A sensor system for detecting a magnetic field strength and a signal demodulation method thereof

Abstract

The application relates to a sensing system for detecting magnetic field intensity and a signal demodulation method thereof, which comprises a laser emission module for emitting a laser signal; a first optical signal adjusting module for adjusting the polarization state of the laser signal and performing first single-pass amplification, and rotating an angle under the action of a magnetic field to be detected to output first polarized light; a second optical signal adjusting module for adjusting the angle of the first polarized light and performing second single-pass amplification and polarization state adjustment to output second polarized light; a polarization beam splitting module for performing polarization beam splitting on the second polarized light to output two beams of orthogonal polarized light; a comparison module for performing gain comparison on the two beams of orthogonal polarized light, processing and displaying the comparison result, and taking the comparison result as an input signal of a controller to apply a magnetic field control voltage to adjust the angle of the first polarized light and obtain a required angle; and a magnetic field intensity module for obtaining the magnetic field intensity to be detected according to the required angle.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of measurement of magnetic field intensity and its sensing device and signal demodulation technology, in particular to a sensing system for detecting magnetic field intensity and a signal demodulation method thereof. BACKGROUND

[0002] With the rapid development of science and technology and industrial production, the detection and analysis of magnetic field, national defense security, exploration of deep sea and space, geological exploration, aerospace and automation control field all play a vital role, and the high-precision measurement of magnetic field also puts forward higher and higher requirements, and the traditional magnetic field sensing technology gradually shows that it is not up to the task, therefore, many fields urgently need to develop some new magnetic field sensing technology to meet various strict application requirements and accurately give the required magnetic field.

[0003] In recent years, there have been cone-shaped optical fiber magnetic field sensing, photonic crystal fiber filled magnetic field sensing, coreless and single-mode optical fiber structure and fiber grating structure magnetic field sensing, and usually rely on power value detection and wavelength shift detection methods for signal demodulation. The traditional power value detection is easily affected by factors such as light source power fluctuation, has large error and low precision, and the high precision of wavelength detection often depends on complex optical equipment, and these optical equipment often depends on imports to have better performance. Therefore, due to the increasing and more accurate requirements of people on magnetic field detection in different fields, a convenient and fast detection device, a low-cost sensing system and a demodulation method for improving detection precision are urgently needed, so as to better meet the requirements of magnetic field measurement precision and simple sensing system in various fields. SUMMARY

[0004] In order to solve the problems existing in the prior art, the purpose of the present application is to provide a sensing system for detecting magnetic field intensity and a signal demodulation method thereof, introduce a traveling wave semiconductor optical amplifier and a polarization controller, and ingeniously design two Faraday rotators and the total rotation angle of the polarization light caused by them, and completely separate the TE mode and TM mode, so as to realize a simple sensing system and high magnetic field detection precision.

[0005] To achieve the above purpose, the present application provides the following scheme:

[0006] A sensing system for detecting magnetic field intensity, comprising:

[0007] A laser emission module for emitting a laser signal;

[0008] A first optical signal adjusting module for adjusting the polarization state of the laser signal and performing first single-pass amplification, and rotating an angle under the action of a magnetic field to be detected, and outputting a first polarized light;

[0009] a second light signal adjustment module, configured to adjust the angle of the first polarized light, and perform second single-pass amplification and polarization state adjustment, and output second polarized light;

[0010] a polarization beam splitting module, configured to perform polarization beam splitting on the second polarized light, and output two beams of orthogonal polarized light;

[0011] a comparison module, configured to perform gain comparison on the two beams of orthogonal polarized light, process and display a comparison result, and use the comparison result as an input signal of a controller, apply a magnetic field control voltage to adjust the angle of the first polarized light, and obtain a required angle;

[0012] a magnetic field strength module, configured to obtain a magnetic field strength to be detected according to the required angle.

[0013] Optionally, the first light signal adjustment module comprises:

[0014] a first polarization controller, configured to perform polarization state adjustment on the laser signal;

[0015] a first semiconductor optical amplifier, configured to perform single-pass amplification on the laser signal after polarization state adjustment;

[0016] a first Faraday rotator, configured to rotate the laser signal after single-pass amplification by an angle under the action of a magnetic field to be detected, and output the first polarized light.

