A method for detecting a weak magnetic field in space based on a mutual coherence magneto-optical sensor

Abstract

This invention discloses a method for detecting weak magnetic fields in space based on a mutually coherent magneto-optical sensor, relating to optical instruments. The invention splits the light source into a probe beam and a gain beam. The probe beam is transmitted through an optically rotating crystal and then combined with the gain beam, resulting in mutual coherence. An optical Fourier transform is performed, outputting a single-point magneto-optical signal as an interference fringe image. Finally, the spatially frequency-domain correlated light intensity gray values ​​in the interference fringe image are extracted. The constructive and destructive interference signals are further obtained and differentially processed to obtain twice the interference magneto-optical signal, thus enhancing the magneto-optical signal and suppressing noise.

Description

Technical Field

[0001] This invention relates to optical instruments, and more particularly to magneto-optical sensors for measuring magnetic variables. Background Technology

[0002] In fields such as deep space and deep-sea exploration, materials analysis, resource exploration, and physical principle analysis, weak magnetic field detection equipment with high resistance to electromagnetic interference is an essential tool for interpreting planetary history, searching for extraterrestrial oceans, guiding drilling, and revealing physical principles. Fluxgate magnetometers, optically pumped magnetometers, diamond NV centers, and superconducting quantum interference devices (SQUs) are currently the tools capable of measuring weak magnetic fields in space. Among them, the core sensing elements of fluxgate magnetometers and optically pumped magnetometers are electromagnetically sensitive elements, making them susceptible to electromagnetic interference. The NV center used in diamond NV centers is a spin quantum sensor with a natural sensitivity to magnetic fields, making it susceptible to magnetic noise interference. Superconducting quantum interference devices require cryogenic cooling and a well-shielded vacuum cavity to operate, making the system complex, expensive, and not portable. Magneto-optic sensors are passive insulators, non-conductive, and neither generate nor induce electromagnetic fields. Signals are transmitted via light, and complete electrical isolation can be achieved between the back-end electronic equipment and the probe. Therefore, magneto-optic sensors have unparalleled advantages in resistance to electromagnetic interference compared to other magnetic field measuring instruments. However, magneto-optical sensors typically can only measure magnetic fields on the order of μT, making it difficult to measure weak spatial magnetic fields on the order of nT. Differential optical path-based magneto-optical sensors are designed to suppress common-mode noise and improve magnetic sensitivity. However, the differential optical path design necessitates a 45° polarization-analyze angle, resulting in a high initial output light intensity and a low available light intensity from the source, which is detrimental to improving the magneto-optical response. Some magneto-optical sensors set the polarization-analyze angle to 90°, using a direct detection optical path to probe the magnetic field. This allows for polarization rejection, resulting in a lower initial output light intensity and providing room for increased light intensity from the source, which is beneficial for the magneto-optical response. However, with a 90° polarization-analyze angle, the magneto-optical sensor exhibits the lowest sensitivity under weak magnetic fields, hindering weak magnetic field detection. Therefore, magneto-optical sensors need further improvements in their ability to detect weak spatial magnetic fields. Summary of the Invention

[0003] To address the weakness of existing magneto-optical sensors in detecting weak spatial magnetic fields, this invention presents a magneto-optical sensor and method for detecting weak spatial magnetic fields based on mutual coherence. The sensor splits the light source into a gain beam and a probe beam. Utilizing the mutual coherence between the two beams, constructive and demagnetizing interference signals are extracted and differentially processed, resulting in an output of twice the interference magneto-optical signal, exhibiting high sensitivity under weak magnetic fields.

[0004] This invention splits the light source into a probe light and a gain light. The probe light is transmitted through an optically rotating crystal and then combined with the gain light, resulting in mutual interference. An optical Fourier transform is then performed to output a single-point magneto-optical signal as an interference fringe image. Finally, the light intensity gray values ​​related to the spatial frequency domain in the interference fringe image are extracted. The constructive and destructive interference signals are further obtained and differentially processed to obtain a double interference magneto-optical signal, thereby enhancing the magneto-optical signal and suppressing noise.

[0005] Therefore, the specific solution of the present invention is: a method for detecting weak magnetic fields in space based on a mutually coherent magneto-optical sensor, wherein the mutually coherent magneto-optical sensor in the method includes: a light source, a single-mode fiber beam splitter, a polarization controller, a single-mode fiber interface, a lens, a polarization device, an optical rotator crystal, a polarization fiber interface, a polarization fiber coupler, a mirror, a grating, and a camera;

[0006] The light source outputs broadband, low-coherence light with a high polarization ratio, which is then split into two by a single-mode fiber beam splitter. The splitting ratio of the single-mode fiber beam splitter is A / B, resulting in two beams: a probe beam and a gain beam.

