Temperature self-calibration optical fiber magnetic field sensing device and method based on optical carrier microwave interference

Abstract

The application discloses a temperature self-calibration optical fiber magnetic field sensing device and method based on optical carrier microwave interference, applied to the technical field of magnetic field detection, comprising a sensing module, three optical fiber gratings with equidistant central wavelengths; a second optical fiber grating is coupled with a magnetostrictive rod; a microwave photon system, comprising a double-arm interferometer, a dispersion compensation optical fiber and a microwave frequency response measurement module; two interference arms of the double-arm interferometer have an arm length difference; a signal processing module is used for processing the microwave frequency response output by the microwave frequency response measurement module, and at least four groups of microwave interference spectra are obtained; the four groups of microwave interference spectra comprise two groups of first microwave interference spectra and two groups of second microwave interference spectra; based on the two groups of first microwave interference spectra, a magnetic field measurement vernier envelope for demodulating a magnetic field is formed; and based on the two groups of second microwave interference spectra, a temperature measurement vernier envelope for demodulating a temperature is formed. The temperature self-calibration optical fiber magnetic field sensing device realizes high-sensitivity demodulation of the temperature and the magnetic field.

Description

Technical Field

[0001] This invention relates to the field of magnetic field detection technology, and in particular to a temperature self-calibrating fiber optic magnetic field sensing device and method based on optical microwave interferometry. Background Technology

[0002] Ocean temperature and magnetic fields are crucial parameters for marine resource development and environmental monitoring. Traditional electrical sensors, such as platinum resistance thermometers, semiconductor temperature sensors, fluxgate magnetometers, and optically pumped magnetometers, rely on metal wires to transmit electrical signals. These are susceptible to seawater corrosion and electromagnetic interference, facing multiple bottlenecks in reliability, durability, and system complexity in complex marine applications. Fiber optic sensing technology, with its advantages of small size, low cost, resistance to electromagnetic interference, and ease of multiplexing and networking, is gradually becoming an ideal solution for marine exploration. Although the structures and principles of fiber optic sensors vary, their demodulation schemes can be broadly categorized into three types: wavelength demodulation, intensity demodulation, and phase demodulation. Wavelength demodulation measures external parameters by monitoring wavelength shifts in the reflection or transmission spectrum, but high-spectral-resolution demodulation equipment is often expensive and has limited response speed. Intensity demodulation primarily senses environmental parameters by measuring changes in light intensity, but it is easily affected by light source fluctuations and link losses, and its measurement accuracy is limited by the sensitivity of the photodetector. Phase demodulation-based sensing technology detects changes in the phase of light waves and further demodulates changes in external sensing parameters. However, its output signal is periodic, suffers from phase ambiguity, and has poor long-term stability.

[0003] Microwave photonics integrates microwave technology with photonics theory, providing a novel demodulation technique for fiber optic sensing systems. Its core idea is to linearly and efficiently map the changes in the optical domain (such as light intensity, wavelength, and phase) caused by external physical quantities (such as strain, temperature, and vibration) sensed by the fiber optic sensor to characteristic parameters such as frequency, amplitude, or phase of the microwave electrical signal. Depending on the implementation method, sensing and demodulation systems based on microwave photonics can be divided into fiber optic sensing technologies based on microwave photonic filters (MPFs) and fiber optic sensing technologies based on optoelectronic oscillators (OEOs). Among these, optically loaded microwave interferometry, as an important branch of microwave photonic filters, recovers the phase difference of optical interference into the phase or amplitude parameters of the microwave signal. This scheme is unaffected by light wave amplitude crosstalk, effectively avoids the influence of polarization changes, and has the advantages of clear fringes and convenient demodulation, thus attracting widespread attention in recent years.

[0004] Although optical-borne microwave interferometry has achieved significant results in realizing high-performance sensing of single parameters (such as strain, temperature, and magnetic field), current research still largely focuses on single-parameter measurements. The fundamental reason for this lies in how to design sensing units and modulation / demodulation architectures within an optical-borne microwave interferometry system so that different physical parameters can produce distinguishable and unique modulation characteristics of microwave signals, and how to establish robust decoupling algorithms. Therefore, there is an urgent need to develop a high-precision magnetic field measurement system with temperature self-calibration capabilities, which can effectively solve the problem of temperature cross-sensitivity, to meet the pressing needs of fields such as marine exploration for multi-parameter and high-reliability measurements.

[0005] This invention provides a temperature self-calibrating fiber optic magnetic field sensing device and method based on optical microwave interferometry to solve the technical problem of cross-sensitivity between temperature and magnetic field in fields such as marine exploration. Summary of the Invention

[0006] The purpose of this invention is to provide a temperature self-calibrating fiber optic magnetic field sensing device and method based on optical microwave interferometry, so as to solve the technical problem of cross-sensitivity between temperature and magnetic field in fields such as marine exploration.

[0007] To address the aforementioned technical problems, this invention provides a temperature self-calibrating fiber optic magnetic field sensing device based on optical microwave interferometry, comprising: The sensing module includes a first fiber grating, a second fiber grating, and a third fiber grating cascaded along the optical path; the center wavelengths of the three fiber gratings are equally spaced; the second fiber grating is coupled to a magnetostrictive rod; A microwave photonic system includes a light source module, an electro-optic modulator, an optical circulator, a two-arm interferometer, a dispersion compensation fiber, a photoelectric detection module, and a microwave frequency response measurement module connected sequentially along an optical path; the optical circulator is connected to the sensing module and the two-arm interferometer respectively, and the two interferometer arms of the two-arm interferometer have a difference in arm length. A signal processing module is connected to the microwave frequency response measurement module. The signal processing module processes the microwave frequency response output by the microwave frequency response measurement module to obtain at least four sets of microwave interference spectra. The four sets of microwave interference spectra include two sets of first microwave interference spectra and two sets of second microwave interference spectra. The first microwave interference spectra include microwave interference spectra where the microwave dip peak frequency changes linearly with the magnetic field. The second microwave interference spectra include microwave interference spectra where the microwave dip peak frequency changes linearly with temperature. Among them, based on the two sets of the first microwave interferometric spectra, a magnetic field measurement vernier envelope for demodulating the magnetic field is formed; Based on the two sets of the second microwave interferometric spectra, a temperature measurement vernier envelope for demodulated temperature is formed.

[0008] Optionally, the sensing module includes a magnetic field strain amplification structure, which includes a first receiving portion and a second receiving portion disposed opposite to each other. The first receiving portion and the second receiving portion are connected by the magnetostrictive rod, one end of the magnetostrictive rod is disposed in the first receiving portion, and the other end of the magnetostrictive rod is disposed in the second receiving portion; The extension direction of the second fiber grating is parallel to the axis of the magnetostrictive rod or has an angle of no more than 1 degree. One end of the second fiber grating is disposed in the first receiving portion, and the other end of the second fiber grating is disposed in the second receiving portion; the grating region of the second fiber grating is located in the area between the first receiving portion and the second receiving portion.

[0009] Optionally, the magnetic field strain amplification structure further includes an external magnet, which is used to provide a pre-magnetic field. The pre-magnetic field is uniformly distributed in the extension direction of the magnetostrictive rod, so that the magnetostrictive rod is in the linear sensing range when it is working.

[0010] Optionally, the first receiving portion or the second receiving portion is provided with a first fiber groove; the first fiber grating is located in the first fiber groove; The first or second accommodating part is provided with a third fiber optic slot; the third fiber optic grating is located in the third fiber optic slot.

[0011] Optionally, the first receiving portion is provided with a first sub-fiber groove, and the second receiving portion is provided with a second sub-fiber groove, with the first sub-fiber groove and the second sub-fiber groove being provided correspondingly along the extension direction of the second fiber grating; One end of the second fiber grating is located in the first sub-fiber slot, and the other end of the second fiber grating is located in the second sub-fiber slot.

[0012] Optionally, the microwave frequency response measurement module includes a high-speed sweep frequency source and a high-speed acquisition card, or a vector network analyzer.

[0013] Optionally, the dual-arm interferometer includes two 1×2 optical couplers, and the splitting ratio of the dual-arm interferometer is 50:50.

[0014] This invention also provides a temperature self-calibrating fiber optic magnetic field sensing method based on optically carried microwave interferometry, using the aforementioned temperature self-calibrating fiber optic magnetic field sensing device based on optically carried microwave interferometry, comprising: The broadband incoherent optical signal generated by the light source module is modulated by an electro-optic modulator and then introduced into the sensing module by an optical circulator. The first, second, and third fiber gratings cascaded along the optical path in the sensing module reflect the optical signal. The reflected light is output to a two-arm interferometer through the optical circulator and split into two paths. The wavelength drift is converted into a time delay change by a dispersion compensation fiber, and then converted into an electrical signal by a photoelectric detection module. The microwave frequency response is obtained by a microwave frequency response measurement module through frequency sweep measurement. The center wavelengths of the three fiber gratings are equally spaced, and the second fiber grating is coupled to a magnetostrictive rod. The signal processing module processes the microwave frequency response to obtain at least four sets of microwave interference spectra; the four sets of microwave interference spectra include two sets of first microwave interference spectra and two sets of second microwave interference spectra; the first microwave interference spectra include microwave interference spectra in which the microwave dip peak frequency changes linearly with the magnetic field; the second microwave interference spectra include microwave interference spectra in which the microwave dip peak frequency changes linearly with the temperature. The two sets of the first microwave interference spectrum are superimposed to form the magnetic field measurement vernier envelope, and the magnetic field is demodulated according to the dip peak frequency drift of the magnetic field measurement vernier envelope. The two sets of the second microwave interference spectra are superimposed to form a temperature measurement vernier envelope, and the temperature is demodulated based on the dip peak frequency drift of the temperature measurement vernier envelope.

