Optical fiber vector weak magnetic field sensor based on Faraday rotation effect

Abstract

The present invention discloses an optical fiber vector weak magnetic field sensor based on the Faraday rotation effect, comprising: an input part, a beam splitting area, and a sensing area; the input part comprises two input optical fibers and two input optical fiber spatial light collimators; the two input optical fibers are respectively connected to the two input optical fiber spatial light collimators; the beam splitting area comprises two polarization cubic crystal beam splitters and a light absorbing sheet; the two polarization cubic crystal beam splitters are respectively connected to the two input optical fiber spatial light collimators; the light absorbing sheet is attached to the light exiting surface of the polarization cubic crystal beam splitter; the sensing area comprises three sensing parts respectively arranged in the Y-axis, Z-axis, and X-axis directions, and the three sensing parts are respectively connected to the polarization cubic crystal beam splitters. The present invention can effectively improve the three-dimensional mechanical calibration error of the magnetic field, thereby solving the three-dimensional non-orthogonality problem of the vector magnetic field sensor, has a compact structure, and realizes a high-sensitivity magnetic field sensing function at the same time.

Description

Technical Field

[0001] The invention relates to the technical field of optical fiber magnetic field sensors, in particular to an optical fiber vector weak magnetic field sensor based on Faraday rotation effect. Background Art

[0002] Magnetic field sensors have important application value in geophysical survey, navigation, military equipment application, biomedical sensing, and aerospace. With the development of application fields such as human-machine exchange, bio-imaging, unmanned monitoring, and industrial intelligent manufacturing, new application requirements for magnetic field sensors have been proposed, such as high sensitivity, high integration, high monitoring accuracy, wearability, low cost, miniaturization, and three-dimensional vector sensing. Most of the existing commercial magnetic field sensors are electrical sensors based on the Hall effect, fluxgate, giant magnetoresistance, superconducting quantum interference, etc. This type of magnetic field sensor has more or less complex structure, limited test dynamic range, temperature control protection, and susceptibility to electromagnetic interference. It is difficult to meet the application requirements of weak magnetic detection in special environments (such as underwater, human wear, etc.).

[0003] Various types of optical fiber sensors have the advantages of simple production, low cost, high sensitivity, small size, compact and light structure, easy integration and multiplexing, and can realize multi-parameter in-situ sensing. This also provides an optional technical solution for the development of new magnetic field monitoring systems, and a large number of research results have emerged. At present, optical fiber magnetic field sensors mainly include Faraday effect type, magnetostrictive effect integrated type, and refractive index control magnetic fluid integrated type. Among them, the refractive index control magnetic fluid integrated optical fiber magnetic field sensor mainly uses the magneto-refractive index control effect of the magnetic fluid to realize light field control, thereby realizing magnetic field sensing. However, most of the existing magnetic fluid integrated optical fiber magnetic field sensors have problems such as low sensitivity, susceptibility to changes in ambient temperature, and non-compact probe structure design, which limits their detection capabilities and wearable performance, so it is difficult to meet the testing requirements of weak magnetic application environments such as medical imaging and magnetic anomaly detection. Magnetostrictive effect integrated optical fiber magnetic field sensor mainly uses the magneto-strain control effect of magnetostrictive materials to control the light field, thereby realizing the magnetic field sensing function. The sensitivity of this type of magnetic field sensor is limited by the weak magnetic response characteristics of magnetostrictive materials, and currently can only achieve weak magnetic test capabilities of the order of pt. In addition, when measuring a magnetic field in a certain direction, the magnetostrictive effect integrated optical fiber magnetic field sensor will be affected by the magnetic field crosstalk in the perpendicular direction, which will cause cross-response and cause magnetic field measurement errors in one dimension, thus limiting the sensitivity and dynamic range of magnetic field measurement of this type of sensor. Therefore, to achieve high-sensitivity three-dimensional vector sensing, this type of magnetic field sensor also needs to solve problems such as the sensor structure is not compact enough, the three-dimensional calibration accuracy is not high, the magnetic field test orthogonal crosstalk, and the need for external temperature control feedback control.

[0004] It is worth noting that all-optical magnetic field sensors represented by spin-conversion non-relaxation atomic magnetometers and optically pumped magnetometers can achieve high-sensitivity magnetic field sensing at room temperature, and the detection limit of all-optical magnetometers is mainly determined by shot noise, so they can achieve high-sensitivity weak magnetic detection response capabilities at the fT level. However, spin-conversion non-relaxation atomic magnetometers currently still have problems such as low time resolution and complex structure, and optically pumped magnetometers need to further reduce their volume to meet the needs of portable medical sensing applications. The magnetic field sensor based on the Faraday rotation effect is also an all-optical magnetometer, which mainly uses magneto-optical materials with magneto-optical rotation effect to regulate the light field (that is, when the light field passes through the magneto-optical material, the polarization direction of the linearly polarized light will be deflected). At present, various optical fiber magnetic field sensors based on the Faraday rotation effect can be made by doping magneto-optical materials into the optical fiber core or making them into diaphragms and integrating them into the end face of the optical fiber. The sensitivity of this type of magnetic field sensing is mainly determined by the Verdet coefficient (optical rotation coefficient) of the magneto-optical material.

