A microwave interferometric fiber-optic sensing system for measuring the Faraday rotation angle

Abstract

The application provides a microwave interference optical fiber sensing system for measuring Faraday rotation angle, comprising an optical carrier microwave generating device, a magneto-optical crystal, a polariscope and a photoelectric detector, the optical carrier microwave generating device is used for generating two routes of orthogonal but incoherent linearly polarized light, each route of linearly polarized light is loaded with a microwave, thereby forming two routes of optical carrier microwave, the two routes of optical carrier microwave are transmitted to the polariscope through the magneto-optical crystal, the magneto-optical crystal is placed in a corresponding intensity magnetic field, after the two routes of optical carrier microwave pass through the magneto-optical crystal, the polarization direction changes, at the polariscope, only microwave interference occurs to the two routes of optical carrier microwave, thereby generating an optical signal carrying a microwave interference signal; the photoelectric detector converts the optical signal into an electrical signal; according to the intensity of the microwave interference signal in the electrical signal, the Faraday rotation angle under the corresponding intensity magnetic field is calculated. The application has better stability, higher measurement accuracy and better anti-interference performance.

Description

Technical Field

[0001] This invention belongs to the field of Faraday rotation angle measurement, and specifically relates to a microwave interferometric fiber optic sensing system for measuring Faraday rotation angle. Background Technology

[0002] The measurement of the Faraday rotation angle is often used in magnetic field and current sensing. Specifically, it typically utilizes the electromagnetic induction effect, placing an optical fiber loop inside a current-carrying coil, combined with... Figure 1 As shown, the initial optical signal provided by the light source is transmitted to the polarizer through the first coupler. The polarizer converts the initial optical signal into linearly polarized light, and then the linearly polarized light is split into two paths through the second coupler. The two linearly polarized lights are converted into circularly polarized light by λ / 4 waveplates and enter the fiber optic loop in opposite directions for circulation. The upper branch linearly polarized light propagates around the fiber optic loop in a clockwise direction and returns to the second coupler from the lower branch λ / 4 waveplate. The lower branch linearly polarized light propagates around the fiber optic loop in a counterclockwise direction and returns to the second coupler from the upper branch λ / 4 waveplate. Based on the Faraday magneto-optical effect, the polarization direction of the two linearly polarized lights rotates when they propagate around the fiber optic loop. As a result, both linearly polarized lights that return to the second coupler carry current information from the fiber optic loop. The two linearly polarized beams carrying current information are transmitted to the polarizer via the second coupler. Interference occurs at the polarizer, generating an interference light signal. This interference signal is then transmitted to the detector via the first coupler for photoelectric conversion. The Faraday rotation angle under a specific magnetic field strength can be determined based on the angle difference between the polarization directions of the linearly polarized beam incident on and exiting the fiber ring. The Faraday rotation angle provided by the fiber ring changes under different magnetic field strengths. Traditional optical Faraday rotation angle sensors are mostly based on the Faraday magneto-optical effect, Malus's law, and polarized light intensity demodulation modes. However, light intensity attenuation, polarization fading, dispersion, and intermodal interference all affect the quality of the sensing signal, thus significantly limiting the stability and accuracy of the sensor. Summary of the Invention

[0003] This invention provides a microwave interferometric fiber optic sensing system for measuring the Faraday rotation angle, in order to solve the problems of low stability and accuracy of current Faraday rotation angle sensors.

[0004] According to a first aspect of the present invention, a microwave interferometric fiber optic sensing system for measuring the Faraday rotation angle is provided, comprising an optical microwave generating device, a magneto-optical crystal, an analyzer, and a photodetector. The optical microwave generating device generates two orthogonal but incoherent linearly polarized beams, each loaded with microwaves, thereby forming two optical microwave beams. The two optical microwave beams are transmitted to the analyzer through the magneto-optical crystal, which is placed in a magnetic field of corresponding strength. After passing through the magneto-optical crystal, the polarization directions of the two optical microwave beams change. At the analyzer, the two optical microwave beams only undergo microwave interference, generating an optical signal carrying a microwave interference signal. The photodetector converts the optical signal into an electrical signal. The Faraday rotation angle under the corresponding magnetic field strength is calculated based on the intensity of the microwave interference signal in the electrical signal.

