Microwave photon cascade four-passband demodulation method and device

Abstract

The application discloses a microwave photon cascade four-passband demodulation method, and belongs to the technical field of microwave photon sensing. A broadband optical signal is made to pass through a fiber sensing element formed by cascading two Mach-Zehnder fiber interferometers with different optical path differences, so as to form a cascade spectrum slice; a swept frequency radio frequency signal is modulated on the cascade spectrum slice, and after dispersion delay and photoelectric conversion are sequentially performed on the obtained modulated optical signal, an electrical signal containing four microwave photon filter passbands respectively corresponding to two optical path differences, a sum of the two optical path differences and a difference between the two optical path differences is obtained; the microwave photon filter passband corresponding to the difference between the two optical path differences in the electrical signal is taken to be demodulated, so that a to-be-measured parameter with temperature common-mode interference suppressed is obtained. The application further discloses a microwave photon cascade four-passband demodulation device. The application can suppress temperature common-mode interference, and does not need to increase additional devices, a calibration process or a data processing module, so that system complexity and implementation cost are effectively reduced.

Description

Technical Field

[0001] This invention relates to a microwave photonic cascaded four-passband demodulation method and apparatus, belonging to the field of microwave photonic sensing technology. Background Technology

[0002] Fiber optic sensing technology boasts advantages such as resistance to electromagnetic interference, high sensitivity, small size, and ease of long-distance transmission, and has been widely applied in fields such as structural health monitoring, industrial measurement, and environmental sensing. Currently, fiber optic sensing research is gradually developing towards higher sensitivity, faster demodulation, multi-parameter measurement, and resistance to environmental interference. Related research mainly focuses on the innovation of novel fiber optic materials, composite interference structures, multi-channel sensing, and demodulation methods for phase, frequency, and wavelength.

[0003] Microwave photonic sensing can map the spectral response of a fiber optic interferometer to the radio frequency domain. Through electro-optic modulation, dispersion delay, and photodetection, the microwave photonic filter passband can be obtained on a vector network analyzer. Changes in optical path difference caused by external parameters such as curvature, strain, and temperature can be manifested as changes in the passband center frequency, amplitude, or phase. Compared with traditional spectrometer demodulation, this method has advantages such as high resolution, fast response speed, and ease of phase measurement.

[0004] However, fiber optic interferometers are also affected by ambient temperature while responding to target parameters. Temperature changes alter the effective refractive index and length of the fiber through thermo-optic and thermal expansion effects, causing optical path difference drift, which is superimposed on the response of the target parameters. Existing technologies typically employ methods such as reference sensors, sensitivity matrix decoupling, special packaging, isothermal control, or digital compensation to reduce temperature crosstalk. However, these methods often require additional components, calibration processes, or data processing modules, leading to a more complex system structure and demodulation process.

[0005] To improve sensing sensitivity, researchers have proposed a microwave photonic cascaded four-passband demodulation technique. This technique involves cascading two interferometers of different lengths or with different free spectral ranges, allowing the two sets of interference responses to interact and generate a vernier effect or multiple combined passbands. In a microwave photonic link, cascading two Mach-Zehnder fiber interferometers with different optical path differences can form independent passbands corresponding to the two optical path differences, as well as combined passbands generated by the addition and subtraction of the two optical path differences. Existing schemes typically select the superimposed passband formed by the addition of optical path differences for demodulation, utilizing its larger equivalent optical path difference to improve sensing sensitivity.

[0006] However, while superimposing the passband enhances the target parametric response, it also superimposes the temperature responses of the two interferometer segments, making temperature crosstalk more pronounced. When both interferometer segments are simultaneously affected by ambient temperature, their common temperature drift is difficult to eliminate through superimposed passbands, thus affecting measurement accuracy and long-term stability. Summary of the Invention

[0007] The purpose of this invention is to overcome the problems of existing fiber optic interferometric microwave photonic sensing systems being susceptible to environmental temperature influences, and existing cascaded interferometers mainly using superimposed passbands to improve sensitivity, which further amplifies temperature crosstalk. This invention provides a microwave photonic cascaded four-passband demodulation method that can accurately acquire the target parameter response while suppressing common-mode interference caused by environmental temperature, without the need for additional devices, calibration processes, or data processing modules, effectively reducing the complexity and implementation cost of the sensing system.

