WO2021184839A1 - 基于Sagnac干涉系统的全偏振法拉第磁场传感器及调制方法 - Google Patents

基于Sagnac干涉系统的全偏振法拉第磁场传感器及调制方法 Download PDF

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WO2021184839A1
WO2021184839A1 PCT/CN2020/134181 CN2020134181W WO2021184839A1 WO 2021184839 A1 WO2021184839 A1 WO 2021184839A1 CN 2020134181 W CN2020134181 W CN 2020134181W WO 2021184839 A1 WO2021184839 A1 WO 2021184839A1
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polarization
magnetic field
light
optical
maintaining fiber
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French (fr)
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张登伟
梁璀
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Zhejiang University
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Zhejiang University
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R33/00—Arrangements or instruments for measuring magnetic variables
    • G01R33/02—Measuring direction or magnitude of magnetic fields or magnetic flux
    • G01R33/032—Measuring direction or magnitude of magnetic fields or magnetic flux using magneto-optic devices, e.g. Faraday or Cotton-Mouton effect
    • G01R33/0322—Measuring direction or magnitude of magnetic fields or magnetic flux using magneto-optic devices, e.g. Faraday or Cotton-Mouton effect using the Faraday or Voigt effect
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01D—MEASURING NOT SPECIALLY ADAPTED FOR A SPECIFIC VARIABLE; ARRANGEMENTS FOR MEASURING TWO OR MORE VARIABLES NOT COVERED IN A SINGLE OTHER SUBCLASS; TARIFF METERING APPARATUS; MEASURING OR TESTING NOT OTHERWISE PROVIDED FOR
    • G01D5/00—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable
    • G01D5/26—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light
    • G01D5/32—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light
    • G01D5/34—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells
    • G01D5/353—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells influencing the transmission properties of an optical fibre
    • G01D5/35306—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells influencing the transmission properties of an optical fibre using an interferometer arrangement
    • G01D5/35322—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells influencing the transmission properties of an optical fibre using an interferometer arrangement using interferometer with one loop with several directions of circulation of the light, e.g. Sagnac interferometer
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R33/00—Arrangements or instruments for measuring magnetic variables
    • G01R33/0011—Arrangements or instruments for measuring magnetic variables comprising means, e.g. flux concentrators, flux guides, for guiding or concentrating the magnetic flux, e.g. to the magnetic sensor
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R33/00—Arrangements or instruments for measuring magnetic variables
    • G01R33/007—Environmental aspects, e.g. temperature variations, radiation, stray fields
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B27/00—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00
    • G02B27/28—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00 for polarising
    • G02B27/283—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00 for polarising used for beam splitting or combining
    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
    • G02F1/09—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on magneto-optical elements, e.g. exhibiting Faraday effect
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02A—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE
    • Y02A90/00—Technologies having an indirect contribution to adaptation to climate change
    • Y02A90/30—Assessment of water resources

Definitions

  • the invention relates to the technical field of optical fiber sensing, in particular to a full-polarization Faraday magnetic field sensor based on a Sagnac interference system and a modulation method.
  • magnetic field measurement technology occupies an increasingly important position in all aspects of scientific research, production and life, from mineral exploration and medical equipment in the civilian field to anti-submarine warfare and auxiliary navigation in the military field.
  • the requirements for magnetic field sensors are becoming increasingly strict, and high-precision, digitization, and miniaturization have become new trends.
  • the optical fiber magnetic field sensor uses optical fibers to transmit optical signals to the area to be detected.
  • the optical signals are modulated by the magnetic field to be measured and their specific properties change.
  • the detector and signal processing system obtain the characteristics of the magnetic field to be measured.
  • the current optical fiber magnetic field sensors are mainly divided into four types: the first one is based on the early MZ or Michelson interference structure, which uses the external magnetic field changes to cause the expansion and deformation of the magnetic material fixed with the optical fiber or grating, resulting in the measurement arm
  • the upper fiber or grating is strained, and the external magnetic field is measured by measuring the phase change or spectrum change of the interferometer.
  • This kind of sensing method has poor environmental stability, mainly because the MZ is a non-common dual-beam interference structure. Any non-common mode interference (temperature, vibration, sound) can cause phase shift and polarization instability.
  • this sensing method cannot measure the vector magnetic field; the second is to use optical fiber microstructure combined with magnetic fluid as the sensitive sensor.
  • the unit uses the FP cavity, MZ structure or Sagnac structure to measure the coherent light intensity or spectrum and the external magnetic field based on the change of the refractive index of the magnetic fluid under the action of a magnetic field.
  • This sensing method has low stability due to optical fiber And magnetic fluids are more sensitive to temperature; the third is to use the high magneto-optical coefficient of magneto-optical crystals.
  • the polarization state of the linearly polarized light propagating in the crystal is deflected, and the angle of deflection is related to the magnetic field.
  • the size, magneto-optical coefficient, and the length of the crystal are in a linear relationship.
  • the magnetic field is measured by measuring the deflection angle of polarized light.
  • the traditional sensing method using the magneto-optical crystal Faraday effect has low sensitivity and poor stability.
  • the fourth is some new measurement methods, including technologies based on surface plasmon resonance, based on Lorentz force, based on atomic magnetometer structure, etc.
  • the traditional Sagnac Faraday magnetic field sensor usually transmits linearly polarized light on the fast axis and slow axis of the polarization-maintaining fiber at the same time.
  • the beam of circularly polarized light produces a phase difference, which is restored to linearly polarized light through a quarter wave plate again, and the phase difference is detected by the detection system after interference, thereby obtaining external magnetic field information.
  • This kind of scheme has the conversion between linear polarization and circular polarization, which is limited by the performance of wave plates and other devices, and there are many uncontrollable errors in the conversion process.
  • the fast axis and slow axis of the polarization-maintaining fiber transmit optical signals at the same time, and there is mode coupling. The system error is large, resulting in low system sensitivity.