[0005] At present, magneto-optical (MO) materials have been widely used in optical isolators, magnetic field sensors, and communication systems. With the advancement of materials science and nano-processing technology, some magneto-optical materials with low noise and high Verdet coefficient have been developed, so that very high Faraday rotation coefficients can be achieved and used to enhance the sensitivity of magnetic field sensors. For example: magnetic nanoparticle (NP) composites can exhibit high-sensitivity magneto-optical response characteristics in different matrices (such as organic matrices). Doping these nanoparticles with rare earth elements, such as lanthanum ions, can further increase their Verdet coefficients. Using these special magneto-optical materials to develop optical fiber magnetic field sensors can achieve high-sensitivity magnetic field sensing in the order of fT. In view of this, it is a feasible solution to apply special materials with high Verdet coefficients to optical fiber magnetic field sensors.

[0006] It should be noted that in practical applications such as environmental magnetic anomaly detection and positioning and medical sensing, one-dimensional or two-dimensional magnetic field sensors cannot fully meet the testing requirements of spatial magnetic fields, so a large number of three-dimensional vector magnetic field sensing technologies need to be developed. Existing three-dimensional vector sensors are mainly made by three-dimensional orthogonal assembly and processing of three one-dimensional magnetic field sensor probes, but there will inevitably be mechanical calibration errors during the three-dimensional orthogonal processing or assembly of the components, which will cause the sensor to have three-dimensional vector sensing errors, and then corresponding compensation calculation technology is required for calibration. Therefore, it is necessary to vigorously develop new vector sensor design solutions and technologies to solve the three-dimensional non-orthogonality problem that is common in vector magnetic field sensors. In addition, in application fields such as target magnetic anomaly detection and biological imaging, magnetic field sensors are required to have weak magnetic detection capabilities of the order of fT. Summary of the invention

[0007] The purpose of the present invention is to provide an optical fiber vector weak magnetic field sensor based on the Faraday rotation effect to solve the technical problems existing in the prior art. It can effectively improve the three-dimensional mechanical calibration error of the magnetic field, thereby solving the three-dimensional non-orthogonality problem of the vector magnetic field sensor. It has a compact structure and realizes a high-sensitivity magnetic field sensing function.

[0008] To achieve the above object, the present invention provides the following solution: The present invention provides an optical fiber vector weak magnetic field sensor based on Faraday rotation effect, comprising: an input part, a beam splitting area, and a sensing area;

[0009] The input part includes two input optical fibers and two input optical fiber spatial light collimators; the two input optical fibers are respectively connected to the two input optical fiber spatial light collimators;

[0010] The beam splitting region includes two polarization cubic crystal beam splitters and a light absorbing plate; the two polarization cubic crystal beam splitters are respectively connected to the two input fiber spatial light collimators; the light absorbing plate is attached to the light output surface of the polarization cubic crystal beam splitter;

[0011] The sensing area includes three sensing parts respectively arranged in the Y-axis, Z-axis and X-axis directions, and the three sensing parts are respectively connected to the polarization cubic crystal beam splitter.

[0012] Preferably, an input fiber spatial light collimator input end is provided at one end of the input fiber spatial light collimator, and the two input optical fibers are respectively connected to the two input fiber spatial light collimators through the input fiber spatial light collimator input ends.

[0013] Preferably, the two polarizing cubic crystal beam splitters are arranged side by side, and the incident light axes of the two polarizing cubic crystal beam splitters are parallel and the directions of the vertical light axes are 90°; the parameters of the two polarizing cubic crystal beam splitters are the same.

[0014] Preferably, the two polarizing cubic crystal beam splitters are both semi-reflective and semi-transparent, the light absorbing sheet is attached to the light output surface of one of the polarizing cubic crystal beam splitters, and the direction of the light output surface is the same as the direction of the incident light axis.

[0015] Preferably, each of the sensing parts includes a polarization combination piece, an output fiber spatial light collimator, and an output fiber, which are connected in sequence; a polarizer is provided on the output fiber; the output fiber spatial light collimator is provided with an output fiber spatial light collimator output end, and the output fiber spatial light collimator is connected to the output fiber via the output fiber spatial light collimator output end.

[0016] Preferably, the optical rotation combination plate comprises two quarter wave plates and a Faraday rotation effect plate, and the Faraday rotation effect plate is arranged between the two quarter wave plates.

[0017] Preferably, the fast axis angles of the two quarter wave plates in the optical rotation combination plate are different, the fast axis angle of the first quarter wave plate is 45°, and the fast axis angle of the second quarter wave plate is -45°.

[0018] Preferably, the Faraday rotation effect sheet is made of Dy x Co (1-x) Fe2O4 nanoparticles, and Dy x Co (1-x) The Fe2O4 nanoparticles were encapsulated by poly(phenylmethyl acrylate) (PBMA) shells.

[0019] Preferably, the optical fiber vector weak magnetic field sensor further includes a packaging shell.

[0020] Preferably, the optical fiber vector weak magnetic field sensor also includes three single-axis polarizer packaging structures, each of which includes a polarizer packaging shell, and the three polarizer packaging shells are used to package the analyzers on the Y-axis, Z-axis, and X-axis, respectively.

