An interferometric fiber optic accelerometer probe and system capable of suppressing temperature cross-sensitivity

Abstract

This application belongs to the field of fiber optic interferometry, specifically disclosing an interferometric fiber optic accelerometer probe and system that can suppress temperature cross-sensitivity. The fiber optic accelerometer probe includes an optical fiber head, a spring assembly, and a heterogeneous reflector. This application utilizes the difference in thermal expansion coefficients between the first and second reflectors in the heterogeneous reflector to achieve differential detection of temperature changes. The optical fiber end face and the heterogeneous reflector form a heterogeneous dual-cavity parallel Fabry-Perot interferometer structure. When external acceleration and ambient temperature change simultaneously, the difference in the changes of the two equivalent cavity lengths, through the established matrix relationship, can effectively separate the acceleration signal and temperature noise, significantly suppressing the temperature cross-sensitivity problem, improving measurement accuracy, and simplifying the signal demodulation process. Through temperature compensation and signal decoupling technology, the system can adapt to a wide temperature range operating environment, enhancing its stability and reliability in extreme environments, making it suitable for harsh applications such as aerospace and earthquake monitoring.

Description

Technical Field

[0001] This application belongs to the field of fiber optic interferometry, and more specifically, relates to an interferometric fiber optic accelerometer probe and system that can suppress temperature cross-sensitivity. Background Technology

[0002] High-precision accelerometers have wide applications in various fields such as mechanical manufacturing, aerospace, earthquake monitoring, and vehicle safety testing. Accurate measurement of acceleration information is required to ensure navigation and control precision, and vehicle crash tests need to accurately record acceleration changes to assess safety performance. Fiber optic 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] The Fabry-Perot interferometer (FPI) is widely used in fiber optic accelerometers due to its simple structure, high sensitivity, and strong common-mode noise suppression capabilities. Its structure typically consists of a single-mode fiber endface and an external inertial mass reflector. When the object being measured accelerates, the relative displacement between the inertial mass and the fiber endface changes the cavity length of the FPI, causing a change in the phase difference between the light reflected from the fiber endface and the light reflected from the inertial mass, resulting in interference within the fiber. By demodulating the phase change through wavelength demodulation and intensity demodulation, acceleration information can be accurately obtained.

[0004] In practical applications, accelerometers based on intrinsic fiber Fabry-Perot interferometers (FPI) suffer from thermal expansion or contraction of the inertial mass material due to ambient temperature fluctuations. This leads to changes in the length of the interferometer cavity and introduces displacement measurement errors, limiting the accelerometer's measurement accuracy and stability. Temperature stability is one of the core challenges faced by fiber Fabry-Perot accelerometers. "Temperature cross-sensitivity" refers to the phenomenon where some sensors, when measuring a certain physical quantity, are affected by temperature changes, making it impossible to accurately distinguish between the physical quantity and the individual effects of temperature on the measurement signal.

[0005] To address the issue of cross-sensitivity of fiber optic pressure sensors (FPS) to temperatures, existing technologies have proposed several solutions. Patent CN115950578A discloses a fiber optic FPS pressure sensor and a pressure detection method. The fiber optic FPS pressure sensor includes a fiber optic probe, a sensitive diaphragm, and a fiber optic grating. One end of the fiber optic probe forms an FP cavity with the sensitive diaphragm. The deformation of the sensitive diaphragm is obtained based on the length change of the FP cavity. The fiber optic grating senses the ambient temperature of the sensitive diaphragm, thereby determining its pressure sensitivity. Combining the deformation of the sensitive diaphragm with its pressure sensitivity to calculate the external pressure value can improve the accuracy of pressure measurement and reduce the influence of the external environment on pressure measurement. The literature "3D printed multicore fiber-tip discriminative sensor for magnetic field and temperature measurements" proposes a 3D-printed multicore fiber tip discrimination sensor for magnetic field and temperature measurement. Using two-photon polymerization 3D printing technology, a bowl-shaped microcantilever beam and a polymer microfluidic permeation microcavity are fabricated on the two core end faces of a multicore fiber, forming two FP cavities exhibiting different sensitivities to magnetic fields and temperatures. The measurement of magnetic fields and temperatures is distinguished by calculating a multi-parameter sensitivity coefficient matrix.

