband light source provides a wide spectrum input light source signal to the optical circulator through the optical fiber;

[0151] 2) The optical circulator transmits the broadband light source signal to the fiber Fabry-Perot sensor through the optical fiber, and receives the reflected light interference signal returned by the fiber Fabry-Perot sensor;

[0152] 3) Using the tunable filter of channel 1 to scan the wavelength, a complete reflection spectrum under the environmental state E0 is obtained;

[0153] 4) Using the coupler, tunable filter, photodetector, signal amplification and conditioning module, and signal acquisition module in sequence to obtain the light intensity signal, and transmit it to the calculation and demodulation module;

[0154] 5) The calculation demodulation module demodulates the interference spectrum signal to obtain the fiber Fabry-Perot cavity length L under the environmental state E0 i ;The initial value of i is 0;

[0155] 6) Change the environmental state and return to step 1) until a cavity length sequence L = {L0, L1…L N}, and the spectrum intensity sequence P = {P0, P1...P N};

[0156] 7) For the cavity length sequence L = {L0, L1…L N} and the spectral intensity sequence P = {P0, P1...P N} is fitted to obtain the relationship between the cavity length and spectral intensity of the optical fiber Fabry-Perot sensor at a single wavelength point λ0.

[0157] Embodiment 9:

[0158] The demodulation method of the high-precision in-situ calibration of the cavity length of the optical fiber Fabry-Perot sensor and the high-speed real-time demodulation device is mainly shown in Example 7, wherein the device for loading the optical fiber Fabry-Perot sensor includes but is not limited to a micro-displacement stage and a pressure generator.

[0159] Embodiment 10:

[0160] The demodulation method of the high-precision in-situ calibration and high-speed real-time demodulation device of the optical fiber Fabry-Perot sensor cavity length is shown in Example 7. During demodulation, the cavity length L fluctuates within the linear range of demodulation. At this time, the cavity length L is proportional to the received light intensity I R The linear range of demodulation is the wavelength range of the λ / 4 monochromatic light source centered at the Q point with the largest slope.

[0161] The approximate linear relationship is as follows:

[0162] I R =αI0L(1)

[0163] In the formula, I R is the light intensity signal; α is the proportional coefficient; L is the cavity length; I0 is the incident light intensity.

[0164] Embodiment 11:

[0165] The demodulation method of the high-precision in-situ calibration and high-speed real-time demodulation device of the optical fiber Fabry-Perot sensor cavity length is shown in Example 7. The step of selecting the single wavelength point λ0 includes:

[0166] Taking the variation range of the cavity length L, that is, the initial cavity length determined when designing the optical fiber Fabry-Perot sensor and the cavity length value when the maximum deformation is reached as variables, the characteristics of the reflection spectrum curves at the single wavelength points of N sparse spectra are compared in turn, and the wavelength value corresponding to a curve that is monotonic, has the highest linearity and the highest sensitivity within the cavity length range is selected as the single wavelength point λ0.

Claims

1. A demodulation method based on high-precision in-situ calibration of the cavity length of an optical fiber Fabry-Perot sensor and a high-speed real-time demodulation device, characterized in that: The following steps are involved: 1) Calibrate the fiber Fabry-Perot sensor in situ to obtain the relationship between the cavity length and spectral intensity of the fiber Fabry-Perot sensor; 2) The broadband light source provides a wide spectrum input light source signal to the optical circulator through the optical fiber; 3) The optical circulator transmits the broadband light source signal to the fiber Fabry-Perot sensor through the optical fiber, and receives the reflected light interference signal returned by the fiber Fabry-Perot sensor; 4) Use the coupler, tunable filter, photodetector, signal amplification and conditioning module, and signal acquisition module in sequence to obtain the signal at wavelength λ i The sparse spectrum under the condition is transmitted to the calculation demodulation module; 5) The calculation and demodulation module selects a wavelength from the multiple optical signals, and processes the light intensity signal corresponding to the wavelength according to the optical fiber Fabry-Perot sensor cavity length-light intensity relationship to obtain the optical fiber Fabry-Perot sensor cavity length corresponding to the current light intensity signal; The steps for in-situ calibration of the fiber optic Fabry-Perot sensor include: s1) The broadband light source provides a wide spectrum input light source signal to the optical circulator through an optical fiber; s2) The optical circulator transmits the broadband light source signal to the optical fiber Fabry-Perot sensor through the optical fiber, and receives the reflected light interference signal returned by the optical fiber Fabry-Perot sensor; s3) using the tunable filter of channel 1 to perform wavelength scanning to obtain a complete reflection spectrum under environmental state E0; s4) sequentially using a coupler, a tunable filter, a photodetector, a signal amplification and conditioning module, and a signal acquisition module to obtain a light intensity signal, and transmit it to a calculation and demodulation module; s5) The calculation demodulation module demodulates the interference spectrum signal to obtain the fiber Fabry-Perot cavity length L under the environmental state E0. i ;The initial value of i is 0; s6) Change the environmental state and return to step s1) until a cavity length sequence L = {L0, L1 ... L N }, and the spectrum intensity sequence P = {P0, P1...P N }; s7) For the cavity length sequence L = {L0, L1…L N } and the spectral intensity sequence P = {P0, P1...P N } is fitted to obtain the relationship between the cavity length and spectral intensity of the optical fiber Fabry-Perot sensor at a single wavelength point λ0.

2. The demodulation method based on the high-precision in-situ calibration and high-speed real-time demodulation device of the optical fiber Fabry-Perot sensor cavity length according to claim 1 is characterized in that: The device for loading the optical fiber Fabry-Perot sensor includes but is not limited to a micro-displacement stage and a pressure generator.

3. The demodulation method based on the high-precision in-situ calibration and high-speed real-time demodulation device of the optical fiber Fabry-Perot sensor cavity length according to claim 2 is characterized in that: During demodulation, the cavity length L fluctuates within the linear range of demodulation. At this time, the cavity length L is related to the received light intensity I R The linear range of demodulation is the wavelength range of the λ / 4 monochromatic light source centered at the Q point with the largest slope. The approximate linear relationship is as follows: I R =αI0L (1) In the formula, I R is the light intensity signal; α is the proportional coefficient; L is the cavity length; I0 is the incident light intensity.

4. The demodulation method based on the high-precision in-situ calibration and high-speed real-time demodulation device of the optical fiber Fabry-Perot sensor cavity length according to claim 1 is characterized in that: The steps of selecting a single wavelength point λ0 include: Taking the variation range of the cavity length L, that is, the initial cavity length determined when designing the optical fiber Fabry-Perot sensor and the cavity length value when the maximum deformation is reached as variables, the characteristics of the reflection spectrum curves at the single wavelength points of N sparse spectra are compared in turn, and the wavelength value corresponding to a curve that is monotonic, has the highest linearity and the highest sensitivity within the cavity length range is selected as the single wavelength point λ0.

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