[0015] Optionally, the signal processing module processes the microwave frequency response to obtain at least four sets of microwave interference spectra, including: The signal processing module sequentially performs inverse Fourier transform, applies a window function, and performs another Fourier transform on the microwave frequency response, and then reconstructs at least four sets of microwave interference spectra.

[0016] Optionally, the reflected signal of the second fiber optic grating and the reflected signal of the first fiber optic grating are respectively transmitted through the double-arm interferometer to form a first pulse pair; The reflected signals of the second fiber grating and the third fiber grating are transmitted through the two-arm interferometer to form a second pulse pair; The signal processing module processes the first pulse pair and the second pulse pair to obtain at least two sets of first microwave interference spectra; the first microwave interference spectra include microwave interference spectra in which the microwave dip peak frequency changes linearly with the magnetic field.

[0017] Optionally, the reflected signal of the first fiber grating and the reflected signal of the third fiber grating are transmitted through the same interferometer arm of the two-arm interferometer to form a third pulse pair; The reflected signals of the first fiber grating and the third fiber grating are transmitted through different interferometer arms of the two-arm interferometer to form a fourth pulse pair; The signal processing module processes the third pulse pair and the fourth pulse pair to obtain at least two sets of second microwave interference spectra; the second microwave interference spectra include microwave interference spectra in which the microwave dip peak frequency changes linearly with temperature.

[0018] The temperature self-calibrating fiber optic magnetic field sensing device based on optically carried microwave interferometry provided by this invention includes: a sensing module comprising a first fiber grating, a second fiber grating, and a third fiber grating cascaded along the optical path; the center wavelengths of the three fiber gratings are equally spaced; the second fiber grating is coupled to a magnetostrictive rod; a microwave photonic system comprising a light source module, an electro-optic modulator, an optical circulator, a two-arm interferometer, a dispersion compensation fiber, a photoelectric detection module, and a microwave frequency response measurement module connected sequentially along the optical path; the optical circulator is connected to the sensing module and the two-arm interferometer respectively, and the two interferometer arms of the two-arm interferometer have a difference in arm length; and a signal processing module, which is connected to the sensing module and the optically carried microwave photonic system. The microwave frequency response measurement module is connected; the signal processing module processes the microwave frequency response output by the microwave frequency response measurement module to obtain at least four sets of microwave interference spectra; the four sets of microwave interference spectra include two sets of first microwave interference spectra and two sets of second microwave interference spectra; the first microwave interference spectra include microwave interference spectra in which the microwave dip peak frequency changes linearly with the magnetic field; the second microwave interference spectra include microwave interference spectra in which the microwave dip peak frequency changes linearly with the temperature; wherein, based on the two sets of first microwave interference spectra, a magnetic field measurement vernier envelope for demodulating the magnetic field is formed; and based on the two sets of second microwave interference spectra, a temperature measurement vernier envelope for demodulating the temperature is formed.

[0019] As can be seen, this temperature self-calibrating fiber optic magnetic field sensing device based on optically carried microwave interferometry maps optical interference signals to the microwave domain using optically carried microwave interferometry. The three fiber gratings cascaded along the optical path have equally spaced center wavelengths, and the second fiber grating is coupled to a magnetostrictive rod. This converts the magnetostrictive deformation caused by changes in the magnetic field into a drift in the center wavelength of the second fiber grating, which is further mapped to a frequency drift in the microwave interferogram or vernier envelope. The microwave photonic system includes a two-arm interferometer with a difference in arm length and a dispersion-compensating fiber, converting the wavelength drift into a time delay variation. The signal processing module processes the microwave frequency response output from the microwave frequency response measurement module to obtain at least four sets of microwave interferograms. These four sets include two sets of first microwave interferograms and two sets of second microwave interferograms. The first microwave interferograms include those where the microwave dip peak frequency changes linearly with the magnetic field; the second microwave interferograms include those where the microwave dip peak frequency changes linearly with temperature. During magnetic field demodulation, the equal spacing of the center wavelengths of the three fiber gratings, coupled with the coupling between the second fiber grating and the magnetostrictive rod, and the use of a dual-arm interferometer with a difference in arm length and dispersion compensation fiber, reduces the impact of temperature drift on the magnetic field demodulation results. Two sets of microwave interferometric spectra, whose microwave dip peak frequency changes linearly with the magnetic field, form the magnetic field measurement vernier envelope for demodulating the magnetic field. During temperature demodulation, the lack of coupling between the first and third fiber gratings and the magnetostrictive rod, along with the use of a dual-arm interferometer with a difference in arm length and dispersion compensation fiber, results in two sets of microwave interferometric spectra, whose microwave dip peak frequency also changes linearly with temperature, forming the temperature measurement vernier envelope. This self-calibrating fiber optic magnetic field sensing device integrates fiber optic interferometric sensing technology with an optically driven microwave interferometric demodulation scheme, achieving high-sensitivity demodulation of both temperature and magnetic fields through vernier enhancement effects.

[0020] The temperature self-calibrating fiber optic magnetic field sensing method based on optical microwave interferometry provided by this invention has the same beneficial effects as the aforementioned temperature self-calibrating fiber optic magnetic field sensing device based on optical microwave interferometry, and will not be described in detail here. Attached Figure Description

[0021] To more clearly illustrate the technical solutions of the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0022] Figure 1 This is a schematic diagram of a temperature self-calibrating fiber optic magnetic field sensing device based on optical microwave interferometry, provided in an embodiment of the present invention. Figure 2This is a schematic diagram of the magnetic field strain amplification structure provided in an embodiment of the present invention; Figure 3 A flowchart of a temperature self-calibration fiber optic magnetic field sensing method based on optical microwave interferometry provided in this embodiment of the invention; Figure 4 A schematic diagram illustrating the sequential order of the six pulses formed according to an embodiment of the present invention; Figure 5 A schematic diagram of the demodulation process of a temperature self-calibrating fiber optic magnetic field sensing device based on optical microwave interferometry provided in an embodiment of the present invention; In the figure: 1. Light source module, 2. Electro-optic modulator, 3. Optical circulator, 4. Sensing module, 41. First receiving part, 42. Second receiving part, 43. Magnetostrictive rod, 44. First fiber optic slot, 45. Second fiber optic slot, 46. External magnet, 5. Two-arm interferometer, 6. Dispersion compensation fiber, 7. Erbium-doped fiber amplifier, 8. Photoelectric detection module, 9. Microwave frequency response measurement module, 10. Signal processing module. Detailed Implementation

[0023] The core of this invention is to provide a temperature self-calibrating fiber optic magnetic field sensing device and method based on optically carried microwave interferometry. Optically carried microwave interferometry, as an important branch of microwave photonic filters, recovers the phase difference of optical interference into the phase or amplitude parameters of the microwave signal. This approach is unaffected by optical wave amplitude crosstalk and can effectively avoid the influence of polarization changes, offering advantages such as clear fringes and convenient demodulation, and has received widespread attention in recent years. Although optically carried microwave interferometry has achieved significant results in realizing high-performance sensing of single parameters (such as strain, temperature, and magnetic field), existing research still largely focuses on single-parameter measurements. The fundamental reason lies in how to design sensing units and modulation / demodulation architectures within an optically carried microwave interferometry system so that different physical parameters can produce distinguishable and unique modulation characteristics of the microwave signal, and establish robust decoupling algorithms. Therefore, there is an urgent need to develop a high-precision magnetic field measurement system with temperature self-calibration capabilities, effectively solving the problem of temperature cross-sensitivity, to meet the pressing needs of fields such as marine exploration for multi-parameter and high-reliability measurements.

[0024] This temperature self-calibrating fiber optic magnetic field sensing device, based on optically carried microwave interferometry, maps optical interference signals to the microwave domain. During magnetic field demodulation, the equal spacing of the center wavelengths of the three fiber gratings, coupling the second fiber grating to the magnetostrictive rod, and the use of a dual-arm interferometer with a difference in arm length and dispersion compensation fiber reduce the impact of temperature drift on the demodulation results. Two sets of microwave interference spectra, based on the linear variation of the microwave dip peak frequency with the magnetic field, form the magnetic field measurement vernier envelope for demodulating the magnetic field. Similarly, during temperature demodulation, the lack of coupling between the first and third fiber gratings and the magnetostrictive rod, along with the dual-arm interferometer with a difference in arm length and dispersion compensation fiber, results in two sets of microwave interference spectra, also based on the linear variation of the microwave dip peak frequency with temperature, forming the temperature measurement vernier envelope. This temperature self-calibrating fiber optic magnetic field sensing device integrates fiber optic interferometry sensing technology with an optically carried microwave interferometry demodulation scheme, achieving high-sensitivity demodulation of both temperature and magnetic fields through vernier enhancement effects.

[0025] To enable those skilled in the art to better understand the present invention, the invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. Obviously, the described embodiments are merely some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0026] The specific structure of the temperature self-calibrating fiber optic magnetic field sensing device based on optical microwave interferometry provided by this invention will be described in detail in the following embodiments.