  • the present invention combines the Sagnac interference system with high stability and high precision and the magneto-optical crystal with high magneto-optical coefficient, and proposes a Sagnac-based interference system.
  • the system's full-polarization Faraday magnetic field sensor and modulation method adopts an independent linearly polarized light transmission method.
  • the linearly polarized light transmitted on the fast axis (or slow axis) of the polarization-maintaining fiber is specifically modulated through the polarization controller, and the magnetic field sensor unit
  • the polarization state of the rear linearly polarized light changes and polarization interference occurs at the output end, and the polarization state change is directly obtained by detecting the light intensity, thereby obtaining the external magnetic field information.
  • the invention adopts a high-performance polarizing device to improve the stability of the sensor, and at the same time, the sensitivity of the system can be effectively improved by using a magnetic flux concentrator in the magnetic field sensing unit.
  • a full-polarization Faraday magnetic field sensor based on the Sagnac interference system including a light source, a fiber coupler, a polarizer, a polarization beam splitter, a polarization controller, a magnetic field sensing unit, a detector, and a polarization maintaining fiber ring;
  • the output port of the light source and the receiving port of the detector are respectively optically connected to two ports on the same side of the optical fiber coupler, one port on the other side of the optical fiber coupler is connected to the polarizer optical fiber, and the polarizer is connected to A port on one side of the polarization beam splitter is connected to a fiber; a port on the other side of the polarization beam splitter is connected to the first polarization-maintaining fiber ring through the first polarization controller, and the other side of the polarization beam splitter is One port is connected to the second polarization-maintaining fiber loop through the second polarization controller, and the two polarization-maintaining fiber loops are both connected to the magnetic field sensing unit;
  • the fast axis directions of the first and second polarization-maintaining fiber loops and the polarization direction of the polarizer are at an angle of 45°, and the included angle directions are opposite;
  • the optical fiber connection adopts polarization-maintaining optical fiber;
  • the magnetic field sensing unit includes a first coupling lens, a first magnetic flux concentrator, a magneto-optical crystal, a second magnetic flux concentrator, and a second coupling lens arranged in sequence along an axial direction, the first coupling lens and The second coupling lens is symmetrical about the magneto-optical crystal, and the first magnetic flux concentrator and the second magnetic flux concentrator are symmetrical about the magneto-optical crystal;
  • the first coupling lens is connected to the first polarization-maintaining fiber ring
  • the second coupling lens is connected to the second polarization-maintaining fiber ring
  • the first magnetic flux concentrator and the second magnetic flux concentrator are both provided with shafts
  • the two ends of the magneto-optical crystal are respectively inserted into the two axial through holes to be fixed
  • the two beams of light output from the first polarization-maintaining fiber ring and the second polarization-maintaining fiber ring can pass through the first coupling lens and the second coupling lens, respectively.
  • the coupling lens is coupled to the axial through hole.
  • the first polarization-maintaining fiber ring and the second polarization-maintaining fiber ring are formed by winding a polarization-maintaining fiber, and the two polarization-maintaining fiber rings have the same diameter, the same number of windings, and the winding directions are opposite.
  • the outer surfaces of both ends of the magneto-optical crystal are plated with antireflection films.
  • the size of the axial through holes of the first magnetic flux concentrator and the second magnetic flux concentrator matches the diameter of the magneto-optical crystal.
  • the invention also discloses an optical signal modulation method based on the above-mentioned fully polarized Faraday magnetic field sensor, which is specifically:
  • the optical signal emitted by the light source passes through the fiber coupler, the polarizer, and the polarization beam splitter in turn, and then is divided into two beams of light transmitted clockwise and counterclockwise, and the two beams of light are respectively transmitted to the first polarization control through the polarization maintaining fiber
  • the second polarization controller using the first polarization controller and the second polarization controller to superimpose the polarization modulation of 45° clockwise and 45° counterclockwise on the two beams respectively;
  • the modulated light transmitted along the clockwise optical path enters the fast axis transmission of the first polarization-maintaining fiber ring, converts the fiber light into spatial light through the first coupling lens, and couples to the axial flux of the first magnetic flux concentrator. Then, it passes through the magneto-optical crystal and the second magnetic flux concentrator in sequence, and then converts the space light into fiber light through the second coupling lens, and enters the slow axis transmission of the second polarization-maintaining fiber ring;
  • the modulated light transmitted along the counterclockwise optical path enters the fast axis of the second polarization-maintaining fiber loop, converts the fiber light into space light through the second coupling lens, and couples to the axial flux of the second magnetic flux concentrator. Then, it passes through the magneto-optical crystal and the first magnetic flux concentrator in sequence, and then converts the space light into fiber light through the first coupling lens, and enters the slow axis transmission of the first polarization-maintaining fiber ring;
  • the magnetic field sensor of the present invention uses a fully polarized Sagnac system combined with a high-efficiency magnetic field sensing unit to measure the magnetic field, and has the advantages of large dynamic range, high magnetic field sensitivity and the like. in particular:
  • the magnetic field sensor proposed in the present invention adopts the Sagnac interference system, which has the advantages of common-path interference compared with the magnetic field measurement method adopting M-Z structure, that is, high stability and small error;
  • the present invention uses a magneto-optical crystal with a high Feld constant, which is less affected by environmental factors such as temperature and vibration than the magnetic field measurement method using magnetic fluid, and can perform vector measurement while having a larger measurement dynamic range. ;
  • the present invention has an innovative principle. It adopts separate linear polarization transmission, polarization controller modulated light signal and direct polarization interference detection and other technical methods, and has better magnetic field sensitivity and System stability.
  • Figure 1 is a schematic diagram of a fully polarized Faraday magnetic field sensor based on the Sagnac interference system in the present invention
  • Figure 2 is a schematic diagram of the magnetic field sensing unit of the present invention.