[0005] In one alternative implementation, based on the intensity A of the microwave interference signal in the electrical signal, a system of equations is established according to the following formula to calculate the Faraday rotation angle θ under the corresponding magnetic field intensity:

[0006]

[0007] Among them, A x cosθ represents the intensity of the microwave-carrying light path through the analyzer, A y sinθ represents the intensity of the microwave-carrying light in the other optical path passing through the analyzer, A x A represents the intensity of one of two orthogonal but incoherent linearly polarized beams. y δ represents the intensity of one of two orthogonal but incoherent linearly polarized beams, and δ represents the phase difference between the two orthogonal but incoherent linearly polarized beams.

[0008] In another optional implementation, the optical microwave generation device includes an optical signal generation device, an electro-optic modulator, a polarizer, a polarization modulator, a polarization beam splitter, a first delay fiber, a second delay fiber, and a polarization beam combiner. The output of the optical signal generation device is connected to the input of the polarization beam splitter in sequence through the electro-optic modulator, the polarizer, and the polarization modulator. The first output of the polarization beam splitter is connected to the first input of the polarization beam combiner through the first delay fiber. The second output is connected to the second input of the polarization beam combiner through the second delay fiber. The output of the polarization beam combiner is connected to the analyzer through the magneto-optical crystal.

[0009] The optical signal generating device is used to generate optical signals in the 1550nm band.

[0010] The electro-optic modulator loads microwaves into the filtered optical signal;

[0011] The polarizer is used to convert a microwave-loaded optical signal into linearly polarized light.

[0012] The polarization modulator modulates the polarization of linearly polarized light loaded with the microwave.

[0013] The polarization beam splitter splits the polarization-modulated linearly polarized light into two orthogonally polarized beams. One of the beams is transmitted to the polarization beam combiner through the first delay fiber, and the other beam is transmitted to the polarization beam combiner through the second delay fiber. The first and second delay fibers have different lengths, so that the two beams transmitted to the polarization beam combiner are incoherent. The two orthogonal and incoherent linearly polarized beams loaded with microwaves are the two optically carried microwaves.

[0014] The polarization combiner combines the two optical microwave beams and transmits them to the analyzer through the magneto-optical crystal.

[0015] In another alternative implementation, the phase difference between two orthogonal but incoherent linearly polarized beams... n(L1-L2), where λ represents the wavelength of the two orthogonal but incoherent linearly polarized beams, n represents the refractive index of the first and second delay fibers, L1 represents the length of the first delay fiber, and L2 represents the length of the second delay fiber.

[0016] In another alternative implementation, after calculating the Faraday rotation angle θ for the corresponding magnetic field strength, the corresponding magnetic field strength B is calculated according to the following formula:

[0017] θ = VBL, where V is the Field coefficient and L is the length of the magneto-optical crystal.

[0018] In another optional implementation, the optical microwave generation device further includes an optical amplifier, which is located between the electro-optic modulator and the polarizer. The optical amplifier amplifies the microwave-loaded optical signal and transmits it to the polarizer. The polarizer converts the amplified optical signal into polarized light.

[0019] In another alternative implementation, the polarization modulator modulates the linearly polarized light loaded with the microwave into 45° linearly polarized light and transmits it to the polarization beamsplitter; the polarization beamsplitter splits the 45° linearly polarized light into two line-polarized lights with orthogonal polarization states and equal intensity.

[0020] In another alternative implementation, a magnetic field generator is also included, which provides a magnetic field of corresponding strength around the magneto-optical crystal, the direction of which is parallel to the vertical orientation of the magneto-optical crystal and the transmission direction of the optical microwave as it passes through the magneto-optical crystal.

