Interference optical fiber accelerometer probe and system capable of inhibiting temperature cross sensitivity

Abstract

The invention belongs to the field of optical fiber interference measurement, and particularly discloses an interference optical fiber accelerometer probe and system capable of restraining temperature cross sensitivity, and the optical fiber accelerometer probe comprises an optical fiber head, a spring group and a heterogeneous reflector. Different thermal expansion coefficients of the first reflecting mirror and the second reflecting mirror in the heterogeneous reflecting mirror are utilized, so that differential detection of temperature change is realized. The end face of the optical fiber and the heterogeneous reflector form a heterogeneous double-cavity parallel Fabry-Perot interference structure, when external acceleration and environment temperature change at the same time, acceleration signals and temperature noise can be effectively separated through the established matrix relational expression by means of the length change difference of two equivalent cavities, the temperature cross sensitivity problem is remarkably restrained, and the interference accuracy is improved. The measurement precision is improved, and the signal demodulation process is simplified. Through temperature compensation and signal decoupling technologies, the system can adapt to a working environment with a wide temperature range, the stability and reliability of the system in an extreme environment are enhanced, and the system is suitable for harsh application scenes such as aerospace and earthquake monitoring.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of optical fiber interferometry, and more particularly, to an interference optical fiber accelerometer probe and system capable of suppressing temperature cross-sensitivity. BACKGROUND

[0002] High-precision accelerometers have a wide range of applications in mechanical manufacturing, aerospace, earthquake monitoring, vehicle safety testing, and other fields. They need to accurately measure acceleration information to ensure navigation and control accuracy. In vehicle crash testing, accurate recording of acceleration changes is needed to evaluate safety performance. Optical fiber accelerometers combine many advantages of fiber optic sensors, such as small size, light weight, high measurement sensitivity, strong multiplexing capability, and resistance to electromagnetic interference, making them ideal for acceleration measurement in extreme environments.

[0003] ‌Extrinsic fiber Fabry-Perot interferometers (FPIs) have been applied in optical fiber accelerometers due to their simple structure, high sensitivity, and strong common-mode noise suppression capabilities. The structure is usually composed of a single-mode fiber end face and an external inertial mass block reflection surface. When the measured object accelerates, the relative displacement between the inertial mass block and the fiber end face changes the cavity length of the FPI, causing the phase difference between the fiber end face reflected light and the inertial mass block reflected light to change, and producing interference in the fiber. By demodulating the phase change through wavelength demodulation, light intensity demodulation, etc., the acceleration information can be accurately obtained.

[0004] In practical applications of accelerometers based on the extrinsic fiber FPI interference structure, environmental temperature fluctuations can cause thermal expansion or contraction of the inertial mass block material, resulting in changes in the interference cavity length and introducing displacement measurement errors, which limits the measurement accuracy and stability of the accelerometer. Temperature stability is one of the core challenges faced by fiber Fabry-Perot type accelerometers. "Temperature cross-sensitivity" refers to the interference of temperature changes on the measurement results of some sensors when measuring a certain physical quantity, making it impossible to accurately distinguish the separate effects of the physical quantity and temperature changes on the measurement signal.

[0005] For the problem of FPI temperature cross-sensitivity, the prior art has proposed some solutions. Patent CN115950578A discloses a fiber Fabry-Perot pressure sensor and a pressure detection method. The fiber Fabry-Perot pressure sensor includes a fiber probe, a sensitive diaphragm, and a fiber grating. The fiber probe forms an FP cavity at one end with the sensitive diaphragm. According to the length change of the FP cavity, the deformation amount of the sensitive diaphragm is obtained. The fiber grating is used to sense the ambient temperature value of the sensitive diaphragm, and thus the pressure sensitivity of the sensitive diaphragm can be determined. By combining the deformation amount of the sensitive diaphragm and the pressure sensitivity of the sensitive diaphragm, the external pressure value can be calculated, which can improve the precision of pressure measurement and reduce the influence of the external environment on pressure measurement. The document "3D printed multicore fiber-tip discriminative sensor for magnetic field and temperature measurements" proposes a 3D printed multicore fiber-tip discriminative sensor for magnetic field and temperature measurements. A bowl-shaped micro-cantilever and a polymer micro-fluid permeation micro-cavity are prepared on the end faces of two cores of a multicore optical fiber by two-photon polymerization 3D printing technology, forming two FP cavities that exhibit different sensitivities to magnetic field and temperature. The multi-parameter sensitivity coefficient matrix is calculated to distinguish between magnetic field and temperature measurements.

[0006] However, these methods have the following defects and deficiencies: although the measurement accuracy can be improved by multi-parameter separation or temperature compensation in theory, the technical implementation generally relies on multi-device integration or complex micro-nano processing technology, which faces engineering challenges such as complex manufacturing process and multi-signal synchronous solution accuracy. SUMMARY

[0007] In view of the defects of the prior art, the purpose of the present application is to provide an interference optical fiber accelerometer probe and system that can suppress temperature cross-sensitivity, aiming to solve the problem of cross-sensitivity between acceleration and temperature in optical fiber sensors.