[0027] Example 1

[0028] Please refer to Figure 1 , Figure 1 This is a schematic diagram of a temperature self-calibrating fiber optic magnetic field sensing device based on optical microwave interferometry, provided as an embodiment of the present invention.

[0029] See Figure 1 This invention provides a temperature self-calibrating fiber optic magnetic field sensing device based on optical microwave interferometry, comprising: Sensing module 4 includes a first fiber grating, a second fiber grating, and a third fiber grating cascaded along the optical path; the center wavelengths of the three fiber gratings are equally spaced; the second fiber grating is coupled to a magnetostrictive rod 43; a microwave photonic system includes a light source module 1, an electro-optic modulator 2, an optical circulator 3, a two-arm interferometer 5, a dispersion compensation fiber 6, a photoelectric detection module 8, and a microwave frequency response measurement module 9 connected sequentially along the optical path; the optical circulator 3 is connected to sensing module 4 and the two-arm interferometer 5 respectively, and the two interferometer arms of the two-arm interferometer 5 have a difference in arm length; a signal processing module 10 is connected to the microwave frequency response measurement module 9. Module 9 is connected; signal processing module 10 is used to process the microwave frequency response output by microwave frequency response measurement module 9, and then obtain at least four sets of microwave interference spectra; the four sets of microwave interference spectra include two sets of first microwave interference spectra and two sets of second microwave interference spectra; the first microwave interference spectrum includes a microwave interference spectrum in which the microwave dip peak frequency changes linearly with the magnetic field; the second microwave interference spectrum includes a microwave interference spectrum in which the microwave dip peak frequency changes linearly with the temperature; wherein, based on the two sets of first microwave interference spectra, a magnetic field measurement vernier envelope for demodulating the magnetic field is formed; based on the two sets of second microwave interference spectra, a temperature measurement vernier envelope for demodulating the temperature is formed.

[0030] The temperature self-calibrating fiber optic magnetic field sensing device based on optically carried microwave interferometry provided in this embodiment includes a sensing module 4, a microwave photonic system, and a signal processing module 10. The microwave photonic system is based on the principle of a multi-tap microwave photonic filter. It demodulates the optical wavelength drift by mapping it to the microwave frequency domain using optically carried microwave interferometry. The sensing module 4 utilizes a first, second, and third fiber grating cascaded along the optical path, with the center wavelengths of the three fiber gratings set at equal intervals. The second fiber grating is coupled to a magnetostrictive rod 43 to sense the magnetic field. A path delay difference is introduced using a two-arm interferometer 5, and the wavelength drift is converted into a time delay variation using a dispersion-compensating fiber 6. Finally, the signal processing module 10 processes the signal by adjusting the microwave frequency response. The process should yield at least four sets of microwave interferometric spectra. These four sets include two sets of first microwave interferometric spectra and two sets of second microwave interferometric spectra. The first microwave interferometric spectra include those where the microwave dip peak frequency changes linearly with the magnetic field. The second microwave interferometric spectra include those where the microwave dip peak frequency changes linearly with temperature. The two sets of first microwave interferometric spectra are superimposed to form a magnetic field measurement vernier envelope. The magnetic field is demodulated based on the dip peak frequency drift of the magnetic field measurement vernier envelope. The two sets of second microwave interferometric spectra are superimposed to form a temperature measurement vernier envelope. The temperature is demodulated based on the dip peak frequency drift of the temperature measurement vernier envelope, thus achieving simultaneous measurement of both magnetic field and temperature parameters, as well as temperature self-calibration during magnetic field measurement.

[0031] Please refer to Figure 1The microwave photonic system includes a light source module 1, an electro-optic modulator 2, an optical circulator 3, a two-arm interferometer 5, a dispersion compensation fiber 6, a photoelectric detection module 8, and a microwave frequency response measurement module 9, which are connected sequentially along the optical path. The optical circulator 3 is connected to the sensing module 4 and the two-arm interferometer 5, respectively. The two interferometer arms of the two-arm interferometer 5 have a difference in arm length.

[0032] This microwave photonic system is based on the principle of a multi-tap microwave photonic filter (MPF). Specifically, the light source module 1 is used to generate a broadband incoherent optical signal; the electro-optic modulator 2 is used to modulate the microwave signal onto an optical carrier; the optical circulator 3 is used to guide the modulated optical signal into the sensing module 4 and receive the reflected light; the dual-arm interferometer 5 is used to introduce multipath delay to form a multi-tap microwave photonic filter; the dispersion compensation fiber 6 is used to convert wavelength changes into time delay changes; the photoelectric detection module 8 is used to convert the reflected light signal into an electrical signal; and the microwave frequency response measurement module 9 is used to provide a microwave sweep frequency source and acquire the microwave interference spectrum.

[0033] In this embodiment, the light source module 1 is a broadband light source with a coherence length on the order of micrometers to ensure that the optical carrier does not interfere optically, and only the microwave envelope interferes. The electro-optic modulation module is a Mach-Zehnder modulator with a bandwidth of not less than 10 GHz and a half-wave voltage of 5 V. The optical circulator 3 is a three-port device with an insertion loss of less than 1 dB. The dual-arm interferometer 5 is a dual-arm Mach-Zehnder interferometer, which includes two 1×2 optical couplers with a splitting ratio of 50:50. The two interferometer arms of the dual-arm interferometer 5 have a length difference of l0 and l1, respectively, to generate reflected signals with different time delays. The photodetector module 8 is a photodetector with a responsivity of 0.8 A / W and a 3 dB bandwidth of 10 GHz. The microwave frequency response measurement module 9 is used to acquire the microwave frequency response of the system, and its sweep frequency range is 1 GHz-11 GHz.

[0034] In this embodiment, the microwave frequency response measurement module includes a high-speed sweep frequency source and a high-speed acquisition card, or a vector network analyzer. That is, in this embodiment, the microwave frequency response measurement module can be a vector network analyzer, or it can be a high-speed sweep frequency source and a high-speed acquisition card.

[0035] As a specific embodiment, the microwave photonics system also includes an erbium-doped fiber amplifier 7, which is positioned between the two-arm interferometer 5 and the photodetector. The erbium-doped fiber amplifier 7 is used to enhance the signal strength. The broadband light source is a spontaneous emission source generated by the erbium-doped fiber amplifier 7, with an output power of 13 dB and a center wavelength of 1550 nm.

[0036] When the microwave photonics system is operating, the incoherent light emitted by the erbium-doped fiber amplifier 7 enters the Mach-Zehnder modulator, where it is intensity modulated by the swept microwave signal output from the first port of the microwave frequency response measurement module 9. The broadband light source uses spontaneous emission generated by the erbium-doped fiber amplifier 7. The modulated optical signal enters the sensing module 4 via the optical circulator 3, is reflected by the first, second, and third fiber gratings, and returns to the optical circulator 3 before entering the Mach-Zehnder interferometer. After being delayed by the two interferometer arms of the Mach-Zehnder interferometer, the optical signal is amplified by the erbium-doped fiber amplifier 7, converted into an electrical signal by a photodetector, and returns to the second port of the microwave frequency response measurement module 9, where the module measures the microwave frequency response.

[0037] In this embodiment, since the coherence length of the erbium-doped fiber amplifier 7 light source is on the order of micrometers, while the optical path difference of each reflection path is on the order of meters, the optical carrier does not interfere; only the microwave envelope interferes, satisfying the conditions for optical-carried microwave interference. The system delay consists of three parts: the first part is a fixed delay related to the physical length of the fiber; the second part is the delay introduced by the fiber passing through the interference arms with different arm lengths; and the third part is the change in delay caused by wavelength variation, which is proportional to the dispersion of the dispersive medium.

[0038] Please refer to Figure 2 , Figure 2 This is a schematic diagram of the magnetic field strain amplification structure provided in an embodiment of the present invention. The sensing module 4 includes a first fiber grating, a second fiber grating, and a third fiber grating cascaded along the optical path; the center wavelengths of the three fiber gratings are equally spaced; the second fiber grating is coupled to a magnetostrictive rod 43. Specifically, the first, second, and third fiber gratings are all sensitive to temperature changes; the coupling of the second fiber grating to the magnetostrictive rod 43 makes it sensitive to both temperature and magnetic field changes; the first and third fiber gratings are not coupled to the magnetostrictive rod 43 and are only sensitive to temperature changes.

[0039] In one specific embodiment, all three fiber gratings are special fiber gratings. Specifically, the first, second, and third fiber gratings are all fiber Bragg gratings (FBGs). The three fiber gratings share the same optical parameters: a center wavelength spacing of 5 nm, a reflectivity greater than 50%, a grating length of 10 mm, a 3 dB bandwidth of approximately 0.3 nm, a wavelength accuracy better than 0.3 nm, and a side-mode suppression ratio better than 20 dB.

[0040] In another specific embodiment, the three fiber gratings can be of different types, wherein the second fiber grating is a polarization-maintaining fiber grating; as long as the center wavelengths of the three fiber gratings are set at equal intervals.

