CN-121430736-B - Dual-mode resonance optical fiber microcavity air pressure measurement system and measurement method

CN121430736BCN 121430736 BCN121430736 BCN 121430736BCN-121430736-B

Abstract

The invention provides a dual-mode resonance optical fiber microcavity air pressure measurement system and a measurement method, which relate to the technical field of optical fiber microcavity air pressure measurement and specifically comprise a sensing probe preparation module, a dual-parameter sensitivity matrix calibration module, an optical fiber laser sensing system construction module, a real-time monitoring change module and a decoupling and output module. And manufacturing an open microcavity on a single-mode fiber by combining femtosecond laser etching with high-temperature tapering to form a micro-nano taper area, thereby obtaining the sensing probe with two resonance valleys with different response characteristics to temperature and air pressure. And obtaining a sensitivity coefficient matrix through calibration, embedding a probe serving as a filter into the annular fiber laser cavity, and constructing the fiber laser with the laser wavelength locked by the resonance valley. The environment change causes laser wavelength drift, and the real-time synchronous measurement of temperature and air pressure is realized by utilizing inverse matrix decoupling, so that the method is suitable for high-precision and anti-interference monitoring of harsh industrial environments such as aeroengines, power transformers and the like.

Inventors

SUN CHANGWEI
GAO WEIXIA
YIN YANFENG
WANG YANCHUN
Fan Qiongxing
LI FEI
LIU NA

Assignees

蚌埠学院

Dates

Publication Date: 20260508
Application Date: 20251208

Claims (9)