[0017] Optionally, the second light signal adjustment module comprises:

[0018] a second Faraday rotator, configured to adjust the angle of the first polarized light according to the applied magnetic field control voltage;

[0019] a focusing lens, configured to cause the first polarized light after angle adjustment to be incident on an active region of a second semiconductor optical amplifier;

[0020] the second semiconductor optical amplifier, configured to perform single-pass amplification on the incident first polarized light;

[0021] a second polarization controller, configured to perform polarization state adjustment on the first polarized light after single-pass amplification, and output the second polarized light.

[0022] Optionally, the comparison module comprises:

[0023] a processing unit, configured to perform detection, amplification and filtering on the two beams of orthogonal polarized light, i.e., TE mode light beams and TM mode light beams, respectively;

[0024] A comparator is used to compare the gain of the TE-mode beam and the TM-mode beam processed by the processing unit. If there is no gain difference between the TE-mode beam and the TM-mode beam, the comparison result is processed and displayed to obtain the angle adjusted by the second Faraday rotator. If there is a gain difference between the TE-mode beam and the TM-mode beam, the comparison result is processed and displayed, and used as an input signal for the controller to apply a magnetic field control voltage to adjust the angle of the second Faraday rotator until there is no gain difference between the TE-mode beam and the TM-mode beam, thus obtaining the current rotation angle of the second Faraday rotator.

[0025] Optionally, the method for obtaining the gain difference between the TE mode beam and the TM mode beam is as follows:

[0026] ΔG=κ×(Γ TE -Γ TM )×g×L

[0027] Where ΔG is the gain difference, κ is a constant coefficient, and Γ TE ,Γ TM denoted as the confinement factor of the optical field in the active region, g is the gain coefficient, and L is the length of the active region of the semiconductor optical amplifier.

[0028] Optionally, the magnetic field strength module includes:

[0029] The magnetic field strength unit is used to determine the specific value of the rotation angle of the first Faraday rotator under the action of the magnetic field to be detected, based on the required angle, and to obtain the magnetic field strength to be detected based on the specific value.

[0030] Optionally, the method for determining the specific value of the rotation angle of the first Faraday rotator under the action of the magnetic field to be detected is as follows:

[0031] θ1 = 90° - θ2

[0032] Where θ1 is the angle of rotation of the polarization state direction under the action of the magnetic field to be detected, and θ2 is the rotation angle of the polarized light by the second Faraday rotator.

[0033] Optionally, the magnetic field strength to be detected is obtained as follows:

[0034] θ1=V×H×d

[0035] Where θ1 is the angle of rotation of the polarization state direction under the action of the magnetic field to be detected, H is the magnetic field strength to be detected, and d is the thickness of the first Faraday rotator.

[0036] To achieve the above objectives, the present invention provides a signal demodulation method for a sensing system for detecting magnetic field strength, comprising:

[0037] A laser signal is emitted, the polarization state of the laser signal is adjusted and the first single-pass amplification is performed, and the angle is rotated under the action of the magnetic field to be detected to output the first polarized light;

[0038] The angle of the first polarized light is adjusted, and a second single-pass amplification and polarization state adjustment are performed to output the second polarized light. The second polarized light is then polarized and split to output two orthogonally polarized beams, namely the TE mode beam and the TM mode beam.

[0039] The gains of the two orthogonally polarized beams are compared, the comparison results are processed and displayed, and used as input signals for the controller. A magnetic field control voltage is applied to adjust the angle of the first polarized beam. The correspondence between the rotation angle of the second Faraday rotator on the first polarized beam and the magnetic field control voltage is calibrated. When there is no gain difference between the TE mode beam and the TM mode beam, the applied voltage is stopped. The current rotation angle of the second Faraday rotator is obtained, and the current rotation direction of the second Faraday rotator is determined. Based on the rotation angle and direction of the second Faraday rotator, the magnetic field strength to be detected is obtained.

[0040] The beneficial effects of this invention are as follows:

[0041] This invention utilizes the polarization sensitivity of traveling-wave semiconductor optical amplifiers. Two Faraday rotators are placed between two identical optical amplifiers operating under the same conditions. The combined rotation angle of the two Faraday rotators on the polarized light signal is 90°, ensuring that the TE and TM modes have the same amplification effect after passing through the two identical traveling-wave semiconductor optical amplifiers. Then, by adjusting the polarization controller, the TE and TM modes are completely separated, resulting in TE and TM modes with no gain difference. Through this ingenious design, the second Faraday rotation can be artificially controlled based on whether there is a gain difference between the completely separated TE and TM modes. The magnetic field control voltage of the device is adjusted until there is no gain difference between the output TE mode and TM mode. Finally, the rotation angle of the Faraday rotator with respect to polarized light in the region where the magnetic field is located is obtained, and thus the magnitude of the magnetic field to be measured is obtained. The entire sensing device is relatively simple, does not involve complex devices with complicated processes and structures, and is not subject to foreign technology control. It is low in cost and the demodulation method is also simple. Based on the Faraday effect, the magnitude of the magnetic field to be measured can be easily and quickly obtained by adjusting the magnetic field control voltage of the Faraday rotator. Moreover, by adjusting the magnetic field control voltage and the comparator to a finer level, the rotation angle caused by the magnetic field to be measured can be accurately obtained, thereby accurately demodulating the magnitude of the magnetic field. Attached Figure Description

[0042] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments 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.

[0043] Figure 1 This is a schematic diagram of a sensing system for detecting magnetic field strength according to an embodiment of the present invention;

[0044] Figure 2 The sawtooth wave voltage applied to the second Faraday rotator by the controller in this embodiment of the invention. Detailed Implementation

[0045] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only 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.

[0046] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0047] like Figure 1 As shown, this embodiment discloses a sensing system for detecting magnetic field strength, comprising: a laser emitting module for emitting a laser signal; a first optical signal conditioning module for adjusting the polarization state of the laser signal and performing a first single-pass amplification, and rotating the laser signal by an angle under the influence of the magnetic field to be detected, outputting first polarized light; a second optical signal conditioning module for adjusting the angle of the first polarized light, performing a second single-pass amplification and polarization state adjustment, and outputting second polarized light; a polarization beam splitting module for splitting the second polarized light into two orthogonally polarized beams; a comparison module for comparing the gain of the two orthogonally polarized beams, processing and displaying the comparison result, and using it as an input signal for a controller to apply a magnetic field control voltage to adjust the angle of the first polarized light to obtain the required angle; and a magnetic field strength module for obtaining the magnetic field strength to be detected according to the required angle.

[0048] Specifically, the light signal emitted by the laser passes through the first optical signal conditioning module, where its polarization state is adjusted and it undergoes corresponding single-pass amplification. Under the influence of the magnetic field to be detected, it rotates by a corresponding angle and outputs first polarized light. The first polarized light enters the second optical signal conditioning module, where its angle is adjusted, and it undergoes corresponding single-pass amplification and polarization state adjustment, outputting second polarized light. The second polarized light passes through a polarization beam splitting module, where it is split into two orthogonally polarized beams. These two orthogonally polarized beams pass through a comparator module, where their gains are compared. The comparison result is processed and displayed, and used as the input signal for the comparator. A magnetic field control voltage is applied to adjust the angle of the first polarized light to obtain the desired angle. The magnetic field strength module then obtains the strength of the magnetic field to be detected based on this desired angle. The entire sensing device is relatively simple, does not involve complex components with intricate processes or structures, and is not subject to foreign technology control. It is low-cost, and the demodulation method is simple. Based on the Faraday effect and the adjustment of the magnetic field control voltage of the Faraday rotator, the magnitude of the magnetic field to be measured can be easily and quickly obtained. Furthermore, by finely adjusting the magnetic field control voltage and the comparator, the rotation angle caused by the magnetic field to be measured can be accurately obtained, thus precisely demodulating the magnitude of the magnetic field.

[0049] Furthermore, the first optical signal conditioning module includes: a first polarization controller for adjusting the polarization state of the laser signal; a first semiconductor optical amplifier for amplifying the polarization-adjusted laser signal in a single pass; and a first Faraday rotator for rotating the amplified laser signal in a single pass under the action of a magnetic field to be detected, and outputting first polarized light.

[0050] Specifically, such as Figure 1 As shown, the optical signal emitted by the laser is polarized by a first polarization controller, ensuring that the TE and TM modes of the initial optical signal incident on the first semiconductor optical amplifier are of equal magnitude. After being amplified by the first semiconductor optical amplifier in a single pass, the TE mode is greater than the TM mode. The polarized light emitted from the first semiconductor optical amplifier is then rotated by a Faraday rotator under the influence of the magnetic field to be detected, resulting in the output of the first polarized light. In this embodiment, the first semiconductor optical amplifier is a traveling-wave amplifier.