[0021] The present invention discloses the following technical effects:

[0022] (1) The present invention realizes light field polarization and beam splitting through a bicubic crystal polarization beam splitter, thereby converting two parallel detection lights into four polarized lights, and then absorbing one light through a light absorber to realize three-way orthogonal polarized detection light output; the three-way orthogonal polarized light enters the optical rotation combination plate respectively to realize magnetic field regulation and sensor response, thereby realizing three-dimensional magnetic field sensing. The entire sensor structure design is more compact, and the polarization beam splitting characteristics of the cube polarization beam splitter are used to reduce the three-dimensional calibration problem of the three-dimensional magnetic field to a two-dimensional orthogonal calibration problem, and the two cubes are easier to align and splice, which can effectively improve the three-dimensional mechanical calibration error of the magnetic field, thereby solving the three-dimensional non-orthogonality problem of the vector magnetic field sensor;

[0023] (2) The present invention uses a magnetic nanoparticle composite material with a high Verdet coefficient to manufacture a Faraday rotator, which realizes a high-sensitivity magnetic field sensing function and can achieve fT-level weak magnetic detection capabilities, thereby meeting the weak magnetic detection application needs in the fields of target magnetic anomaly detection and biological imaging. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0025] Figure 1 This is a schematic diagram of the structure of the optical fiber vector weak magnetic field sensor of the present invention;

[0026] Figure 2 This is a schematic diagram of the packaging shell structure of the optical fiber vector weak magnetic field sensor of the present invention;

[0027] FIG3 is a schematic diagram of a Y-axis analyzer assembly of the present invention; wherein FIG3(a) is a schematic diagram of the external structure of the Y-axis analyzer assembly, and FIG3(b) is a schematic diagram of the internal structure of the Y-axis analyzer assembly;

[0028] Figure 4 It is a schematic diagram of the assembly structure of the optical fiber vector weak magnetic field sensor of the present invention;

[0029] Figure 5 It is a schematic diagram of the one-dimensional structure of the Y-axis and Z-axis sensing probes of the present invention;

[0030] Figure 6 It is a schematic diagram of the one-dimensional structure of the X-axis sensing probe of the present invention;

[0031] Figure 7 It is a schematic diagram of the sensing system of the optical fiber vector weak magnetic field sensor of the present invention;

[0032] Figure 8 This is a schematic diagram of the beam splitting principle of the first polarization cubic crystal beam splitter of the present invention;

[0033] In the figure, 1 is a laser light source, 2 is a 1:3 optical splitter, 3 is an optical fiber vector weak magnetic field sensor, 301A is a first input optical fiber, 301B is a first optical fiber space light collimator input end, 302A is a second input optical fiber, 302B is a second optical fiber space light collimator input end, 303 is a first polarization cubic crystal beam splitter, 304 is a second polarization cubic crystal beam splitter, 305A is a first quarter wave plate, 305B is a first Faraday rotation effect plate, 305C is a second quarter wave plate, 305D is an output end of a third optical fiber space light collimator, 305E is a first output optical fiber, 306A is a third quarter wave plate, 306B is a second Faraday rotation effect plate, 306C is a fourth quarter wave plate, and 306D is a fourth optical fiber space light collimator. The output end of the collimator, 306E is the second output optical fiber, 307A is the fifth quarter wave plate, 307B is the third Faraday rotation effect plate, 307C is the sixth quarter wave plate, 307D is the output end of the fifth optical fiber spatial light collimator, 307E is the third output optical fiber, 307F is the light absorbing plate, 308 is the packaging shell, 401 is the Y-axis polarizer assembly, 401A is the Y-axis polarizer, 401B is the Y-axis polarizer packaging shell, 402 is the Z-axis polarizer assembly, 402A is the Z-axis polarizer, 403 is the X-axis polarizer assembly, 403A is the X-axis polarizer, 501 is the Y-axis photoelectric detector, 502 is the Z-axis photoelectric detector, 503 is the X-axis photoelectric detector, 504 is the reference light path photoelectric detector, 6 is the data acquisition device, and 7 is the PC computer end. DETAILED DESCRIPTION

[0034] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0035] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0036] Reference Figure 1 As shown, this embodiment provides an optical fiber vector weak magnetic field sensor based on Faraday rotation effect, comprising: an input part, a beam splitting area, and a sensing area, wherein the input part, the beam splitting area, and the sensing area are connected in sequence;

[0037] The input part includes two input optical fibers and two input optical fiber spatial light collimators. An input optical fiber spatial light collimator input end is provided at one end of the input optical fiber spatial light collimator. The two input optical fibers are respectively connected to the two input optical fiber spatial light collimators through the input optical fiber spatial light collimator input ends; the two input optical fiber spatial light collimator input ends are respectively connected to the two input optical fibers through FC (Fibre Channel) interfaces; the input optical fiber spatial light collimator is used to convert the optical fiber light input by the input optical fiber into parallel spatial detection light.