[0008] The first aspect of the present application relates to an interference optical fiber accelerometer probe that can suppress temperature cross-sensitivity, comprising an optical fiber head, a spring group, and a heterogeneous mirror. The heterogeneous mirror is composed of a first mirror and a second mirror in parallel in the optical path. The two mirrors have different thermal expansion coefficients, and they form a heterogeneous double-cavity Fabry-Perot interference cavity with the optical fiber end face of the optical fiber head. The equivalent cavity lengths of the two Fabry-Perot cavities are different. The size of the spring group matches the diameter of the optical fiber. One end is fixed on the optical fiber end face of the optical fiber head, and the other end is connected to the heterogeneous step mirror, forming a spring-mass system.

[0009] Preferably, the step boundary line of the heterogeneous mirror is parallel to the optical fiber end face and within the beam cross-section, and the step side wall is perpendicular to the optical fiber end face.

[0010] Preferably, the first mirror and the second mirror are both parallel to the fiber end face, and the first distance is not equal to the second distance, the first distance being the vertical distance between the first mirror and the fiber end face, and the second distance being the vertical distance between the second mirror and the fiber end face.

[0011] Preferably, the absolute value of the difference between the first distance and the second distance ranges from 1 m-300μm.

[0012] It should be noted that the above preferred embodiments of the present application can ensure that the spatial frequency corresponding to the peak value in the fast Fourier transform curve is separated, and is adapted to the two-photon polymerization 3D printing technology.

[0013] Preferably, the spring set is prepared on the fiber end face of the fiber head by a 3D printing technology.

[0014] It should be noted that the above preferred embodiments of the present application have the characteristics of high precision and customizability, and can realize rapid manufacturing of complex micro-nano structures, thereby ensuring high performance and high reliability of the micro-nano spring set.

[0015] Preferably, the springs in the spring set are symmetrically distributed on the fiber end face, and the number ranges from 1 to 6.

[0016] It should be noted that the above preferred embodiments of the present application can balance the load, keep the heterogeneous stepped mirror horizontal, avoid overly complex structure or unnecessary weight increase, and maintain the flexibility and stability of the structure.

[0017] Preferably, the reflecting surface of the first mirror is coated with a thin film material with a reflectivity of 0.04-1, the reflecting surface of the second mirror is coated with a thin film material with a reflectivity of 0.04-1, and the fiber end face of the fiber head is coated with a thin film material with a reflectivity of 0.03-1.

[0018] It should be noted that the high-reflectivity coating material can effectively reflect the light signal, interfere with the reflected light from the end face to form a beat frequency signal, thereby realizing measurement of the cavity length, and improving the light utilization rate and the spectral resolution of the system.

[0019] The second aspect of the present application relates to a fiber-optic accelerometer system capable of inhibiting temperature cross-sensitivity, comprising a detection light source, an optical module, a fiber-optic accelerometer probe as described in the first aspect, and a photoelectric detection demodulation module; the detection light source is configured to provide a wide-spectrum laser as incident light; the optical module comprises three ports, the first port is connected to the detection light source, the second port is connected to the fiber-optic accelerometer probe, and the third port is connected to the photoelectric detection demodulation module; the incident light enters the optical module through the first port, enters the fiber-optic accelerometer probe through the second port, and is configured to form first reflected light through the fiber end face of the fiber-optic head, form second reflected light through the first mirror after transmission through the fiber end face, and form third reflected light through the second mirror; the first reflected light, the second reflected light, and the third reflected light interfere with each other to form interference light, and the superimposed interference light signal is output to the third port through the second port and then enters the photoelectric detection demodulation module; the photoelectric detection demodulation module is configured to detect the light intensity of the superimposed interference signal, demodulate the acceleration information of the object to be measured and the temperature information of the surrounding environment, and deduct the temperature information of the surrounding environment from the acceleration information in the demodulation process to remove the temperature cross-sensitivity.

[0020] Preferably, the photoelectric detection demodulation module realizes demodulation by the following method: acquiring the spatial frequency of the fast Fourier transform curve of the reference light signal and the measured interference optical signal respectively; calculating the two initial cavity lengths of the heterogeneous double-cavity parallel Fabry-Perot interference cavity according to the spatial frequency of the reference light signal, and calculating the two actual cavity lengths of the heterogeneous double-cavity parallel Fabry-Perot interference cavity according to the spatial frequency of the measured interference optical signal; calculating the two cavity length change values of the heterogeneous double-cavity parallel Fabry-Perot interference cavity; and the two cavity length change values are corrected by a sensitivity coefficient matrix to obtain the acceleration signal of the object to be measured and the ambient temperature noise.

