CN113009384B - Vector magnetic field sensor, preparation method and detection system - Google Patents

Abstract

This application relates to a vector magnetic field sensor, a preparation method and a detection system, and relates to the technical field of optical fiber magnetic field sensing. The vector magnetic field sensor includes a single-mode optical fiber, a small-diameter polarization-maintaining optical fiber, a magnetic fluid and a quartz capillary. The small-diameter polarization-maintaining optical fiber is Both ends are connected to single-mode optical fibers respectively. The quartz capillary tube is set on the thin-diameter polarization-maintaining optical fiber. The magnetic fluid is set in the quartz capillary tube. The long-period grating is engraved on the thin-diameter polarization-maintaining optical fiber. The vector magnetic field sensor provided by the invention solves the problems of existing magnetic field sensors with limited sensitivity, insufficient measurement accuracy, poor anti-interference ability, and inability to simultaneously measure magnetic field intensity and magnetic field direction.

Description

Vector magnetic field sensor, preparation method and detection system

Technical field

The invention relates to the technical field of optical fiber magnetic field sensing, and in particular to a vector magnetic field sensor, a preparation method and a detection system.

Background technique

Continuous vector magnetic field sensing technology plays an extremely important role in navigation, space exploration, military and other fields. Traditional magnetic field sensors mainly use magnetoresistive, magnetic diode, etc. Traditional magnetic sensors are susceptible to interference from electromagnetic and other environmental factors, and are not conducive to long-distance transmission. In extreme environments, the performance of conventional magnetic field sensors can be affected or even malfunction.

Optical fiber magnetic field sensors have obvious advantages over traditional magnetic field sensors in their compact structure, fast response, and high sensitivity. With the development of nanotechnology, combining functional nanomaterials with optical fibers can effectively realize magnetic field sensing, especially for weak magnetic field measurements. Magnetic fluid is an important nanomaterial and has rich magneto-optical properties such as tunable refractive index, tunable birefringence, tunable transmittance, etc. With the development of special optical fiber technology, optical fiber magnetic field sensing can be achieved by combining optical fiber devices with magnetic fluid. However, most devices combined with magnetic fluid can only measure the magnetic field intensity, but cannot identify the direction of the magnetic field, which limits the optical fiber Application range of magnetic field sensors.

The polarization-maintaining fiber long-period grating performs periodic refractive index modulation on the polarization-maintaining fiber, coupling the core fundamental mode to the orthogonal polarization cladding mode. Due to the special asymmetric structure of the polarization-maintaining fiber, its cladding mode is asymmetric. Environmental refractive index properties. Polarization-maintaining fiber long-period grating based on polarized light measurement is an important research direction in fiber vector sensing technology.

Contents of the invention

Based on this, the purpose of the present invention is to propose a vector magnetic field sensor to solve the problem that existing magnetic field sensors cannot simultaneously measure magnetic field intensity and magnetic field direction.

The invention proposes a vector magnetic field sensor. The vector magnetic field sensor includes a single-mode optical fiber, a small-diameter polarization-maintaining optical fiber, a magnetic fluid and a quartz capillary. The two ends of the small-diameter polarization-maintaining optical fiber are respectively connected to the single-mode optical fiber. The quartz capillary tube is sleeved on the small-diameter polarization-maintaining optical fiber, the magnetic fluid is provided in the quartz capillary tube, and a long-period grating is written on the small-diameter polarization-maintaining optical fiber.