[0038] In this embodiment, the two input optical fibers are respectively the first input optical fiber 301A and the second input optical fiber 302A; the two input optical fiber spatial light collimators are respectively the first optical fiber spatial light collimator and the second optical fiber spatial light collimator; the input ends of the first optical fiber spatial light collimator and the second optical fiber spatial light collimator are respectively the first optical fiber spatial light collimator input end 301B and the second optical fiber spatial light collimator input end 302B; the first input optical fiber 301A and the second input optical fiber 302A are respectively connected to the first optical fiber spatial light collimator input end 301B and the second optical fiber spatial light collimator input end 302B; the two input optical fibers are arranged in parallel along the Y-axis direction.

[0039] The beam splitting region includes two polarization cubic crystal beam splitters and a light absorbing plate 307F;

[0040] The two polarization cubic crystal beam splitters are respectively connected to the two input fiber spatial light collimators; the light absorbing sheet 307F is attached to the light output surface of the polarization cubic crystal beam splitter;

[0041] In this embodiment, the polarization cubic crystal beam splitter adopts an LBTEK broadband polarization beam splitter cube of model PBS604, which is made of B-BK7 material; the two polarization cubic crystal beam splitters are respectively a first polarization cubic crystal beam splitter 303 and a second polarization cubic crystal beam splitter 304; the incident light axis directions of the first polarization cubic crystal beam splitter 303 and the second polarization cubic crystal beam splitter 304 are parallel (in the Y-axis direction), and are perpendicular to the light axis directions at 90° (in the Z-axis direction and the X-axis direction respectively), and are assembled and arranged side by side; the first fiber space light collimator and the second fiber space light collimator are respectively vertically connected to the incident light planes of the first polarization cubic crystal beam splitter 303 and the second polarization cubic crystal beam splitter 304; the parameters of the first polarization cubic crystal beam splitter 303 and the second polarization cubic crystal beam splitter 304 are the same. The first polarization cubic crystal beam splitter 303 and the second polarization cubic crystal beam splitter 304 are semi-reflective and semi-transparent. The light absorbing sheet 307F is attached to the Y-axis light output surface of the second polarization cubic crystal beam splitter 304 .

[0042] The sensing area includes three sensing parts, and the structures and parameters of the three sensing parts are the same, which are respectively a first sensing part, a second sensing part, and a third sensing part arranged in the positive directions of the Y axis, the Z axis, and the X axis; each of the sensing parts includes a light rotation combination piece, an output fiber spatial light collimator, and an output fiber connected in sequence; the output fiber spatial light collimator is provided with an output fiber spatial light collimator output end, and the output fiber spatial light collimator is connected to the output fiber through the output fiber spatial light collimator output end; the light rotation combination piece includes two quarter wave plates, A Faraday rotation effect plate, two quarter wave plates are respectively connected to the polarization cube crystal beam splitter and the output fiber spatial light collimator, the Faraday rotation effect plate is arranged between the two quarter wave plates, the two quarter wave plates and the Faraday rotation effect plate form a rectangular sandwich structure, which is arranged in the rectangular slot of the polarization cube crystal beam splitter; the output end of the output fiber spatial light collimator is connected to the output fiber through an FC interface, the output fiber is provided with a polarizer, and the other end of the output fiber is connected to the FC interface.

[0043] In this embodiment, the first sensing portion in the positive direction of the Y-axis includes a first quarter wave plate 305A, a first Faraday rotation effect plate 305B, a second quarter wave plate 305C, a third fiber space light collimator, and a first output fiber 305E, which are sequentially arranged along the positive direction of the Y-axis. A Y-axis polarizer 401A is provided on the first output fiber 305E, wherein the first quarter wave plate 305A is close to the Y-axis output light surface of the first polarization cubic crystal beam splitter 303, and the third fiber space light collimator is connected to the first output fiber 305E through the output end 305D of the third fiber space light collimator; the second sensing portion in the positive direction of the Z-axis includes a third quarter wave plate 306A, a second Faraday rotation effect plate 306B, a fourth quarter wave plate 306C, a fourth fiber space light collimator, and a second output fiber 306E, which are sequentially arranged along the positive direction of the Z-axis. A Z-axis analyzer 402A is provided on the optical fiber 306E, wherein the third quarter wave plate 306A is in close contact with the Z-axis output light surface of the first polarization cubic crystal beam splitter 303, and the fourth optical fiber spatial light collimator is connected to the second output optical fiber 306E through the output end 306D of the fourth optical fiber spatial light collimator; the third sensing part in the positive direction of the X-axis includes a fifth quarter wave plate 307A, a third Faraday rotation effect plate 307B, a sixth quarter wave plate 307C, a fifth optical fiber spatial light collimator, and a third output optical fiber 307E which are sequentially arranged along the positive direction of the X-axis, and an X-axis analyzer 403A is provided on the third output optical fiber 307E, wherein the fifth quarter wave plate 306A is in close contact with the X-axis output light surface of the second polarization cubic crystal beam splitter 304, and the fifth optical fiber spatial light collimator is connected to the third output optical fiber 307E through the output end 307D of the fifth optical fiber spatial light collimator.