[0007] The probe light passes through a single-mode fiber in a single-mode fiber beam splitter with a splitting ratio of A. This single-mode fiber is wound around a first polarization controller. Adjusting the first polarization controller outputs linearly polarized light through the first single-mode fiber interface. The linearly polarized light is collimated by a first achromatic lens, then transmitted through a polarization device and an optical rotator crystal, and focused at the first polarization fiber interface by a second achromatic lens. The polarization axis of the polarization device is the same as the initial polarization direction of the linearly polarized light, and the polarization direction of the first polarization fiber interface is perpendicular to the initial polarization direction of the linearly polarized light. The first polarization fiber interface is part of a polarization fiber coupler with a coupling ratio of C.

[0008] The gain light is in the single-mode fiber of a single-mode fiber beam splitter with a splitting ratio of B; the single-mode fiber is wound around a second polarization controller, and the second polarization controller is adjusted so that the polarization direction of the output light of the second single-mode fiber interface is the same as the polarization direction that the second polarization fiber interface can pass through; the second polarization fiber interface is another part of the polarization fiber coupler and has a coupling ratio of D.

[0009] The probe light and gain light interfere after being combined by the polarization fiber coupler and output from the third polarization fiber interface. The collimated beam is then collimated by the third achromatic lens, and reflected by the mirror to the grating. The grating performs an optical Fourier transform on the collimated beam, and the output interference fringes are captured by the camera. Finally, the camera outputs the interference fringe image.

[0010] To make the optical path difference Within the coherence length, the length of the single-mode fiber containing the probe light in the single-mode fiber beam splitter plus the length of the spatial optical path of the probe light is equal to the length of the single-mode fiber containing the gain light in the single-mode fiber beam splitter; at the same time, the lengths of the polarized fibers into the corresponding polarized fiber interfaces of the probe light and polarized light are equal.

[0011] When the magnetic field of the space to be measured is very weak, the magneto-optical response of the interference term is greater than that of the DC term. Fully utilizing the magneto-optical response of the interference term is beneficial to the magneto-optical sensor's ability to detect weak magnetic fields in space.

[0012] Based on this discovery, the method for detecting weak magnetic fields in space is as follows:

[0013] Step 1: Convert the interference fringe image into a two-dimensional grayscale matrix. One dimension is the spatial frequency domain distribution of light, and the other dimension represents the position of the detection point. The grayscale value represents the light intensity signal.

[0014] Step 2: Extract a gray value in the spatial frequency domain from the two-dimensional gray values ​​and draw an interference line; at the same time, preprocess the line to achieve noise suppression; the preprocessing methods include: mean filtering, Gaussian filtering, and median filtering;

[0015] Step 3: Take the envelope of the interference lines to extract the constructive interference signal;

[0016] Methods for obtaining the upper envelope include Hilbert transform, extreme point interpolation, sliding window smoothing, and adaptive algorithms; finally, the upper envelope is integrated over the spatial frequency domain to obtain a magneto-optical signal related to the constructive interference.

[0017] Step 4: Remove the envelope of the interference lines to extract the interference cancellation signal;

[0018] Methods for extracting the lower envelope include Hilbert transform, extremum interpolation, sliding window smoothing, wavelet transform, and differential algorithm. Finally, the lower envelope is integrated over the spatial frequency domain to obtain a magneto-optical signal related to the destructive interference.

[0019] Step 5: Perform differential processing on the constructive and demagnetizing optical signals to obtain a magneto-optical signal with twice the interference term as the output signal I. out .

[0020] Furthermore, before the probe light and gain light are combined at the polarization fiber coupler, the probe photoelectric field is:

[0021] (1);

[0022] Where k is the wavelength of the light source, E d(k) is the electric field intensity of the probe light in different wavelength bands, s(k) is the electric field intensity of the light source in different wavelength bands, A is the splitting ratio of the probe light after the light source is split by the single-mode fiber beam splitter, C is the coupling ratio of the probe light coupled into the polarization fiber coupler, T is the transmittance of the optically active crystal, V is the Wilder coefficient of the optically active crystal, E is the magnetic field of the space to be measured, L is the thickness of the optically active crystal, and z d It is the optical path length of the probe light.