[0006] However, these methods have the following drawbacks and shortcomings: although in theory, measurement accuracy can be improved through multi-parameter separation or temperature compensation, their technical implementation generally relies on multi-device integration or complex micro-nano fabrication technology, and faces engineering challenges such as complex manufacturing processes and the accuracy of multi-signal synchronous solution. Summary of the Invention

[0007] To address the shortcomings of existing technologies, the purpose of this application is to provide an interferometric fiber optic accelerometer probe and system that can suppress temperature cross-sensitivity, aiming to solve the problem of cross-sensitivity between acceleration and temperature in fiber optic sensors.

[0008] The first aspect of this application relates to an interferometric fiber optic accelerometer probe capable of suppressing temperature cross-sensitivity, comprising an optical fiber head, a spring assembly, and a heterogeneous reflector; the heterogeneous reflector consists of a first reflector and a second reflector connected in parallel along the optical path, the two reflectors having different coefficients of thermal expansion, and together with the optical fiber end face of the optical fiber head, forming a heterogeneous dual-cavity parallel Fabry-Perot interferometer cavity, the equivalent cavity lengths of the two Fabry-Perot cavities being different; the size of the spring assembly matches the diameter of the optical fiber, one end is fixed to the optical fiber end face of the optical fiber head, and the other end is connected to the heterogeneous stepped reflector, forming a spring-oscillator system.

[0009] Preferably, the stepped boundary line of the heterogeneous reflector is parallel to the fiber end face and within the beam cross-section, and the stepped sidewall is perpendicular to the fiber end face.

[0010] Preferably, 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.

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

[0012] It should be noted that the above-mentioned preferred solution of this application can ensure that the peak corresponding to the spatial frequency in the fast Fourier transform curve is separated and is compatible with the two-photon polymerization 3D printing technology used.

[0013] Preferably, the spring assembly is fabricated on the fiber end face of the fiber optic head using 3D printing technology.

[0014] It should be noted that the above-mentioned preferred solution of this application has the characteristics of high precision and customizability, which can realize the rapid manufacturing of complex micro-nano structures and ensure the high performance and high reliability of micro-nano spring assemblies.

[0015] Preferably, 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.

[0016] It should be noted that the above-mentioned preferred solution of this application can achieve balanced load, keep the heterogeneous stepped reflector horizontal, and avoid the structure from being too complicated or adding unnecessary weight, thus maintaining the flexibility and stability of the structure.

[0017] Preferably, 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.

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

[0019] The second aspect of this application relates to a fiber optic accelerometer system capable of suppressing 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 broadband laser as incident light; the optical module includes three ports, a first port connected to the detection light source, a second port connected to the fiber optic accelerometer probe, and a third port connected to the photoelectric detection 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, configured such that a portion passes through the fiber optic head... The optical fiber end face forms the first reflected light, and another part is transmitted through the optical fiber end face to form the second reflected light through the first reflector and the third reflected light through the second reflector. 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 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 under test and the temperature information of the surrounding environment. In the demodulation process, the temperature information of the surrounding environment is subtracted from the acceleration information to remove temperature cross-sensitivity.

[0020] Preferably, the photoelectric detection demodulation module achieves demodulation in the following manner: acquiring the spatial frequencies of the fast Fourier transform curves of the reference optical signal and the measured interference optical signal respectively; calculating the two initial cavity lengths of the heterogeneous dual-cavity parallel Fabry-Perot interferometer based on the spatial frequency of the reference optical signal; calculating the two actual cavity lengths of the heterogeneous dual-cavity parallel Fabry-Perot interferometer based on the spatial frequency of the measured interference optical signal; calculating the changes in the two cavity lengths of the heterogeneous dual-cavity parallel Fabry-Perot interferometer; and correcting the two cavity length changes using a sensitivity coefficient matrix to obtain the acceleration signal of the object under test and the ambient temperature noise.