[0021] Preferably, the sensitivity coefficient matrix is as follows:

[0022] wherein, is the external acceleration, is the change in ambient temperature, the sensitivity coefficients of the first distance and the second distance to acceleration are the same and are denoted as , the sensitivity coefficients of the first distance and the second distance to temperature are different and are denoted as , , the two cavity length change values are denoted as and .

[0023] Overall, compared with the prior art, the above technical solutions conceived by the present application have the following beneficial effects: (1) The application provides an interferometric fiber accelerometer probe capable of inhibiting temperature cross-sensitivity, comprising a fiber head, a spring set and a heterogeneous mirror; the heterogeneous mirror is composed of a first mirror and a second mirror connected in parallel in the optical path, the two mirrors have different thermal expansion coefficients, and the fiber head and the fiber end face of the fiber head form a heterogeneous double-cavity Fabry-Perot interference cavity, and the equivalent two Fabry-Perot cavities have different cavity lengths; the size of the spring set matches the diameter of the fiber, one end is fixed on the fiber end face of the fiber head, and the other end is connected with the heterogeneous step mirror to form a spring-mass system. The application utilizes the different thermal expansion coefficients of the first mirror and the second mirror to realize differential detection of temperature changes. When the environmental temperature changes, the displacements of the two mirrors are different, and through the established matrix relationship, the acceleration signal and the temperature noise can be effectively separated, and the temperature cross-sensitivity problem can be significantly inhibited. In addition, the system can simultaneously detect acceleration and temperature changes, realize multi-parameter measurement function, expand the application range in complex environment, and is suitable for scenes requiring high-precision acceleration measurement and temperature monitoring. The probe structure is compact, realizing highly integrated design, which not only reduces the volume of the probe (the radius reaches millimeter level), facilitates installation and application, but also reduces the manufacturing cost.

[0024] (2) The application provides a fiber accelerometer system capable of inhibiting temperature cross-sensitivity, and the heterogeneous double-cavity parallel Fabry-Perot interference structure utilizes the difference between the two equivalent cavity lengths, which not only improves the measurement accuracy, but also simplifies the signal demodulation process. The system uses a wide-spectrum light source to provide stable light signals, and combines with fast Fourier transform (FFT) demodulation technology, so that the cavity length change information can be quickly and accurately extracted, and the real-time performance and measurement accuracy of the system are further improved, meeting the demand of high-precision acceleration measurement. In addition, through temperature compensation and signal decoupling technology, the system can adapt to a wide temperature range of working environment, significantly enhancing the stability and reliability of the system in extreme environment, and being suitable for harsh application scenes such as aerospace and earthquake monitoring. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 is a structure schematic diagram of an interferometric fiber accelerometer probe provided by an embodiment of the application.

[0026] Figure 2 is a cross-sectional view of the interferometric fiber accelerometer probe provided by the application.

[0027] Figure 3 is a structure schematic diagram of a heterogeneous step mirror provided by an embodiment of the application.

[0028] Figure 4 is a structure schematic diagram of a fiber accelerometer system provided by an embodiment of the application.

[0029] Figure 5 is a reference light and measured light comparison schematic provided by the embodiment of the application when the external acceleration changes and the ambient temperature is constant, wherein (a) is a light intensity signal comparison schematic, and (b) is a Fourier transform schematic corresponding to the light intensity signal.

[0030] Figure 6 is a reference light and measured light comparison schematic provided by the embodiment of the application when the external acceleration is constant and the ambient temperature changes, wherein (a) is a light intensity signal comparison schematic, and (b) is a Fourier transform schematic corresponding to the light intensity signal.

[0031] Figure 7 is a reference light and measured light comparison schematic provided by the embodiment of the application when the external acceleration and the ambient temperature change simultaneously, wherein (a) is a light intensity signal comparison schematic, and (b) is a Fourier transform schematic corresponding to the light intensity signal.

[0032] In all the drawings, the same reference signs are used to represent the same elements or structures, wherein: 1 is a detection light source, 2 is an optical module, 3 is an interference optical fiber accelerometer probe, 4 is a photoelectric detection demodulation module, 5 is an optical fiber head, 6 is a micro-nano spring set, 7 is a second mirror, 8 is a first mirror, and 9 is a heterogeneous step mirror. DETAILED DESCRIPTION

[0033] In order to make the purpose, technical scheme and advantages of the application more clear, the application is further described in detail below in combination with the drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the application and not to limit the application.

[0034] The embodiments of the application are described below in combination with the drawings in the embodiments of the application.