[0023] Furthermore, before the gain light and probe light are combined at the polarization fiber coupler, the gain photoelectric field is:

[0024] (2);

[0025] Among them, E e (k) represents the electric field intensity of the gain light at different wavelengths, B is the splitting ratio of the gain light after the light source is split by the single-mode fiber beam splitter, and z e It is the optical path length of the probe light.

[0026] Furthermore, the spatial frequency domain light intensity of the camera output interference fringes for:

[0027] (3);

[0028] Where S(k) is the light intensity of the light source in different wavelength bands. It is the optical path difference between the probe light and the gain light;

[0029] Differentiating formula (3) yields:

[0030] (4);

[0031] Formula 4 shows that when the magnetic field of the space to be measured is very weak, the magneto-optical response of the interference term is greater than that of the magneto-optical response of the DC term.

[0032] Furthermore, the formula for calculating the magneto-optical signal related to constructive interference in step 3 is shown below:

[0033] (5);

[0034] Where I a It is an interferometric constructive magneto-optical signal, and S is a positive correlation factor.

[0035] Furthermore, in step 4, the formula for calculating the magneto-optical signal related to interference destructive correlation is:

[0036] (6);

[0037] Where I b It is an interference phase demagnetization optical signal.

[0038] Furthermore, in step 5, the output signal I out for:

[0039] (7);

[0040] Where I out It is the output signal.

[0041] Furthermore, in order for the output signal to have optimal response to weak magnetic fields, the optical path needs to minimize the gain coefficient of the interference terms. First, without damaging the optical components, test the output light intensity of the light source to the maximum; then, select high ratios for the splitting ratio A / B of the single-mode fiber beam splitter and the coupling ratio C / D of the polarization fiber coupler; where A is greater than B and C is greater than D.

[0042] Therefore, the proportion of the light source allocated to gain light is very small. It is generally achieved by increasing the camera's gain or exposure time to ensure the gain light reaches an appropriate exposure grayscale value in the camera's output. For example, in an 8-bit camera, the exposure grayscale value of the gain light is 2. 8 / 2; therefore, the parameter It can achieve the maximum value; at the same time, the camera output will not be oversaturated.

[0043] The probe light accounts for the largest proportion of the light source; since the polarization-analysis angle of the magneto-optical sensor is set to 90°; after the probe light is polarized by the first polarization fiber interface, the intensity of the probe light incident on the camera is very weak; therefore, the parameters It can reach the maximum value; at the same time, the camera output will not be oversaturated.

[0044] The beneficial effect of this invention is that it can detect extremely weak spatial magnetic fields compared to traditional magneto-optical sensors. This is because the invention utilizes differential processing of constructive and demagnetizing magneto-optical signals to suppress common-mode noise and achieve a magneto-optical response with twice the interference term. Furthermore, the magneto-optical sensor described in this invention employs a mutually coherent optical path design. Through high-power light source output, selection of a high splitting ratio (A / B) for the single-mode fiber beam splitter (1×2) and a high coupling ratio (C / D) for the polarization fiber coupler (2×1), setting a 90° polarization-analyzing angle, and high-gain camera assistance, the magneto-optical response of the interference term can be optimized. Attached Figure Description

[0045] Figure 1 This is a design diagram of a self-coherent magneto-optical sensor based on the present invention.

[0046] In the diagram: 1. Light source, 2. Single-mode fiber beam splitter (1×2), 3. First polarization controller, 4. First single-mode fiber interface, 5. First achromatic lens, 6. Polarization device, 7. Optical rotator crystal, 8. Second achromatic lens, 9. First polarization fiber interface, 10. Second polarization controller, 11. Second single-mode fiber interface, 12. Second polarization fiber interface, 13. Polarization fiber coupler (2×1), 14. Third polarization fiber interface, 15. Third achromatic lens, 16. Mirror, 17. Grating, 18. Camera.

[0047] Figure 2 This is a schematic diagram of the weak magnetic field extraction method of the present invention; (a) is an interference fringe image, (b) is an interference line, and (c) is an interference line obtained by taking the upper and lower envelopes.

[0048] Figure 3 This is a flowchart of signal processing. Detailed Implementation

[0049] Figure 1 The design scheme for a magneto-optical sensor based on mutual coherence includes a light source (1), a single-mode fiber beam splitter (1×2) (2), a polarization controller (3), a single-mode fiber interface (4), an achromatic lens (5), a polarization device (6), an optical rotator (7), an achromatic lens (8), a polarization fiber interface (9), a polarization controller (10), a single-mode fiber interface (11), a polarization fiber interface (12), a polarization fiber coupler (2×1) (13), a polarization fiber interface (14), an achromatic lens (15), a mirror (16), a grating (17), and a camera (18).