1. A dual mode resonant fiber microcavity air pressure measurement system, comprising: The sensing probe preparation module is used for forming an open type microcavity penetrating through the cladding and partially cutting into the fiber core in the fiber core and the cladding area of the standard communication single-mode fiber through femtosecond laser etching, carrying out high Wen Lazhui on the open type microcavity to form a micro-nano cone area so as to prepare the sensing probe of the micro-cavity Mach-Zehnder interferometer in the open type micro-tapered fiber, wherein the interference spectrum of the sensing probe has at least two resonance valleys in a C+L wave band; the dual-parameter sensitivity matrix calibration module is used for placing the sensing probe in a calibration cavity for independently controlling temperature and air pressure, recording the output interference spectrum of the sensing probe under the illumination of a wide-spectrum light source, selecting two resonance valleys with different response characteristics to the temperature and the air pressure, monitoring the drift amount of the central wavelength along with the temperature and the air pressure of the calibration cavity, and calibrating the sensitivity coefficient matrix of the sensing probe through linear fitting; The optical fiber laser sensing system construction module is used for taking a sensing probe as a wavelength selection filter, accessing the sensing probe into a prefabricated annular optical fiber laser resonant cavity, and constructing an optical fiber laser for determining the output laser wavelength according to the resonance valley position by utilizing the filtering characteristic of the sensing probe and the mode competition of the laser; the real-time monitoring change module is used for deploying the optical fiber laser system integrated with the sensing probe at a calibrated monitoring point, when the ambient temperature and the air pressure change, the interference spectrum of the sensing probe shifts to cause the jump or continuous shift of the output laser wavelength of the optical fiber laser, and the wavelength change quantity is monitored and quantized in real time through the high-resolution optical wavelength meter; and the decoupling and outputting module is used for substituting the wavelength variation into an inverse matrix of the sensitivity coefficient matrix to calculate, and decoupling the temperature variation and the air pressure variation of the monitoring point in real time.
2. The dual mode resonant fiber microcavity air pressure measurement system of claim 1 wherein the radial width of the defined open microcavity is in the range of The axial length range is And the etching depth is not lower than the sum of the diameter of the cladding of the standard single-mode fiber and the depth of the cut-in fiber core, and the value range of the depth of the cut-in fiber core is The open type microcavity integral cladding is cut into the fiber core to realize the direct interaction between the fiber core light guide mode and the internal and external environments of the open type microcavity; The cone waist diameter of the micro-nano cone region formed by the high-temperature cone drawing is in the range of The length of the cone area is in the range of The micro-nano cone area is positioned at the axial center of the open microcavity and is used for enhancing the coupling efficiency of the fiber core fundamental mode and the cladding mode, and the depth of the resonance valley of the interference spectrum is more than 10dB, so that at least two resonance valleys are ensured to have contrast and detectability; the interference spectrum generated by the sensing probe is formed by interference between a fiber core fundamental mode and an excited multi-order cladding mode, one of two resonance valleys with different response characteristics to temperature and air pressure is a main resonance valley formed by interference between the fundamental mode and a low-order cladding mode, the other is a secondary resonance valley formed by interference between the fundamental mode and a high-order cladding mode, and the wavelength interval between the main resonance valley and the secondary resonance valley is within a [20nm,80nm ] interval.
3. The dual-mode resonant fiber microcavity air pressure measurement system of claim 2 wherein calibrating the sensitivity coefficient matrix specifically comprises: In a calibration cavity with the temperature and air pressure control precision being better than +/-0.1 ℃ and +/-0.01 MPa, changing the temperature in a temperature measurement range by using a fixed temperature step length to obtain a group of temperature calibration points as a variable-temperature sequence; under the state of each calibration point group, a broadband light source is used for irradiating the sensing probe, the transmission interference spectrum output by the sensing probe is collected through a spectrum analyzer, and the center wavelength of a preselected main resonance valley and the center wavelength of a secondary resonance valley in the spectrum are recorded; The standard room temperature of 25 ℃ and the standard atmospheric pressure of 101.325Kpa are preset as references, and the wavelength drift amount of each standard point group relative to two resonance valleys in the reference state is calculated according to the following formula: ; Wherein, the The wavelength drift quantity of the main valley in the q state of the standard point group is represented; Representing the center wavelength of the main valley in the q state of the calibration point group; the central wavelength of the main valley in the reference state is represented, q is the index of the set of calibration points; Similarly, the wavelength drift of the secondary valley in the q state of the standard point group is obtained and is recorded as ; Simultaneously, corresponding temperature variation and air pressure variation are recorded: ; Wherein, the Respectively representing the temperature variation and the air pressure variation of the q-th standard point group; 、 respectively representing the temperature and the air pressure of q standard point groups; 、 respectively representing the temperature and the air pressure in the reference state; And directly determining a sensitivity coefficient matrix by solving a least square solution of an overdetermined equation set for data of all the calibration point sets, wherein the overdetermined equation set has the following formula: ; ; Wherein, the 、 The sensitivity coefficients of the primary valley and the secondary valley to temperature are respectively; 、 the sensitivity coefficients of the primary valley and the secondary valley to the air pressure are respectively expressed as a sensitivity coefficient matrix ; Calculating determinant value of sensitivity coefficient matrix, verifying that absolute value of determinant value is greater than preset threshold value so as to ensure that sensitivity coefficient matrix is reversible and can implement effective temperature and air pressure distinguishing measurement, then storing sensitivity coefficient matrix and its inverse matrix in demodulation unit of optical fiber laser.