[0051] Furthermore, the second optical signal conditioning module includes: a second Faraday rotator for adjusting the angle of the first polarized light according to the applied magnetic field control voltage; a focusing lens for incidenting the first polarized light after angle adjustment onto the active region of the second semiconductor optical amplifier; a second semiconductor optical amplifier for single-pass amplification of the incident first polarized light; and a second polarization controller for adjusting the polarization state of the single-pass amplified first polarized light and outputting second polarized light.

[0052] Specifically, such as Figure 1As shown, the magnetic field of the second Faraday rotator is independent of the magnetic field to be measured. By adjusting the magnitude of the magnetic field of the second Faraday rotator through a controller, the polarized light emitted from the first semiconductor optical amplifier is rotated by a certain angle according to the demodulation requirements. The emitted light signal from the second Faraday rotator is then incident on the active region of the second semiconductor optical amplifier through a focusing lens. In this embodiment, the second semiconductor optical amplifier is a traveling wave amplifier. Furthermore, the structural parameters of the first and second semiconductor optical amplifiers are exactly the same, and their operating conditions are also the same, meaning that the single-pass amplification effect for the traveling wave is identical.

[0053] Further, the processing unit is used to detect, amplify, and filter the two orthogonally polarized beams, namely the TE-mode beam and the TM-mode beam, respectively; the comparator is used to compare the gain of the TE-mode beam and the TM-mode beam processed by the processing unit. If there is no gain difference between the TE-mode beam and the TM-mode beam, the comparison result is processed and displayed to obtain the angle adjusted by the second Faraday rotator. If there is a gain difference between the TE-mode beam and the TM-mode beam, the comparison result is processed and displayed, and used as the input signal of the controller to apply a magnetic field control voltage to adjust the angle of the second Faraday rotator until there is no gain difference between the TE-mode beam and the TM-mode beam, and the current rotation angle of the second Faraday rotator is obtained.

[0054] Specifically, after amplification, the light is incident on the polarization beam splitter via the second polarization controller. The polarization beam splitter outputs two orthogonal polarized beams, namely the TE mode beam and the TM mode beam, which are detected, amplified, and filtered respectively. Then, they are input to a comparator. The comparator compares the electrical signals output by the two orthogonal polarized beams (i.e., the TE mode beam and the TM mode beam), processes and displays them, and also serves as the input signal for the controller. Based on the magnitude of the comparison signal, the controller adjusts the magnetic field of the second Faraday rotator to obtain the desired rotation direction and angle.

[0055] Furthermore, the magnetic field strength unit is used to determine the specific value of the rotation angle of the first Faraday rotator under the action of the magnetic field to be detected, according to the required angle, and to obtain the magnetic field strength to be detected based on the specific value.

[0056] Specifically, semiconductor optical amplifiers exhibit strong polarization sensitivity, with a gain difference of nearly 10 dB between the TE and TM modes, degrading their performance and limiting their application in communications. Therefore, structural optimization and usage design are necessary to reduce or eliminate the impact of polarization sensitivity, making them polarization-independent. This polarization sensitivity can be utilized to design related sensors. By designing the semiconductor optical amplifier as a traveling-wave amplifier, a first polarization controller adjusts the polarization state of the optical signal, ensuring that the initial TE and TM modes of the incident optical signal are of equal magnitude. After single-pass amplification by the first semiconductor optical amplifier, the TE mode > the TM mode, with a gain difference ΔG of κ × (Γ). TE -Γ TM )×g×L, where κ is a constant coefficient, L is the active region length of the semiconductor optical amplifier, g is the gain coefficient, and Γ is the confinement factor of the active region optical field.