[0044] To further optimize the solution, the manufacturing process of the Faraday rotation effect sheet includes:

[0045] The first step is to make Dy x Co (1-x) Fe2O4 particle mixed solution:

[0046] First, ethylene glycol (EG) and 1-decyl-3-methylimidazolium hexafluorophosphate (IL) are mixed and heated in a round-bottom flask as a reaction solvent, and then water-based FeCl3, CoCl2 and IL are injected into the reaction solvent to form a mixture; secondly, the mixture is refluxed, aged, cooled, diluted, centrifuged, and washed to obtain Dy x Co (1-x) Fe2O4 nanoparticles, the obtained Dy x Co (1-x) Fe2O4 nanoparticles were dispersed in chloroform to prepare Dy x Co (1-x) Fe2O4 particle mixed solution;

[0047] The second step is to prepare Dy x Co (1-x) Fe2O4 nanoparticles:

[0048] First, benzyl methacrylate (BMA) solution and chloroform-synthesized PBMA particle solution were mixed to obtain a mixed solution; secondly, Dy prepared in the first step was added to the mixed solution. x Co (1-x) After the Fe2O4 particle mixed solution was ultrasonically treated, irradiated with a UV light source, and cooled, the PBMA mixed particles gradually solidified into a colloid, and the Dy x Co (1-x) Fe2O4 nanoparticles; the PBMA shell stabilizes the nanoparticles and prevents the particles from aggregating in the composite material.

[0049] The third step is to use a mold to process the colloid into a Faraday rotation effect plate; the Faraday rotation effect plate has a very high optical rotation coefficient, which can enable the sensor to achieve ft-level magnetic field detection capabilities.

[0050] According to a further optimization scheme, the fast axis angles of the two quarter wave plates in the optical rotation assembly are different, the fast axis angle of the first quarter wave plate is 45°, and the fast axis angle of the second quarter wave plate is -45°.

[0051] To further optimize the solution, the two input optical fibers and the three output optical fibers are respectively connected with pigtail jumpers with jumper plugs to facilitate integrated connection with an external demodulation system.

[0052] Further optimizing the scheme, the optical fiber vector weak magnetic field sensor 3 also includes a packaging shell 308, and the packaging shell 308 is made of high-strength plastic material; in this embodiment, the high-strength plastic material is polycarbonate, and the compression strength is 78-125MPa; the packaging shell 308 is used to package the sensor probe; the sensor probe includes five optical fiber space light collimators, a beam splitting area, and three optical rotation combination sheets. The packaging shell is provided with a card slot and / or a groove for packaging and fixing each device in the sensor probe, such as Figure 2 As shown; in addition, when in standby mode, the FC interfaces connected to the first fiber space light collimator input end 301B, the second fiber space light collimator input end 302B, the third fiber space light collimator output end 305D, the fourth fiber space light collimator output end 306D, and the fifth fiber space light collimator output end 307D are sealed by sleeves.

[0053] Further optimizing the scheme, the optical fiber vector weak magnetic field sensor 3 also includes three single-axis polarizer packaging structures, and the three single-axis polarizer packaging structures all include a polarizer packaging shell, which is used to package the polarizers on the Y-axis, Z-axis, and X-axis and the FC interfaces at both ends of the output optical fiber, respectively, to form three polarizer components to prevent the polarizer from being subjected to external interference such as collision and pressure. In this embodiment, the three polarizer components include a Y-axis polarizer component 401, a Z-axis polarizer component 402, and an X-axis polarizer component 403; the polarizer component is described by taking the Y-axis polarizer component 401 as an example, as shown in FIG3, the Y-axis polarizer 401A and the FC interfaces at both ends of the first output optical fiber 305E are packaged in a Y-axis polarizer packaging shell 401B.

[0054] The assembly structure of the optical fiber vector weak magnetic field sensor 3 is as follows: Figure 4 As shown, the packaged probe and three polarizer components are assembled, and the Y-axis polarizer component 401, the Z-axis polarizer component 402, the X-axis polarizer component 403, and the input part are respectively packaged into an integrated detachable polarizer component using high-strength plastic and FC interfaces. When the optical fiber vector weak magnetic field sensor 3 is on standby, the FC interfaces of the two input ends and the three output ends can be disassembled and sealed. When the optical fiber vector weak magnetic field sensor 3 is working, the FC interfaces of the two input ends and the three output ends can be connected to the corresponding slots for use.

[0055] The schematic diagram of the one-dimensional structure of the Y-axis and Z-axis sensor probes is as follows: Figure 5 As shown, the one-dimensional structure diagram of the X-axis sensor probe is as follows Figure 6The working process of the optical fiber vector weak magnetic field sensor based on the Faraday rotation effect of the present invention includes: sequentially connecting and setting a laser light source 1, a 1:3 optical splitter 2, an optical fiber vector weak magnetic field sensor 3, a Y-axis polarizer assembly 401, a Z-axis polarizer assembly 402, an X-axis polarizer assembly 403, a Y-axis photoelectric detector 501, a Z-axis photoelectric detector 502, an X-axis photoelectric detector 503, a reference optical path photoelectric detector 504, a data collector 6, and a PC terminal 7, as shown in FIG. Figure 7 As shown;