4. The dual-mode resonant fiber microcavity air pressure measurement system of claim 1 wherein the annular fiber laser resonator has a specific composition and connection relationship of: The output tail fiber of the pumping source is connected with the pumping port of the wavelength division multiplexer, the public port of the wavelength division multiplexer is connected with one end of an erbium-doped fiber serving as a gain medium, the other end of the erbium-doped fiber is connected with the input end of the optical isolator, the output end of the optical isolator is connected with the input end of the sensing probe, and the output end of the sensing probe is connected with the signal port of the wavelength division multiplexer, so that a closed annular fiber laser resonant cavity is formed; The specific implementation mode of the process for constructing the fiber laser for outputting the laser wavelength according to the position of the resonance valley is as follows: Extracting the minimum value of the transmission spectrum of the sensing probe at the resonance valley, and taking the minimum value as a wavelength selective filter to meet the threshold condition of laser oscillation starting, namely , wherein, At the wavelength of the erbium-doped fiber Net gain in location; representing a transmission spectrum of the sensing probe; After the pumping power exceeds the threshold value, the competition of the cavity mode makes the final oscillation laser wavelength limited at the position of relatively highest loss in the transmission spectrum of the sensing probe, namely at the resonance valley, namely Thereby realizing that the output laser wavelength is determined by the resonance valley position of the sensing probe; in order to improve the resolution of air pressure sensing, the optical fiber laser works in a single longitudinal mode or a few longitudinal modes by optimizing parameters of the annular optical fiber laser resonant cavity and utilizing mode competition, and specifically meets the following conditions: The total cavity length of the annular optical fiber laser resonant cavity is limited in the range of 10m and 50m, the corresponding longitudinal mode interval is larger than the corresponding value of the 3dB bandwidth of the resonant valley serving as a filtering window in the transmission spectrum of the sensing probe in the frequency domain, the product of the effective refractive index of the optical fiber and the physical cavity length of the annular optical fiber laser resonant cavity is calculated, the ratio of the light velocity in vacuum to the product is the longitudinal mode interval, under the condition, only one or a plurality of longitudinal modes fall in the resonant Gu Lvbo window, and a narrow line width output is finally formed through mode competition, the line width is smaller than 1/10 of the corresponding value of the 3dB bandwidth of the resonant valley in the frequency domain, and the line width is smaller than 10MHz.
5. The dual-mode resonant fiber microcavity air pressure measurement system of claim 1, wherein the fiber laser is fixed at a monitoring point, the calibrated monitoring point comprises but is not limited to a pressure measuring hole of an aeroengine compressor section casing, the sensing probe is fixed in the pressure measuring hole, an open microcavity is directly exposed to the air pressure environment of an engine runner, and the dissolved air in power transformer oil is in a sampling cavity of an air chamber of an on-line monitoring system; When the ambient temperature and the air pressure change, the spectral drift of the sensing probe can cause the output laser wavelength of the fiber laser to change in the following two modes: The first mode is a continuous tuning mode, and when the spectral drift amount of the sensing probe is smaller than the interval between adjacent longitudinal modes of the fiber laser due to environmental change, the output laser wavelength is represented as continuous wavelength tuning in the filtering range of a single resonance valley; the second mode is a mode hopping mode, when the spectral drift amount of the sensing probe is not smaller than the interval between adjacent longitudinal modes of the laser due to environmental change, the output laser wavelength is in hopping among different longitudinal modes, and the new wavelength after hopping is still locked at the resonant valley after the drift; In the second mode, the total shift of the resonant valley caused by environmental change is roughly estimated by recording the jump times and longitudinal mode intervals of the laser wavelength and combining the effective cavity length and the group refractive index of the laser, and the rough estimation formula is as follows: ; Wherein, the Indicating the total shift amount of the resonance valley, N indicating the number of forward or reverse hops, Indicating the group refractive index of the fiber laser, Indicating the effective cavity length of the fiber laser.