[0057] The thickness d of the first Faraday rotator is designed based on the maximum possible value of the magnetic field to be measured, ensuring that the rotation angle θ1 = V × H × d in the polarization direction does not exceed 90°. That is, the thickness of the Faraday rotator can be designed according to the range of the magnitude of the magnetic field to be measured; different thicknesses d are suitable for detecting magnetic fields of different magnitudes. The beam emitted from the first semiconductor optical amplifier enters the first Faraday rotator located in the region of the magnetic field to be measured. If there is a magnetic field parallel to the beam's propagation direction in the environment, the polarized light will rotate by an angle not exceeding 90°. After rotation, the beam enters the second Faraday rotator, which is unaffected by the magnetic field to be measured. The controller applies voltage to change the magnetic field of the environment where the second Faraday rotator is located, causing the polarized light to rotate by an angle θ2 when passing through the second Faraday rotator. The angle is 0-90°. Specifically, the required rotation angle is: after the beam passes through the first and second Faraday rotators, the total rotation angle of the polarized light is 90°. The two semiconductor traveling-wave amplifiers produce the same amplification effect for the TE and TM modes. That is, after amplification by the two traveling-wave amplifiers and rotation of the polarized light by the two Faraday rotators, the gains of the TE and TM modes are the same, TE mode = TM mode. If the gains of the TE and TM modes output by the comparator are still different after rotating θ2 by 90°, the controller applies a reverse magnetic field control voltage to the second Faraday rotator, generating an opposite magnetic field that causes θ2 to rotate in the opposite direction. To ensure more precise voltage application to the second Faraday rotator and eliminate errors caused by sudden adjustments, a sawtooth wave voltage is used for the applied magnetic field. Figure 2 As shown.

[0058] The beam emitted from the second Faraday rotator is coupled to the second semiconductor optical amplifier through a focusing lens and amplified again. After amplification, it passes through the second polarization controller and the polarization beam splitter in sequence. The second polarization controller is adjusted so that the polarization beam splitter can completely separate the two orthogonal polarized beams to obtain TE mode and TM mode beams respectively. Then, they are detected, amplified and filtered respectively, and then input to the comparator to compare the magnitudes of the TE mode and TM mode.

[0059] The comparator's output is processed and displayed, and also used as the input signal for the controller. If the comparator's result is TE mode ≠ TM mode, the controller adjusts the magnetic field control voltage of the second Faraday rotator to rotate the polarized light output from the first Faraday rotator by an angle until the comparator output shows TE mode = TM mode. At the same time, the specific value of the controller's magnetic field control voltage, whether it is a positive or negative voltage, and the angle of polarization rotation are all processed accordingly and displayed together with the comparator's output.

[0060] The signal process is as follows: Demodulation preparation: Calibrate the one-to-one correspondence between the rotation angle θ2 of the second Faraday rotator on the polarized light and the magnetic field control voltage U; Demodulation: After separating the orthogonal polarized light, adjust the magnetic field control voltage of the controller according to the result of the comparator output until the comparator output TE mode = TM mode. At this time, stop increasing the applied voltage U. According to the one-to-one correspondence between θ2 and the magnetic field control voltage U, the specific value of θ2 at this time can be obtained, and θ1 = 90° - θ2. Then, according to θ1 = V × H × d, the magnitude of the magnetic field to be measured can be demodulated.

[0061] This embodiment also discloses a signal demodulation method for a sensing system for detecting magnetic field strength, comprising: emitting a laser signal; adjusting the polarization state and performing a first single-pass amplification on the laser signal; rotating the laser signal under the influence of the magnetic field to be detected to output a first polarized light; adjusting the angle of the first polarized light; performing a second single-pass amplification and polarization state adjustment to output a second polarized light; splitting the second polarized light into two orthogonally polarized beams, namely a TE-mode beam and a TM-mode beam; comparing the gain of the two orthogonally polarized beams; processing and displaying the comparison result and using it as an input signal for a controller; applying a magnetic field control voltage to adjust the angle of the first polarized light; calibrating the correspondence between the rotation angle of the second Faraday rotator on the first polarized light and the magnetic field control voltage; stopping the increase of the applied voltage when there is no gain difference between the TE-mode beam and the TM-mode beam; obtaining the current rotation angle of the second Faraday rotator and determining the current rotation direction of the second Faraday rotator; and obtaining the magnetic field strength to be detected based on the rotation angle and direction of the second Faraday rotator.

