Magnetic field sensor based on periodic structure filling of optical fiber resonator

Abstract

The application discloses a kind of magnetic field sensors based on periodic structure filled by optical fiber resonant cavity, it includes broadband light source, first single-mode optical fiber, periodic structure, second single-mode optical fiber, spectrometer;The light output by broadband light source is coupled into the single-mode core of first single-mode optical fiber, then propagates to periodic structure to carry out interference superposition, and the light after interference superposition is transmitted to spectrometer by second single-mode optical fiber;Periodic structure includes multiple single-mode optical fibers and is filled with magnetic fluid between adjacent single-mode optical fibers;Periodic structure satisfies phase condition: so that the light intensity output to spectrometer is interfered and superposed greatly, wherein Δn is the effective refractive index difference between core mode and cladding mode, L is sensor length, and λ is central wavelength.The application also provides a kind of periodic structure manufacturing method.The application solves the problems of insufficient sensitivity and easy leakage failure of existing optical fiber magnetic field sensor.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of electromagnetic detection, and particularly relates to a magnetic field sensor based on a periodical structure filled in a fiber resonant cavity, which is used for magnetic field detection and applied in fields such as geological detection, power monitoring, space electromagnetic detection and medical treatment. BACKGROUND

[0002] As an intangible physical quantity, the magnetic field affects the precision, resolution and availability of instruments and devices in the working process of precise intelligent devices and network devices. Therefore, it is very important to monitor the magnetic field environment. The fiber sensing technology mainly uses various integrated fiber devices and supporting demodulation methods to study the accurate values and change rules of physical quantities such as refractive index, temperature, stress and magnetism in the environment. The fiber sensing technology has been partially industrialized in the fields of aviation, mining and health detection. Therefore, the fiber magnetic field detector emerges as the times require. However, the fiber magnetic field detectors on the market have the following shortcomings:

[0003] (1) The wrapped magnetic fluid is easy to leak;

[0004] (2) The sensor relies on the evanescent field to obtain sensing sensitivity, and the evanescent field energy of light is small, so the sensitivity of the fiber magnetic field sensor is low;

[0005] (3) The external quartz / plastic sleeve increases the volume of the fiber structure, and cannot accurately measure the magnetic field change of a single point. SUMMARY

[0006] The application aims to provide a magnetic field sensor based on a periodical structure filled in a fiber resonant cavity and a manufacturing method of the periodical structure, which solves the problems of insufficient sensitivity and easy leakage of the existing fiber magnetic field sensor.

[0007] The technical scheme adopted by the application is as follows:

[0008] A magnetic field sensor based on a periodical structure filled in a fiber resonant cavity comprises a broadband light source, a first single-mode fiber, a periodical structure, a second single-mode fiber and a spectrometer.

[0009] The light output by the broadband light source is coupled into the single-mode core of the first single-mode fiber, and then propagates to the periodical structure for interference superposition. The light subjected to interference superposition is transmitted to the spectrometer through the second single-mode fiber.

[0010] The periodical structure comprises multiple single-mode fibers and a filled magnetic fluid arranged between adjacent single-mode fibers.

[0011] The periodical structure satisfies a phase condition. The light intensity output to the optical spectrum analyzer is subjected to larger interference superposition, wherein △n is the effective refractive index difference between the core mode and the cladding mode, L is the length of the sensor, and λ is the center wavelength.

[0012] According to the above scheme, the encapsulated magnetic fluid is sealed by the PDMS glue after the magnetic fluid is injected into the hollow optical fiber, so that the leakage of the magnetic fluid is avoided.

[0013] According to the above scheme, the outer diameter of the encapsulated magnetic fluid is the same as the outer diameter of the single-mode optical fiber.

[0014] According to the above scheme, the length ratio of the single-mode optical fiber to the encapsulated magnetic fluid is 1:2.

[0015] According to the above scheme, the length of the periodic structure is 3000 μm.

[0016] According to the above scheme, the first single-mode optical fiber, the single-mode optical fiber and the second single-mode optical fiber are of the same type.