6. A dual mode resonant fiber microcavity air pressure measurement system as claimed in claim 3 wherein quantifying the wavelength variation using a static mapping method comprises: calculating absolute difference between current output laser wavelength and two central wavelengths measured in reference state, and representing as And Wherein, the method comprises the steps of, Indicating the current output laser wavelength, A center wavelength of the secondary valley in the reference state; If it is Judging that the current laser is locked in the main valley, and directly calculating the wavelength variation of the main valley as Wherein, the method comprises the steps of, Representing the wavelength variation of the current main valley; meanwhile, based on the linear corresponding assumption, the wavelength variation of the secondary valley is primarily estimated to be Wherein, the method comprises the steps of, Indicating the current wavelength change of the sub-valley, otherwise, if the laser is determined to be locked in the sub-valley, calculating And initially estimate 。
7. The dual-mode resonant fiber microcavity air pressure measurement system of claim 6, wherein when a mode jump of the output laser wavelength is detected, or when the absolute value of the change of the physical quantity in unit time calculated by adopting a static mapping method is larger than a preset threshold, a dynamic iteration method is started for quantification, and the dynamic iteration method comprises the following steps: Setting the iteration times as zero, taking the temperature and air pressure values calculated in the last time as current estimated values, and taking a reference state as the current estimated values if no historical calculated values exist; According to the current estimated value and the calibrated sensitivity coefficient matrix, calculating the theoretical wavelength of the main valley, wherein the formula is as follows: ; Wherein, the A theoretical wavelength representing a principal valley; 、 respectively representing the temperature and air pressure in the current estimated value, and similarly, obtaining the theoretical wavelength of the secondary valley, which is recorded as ; Comparing the output laser wavelength measured in real time with the theoretical wavelengths of the primary valley and the secondary valley respectively, selecting one with the smallest difference as the current locking valley, and calculating the temporary wavelength variation as Where r represents a primary valley or a secondary valley, and r is i or j; combining the temporary wavelength variation with another corresponding variation which is not used as the current locking valley to form a vector, and calculating updated temperature and air pressure values by using an inverse matrix of the sensitivity coefficient matrix; And if the absolute difference value of the updated temperature and the current estimated value is smaller than the set threshold value, the iteration is ended, the temporary wavelength variation in the last iteration is output, and otherwise, the updated temperature and the air pressure value are used as the current estimated value, and the iteration is continued.
8. The dual-mode resonant fiber microcavity air pressure measurement system of claim 6 wherein decoupling the temperature change from the air pressure change comprises: based on the real-time wavelength variation of the two resonance valleys, an input vector is formed, expressed as ; And calling a sensitivity coefficient matrix and an inverse matrix thereof, and performing matrix multiplication operation to obtain an output vector containing temperature and air pressure variation, wherein the formula is as follows: ; Wherein, the An output vector including the amounts of change in temperature and air pressure; 、 respectively representing the temperature change rate and the air pressure change quantity; An inverse matrix representing a sensitivity coefficient matrix; the definition of the sensitivity coefficient matrix and the inverse matrix of the sensitivity coefficient matrix and the meaning of parameters are as follows: ; ; Wherein D is determinant of sensitivity coefficient matrix; and adding the solved temperature variation and the air pressure variation with the environmental values of the known monitoring points respectively to obtain a real-time absolute air pressure value and a real-time absolute temperature value.
9. A dual-mode resonant fiber microcavity air pressure measurement method, characterized in that the dual-mode resonant fiber microcavity air pressure measurement method is performed by the dual-mode resonant fiber microcavity air pressure measurement system according to any one of claims 1-8, and the specific steps include: step 1, forming an open microcavity penetrating through a cladding and partially cutting into the fiber core in a fiber core and cladding area of a standard communication single-mode fiber by femtosecond laser etching, carrying out high Wen Lazhui on the open microcavity to form a micro-nano cone area so as to prepare an open micro-tapered intra-fiber microcavity Mach-Zehnder interferometer sensing probe, wherein the interference spectrum of the sensing probe is provided with at least two resonance valleys in a C+L wave band; Step 2, placing the sensing probe in a calibration cavity for independently controlling temperature and air pressure, recording an interference spectrum output by the sensing probe under the illumination of a wide-spectrum light source, selecting two resonance valleys with different response characteristics to the temperature and the air pressure, monitoring the drift amount of the central wavelength along with the temperature and the air pressure of the calibration cavity, and calibrating a sensitivity coefficient matrix of the sensing probe by linear fitting; Step 3, the sensing probe is used as a wavelength selective filter and is connected into a prefabricated annular optical fiber laser resonant cavity, and the optical fiber laser for outputting laser wavelength is constructed by utilizing the filter characteristic of the sensing probe and the mode competition of the laser; The method comprises the steps of (4) disposing an optical fiber laser system integrated with a sensing probe at a calibrated monitoring point, when the ambient temperature and the air pressure change, shifting an interference spectrum of the sensing probe to cause jump or continuous shift of the output laser wavelength of the optical fiber laser, and monitoring and quantifying the wavelength change in real time through a high-resolution optical wavelength meter; and 5, substituting the wavelength variation into an inverse matrix of the sensitivity coefficient matrix for calculation, and decoupling the temperature variation and the air pressure variation of the monitoring point in real time.