[0035] In a first aspect, the application provides an interference optical fiber accelerometer probe capable of suppressing temperature cross-sensitivity, comprising an optical fiber head, a spring set and a heterogeneous mirror; the heterogeneous mirror is composed of a first mirror and a second mirror in parallel in the optical path, the two mirrors have different thermal expansion coefficients, and the mirrors and the optical fiber end face of the optical fiber head form a heterogeneous double-cavity Fabry-Perot interference cavity, and the equivalent two Fabry-Perot cavities have different cavity lengths; the size of the spring set matches the diameter of the optical fiber, one end is fixed on the optical fiber end face of the optical fiber head, and the other end is connected to the heterogeneous step mirror to form a spring-mass system.

[0036] Preferably, the step boundary line of the heterogeneous mirror is parallel to the optical fiber end face and within the cross section of the light beam, and the step side wall is perpendicular to the optical fiber end face.

[0037] Preferably, the first mirror and the second mirror are both parallel to the fiber end face, and the first distance is not equal to the second distance, the first distance being the vertical distance between the first mirror and the fiber end face, and the second distance being the vertical distance between the second mirror and the fiber end face.

[0038] Preferably, the absolute value of the difference between the first distance and the second distance ranges from 1 μm to 300 μm.

[0039] Preferably, the spring group is prepared on the fiber end face of the fiber head by a 3D printing technology.

[0040] Preferably, the springs in the spring group are symmetrically distributed on the fiber end face, and the number of the springs ranges from 1 to 6.

[0041] Preferably, the wire diameter of the micro-nano spring is 1 μm to 15 μm, the pitch is 10 μm to 100 μm, the free length is 50 μm to 1000 μm, and the spring diameter is 50 μm to 150 μm. The low stiffness of the micro-nano spring makes the device more sensitive to external acceleration. By changing the size parameters of the micro-nano spring, the device can achieve high sensitivity detection in different frequency ranges.

[0042] Preferably, the reflecting surface of the first mirror is coated with a thin film material with a reflectivity of 0.04 to 1, and the reflecting surface of the second mirror is coated with a thin film material with a reflectivity of 0.04 to 1.

[0043] In a second aspect, the application provides a fiber accelerometer system capable of inhibiting temperature cross-sensitivity, comprising a detection light source, an optical module, a fiber accelerometer probe as described in the first aspect, and a photoelectric detection demodulation module; the detection light source is configured to provide a wide-spectrum laser as incident light; the optical module comprises three ports, the first port is connected to the detection light source, the second port is connected to the fiber accelerometer probe, and the third port is connected to the photoelectric detection demodulation module; the incident light enters the optical module through the first port, and is input into the fiber accelerometer probe through the second port; the fiber accelerometer probe is configured to form first reflected light through the fiber end face of the fiber head, and to form second reflected light through the first mirror and third reflected light through the second mirror after the fiber end face transmits the other part of the light; the first reflected light, the second reflected light, and the third reflected light interfere with each other to form interference light, and the superimposed interference signal is output to the third port through the second port and then enters the photoelectric detection demodulation module; the photoelectric detection demodulation module is configured to detect the light intensity of the superimposed interference signal, demodulate the acceleration information of the object to be measured and the temperature information of the surrounding environment, and deduct the temperature information of the surrounding environment from the acceleration information in the demodulation process, thereby removing the temperature cross-sensitivity.

[0044] Preferably, the photoelectric detection demodulation module realizes demodulation by the following way: obtaining the spatial frequency of the fast Fourier transform curve of the reference light signal and the measured interference optical signal respectively; according to the spatial frequency of the reference light signal, solving the two initial cavity lengths of the heterogeneous double-cavity parallel Fabry-Perot interference cavity; according to the spatial frequency of the measured interference optical signal, solving the two actual cavity lengths of the heterogeneous double-cavity parallel Fabry-Perot interference cavity; calculating the two cavity length change values of the heterogeneous double-cavity parallel Fabry-Perot interference cavity; the two cavity length change values are corrected by the sensitivity coefficient matrix to obtain the acceleration signal of the measured object and the ambient temperature noise.

[0045] The reference light signal is the signal transmitted by the fiber-optic accelerometer probe when the heterogeneous echelle mirror is located at the reference point position. The reference point position is measured when the acceleration is zero and the environment is stable and constant, at which time the measured object is not introduced.

[0046] The measured interference optical signal is obtained by fixing the fiber-optic accelerometer probe on the measured object to realize vibration acceleration measurement.

[0047] Preferably, the sensitivity coefficient matrix is as follows:

[0048] wherein, is the external acceleration, is the ambient temperature change, the sensitivity coefficients of the first distance and the second distance to the acceleration are the same, denoted as , the sensitivity coefficients of the first distance and the second distance to the temperature are different, denoted as , , the two cavity length change values are denoted as and .

[0049] Preferably, the detection light source is a wide-spectrum light source, which has the advantage of covering a wider wavelength range to provide a wide-spectrum laser. Of course, other detection light sources can also be selected according to requirements.