The vector magnetic field sensor proposed by the present invention sets the magnetic fluid to have adjustable refractive index characteristics under the action of a magnetic field, and the nanoparticles have chain-like aggregation characteristics. The existence of optical fiber will break the balance of the chain arrangement of magnetic fluid nanoparticles, causing the nanoparticles to be sparsely distributed in the plane where the magnetic field passes through the optical fiber, and the surface of the optical fiber perpendicular to it will be rich in nanoparticles, thus forming high and low levels on the surface of the optical fiber in two orthogonal directions. Refractive index distribution. Polarization-maintaining fiber is an asymmetric structure fiber with strong birefringence. Polarization-maintaining fiber long-period grating can couple the core fundamental mode to high-order orthogonal polarization cladding mode, and the polarization-maintaining fiber long-period grating cladding mode has Asymmetric environmental refractive index characteristics, through the interaction between the cladding mode evanescent field and the magnetic fluid, can realize the simultaneous measurement of the external magnetic field intensity and direction by monitoring the spectral resonance wavelength shift of the cladding mode.

Further, the cladding diameter of the polarization-maintaining optical fiber is 80 microns.

Further, the period range of the long-period grating is 250-400 microns.

Further, both ends of the quartz capillary tube are injection molded with UV curing glue.

Further, the magnetic fluid is water-based magnetic fluid.

The invention also proposes a method for preparing a vector magnetic field sensor, which method includes:

Writing long-period fiber gratings on thin-diameter polarization-maintaining optical fibers: Welding a preset length of thin-diameter polarization-maintaining fibers in the middle of a single-mode fiber, and writing long-period fiber gratings on the thin-diameter polarization-maintaining fibers using carbon dioxide laser;

Put the quartz capillary tube outside the polarization-maintaining fiber long-period grating, maintain the constant axial pulling force of the polarization-maintaining fiber long-period grating fiber, use UV curing glue to encapsulate one end of the quartz capillary tube, and use a syringe to introduce the magnetic fluid into the place after the UV curing glue is solidified. In the quartz capillary tube, the other end of the quartz capillary tube is sealed with the ultraviolet curing glue.

The vector magnetic field sensor preparation method proposed by the present invention uses a carbon dioxide laser to prepare a long-period fiber grating on a small-diameter polarization-maintaining fiber. The long-period fiber grating has small insertion loss, flexible design, and high refractive index sensitivity.

The invention also proposes a vector magnetic field sensor detection system. The vector magnetic field sensor detection system includes: a vector magnetic field sensor, a broadband light source, a spectrometer, a polarizer, a polarization controller and a magnetic field generator; wherein, the broadband light source, the The polarizer, the polarization controller, the vector magnetic field sensor and the spectrometer are connected in sequence. The vector magnetic field sensor is located in the magnetic field generator, and the magnetic field generator is driven by a regulated power supply.

Furthermore, the magnetic field generator is also equipped with a Tesla magnetometer.

Further, the magnetic field generator is a rotatable magnetic field generator.

The vector magnetic field sensor detection system proposed by the present invention uses a spectrometer to monitor the change of the resonant wavelength of the transmission spectrum of the packaged polarization-maintaining optical fiber long-period grating under the action of an external magnetic field, and obtains the variation pattern of the grating resonant peak wavelength with the magnetic field intensity and magnetic field direction.

Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention.

Description of the drawings

The drawings described here are used to provide a further understanding of the present application and constitute a part of the present application. The illustrative embodiments of the present application and their descriptions are used to explain the present application and do not constitute an improper limitation of the present application. In the attached picture:

Figure 1 is a schematic structural diagram of a vector magnetic field sensor proposed in the first embodiment of the present invention;

Figure 2 is a schematic structural diagram of the vector magnetic field sensor detection system proposed in the second implementation of the present invention;

Figure 3 is a magnetic field intensity response diagram of the vector magnetic field sensor proposed in the first embodiment of the present invention under different magnetic field directions;

Figure 4 is a diagram showing the variation of the transmission spectrum of the vector magnetic field sensor with the direction of the magnetic field under a constant magnetic field intensity according to the first embodiment of the present invention;

FIG. 5 is a magnetic field direction response diagram of a vector magnetic field sensor under a constant magnetic field according to the first embodiment of the present invention.