[0008] The present invention specifically adopts the following technical solutions to solve the above-mentioned technical problems: A microwave photonic cascaded four-passband demodulation method involves passing a broadband optical signal through a fiber optic sensing element composed of two cascaded Mach-Zehnder fiber interferometers with different optical path differences, forming a cascaded spectral slice. A swept-frequency radio frequency signal is modulated onto the cascaded spectral slice, and the resulting modulated optical signal is sequentially subjected to dispersion delay and photoelectric conversion to obtain an electrical signal containing four microwave photonic filter passbands corresponding to two optical path differences, the sum of two optical path differences, and the difference between two optical path differences, respectively. Based on the demodulation of the electrical signal, a non-ambient temperature parameter acting on the fiber optic sensing element is obtained. The fiber optic sensing element is configured such that the parameter to be measured acts only on one of the Mach-Zehnder fiber interferometers, and the two Mach-Zehnder fiber interferometers are under the same ambient temperature. Specifically, the parameter to be measured acting on the fiber optic sensing element is obtained by demodulating the microwave photonic filter passband corresponding to the difference between two optical path differences in the electrical signal to obtain a parameter to be measured with suppressed temperature common-mode interference.

[0009] Preferably, both Mach-Zehnder fiber interferometers are seven-core fiber Mach-Zehnder interferometers.

[0010] Preferably, the parameter to be measured is one of the following physical parameters: curvature, strain, displacement, and pressure.

[0011] Based on the same inventive concept, the following technical solutions can also be obtained: A microwave photonic cascaded four-band demodulation device includes: A light source used to generate broadband optical signals; The fiber optic sensing element is composed of two Mach-Zehnder fiber interferometers with different optical path differences cascaded together, which is used to form a cascaded spectral slice after broadband optical signals pass through it. An electro-optic modulator is used to electro-optically modulate a swept radio frequency signal onto the cascaded spectral slice; Dispersive elements are used to perform dispersive delay on the modulated optical signal output by the electro-optic modulator; A photodetector is used to perform photoelectric conversion on a dispersive delayed modulated optical signal to obtain an electrical signal whose frequency response includes four microwave photonic filter passbands. The four microwave photonic filter passbands correspond to two optical path differences, the sum of two optical path differences, and the difference between two optical path differences, respectively. A signal processing module is used to demodulate the electrical signal to obtain the non-ambient temperature parameter acting on the fiber optic sensing element. The fiber optic sensing element is configured such that the parameter to be measured acts only on one of the Mach-Zehnder fiber interferometers, and the two Mach-Zehnder fiber interferometers are under the same ambient temperature; the parameter to be measured acting on the fiber optic sensing element is obtained by demodulating the electrical signal, specifically by taking the microwave photonic filter passband corresponding to the difference between the two optical path differences in the electrical signal and demodulating it to obtain the parameter to be measured with temperature common-mode interference suppressed.

[0012] Preferably, both Mach-Zehnder fiber interferometers are seven-core fiber Mach-Zehnder interferometers.

[0013] Preferably, the parameter to be measured is one of the following physical parameters: curvature, strain, displacement, and pressure.

[0014] Compared with the prior art, the technical solution of the present invention has the following beneficial effects: This invention utilizes two cascaded Mach-Zehnder fiber interferometers with different optical path differences to construct a four-passband microwave photonic filter response. Unlike existing technologies that use superimposed passbands to improve sensitivity, this invention selects differential passbands for sensing demodulation, which can effectively suppress common-mode crosstalk caused by ambient temperature. Furthermore, it eliminates the need for additional devices, calibration processes, or data processing modules, thereby effectively reducing the complexity and implementation cost of the sensing system. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the system structure of a specific embodiment of the microwave photonic cascaded four-band demodulation device of the present invention; Figure 2 The diagram below shows the structure of the fiber optic sensing element in a specific embodiment. It is composed of two cascaded seven-core fiber Mach-Zehnder interferometers of different lengths. The first seven-core fiber interferometer has a fiber length of 16.2 cm, and the second seven-core fiber interferometer has a fiber length of 33.4 cm. Figure 3 The diagram shows the four microwave photonic filter passbands generated in a specific embodiment and their frequency shift characteristics under the influence of external parameters; where (a) is the four-passband response in the initial state, (b) is the frequency shift characteristics of the four passbands when only the first seven-core fiber interferometer is subjected to external parameters, and (c) is the frequency shift characteristics of the four passbands when both seven-core fiber interferometers are subjected to the same temperature change. Detailed Implementation