[0050] Preferably, the optical module is a fiber-optic circulator, which has the functions of inputting the laser emitted by the wide-spectrum light source into the fiber-optic accelerometer probe, inputting the light signal reflected by the fiber-optic accelerometer probe into the photoelectric detection demodulation module, and has the advantages of low transmission loss, high echo loss, light signal isolation, etc. It can also be a waveguide structure or other optical structure with the function of a fiber-optic circulator.

[0051] Preferably, the end face of the second port is the fiber end face of the fiber head, and the surface is coated with a first thin film material having a reflectivity of 0.03-1. The reflectivity of the thin film material directly affects the loss of the detection light and the signal strength received by the photodetector. Increasing the reflectivity of the thin film material can effectively reduce the loss of the detection light, enhance the signal strength, and thus improve the detection accuracy and reduce the noise. When the optical module is a waveguide structure or other optical structure, the port end face can be selected as a fiber end face or an end face structure of other light transmission medium according to the design needs.

[0052] Embodiments As shown in Figure 1 and Figure 2 , the embodiment provides an interference fiber accelerometer probe 3 capable of suppressing temperature cross-sensitivity, which comprises a fiber head 5, a micro-nano spring group 6, and a heterogeneous step mirror 9.

[0053] The mode field diameter of the fiber head 5 is 10.2 μm, and the reflectivity of the fiber end face of the fiber head 5 is selected to be 0.06. The reflectivity of the heterogeneous step mirror 9 fixed on the object to be measured is selected to be 0.06. The fiber end face of the fiber head 5 and the heterogeneous step mirror 9 are placed in parallel, the central axis of the fiber head is placed opposite to the step boundary position of the heterogeneous step mirror, and the two are connected by four symmetrically placed springs, with a medium refractive index of = 1. When the external acceleration is 0, at room temperature, the distances between the fiber end face of the fiber head 5 and the first reflecting surface and the second reflecting surface of the heterogeneous step mirror 9 are selected to be 250 μm and 300 μm, respectively. The sensitivity coefficients of the first vertical distance and the second vertical distance to acceleration are 3.83 μm / mg, the sensitivity coefficient of the first vertical distance to temperature is 1.38 μm / ℃, and the sensitivity coefficient of the second vertical distance to temperature is 0.23 μm / ℃. The heterogeneous step mirror and the fiber end face of the fiber head form a heterogeneous double-cavity Fabry-Perot interference cavity, and the optical signal passes through the two equivalent cavities simultaneously.

[0054] As shown in Figure 3 , the two mirrors in the heterogeneous step mirror 9 are different in height, forming a step shape, so that the reflected light is not symmetrical up and down in the plane. The beat frequency signal is formed by the asymmetric reflected light and the reflected light of the fiber end face, and the cavity length of the two FP cavities can be calculated by demodulating the beat frequency signal. Specifically, the first mirror 8 is semicircular, the second mirror 7 is circular, the thickness of the first mirror 8 is greater than that of the second mirror 7, and the thermal expansion coefficient of the first mirror 8 is greater than that of the second mirror 7. After the two mirrors are processed, they are nested together, i.e., the semilunar mirror is nested in the middle position of the circular mirror, forming a circular step shape opposite to the fiber end face.

[0055] The micro-nano spring group 6 and the heterogeneous step mirror constitute a spring-mass system. The spring-mass system is generally composed of a spring, a test mass, and damping caused by air or structure. In the embodiment, the micro-nano spring group plays the role of the spring, the heterogeneous step mirror is the test mass, and the air resistance is the damping. According to Newton's second law, the kinematic equation of the test mass can be expressed as:

[0056] wherein, is the mass of the test mass, is the displacement of the test mass, is the damping coefficient, is the spring stiffness coefficient, is the external input acceleration.

[0057] The Laplace transform is performed on the above formula, and the amplitude-frequency response characteristics of the mass are obtained as:

[0058] wherein, is the angular frequency of the external acceleration, is the intrinsic angular frequency of the spring-mass system. When , the relationship between the external acceleration and the displacement of the test mass satisfies:

[0059] The acceleration signal of the spring-mass system can be converted into the displacement signal of the test mass for measurement.

[0060] The basic principle of suppressing temperature cross-sensitivity of the application is as follows: When only the external acceleration exists, the first mirror and the second mirror of the heterogeneous step mirror move by the same distance, so that the change amounts of the first vertical distance and the second vertical distance are the same, denoted as ; therefore, the sensitivity coefficients of the first vertical distance and the second vertical distance to the acceleration are the same, denoted as (the factory calibration), and .

[0061] When only the environmental temperature change exists, the first mirror and the second mirror of the heterogeneous step mirror move by the same distance, and because the material thermal expansion coefficients of the first mirror and the second mirror are different, the change amounts of the first vertical distance and the second vertical distance are different, denoted as and ; therefore, the sensitivity coefficients of the first vertical distance and the second vertical distance to the temperature are different, denoted as , (Factory calibrated), and , .