  • FIG. 3 is a schematic diagram of the relationship between the polarization state of the optical signal before and after passing through the magnetic field sensing unit and the polarization direction of the polarizer;
  • FIG. 4 is a schematic diagram of the transmission mode of the optical signal before and after passing through the magnetic field sensing unit in the polarization maintaining fiber;
  • the full polarization Faraday magnetic field sensor based on the Sagnac interference system proposed by the present invention includes a light source 1, a fiber coupler 2, a polarizer 3, a polarization beam splitter 4, a first polarization controller 5, and a second polarization Controller 6, magnetic field sensing unit 7, detector 10, first polarization-maintaining fiber ring 6, second polarization-maintaining fiber ring 8;
  • light source 1 is connected to port 21 of fiber coupler 2 through a polarization-maintaining fiber, and fiber coupler 2
  • the port 22 of the optical fiber is connected to the detector 10 through the polarization-maintaining fiber
  • the port 23 of the fiber coupler 2 is connected to the port 31 of the polarizer 3 through the polarization-maintaining fiber
  • the port 32 of the polarizer 3 is connected to the polarization beam splitter through the polarization-maintaining fiber.
  • the port 41 of 4 is connected, the port 42 of the polarization beam splitter 4 is connected to the port 51 of the first polarization controller 5 through the polarization maintaining fiber, and the port 52 of the first polarization controller 5 is connected to the port 61 of the first polarization maintaining fiber ring 6 Connected, the port 92 of the second polarization controller 9 is connected to the port 82 of the second polarization-maintaining fiber ring 8.
  • the angle between the fast axis direction of the first polarization-maintaining fiber ring 6 and the polarization direction of the polarizer 3 is 45° clockwise (Or 45° counterclockwise), the corresponding angle between the fast axis direction of the second polarization-maintaining fiber ring 8 and the polarization direction of the polarizer 3 is 45° counterclockwise (or 45° clockwise), that is, the first
  • the angle between the fast axis directions of the polarization maintaining fiber ring 6 and the second polarization maintaining fiber ring 8 and the polarization direction of the polarizer 3 is 45°, and the angle directions are opposite.
  • the port 62 of the first polarization-maintaining fiber loop 6 and the port 81 of the second polarization-maintaining fiber loop 8 are respectively connected to the two ports of the magnetic field sensing unit 7. There is a fiber light-spatial light-fiber light at the magnetic field sensing unit 7.
  • the first polarization-maintaining fiber ring 6 and the second polarization-maintaining fiber ring 8 are wound by the polarization-maintaining fiber, the number of polarization-maintaining fiber turns is the same, the diameter of the polarization-maintaining fiber loop is the same, and the two polarization-maintaining fibers are wound in opposite directions, that is, the first A polarization-maintaining fiber ring 6 is wound clockwise (or counterclockwise), and the corresponding second polarization-maintaining fiber ring 8 is wound counterclockwise (or clockwise) to eliminate errors caused by the Sagnac effect.
  • the magnetic field sensing unit 7 mainly includes a coupling lens, a magnetic flux concentrator and a magneto-optical crystal.
  • the left end of the magnetic field sensing unit 7 is connected to the first polarization-maintaining fiber ring 6 through the first coupling lens 11.
  • the first coupling lens 11 When the light on the clockwise optical path enters the first coupling lens 11 through the polarization-maintaining fiber ring 6, the first coupling lens 11 is equipped with Polarization-maintaining fiber has the ability to convert light into spatial light, and at the same time it has the ability to shrink the beam and make it enter the magneto-optical crystal at a specific angle; the magneto-optical crystal 13 has a high Feld constant; the first magnetic flux concentrator 12 and the second magnetic flux concentrator 12 The magnetic flux concentrator 14 is placed at both ends of the magneto-optical crystal 13, and both ends of the magneto-optical crystal partially extend into the axial through hole of the magnetic flux concentrator; the right end of the magnetic field sensor unit 7 is connected to the second coupling lens 15 through the second coupling lens 15 The polarization-maintaining fiber ring 8 is connected.
  • the second coupling lens 15 When the light on the clockwise optical path exits from the second coupling lens 15, the second coupling lens 15 has the ability to convert spatial light into fiber light. In the same way, when the light on the counterclockwise optical path enters the magnetic field sensing unit 7 from the second coupling lens 15 and exits the first coupling lens 11, the second coupling lens 15 also has a function of converting polarization-maintaining fiber light into spatial light. At the same time, it has the ability to shrink the beam and make it incident on the magneto-optical crystal along a specific angle. The first coupling lens 11 also has the ability to convert spatial light into fiber light. In summary, the two coupling lenses have the same functions of shrinking the incident light, controlling the direction, and coupling the outgoing light to the optical fiber.
  • the working principle of the present invention is:
  • the basic principle of polarization detection using the Sagnac system is shown in equation (1). It can be seen that the interference output light intensity is related to the polarization angle of the two beams and the phase difference of the two beams. It is analogous to a gyro.
  • the Sagnac effect is The phase change information needs to be obtained. Therefore, various technical means are used to eliminate the errors introduced by the change of the polarization state, mainly various birefringence; the present invention takes the polarization rotation caused by the Faraday effect as the target quantity, and adopts the forward and reverse surround ring, etc. The method suppresses the generation of phase difference, so that equivalent detection accuracy can be obtained in the final detection system.
  • I represents the intensity of the detected optical signal
  • I 1 and I 2 represent the intensity of the non-interference optical signal transmitted along the clockwise and counterclockwise optical path
  • I 12 represents the intensity of the interference optical signal transmitted along the clockwise and counterclockwise optical path
  • a 1 and A 2 respectively represent the amplitude of the optical signal transmitted along the clockwise and counterclockwise optical path
  • ⁇ represents the phase difference of the optical signal transmitted along the clockwise and counterclockwise optical path
  • ⁇ F represents the Faraday deflection angle caused by the magnetic field.
  • the angles between the polarization direction of the polarizer in the present invention and the two main axes of the polarization-maintaining fiber ring are 45° clockwise and counterclockwise, respectively.