[0016] To address the issues of existing fiber optic interferometric microwave photonic sensing systems being susceptible to ambient temperature fluctuations, and the problem that existing cascaded interferometers primarily utilize superimposed passbands to enhance sensitivity while further amplifying temperature crosstalk, this invention offers a solution. Based on existing microwave photonic cascaded four-passband demodulation devices, the measured parameter is applied only to one Mach-Zehnder fiber interferometer within the cascaded interferometer, with both Mach-Zehnder interferometers operating at the same ambient temperature. Furthermore, it abandons the existing method of using superimposed passbands for demodulation, instead selecting differential passbands for demodulation, thereby effectively suppressing common-mode crosstalk caused by ambient temperature.

[0017] The present invention specifically adopts the following technical solutions to solve the above-mentioned technical problems: A microwave photonic cascaded four-passband demodulation method involves passing a broadband optical signal through a fiber optic sensing element composed of two cascaded Mach-Zehnder fiber interferometers with different optical path differences, forming a cascaded spectral slice. A swept-frequency radio frequency signal is modulated onto the cascaded spectral slice, and the resulting modulated optical signal is sequentially subjected to dispersion delay and photoelectric conversion to obtain an electrical signal containing four microwave photonic filter passbands corresponding to two optical path differences, the sum of two optical path differences, and the difference between two optical path differences, respectively. Based on the demodulation of the electrical signal, a non-ambient temperature parameter acting on the fiber optic sensing element is obtained. The fiber optic sensing element is configured such that the parameter to be measured acts only on one of the Mach-Zehnder fiber interferometers, and the two Mach-Zehnder fiber interferometers are under the same ambient temperature. Specifically, the parameter to be measured acting on the fiber optic sensing element is obtained by demodulating the microwave photonic filter passband corresponding to the difference between two optical path differences in the electrical signal to obtain a parameter to be measured with suppressed temperature common-mode interference.

[0018] A microwave photonic cascaded four-band demodulation device includes: A light source used to generate broadband optical signals; The fiber optic sensing element is composed of two Mach-Zehnder fiber interferometers with different optical path differences cascaded together, which is used to form a cascaded spectral slice after broadband optical signals pass through it. An electro-optic modulator is used to electro-optically modulate a swept radio frequency signal onto the cascaded spectral slice; Dispersive elements are used to perform dispersive delay on the modulated optical signal output by the electro-optic modulator; A photodetector is used to perform photoelectric conversion on the modulated optical signal after dispersion delay to obtain an electrical signal containing four microwave photonic filter passbands corresponding to two optical path differences, the sum of two optical path differences, and the difference between two optical path differences, respectively. A signal processing module is used to demodulate the electrical signal to obtain the non-ambient temperature parameter acting on the fiber optic sensing element. The fiber optic sensing element is configured such that the parameter to be measured acts only on one of the Mach-Zehnder fiber interferometers, and the two Mach-Zehnder fiber interferometers are under the same ambient temperature; the parameter to be measured acting on the fiber optic sensing element is obtained by demodulating the electrical signal, specifically by taking the microwave photonic filter passband corresponding to the difference between the two optical path differences in the electrical signal and demodulating it to obtain the parameter to be measured with temperature common-mode interference suppressed.

[0019] The Mach-Zehnder fiber interferometer can adopt various existing structures. Preferably, both Mach-Zehnder fiber interferometers are seven-core fiber Mach-Zehnder interferometers.

[0020] The parameter to be measured can be any physical parameter other than temperature. Preferably, the parameter to be measured is one of the following physical parameters: curvature, strain, displacement, and pressure.

[0021] To facilitate public understanding, the technical solution of the present invention will be described in detail below through a specific embodiment and in conjunction with the accompanying drawings: The microwave photonic cascaded four-passband demodulation device in this embodiment is similar to existing microwave photonic cascaded four-passband demodulation devices, such as... Figure 1 As shown, the system includes a broadband light source (BOS), an optical isolator (ISO), a first fiber Mach-Zehnder interferometer (Interferometer1), a second fiber Mach-Zehnder interferometer (Interferometer2), a polarization controller (PC), an electro-optic modulator (EOM), a dispersion compensation fiber (DCF), an erbium-doped fiber amplifier (EDFA), and a photodetector (PD) connected sequentially along the optical path, as well as a vector network analyzer (VNA) connected to the electro-optic modulator and the photodetector, respectively.