[0017] According to the above scheme, the single-mode optical fiber at the first section of the periodic structure and the first single-mode optical fiber are the same single-mode optical fiber.

[0018] According to the above scheme, the single-mode optical fiber at the last section of the periodic structure and the second single-mode optical fiber are the same single-mode optical fiber.

[0019] According to the above scheme, the cladding diameter of the first single-mode optical fiber, the single-mode optical fiber and the second single-mode optical fiber is 125 μm, and the single-mode core diameter of the first single-mode optical fiber, the single-mode optical fiber and the second single-mode optical fiber is 6 μm.

[0020] According to the above scheme, the single-mode optical fiber and the encapsulated magnetic fluid are fused by a fiber fusion machine.

[0021] According to the above scheme, the maximum output power of the broadband light source is 100 mW, the center wavelength is 1550 nm, and the 3dB bandwidth is 200 nm; and the minimum resolution of the optical spectrum analyzer is 0.02 nm, and the wavelength scanning range covers 1000 nm-2000 nm.

[0022] The working mode is as follows: the light output by the broadband light source is coupled into the single-mode core of the first single-mode optical fiber, and then propagates to the periodic structure composed of the single-mode optical fiber and the encapsulated magnetic fluid; since the periodic structure satisfies the phase condition: The light intensity output to the optical spectrum analyzer is subjected to larger interference superposition, wherein △n is the effective refractive index difference between the core mode and the cladding mode, L is the length of the sensor, and λ is the center wavelength.

[0023] Sensing principle: magnetic field change Delta T -> magnetic fluid refractive index change Delta n -> wavelength shift Delta lambda - high sensitivity. The principle of the evanescent field sensor: magnetic field change Delta T -> magnetic fluid refractive index change Delta n -> cladding effective refractive index change Delta n_cl -> wavelength shift Delta lambda - low sensitivity, so the sensitivity of the sensor of the present application is much higher than that of the existing sensor.

[0024] The present application also provides a method for manufacturing the periodic structure of the above-mentioned magnetic field sensor based on the periodic structure filled in the optical fiber resonant cavity, which comprises the following steps:

[0025] A plurality of single-mode hollow optical fibers and a plurality of single-mode optical fibers are taken, one single-mode hollow optical fiber is arranged between adjacent single-mode optical fibers, and the single-mode hollow optical fiber is fused with the single-mode optical fiber;

[0026] The cladding of the single-mode hollow optical fiber is opened;

[0027] The magnetic fluid is pumped into the syringe through the syringe pump, and the magnetic fluid in the syringe is introduced into the core of the single-mode hollow optical fiber through the capillary;

[0028] When the core of the single-mode hollow optical fiber is filled with the magnetic fluid, the PDMS colloid is pumped into the syringe through the syringe pump, the PDMS colloid in the syringe is introduced into the gap of the single-mode hollow optical fiber through the capillary, and the PDMS colloid is solidified through the heating and drying device.

[0029] The present application has the following advantages:

[0030] The periodic structure is formed by coupling the magnetic fluid with the single-mode optical fiber, and the sensitivity of the magnetic field sensor is effectively improved;

[0031] The cascaded resonant cavity filled with the magnetic fluid is equivalent to inserting a plurality of multi-mode optical fibers into the single-mode optical fiber, and the strong refractive index modulation method of the multi-mode optical fiber is used to greatly reduce the size of the sensor;

[0032] In the manufacturing process, the magnetic fluid is directly filled into the hollow optical fiber and then fused with the single-mode optical fiber, which avoids the problem of magnetic fluid leakage of other optical fiber magnetic field sensors;

[0033] No external quartz / plastic sleeve is needed, the volume of the sensor is reduced, and the magnetic field change of a single point position can be accurately measured;

[0034] The present application retains the advantages of all-fiber devices and has excellent mechanical properties. BRIEF DESCRIPTION OF DRAWINGS

[0035] The present application will be further described below in combination with the drawings and examples, and the drawings show:

[0036] Figure 1is a structure diagram of a magnetic field sensor based on a periodic structure filled by a fiber resonant cavity;