Description of main component symbols

Detailed ways

In order to make the purpose, technical solutions and advantages of the present application clearer, the present application will be described and illustrated below in conjunction with the drawings and embodiments. It should be understood that the specific embodiments described here are only used to explain the present application and are not used to limit the present application. Based on the embodiments proposed in this application, all other embodiments obtained by those of ordinary skill in the art without any creative work shall fall within the scope of protection of this application.

Obviously, the drawings in the following description are only some examples or embodiments of the present application. For those of ordinary skill in the art, without exerting creative efforts, the present application can also be applied according to these drawings. Other similar scenarios. In addition, it will also be appreciated that, although such development efforts may be complex and lengthy, the technology disclosed in this application will be readily apparent to those of ordinary skill in the art relevant to the disclosure of this application. Some design, manufacturing or production changes based on the content are only conventional technical means and should not be understood as insufficient content disclosed in this application.

Reference in this application to "an embodiment" means that a particular feature, structure or characteristic described in connection with the embodiment may be included in at least one embodiment of the application. The appearances of this phrase in various places in the specification are not necessarily all referring to the same embodiment, nor are separate or alternative embodiments mutually exclusive of other embodiments. It is explicitly and implicitly understood by those of ordinary skill in the art that the embodiments described in this application may be combined with other embodiments without conflict.

Unless otherwise defined, the technical terms or scientific terms involved in this application shall have the usual meanings understood by those with ordinary skills in the technical field to which this application belongs. "A", "an", "a", "the" and other similar words used in this application do not indicate a quantitative limit and may indicate singular or plural numbers. The terms "include", "comprises", "having" and any variations thereof involved in this application are intended to cover non-exclusive inclusion; for example, a process, method, system, product or product that includes a series of steps or modules (units). The equipment is not limited to the listed steps or units, but may also include steps or units that are not listed, or may further include other steps or units inherent to these processes, methods, products or equipment. Words such as "connected", "connected", "coupled" and the like mentioned in this application are not limited to physical or mechanical connections, but may include electrical connections, whether direct or indirect. The "plurality" mentioned in this application refers to two or more than two. "And/or" describes the relationship between related objects, indicating that three relationships can exist. For example, "A and/or B" can mean: A alone exists, A and B exist simultaneously, and B exists alone. The character "/" generally indicates that the related objects are in an "or" relationship. The terms “first”, “second”, “third”, etc. used in this application are only used to distinguish similar objects and do not represent a specific ordering of the objects.

The first embodiment of the present invention provides a vector magnetic field sensor 11. The vector magnetic field sensor 11 includes a single-mode optical fiber 1, a small-diameter polarization-maintaining optical fiber 3, a magnetic fluid 4 and a quartz capillary tube 5.

Specifically, both ends of the thin-diameter polarization-maintaining optical fiber 3 are connected to the single-mode optical fiber 1 respectively. The quartz capillary 5 is set on the thin-diameter polarization-maintaining optical fiber 3. The magnetic fluid 4 is set in the quartz capillary 5. The thin-diameter polarization-maintaining optical fiber 3 There is a long period grating inscribed on it.

The vector magnetic field sensor 11 proposed in the first embodiment of the present invention sets the magnetic fluid 4 to have adjustable refractive index characteristics under the action of a magnetic field, and the nanoparticles have chain-like aggregation characteristics. The existence of optical fiber will break the balance of the chain arrangement of magnetic fluid nanoparticles, causing the nanoparticles to be sparsely distributed in the plane where the magnetic field passes through the optical fiber, and the surface of the optical fiber perpendicular to it will be rich in nanoparticles, thus forming high and low levels on the surface of the optical fiber in two orthogonal directions. Refractive index distribution. Polarization-maintaining fiber 3 is an asymmetric structure fiber with strong birefringence. The long-period grating of polarization-maintaining fiber 3 can couple the core fundamental mode to the high-order orthogonal polarization cladding mode, and the long-period polarization-maintaining fiber 3 The grating cladding mode has asymmetric environmental refractive index characteristics. Through the interaction between the evanescent field of the cladding mode and the magnetic fluid 4, the intensity and direction of the external magnetic field can be measured simultaneously by monitoring the spectral resonance wavelength shift of the cladding mode.