[0050] The light source (1) outputs broadband low-coherence light with a high polarization ratio, and the output power is adjusted to the highest state. The single-mode fiber beam splitter (1×2) (2) receives the output light from the light source (1) and splits the light into probe light and gain light, which enter the two single-mode fibers respectively.

[0051] The single-mode fiber containing the probe light has a splitting ratio of A and is wound around a polarization controller (3). Adjusting the polarization controller (3) changes the polarization state of the probe light, causing it to diverge from the single-mode fiber interface (4) and output linearly polarized light. Subsequently, the linearly polarized light passes through an achromatic lens (5) to become collimated light, transmits through a polarization device (6) and an optical rotator (7), and is focused by an achromatic lens (8) onto a polarization fiber interface (9). The polarization axis of the polarization device (6) is the same as the initial polarization direction of the linearly polarized light. The specific polarization direction that the polarization fiber interface (9) can pass through is perpendicular to the initial polarization direction of the linearly polarized light. At this time, the polarization-analyzing angle is close to 90°. The polarization fiber interface (9) is one of the polarization fiber input interfaces of the polarization fiber coupler (2×1) (13) and has a coupling ratio of C.

[0052] The single-mode fiber containing the gain light has a splitting ratio of B and is wound around a polarization controller (10). Adjusting the polarization controller (10) changes the polarization state of the gain light, causing it to diverge from the single-mode fiber interface (11) and output linearly polarized light. The polarization direction of the linearly polarized light is the same as the specific polarization direction that the polarization fiber interface (12) can pass through. The polarization fiber interface (12) is one of the polarization fiber input interfaces of the polarization fiber coupler (2×1) (13) and has a coupling ratio of D.

[0053] The length of the single-mode fiber between the single-mode fiber splitter (1×2) (2) and the single-mode fiber interface (4), plus the length of the spatial optical path between the single-mode fiber interface (4) and the polarized fiber interface (9), must be equal to the length of the single-mode fiber between the single-mode fiber splitter (1×2) (2) and the single-mode fiber interface (11). The length of the polarized fiber between the polarized fiber interface (9) and the polarized fiber coupler (2×1) (13) is equal to the length of the polarized fiber between the polarized fiber interface (12) and the polarized fiber coupler (2×1) (13). The splitting ratio A+B=1, and A≫B. The coupling ratio C+D=1, and C≫D.

[0054] The probe light and gain light are combined at the polarization fiber coupler (2×1) (13) and output from the polarization fiber interface (14), and collimated by the achromatic lens (15). The collimated beam is reflected at a specific angle to the grating (17) through the mirror (15). The interference fringes output by the grating (18) are captured by the camera (18). In the gain setting of the camera (18), the spatial optical path of the probe light should be blocked, and then the gain of the camera (18) should be adjusted so that the exposure level of the gain light in the camera (18) is in the middle of the entire exposure range.

[0055] A weak magnetic field in the space to be measured is placed at the optically active crystal (7). Finally, the camera (18) outputs an interference fringe image, as shown below. Figure 2 As shown in (a). To extract the magnetic field signal characterized in the interference fringe image, a weak magnetic signal extraction method was further implemented, the specific details and process of which are as follows: Figure 2 As shown:

[0056] Step 1: Convert the interference fringe image into a two-dimensional grayscale matrix. One dimension is the spatial frequency domain distribution of light, and the other dimension represents the position of the detection point. The grayscale value represents the light intensity signal.

[0057] Step 2: Extract a gray value from the spatial frequency domain of the two-dimensional grayscale values ​​and draw an interference line, such as... Figure 2 (b) Simultaneously, the line is preprocessed to suppress noise. Preprocessing methods include, but are not limited to, mean filtering, Gaussian filtering, and median filtering.

[0058] Step 3: Obtain the upper envelope of the interference lines. Methods for obtaining the upper envelope include, but are not limited to, the Hilbert transform method, extremum interpolation, sliding window smoothing, and adaptive algorithms. Finally, integrate the upper envelope over the spatial frequency domain to obtain a magneto-optical signal related to the constructive interference.