[0062] When the external acceleration and the ambient temperature change exist at the same time, the first mirror and the second mirror of the heterogeneous step mirror move different distances, and the change amounts of the first vertical distance and the second vertical distance are different, which are respectively denoted as and At this time, the external acceleration and the ambient temperature change can be obtained by solving the following matrix relationship, and the temperature information of the surrounding environment is deducted from the acceleration information to achieve the goal of removing the temperature cross-sensitivity:

[0063] As shown in Figure 4 , the embodiment also provides a fiber-optic accelerometer system capable of suppressing temperature cross-sensitivity, which comprises a detection light source 1, an optical module 2, an interference fiber-optic accelerometer probe 3, and a photoelectric detection demodulation module 4. The wavelength range of the detection light source 1 is set to 1500 nm to 1600 nm, and the output optical power is selected to be 1 mW. The optical module 2 is a fiber-optic circulator, which controls the one-way transmission of the optical signal on one hand and separates the input light and the output light signal on the other hand. It comprises a first port, a second port, and a third port; the first port is connected to the detection light source 1, the second port is connected to the displacement detection module fiber-optic accelerometer probe 3, and the third port is connected to the photoelectric detection demodulation module 4. The input light of the first port is output through the second port, the reflected light of the end face of the second port interferes with the reflected light of the reflection surface of the fiber-optic accelerometer probe to form a beat frequency signal, which is then output to the photoelectric detection demodulation module through the third port; the photoelectric detection demodulation module 4 is used to convert the optical signal into an electrical signal and then perform fast Fourier transform to obtain the spatial frequency of the curve, calculate the cavity length of the heterogeneous double-cavity parallel Fabry-Perot interference cavity in the fiber-optic sensing probe according to the spatial frequency, and further obtain the acceleration signal of the measured object and the ambient temperature noise.

[0064] To verify the function of the above fiber-optic accelerometer system, the reflected light electric field generated by the end face of the second port is expressed as:

[0065] The reflected light electric field generated by the reflection surface of the fiber-optic accelerometer probe is expressed as:

[0066] Among them, represents the reflected light electric field through the first mirror, represents the reflected light electric field through the second mirror.

[0067] The signal optical field output by the third port of the optical module 2 is represented as:

[0068] wherein, is the electric field of the incident light, , are the reflectivities of the fiber end face of the second port and the heterogeneous step mirror of the fiber accelerometer probe respectively, is the refractive index of the medium between the fiber end face and the heterogeneous step mirror, is the wavelength of the incident light, is the vertical distance between the fiber end face and the first reflecting surface of the heterogeneous step mirror, is the vertical distance between the fiber end face and the second reflecting surface of the heterogeneous step mirror.

[0069] The output light intensity (beat signal) of the photodetector module is represented as a function of the optical frequency:

[0070] The above output light intensity is regarded as a function of the reciprocal of the wavelength of the incident light , and a fast Fourier transform is performed, and the spatial frequencies of the fast Fourier transform curve are , , When the vertical distances between the first reflecting surface and the second reflecting surface of the heterogeneous step mirror and the fiber end face of the fiber head , change, the change amount of the spatial frequencies of the Fourier transform curve relative to the reference point is measured to obtain the change values of the two cavity lengths of the heterogeneous double-cavity parallel Fabry-Perot interference structure , . The cavity length change values , are substituted into the following sensitivity coefficient matrix for correction to obtain the acceleration of the object to be measured and the change of the ambient temperature .

[0071]

[0072] As can be seen from the above, the application effectively separates the acceleration signal and the temperature noise, and significantly suppresses the temperature cross-sensitivity problem.

[0073] As Figure 5As shown in (a), both the reference light intensity signal and the measured light intensity signal exhibit obvious beat frequency effects in their spectra. Fast Fourier Transform (FFT) reveals that both signals contain four peaks in their spectra, arranged from low to high frequency: DC signal, interference signal between reflected light from the first and second reflecting surfaces, interference signal between reflected light from the fiber end face and the first reflecting surface, and interference signal between reflected light from the fiber end face and the second reflecting surface. Figure 5 As shown in (b), for the reference light intensity signal, at this time = 0mg, the spatial frequencies corresponding to the last two peaks in the Fast Fourier Transform (FFT) spectrum are 500.00μm and 600.00μm, respectively; for the measured light intensity signal, keeping the ambient temperature constant and applying external acceleration, the spatial frequencies corresponding to the last two peaks in the FFT spectrum are 510.96μm and 610.96μm, respectively. Comparing the spatial frequencies of the FFT curves of the two light intensity signals, the change in the length of both cavities of the heterogeneous dual-cavity parallel Fabry-Perot interferometer structure is found to be 5.48μm. Substituting this into the sensitivity coefficient matrix for correction, the acceleration of the object under test is obtained as 1.43mg, and the ambient temperature change is 0℃.