[0041] In one specific embodiment, the first fiber grating, the second fiber grating, and the third fiber grating cascaded along the optical path are all disposed on the magnetic field strain amplification structure. The sensing module 4 includes the magnetic field strain amplification structure, which includes a first receiving portion 41 and a second receiving portion 42 disposed opposite to each other. The first receiving portion 41 and the second receiving portion 42 are connected by a magnetostrictive rod 43, one end of which is disposed in the first receiving portion 41, and the other end of which is disposed in the second receiving portion 42. The extension direction of the second fiber grating is parallel to or has an angle of no more than 1 degree with the axis of the magnetostrictive rod 43. One end of the second fiber grating is disposed in the first receiving portion 41, and the other end of which is disposed in the second receiving portion 42. The grating region of the second fiber grating is located in the area between the first receiving portion 41 and the second receiving portion 42. Specifically, the first receiving portion 41 and the second receiving portion 42 are provided with second fiber optic grooves 45; one end of the second fiber optic grating is located in the second fiber optic groove 45 of the first receiving portion 41, and the other end of the second fiber optic grating is located in the second fiber optic groove 45 of the second receiving portion 42. The magnetic field strain amplification structure also includes an external magnet 46, which is used to provide a pre-magnetic field. The pre-magnetic field is uniformly distributed in the extension direction of the magnetostrictive rod 43, so that the magnetostrictive rod 43 is in the linear sensing range when it works. In this embodiment, the external magnet 46 can be a single external magnet, which is consistent with the extension direction of the magnetostrictive rod 43; the external magnet 46 can also be a first external magnet and a second external magnet symmetrically arranged about the extension direction of the magnetostrictive rod 43, as long as the pre-magnetic field provided by the external magnet 46 is uniformly distributed in the extension direction of the magnetostrictive rod 43, so that the magnetostrictive rod 43 is in the linear sensing range of the pre-magnetic field when it works. In this embodiment, the external magnet 46 is placed in the magnet groove of the magnetic field strain amplification structure.

[0042] The first receiving portion 41 or the second receiving portion 42 is provided with a first fiber optic slot 44; the first fiber optic grating is located within the first fiber optic slot 44; the first receiving portion 41 or the second receiving portion 42 is provided with a third fiber optic slot; the third fiber optic grating is located within the third fiber optic slot. In this embodiment, both the first fiber optic grating and the third fiber optic grating are bonded to one side surface of the magnetic field strain amplification structure using ultraviolet adhesive, so that they are not affected by the deformation of the magnetostrictive material while matching the temperature response of the second fiber optic grating.

[0043] In this embodiment, the second fiber grating is coupled to the magnetostrictive rod 43 via a magnetic field strain amplification structure. The magnetic field sensing principle is as follows: the magnetostrictive rod 43 undergoes expansion and contraction deformation under the action of an external magnetic field, thereby causing the magnetic field strain amplification structure to move along the axial direction of the magnetostrictive rod 43. One end of the second fiber grating is disposed in the first receiving portion 41, and the other end of the second fiber grating is disposed in the second receiving portion 42 (i.e., the second fiber grating spans the first receiving portion 41 and the second receiving portion 42 of the magnetic field strain amplification structure), and the grating region of the second fiber grating is located in the area between the first receiving portion 41 and the second receiving portion 42. This effectively transforms the movement of the magnetic field strain amplification structure into a stress effect on the second fiber grating, thereby causing a drift in the center wavelength of the second fiber grating. The system maps the wavelength drift of the second fiber grating onto the microwave photonics system to achieve magnetic field sensing.

[0044] In this embodiment, both the first receiving portion 41 and the second receiving portion 42 are rigid receiving portions. Their shapes can be any geometric shape that is symmetrical about its own axis. The second fiber grating can be disposed on any surface of the magnetic field strain amplification structure (i.e., the first receiving portion 41 and the second receiving portion 42), as long as the extension direction of the second fiber grating is parallel to the axis of the magnetostrictive rod 43 or has an angle of no more than 1 degree; one end of the second fiber grating is disposed in the first receiving portion 41, and the other end of the second fiber grating is disposed in the second receiving portion 42; the grating region of the second fiber grating is located in the area between the first receiving portion 41 and the second receiving portion 42.

[0045] In another specific embodiment, the first receiving portion 41 is provided with a first sub-fiber groove, and the second receiving portion 42 is provided with a second sub-fiber groove. The first sub-fiber groove and the second sub-fiber groove are provided correspondingly along the extension direction of the second fiber grating. One end of the second fiber grating is located in the first sub-fiber groove, and the other end of the second fiber grating is located in the second sub-fiber groove.

[0046] The first fiber grating and the third fiber grating can be disposed on any surface of the first receiving portion 41 or any surface of the second receiving portion 42. The first fiber grating and the third fiber grating are not disposed simultaneously in the first receiving portion 41 and the second receiving portion 42 to avoid coupling with the magnetostrictive rod 43. The first fiber grating and the third fiber grating are disposed on the magnetic field strain amplification structure by bonding or adhesive bonding.

[0047] In this embodiment, the first and third fiber gratings can be disposed on the magnetic field strain amplification structure by bonding or other means. As a feasible embodiment, the first and third fiber gratings are correspondingly disposed within the first fiber slot 44 and the third fiber slot, respectively, and are disposed on the magnetic field strain amplification structure by bonding or adhesive bonding. Correspondingly, the first and third fiber slots can be disposed on any surface of the first receiving portion 41 or any surface of the second receiving portion 42, as long as the first and third fiber gratings are not coupled to the magnetostrictive rod 43.

[0048] In another specific embodiment, the second fiber Bragg grating is bonded to the magnetic field strain amplification structure using UV-curable adhesive, with its magnetic sensing direction along the length of the magnetostrictive rod 43, and the adhesive layer thickness controlled within 0.1 mm. The two ends of the magnetostrictive rod 43 are respectively bonded to the first receiving portion 41 and the second receiving portion 42. Under the influence of an external magnetic field, the magnetostrictive rod 43 deforms, thereby causing the magnetic field strain amplification structure to move, thus applying stress to the second fiber Bragg grating. This stress on the second fiber Bragg grating is converted into a drift in its center wavelength. The center wavelength drift of the second fiber Bragg grating is mapped onto a microwave photonics system to achieve sensing.

[0049] To eliminate the influence of temperature changes on magnetic field sensing, the first and third fiber gratings are bonded to the fiber slots of the magnetic field strain amplification structure, enabling them to achieve the same temperature drift response as the second fiber grating. In magnetic field measurement, since the selected pulse's response to temperature depends only on the wavelength difference between the three fiber gratings, and the three fiber gratings are equally spaced, the influence of temperature response on magnetic field measurement can cancel each other out. The magnetostrictive rod 43 is adjusted to the linear sensing range by providing a pre-magnetic field through an external magnet.

[0050] In other embodiments, the sensing module 4 includes multiple magnetic field strain amplification structures. These multiple magnetic field strain amplification structures can be arranged sequentially along the optical path or in parallel. Each magnetic field strain amplification structure is equipped with a second fiber grating for detecting the magnetic field strength at a corresponding location. The specific structure, connection relationship, and working principle of the multiple magnetic field strain amplification structures are the same as or similar to those in the aforementioned embodiments, and will not be repeated here to avoid repetition.

[0051] At the output of the microwave photonics system, the microwave frequency response measurement module 9 measures the system's microwave frequency response. The signal processing module 10, connected to the output of the microwave photonics system, processes the microwave frequency response output by the microwave frequency response measurement module 9 to obtain at least four sets of microwave interference spectra. These four sets of microwave interference spectra include two sets of first microwave interference spectra and two sets of second microwave interference spectra. The first microwave interference spectra include those where the microwave dip peak frequency changes linearly with the magnetic field. The second microwave interference spectra include those where the microwave dip peak frequency changes linearly with temperature. Based on the two sets of first microwave interference spectra, a magnetic field measurement vernier envelope for demodulating the magnetic field is formed. Based on the two sets of second microwave interference spectra, a temperature measurement vernier envelope for demodulating the temperature is formed.

[0052] In one specific embodiment, the signal processing module includes an analog-to-digital conversion unit, a processor, and a storage unit; the analog-to-digital conversion unit is used to convert the analog signal output by the microwave frequency response measurement module into a digital signal, and the processor is used to sequentially perform inverse Fourier transform, time-domain windowing, and Fourier transform on the digital signal to reconstruct at least four sets of microwave interference spectra.

[0053] Specifically, the processor performs the following processing: performing an inverse Fourier transform on the digital signal to obtain the time-domain impulse response; applying a window function to the time-domain impulse response based on the combination of target pulse pairs; performing a Fourier transform on the windowed time-domain signal to reconstruct a single set of microwave interference spectra corresponding to the target pulse pair; repeating the above operations, selecting different target pulse pairs to obtain two sets of first microwave interference spectra and two sets of second microwave interference spectra, for a total of at least four sets of microwave interference spectra. The two sets of first microwave interference spectra are superimposed to form a magnetic field measurement vernier envelope, and the magnetic field is demodulated based on the dip peak frequency shift of the magnetic field measurement vernier envelope; the two sets of second microwave interference spectra are superimposed to form a temperature measurement vernier envelope, and the temperature is demodulated based on the dip peak frequency shift of the temperature measurement vernier envelope.

[0054] It should be noted that the specific implementation methods of the inverse Fourier transform, the window function type and parameter selection, and the Fourier transform can be implemented by those skilled in the art by referring to common knowledge and conventional technical means in the fields of microwave photonics and digital signal processing, and will not be elaborated here.