  • the two beams of light are respectively superimposed clockwise 45° and counterclockwise 45° polarization modulation on them at the starting end using a polarization controller, so that they are transmitted along the fast axis of the two polarization-maintaining fiber loops with opposite winding directions.
  • the Faraday deflection angles of the same size and opposite directions are generated respectively.
  • the interference light intensity is equation (2). It can be seen that the interference signal intensity has the maximum relative to the Faraday deflection angle at this time.
  • the rate of change is
  • the light emitted by the light source is divided into two after passing through the fiber coupler, polarizer, and polarization beam splitter, and the two linearly polarized lights are respectively modulated by the first polarization controller and the second polarization controller.
  • the modulation method is: the first polarization controller 5 and the second polarization controller 9 respectively superimpose the polarization modulation of 45° clockwise and 45° counterclockwise on the two beams of light.
  • the modulated two beams of light enter two polarization-maintaining fiber loops that are wound clockwise and counterclockwise respectively.
  • the first polarization-maintaining fiber loop on the clockwise optical path is clockwise wound
  • the one on the counterclockwise optical path is The second polarization-maintaining fiber loop is wound counterclockwise.
  • the two beams of linearly polarized light are respectively transmitted along the fast axis of the polarization-maintaining fiber ring.
  • they pass the conversion of fiber light-spatial light-fiber light, and are respectively coupled into the slow axis of the two polarization-maintaining fiber rings.
  • the main interference light on the slow axis can reach the exit point at the same time for polarization interference and the crystal Faraday effect.
  • the resulting orthogonal component of the polarized light is transmitted along the fast axis and will be separated from the main interference light at the exit point to ensure that the polarization interference result is not affected.
  • the fast-axis light emitted from the port 62 of the first polarization-maintaining fiber ring 6 is coupled to the axial through hole of the first magnetic flux concentrator 12 through the first coupling lens 11,
  • the first coupling lens 11 converts the optical fiber light into spatial light, and at the same time reduces the beam diameter to several times to tens of times smaller than the diameter of the magneto-optical crystal, and adjusts the beam to enter the left end face of the magneto-optical crystal, after passing through the magneto-optical crystal.
  • the light transmitted along the fast axis emitted from the port 81 of the second polarization-maintaining fiber ring 8 is coupled to the axial through hole of the second magnetic flux concentrator 14 through the second coupling lens 15, and the second coupling
  • the lens 15 converts the optical fiber light into spatial light, and at the same time reduces the beam diameter to several times to tens of times smaller than the diameter of the magneto-optical crystal, and adjusts the beam to enter the right end surface of the magneto-optical crystal, pass through the magneto-optical crystal, and exit from the left end surface.
  • the first magnetic flux concentrator 12 collects the lines of magnetic force, and then couples the spatial light into the polarization-maintaining fiber through the first coupling lens, and enters the slow axis transmission of the first polarization-maintaining fiber ring 6.
  • the magnetic field sensor unit is subjected to a magnetic field along the direction of the magneto-optical crystal, the polarized light passing through the magneto-optical crystal is Faraday deflected due to the Faraday effect, which causes the change of the polarization interference light intensity, which can be obtained by detecting the light intensity and information processing External magnetic field information.
  • a proton exchange Y waveguide with high polarization extinction ratio is used to realize the functions of polarizer and polarization beam splitter;
  • the polarization controller uses EOSPACE’s lithium niobate electro-optical modulation polarization controller, which can achieve any input polarization state through voltage control Conversion to any output polarization state, and the response time is less than 100ns;
  • the magneto-optical crystal 12 uses a cylindrical Ga:YIG crystal with a diameter of 1.8mm, a length of 2.7mm, and a magneto-optical Feld constant of 8400rad/m/T ;
  • the magnetic flux concentrator 11 is a cylindrical body and a truncated cone structure, in which the cylindrical body has a diameter of 22mm, a length of 13mm, a bottom of the truncated cone with a diameter of 13mm, a length of 13mm, a cone angle of 22°, a through hole diameter of 1.8mm, and both ends of the magneto-optical
  • the polarization extinction ratio of the polarization-maintaining fiber in the known system is about 40dB, and the polarization extinction ratio of the Y-waveguide is about 60dB.
  • a total reflection film may be plated on the inner surface part of the two end faces of the magneto-optical crystal, and a reflecting cavity is formed inside the magneto-optical crystal, so that the light beam is incident on the magneto-optical crystal at a certain angle.
  • the reflection cavity of the crystal it is emitted after multiple reflections to increase the optical path.
  • the change of the polarization state of the optical signal can be linearly accumulated with the increase of the optical path, so the magnetic field sensitivity of the system can be effectively improved.
  • the fully polarized Faraday magnetic field sensor based on the Sagnac interference system proposed in the present invention has the advantages of large dynamic range, high stability, high magnetic field sensitivity, easy miniaturization, etc., and has broad applications in both civilian and military fields. Application prospects.