[0022] The broadband optical signal generated by the broadband light source passes sequentially through a first fiber Mach-Zehnder interferometer and a second fiber Mach-Zehnder interferometer with different optical path differences to form a cascaded spectral slice. An electro-optic modulator modulates a swept-frequency radio frequency signal onto the cascaded spectral slice to generate a modulated optical signal. This signal is then subjected to dispersion delay via a dispersion-compensating fiber and photoelectric conversion via a photodetector to obtain an electrical signal containing four microwave photonic filter passbands corresponding to two optical path differences, the sum of two optical path differences, and the difference between two optical path differences, respectively. The RF output and RF input of a vector network analyzer are connected to the RF input of the electro-optic modulator and the electrical output of the photodetector, respectively, to modulate the swept-frequency radio frequency signal onto the optical signal, measure the amplitude-frequency response and phase-frequency response of the four microwave photonic filter passbands in the electrical signal, and then demodulate to obtain the parameter to be measured. A polarization controller is used to adjust the polarization state of the optical signal entering the electro-optic modulator, and an erbium-doped fiber amplifier is used to compensate for optical power loss in the link.

[0023] In this embodiment, both the first and second fiber optic Mach-Zehnder interferometers are seven-core fiber optic Mach-Zehnder interferometers. Figure 2 As shown, the seven-core fiber Mach-Zehnder interferometer employs an SMF-SCF-SMF structure, which involves fusing a seven-core fiber between two single-mode fiber segments. When incident light enters the seven-core fiber from the single-mode fiber, it primarily excites two supermodes with different effective refractive indices at the fusion interface. These two supermodes propagate together within the seven-core fiber, gradually accumulating a phase difference due to their different propagation constants. Upon reaching the second fusion point, the two supermodes recouple back into the single-mode fiber and interfere, thus forming a periodic interference spectrum. Figure 2 The two interferometers in the study have identical structures, but their seven-core fiber lengths are 16.2 cm and 33.4 cm, respectively. Due to the different propagation lengths, they produce different optical path differences and free spectral ranges, which can be used to subsequently construct microwave photonic filter passbands with different characteristic frequencies. For ease of description, the interferometer with a seven-core fiber length of 16.2 cm is designated as the short interferometer, and the interferometer with a seven-core fiber length of 33.4 cm is designated as the long interferometer. Under the same ambient temperature, non-temperature parameters such as curvature, strain, displacement, and pressure act only on one of the seven-core fiber Mach-Zehnder interferometers, while the other seven-core fiber Mach-Zehnder interferometer is unaffected by these parameters.

[0024] The technical principles of the present invention will be further explained in detail below: After the optical signal is coupled from a single-mode fiber into a seven-core fiber, it excites transmission modes with different effective refractive indices. These modes accumulate phase differences during propagation and recouple at the output, causing interference. The optical path difference of the i-th seven-core fiber interferometer is expressed as: In the formula, For the first i The optical path difference of the interferometer The effective refractive index difference between the two modes involved in the interference. The length of the seven-core optical fiber is given. The optical path difference between the short and long interferometers is denoted as OPDs and OPD, respectively. l .

[0025] When two seven-core fiber optic interferometers are cascaded, the total transmission function is the product of the transmission functions of the two interferometers. Expanding using the product-to-difference relationship of trigonometric functions, the cascaded interference spectrum contains four periodic components corresponding to the optical path difference of the short interferometer, the difference between the optical path differences of the two interferometers, the optical path difference of the long interferometer, and the sum of the optical path differences of the two interferometers, respectively. These are: like Figure 3 As shown, in a microwave photonic link, cascading two seven-core fiber interferometers with different optical path differences allows for the analysis of vector network analyzers. Four separate microwave photonic filter passbands are formed in the amplitude-frequency response. These four passbands correspond to the optical path difference between the two interferometers themselves, as well as the subtraction and addition terms of their optical path differences, thus constituting a typical cascaded four-passband response. The four corresponding equivalent optical path differences are as follows: When the operating wavelength is narrow and the effective refractive index difference of the participating interference modes varies negligibly with wavelength, the free spectral range of the interference spectrum is approximately inversely proportional to the corresponding equivalent optical path difference. Let the total dispersion of the dispersion-compensating fiber be... D The center wavelength of the broadband light source's operating band is λ If 0, then the center frequency of the first-order microwave photonic filter passband can be expressed as: make: Then we have: As can be seen from the above formula, under the condition that the center wavelength and the total dispersion of the dispersion compensation fiber remain unchanged, the center frequency of the microwave passband is proportional to its corresponding equivalent optical path difference. Figure 3 (a) in the figure represents the initial four-passband response of the system without any external disturbance. The horizontal axis represents the frequency f (MHz), and the vertical axis represents the amplitude (dB). The four passbands on the vector network analyzer, arranged in ascending order of center frequency, are denoted as follows: f 1. f 2. f 3. f 4, then: in, f 1 represents the independent passband corresponding to the short interferometer. f 2 represents the differential passband formed by subtracting the optical path differences between the two interferometers. f 3 represents the independent passband corresponding to the long interferometer. f 4 represents the superimposed passband formed by adding the optical path differences of the two interferometers. When the effective refractive index difference between the two seven-core optical fibers participating in the interference modes is close, and the following conditions are met: At that time, the four passbands satisfy: By appropriately selecting the lengths of two seven-core optical fibers, the center frequency interval between adjacent passbands can be made greater than the passband bandwidth, thereby avoiding passband overlap or aliasing.