[0056] In the input part, the laser light source 1 is divided into three beams of light after passing through the 1:3 splitter 2. One beam of light enters the reference light path photoelectric detector 504 as a reference light, which is used to monitor the power change of the laser light source 1 and eliminate the fluctuation interference of the laser light source 1; the other two beams of light are injected into the first fiber space light collimator and the second fiber space light collimator through the first input optical fiber 301A and the second input optical fiber 302A respectively through the first fiber space light collimator input end 301B and the second fiber space light collimator input end 302B, and the first incident light and the second incident light are converted from optical fiber light into parallel space detection light, and then the two parallel space detection lights are injected into the first polarization cubic crystal beam splitter 303 and the second polarization cubic crystal beam splitter 304 respectively; wherein, the first incident light and the second incident light are non-polarized light.

[0057] In the beam splitting region, the first polarization cubic crystal beam splitter 303 splits the first incident light perpendicularly incident along the positive direction of the Y axis into two, namely, a first P wave transmitted along the semi-transmitting surface and a first S wave reflected along the semi-reflecting surface. Figure 8 shown.

[0058] The first P wave is emitted along the positive direction of the Y axis, and the first P wave has the same direction as the parallel space detection light converted from the first incident light, and the first P wave enters the first optical rotation combination plate and is regulated by the magnetic field in the Y axis direction. The first S wave is emitted along the positive direction of the Z axis, and the first S wave is perpendicular to the parallel space detection light converted from the first incident light, and the first S wave enters the second optical rotation combination plate and is regulated by the magnetic field in the Y axis direction. The second polarization cubic crystal beam splitter 304 splits the second incident light perpendicularly incident along the positive direction of the Y axis into two, and the second P wave transmitted along the semi-transmissive surface is emitted along the positive direction of the Y axis, and the second P wave has the same direction as the parallel space detection light converted from the second incident light, and the second P wave is absorbed by the light absorbing plate 307F after being emitted and treated as useless light; the second S wave reflected along the semi-reflective surface is emitted along the positive direction of the X axis, and the second S wave is perpendicular to the parallel space detection light converted from the second incident light, and the second S wave enters the third optical rotation combination plate and is regulated by the magnetic field in the X axis direction. Since the first incident light and the second incident light are incident into the sensor in parallel along the positive direction of the Y axis, and the vertical output light axis of the first polarization cubic crystal beam splitter is perpendicular to the vertical output light axis of the second polarization cubic crystal, only two incident lights are needed to be injected into the vector optical fiber weak magnetic field sensor. By utilizing the orthogonal beam splitting characteristics of the polarization cubic crystal, the first incident light can realize the sensing of the Y and Z axes, and the second incident light can realize the sensing of the X axis. Therefore, this design of the beam splitting area does not need to use three incident ends for three-dimensional orthogonal splicing, but only needs to use two input ends to realize three-dimensional orthogonal beam splitting, reducing the three-dimensional calibration problem to a two-dimensional calibration problem, greatly improving the three-dimensional calibration accuracy.

[0059] In the sensing area, the first P wave in the Y-axis direction is linearly polarized light when entering the sensing area, and becomes circularly polarized light after passing through the first quarter-wave plate 305A. When the magnetic field acts on the positive direction of the Y-axis, according to the Faraday rotation effect, the polarization degree of the circularly polarized light changes when passing through the first Faraday rotation effect plate 305B. The circularly polarized light with changed polarization degree becomes linearly polarized light (P wave) after passing through the second quarter-wave plate 305C; the intensity of the linearly polarized light after exiting the second quarter-wave plate 305C changes, and is converted into fiber light after being coupled and injected into the third fiber spatial light collimator, and enters the first output fiber 305E through the FC interface. The polarized light passes through the Y-axis analyzer 401A and enters the Y-axis photodetector 501. When the first S wave in the Z-axis direction enters the sensing area, it is linearly polarized light. After passing through the third quarter-wave plate 306A, it becomes circularly polarized light. When the magnetic field acts on the positive direction of the Z-axis, according to the Faraday rotation effect, the polarization degree of the circularly polarized light changes when passing through the second Faraday rotation effect plate 306B. After the polarization degree changes, the circularly polarized light becomes linearly polarized light (S wave) after passing through the fourth quarter-wave plate 306C. The intensity of the linearly polarized light after exiting the fourth quarter-wave plate 306C changes, and after being coupled and injected into the fourth fiber spatial light collimator, it is converted into fiber light and enters the second output fiber 306E through the FC interface. The polarized light passes through the Z-axis polarizer 402A and enters the Z-axis photodetector 502. When the second S wave in the X direction enters the sensing area, it is linearly polarized light. After passing through the fifth quarter wave plate 307A, it becomes circularly polarized light. When the magnetic field acts on the positive direction of the X axis, according to the Faraday rotation effect, the polarization degree of the circularly polarized light changes when passing through the third Faraday rotation effect plate 307B. After the polarization degree changes, the circularly polarized light becomes linearly polarized light (S wave) after passing through the sixth quarter wave plate 307C. The light intensity of the linearly polarized light after exiting the sixth quarter wave plate 307C changes, and after being coupled and injected into the fifth fiber spatial light collimator, it is converted into fiber light, and enters the third output fiber 307E through the FC interface. After passing through the X-axis analyzer 403A, the polarized light enters the X-axis photodetector 503. The electrical signals output by the Y-axis photodetector 501, the Z-axis photodetector 502, the X-axis photodetector 503, and the reference light path photodetector 504 are respectively photoelectrically demodulated and enter the data acquisition device 6. The signal processing system of the PC computer terminal 7 performs signal processing, and the magnitude of the magnetic field intensity is calculated using the Faraday rotation effect and the Jones matrix principle. The specific principle of using the Faraday rotation effect and the Jones matrix principle to calculate the magnetic field strength is:

[0060] By utilizing the magneto-optical rotation characteristics of the Faraday rotation effect plate, the linearly polarized detection light incident on the optical rotation combination plate is polarized and rotated, and then the intensity is monitored by the analyzer and detector combination of the external demodulation system, and finally the magnetic field change is calibrated and settled, thereby realizing the magnetic field sensing response.

[0061] The Faraday magneto-optical effect formula is shown in formula (1):

[0062] θ=VHL………………………………(1)

[0063] Where θ is the Faraday rotation angle; H is the magnetic field intensity; V is the Verdet constant, which represents the magneto-optical coefficient of the magneto-optical material, which is determined by the material properties and the working wavelength; L is the length of light passing through the magneto-optical material; in the rectangular coordinate system, the magnetic field H is decomposed into three orthogonal magnetic fields, corresponding to the X, Y, and Z axes of the rectangular coordinate system, respectively. Assuming that the angles between the magnetic field and the Z, X, and Y directions are λ1, λ2, and λ3 respectively, the magnetic field intensity components H in the three directions of the X, Y, and Z axes are X , H Y , H Z As shown in formula (2):

[0064]

[0065] cos 2 λ1+cos 2 λ2+cos 2 λ3=1

[0066] The optical fiber vector weak magnetic field sensor 3 uses the characteristics of the polarization cubic crystal beam splitter to use the first S wave as the detection light in the Z direction, the first P wave as the detection light in the Y direction, and the second S wave as the detection light in the X direction. Each dimension of the detection light signal is transmitted and regulated and monitored in the order of entering and exiting the polarization cubic crystal, entering the optical rotation assembly, coupling into the output optical fiber, and then to the analyzer and detection of the external monitoring system.

[0067] The polarization cubic crystal beam splitter has an operating wavelength range of 1200nm to 1600nm, and an extinction ratio greater than 1000:1. The selected polarization cubic crystal beam splitter is coated with an anti-reflection film. Every time it passes through 2N sides (equivalent to passing through N lenses), the light intensity lost is (1-0.996 2N )×100%, where the S-wave transmittance T S About 0.015%, P wave transmittance T P It is about 98.365%. In addition, the relationship between transmittance and reflectivity is shown in equations (3) and (4):

[0068] T S +R S =1……………………………………(3)

[0069] T P +R P =1……………………………………(4)

[0070] In formula (3) and formula (4), T S , R S are the transmittance and reflectance of S wave at the polarization splitting film, T P , R P are the transmittance and reflectance of the P wave at the polarization splitting film, respectively. Combining equations (3) and (4), we can get the reflectance R of the S wave at the polarization splitting film. S About 99.985%.

[0071] For the Z-axis detection signal:

[0072] In the process of light entering and exiting the polarization cubic crystal, it is considered that the light passes through one lens and one polarization splitter film. The intensity of the first S wave after exiting the cubic crystal can be expressed as formula (5):

[0073] E S1 =E0×0.99985×0.996 2 …………………………(5)

[0074] In formula (5), E0 is the intensity of the incident light before it enters the cubic crystal, E S1 is the intensity of the first S wave after exiting the cubic crystal, that is, the intensity of the first quarter-wave plate incident on the optical rotation assembly is E S1 The first quarter wave plate of the optical rotation combination converts the incident first S wave into right circularly polarized light or left circularly polarized light, and then the second quarter wave plate converts the circularly polarized light into linearly polarized light. The light intensity E of the first S wave after passing through the optical rotation combination S2 After simplification by Jones matrix operation, it is shown in formula (6):

[0075]

[0076] Among them, θ Z is the Faraday rotation angle in the Z-axis direction caused by the external magnetic field.

[0077] After emitting the second quarter-wave plate, the first S wave enters the polarization analyzer from the single-mode optical fiber. The polarization angle of the first S wave is 0°. The light intensity entering the photodetector after passing through the polarization analyzer is shown in formula (7):

[0078] E SZ =E S2 ……………………………………(7)

[0079] In formula (7), E SZ It is the light intensity after the first S wave passes through the analyzer, that is, the light intensity before entering the photodetector.