[0059] Step 4: Remove the envelope of the interference lines, such as... Figure 2 The dotted line in (c) indicates this. Methods for extracting the lower envelope include, but are not limited to, Hilbert transform, extremum interpolation, sliding window smoothing, wavelet transform, and difference algorithms. Finally, the lower envelope is integrated over the spatial frequency domain to obtain a magneto-optical signal related to the destructive interference.

[0060] Step 5: Perform differential processing on the constructive and demagnetizing optical signals of the interference phase to obtain a magneto-optical signal with twice the interference term as the output signal.

[0061] by Figure 2 Taking the single interference fringe image shown in (a) as an example, a single magnetic field corresponds to one interference fringe. The interference fringes are plotted as curves, such as... Figure 2 As shown in (b). Then, the interference fringe curve is preprocessed, and the processed interference fringe curve is shown in [image / description]. Figure 2 The solid line in (c) shows the upper envelope curve of the interference fringes. Figure 2 The dashed line in (c) shows the upper envelope. Integrating the upper envelope over the spatial frequency domain yields a magneto-optical signal related to the constructive interference. Taking the lower envelope of the interference fringes gives the lower envelope curve, as shown in [image / description]. Figure 2 The dotted line in (c) shows the signal. Integrating the lower envelope curve over the spatial frequency domain yields a magneto-optical signal that is destructively related to the interference. Finally, subtracting the destructively related magneto-optical signal from the constructive interference signal yields a magneto-optical signal with twice the interference term, corresponding to the single-point magnetic field signal.

Claims

1. A method for detecting weak magnetic fields in space based on a mutually coherent magneto-optical sensor, wherein the mutually coherent magneto-optical sensor comprises: Light source, single-mode fiber beam splitter, polarization controller, single-mode fiber interface, lens, polarization device, optical rotator crystal, polarization fiber interface, polarization fiber coupler, mirror, grating and camera; The light source outputs broadband, low-coherence light with a high polarization ratio, which is then split into two by a single-mode fiber beam splitter. The splitting ratio of the single-mode fiber beam splitter is A / B, resulting in two beams: a probe beam and a gain beam. The probe light passes through a single-mode fiber in a single-mode fiber beam splitter with a splitting ratio of A. This single-mode fiber is wound around a first polarization controller. Adjusting the first polarization controller outputs linearly polarized light through the first single-mode fiber interface. The linearly polarized light is collimated by a first achromatic lens, then transmitted through a polarization device and an optical rotator crystal, and focused at the first polarization fiber interface by a second achromatic lens. The polarization axis of the polarization device is the same as the initial polarization direction of the linearly polarized light, and the polarization direction of the first polarization fiber interface is perpendicular to the initial polarization direction of the linearly polarized light. The first polarization fiber interface is part of a polarization fiber coupler with a coupling ratio of C. The gain light is in the single-mode fiber of a single-mode fiber beam splitter with a splitting ratio of B; the single-mode fiber is wound around a second polarization controller, and the second polarization controller is adjusted so that the polarization direction of the output light of the second single-mode fiber interface is the same as the polarization direction that the second polarization fiber interface can pass through; the second polarization fiber interface is another part of the polarization fiber coupler and has a coupling ratio of D. The probe light and gain light interfere after being combined by the polarization fiber coupler and output from the third polarization fiber interface. The collimated beam is then collimated by the third achromatic lens, and reflected by the mirror to the grating. The grating performs an optical Fourier transform on the collimated beam, and the output interference fringes are captured by the camera. Finally, the camera outputs the interference fringe image. To make the optical path difference Within the coherence length, the length of the single-mode fiber containing the probe light in the single-mode fiber beam splitter plus the length of the spatial optical path of the probe light is equal to the length of the single-mode fiber containing the gain light in the single-mode fiber beam splitter; at the same time, the lengths of the polarized fibers into the corresponding polarized fiber interfaces of the probe light and polarized light are equal. When the magnetic field of the space to be measured is very weak, the magneto-optical response of the interference term is greater than that of the DC term. Fully utilizing the magneto-optical response of the interference term is beneficial to the magneto-optical sensor's ability to detect weak magnetic fields in space. Based on this discovery, the method for detecting weak magnetic fields in space is as follows: Step 1: Convert the interference fringe image into a two-dimensional grayscale matrix. One dimension is the spatial frequency domain distribution of light, and the other dimension represents the position of the detection point. The grayscale value represents the light intensity signal. Step 2: Extract a gray value in the spatial frequency domain from the two-dimensional gray values ​​and draw an interference line; at the same time, preprocess the line to achieve noise suppression. Preprocessing techniques include: mean filtering, Gaussian filtering, and median filtering; Step 3: Take the envelope of the interference lines to extract the constructive interference signal; Methods for obtaining the upper envelope include Hilbert transform, extreme point interpolation, sliding window smoothing, and adaptive algorithms; finally, the upper envelope is integrated over the spatial frequency domain to obtain a magneto-optical signal related to the constructive interference. Step 4: Remove the envelope of the interference lines to extract the interference cancellation signal; Methods for extracting the lower envelope include Hilbert transform, extremum interpolation, sliding window smoothing, wavelet transform, and differential algorithm. Finally, the lower envelope is integrated over the spatial frequency domain to obtain a magneto-optical signal related to the destructive interference. Step 5: Differential processing of the interference constructive and interference destructive magneto-optical signals to obtain a doubled interference term magneto-optical signal as the output signal I out .