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Abstract

一种基于Sagnac干涉系统的全偏振法拉第磁场传感器及调制方法，包括光源（1）、光纤耦合器（2）、起偏器（3）、偏振分束器（4）、偏振控制器（5、9）、磁场传感单元（7）、探测器（10）以及保偏光纤（6、8）。光信号由光源（1）发出，依次经过光纤耦合器（2）、起偏器（3），由偏振分束器（4）分为顺时针、逆时针两路，两条光路中分别存在偏振控制器（5、9）和保偏光纤环（6、8），两个保偏光纤环（6、8）的快轴方向与起偏器（3）偏振方向的夹角分别为顺时针45°和逆时针45°，两个保偏光纤环（6、8）绕制方向相反且直径、圈数相等以抵消Sagnac效应带来的误差，磁场传感单元（7）主要由耦合透镜（11、15）、磁通聚集器（12、14）和磁光晶体（13）组成，外界磁场对光信号偏振态产生影响，通过对输出光信号偏振干涉结果的检测，即可实现对磁场的测量。

Description

基于Sagnac干涉系统的全偏振法拉第磁场传感器及调制方法 技术领域
本发明涉及光纤传感技术领域，具体涉及一种基于Sagnac干涉系统的全偏振法拉第磁场传感器及调制方法。
背景技术
随着科技的进步和社会的发展，磁场测量技术在科学研究和生产生活的方方面面占据了越来越重要的位置，从民用领域的矿产探测、医疗器械到军用领域的反潜作战、辅助导航，因此对磁场传感器的要求也日趋严格，高精度、数字化、小型化成为新的趋势。
传统的磁场传感器将磁场信号转换为电信号进行测量，但其很容易受到环境电磁场的干扰，理论和实际应用精度不高。因此，光纤传感应运而生。光纤传感自诞生以来就得到飞速发展，其具备抗电磁干扰、动态范围大、测量精度高、易于小型化等优点，应用前景广阔。
光纤磁场传感器是利用光纤传输光信号至待探测区域，光信号受到待测磁场的调制，特定性质发生变化，之后由探测器和信号处理系统获得待测磁场的特性。根据工作原理的不同，目前的光纤磁场传感器主要分为四种：第一种是早期的基于M-Z或Michelson干涉结构，利用外界磁场变化引起与光纤或光栅固联的磁性材料伸缩形变，导致测量臂上光纤或光栅发生应变，通过测量干涉仪相位的变化或光谱的变化，测量外界磁场，这种传感方式环境稳定性较差，主要因为M-Z为非共路双光束干涉结构，两干涉臂上任何非共模干扰(温度、振动、声音)都能导致相位漂移和偏振不稳定性，此外，这种传感方式无法进行矢量磁场的测量；第二种是使用光纤微结构结合磁流体作为敏感单元，基于磁场作用下磁流体折射率发生变化的特性，利用F-P腔、M-Z结构或Sagnac结构测量相干后的光强或光谱，测量外界磁场，这种传感方式稳定性较低，原因在于光纤和磁流体对温度较敏感；第三种是利用磁光晶体的高磁光系数，磁场平行于光的传播方向时，在晶体中传播的线偏振光的偏振态发生偏转，偏转的角度与磁场大小、磁光系数、 晶体的长度成线性关系，通过测量偏振光的偏转角度测量磁场，传统的利用磁光晶体法拉第效应的传感方式灵敏度不高，稳定性较差，通过增加磁光晶体长度的方法可以提高灵敏度，但增加了传感器的体积，无法做到小型化；第四种是一些新型的测量方法，包括基于表面等离子体共振、基于洛伦兹力、基于原子磁力仪结构等技术，再利用功能型光纤传感器测量相位、光程、偏振态或折射率，实现对外界磁场的测量，这类传感方式灵敏度不高，稳定性和带宽问题一直无法解决，且只能标量测量，不利于诸多应用场合。
另外，传统的Sagnac法拉第磁场传感器通常使线偏振光同时在保偏光纤的快轴和慢轴传输，经过四分之一波片转换为左旋和右旋圆偏振光，被外界磁场调制后，两束圆偏振光产生相位差，再次经过四分之一波片恢复为线偏振光，进行干涉后由探测系统检测相位差，从而得到外界磁场信息。这种方案存在线偏光与圆偏光之间的转换，受限于波片等器件的性能，转换过程存在诸多不可控误差，此外，保偏光纤快轴和慢轴同时传输光信号，存在模式耦合，系统误差较大，导致系统灵敏度不高。
发明内容
为了解决现有的磁场传感器稳定性较差、检测精度较低的缺陷，本发明结合具有高稳定性、高精度的Sagnac干涉系统以及具有高磁光系数的磁光晶体，提出一种基于Sagnac干涉系统的全偏振法拉第磁场传感器及调制方法，采用了独立的线偏光传输方式，通过偏振控制器对在保偏光纤快轴(或慢轴)上传输的线偏光进行特定调制，经过磁场传感单元后线偏光偏振态发生变化并在输出端发生偏振干涉，通过检测光强直接获取偏振态变化，从而得到外界磁场信息。本发明采用高性能偏振器件用于提升传感器的稳定性，同时在磁场传感单元中通过采用磁通聚集器能够有效提高系统灵敏度。
为了实现上述目的，本发明采用如下技术方案：
一种基于Sagnac干涉系统的全偏振法拉第磁场传感器，包括光源、光纤耦合器、起偏器、偏振分束器、偏振控制器、磁场传感单元、探测器以及保偏光纤环；
所述光源的输出端口和探测器的接收端口分别与光纤耦合器同一侧的两个端口光纤连接，光纤耦合器另一侧的一个端口与起偏器光纤连接，且所述的起偏器与偏振分束器一侧的一端口光纤连接；所述的偏振分束器另一侧的一端口通过 第一偏振控制器与第一保偏光纤环光纤连接，且偏振分束器该侧的另一端口通过第二偏振控制器与第二保偏光纤环光纤连接，两个保偏光纤环均与磁场传感单元相连；