Description

Dual-mode resonance optical fiber microcavity air pressure measurement system and measurement method Technical Field The invention relates to the technical field of optical fiber microcavity air pressure measurement, in particular to a dual-mode resonance optical fiber microcavity air pressure measurement system and a measurement method. Background Real-time state monitoring of high-end equipment such as aeroengines, large-scale power transformers and the like is critical to safe and stable operation of the high-end equipment. Taking an aeroengine as an example, the dynamic and accurate measurement of the internal air pressure of a compressor section is a key for evaluating the performance of the engine and preventing surge, and in a power transformer, the pressure and temperature change of dissolved gas in oil are the core basis for diagnosing internal latent faults. Conventional electrical barometric sensors (e.g., piezoresistive, capacitive) are widely used, but often face challenges of electromagnetic interference, flammability risk, and long-term stability deficiency in the above-mentioned scenarios. In recent years, the optical fiber sensing technology provides a new idea for physical quantity measurement in a severe environment by virtue of the advantages of intrinsic safety, electromagnetic interference resistance, corrosion resistance and the like. Among them, the microstructure-based optical fiber sensor is a research hotspot due to its high sensitivity and small-sized characteristics. Currently, optical fiber sensing schemes for gas pressure can be mainly classified into an optical fiber bragg grating type, a fabry-perot interference type, a mach-zehnder interference type, and the like. Fiber bragg gratings are typically less sensitive to air pressure and have a response that severely crosses temperature, require compensation by means of complex reference gratings or special packaging, are structurally complex and add uncertainty. The intrinsic or extrinsic Fabry-Perot cavity air pressure sensor has high sensitivity, but has precise manufacturing process and high cost, and the absolute demodulation of the cavity length is easy to be disturbed by temperature, and the demodulation precision is limited in a wide temperature range and variable air pressure dynamic scene. The optical fiber sensor based on Mach-Zehnder interference principle has the advantages of relatively simple and convenient manufacture and designable sensitivity by designing special structures (such as cone, dislocation, microcavity and the like) to excite the interference of the cladding mode and the fiber core fundamental mode and being sensitive to the change of the environment refractive index (related to gas density and pressure). However, most of the existing optical fiber air pressure sensors with single-mode interference structures generally show wide-spectrum modulation or single resonance valley, are equally sensitive to temperature and are difficult to distinguish, and monitoring of broadband spectrum of the optical fiber air pressure sensors depends on expensive high-resolution spectrum analyzers, so that low-cost and high-resolution real-time dynamic measurement is difficult to realize. The sensor is directly connected into a laser cavity, spectrum movement is converted into laser wavelength jump by utilizing the narrow-band filtering characteristic of the sensor, and the sensor is an effective way for improving resolution and measuring speed, but how to realize high-sensitivity response to air pressure and effective distinguishing capability to temperature and air pressure in a miniaturized and integrated sensing probe, ensure stable integration of the sensor and a laser system, and is still a prominent bottleneck for the technology to practical engineering application. Disclosure of Invention The invention aims to provide a dual-mode resonance optical fiber microcavity air pressure measurement system and a measurement method, which are used for solving the problems in the background technology. A dual mode resonant fiber microcavity air pressure measurement system comprising: The sensing probe preparation module is used for forming an open type microcavity penetrating through the cladding and partially cutting into the fiber core in the fiber core and the cladding area of the standard communication single-mode fiber through femtosecond laser etching, carrying out high Wen Lazhui on the open type microcavity to form a micro-nano cone area so as to prepare the sensing probe of the micro-cavity Mach-Zehnder interferometer in the open type micro-tapered fiber, wherein the interference spectrum of the sensing probe has at least two resonance valleys in a C+L wave band; the dual-parameter sensitivity matrix calibration module is used for placing the sensing probe in a calibration cavity for independently controlling temperature and air pressure, recording the output interference spectrum of the sensing probe under the ill