2. The method for detecting weak magnetic fields in space based on a mutually coherent magneto-optical sensor as described in claim 1, characterized in that, To ensure optimal response to weak magnetic fields, the optical path needs to minimize the gain coefficient of the interference terms. First, without damaging the optical components, test the output light intensity of the light source to the maximum; then, select high ratios for the splitting ratio A / B of the single-mode fiber beam splitter and the coupling ratio C / D of the polarization fiber coupler; where A is greater than B and C is greater than D. Therefore, the proportion of the light source allocated to gain light is very small. It is generally achieved by increasing the camera's gain or exposure time to ensure the gain light reaches an appropriate exposure grayscale value in the camera's output. For example, in an 8-bit camera, the exposure grayscale value of the gain light is 2. 8 / 2; therefore, the parameter It can achieve the maximum value; at the same time, the camera output will not be oversaturated. The probe light accounts for the largest proportion of the light source; since the polarization-analysis angle of the magneto-optical sensor is set to 90°; after the probe light is polarized by the first polarization fiber interface, the intensity of the probe light incident on the camera is very weak; therefore, the parameters It can reach the maximum value; at the same time, the camera output will not be oversaturated.

3. The method for detecting weak magnetic fields in space based on a mutually coherent magneto-optical sensor as described in claim 1, characterized in that, Before the probe light and gain light are combined at the polarization fiber coupler, the probe photoelectric field is: （1）； Where k is the wavelength of the light source, E d (k) is the electric field intensity of the probe light in different wavelength bands, s(k) is the electric field intensity of the light source in different wavelength bands, A is the splitting ratio of the probe light after the light source is split by the single-mode fiber beam splitter, C is the coupling ratio of the probe light coupled into the polarization fiber coupler, T is the transmittance of the optically active crystal, V is the Wilder coefficient of the optically active crystal, E is the magnetic field of the space to be measured, L is the thickness of the optically active crystal, and z d It is the optical path length of the probe light.

4. The method for detecting weak magnetic fields in space based on a mutually coherent magneto-optical sensor as described in claim 3, characterized in that, Before the gain light and probe light are combined at the polarization fiber coupler, the gain photoelectric field is: （2）； Among them, E e (k) represents the electric field intensity of the gain light at different wavelengths, B is the splitting ratio of the gain light after the light source is split by the single-mode fiber beam splitter, and z e It is the optical path length of the probe light.

5. The method for detecting weak magnetic fields in space based on a mutually coherent magneto-optical sensor as described in claim 4, characterized in that, Spatial frequency domain light intensity of camera output interference fringes for: （3）； Where S(k) is the light intensity of the light source in different wavelength bands. It is the optical path difference between the probe light and the gain light; Differentiating formula (3) yields: （4）； Formula 4 shows that when the magnetic field of the space to be measured is very weak, the magneto-optical response of the interference term is greater than that of the magneto-optical response of the DC term.

6. The method for detecting weak magnetic fields in space based on a mutually coherent magneto-optical sensor as described in claim 5, characterized in that, The formula for calculating the magneto-optical signal related to constructive interference in step 3 is shown below: （5）； Where I a It is an interferometric constructive magneto-optical signal, and S is a positive correlation factor.

7. The method for detecting weak magnetic fields in space based on a mutually coherent magneto-optical sensor as described in claim 6, characterized in that, In step 4, the formula for calculating the magneto-optical signal with destructive interference correlation is: （6）； Where I b It is an interference phase demagnetization optical signal.

8. The method for detecting weak magnetic fields in space based on a mutually coherent magneto-optical sensor as described in claim 7, characterized in that, In step 5, the output signal I out for: （7）； Where I out It is the output signal.

Images