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

[0022]

[0023] 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 .

[0024] Overall, the technical solutions conceived in this application have the following beneficial effects compared with the prior art:

[0025] (1) This application provides an interferometric fiber optic accelerometer probe that can suppress temperature cross-sensitivity, including an optical fiber head, a spring assembly, and a heterogeneous reflector. The heterogeneous reflector consists of a first reflector and a second reflector connected in parallel on the optical path. The two reflectors have different coefficients of thermal expansion and together with the optical fiber end face of the optical fiber head, they form a heterogeneous dual-cavity parallel Fabry-Perot interferometer cavity, with the equivalent cavity lengths of the two Fabry-Perot cavities being different. The size of the spring assembly matches the diameter of the optical fiber. One end is fixed to the optical fiber end face of the optical fiber head, and the other end is connected to the heterogeneous stepped reflector, forming a spring-oscillator system. This application utilizes the difference in the coefficients of thermal expansion of the first and second reflectors to achieve differential detection of temperature changes. When the ambient temperature changes, the displacements of the two reflectors are different. Through the established matrix relationship, the acceleration signal and temperature noise can be effectively separated, significantly suppressing the temperature cross-sensitivity problem. In addition, the system can simultaneously detect acceleration and temperature changes, realize multi-parameter measurement functions, expand its application range in complex environments, and is suitable for scenarios requiring high-precision acceleration measurement and temperature monitoring. The probe has a compact structure and a highly integrated design, which not only reduces the probe size (radius on the order of millimeters), making it easier to install and apply, but also reduces manufacturing costs.

[0026] (2) This application provides a fiber optic accelerometer system that can suppress temperature cross-sensitivity. The heterogeneous dual-cavity parallel Fabry-Perot interferometer structure utilizes the difference in the lengths of the two equivalent cavities, which not only improves the measurement accuracy but also simplifies the signal demodulation process. The system uses a broadband light source to provide a stable optical signal and combines it with Fast Fourier Transform (FFT) demodulation technology to quickly and accurately extract cavity length change information, further improving the system's real-time performance and measurement accuracy, and meeting the requirements of high-precision acceleration measurement. In addition, through temperature compensation and signal decoupling technology, the system can adapt to a wide temperature range of operating environments, significantly enhancing its stability and reliability in extreme environments, making it suitable for harsh application scenarios such as aerospace and earthquake monitoring. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the structure of an interferometric fiber optic accelerometer probe that can suppress temperature cross-sensitivity, provided in an embodiment of this application.

[0028] Figure 2 This is a cross-sectional view of the interferometric fiber optic accelerometer probe provided in an embodiment of this application.

[0029] Figure 3 This is a schematic diagram of the heterogeneous stepped reflector structure provided in the embodiments of this application.

[0030] Figure 4 This is a schematic diagram of a fiber optic accelerometer system structure that can suppress temperature cross-sensitivity, provided in an embodiment of this application.

[0031] Figure 5 This is a schematic diagram comparing reference light and measured light under varying external acceleration and constant ambient temperature, provided in an embodiment of this application. (a) is a schematic diagram comparing light intensity signals, and (b) is a schematic diagram of the Fourier transform corresponding to the light intensity signals.

[0032] Figure 6 This is a schematic diagram comparing reference light and measured light when the external acceleration remains constant and the ambient temperature changes, provided in an embodiment of this application. (a) is a schematic diagram comparing light intensity signals, and (b) is a schematic diagram of the Fourier transform corresponding to the light intensity signals.

[0033] Figure 7 This is a schematic diagram comparing reference light and measured light when external acceleration and ambient temperature change simultaneously, provided in an embodiment of this application. (a) is a schematic diagram comparing light intensity signals, and (b) is a schematic diagram of the Fourier transform corresponding to the light intensity signals.