[0055] The signal processing module 10 is used to sequentially perform inverse Fourier transform, apply a window function, and perform another Fourier transform on the microwave frequency response, reconstructing at least four sets of microwave interference spectra. The detection principle of the signal processing module 10 is as follows: The total signal of the temperature self-calibrating fiber optic magnetic field sensor based on optical microwave interferometry after photoelectric detection and microwave synchronous detection is expressed as follows: ; in, and These represent the amplitude and phase of the microwave signal, respectively; Ω is the microwave scanning frequency; and t is the detection time. Using the microwave frequency response measurement module 9, a frequency scan can be performed to obtain the microwave signal reflection spectrum. After performing an inverse Fourier transform, the time-domain impulse response can be obtained. ; Where M is the modulation amplitude, ranging from 0 to 1. Let be the amplitude reflection coefficient seen by the photodetector for the i-th reflector. , The propagation delay of the reflected signal corresponding to the i-th fiber grating reflection point, The distance from the fiber grating to the circulator corresponds to n, where n is the refractive index of the fiber core. Let W be the length of the arm passing through the interferometer, W be the length of the common circuit, and c be the speed of light in a vacuum.

[0056] Since X(t) is The function, i.e. the reflected signal, is a pulse function related to the position of the reflection point, and the peak value of the function corresponds to the position of the reflection point. This determines the spatial resolution, which is the minimum distance between two reflection points.

[0057] Construct an interference structure by selecting any two reflection peaks. If the window function is expressed as... Then, the time-domain signal after applying the window function is subjected to another Fourier transform and returned to the microwave domain for microwave interference reconstruction. The optical path difference (OPD) of the microwave interference spectrum of the optically carried microwave interference (i.e., the microwave interference spectrum of the Fabry-Perot interferometer described below) can be defined as: ; in, Let i be the distance between the i-th and j-th gratings. Let be the distance from the i-th fiber grating to the optical circulator. Let be the distance from the j-th fiber grating to the optical circulator.

[0058] The free spectral range (FSR) of the reconstructed microwave interferometry spectrum is a function of the optical path difference (OPD), and can be expressed as: ; The resonant frequency (dip frequency) of this microwave interference spectrum can be expressed as: ; The wavelength of a fiber grating drifts under the influence of external sensing parameters. The dispersion effect of the dispersion-compensating fiber 6 (DCF) converts the center wavelength drift of the fiber grating into frequency response fluctuations in the microwave photonics system. ; Where D represents the total dispersion of the dispersion-compensating fiber 6. This refers to the difference in the center wavelengths of the fiber gratings that make up the interferometer.

[0059] The microwave photonic system constitutes a six-tap microwave photonic filter, and operates in an incoherent state due to the use of an incoherent broadband light source system.

[0060] The reflected signals of the second fiber grating and the first fiber grating are transmitted through the double-arm interferometer 5 to form a first pulse pair, and the reflected signals of the second fiber grating and the third fiber grating are transmitted through the double-arm interferometer 5 to form a second pulse pair. The signal processing module 10 processes the first and second pulse pairs to obtain at least two sets of first microwave interference spectra. The two sets of first microwave interference spectra are superimposed to form the envelope of the magnetic field measurement vernier. The frequency change of the dip in the envelope of the magnetic field measurement vernier can be expressed as: ; in, To select the optical path difference of the first set of interferometers composed of pulses P2s and P1s, To select the optical path difference of the second set of interferometers composed of pulses P2s and P3s, The optical path difference of the first set of interferometers changed under the influence of a magnetic field. The optical path difference is altered by the magnetic field affecting the second set of interferometers. represents the optical path difference of the first interferometer group as a function of temperature, and represents the optical path difference of the second interferometer group as a function of temperature.

[0061] Since the center wavelength shift of the two sets of first microwave interference spectra caused by temperature changes is only related to the wavelength difference of the fiber gratings, when the wavelength difference between the two sets of fiber gratings constituting the two sets of first microwave interference spectra is equal, the microwave photonic system is theoretically unaffected by temperature. At this point, the frequency drift of the vernier envelope in magnetic field measurement is only related to the change in magnetic field. Furthermore, since the direction of the frequency dip peak shift is opposite to that of the two sets of first microwave interference spectra when the magnetic field changes, this can enhance the vernier effect and further amplify the sensitivity of magnetic field measurement.

[0062] The reflected signals of the first and third fiber gratings are transmitted through the same interferometer arm of the dual-arm interferometer 5 to form a third pulse pair, and the reflected signals of the first and third fiber gratings are transmitted through different interferometer arms of the dual-arm interferometer 5 to form a fourth pulse pair. The signal processing module 10 processes the third and fourth pulse pairs to obtain at least two sets of second microwave interference spectra. The two sets of second microwave interference spectra are superimposed to form the temperature measurement vernier envelope. The frequency change of the dip in the temperature measurement vernier envelope can be expressed as: ; in, To select the optical path difference of the third interferometer consisting of pulses P1s and P3s, To select the optical path difference of the fourth interferometer group composed of pulses P3s and P3l, The optical path difference of the third interferometer group changes due to temperature variations. The optical path difference of the fourth interferometer group, which also originates from the third fiber optic grating, theoretically changes synchronously, so there is no increment.

[0063] The center wavelength shift of the two sets of second microwave interference spectra caused by temperature changes is only related to the wavelength difference of the fiber grating. That is, the ambient temperature can be sensed by detecting the shift of the dip frequency of the temperature measurement vernier envelope.

[0064] It should be noted that the above formula is based on the core mathematical model for the signal processing module to achieve microwave interferometric spectrum reconstruction and vernier envelope extraction. For the specific derivation of the formula, the selection principle of the window function type, and the parameter matching relationship between the inverse Fourier transform and the Fourier transform, those skilled in the art can refer to relevant content in the fields of microwave photonics and digital signal processing to achieve the microwave interferometric spectrum reconstruction and vernier envelope extraction of this application; therefore, the complete derivation process will not be elaborated here.

[0065] The temperature self-calibration fiber optic magnetic field sensing device based on optical microwave interferometry provided in this embodiment breaks through the limitations of low signal-to-noise ratio and resolution of broadband light source systems. It builds a demodulation system based on microwave photons to conduct dual-parameter sensing experiments on temperature and magnetic field, and maps the changes of external sensing parameters to the microwave domain for demodulation, thereby improving the demodulation rate and resolution.

[0066] The temperature self-calibrating fiber optic magnetic field sensing device based on optically carried microwave interferometry provided by this invention maps optical interference signals to the microwave domain using optically carried microwave interferometry. Three fiber gratings cascaded along the optical path are arranged with equal center wavelengths, and the second fiber grating is coupled to a magnetostrictive rod. This converts the magnetostrictive deformation caused by changes in the magnetic field into a drift in the center wavelength of the second fiber grating, which is further mapped to a frequency drift in the microwave interferogram or vernier envelope. The microwave photonic system includes a two-arm interferometer with a difference in arm length and a dispersion-compensating fiber, converting the wavelength drift into a time delay variation. The signal processing module processes the microwave frequency response output from the microwave frequency response measurement module to obtain at least four sets of microwave interferograms. These four sets of microwave interferograms include two sets of first microwave interferograms and two sets of second microwave interferograms. The first microwave interferograms include those where the microwave dip peak frequency changes linearly with the magnetic field; the second microwave interferograms include those where the microwave dip peak frequency changes linearly with temperature. During magnetic field demodulation, the equal spacing of the center wavelengths of the three fiber gratings, coupled with the coupling between the second fiber grating and the magnetostrictive rod, and the use of a dual-arm interferometer with a difference in arm length and dispersion compensation fiber, reduces the impact of temperature drift on the magnetic field demodulation results. Two sets of microwave interferometric spectra, whose microwave dip peak frequency changes linearly with the magnetic field, form the magnetic field measurement vernier envelope for demodulating the magnetic field. During temperature demodulation, the lack of coupling between the first and third fiber gratings and the magnetostrictive rod, along with the use of a dual-arm interferometer with a difference in arm length and dispersion compensation fiber, allows for the formation of a temperature measurement vernier envelope based on two sets of microwave interferometric spectra whose microwave dip peak frequency changes linearly with temperature. This self-calibrating fiber optic magnetic field sensing device integrates fiber optic interferometric sensing technology with an optically driven microwave interferometric demodulation scheme, achieving high-sensitivity demodulation of both temperature and magnetic fields through vernier enhancement effects.

[0067] The specific details of the temperature self-calibration fiber optic magnetic field sensing method based on optical microwave interferometry provided by this invention will be described in detail in the following embodiments.

[0068] Example 2

[0069] Please refer to Figure 3 , Figure 3 The flowchart illustrates a temperature self-calibration fiber optic magnetic field sensing method based on optical microwave interferometry, as provided in this embodiment of the invention.

[0070] See Figure 3 In this embodiment of the invention, the temperature self-calibrating fiber optic magnetic field sensing method based on optically carried microwave interferometry includes: S101: The broadband incoherent optical signal generated by the light source module is modulated by an electro-optic modulator and then introduced into the sensing module by an optical circulator. The first, second, and third fiber gratings cascaded along the optical path in the sensing module reflect the optical signal. The reflected light is output to the dual-arm interferometer through the optical circulator and split into two paths. The wavelength drift is converted into a time delay change by the dispersion compensation fiber and then converted into an electrical signal by the photoelectric detection module. The microwave frequency response is obtained by the microwave frequency response measurement module through frequency sweep measurement. The center wavelengths of the three fiber gratings are set at equal intervals, and the second fiber grating is coupled to the magnetostrictive rod.