[0026] Taking the application of only an external parameter to be measured to a short interferometer as an example, such as Figure 3 As shown in (b), the response changes of the four passbands are observed when only interferometer 1 is subjected to external parameters (e.g., curvature, strain, or temperature changes). Solid lines in the figure represent the original passbands, and dashed lines represent the changed passbands. Since only the optical path difference of interferometer 1 changes, while interferometer 2 remains constant, therefore: the independent passband directly corresponding to interferometer 1... Frequency shift will occur; due to Determined superposition passband Frequency shift can also occur; by Determined differential passband Frequency shifts will also occur; the independent passband is only related to interferometer 2. It remains essentially unchanged. This is exactly the result shown in the graph: Blue shift occurs; Redshift occurs; Almost no drift; A blue shift has occurred.

[0027] Let the change in optical path difference caused by this parameter be... δ S The optical path difference of the long interferometer remains constant, and OPDs > OPD is always satisfied throughout the entire measurement range. l The changes in the center frequencies of the four passbands are: From the above formula, we can see that f 1 and f The frequency shift directions of 4 are the same, and the differential passband is... f The frequency shift direction of 2 is opposite to that of the interferometer, and the independent passband corresponds to the long interferometer. f 2 remains essentially unchanged, and: Therefore, it can be tracked f 1. f 2 or f Any passband in section 4 demodulates the external parameters applied to the short interferometer; simultaneously, it can utilize... f 3. Monitor the status of the reference interferometer.

[0028] Unlike existing technologies that use superimposed passbands f 4. To improve sensitivity, the present invention uses the differential passband of the electrical signal corresponding to the difference between two optical path differences to perform demodulation. f 2. By demodulating the changes in amplitude, frequency, or phase, the measured parameter with suppressed temperature common-mode interference can be obtained.

[0029] To evaluate the ability of the differential passband to suppress common-mode temperature disturbances, temperature calibrations were first performed on both the short and long interferometers. Figure 3 (c) in the diagram represents the variation of the four passbands when both interferometers are subjected to the same ambient temperature change simultaneously. In this case, the optical path difference between the two interferometers will change; therefore, the independent passband corresponding to interferometer 1 is... Frequency shift will occur; the independent passband corresponding to interferometer 2 Frequency shifts and superimposed passbands can also occur. The cumulative effect of changes in both will result in a more pronounced frequency shift; differential passband Since the changes in both are canceled out during the subtraction operation, almost no frequency shift occurs. This is precisely the phenomenon shown in the figure: Approximate blueshift; Approximate blueshift; The blue shift is more pronounced; Almost no drift. This means It is insensitive to common external disturbances of the two interferometers, and in particular, it has a natural ability to suppress common temperature changes. Tracking when only the temperature of the short interferometer is changed The fitted relationship is obtained: When only the temperature of the long interferometer is changed, tracking The fitted relationship is obtained: ;in, and The temperature frequency sensitivity is defined for two independent passbands. Subsequently, the two interferometers are placed in the same temperature environment. This ensures that the measurement range consistently meets the following requirements. At that time, the temperature responses of the differential passband and the superimposed passband are respectively: The above equation shows that the superimposed passband accumulates the temperature responses of the two interferometer segments, while the differential passband subtracts the temperature responses of the two interferometer segments. The temperature frequency sensitivity of the two independent passbands should be based on the actual calibration results. The above calibration results show that... and With the same direction and similar values, the residual temperature sensitivity of the differential passband The temperature common-mode suppression is effectively achieved by reducing the passband by about an order of magnitude compared to any independent passband. The above results are determined by the actual fitting coefficients, rather than by the length relationship between the two seven-core fiber segments.