[0074] like Figure 6 As shown in (a), both the reference light intensity signal and the measured light intensity signal exhibit obvious beat frequency effects in their spectra. Fast Fourier Transform (FFT) reveals that both signals contain four peaks in their spectra, arranged from low to high frequency: DC signal, interference signal between reflected light from the first and second reflecting surfaces, interference signal between reflected light from the fiber end face and the first reflecting surface, and interference signal between reflected light from the fiber end face and the second reflecting surface. Figure 6 As shown in (b), for the reference light intensity signal, at this time At 0℃, the spatial frequencies corresponding to the last two peaks in the Fast Fourier Transform (FFT) spectrum are 500.00μm and 600.00μm, respectively. For the measured light intensity signal, changing the ambient temperature while keeping the external acceleration constant, the spatial frequencies corresponding to the last two peaks in the FFT spectrum are 494.60μm and 599.10μm, respectively. Comparing the spatial frequencies of the FFT curves of the two light intensity signals, the changes in the lengths of the two cavities of the heterogeneous dual-cavity parallel Fabry-Perot interferometer structure are obtained as 2.70μm and 0.45μm, respectively. Substituting these values ​​into the sensitivity coefficient matrix for correction, the acceleration of the object under test is found to be 0mg, and the ambient temperature change is 1.96℃.

[0075] like Figure 7As shown in (a), both the reference light intensity signal and the measured light intensity signal exhibit obvious beat frequency effects in their spectra. Fast Fourier Transform (FFT) reveals that both signals contain four peaks in their spectra, arranged from low to high frequency: DC signal, interference signal between reflected light from the first and second reflecting surfaces, interference signal between reflected light from the fiber end face and the first reflecting surface, and interference signal between reflected light from the fiber end face and the second reflecting surface. Figure 7 As shown in (b), for the reference light intensity signal, at this time = 0mg、 At 0℃, the spatial frequencies corresponding to the last two peaks in the Fast Fourier Transform (FFT) spectrum are 500.00μm and 600.00μm, respectively. For the measured light intensity signal, with simultaneous changes in ambient temperature and external acceleration, the spatial frequencies corresponding to the last two peaks in the FFT spectrum are 512.30μm and 618.46μm, respectively. Comparing the spatial frequencies of the FFT curves of the two light intensity signals, the changes in the lengths of the two cavities of the heterogeneous dual-cavity parallel Fabry-Perot interferometer structure are obtained as 6.15μm and 9.23μm, respectively. Substituting these values ​​into the sensitivity coefficient matrix for correction, the acceleration of the object under test is found to be 2.57mg, and the change in ambient temperature is 2.68℃.

[0076] It should be understood that expressions such as “comprising” and “may include” used in this application indicate the existence of the disclosed functions, operations, or constituent elements, and do not limit one or more additional functions, operations, and constituent elements. In this application, terms such as “comprising” and / or “having” are to be interpreted as indicating a particular characteristic, number, operation, constituent element, component, or combination thereof, but not to exclude the existence or possibility of adding one or more other characteristics, numbers, operations, constituent elements, components, or combinations thereof.

[0077] Furthermore, in this application, the expression "and / or" includes any and all combinations of the associated listed words. For example, the expression "A and / or B" may include A, may include B, or may include both A and B.

[0078] In the description of the embodiments of the present application, it should be noted that unless otherwise clearly specified and limited, the term "connection" should be understood broadly, for example, "connection" can be detachable connection, or can be non-detachable connection; can be direct connection, or can be indirect connection through intermediate medium. Among them, "fixed connection" refers to the relative position relationship after connection is unchanged. "Rotary connection" refers to the relative rotation after connection. "Sliding connection" refers to the relative sliding after connection. The orientation language mentioned in the embodiments of the present application, such as "top", "bottom", "inner", "outer", "left", "right", etc., is only the direction of the drawing, therefore, the orientation language used is to better, more clearly illustrate and understand the embodiments of the present application, and is not indicative or implied that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, therefore, it cannot be understood as a limitation on the embodiments of the present application.

[0079] In addition, in the embodiments of the present application, the mathematical concepts mentioned, such as symmetry, equality, parallel, perpendicular, etc. These limitations are all for the current process level, and are not strictly defined in the mathematical sense, and a small amount of deviation is allowed, such as approximately symmetric, approximately equal, approximately parallel, approximately perpendicular, etc. For example, A is parallel to B, which means that A and B are parallel or approximately parallel, and the included angle between A and B can be between 0 degrees and 10 degrees. A is perpendicular to B, which means that A and B are perpendicular or approximately perpendicular, and the included angle between A and B can be between 80 degrees and 100 degrees.