Furthermore, in order to improve the sensitivity of the vector magnetic field sensor 11, in the first embodiment of the present invention, the cladding diameter of the polarization-maintaining optical fiber 3 is 80 microns. By setting the optical fiber to a fine-clad fiber, the smaller the fiber diameter, the higher the environmental refractive index sensitivity.

Furthermore, in the embodiment of the present invention, the period range of the long period grating is 250-400 microns. This makes the long-period grating mode the higher-order cladding mode LP14. The higher the order of the long-period grating mode, the higher the environmental refractive index sensitivity.

It can be understood that since the magnetic fluid 4 is provided in the quartz capillary tube 5 and the magnetic fluid 4 is in a liquid form, in order to achieve a good sealing effect, UV curing glue 2 is injected at both ends of the quartz capillary tube 5 in this embodiment of the present invention. By injecting UV curing glue 2 at both ends of the capillary tube 5 , the vector magnetic field sensor 11 has good sealing properties, and at the same time, the connection strength between the polarization-maintaining optical fiber 3 and the single-mode optical fiber 1 is enhanced.

Furthermore, in the embodiment of the present invention, the magnetic fluid 4 is a water-based magnetic fluid (EMG 605). By using this kind of magnetic fluid 4, it has the characteristics of good magnetic effect and uniform particle size.

The present invention also proposes a method for preparing a vector magnetic field sensor 11, which method specifically includes:

Writing long-period gratings on thin-diameter polarization-maintaining optical fiber 3: Welding the thin-diameter polarization-maintaining fiber 3 with a length of 5 cm in the middle of the single-mode fiber 1, using carbon dioxide laser to write long-period fiber gratings on the small-diameter polarization-maintaining fiber 3; quartz The capillary tube 5 is placed outside the long period grating of the polarization-maintaining optical fiber 3 to maintain a constant pulling force in the axial direction of the long-period grating fiber of the polarization-maintaining optical fiber 3. One end of the quartz capillary tube 5 is encapsulated with UV curing glue 2. After the UV curing glue 2 is cured, the magnetic fluid is injected with a syringe. 4 is introduced into the quartz capillary tube 5, and the other end of the quartz capillary tube 5 is sealed with UV curing glue 2.

Using the above preparation method, a long-period fiber grating is prepared on a small-diameter polarization-maintaining fiber using a carbon dioxide laser. The long-period fiber grating has small insertion loss, flexible design, and high refractive index sensitivity.

Please refer to Figure 2, which is a vector magnetic field sensor detection system proposed in the second embodiment of the present invention. It is used to detect changes in the resonant wavelength of the packaged polarization-maintaining fiber long-period grating transmission spectrum under the action of an external magnetic field using a spectrometer to obtain the grating resonance peak. The wavelength changes with the strength and direction of the magnetic field. Specifically, the vector magnetic field sensor detection system includes: vector magnetic field sensor 11, broadband light source 6, spectrometer 13, polarizer 7, polarization controller 8 and magnetic field generator 10; among which, broadband light source 6, polarizer 7, polarization control The device 8, the vector magnetic field sensor 11 and the spectrometer 13 are connected in sequence. The vector magnetic field sensor 11 is installed in the magnetic field generator 10. The magnetic field generator 10 is driven by a regulated power supply 9.

In addition, in the magnetic field sensor detection system proposed in the second embodiment of the present invention, the magnetic field generator 10 is also equipped with a Tesla magnetometer 12 for detecting and recording changes in magnetic induction intensity.

Moreover, the magnetic field generator 10 adopts a rotatable magnetic field generator, which can realize the magnetic field action at different angles and facilitate the acquisition of parameter values of the magnetic field generator 10 action at different angles.