[0037] Figure 2 is a schematic diagram of injection of a magnetic fluid of a periodic structure;

[0038] Figure 3 is a schematic diagram of potting of a magnetic fluid of a periodic structure;

[0039] In the figure: 1, broadband light source, 2, first single-mode optical fiber, 3, periodic structure, 3.1, single-mode optical fiber, 3.2, potted magnetic fluid, 4, second single-mode optical fiber, 5, optical spectrum analyzer, 6, magnetic fluid, 7, injection pump, 8, syringe, 9, capillary, 10, core of single-mode hollow optical fiber, 11, single-mode core, 13, PDMS colloid, 14, cured PDMS colloid, 15, heating and drying device. DETAILED DESCRIPTION

[0040] In order to make the purpose, technical scheme and advantages of the present application more clear, the present application is further described in detail below in combination with the drawings and examples. It should be understood that the specific examples described herein are only used to explain the present application and are not used to limit the present application.

[0041] Reference Figure 1 A magnetic field sensor based on a periodic structure filled by a fiber resonant cavity, comprising a broadband light source 1, a first single-mode optical fiber 2, a periodic structure 3, a second single-mode optical fiber 4, and an optical spectrum analyzer 5; the periodic structure 3 satisfies the phase condition: so that the light intensity output to the optical spectrum analyzer is greatly interfered and superimposed, wherein△n is the effective refractive index difference between the core mode and the cladding mode, L is the length of the sensor, and λ is the center wavelength. The light output by the broadband light source 1 is coupled into the single-mode core 11 of the first single-mode optical fiber 2, then propagates to the periodic structure 3 for interference and superposition, and the light interfered and superimposed is transmitted to the optical spectrum analyzer 5 through the second single-mode optical fiber 4. In the present application, the periodic structure 3 comprises multiple sections of single-mode optical fibers 3.1 and potted magnetic fluids 3.2 arranged between adjacent single-mode optical fibers 3.1. In order to simplify the manufacturing process and ensure the accuracy of the sensor, the first section of single-mode optical fiber 3.1 of the periodic structure 3 can be the same single-mode optical fiber as the first single-mode optical fiber 2; and the last section of single-mode optical fiber 3.1 of the periodic structure 3 can be the same single-mode optical fiber as the second single-mode optical fiber 4.

[0042] In the present application, the potted magnetic fluid 3.2 is composed of a magnetic fluid 6 injected by a hollow optical fiber and sealed by a PDMS colloid 13, which can avoid leakage of the magnetic fluid. In order to ensure the accuracy of the sensor, the outer diameter of the potted magnetic fluid 3.2 is the same as the outer diameter of the single-mode optical fiber 3.1.

[0043] Specific examples:

[0044] The magnetic field sensor based on the periodic structure filled by the fiber cavity has a magnetic field sensitivity of 2 nm / mT and a refractive index sensitivity of 1000 nm / RIU (Refractive Index Unit). The periodic structure 3 is formed by the single mode fiber 3.1 and the encapsulated magnetic fluid 3.2. The length of the single mode fiber 3.1 is 200 μm, and the length of the encapsulated magnetic fluid 3.2 is 400 μm. The length ratio of the single mode fiber 3.1 to the encapsulated magnetic fluid 3.2 is 1:2. The total length of the periodic structure 3 is 3000 μm. The cladding diameter of the single mode fiber 3.1 is 125 μm, and the core diameter of the single mode fiber 3.1 is 6 μm. The encapsulated magnetic fluid 3.2 is formed by the hollow core fiber with a cladding diameter of 125 μm, the magnetic fluid 6 is injected into the hollow core fiber, and the PDMS colloid 13 is used to seal the hollow core fiber. The single mode fiber 3.1 and the encapsulated magnetic fluid 3.2 are fused by a commercial fiber fusion machine. The maximum output power of the broadband light source 1 is 100 mW, the center wavelength is 1550 nm, and the 3dB bandwidth is 200 nm. The minimum resolution of the optical spectrum analyzer 5 is 0.02 nm, and the wavelength scanning range covers 1000 nm-2000 nm.