所述的第一保偏光纤环和第二保偏光纤环的快轴方向与所述的起偏器的偏振方向夹角呈45°，且夹角方向相反；所述的光纤连接采用保偏光纤；
所述的磁场传感单元包括沿轴向依次布置的第一耦合透镜、第一磁通聚集器、磁光晶体、第二磁通聚集器、第二耦合透镜，所述的第一耦合透镜和第二耦合透镜关于磁光晶体对称，所述的第一磁通聚集器和第二磁通聚集器关于磁光晶体对称；
所述的第一耦合透镜与第一保偏光纤环相连，第二耦合透镜与第二保偏光纤环的相连；所述的第一磁通聚集器和第二磁通聚集器均设有轴向通孔，磁光晶体的两端面分别插入两个轴向通孔中固定；从第一保偏光纤环和第二保偏光纤环输出的两束光能够分别经第一耦合透镜和第二耦合透镜耦合至所述的轴向通孔中。
优选的，所述的第一保偏光纤环和第二保偏光纤环由保偏光纤绕制而成，两个保偏光纤环的直径相同、绕制圈数相同、绕制方向相反。
优选的，所述的磁光晶体两端面的外表面均镀有增透膜。
优选的，所述的第一磁通聚集器和第二磁通聚集器的轴向通孔大小与磁光晶体的直径大小匹配。
本发明还公开了一种基于上述全偏振法拉第磁场传感器的光信号调制方法，具体为：
1)光源出射的光信号依次经过光纤耦合器、起偏器、偏振分束器后分为沿顺时针、逆时针传输的两束光，两束光通过保偏光纤分别传输至第一偏振控制器和第二偏振控制器，利用第一偏振控制器和第二偏振控制器分别在两束光上叠加顺时针45°、逆时针45°的偏振调制；
2)调制后的沿顺时针光路传输的光进入第一保偏光纤环的快轴传输，经第一耦合透镜将光纤光转换为空间光，并耦合至第一磁通聚集器的轴向通孔中，然后依次穿过磁光晶体和第二磁通聚集器，再经第二耦合透镜将空间光转换为光纤光，进入第二保偏光纤环的慢轴传输；
3)调制后的沿逆时针光路传输的光进入第二保偏光纤环的快轴传输，经第二耦合透镜将光纤光转换为空间光，并耦合至第二磁通聚集器的轴向通孔中，然 后依次穿过磁光晶体和第一磁通聚集器，再经第一耦合透镜将空间光转换为光纤光，进入第一保偏光纤环的慢轴传输；
4)沿顺时针光路、逆时针光路传输的光经过磁光晶体后分别产生大小相同、方向相反的法拉第偏转角，且两束光分别各沿快、慢轴传输一半光程，同时返回偏振分束器发生偏振干涉，再经起偏器、光纤耦合器后由探测器对干涉信号进行获取。
本发明具备的有益效果是：
本发明的磁场传感器利用全偏振Sagnac系统结合高效磁场传感单元对磁场进行测量，具有大动态范围、高磁场灵敏度等优点。具体而言：
(1)本发明提出的磁场传感器采用Sagnac干涉系统，与采用M-Z等结构的磁场测量方法相比具有共路干涉的优势，即稳定性高、误差小；
(2)本发明采用高费尔德常数的磁光晶体，与采用磁流体的磁场测量方法相比受温度、振动等环境因素影响小，且可以进行矢量测量，同时具备较大的测量动态范围；
(3)本发明与传统的Sagnac法拉第磁场传感器相比，具有创新的原理，采用单独的线偏光传输、偏振控制器调制光信号以及直接的偏振干涉检测等技术方法，具有更好的磁场灵敏度和系统稳定性。
附图说明
图1是本发明中基于Sagnac干涉系统的全偏振法拉第磁场传感器的示意图；
图2是本发明中磁场传感单元的示意图；
图3为经过磁场传感单元前后光信号偏振态与起偏器偏振方向夹角关系示意图；
图4为经过磁场传感单元前后光信号在保偏光纤中传输方式示意图；
图中：1.光源，2.光纤耦合器，3.起偏器，4.偏振分束器，5.第一偏振控制器，6.保偏光纤环，7.磁场传感单元，8.保偏光纤环，9.第二偏振控制器，10.探测器，11.第一耦合透镜，12.第一磁通聚集器，13.磁光晶体，14.第二磁通聚集器，15.第二耦合透镜。
具体实施方式
下面结合附图和实施例对本发明作进一步说明。
如图1所示，本发明提出的基于Sagnac干涉系统的全偏振法拉第磁场传感 器包括光源1、光纤耦合器2、起偏器3、偏振分束器4、第一偏振控制器5、第二偏振控制器6、磁场传感单元7、探测器10、第一保偏光纤环6、第二保偏光纤环8；光源1通过保偏光纤与光纤耦合器2的端口21连接，光纤耦合器2的端口22通过保偏光纤与探测器10相连，光纤耦合器2的端口23通过保偏光纤与起偏器3的端口31连接，起偏器3的端口32通过保偏光纤与偏振分束器4的端口41连接，偏振分束器4的端口42通过保偏光纤与第一偏振控制器5的端口51连接，第一偏振控制器5的端口52与第一保偏光纤环6的端口61连接，第二偏振控制器9的端口92与第二保偏光纤环8的端口82连接，第一保偏光纤环6的快轴方向与起偏器3的偏振方向夹角为顺时针45°(或逆时针45°)，对应的第二保偏光纤环8的快轴方向与起偏器3的偏振方向夹角为逆时针45°(或顺时针45°)，即所述的第一保偏光纤环6和第二保偏光纤环8的快轴方向与所述的起偏器3的偏振方向夹角呈45°，且夹角方向相反。第一保偏光纤环6的端口62和第二保偏光纤环8的端口81分别与磁场传感单元7两个端口连接，在磁场传感单元7处存在光纤光－空间光－光纤光的转换；其中第一保偏光纤环6和第二保偏光纤环8由保偏光纤绕制，保偏光纤圈数相同，保偏光纤环直径相同，两保偏光纤环绕制方向相反，即第一保偏光纤环6顺时针(或逆时针)绕制，对应的第二保偏光纤环8逆时针(或顺时针)绕制，以消除Sagnac效应带来的误差。