[0071] In this embodiment, during system operation, since the coherence length of the light source is on the order of micrometers and the optical path difference of each reflection path is on the order of meters, the optical carrier does not interfere; only the microwave envelope interferes, satisfying the conditions for optical-carried microwave interference. The system delay consists of three parts: the first part is a fixed delay related to the physical length of the optical fiber; the second part is the delay introduced by the optical fiber passing through the interference arms with different arm lengths; and the third part is the change in delay caused by wavelength variation, which is proportional to the dispersion of the dispersive medium.

[0072] As a specific embodiment, the microwave photonics system includes an erbium-doped fiber amplifier 7. Specifically, the incoherent light emitted by the erbium-doped fiber amplifier 7 enters a Mach-Zehnder modulator (i.e., an electro-optic modulator 2), where it is intensity modulated by a swept-frequency microwave signal output from the first port of the microwave frequency response measurement module 9. The broadband light source is a spontaneous emission source generated by the erbium-doped fiber amplifier 7. The modulated optical signal enters the sensing module 4 via an optical circulator 3, is reflected by the first, second, and third fiber gratings, and returns to the optical circulator 3, then enters the Mach-Zehnder interferometer. After being delayed by the two interferometer arms of the Mach-Zehnder interferometer, the optical signal is amplified by the erbium-doped fiber amplifier 7, converted into an electrical signal by a photodetector, and returns to the second port of the microwave frequency response measurement module 9, where the microwave frequency response measurement module 9 measures the microwave frequency response.

[0073] S102: The signal processing module processes the microwave frequency response and obtains at least four sets of microwave interference spectra; the four sets of microwave interference spectra include two sets of first microwave interference spectra and two sets of second microwave interference spectra; the first microwave interference spectrum includes a microwave interference spectrum in which the microwave dip peak frequency changes linearly with the magnetic field; the second microwave interference spectrum includes a microwave interference spectrum in which the microwave dip peak frequency changes linearly with the temperature.

[0074] In this step, the signal processing module 10 processes the microwave frequency response to obtain at least four sets of microwave interference spectra, including: the signal processing module 10 sequentially performs inverse Fourier transform, applies a window function, and performs Fourier transform on the microwave frequency response, and then reconstructs to obtain at least four sets of microwave interference spectra.

[0075] Specifically, signal processing module 10 performs an inverse Fourier transform on the microwave frequency response to obtain a time-domain pulse. Please refer to [link / reference needed]. Figure 4 , Figure 4 This is a schematic diagram illustrating the sequential order of the six pulses generated according to an embodiment of the present invention. The time-domain pulses include six main pulses, corresponding to: the reflected pulses (P1s, P1l) formed after the first fiber optic grating is transmitted through the short and long arms of the two-arm interferometer 5; the reflected pulses (P2s, P2l) formed after the second fiber optic grating is transmitted through the short and long arms of the two-arm interferometer 5; and the reflected pulses (P3s, P3l) formed after the third fiber optic grating is transmitted through the short and long arms of the two-arm interferometer 5. In this embodiment, the pulse interval and arrangement order can be adjusted according to the actual measurement situation, which will not be elaborated here.

[0076] For magnetic field measurement, the reflected signals of the second fiber grating and the first fiber grating are transmitted through the double-arm interferometer 5 to form a first pulse pair; the reflected signals of the second fiber grating and the third fiber grating are transmitted through the double-arm interferometer 5 to form a second pulse pair; the signal processing module 10 processes the first pulse pair and the second pulse pair to obtain at least two sets of first microwave interference spectra; the first microwave interference spectrum includes a microwave interference spectrum in which the microwave dip peak frequency changes linearly with the magnetic field.

[0077] Specifically, the reflected signals of the second fiber grating and the first fiber grating are transmitted through the same or different interferometer arms of the dual-arm interferometer 5 and then processed to form a first pulse pair; the reflected signals of the second fiber grating and the third fiber grating are transmitted through the same or different interferometer arms of the dual-arm interferometer 5 and then processed to form a second pulse pair; the signal processing module 10 processes the first pulse pair and the second pulse pair to obtain at least two sets of first microwave interference spectra; the first microwave interference spectrum includes a microwave interference spectrum in which the microwave dip peak frequency changes linearly with the magnetic field.

[0078] The signal processing module 10 performs an inverse Fourier transform on the microwave frequency response output by the microwave frequency response measurement module 9 to obtain a time-domain impulse response (time-domain signal), whose time-domain waveform includes multiple pulse peaks corresponding to different optical paths; the target pulse (such as the first pulse pair and the second pulse pair) is selected and time-domain windowed (i.e., a window function is applied), and then reconstructed into a microwave interference spectrum, such as the first microwave interference spectrum and the second microwave interference spectrum, by Fourier transform.

[0079] As a specific embodiment, for magnetic field measurement, a reflected pulse P1s formed by the transmission and processing of a first fiber optic grating through the short arm of a two-arm interferometer 5 and a reflected pulse P2s formed by the transmission and processing of a second fiber optic grating through the short arm of a two-arm interferometer 5 are selected. The reflected pulses P1s and P2s form a first pulse pair. The first pulse pair is then subjected to a window function and a Fourier transform in sequence, and reconstructed to obtain a first set of first microwave interference spectra (i.e., the microwave interference spectrum of the Fabry-Perot interferometer). The microwave dip peak frequency of this first set of first microwave interference spectra increases with the increase of the magnetic field, and it is sensitive to the magnetic field with a positive sign. The second fiber optic grating is transmitted through the short arm of the double-arm interferometer 5 and the resulting reflected pulse P2s is processed. The third fiber optic grating is transmitted through the short arm of the double-arm interferometer 5 and the resulting reflected pulse P3s is processed. The reflected pulses P2s and P3s form a second pulse pair. The second pulse pair is then subjected to window functions and Fourier transforms in sequence, and reconstructed to obtain the second set of first microwave interference spectra (i.e., the microwave interference spectrum of the Fabry-Perot interferometer). The microwave dip peak frequency of this second set of first microwave interference spectra decreases with increasing magnetic field, and it is sensitive to magnetic fields with a negative sensitivity sign.

[0080] For temperature measurement, the reflected signals of the first fiber grating and the third fiber grating are transmitted through the same interferometer arm of the dual-arm interferometer 5 to form a third pulse pair; the reflected signals of the first fiber grating and the third fiber grating are transmitted through different interferometer arms of the dual-arm interferometer 5 to form a fourth pulse pair; the signal processing module 10 processes the third pulse pair and the fourth pulse pair to obtain at least two sets of second microwave interference spectra; the second microwave interference spectrum includes a microwave interference spectrum in which the microwave dip peak frequency changes linearly with temperature.

[0081] As a specific embodiment, for temperature measurement, a reflected pulse P1s formed by the first fiber optic grating after transmission through the short arm of the double-arm interferometer 5 and a reflected pulse P3s formed by the third fiber optic grating after transmission through the short arm of the double-arm interferometer 5 are selected; wherein, the reflected pulses P1s and P3s form a third pulse pair; the third pulse pair is then subjected to window function and Fourier transform sequentially, and then reconstructed to obtain the first set of second microwave interference spectra (i.e., the microwave interference spectrum of the Fabry-Perot interferometer). The microwave dip peak frequency of the first set of second microwave interference spectra increases with increasing temperature, and it is temperature sensitive with a positive sign. The reflected pulse P3s, generated by the transmission of the third fiber optic grating through the short arm of the double-arm interferometer 5 and the reflected pulse P1l, generated by the transmission of the first fiber optic grating through the long arm of the double-arm interferometer 5 and the processing thereof, are selected. The reflected pulses P3s and P1l form a fourth pulse pair. The fourth pulse pair is then subjected to window functions and Fourier transforms in sequence, and reconstructed to obtain the second set of second microwave interference spectra (i.e., the microwave interference spectrum of the Fabry-Perot interferometer). The microwave dip peak frequency of the second set of second microwave interference spectra increases with increasing temperature, and it is temperature sensitive with a positive sign.

[0082] S103: The two sets of first microwave interference spectra are superimposed to form the magnetic field measurement vernier envelope, and the magnetic field is demodulated based on the frequency drift of the dip peak of the magnetic field measurement vernier envelope.

[0083] In this step, the signal processing module 10 processes the first pulse pair and the second pulse pair to obtain at least two sets of first microwave interference spectra. The first microwave interference spectrum includes a microwave interference spectrum in which the microwave dip peak frequency changes linearly with the magnetic field. The two sets of first microwave interference spectra are superimposed to form the magnetic field measurement vernier envelope, and the magnetic field is demodulated based on the dip peak frequency drift of the magnetic field measurement vernier envelope.

[0084] Specifically, the first set of first microwave interferometric spectra and the second set of first microwave interferometric spectra are superimposed to form a magnetic field measurement vernier envelope. The magnetic field change is demodulated by tracking the frequency drift of the dip peak in the magnetic field measurement vernier envelope. Since the frequency of the microwave dip peak in the first set of first microwave interferometric spectra increases with increasing magnetic field, it is sensitive to the magnetic field and has a positive sensitivity sign; while the frequency of the microwave dip peak in the second set of first microwave interferometric spectra decreases with increasing magnetic field, it is also sensitive to the magnetic field and has a negative sensitivity sign. The formed magnetic field measurement vernier envelope can create an enhanced vernier effect, further amplifying the sensitivity of magnetic field detection. Because the center wavelengths of the three fiber gratings are consistent, the microwave dip peak frequencies of the first and second sets of first microwave interferometric spectra, which are affected by temperature, can cancel each other out. The free spectral range of the superimposed first microwave interferometric spectrum is unaffected by temperature changes, thus eliminating the cross-sensitivity between temperature and magnetic field.