As shown in Figure 2, calibrate the fast axis and slow axis directions of the long period grating of the polarization-maintaining fiber 3 in the vector magnetic field sensor 11, connect the vector magnetic field sensor 11 to the vector magnetic field sensor detection system, and reasonably adjust the polarizer 7 and polarization controller 8 The incident polarized light enters the long-period grating of the polarization-maintaining fiber 3 respectively along the fast axis and slow axis of the polarization-maintaining fiber 3, and the fast-axis and slow-axis transmission spectra of the vector magnetic field sensor 11 without external magnetic field can be obtained on the spectrometer respectively. The fast-axis and slow-axis transmission spectra of the vector magnetic field sensor 11 under different magnetic field directions are studied separately, and the variation of the resonance peak wavelength with the magnetic field intensity is studied. As shown in Figure 3, the magnetic field response of the fast-axis and slow-axis mode resonance peaks can be obtained. When the magnetic field intensity changes in the range of 0~10.5mT, the magnetic field response in four different directions has good linearity. In order to achieve more accurate magnetic field strength measurement, the variation range of the detected magnetic field strength should be between 0 and 10.5mT. When the direction of the external magnetic field is parallel to the slow axis of the fiber, the fast-axis mode and the slow-axis mode have the highest magnetic field response sensitivity. When the direction of the external magnetic field is perpendicular to the slow axis of the fiber, the fast-axis mode and the slow-axis mode have the lowest magnetic field response sensitivity. The other two The magnetic field response sensitivity in each direction is between the highest sensitivity and the lowest sensitivity, indicating that the magnetic field vector magnetic field sensor 11 can measure magnetic field intensity in multiple directions.

When the above-mentioned vector magnetic field sensor detection system detects the magnetic field intensity and magnetic field direction, the magnetic field intensity of the detected magnetic field is between 0 and 10.5mT. The detection method is to use a spectrometer to monitor the changes in the resonance peak of the transmission spectrum of the polarization-maintaining fiber long-period grating cladding mode.

In addition, the polarization-maintaining fiber 3 long period grating cladding mode resonance peak is used as the sensing detection peak. Both the fast axis and slow axis cladding mode resonance peaks can be used as sensing detection peaks. The resonance peak of the slow axis mode has higher refraction. rate sensitivity.

As shown in Figure 4, in order to verify that the vector magnetic field sensor 11 has the ability to measure the direction of the magnetic field, the magnetic field intensity is fixed at 7.0mT, and the fast-axis cladding mode transmission spectrum is monitored with 360° changes in the direction of the magnetic field, where (a) is the direction of the magnetic field given by When the direction of the magnetic field changes from 0° to 90°, the transmission spectrum changes with the magnetic field. (b) When the direction of the magnetic field changes from 90° to 180°, the transmission spectrum changes with the magnetic field. (c) When the direction of the magnetic field changes from 180° to 270° When , the transmission spectrum changes with the magnetic field. (d) shows the change of the transmission spectrum with the magnetic field when the magnetic field direction changes from 270° to 0°.

When the magnetic field strength changes from parallel to the slow axis of the fiber to perpendicular to the slow axis of the fiber, the spectrum undergoes a blue shift. Anyway, the spectrum is red-shifted. In order to further analyze the vector magnetic field sensing characteristics of this magnetic field sensor, the magnetic field strengths were fixed at 7.0mT and 11.0mT respectively, where the magnetic field direction changes range from 0 to 360°, and the fast-axis and slow-axis cladding mode resonant wavelengths were monitored as the magnetic field direction changes. The change. As shown in Figure 4, under different magnetic field strengths, the offset of the fast-axis and slow-axis mode resonance wavelengths changes significantly with the direction of the magnetic field, showing a figure-8 shape in polar coordinates, proving that the invented magnetic field sensor can achieve Identification of magnetic field direction within the range of 0~90°.