[0021] In another alternative implementation, a microwave signal generator and an electrical spectrum analyzer are also included, wherein the microwave signal generator is used to provide a corresponding microwave signal to the electro-optic modulator; and the electrical spectrum analyzer measures the intensity of the microwave interference signal in the electrical signal.

[0022] In another alternative implementation, the two optically-carrying microwaves do not interfere with each other.

[0023] The beneficial effects of this invention are:

[0024] This invention loads microwaves onto two orthogonal but incoherent linearly polarized beams, forming two optically-borne microwaves. These two optically-borne microwaves are transmitted to an analyzer via a magneto-optical crystal. At the analyzer, only microwave interference occurs. The Faraday rotation angle is calculated using the intensity of the microwave interference signal. Since the interference in this invention only occurs between the microwave envelopes of the optically-borne microwaves, and light does not interfere, this invention avoids the problems of mode distribution and packaging found in current single-mode fiber optic sensing. Furthermore, microwave wavelengths are much longer than light wavelengths, resulting in better stability for microwave interferometers compared to optical interferometers. For microwave interference, polarization fading, dispersion, and intermodal interference have minimal impact on the signal quality of the system. Compared to traditional demodulation methods, the use of interference improves measurement accuracy. Therefore, this system is more stable and has higher measurement precision. Additionally, since the magneto-optical crystal can provide a large Faraday rotation angle under the influence of a magnetic field, this invention utilizes the magneto-optical crystal to measure the Faraday rotation angle, thereby improving measurement accuracy. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the circuit principle of a traditional Faraday rotation angle sensor;

[0026] Figure 2 This is a schematic diagram of an embodiment of the microwave interferometric fiber optic sensing system for measuring the Faraday rotation angle of the present invention;

[0027] Figure 3 This is a schematic diagram of another embodiment of the microwave interferometric fiber optic sensing system for measuring the Faraday rotation angle according to the present invention. Detailed Implementation

[0028] To enable those skilled in the art to better understand the technical solutions in the embodiments of the present invention, and to make the above-mentioned objectives, features and advantages of the embodiments of the present invention more apparent and understandable, the technical solutions in the embodiments of the present invention will be further described in detail below with reference to the accompanying drawings.

[0029] In the description of this invention, unless otherwise specified and limited, it should be noted that the term "connection" should be interpreted broadly. For example, it can be a mechanical connection or an electrical connection, or it can be a connection between two internal components. It can be a direct connection or an indirect connection through an intermediate medium. Those skilled in the art can understand the specific meaning of the above term according to the specific circumstances.

[0030] See Figure 2 This is a schematic diagram of an embodiment of the microwave interferometric fiber optic sensing system for measuring the Faraday rotation angle according to the present invention. The system may include an optical microwave generator, a magneto-optical crystal, an analyzer, and a photodetector. The optical microwave generator produces two orthogonal but incoherent linearly polarized beams, each loaded with microwaves, thus forming two optical microwave beams. These two beams are transmitted to the analyzer via the magneto-optical crystal, which is placed in a magnetic field of corresponding strength. After passing through the magneto-optical crystal, the polarization directions of the two optical microwave beams change. At the analyzer, the two beams undergo microwave interference, generating an optical signal carrying a microwave interference signal. The photodetector converts the optical signal into an electrical signal. Based on the intensity of the microwave interference signal in the electrical signal, the Faraday rotation angle under the corresponding magnetic field strength is calculated.

[0031] In this embodiment, the output of the optical microwave generator is connected to one end of a magneto-optical crystal, the other end of the magneto-optical crystal is connected to the input of an analyzer, and the output of the analyzer is connected to a photodetector. The direction of the magnetic field of the magneto-optical crystal can be parallel to the vertical orientation of the magneto-optical crystal (i.e., the transmission direction of the optical microwave as it passes through the magneto-optical crystal), thus ensuring the accuracy of the Faraday rotation angle measurement. Both optical microwave paths include linearly polarized light and microwaves. After each optical microwave path passes through the magneto-optical crystal, the polarization directions of its linearly polarized light and microwaves change. After the two optical microwave paths are transmitted to the analyzer, no linear interference occurs between the two optical microwave paths; only microwave interference occurs.