[0085] S104: The two sets of second microwave interference spectra are superimposed to form the temperature measurement vernier envelope, and the temperature is demodulated based on the frequency shift of the dip peak of the temperature measurement vernier envelope.

[0086] In this step, the signal processing module 10 processes the third and fourth pulse pairs to obtain at least two sets of second microwave interference spectra. The second microwave interference spectra include microwave interference spectra in which the microwave dip peak frequency changes linearly with temperature. The two sets of second microwave interference spectra are superimposed to form the temperature measurement vernier envelope, and the temperature is demodulated based on the dip peak frequency drift of the temperature measurement vernier envelope.

[0087] Specifically, the first and second sets of second microwave interferometric spectra are superimposed to form a temperature measurement vernier envelope. Temperature changes are demodulated by tracking the frequency drift of the dip peaks in this envelope. The frequency of the microwave dip peaks in the first set of second microwave interferometric spectra increases with increasing temperature, indicating temperature sensitivity with a positive sign. Similarly, the frequency of the microwave dip peaks in the second set of second microwave interferometric spectra also increases with increasing temperature, exhibiting temperature sensitivity with a positive sign. The superposition of these two sets of second microwave interferometric spectra forms the temperature measurement vernier envelope, and high-sensitivity temperature demodulation is achieved by tracking the frequency drift of the dip peaks within this envelope.

[0088] Please refer to Figure 5 , Figure 5 This is a schematic diagram of the demodulation process of a temperature self-calibrating fiber optic magnetic field sensing device based on optical microwave interferometry, provided in an embodiment of the present invention. Figure 5 The present invention includes Figures I, II, and III. Figure I is a schematic diagram of the time-domain impulse response provided in this embodiment. Figure I shows that the signal processing module 10 performs an inverse Fourier transform on the microwave frequency response measured by the microwave frequency response measurement module 9 to obtain the time-domain impulse response h(τ). The time-domain impulse response contains six main pulses, corresponding to the reflected signals of the three fiber gratings formed by the two interferometer arms of the dual-arm interferometer 5, namely P1s, P1l, P2s, P2l, P3s, and P3l. Each pulse peak is separated from the others in the time domain, and any target pulse can be independently extracted by time-domain windowing. Figure II is a schematic diagram of the microwave interference spectrum provided in this embodiment. Figure II shows that after the signal processing module 10 performs time-domain windowing on the selected target pulse pair (such as P1s and P2s), the corresponding microwave interference spectrum is reconstructed by Fourier transform. The microwave interference spectrum is a Fabry-Perot interference spectrum, and its free spectral range is determined by the optical path difference between the two pulses constituting the interference spectrum.

[0089] Figure III illustrates the variation of the dip peak of the temperature measurement vernier envelope with the magnetic field, or the variation of the dip peak of the magnetic field measurement vernier envelope with temperature, provided in an embodiment of the present invention. As shown in Figure III, the dip peak of the magnetic field measurement vernier envelope is formed by superimposing two sets of microwave interferometric spectra sensitive to the magnetic field with opposite sensitivity signs (e.g., the first microwave interferometric spectrum constructed from P1s and P2s, and the second microwave interferometric spectrum constructed from P2s and P3s). When the external magnetic field changes, the position of the dip peak in the magnetic field measurement vernier envelope drifts along the frequency axis. The magnetic field change can be demodulated by tracking the frequency drift of the dip peak. Figure III can also illustrate the superposition of two sets of temperature-sensitive microwave interferometric spectra to form the temperature measurement vernier envelope. The temperature change is demodulated by tracking the frequency drift of the dip peak. The dip peak drift of the vernier envelope is linearly related to both the magnetic field strength and the temperature change, thereby achieving high-sensitivity dual-parameter synchronous measurement of magnetic field and temperature, and temperature self-calibration.

[0090] In this embodiment, the order of steps S103 and S104 can be interchanged, which will not be described in detail here.

[0091] Furthermore, in magnetic field measurement, since the response of the selected pulse to temperature is only related to the difference in the center wavelengths of the three fiber gratings, the P1s, P2s and P3s pulses are each composed of three fiber gratings with equally spaced center wavelengths. When the temperature changes, the center wavelengths of the three fiber gratings drift synchronously, and the wavelength difference between each pulse pair remains unchanged. Therefore, the influence of temperature response on magnetic field measurement can be eliminated, thereby realizing temperature self-calibrated magnetic field sensing.

[0092] The temperature self-calibration fiber optic magnetic field sensing method based on optically carried microwave interferometry provided by this invention maps optical interference signals to the microwave domain using optically carried microwave interferometry. Three fiber gratings cascaded along the optical path have equally spaced center wavelengths, and the second fiber grating is coupled to a magnetostrictive rod. This converts the magnetostrictive deformation caused by changes in the magnetic field into a drift in the center wavelength of the second fiber grating, which is further mapped to a frequency drift in the microwave interferogram or vernier envelope. The microwave photonic system includes a two-arm interferometer with a difference in arm length and a dispersion-compensating fiber, converting the wavelength drift into a time delay variation. A signal processing module processes the microwave frequency response output from the microwave frequency response measurement module to obtain at least four sets of microwave interferograms. These four sets include two sets of first microwave interferograms and two sets of second microwave interferograms. The first microwave interferograms include those where the microwave dip peak frequency changes linearly with the magnetic field; the second microwave interferograms include those where the microwave dip peak frequency changes linearly with temperature. During magnetic field demodulation, the equal spacing of the center wavelengths of the three fiber gratings, coupled with the coupling between the second fiber grating and the magnetostrictive rod, and the use of a dual-arm interferometer with a difference in arm length and dispersion compensation fiber, reduces the impact of temperature drift on the magnetic field demodulation results. Two sets of microwave interferometric spectra, whose microwave dip peak frequency changes linearly with the magnetic field, form the magnetic field measurement vernier envelope for demodulating the magnetic field. During temperature demodulation, the lack of coupling between the first and third fiber gratings and the magnetostrictive rod, along with the use of a dual-arm interferometer with a difference in arm length and dispersion compensation fiber, results in two sets of microwave interferometric spectra, whose microwave dip peak frequency also changes linearly with temperature, forming the temperature measurement vernier envelope. This self-calibrating fiber optic magnetic field sensing device integrates fiber optic interferometric sensing technology with an optically driven microwave interferometric demodulation scheme, achieving high-sensitivity demodulation of both temperature and magnetic fields through vernier enhancement effects.

[0093] In another feasible embodiment, the temperature self-calibrating fiber optic magnetic field sensing device based on optical microwave interferometry of this embodiment can also be extended for two-dimensional magnetic field measurement. Specifically, two magnetic field strain amplification structures (i.e., two sets of magnetic field sensitive units) can be set in the same sensing module, or the two magnetic field strain amplification structures can be arranged in mutually orthogonal directions, so that the extension direction (i.e., the length direction) of each magnetostrictive rod corresponds to the two orthogonal components of the magnetic field to be measured. The fiber gratings in each magnetic field strain amplification structure can be set to different center wavelengths or different spatial positions, so that they have distinguishable reflection peaks in the time-domain pulse response. The signal processing module performs windowing, frequency domain reconstruction, and envelope frequency drift extraction on the corresponding pulse pairs to obtain the magnetic field components in the two orthogonal directions, and further calculates the magnitude and direction of the magnetic field vector.

[0094] Furthermore, multiple magnetic field strain amplification structures can be cascaded along the same fiber optic link, or connected to the same microwave photonic system via optical switches, wavelength division multiplexing, and / or time division multiplexing. By configuring different fiber optic gratings with different center wavelengths, reflection positions, or time-domain delays for different magnetic field strain amplification structures, the identification and independent demodulation of different measurement points can be achieved during signal processing, thereby forming a multi-point array or quasi-distributed magnetic field monitoring system. This structure facilitates large-scale, multi-point continuous magnetic field observation in marine environments, long-distance pipelines, port channels, and underwater target detection scenarios.

[0095] This invention combines a cascaded fiber grating with a magnetostrictive rod-magnetic field strain amplification structure, converting the magnetostrictive deformation caused by magnetic field changes into a fiber grating center wavelength drift, which is further mapped to a frequency drift in the microwave interference spectrum or vernier envelope. The sensing structure is compact and simple to fabricate. Furthermore, by orthogonally arranging multiple magnetic field sensing units or cascading multiple sensing probes, two-dimensional vector magnetic field measurement and multi-point array distributed measurement can be achieved, making it suitable for large-scale magnetic field monitoring scenarios.

[0096] Furthermore, this invention introduces a two-arm Mach-Zehnder interferometer to form a six-tap microwave photonic filter, reconstructing multiple microwave interference spectra through time-domain pulse selection. By selecting pulses P1s and P2s to construct magnetic field-sensitive interference spectra with opposite signs from P2s and P3s, the envelope frequency drift caused by the magnetic field is enhanced, effectively improving the magnetic field measurement sensitivity. Simultaneously, the center wavelengths of the three fiber gratings are equally spaced, ensuring that the synchronous drift of the grating wavelengths caused by temperature changes cancels each other out in the wavelength difference between pulse pairs. This reduces the impact of temperature drift on the magnetic field demodulation results, achieving temperature self-calibration and improving the system's anti-interference capability and measurement reliability.