[0080] The above is only a specific implementation of the present application, but the protection scope of the present application is not limited thereto, any person skilled in the art can easily think of changes or replacements within the technical range disclosed by the present application, which should be covered within the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.

Claims

1. An interferometric fiber optic accelerometer probe capable of suppressing temperature cross-sensitivity, characterized in that, Includes fiber optic connectors, spring assemblies, and heterogeneous reflectors; The heterogeneous mirror consists of a first mirror and a second mirror connected in parallel in the optical path. The two mirrors have different coefficients of thermal expansion. Together with the fiber end face of the fiber head, they form a heterogeneous dual-cavity parallel Fabry-Perot interference cavity. The two equivalent Fabry-Perot cavities have different cavity lengths. The size of the spring assembly matches the diameter of the optical fiber. One end is fixed to the end face of the optical fiber head, and the other end is connected to the heterogeneous stepped reflector, forming a spring-oscillator system.

2. The interferometric fiber optic accelerometer probe as described in claim 1, characterized in that, The stepped boundary line of the heterogeneous mirror is parallel to the fiber end face and within the beam cross-section, while the stepped sidewall is perpendicular to the fiber end face.

3. The interferometric fiber optic accelerometer probe as described in claim 2, characterized in that, Both the first and second reflectors are parallel to and directly opposite the fiber end face, and the first distance is not equal to the second distance. The first distance is the vertical distance between the first reflector and the fiber end face, and the second distance is the vertical distance between the second reflector and the fiber end face.

4. The interferometric fiber optic accelerometer probe as described in claim 3, characterized in that, The absolute value of the difference between the first distance and the second distance ranges from 1μm to 300μm.

5. The interferometric fiber optic accelerometer probe as described in claim 1, characterized in that, The spring assembly is fabricated on the fiber end face of the fiber optic head using 3D printing technology.

6. The interferometric fiber optic accelerometer probe as described in claim 1, characterized in that, The springs in the spring group are symmetrically distributed on the end face of the optical fiber, and the number ranges from 1 to 6.

7. The interferometric fiber optic accelerometer probe as described in claim 1, characterized in that, The reflective surface of the first reflector is coated with a thin film material with a reflectivity of 0.04-1, the reflective surface of the second reflector is coated with a thin film material with a reflectivity of 0.04-1, and the fiber end face of the fiber head is coated with a thin film material with a reflectivity of 0.03-1.

8. A fiber optic accelerometer system capable of suppressing temperature cross-sensitivity, characterized in that, Includes a detection light source, an optical module, a fiber optic accelerometer probe as described in any one of claims 1 to 7, and a photoelectric detection and demodulation module; The detection light source is configured to provide a broadband laser as the incident light; The optical module includes three ports: the first port is connected to the detection light source, the second port is connected to the fiber optic accelerometer probe, and the third port is connected to the photoelectric detection and demodulation module. The incident light enters the optical module through the first port and is input to the fiber optic accelerometer probe through the second port. It is configured such that: part of the light is reflected as first reflected light through the fiber end face of the fiber optic head, and the other part is reflected as second reflected light and third reflected light through the first and second mirrors respectively after being transmitted through the fiber end face. The first, second, and third reflected lights interfere with each other to form interference light. The superimposed interference light signal is output through the second port to the third port and then enters the photoelectric detection and demodulation module. The photoelectric detection and demodulation module is configured to detect the light intensity of the superimposed interference signal, demodulate the acceleration information of the object under test and the temperature information of the surrounding environment, and subtract the temperature information of the surrounding environment from the acceleration information during the demodulation process to remove temperature cross-sensitivity.

9. The fiber optic accelerometer system as described in claim 8, characterized in that, The photoelectric detection demodulation module achieves demodulation in the following manner: The spatial frequencies of the fast Fourier transform curves of the reference optical signal and the measured interferometric optical signal are obtained respectively. Based on the spatial frequency of the reference optical signal, the two initial cavity lengths of the heterogeneous dual-cavity parallel Fabry-Perot interferometer are calculated, and based on the spatial frequency of the measured interference optical signal, the two actual cavity lengths of the heterogeneous dual-cavity parallel Fabry-Perot interferometer are calculated. Calculate the changes in the lengths of the two cavity components of a heterogeneous dual-cavity parallel Fabry-Perot interferometer cavity; The two cavity length changes are corrected by the sensitivity coefficient matrix to obtain the acceleration signal of the object under test and the ambient temperature noise.

10. The fiber optic accelerometer system as described in claim 9, characterized in that, The sensitivity coefficient matrix is ​​as follows: in, Accelerating the external environment, For changes in ambient temperature, the sensitivity coefficients of the first and second distances to acceleration are the same, denoted as . The sensitivity coefficients of the first and second distances to temperature are different, and are denoted as follows: , The changes in the lengths of the two cavities are denoted as follows: and .

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