[0045] Referring to Figure 2 and Figure 3 The method for manufacturing the periodic structure 3 includes the following steps:

[0046] A plurality of sections of the single mode hollow core fiber and a plurality of sections of the single mode fiber 3.1 are provided. A single mode hollow core fiber is arranged between adjacent single mode fibers 3.1, and the single mode hollow core fiber is fused with the single mode fiber 3.1.

[0047] The cladding of the single mode hollow core fiber is opened.

[0048] The magnetic fluid 6 is pumped into the syringe 8 by the injection pump 7, and the magnetic fluid 6 in the syringe 8 is introduced into the core 10 of the single mode hollow core fiber through the capillary 9.

[0049] When the core 10 of the single mode hollow core fiber is filled with the magnetic fluid 6, the PDMS colloid 13 is pumped into the syringe 8 by the injection pump 7, and the PDMS colloid 13 in the syringe 8 is introduced into the gap of the single mode hollow core fiber through the capillary 9. The cured PDMS colloid 14 is wrapped around the magnetic fluid 6 by heating and drying the device 15.

[0050] It should be understood that those skilled in the art can make improvements or changes according to the above description, and all these improvements and changes shall fall within the protection scope of the appended claims of the present application.

Claims

1. A magnetic field sensor based on a periodic structure filled with an optical fiber resonant cavity, characterized in that: It includes a broadband light source, a first single-mode fiber, a periodic structure, a second single-mode fiber, and a spectrometer; The light output from the broadband light source is coupled into the single-mode core of the first single-mode fiber, and then propagates to the periodic structure for interference superposition. The light after interference superposition is transmitted to the spectrometer via the second single-mode fiber. The periodic structure includes multiple segments of single-mode optical fiber and a potting magnetic fluid placed between adjacent single-mode optical fibers; the potting magnetic fluid is formed by injecting magnetic fluid into hollow optical fibers and then sealing them with PDMS colloid. The periodic structure satisfies the phase condition: This results in a large interference superposition of the light intensity output to the spectrometer, where ∆n is the effective refractive index difference between the fiber core fundamental mode and the cladding mode, L is the sensor length, and λ is the center wavelength.

2. The magnetic field sensor based on a periodic structure filled with an optical fiber resonant cavity according to claim 1, characterized in that: The outer diameter of the encapsulating magnetic fluid is the same as the outer diameter of the single-mode optical fiber.

3. The magnetic field sensor based on a periodic structure filled with an optical fiber resonant cavity according to claim 1, characterized in that: The single-mode fiber in the first segment of the periodic structure is the same as the first single-mode fiber.

4. The magnetic field sensor based on a periodic structure filled with an optical fiber resonant cavity according to claim 1, characterized in that: The single-mode fiber at the end of the periodic structure and the second single-mode fiber use the same single-mode fiber.

5. The magnetic field sensor based on a periodic structure filled with an optical fiber resonant cavity according to claim 1, characterized in that: The first single-mode fiber, the single-mode fiber, and the second single-mode fiber are of the same type.

6. The magnetic field sensor based on a periodic structure filled with an optical fiber resonant cavity according to claim 1, characterized in that: Single-mode optical fiber and encapsulating magnetofluid are fused together using an optical fiber fusion splicer.

7. A method for fabricating the periodic structure of a magnetic field sensor based on a periodic structure filled with an optical fiber resonant cavity as described in claims 1-6, characterized in that: The method includes the following steps: Take multiple segments of single-mode hollow fiber and multiple segments of single-mode fiber, set a single-mode hollow fiber between adjacent single-mode fibers, and fusion splice the single-mode hollow fiber with the single-mode fiber. Open the cladding of the single-mode hollow fiber; The magnetic fluid is pumped into the syringe by the injection pump, and the magnetic fluid in the syringe is introduced into the core of the single-mode hollow optical fiber through the capillary tube. After the core of the single-mode hollow fiber is filled with magnetofluid, PDMS colloid is pumped into the syringe by a syringe pump. The PDMS colloid in the syringe is introduced into the gap of the single-mode hollow fiber through a capillary tube and cured by a heating and drying device.

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