[0034] In all the accompanying drawings, the same reference numerals are used to denote the same elements or structures, wherein:

[0035] 1 is the detection light source, 2 is the optical module, 3 is the interferometric fiber optic accelerometer probe, 4 is the photoelectric detection demodulation module, 5 is the fiber optic head, 6 is the micro-nano spring assembly, 7 is the second reflector, 8 is the first reflector, and 9 is the heterogeneous stepped reflector. Detailed Implementation

[0036] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0037] The embodiments of this application are described below with reference to the accompanying drawings.

[0038] In a first aspect, this application provides an interferometric fiber optic accelerometer probe capable of suppressing temperature cross-sensitivity, comprising an optical fiber head, a spring assembly, and a heterogeneous reflector; the heterogeneous reflector consists of a first reflector and a second reflector connected in parallel along the optical path, the two reflectors having different coefficients of thermal expansion, and together with the optical fiber end face of the optical fiber head, they form a heterogeneous dual-cavity parallel Fabry-Perot interferometer cavity, the equivalent cavity lengths of the two Fabry-Perot cavities being different; the size of the spring assembly matches the diameter of the optical fiber, one end is fixed to the optical fiber end face of the optical fiber head, and the other end is connected to the heterogeneous stepped reflector, forming a spring-oscillator system.

[0039] Preferably, the stepped boundary line of the heterogeneous reflector is parallel to the fiber end face and within the beam cross-section, and the stepped sidewall is perpendicular to the fiber end face.

[0040] Preferably, 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.

[0041] Preferably, the absolute value of the difference between the first distance and the second distance is in the range of 1μm-300μm.

[0042] Preferably, the spring assembly is fabricated on the fiber end face of the fiber optic head using 3D printing technology.

[0043] Preferably, 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.

[0044] Preferably, the micro / nano spring has a wire diameter of 1 μm to 15 μm, a pitch of 10 μm to 100 μm, a free length of 50 μm to 1000 μm, and a spring mean diameter of 50 μm to 150 μm. The low stiffness of this micro / nano spring allows the device to respond more sensitively to external accelerations. By changing the dimensional parameters of the micro / nano spring, the device can achieve high-sensitivity detection within different frequency ranges.

[0045] Preferably, the reflective surface of the first reflector is coated with a thin film material with a reflectivity of 0.04-1, and the reflective surface of the second reflector is coated with a thin film material with a reflectivity of 0.04-1.

[0046] Secondly, this application provides a fiber optic accelerometer system capable of suppressing temperature cross-sensitivity, including 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 broadband laser as incident light; the optical module includes three ports, a first port connected to the detection light source, a second port connected to the fiber optic accelerometer probe, and a third port connected to the photoelectric detection 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, and is configured such that a portion passes through the fiber optic... The optical fiber end face of the head forms a first reflected light, and another part is transmitted through the optical fiber end face to form a second reflected light through a first reflecting mirror and a third reflected light through a second reflecting mirror. 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. In the demodulation process, the temperature information of the surrounding environment is subtracted from the acceleration information to remove temperature cross-sensitivity.

[0047] Preferably, the photoelectric detection demodulation module achieves demodulation in the following manner: acquiring the spatial frequencies of the fast Fourier transform curves of the reference optical signal and the measured interference optical signal respectively; calculating the two initial cavity lengths of the heterogeneous dual-cavity parallel Fabry-Perot interferometer based on the spatial frequency of the reference optical signal; calculating the two actual cavity lengths of the heterogeneous dual-cavity parallel Fabry-Perot interferometer based on the spatial frequency of the measured interference optical signal; calculating the changes in the two cavity lengths of the heterogeneous dual-cavity parallel Fabry-Perot interferometer; and correcting the two cavity length changes using a sensitivity coefficient matrix to obtain the acceleration signal of the object under test and the ambient temperature noise.

[0048] The reference optical signal is the signal transmitted by the fiber optic accelerometer probe when the heterostructure stepped reflector is located at the reference point. The reference point position is measured when the acceleration is zero and the environment is stable and constant, without the object under test being introduced.

[0049] The actual measurement of interferometric optical signals involves fixing the fiber optic accelerometer probe to the object under test, thereby measuring the vibration acceleration.