如图2所示，所述的磁场传感单元7主要包括耦合透镜、磁通聚集器和磁光晶体。磁场传感单元7左端通过第一耦合透镜11与第一保偏光纤环6相连，当顺时针光路上的光经保偏光纤环6进入第一耦合透镜11时，第一耦合透镜11具备将保偏光纤光转换为空间光的能力，同时具备将光束缩小并使其沿特定角度入射磁光晶体的能力；磁光晶体13具有高费尔德常数；第一磁通聚集器12和第二磁通聚集器14置于磁光晶体13两端，且磁光晶体两端均部分伸入磁通聚集器的轴向通孔中；磁场传感单元7右端通过第二耦合透镜15与第二保偏光纤环8相连，当顺时针光路上的光从第二耦合透镜15出射时，第二耦合透镜15具备将空间光转换为光纤光的能力。同理，当逆时针光路上的光从第二耦合透镜15进入磁场传感单元7，并从第一耦合透镜11出射时，第二耦合透镜15同样具备将保偏光纤光转换为空间光的能力，同时具备将光束缩小并使其沿特定角度入射磁光晶体的能力，第一耦合透镜11同样具备将空间光转换为光纤光的能力。综上，两个耦合透镜均具备相同的将入射光缩束、控制方向以及将出射光耦合至光纤的 功能。
本发明的工作原理为：
利用Sagnac系统进行偏振检测的基本原理如式(1)所示，可以看出，其干涉输出光强与两束光的偏振夹角以及两束光的相位差有关，类比于陀螺，Sagnac效应是需要得到相位变化信息，因此要通过各种技术手段消除偏振态的变化引入的误差，主要是各种双折射；本发明将法拉第效应引起的偏振旋转作为目标量，通过采用正反向环绕环等手段抑制相位差的产生，从而在最终的检测系统中可以得到等效的检测精度。
Figure PCTCN2020134181-appb-000001
式中，I表示检测到的光信号强度，I 1、I 2分别表示沿顺时针、逆时针光路传输的非干涉光信号强度，I 12表示沿顺时针、逆时针光路传输的干涉光信号强度，A 1、A 2分别表示沿顺时针、逆时针光路传输的光信号振幅，δ表示沿顺时针、逆时针光路传输的光信号相位差，θ F表示磁场引起的法拉第偏转角。
本发明中的起偏器的偏振方向与保偏光纤环的两个主轴夹角分别为顺时针和逆时针45°，线偏光经过偏振分束器后变为分别沿顺时针、逆时针传输的两束光，在起始端利用偏振控制器分别在其上叠加顺时针45°、逆时针45°的偏振调制，使其均沿绕制方向相反的两个保偏光纤环的快轴传输，经过晶体后分别产生大小相同、方向相反的法拉第偏转角，如图3所示，经过检偏、偏振干涉后，干涉光强为式(2)，可见此时干涉信号强度相对于法拉第偏转角具有最大的变化率：
Figure PCTCN2020134181-appb-000002
Figure PCTCN2020134181-appb-000003
在本发明的一个具体实施中，光源发出的光经光纤耦合器、起偏器、偏振分束器后一分为二，两束线偏光分别经过第一偏振控制器、第二偏振控制器调制，调制方法为：第一偏振控制器5和第二偏振控制器9分别在两束光上叠加顺时针45°、逆时针45°的偏振调制。调制后的两束光进入两个分别沿顺时针、逆时针绕制的保偏光纤环，此处选用在顺时针光路上的第一保偏光纤环为顺时针绕制，逆时针光路上的第二保偏光纤环为逆时针绕制。两束线偏光在到达磁场传感单元前分别沿保偏光纤环的快轴传输，在传感单元处经过光纤光－空间光－光纤光的转换，分别耦合入两个保偏光纤环的慢轴进行传输，如下图4所示，这样顺时针、 逆时针传输光分别各沿快、慢轴传输一半光程，慢轴上的主干涉光可以同时到达出射点进行偏振干涉，同时晶体法拉第效应引起的偏振光正交分量由于沿快轴传输，会在出射点与主干涉光拉开一段距离，保证偏振干涉结果不受影响。
光束在经过磁场传感单元时，由第一保偏光纤环6的端口62出射的沿快轴传输的光经第一耦合透镜11耦合至第一磁通聚集器12的轴向通孔中，所述的第一耦合透镜11将光纤光转换为空间光，同时将光束直径缩小至小于磁光晶体直径数倍至数十倍，同时调整光束入射磁光晶体左端面，穿过磁光晶体后由右端面出射，经第二磁通聚集器14收集磁力线，再经第二耦合透镜将空间光耦合入保偏光纤，进入第二保偏光纤环8的慢轴传输。
同理，由第二保偏光纤环8的端口81出射的沿快轴传输的光经第二耦合透镜15耦合至第二磁通聚集器14的轴向通孔中，所述的第二耦合透镜15将光纤光转换为空间光，同时将光束直径缩小至小于磁光晶体直径数倍至数十倍，同时调整光束入射磁光晶体右端面，穿过磁光晶体后由左端面出射，经第一磁通聚集器12收集磁力线，再经第一耦合透镜将空间光耦合入保偏光纤，进入第一保偏光纤环6的慢轴传输。当磁场传感单元受到沿磁光晶体方向的磁场作用时，由于法拉第效应使经过磁光晶体的偏振光发生法拉第偏转，从而引起偏振干涉光强的变化，通过检测光强和信息处理即可得到外界磁场信息。
本实例中采用具有高偏振消光比的质子交换Y波导实现起偏器和偏振分束器功能；偏振控制器采用EOSPACE公司的铌酸锂电光调制偏振控制器，通过电压控制可以实现任意输入偏振态到任意输出偏振态的转换，且响应时间小于100ns；磁光晶体12采用圆柱体Ga：YIG晶体，其直径为1.8mm、长度为2.7mm，其磁光费尔德常数为8400rad/m/T；磁通聚集器11为圆柱体加圆台体结构，其中圆柱体直径22mm、长度13mm，圆台体底面直径13mm、长度13mm、锥角22°，通孔直径1.8mm，磁光晶体13的两端面伸入第一磁通聚集器11和第二磁通聚集器14轴向通孔中的长度均为0.3mm，制作磁通聚集器所用材料为坡莫合金1J85，经仿真和实验验证，该磁通聚集器可将环境磁场放大400倍以上。