[0032] The light intensities A1 and A2 of the two optically carried microwaves after passing through the analyzer can be expressed as follows:

[0033] A1=A X cos2=A Y sin(1)

[0034] Among them, A x A represents the intensity of one of two orthogonal but incoherent linearly polarized beams. y θ represents the light intensity of one of two orthogonal but incoherent linearly polarized beams, and θ represents the Faraday rotation angle under the corresponding magnetic field strength.

[0035] At the analyzer, the intensity of the microwave interference signal generated by the microwave interference of the two optical microwaves can be expressed as:

[0036]

[0037] Where δ represents the phase difference between two orthogonal but incoherent linearly polarized beams.

[0038] Substituting formula (1) into formula (2), this embodiment can establish a set of equations based on the intensity A of the microwave interference signal in the electrical signal, and calculate the Faraday rotation angle θ under the corresponding intensity magnetic field according to the following formulas:

[0039]

[0040] Among them, A x cosθ represents the intensity of the microwave-carrying light path through the analyzer, A y sinθ represents the intensity of the microwave-carrying light in the other optical path passing through the analyzer, A x A represents the intensity of one of two orthogonal but incoherent linearly polarized beams. y δ represents the intensity of the other linearly polarized light in two orthogonal but incoherent linearly polarized lights, and δ represents the phase difference between the two orthogonal but incoherent linearly polarized lights. Since the above formula (3) includes three unknown parameters, the Faraday rotation angle under the corresponding intensity magnetic field can be calculated by collecting the intensity A of multiple microwave interference signals and establishing a set of equations.

[0041] Furthermore, after calculating the Faraday rotation angle θ under the corresponding magnetic field strength, the corresponding magnetic field strength B can be calculated using the following formula:

[0042] θ = VBL, where V is the Field coefficient and L is the length of the magneto-optical crystal.

[0043] As can be seen from the above embodiments, the present invention loads microwaves onto two orthogonal but incoherent linearly polarized beams to form two optically carried microwaves. These two optically carried microwaves are transmitted to an analyzer through a magneto-optical crystal. Only microwave interference occurs at the analyzer, and the Faraday rotation angle is calculated using the intensity of the microwave interference signal. Since the interference in the present invention only occurs between the microwave envelopes of the optically carried microwaves, and the light does not interfere, the present invention does not face the problems of mode distribution and packaging in current single-mode fiber optic sensing. At the same time, the wavelength of microwaves is much longer than that of light waves, and the stability of its interferometer is better than that of optical interferometers. For microwave interference, the polarization fading, dispersion, and intermodal interference of light waves have little impact on the signal quality of the system. Moreover, compared with traditional demodulation methods, the use of interference improves the measurement accuracy. Therefore, the system is more stable and has higher measurement accuracy. In addition, since the magneto-optical crystal can provide a large Faraday rotation angle under the action of a magnetic field, the present invention uses the magneto-optical crystal to measure the Faraday rotation angle, which can improve the measurement accuracy.

[0044] See Figure 3 This is a schematic diagram of another embodiment of the microwave interferometric fiber optic sensing system for measuring the Faraday rotation angle according to the present invention. Figure 3 and Figure 2 The difference in the illustrated embodiment is that the optical microwave generation device includes an optical signal generation device, an electro-optic modulator, a polarizer, a polarization modulator, a polarization beam splitter, a first delay fiber, a second delay fiber, and a polarization combiner. The output of the optical signal generation device is sequentially connected to the input of the polarization beam splitter via the electro-optic modulator, the polarizer, and the polarization modulator. The first output of the polarization beam splitter is connected to the first input of the polarization combiner via the first delay fiber, and the second output is connected to the second input of the polarization combiner via the second delay fiber. The output of the polarization combiner is connected to the analyzer via the magneto-optical crystal. The optical signal generation device is used to generate an optical signal with a 1550nm wavelength filtered out from the input optical signal. The electro-optic modulator adds microwave... The microwave-loaded optical signal is loaded into the filtered optical signal; the polarizer is used to convert the microwave-loaded optical signal into linearly polarized light; the polarization modulator modulates the polarization of the microwave-loaded linearly polarized light (e.g., modulates it into 45° linearly polarized light); the polarization beamsplitter splits the polarization-modulated linearly polarized light into two orthogonally polarized lines, one of which is transmitted to the polarization combiner through the first delay fiber, and the other is transmitted to the polarization combiner through the second delay fiber. The first and second delay fibers have different lengths, so that the two orthogonal and incoherent linearly polarized lines transmitted to the polarization combiner are incoherent. The two orthogonal and incoherent linearly polarized lines loaded with microwaves are the two optical microwave-loaded lines; the polarization combiner combines the two optical microwave-loaded lines and transmits them to the analyzer through the magneto-optical crystal.