The present invention provides a technical solution, which has the following advantages: by using carbon dioxide laser to perform periodic refractive index modulation on the thin-diameter polarization-maintaining fiber 3, a long-period fiber grating with higher asymmetric refractive index characteristics is prepared. It has high refractive index sensitivity within the frequency tuning range; the vector magnetic field sensor detection system uses polarized light as the detection light source to overcome the impact of the high polarization-related loss of the device on the measurement results during the fiber sensing process; by treating the fine particles wrapped with magnetic fluid 4 The magnetic field response of the long-period grating of the polarization-maintaining fiber 3 was tested, and the changing patterns of the fast-axis and slow-axis cladding mode resonant wavelengths of the polarization-maintaining fiber 3 long-period grating with the magnetic field intensity and magnetic field direction were obtained, and the period range was selected to be 250-400 Micron grating period, appropriate grating resonant wavelength, appropriate detected magnetic field intensity range and water-based magnetic fluid make the magnetic field sensor have a high response to the magnetic field intensity and magnetic field direction.

The technical features of the above-described embodiments can be combined in any way. To simplify the description, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, All should be considered to be within the scope of this manual.

The above-described embodiments only express several implementation modes of the present application, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the invention patent. It should be noted that, for those of ordinary skill in the art, several modifications and improvements can be made without departing from the concept of the present application, and these all fall within the protection scope of the present application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims (8)

1. The vector magnetic field sensor is characterized by comprising a single-mode fiber, a small-diameter polarization maintaining fiber, magnetic fluid and a quartz capillary tube, wherein two ends of the small-diameter polarization maintaining fiber are respectively connected with the single-mode fiber, the quartz capillary tube is sleeved on the small-diameter polarization maintaining fiber, the magnetic fluid is arranged in the quartz capillary tube, a long-period grating is inscribed on the small-diameter polarization maintaining fiber, and the cladding diameter of the small-diameter polarization maintaining fiber is 80 microns.

2. The vector magnetic field sensor of claim 1, wherein the long period grating has a period in the range of 250-400 microns.

3. The vector magnetic field sensor of claim 1, wherein the quartz capillary tube is injection molded with ultraviolet curable glue at both ends.

4. The vector magnetic field sensor of claim 1, wherein the magnetic fluid is a water-based magnetic fluid.

5. A method of manufacturing a vector magnetic field sensor according to any one of claims 1-4, characterized in that the method comprises:

writing a thin-diameter polarization maintaining fiber long period grating: welding a small-diameter polarization maintaining fiber with a preset length in the middle of a single-mode fiber, and inscribing a long-period fiber grating on the small-diameter polarization maintaining fiber through carbon dioxide laser;

sleeving a quartz capillary tube outside the polarization maintaining optical fiber long period grating, keeping the axial constant tension of the polarization maintaining optical fiber long period grating optical fiber, sealing one end of the quartz capillary tube by using ultraviolet curing glue, introducing magnetic fluid into the quartz capillary tube by using an injector after the ultraviolet curing glue is cured, and sealing the other end of the quartz capillary tube by using the ultraviolet curing glue; the preset length of the small-diameter polarization maintaining optical fiber is 5 cm.

6. The detection system of a vector magnetic field sensor according to any one of claims 1 to 4, wherein the detection system comprises: broadband light source, spectrometer, polarizer, polarization controller and magnetic field generator; the broadband light source, the polarizer, the polarization controller, the vector magnetic field sensor and the spectrometer are sequentially connected, the vector magnetic field sensor is arranged in the magnetic field generator, and the magnetic field generator is driven by a stabilized voltage power supply.

7. The system of claim 6, wherein a tesla magnetometer is further disposed within the magnetic field generator.

8. The vector magnetic field sensor detection system of claim 6, wherein the magnetic field generator is a rotatable magnetic field generator.