[0080] Combining formula (5) to formula (7), ESZ As shown in formula (8):

[0081]

[0082] The first S wave enters the photodetector after passing through the sensing area. The function of the photodetector is to convert the optical signal into an electrical signal. SZ The detection current I converted into an electrical signal in the Z-axis direction θZ , that is, the sensor monitoring signal in the Z-axis direction, as shown in formula (9):

[0083]

[0084] In formula (9), the detection current of the reference light path light intensity E0 converted into an electrical signal in the photodetector is I0, that is, θ Z The detection current detected by the photodetector when the external magnetic field strength is equal to 0. Using the relationship between the electrical signal of the reference optical path in the photodetector and the electrical signal of the Z-axis sensing optical path in the photodetector, the rotation angle θ generated by the Faraday effect is calculated by formula (9): Z , and then use formula (1) to calibrate and calculate the external magnetic field.

[0085] Similarly, the analysis angle of the X-axis analyzer is 0° with the polarization angle of the second S wave, and the sensing monitoring signal in the X-axis direction is obtained, as shown in formula (10):

[0086]

[0087] In formula (10), I θX is the detection current of the electrical signal in the X-axis direction, that is, the sensing monitoring signal in the X-axis direction, θ X is the Faraday rotation angle in the X-axis direction caused by the external magnetic field.

[0088] The analysis angle of the Y-axis analyzer is 0° to the polarization angle of the first P wave, so the sensor monitoring signal in the Y-axis direction is:

[0089]

[0090] In formula (11), I θY is the detection current of the electrical signal in the Y-axis direction, that is, the sensing monitoring signal in the Y-axis direction, θ Y is the Faraday rotation angle in the Y-axis direction caused by the external magnetic field.

[0091] According to the detection current I0 and I θX ,I θY ,I θZ , the angle θ can be calculated by equations (9), (10), and (11): X ,θY ,θ Z The magnetic field strength H in the X, Y, and Z directions is measured by formula (1) X , H Y , H Z , and then combine formula (2) to calculate the corresponding magnetic field distribution. Based on the above principle, the magnetic field sensing function of the vector optical fiber vector weak magnetic field sensor in three directions is realized.

[0092] The embodiments described above are only descriptions of the preferred modes of the present invention, and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should all fall within the protection scope determined by the claims of the present invention.

Claims

1. Fiber optic vector weak magnetic field sensor based on Faraday rotation effect, It is characterized in that include: Input part, beam splitting area, sensing area; The input part includes two input optical fibers and two input optical fiber spatial light collimators; the two input optical fibers are respectively connected to the two input optical fiber spatial light collimators; The beam splitting region comprises two polarization cubic crystal beam splitters and a light absorbing plate (307F); the two polarization cubic crystal beam splitters are respectively connected to the two input optical fiber spatial light collimators; the light absorbing plate (307F) is attached to the light output surface of the polarization cubic crystal beam splitter; The sensing area includes three sensing parts respectively arranged in the Y-axis, Z-axis and X-axis directions, and the three sensing parts are respectively connected to the polarization cubic crystal beam splitter; An input fiber spatial light collimator input end is provided at one end of the input fiber spatial light collimator, and the two input optical fibers are respectively connected to the two input fiber spatial light collimators through the input fiber spatial light collimator input ends; The two polarizing cubic crystal beam splitters are arranged side by side, and the incident light axes of the two polarizing cubic crystal beam splitters are parallel and the vertical light axis direction is 90°; the parameters of the two polarizing cubic crystal beam splitters are the same; The two polarization cubic crystal beam splitters both adopt a semi-reflective semi-mirror, the light absorbing sheet (307F) is attached to the light output surface of one of the polarization cubic crystal beam splitters, and the direction of the light output surface is the same as the direction of the incident light axis; Each of the sensing parts comprises an optical rotation assembly, an output fiber spatial light collimator, and an output fiber, which are connected in sequence; a polarizer is provided on the output fiber; the output fiber spatial light collimator is provided with an output fiber spatial light collimator output end, and the output fiber spatial light collimator is connected to the output fiber through the output fiber spatial light collimator output end; The optical fiber vector weak magnetic field sensor (3) further comprises three single-axis analyzer packaging structures, each of which comprises an analyzer packaging shell, and the three analyzer packaging shells are used to package the analyzers on the Y axis, the Z axis and the X axis respectively.

2. The optical fiber vector weak magnetic field sensor based on Faraday rotation effect according to claim 1, It is characterized in that The optical rotation combination plate comprises two quarter wave plates and a Faraday rotation effect plate, and the Faraday rotation effect plate is arranged between the two quarter wave plates.

3. The optical fiber vector weak magnetic field sensor based on Faraday rotation effect according to claim 2, It is characterized in that The fast axis angles of the two quarter wave plates in the optical rotation combination plate are different. The fast axis angle of the first quarter wave plate is 45°, and the fast axis angle of the second quarter wave plate is -45°.

4. The optical fiber vector weak magnetic field sensor based on Faraday rotation effect according to claim 2, It is characterized in that The Faraday rotation effect sheet is made of Dy x Co (1-x) Fe 2 O 4 Made of nanoparticle material, and Dy x Co (1-x) Fe 2 O 4 The nanoparticles are encapsulated by a poly(phenylmethyl acrylate) (PBMA) shell.

5. The optical fiber vector weak magnetic field sensor based on Faraday rotation effect according to claim 1, It is characterized in that The optical fiber vector weak magnetic field sensor (3) also includes a packaging shell (308).

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