[0045] In this embodiment, since magneto-optical crystals respond differently to light of different wavelengths, an optical signal generation device is provided to generate an optical signal in the 1550nm band. This optical signal generation device can be a 1550nm single-frequency laser or it can consist of a broadband light source and a filter. The filter can be connected to the broadband light source, which provides an initial optical signal with a wavelength of 1530-1580nm. The filter filters out the optical signal in the 1550nm band and transmits it to the electro-optic modulator. Because magneto-optical crystals can provide a large Faraday rotation angle under the action of a magnetic field and have a large Feld coefficient at 1550nm, this invention utilizes magneto-optical crystals to facilitate the measurement of the Faraday rotation angle. The polarization modulator can modulate the linearly polarized light loaded with microwaves into 45° linearly polarized light and transmit it to the polarization beamsplitter. The polarization beamsplitter splits the 45° linearly polarized light into two line-polarized lights with orthogonal polarization states and equal intensity. This invention modulates linearly polarized light into 45° linearly polarized light, which is then split into two linearly polarized beams of equal intensity by a polarization beam splitter. This ensures that the microwave signal intensities are also equal, thereby improving the microwave interference contrast and making the microwave interference phenomenon more pronounced. This embodiment may also include a microwave signal generator to provide the corresponding microwave signal to the electro-optic modulator; it may also include a magnetic field generator and an electrical spectrum analyzer. The magnetic field generator provides a corresponding magnetic field around the magneto-optic crystal and can be controlled by a DC power supply; the electrical spectrum analyzer measures the intensity of the microwave interference signal in the electrical signal. Furthermore, the optical microwave generation device in this embodiment includes an optical amplifier located between the electro-optic modulator and the polarizer. The optical amplifier amplifies the microwave-loaded optical signal and transmits it to the polarizer; the polarizer converts the amplified optical signal into polarized light. This optical amplifier can be an erbium-doped fiber amplifier. By placing the optical amplifier between the electro-optic modulator and the polarizer, this invention avoids the optical amplifier affecting subsequent polarization.

[0046] In this embodiment, the intensity of the optical signal after electro-optic modulation of the 1550nm band optical signal by the electro-optic modulator can be expressed as:

[0047] Where A0 is the intensity of the optical signal in the 1550nm band, m a It is the electro-optic modulation coefficient, ω m w0 is the frequency of the input microwave signal, and w0 is the frequency of the 1550nm optical signal. It is the initial phase of the 1550nm band optical signal;

[0048] The electro-optically modulated optical signal, after being amplified by an optical amplifier, can be represented as:

[0049]

[0050] Where, m f This is the magnification factor;

[0051] The amplified optical signal is converted into linearly polarized light by a polarizer. The linearly polarized light is modulated into 45° linearly polarized light by a polarization controller, and then enters a polarization beam splitter. The polarization beam splitter splits the 45° linearly polarized light into two linearly polarized lights with orthogonal polarization states and equal intensity E. x and E y It can be represented as:

[0052]

[0053] At this time, the intermediate frequency of the two channels is ω m The microwave signal strength can be expressed as:

[0054]

[0055] Similarly, in this embodiment, based on the intensity A of the microwave interference signal in the electrical signal, a system of equations can be established according to the following formula to calculate the Faraday rotation angle θ under the corresponding magnetic field intensity:

[0056]

[0057] Among them, A x cosθ represents the intensity of the microwave-carrying light path through the analyzer, A y sinθ represents the intensity of the microwave-carrying light in the other optical path passing through the analyzer, A x A represents the intensity of one of two orthogonal but incoherent linearly polarized beams. y δ represents the intensity of one of two orthogonal but incoherent linearly polarized beams, and δ represents the phase difference between the two orthogonal but incoherent linearly polarized beams.