[0050] Preferably, the sensitivity coefficient matrix is ​​as follows:

[0051]

[0052] 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 .

[0053] Preferably, the detection light source is a broadband light source, which has the advantage of covering a wider wavelength range to provide broadband laser light. Of course, other detection light sources can also be selected according to requirements.

[0054] Preferably, the optical module is a fiber optic circulator, which functions to input the laser emitted by the broadband light source into the fiber optic accelerometer probe, and then input the optical signal reflected from the fiber optic accelerometer probe into the photoelectric detection and demodulation module. It features low transmission loss, high return loss, and optical signal isolation. Alternatively, it can be a waveguide structure with fiber optic circulator functionality or other optical structures.

[0055] Preferably, the end face of the second port is the fiber end face of an optical fiber head, and its surface is coated with a first thin film material. The reflectivity of the first thin film material is 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, thereby improving detection accuracy and reducing noise. When the optical module is a waveguide structure or other optical structure, the end face of this port can be selected as an optical fiber end face or an end face structure of other optical transmission media according to design requirements.

[0056] Example

[0057] like Figure 1 and Figure 2 As shown, this embodiment provides an interferometric fiber optic accelerometer probe 3 that can suppress temperature cross-sensitivity, including an optical fiber head 5, a micro-nano spring assembly 6, and a heterogeneous stepped reflector 9.

[0058] The mode field diameter of fiber optic connector 5 is 10.2 μm, and the reflectivity of the fiber end face of fiber optic connector 5 is selected as 0.06. The reflectivity of the heterostructure stepped-reflector 9, fixed to the object under test, is also selected as 0.06. The fiber end face of fiber optic connector 5 is placed parallel to the heterostructure stepped-reflector 9, and the central axis of the fiber optic connector is directly opposite the step boundary of the heterostructure stepped-reflector. The two are connected by four symmetrically placed springs, and the refractive index of the medium between them is [insert value here]. = 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 and second reflecting surfaces of the heterogeneous stepped reflector 9 are selected as 250 μm and 300 μm, respectively. The sensitivity coefficients of the first and second perpendicular distances to acceleration are... The sensitivity coefficient of the first vertical distance to temperature is 3.83 μm / mg. The sensitivity coefficient of the second vertical distance to temperature is 1.38 μm / ℃. The value is 0.23 μm / ℃. The heterogeneous stepped-reflector and the fiber end face of the fiber head form a heterogeneous dual-cavity parallel Fabry-Perot interferometer cavity, through which the optical signal passes simultaneously through two equivalent cavities.

[0059] like Figure 3 As shown, the two mirrors in the heterogeneous stepped reflector 9 have different heights, forming a stepped shape. This means the reflected light is not vertically symmetrical in the plane. The asymmetrical reflected light and the reflected light from the fiber end face form a beat frequency signal. Demodulating the beat frequency signal allows the cavity lengths of the two FP cavities to be calculated. Specifically, the first reflector 8 is semi-circular, and the second reflector 7 is circular. The thickness of the first reflector 8 is greater than that of the second reflector 7, and its coefficient of thermal expansion is also greater. After processing, the two mirrors are nested together; that is, the semi-circular reflector is nested in the middle of the circular reflector, forming a circular stepped shape facing the fiber end face.

[0060] The micro-nano spring assembly 6 and the heterogeneous stepped reflector constitute a spring-oscillator system. A spring-oscillator system generally consists of a spring, a test mass, and damping from air or structure. In this embodiment, the micro-nano spring assembly acts as the spring, the heterogeneous stepped reflector is the test mass, and air resistance is the damping. According to Newton's second law, the kinematic equation of the test mass can be expressed as:

[0061]

[0062] in, It is the quality of inspection. It is the displacement for quality inspection. It is the buffer coefficient. It is the spring constant. It is external input acceleration.