[0097] This invention maps optical interference signals to the microwave domain using optically carried microwave interferometry. A dual-arm interferometer structure is introduced to construct multiple pulse pairs. By selecting different pulse pairs, temperature-sensitive and magnetic field-sensitive microwave interference spectra are reconstructed. The envelope frequency drift is extracted using the vernier enhancement effect, achieving high-sensitivity synchronous demodulation of temperature and magnetic fields. This sensor can further realize multi-dimensional vector magnetic field measurement and network array observation, making it suitable for long-term, high-precision magnetic field gradient detection in marine environments.

[0098] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on its differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. For the apparatus disclosed in the embodiments, since it corresponds to the method disclosed in the embodiments, the description is relatively simple; relevant parts can be referred to in the method section.

[0099] Those skilled in the art will further recognize that the units and algorithm steps of the various examples described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, computer software, or a combination of both. To clearly illustrate the interchangeability of hardware and software, the components and steps of the various examples have been generally described in terms of functionality in the foregoing description. Whether these functions are implemented in hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementations should not be considered beyond the scope of this invention.

[0100] The steps of the methods or algorithms described in conjunction with the embodiments disclosed herein can be implemented directly by hardware, a software module executed by a processor, or a combination of both. The software module can be located in random access memory (RAM), main memory, read-only memory (ROM), electrically programmable ROM, electrically erasable programmable ROM, registers, hard disk, removable disk, CD-ROM, or any other form of storage medium known in the art.

[0101] Finally, it should be noted that in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes the element.

[0102] The above provides a detailed description of the temperature self-calibration fiber optic magnetic field sensing device and method based on optically carried microwave interferometry provided by this invention. Specific examples have been used to illustrate the principles and implementation methods of this invention. The descriptions of the above embodiments are merely for the purpose of helping to understand the method and core ideas of this invention. It should be noted that those skilled in the art can make various improvements and modifications to this invention without departing from its principles, and these improvements and modifications also fall within the protection scope of this invention.

Claims

1. A temperature self-calibrating fiber optic magnetic field sensing device based on optical microwave interferometry, characterized in that, include: The sensing module includes a first fiber grating, a second fiber grating, and a third fiber grating cascaded along the optical path; the center wavelengths of the three fiber gratings are equally spaced; the second fiber grating is coupled to a magnetostrictive rod; A microwave photonic system includes a light source module, an electro-optic modulator, an optical circulator, a two-arm interferometer, a dispersion compensation fiber, a photoelectric detection module, and a microwave frequency response measurement module connected sequentially along an optical path; the optical circulator is connected to the sensing module and the two-arm interferometer respectively, and the two interferometer arms of the two-arm interferometer have a difference in arm length. A signal processing module is connected to the microwave frequency response measurement module. The signal processing module processes the microwave frequency response output by the microwave frequency response measurement module to obtain at least four sets of microwave interference spectra. The four sets of microwave interference spectra include two sets of first microwave interference spectra and two sets of second microwave interference spectra. The first microwave interference spectra include microwave interference spectra where the microwave dip peak frequency changes linearly with the magnetic field. The second microwave interference spectra include microwave interference spectra where the microwave dip peak frequency changes linearly with temperature. Among them, based on the two sets of the first microwave interferometric spectra, a magnetic field measurement vernier envelope for demodulating the magnetic field is formed; Based on the two sets of the second microwave interferometric spectra, a temperature measurement vernier envelope for demodulated temperature is formed.

2. The temperature self-calibrating fiber optic magnetic field sensing device based on optical microwave interferometry according to claim 1, characterized in that, The sensing module includes a magnetic field strain amplification structure, which includes a first receiving portion and a second receiving portion disposed opposite to each other. The first receiving portion and the second receiving portion are connected by the magnetostrictive rod, one end of the magnetostrictive rod is disposed in the first receiving portion, and the other end of the magnetostrictive rod is disposed in the second receiving portion; The extension direction of the second fiber grating is parallel to the axis of the magnetostrictive rod or has an angle of no more than 1 degree. One end of the second fiber grating is disposed in the first receiving portion, and the other end of the second fiber grating is disposed in the second receiving portion; the grating region of the second fiber grating is located in the area between the first receiving portion and the second receiving portion.

3. The temperature self-calibrating fiber optic magnetic field sensing device based on optical microwave interferometry according to claim 2, characterized in that, The magnetic field strain amplification structure also includes an external magnet, which is used to provide a pre-magnetic field. The pre-magnetic field is uniformly distributed in the extension direction of the magnetostrictive rod, so that the magnetostrictive rod is in the linear sensing range when it is working.

4. The temperature self-calibrating fiber optic magnetic field sensing device based on optical microwave interferometry according to claim 2, characterized in that, The first receiving portion or the second receiving portion is provided with a first optical fiber groove; the first fiber grating is located in the first optical fiber groove; The first or second accommodating part is provided with a third fiber optic slot; the third fiber optic grating is located in the third fiber optic slot.

5. The temperature self-calibrating fiber optic magnetic field sensing device based on optical microwave interferometry according to claim 2, characterized in that, The first receiving portion is provided with a first sub-fiber groove, and the second receiving portion is provided with a second sub-fiber groove. The first sub-fiber groove and the second sub-fiber groove are arranged correspondingly along the extension direction of the second fiber grating. One end of the second fiber grating is located in the first sub-fiber slot, and the other end of the second fiber grating is located in the second sub-fiber slot.

6. The temperature self-calibrating fiber optic magnetic field sensing device based on optical microwave interferometry according to claim 1, characterized in that, The microwave frequency response measurement module includes a high-speed sweep frequency source and a high-speed acquisition card, or a vector network analyzer.

7. The temperature self-calibrating fiber optic magnetic field sensing device based on optical microwave interferometry according to claim 1, characterized in that, The dual-arm interferometer includes two 1×2 optical couplers, and the beam splitting ratio of the dual-arm interferometer is 50:

50.

8. A temperature self-calibrating fiber optic magnetic field sensing method based on optically carried microwave interferometry, using the temperature self-calibrating fiber optic magnetic field sensing device based on optically carried microwave interferometry as described in any one of claims 1 to 7, characterized in that, include: The broadband incoherent optical signal generated by the light source module is modulated by an electro-optic modulator and then introduced into the sensing module by an optical circulator. The first, second, and third fiber gratings cascaded along the optical path in the sensing module reflect the optical signal. The reflected light is output to a two-arm interferometer through the optical circulator and split into two paths. The wavelength drift is converted into a time delay change by a dispersion compensation fiber, and then converted into an electrical signal by a photoelectric detection module. The microwave frequency response is obtained by a microwave frequency response measurement module through frequency sweep measurement. The center wavelengths of the three fiber gratings are equally spaced, and the second fiber grating is coupled to a magnetostrictive rod. The signal processing module processes the microwave frequency response to obtain at least four sets of microwave interference spectra; the four sets of microwave interference spectra include two sets of first microwave interference spectra and two sets of second microwave interference spectra; the first microwave interference spectra include microwave interference spectra in which the microwave dip peak frequency changes linearly with the magnetic field; the second microwave interference spectra include microwave interference spectra in which the microwave dip peak frequency changes linearly with the temperature. The two sets of the first microwave interference spectrum are superimposed to form the magnetic field measurement vernier envelope, and the magnetic field is demodulated according to the dip peak frequency drift of the magnetic field measurement vernier envelope. The two sets of the second microwave interference spectra are superimposed to form a temperature measurement vernier envelope, and the temperature is demodulated based on the dip peak frequency drift of the temperature measurement vernier envelope.

9. The temperature self-calibrating fiber optic magnetic field sensing method based on optical microwave interferometry according to claim 8, characterized in that, The signal processing module processes the microwave frequency response to obtain at least four sets of microwave interference spectra, including: The signal processing module sequentially performs inverse Fourier transform, applies a window function, and performs another Fourier transform on the microwave frequency response, and then reconstructs at least four sets of microwave interference spectra.

10. The temperature self-calibrating fiber optic magnetic field sensing method based on optical microwave interferometry according to claim 8, characterized in that, The reflected signal of the second fiber grating and the reflected signal of the first fiber grating are respectively transmitted through the double-arm interferometer to form a first pulse pair; The reflected signals of the second fiber grating and the third fiber grating are transmitted through the two-arm interferometer to form a second pulse pair; The signal processing module processes the first pulse pair and the second pulse pair to obtain at least two sets of first microwave interference spectra; The first microwave interference spectrum includes a microwave interference spectrum in which the microwave dip peak frequency changes linearly with the magnetic field.

11. The temperature self-calibrating fiber optic magnetic field sensing method based on optical microwave interferometry according to claim 8, characterized in that, The reflected signals of the first fiber grating and the third fiber grating are transmitted through the same interferometer arm of the two-arm interferometer to form a third pulse pair; The reflected signals of the first fiber grating and the third fiber grating are transmitted through different interferometer arms of the two-arm interferometer to form a fourth pulse pair; The signal processing module processes the third pulse pair and the fourth pulse pair to obtain at least two sets of second microwave interference spectra; The second microwave interference spectrum includes a microwave interference spectrum in which the microwave dip peak frequency changes linearly with temperature.

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