[0058] In this embodiment, the phase difference between two orthogonal but incoherent linearly polarized beams

[0059] Where λ represents the wavelength of the two orthogonal but incoherent linearly polarized beams, n represents the refractive index of the first and second delay fibers, L1 represents the length of the first delay fiber, and L2 represents the length of the second delay fiber.

[0060] As can be seen from the above embodiments, the present invention loads microwaves onto two orthogonal but incoherent linearly polarized beams to form two optically carried microwaves. These two optically carried microwaves are transmitted to an analyzer through a magneto-optical crystal. Only microwave interference occurs at the analyzer, and the Faraday rotation angle is calculated using the intensity of the microwave interference signal. Since the interference in the present invention only occurs between the microwave envelopes of the optically carried microwaves, and the light does not interfere, the present invention does not face the problems of mode distribution and packaging in current single-mode fiber optic sensing. At the same time, the wavelength of microwaves is much longer than that of light waves, and the stability of its interferometer is better than that of optical interferometers. For microwave interference, the polarization fading, dispersion, and intermodal interference of light waves have little impact on the signal quality of the system. Moreover, compared with traditional demodulation methods, the use of interference improves the measurement accuracy. Therefore, the present system is more stable, has higher measurement accuracy, and better anti-interference capabilities. In addition, since the magneto-optical crystal can provide a large Faraday rotation angle under the action of a magnetic field, the present invention uses the magneto-optical crystal to measure the Faraday rotation angle, which can improve the measurement accuracy.

[0061] Other embodiments of the invention will readily occur to those skilled in the art upon consideration of the specification and practice of the invention disclosed herein. This application is intended to cover any variations, uses, or adaptations of the invention that follow the general principles of the invention and include common knowledge or customary techniques in the art not disclosed herein. The specification and examples are to be considered exemplary only, and the true scope and spirit of the invention are indicated by the following claims.

[0062] It should be understood that the present invention is not limited to the precise structure described above and shown in the accompanying drawings, and various modifications and changes can be made without departing from its scope. The scope of the invention is defined solely by the appended claims.

Claims

1. A microwave interferometric fiber optic sensing system for measuring the Faraday rotation angle, characterized in that, The system includes an optical microwave generator, a magneto-optical crystal, an analyzer, and a photodetector. The optical microwave generator produces two orthogonal but incoherent linearly polarized beams, each loaded with microwaves, thus forming two optical microwave beams. These two optical microwave beams are transmitted to the analyzer via the magneto-optical crystal, which is placed in a magnetic field of corresponding strength. After passing through the magneto-optical crystal, the polarization directions of the two optical microwave beams change. At the analyzer, the two optical microwave beams only undergo microwave interference, generating an optical signal carrying a microwave interference signal. The photodetector converts the optical signal into an electrical signal. Based on the intensity of the microwave interference signal in the electrical signal, the Faraday rotation angle under the corresponding magnetic field strength is calculated. The optical microwave generation device includes an optical signal generation device, an electro-optic modulator, a polarizer, a polarization modulator, a polarization beam splitter, a first delay fiber, a second delay fiber, and a polarization beam combiner. The output of the optical signal generation device is connected to the input of the polarization beam splitter in sequence through the electro-optic modulator, the polarizer, and the polarization modulator. The first output of the polarization beam splitter is connected to the first input of the polarization beam combiner through the first delay fiber. The second output is connected to the second input of the polarization beam combiner through the second delay fiber. The output of the polarization beam combiner is connected to the analyzer through the magneto-optical crystal. The optical signal generating device is used to generate optical signals in the 1550nm band. The electro-optic modulator loads microwaves into the filtered optical signal; The polarizer is used to convert a microwave-loaded optical signal into linearly polarized light. The polarization modulator modulates the polarization of linearly polarized light loaded with the microwave. The polarization beam splitter splits the polarization-modulated linearly polarized light into two orthogonally polarized beams. One of the beams is transmitted to the polarization beam combiner through the first delay fiber, and the other beam is transmitted to the polarization beam combiner through the second delay fiber. The first and second delay fibers have different lengths, so that the two beams transmitted to the polarization beam combiner are incoherent. The two orthogonal and incoherent linearly polarized beams loaded with microwaves are the two optically carried microwaves. The polarization combiner combines the two optical microwave beams and transmits the beams to the analyzer through the magneto-optical crystal.