[0063] Applying a Laplace transform to the above equation yields the amplitude-frequency response characteristics of the oscillator as follows:

[0064]

[0065] in, It is the angular frequency of the external acceleration. It is the eigenfrequency of the spring-oscillator system. At that time, the relationship between the external acceleration and the displacement of the test mass satisfies:

[0066]

[0067] The acceleration signal of the spring-oscillator system can be converted into a displacement signal for mass inspection and measurement.

[0068] The basic principle behind this application for suppressing temperature cross-sensitivity is as follows:

[0069] When only external acceleration exists At that time, the first and second mirrors of the heterogeneous stepped-reflector move the same distance, and therefore the changes in the first and second vertical distances are the same, denoted as . Therefore, the sensitivity coefficients for acceleration are the same for both the first and second vertical distances, denoted as . (It has been calibrated before leaving the factory), and .

[0070] When only ambient temperature changes exist At that time, the first and second mirrors of the heterogeneous stepped reflector move the same distance. Because the thermal expansion coefficients of the materials of the first and second mirrors are different, the changes in the first and second vertical distances are different, denoted as . and Therefore, the sensitivity coefficients of the first and second vertical distances to temperature are different, and are denoted as follows: , (It has been calibrated before leaving the factory), and , .

[0071] When external acceleration exists simultaneously and changes in ambient temperature At that time, the first and second mirrors of the heterogeneous stepped-reflector move different distances, and the changes in the first and second vertical distances are different, denoted as . and At this point, the external acceleration can be obtained by solving the following matrix relationship. and changes in ambient temperature By subtracting ambient temperature information from acceleration data, the goal of eliminating temperature cross-sensitivity is achieved.

[0072]

[0073] like Figure 4 As shown, this embodiment also provides a fiber optic accelerometer system capable of suppressing temperature cross-sensitivity, including: a detection light source 1, an optical module 2, an interferometric fiber optic accelerometer probe 3, and a photoelectric detection demodulation module 4. The wavelength range of the detection light source 1 is set to 1500nm to 1600nm, and the output optical power is selected to be 1mW. The optical module 2 is a fiber optic circulator, which controls the unidirectional transmission of the optical signal on the one hand, and separates the input and output optical signals on the other hand. It includes 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 from the first port is output through the second port. The reflected light from the end face of the second port interferes with the reflected light from the reflective surface of the fiber optic accelerometer probe to form a beat frequency signal, which is then output from the third port to the photoelectric detection and demodulation module. The photoelectric detection and demodulation module 4 is used to convert the optical signal into an electrical signal and then perform a fast Fourier transform to obtain the spatial frequency of the curve. Based on the spatial frequency, the cavity length of the heterogeneous dual-cavity parallel Fabry-Perot interferometer cavity in the fiber optic sensing probe is calculated, and the acceleration signal of the object under test and the ambient temperature noise are further obtained.

[0074] To verify the functionality of the fiber optic accelerometer system described above, the reflected photoelectric field generated at the end face of the second port is represented as:

[0075]

[0076] The reflected photoelectric field generated by the reflective surface of the fiber optic accelerometer probe is represented as:

[0077]

[0078] in, This represents the reflected photoelectric field after passing through the first reflecting mirror. This represents the reflected photoelectric field after passing through the second reflecting mirror.

[0079] The signal photoelectric field output from the third port of optical module 2 is represented as follows:

[0080]

[0081] in, Let be the electric field of the incident light. , The reflectivities are the fiber end face of the second port and the heterostructure stepped reflector of the fiber optic accelerometer probe, respectively. The refractive index of the medium between the fiber end face and the heterostructure stepped-back mirror. Where is the wavelength of the incident light. This is the perpendicular distance between the fiber end face and the first reflecting surface of the heterostructure stepped mirror. This is the vertical distance between the fiber end face and the second reflecting surface of the heterogeneous stepped reflector.