已知系统中保偏光纤的偏振消光比约为40dB，Y波导偏振消光比约为60dB，所对应的最小可分辨偏振旋转角度为Δθ＝arctan(1/10 4)≈10 -4rad，Sagnac干涉系统的最小分辨率约为10 －6rad，因此，在不考虑晶体内反射增强技术的情况下，该系统的理论磁场灵敏度为ΔT＝10 -4(rad)/8400(rad/m/T)/2.7mm/ 400≈11nT。
在本发明的一个具体实施中，还可以在所述的磁光晶体两端面的内表面部分区域镀上全反膜，在磁光晶体内部形成反射腔，使光束以一定的角度入射至磁光晶体的反射腔内，多次反射后再出射以增加光程。根据法拉第效应原理，光信号偏振态的变化可以随着光程的增加而线性累积，因此可以有效提高该系统的磁场灵敏度。
本发明所提出的基于Sagnac干涉系统的全偏振法拉第磁场传感器作为一种新型磁场传感器，具有动态范围大、稳定性高、磁场灵敏度高、易于小型化等优点，在民用和军用领域均有着广阔的应用前景。
以上所述的实施例只是本发明的一种较佳的方案，然其并非用以限制本发明。有关技术领域的普通技术人员，在不脱离本实用新型的精神和范围的情况下，还可以做出各种变化和变型。因此凡采取等同替换或等效变换的方式所获得的技术方案，均落在本发明的保护范围内。

Claims (5)

  1. 一种基于Sagnac干涉系统的全偏振法拉第磁场传感器，其特征在于，包括光源(1)、光纤耦合器(2)、起偏器(3)、偏振分束器(4)、偏振控制器、磁场传感单元(7)、探测器(10)以及保偏光纤环；
    所述光源(1)的输出端口和探测器(10)的接收端口分别与光纤耦合器(2)同一侧的两个端口光纤连接，光纤耦合器(2)另一侧的一个端口与起偏器(3)光纤连接，且所述的起偏器(3)与偏振分束器(4)一侧的一端口光纤连接；所述的偏振分束器(4)另一侧的一端口通过第一偏振控制器(5)与第一保偏光纤环(6)光纤连接，且偏振分束器(4)该侧的另一端口通过第二偏振控制器(9)与第二保偏光纤环(8)光纤连接，两个保偏光纤环均与磁场传感单元(7)相连；
    所述的第一保偏光纤环(6)和第二保偏光纤环(8)的快轴方向与所述的起偏器(3)的偏振方向夹角呈45°，且夹角方向相反；所述的光纤连接采用保偏光纤；
    所述的磁场传感单元(7)包括沿轴向依次布置的第一耦合透镜(11)、第一磁通聚集器(12)、磁光晶体(13)、第二磁通聚集器(14)、第二耦合透镜(15)，所述的第一耦合透镜(11)和第二耦合透镜(15)关于磁光晶体(13)对称，所述的第一磁通聚集器(12)和第二磁通聚集器(14)关于磁光晶体(13)对称；
    所述的第一耦合透镜(11)与第一保偏光纤环(6)相连，第二耦合透镜(15)与第二保偏光纤环(8)的相连；所述的第一磁通聚集器(12)和第二磁通聚集器(14)均设有轴向通孔，磁光晶体(13)的两端面分别插入两个轴向通孔中固定；从第一保偏光纤环(6)和第二保偏光纤环(8)输出的两束光能够分别经第一耦合透镜(11)和第二耦合透镜(15)耦合至所述的轴向通孔中。
  2. 如权利要求1所述的基于Sagnac干涉系统的全偏振法拉第磁场传感器，其特征在于，所述的第一保偏光纤环(6)和第二保偏光纤环(8)由保偏光纤绕制而成，两个保偏光纤环的直径相同、绕制圈数相同、绕制方向相反。
  3. 如权利要求1所述的基于Sagnac干涉系统的全偏振法拉第磁场传感器，其特征在于，所述的磁光晶体(13)两端面的外表面均镀有增透膜。
  4. 如权利要求1所述的基于Sagnac干涉系统的全偏振法拉第磁场传感器，其特征在于，所述的第一磁通聚集器(12)和第二磁通聚集器(14)的轴向通孔 大小与磁光晶体(13)的直径大小匹配。
  5. 一种基于权利要求1所述的全偏振法拉第磁场传感器的光信号调制方法，其特征在于，包括以下步骤：
    1)光源(1)出射的光信号依次经过光纤耦合器(2)、起偏器(3)、偏振分束器(4)后分为沿顺时针、逆时针传输的两束光，两束光通过保偏光纤分别传输至第一偏振控制器(5)和第二偏振控制器(9)，利用第一偏振控制器(5)和第二偏振控制器(9)分别在两束光上叠加顺时针45°、逆时针45°的偏振调制；
    2)调制后的沿顺时针光路传输的光进入第一保偏光纤环(6)的快轴传输，经第一耦合透镜(11)将光纤光转换为空间光，并耦合至第一磁通聚集器(12)的轴向通孔中，然后依次穿过磁光晶体(13)和第二磁通聚集器(14)，再经第二耦合透镜(15)将空间光转换为光纤光，进入第二保偏光纤环(8)的慢轴传输；
    3)调制后的沿逆时针光路传输的光进入第二保偏光纤环(8)的快轴传输，经第二耦合透镜(15)将光纤光转换为空间光，并耦合至第二磁通聚集器(14)的轴向通孔中，然后依次穿过磁光晶体(13)和第一磁通聚集器(12)，再经第一耦合透镜(11)将空间光转换为光纤光，进入第一保偏光纤环(6)的慢轴传输；
    4)沿顺时针光路、逆时针光路传输的光经过磁光晶体(13)后分别产生大小相同、方向相反的法拉第偏转角，且两束光分别各沿快、慢轴传输一半光程，同时返回偏振分束器(4)发生偏振干涉，再经起偏器(3)、光纤耦合器(2)后由探测器(10)对干涉信号进行获取。
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