[0062] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made to the technical solutions of the present invention by those skilled in the art without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A sensing system for detecting magnetic field strength, characterized in that, include: Laser emitting module, used to emit laser signals; The first optical signal conditioning module is used to adjust the polarization state of the laser signal and perform a first single-pass amplification, and rotate the angle under the action of the magnetic field to be detected to output the first polarized light; The second optical signal conditioning module is used to adjust the angle of the first polarized light, perform a second single-pass amplification and polarization state adjustment, and output the second polarized light. The polarization beam splitter module is used to split the second polarized light into two orthogonally polarized beams. The comparison module is used to compare the gains of the two orthogonally polarized beams, process and display the comparison results, and use them as input signals for the controller to apply a magnetic field to control the voltage and adjust the angle of the first polarized beam to obtain the required angle. The comparison module includes: The processing unit is used to detect, amplify, and filter the two orthogonally polarized beams, namely the TE mode beam and the TM mode beam, respectively. A comparator is used to compare the gain of the TE-mode beam and the TM-mode beam processed by the processing unit. If there is no gain difference between the TE-mode beam and the TM-mode beam, the comparison result is processed and displayed to obtain the angle adjusted by the second Faraday rotator. If there is a gain difference between the TE-mode beam and the TM-mode beam, the comparison result is processed and displayed, and used as an input signal for the controller to apply a magnetic field control voltage to adjust the angle of the second Faraday rotator until there is no gain difference between the TE-mode beam and the TM-mode beam, and the current rotation angle of the second Faraday rotator is obtained. The magnetic field strength module is used to obtain the magnetic field strength to be detected according to the required angle.

2. The sensing system for detecting magnetic field strength according to claim 1, characterized in that, The first optical signal conditioning module includes: A first polarization controller is used to adjust the polarization state of the laser signal; The first semiconductor optical amplifier is used to amplify the polarization-adjusted laser signal in a single pass. The first Faraday rotator is used to rotate the single-pass amplified laser signal by an angle under the action of the magnetic field to be detected, and output the first polarized light.

3. The sensing system for detecting magnetic field strength according to claim 1, characterized in that, The second optical signal conditioning module includes: A second Faraday rotator is used to adjust the angle of the first polarized light according to the voltage controlled by the applied magnetic field; A focusing lens is used to direct the first polarized light, after its angle adjustment, onto the active region of the second semiconductor optical amplifier; The second semiconductor optical amplifier is used to amplify the incident first polarized light in a single pass. The second polarization controller is used to adjust the polarization state of the first polarized light after single-pass amplification and output the second polarized light.

4. The sensing system for detecting magnetic field strength according to claim 1, characterized in that, The method for obtaining the gain difference between the TE mode beam and the TM mode beam is as follows: ΔG=κ×(Γ TE -C TM )×g×L Where ΔG is the gain difference, κ is a constant coefficient, and Γ TE ,Γ TM denoted as the confinement factor of the optical field in the active region, g is the gain coefficient, and L is the length of the active region of the semiconductor optical amplifier.

5. The sensing system for detecting magnetic field strength according to claim 2, characterized in that, The magnetic field strength module includes: The magnetic field strength unit is used to determine the specific value of the rotation angle of the first Faraday rotator under the action of the magnetic field to be detected, based on the required angle, and to obtain the magnetic field strength to be detected based on the specific value.

6. The sensing system for detecting magnetic field strength according to claim 5, characterized in that, The method for determining the specific value of the rotation angle of the first Faraday rotator under the action of the magnetic field to be detected is as follows: θ1 = 90° - θ2 Where θ1 is the angle of rotation of the polarization state direction under the action of the magnetic field to be detected, and θ2 is the rotation angle of the polarized light by the second Faraday rotator.

7. The sensing system for detecting magnetic field strength according to claim 5, characterized in that, The magnetic field strength to be detected is obtained as follows: θ1=V×H×d Where θ1 is the angle of rotation of the polarization state direction under the action of the magnetic field to be detected, H is the magnetic field strength to be detected, and d is the thickness of the first Faraday rotator.

8. A signal demodulation method applied to a sensing system for detecting magnetic field strength according to any one of claims 1-7, characterized in that, include: A laser signal is emitted, the polarization state of the laser signal is adjusted and the first single-pass amplification is performed, and the angle is rotated under the action of the magnetic field to be detected to output the first polarized light; The angle of the first polarized light is adjusted, and a second single-pass amplification and polarization state adjustment are performed to output the second polarized light. The second polarized light is then polarized and split to output two orthogonally polarized beams, namely the TE mode beam and the TM mode beam. The gains of the two orthogonally polarized beams are compared, the comparison results are processed and displayed, and used as input signals for the controller. A magnetic field control voltage is applied to adjust the angle of the first polarized beam. The correspondence between the rotation angle of the second Faraday rotator on the first polarized beam and the magnetic field control voltage is calibrated. When there is no gain difference between the TE mode beam and the TM mode beam, the applied voltage is stopped. The current rotation angle of the second Faraday rotator is obtained, and the current rotation direction of the second Faraday rotator is determined. Based on the rotation angle and direction of the second Faraday rotator, the magnetic field strength to be detected is obtained.

Images