[0082] The output light intensity (beat frequency signal) of the photoelectric detection module can be expressed as a function of the light frequency:

[0083]

[0084] The output light intensity described above can be considered as the reciprocal of the incident light wavelength. The function is subjected to a Fast Fourier Transform (FFT), and the spatial frequencies of the FFT curves are respectively... , , The vertical distance between the first and second reflecting surfaces of the heterostructure stepped-back mirror and the fiber end face of the fiber optic head. , When changes occur, the length changes of the two cavities in the heterogeneous dual-cavity parallel Fabry-Perot interferometer structure are obtained by measuring the change in the spatial frequency of the Fourier transform curve relative to the reference point. , The change in cavity length , Substitute the values ​​into the following sensitivity coefficient matrix for correction to obtain the acceleration of the object under test. and changes in ambient temperature .

[0085]

[0086] As can be seen from the above, this application achieves effective separation of acceleration signals and temperature noise, and significantly suppresses the temperature cross-sensitivity problem.

[0087] like Figure 5 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 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℃.

[0088] 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℃.

[0089] 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℃.

[0090] 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.

[0091] 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.

[0092] In the description of the embodiments of this application, it should be noted that, unless otherwise explicitly specified and limited, the term "connection" should be interpreted broadly. For example, "connection" can be a detachable connection or a non-detachable connection; it can be a direct connection or an indirect connection through an intermediate medium. "Fixed connection" refers to a connection where the relative positional relationship remains unchanged after connection. "Rotary connection" refers to a connection where the components can rotate relative to each other after connection. "Sliding connection" refers to a connection where the components can slide relative to each other after connection. The directional terms mentioned in the embodiments of this application, such as "top," "bottom," "inner," "outer," "left," and "right," are only for reference to the directions in the accompanying drawings. Therefore, the directional terms used are for better and clearer explanation and understanding of the embodiments of this application, and are not intended to indicate or imply that the device or component referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the embodiments of this application.

[0093] Furthermore, the mathematical concepts mentioned in the embodiments of this application, such as symmetry, equality, parallelism, and perpendicularity, are limitations specific to the current technological level, rather than absolute and strict mathematical definitions. Slight deviations are permissible; approximations of symmetry, equality, parallelism, and perpendicularity are all acceptable. For example, "A and B are parallel" means that A and B are parallel or approximately parallel, and the angle between A and B can be between 0 and 10 degrees. "A and B are perpendicular" means that A and B are perpendicular or approximately perpendicular, and the angle between A and B can be between 80 and 100 degrees.

[0094] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A fiber optic accelerometer system capable of suppressing temperature cross-sensitivity, characterized in that, This includes a detection light source, an optical module, a fiber optic accelerometer probe, 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. The interferometric fiber optic accelerometer probe includes an optical fiber head, a spring assembly, and a heterogeneous reflector. The heterogeneous reflector consists of a first and a second reflector connected in parallel along the optical path. The two reflectors have different coefficients of thermal expansion, and together with the fiber end face of the optical fiber head, they form a heterogeneous dual-cavity parallel Fabry-Perot interferometer cavity. The equivalent cavity lengths of the two Fabry-Perot cavities are different. The spring assembly is sized to match the fiber diameter, with one end fixed to the fiber end face of the optical fiber head and the other end connected to the heterogeneous stepped reflector, forming a spring-oscillator system. The photoelectric detection and demodulation module uses the following method... Demodulation is achieved by: acquiring the spatial frequencies of the fast Fourier transform curves of the reference optical signal and the measured interference optical signal; calculating the two initial cavity lengths of the heterogeneous dual-cavity parallel Fabry-Perot interferometer based on the spatial frequency of the reference optical signal, and calculating the two actual cavity lengths of the heterogeneous dual-cavity parallel Fabry-Perot interferometer based on the spatial frequency of the measured interference optical signal; calculating the changes in the two cavity lengths of the heterogeneous dual-cavity parallel Fabry-Perot interferometer; and correcting the two cavity length changes using a sensitivity coefficient matrix to obtain the acceleration signal of the object under test and the ambient temperature noise. 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 .

2. The fiber optic accelerometer system 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 fiber optic accelerometer system 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 fiber optic accelerometer system 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 fiber optic accelerometer system 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 fiber optic accelerometer system 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 fiber optic accelerometer system 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.

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