2. The microwave interferometric fiber optic sensing system for measuring the Faraday rotation angle according to claim 1, characterized in that, Based on the intensity A of the microwave interference signal in the electrical signal, a system of equations is established according to the following formulas to calculate the Faraday rotation angle under the corresponding magnetic field intensity. : ， in, This indicates the intensity of the microwave light carried by the optical wave passing through the analyzer. This indicates the intensity of the microwave light carried by the other optical path passing through the analyzer. This represents the light intensity of one of two orthogonal but incoherent linearly polarized beams. This represents the light intensity of one of two orthogonal but incoherent linearly polarized beams. This represents the phase difference between two orthogonal but incoherent linearly polarized beams.

3. The microwave interferometric fiber optic sensing system for measuring the Faraday rotation angle according to claim 1, characterized in that, Phase difference between two orthogonal but incoherent linearly polarized beams , in, L1 represents the wavelength of two orthogonal but incoherent linearly polarized beams, n represents the refractive index of the first and second delay fibers, L1 represents the length of the first delay fiber, and L2 represents the length of the second delay fiber.

4. The microwave interferometric fiber optic sensing system for measuring the Faraday rotation angle according to claim 1 or 2, characterized in that, The Faraday rotation angle under the corresponding magnetic field strength was calculated. Then, the corresponding magnetic field strength B is calculated using the following formula: , where V is the Feld coefficient and L is the length of the magneto-optical crystal.

5. The microwave interferometric fiber optic sensing system for measuring the Faraday rotation angle according to claim 1, characterized in that, The optical microwave generation device further includes an optical amplifier, which is located between the electro-optic modulator and the polarizer. The optical amplifier amplifies the optical signal loaded with microwaves and transmits it to the polarizer. The polarizer converts the amplified optical signal into polarized light.

6. The microwave interferometric fiber optic sensing system for measuring the Faraday rotation angle according to claim 1, characterized in that, The polarization modulator modulates the linearly polarized light loaded with the microwave into 45° linearly polarized light and transmits it to the polarization beam splitter; the polarization beam splitter splits the 45° linearly polarized light into two line polarized lights with orthogonal polarization states and equal intensity.

7. The microwave interferometric fiber optic sensing system for measuring the Faraday rotation angle according to claim 1, characterized in that, It also includes a magnetic field generator, which provides a magnetic field of corresponding strength around the magneto-optical crystal. The direction of the magnetic field is parallel to the vertical orientation of the magneto-optical crystal and the transmission direction of the optical microwave as it passes through the magneto-optical crystal.

8. The microwave interferometric fiber optic sensing system for measuring the Faraday rotation angle according to claim 1, characterized in that, It also includes a microwave signal generator and an electrical spectrum analyzer. The microwave signal generator is used to provide a corresponding microwave signal to the electro-optic modulator. The electrical spectrum analyzer measures the intensity of the microwave interference signal in the electrical signal.

9. The microwave interferometric fiber optic sensing system for measuring the Faraday rotation angle according to claim 1 or 2, characterized in that, The two optical microwave channels do not interfere with each other.

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