[0030] In a curvature sensing example, a 33.4 cm long interferometer is selected as the curvature sensing unit, and a 16.2 cm short interferometer is selected as the reference unit. Both interferometers are affected by changes in ambient temperature, while curvature is applied only to the long interferometer. Let the curvature frequency sensitivity of the long interferometer be... The frequency shift of the differential passband is expressed as: when: At that time, there were: In the formula, This represents the change in curvature relative to the initial state. This represents the change in ambient temperature. A calibration relationship between the differential passband frequency shift and the change in curvature is established beforehand. And track in real time By determining the center frequency, one can obtain the curvature measurement results where temperature crosstalk is suppressed.

Claims

1. A microwave photonic cascaded four-passband demodulation method, comprising: passing a broadband optical signal through a fiber optic sensing element composed of two Mach-Zehnder fiber interferometers cascaded with different optical path differences to form a cascaded spectral slice; modulating a swept-frequency radio frequency signal onto the cascaded spectral slice; and sequentially performing dispersion delay and photoelectric conversion on the obtained modulated optical signal to obtain an electrical signal containing four microwave photonic filter passbands corresponding to two optical path differences, the sum of two optical path differences, and the difference between two optical path differences; and demodulating the electrical signal to obtain a non-ambient temperature parameter acting on the fiber optic sensing element; characterized in that... The fiber optic sensing element is configured such that the parameter to be measured acts only on one of the Mach-Zehnder fiber interferometers, and the two Mach-Zehnder fiber interferometers are under the same ambient temperature; the parameter to be measured acting on the fiber optic sensing element is obtained by demodulating the electrical signal, specifically by taking the microwave photonic filter passband corresponding to the difference between the two optical path differences in the electrical signal and demodulating it to obtain the parameter to be measured with temperature common-mode interference suppressed.

2. The microwave photonic cascaded four-passband demodulation method as described in claim 1, characterized in that, Both of the aforementioned Mach-Zehnder fiber interferometers are seven-core fiber Mach-Zehnder interferometers.

3. The microwave photonic cascaded four-passband demodulation method as described in claim 1, characterized in that, The parameter to be measured is one of the following physical parameters: curvature, strain, displacement, and pressure.

4. A microwave photonic cascaded four-band demodulation device, comprising: A light source used to generate broadband optical signals; The fiber optic sensing element is composed of two Mach-Zehnder fiber interferometers with different optical path differences cascaded together, which is used to form a cascaded spectral slice after broadband optical signals pass through it. An electro-optic modulator is used to modulate a swept radio frequency signal onto the cascaded spectral slice; Dispersive elements are used to perform dispersive delay on the modulated optical signal output by the electro-optic modulator; A photodetector is used to perform photoelectric conversion on a dispersive delayed modulated optical signal to obtain an electrical signal whose frequency response includes four microwave photonic filter passbands. The four microwave photonic filter passbands correspond to two optical path differences, the sum of two optical path differences, and the difference between two optical path differences, respectively. A signal processing module is used to demodulate the electrical signal to obtain the non-ambient temperature parameter acting on the fiber optic sensing element. The feature is that the fiber optic sensing element is configured such that the parameter to be measured acts only on one of the Mach-Zehnder fiber interferometers, and the two Mach-Zehnder fiber interferometers are under the same ambient temperature; the parameter to be measured acting on the fiber optic sensing element is obtained based on the demodulation of the electrical signal, specifically by taking the microwave photonic filter passband corresponding to the difference between the two optical path differences in the electrical signal and demodulating it to obtain the parameter to be measured with temperature common-mode interference suppressed.

5. The microwave photonic cascaded four-band demodulation device as described in claim 4, characterized in that, Both of the aforementioned Mach-Zehnder fiber interferometers are seven-core fiber Mach-Zehnder interferometers.

6. The microwave photonic cascaded four-band demodulation device as described in claim 4, characterized in that, The parameter to be measured is one of the following physical parameters: curvature, strain, displacement, and pressure.

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