A magnetic field and temperature sensing structure of a three-core optical fiber with magnetic fluid and side-decladding

Abstract

The invention discloses a magnetic fluid and side-decladding three-core optical fiber magnetic field and temperature sensing structure. The structure comprises a broadband light source (1), a 1×3 coupler (2), a first coupling module (3), a three-core optical fiber sensing structure (4), a second coupling module (5), a 3×1 coupler (6), and a detector (7). The three-core optical fiber sensing structure (4) comprises a cladding (4‑1), a first fiber core (4‑2), a second fiber core (4‑3), a third fiber core (4‑4), a decladding region (4‑5) filled with magnetic fluid, and a quartz glass capillary (4‑6). The first fiber core (4‑2), the second fiber core (4‑3), and the decladding region (4‑5) filled with magnetic fluid form an MZI structure. The third fiber core (4‑4) is written with FBG and is only modulated by temperature. Therefore, the change of light wavelength is only related to temperature. Since both the magnetic field and temperature change the refractive index of the magnetic fluid, the light intensity changes. Therefore, by demodulating the change of light intensity and light wavelength, the magnetic field and temperature dual parameter measurement can be realized.

Description

Technical Field

[0001] The present invention belongs to the field of optical fiber sensing technology, and particularly relates to a magnetic field and temperature sensing structure of a magnetic fluid and a three-core optical fiber with the cladding removed on the side. The magnetic fluid and the three-core optical fiber with the cladding removed on the side are combined, and the characteristics of the refractive index of the magnetic fluid being sensitive to the magnetic field and the characteristics of the FBG being sensitive to the temperature are utilized to realize dual parameter measurement of the magnetic field and the temperature. Background Art

[0002] Magnetic sensors are devices that can convert various magnetic fields and their changing quantities into electrical signal outputs. Magnetic fields and information related to magnetic fields exist in many places in nature and human society. The magnetic field generated by artificial permanent magnets can be used as a carrier of many information. Therefore, the tasks of detecting, collecting, storing, converting, and monitoring various magnetic fields and various information carried in the magnetic field naturally fall on magnetic field sensors. Although traditional magnetic field sensors, such as Hall sensors, magnetoresistive sensors, fluxgate sensors, and induction coil sensors, have relatively mature technologies, they are difficult to apply in some fields due to their high power consumption, large size, complex structure, susceptibility to electromagnetic interference, and high requirements for the surrounding environment, and cannot meet the detection needs. Optical fiber magnetic field sensors inherit the advantages of optical fiber sensors, and have outstanding advantages such as small size, corrosion resistance, strong anti-electromagnetic interference ability, convenience for distributed multi-point detection, and all-optical transmission. They have become a research hotspot in the field of magnetic field sensing. There are many types of optical fiber-based magnetic field sensors, such as magnetic field sensors based on fiber grating structures, magnetic field sensors based on MZI, magnetic field sensors based on evanescent wave mechanisms, and magnetic field sensors based on surface plasmon resonance, etc. They can be applied to different magnetic field combinations according to different sensing performances.

[0003] At present, the optical fiber-based magnetic field sensors mainly include the following according to different sensing mechanisms: optical fiber magnetic field sensors based on magnetostrictive materials, which mainly use the magnetostrictive effect of magnetostrictive materials for magnetic field sensing; optical fiber microstructure magnetic field sensors based on magnetic fluids, which mainly use the adjustable magnetostrictive refractive index of magnetic fluids to achieve magnetic field sensing. Due to the adjustable magnetostrictive refractive index of magnetic fluids, the refractive index of magnetic fluids will change under an external magnetic field. When the external magnetic field is parallel to the direction of the transmitted light, the refractive index of the magnetic fluid increases with the increase of the external magnetic field. When the direction of the external magnetic field is perpendicular to the direction of the transmitted light, the refractive index of the magnetic fluid decreases with the increase of the external magnetic field. Generally, the cladding of the optical fiber is thinned, such as using a micromachining process to remove the cladding or using a thin-core optical fiber with cladding corrosion, so that the refractive index of the magnetic fluid can be close to the refractive index of the optical fiber cladding, and then the magnetic fluid and the microstructure optical fiber are encapsulated using a quartz glass capillary. When there is a magnetic field, the refractive index of the magnetic fluid changes, thereby changing the refractive index of the cladding, which in turn affects the wavelength of the output light. By demodulating the change in the output light, the magnetic field is detected. The refractive index of the magnetic fluid is also affected by temperature, thus affecting the measurement results. In current reports, by writing FBG, the refractive index characteristics of the magnetic fluid and the temperature sensitivity of FBG are used to achieve dual parameter measurement of magnetic field and temperature.

[0004] The communication capacity of single-mode, single-core optical fiber is about to reach its upper limit. In order to meet people's growing demand for information transmission capacity, there have been many studies on triple-core optical fiber in recent years. Three-core optical fiber is a special optical fiber with three cores embedded in the cladding. The magnetic field sensor obtained by combining three-core optical fiber with magnetic fluid has a simple structure and high sensitivity.

[0005] The present invention adopts an optical fiber magnetic field sensing structure that combines a magnetic fluid with a three-core optical fiber with the cladding removed from the side. By combining the magnetic fluid with the three-core optical fiber with the cladding removed from the side, the refractive index of the magnetic fluid is sensitive to the magnetic field and the FBG is sensitive to temperature, thereby realizing dual parameter measurement of the magnetic field and the temperature. Summary of the invention

[0006] The purpose of the present invention is to provide a magnetic fluid and side-decladding three-core optical fiber magnetic field and temperature sensing structure, which can realize the detection of magnetic field.

[0007] To achieve the above object, the present invention adopts the following technical solution:

[0008] The present invention comprises a broadband light source (1), a 1×3 coupler (2), a first coupling module (3), a three-core optical fiber sensing structure (4), a second coupling module (5), a 3×1 coupler (6), and a detector (7), and is characterized in that: the 1×3 coupler (2) comprises an input optical fiber (2-1), a first output optical fiber (2-2), a second output optical fiber (2-3), and a third output optical fiber (2-4); the first coupling module (3) comprises a first optical waveguide (3-1), a second optical waveguide (3-2), and a third optical waveguide (3-3), which are 3 mm long, 1 mm wide, and 3 mm high; the three-core optical fiber sensing structure (4) comprises a cladding (4-1), a first fiber core (4-2), a second fiber core (4-3), and a third fiber core ( 4-4), a decladding region (4-5) filled with a magnetic fluid, and a quartz glass capillary (4-6), the diameter of the cladding (4-1) is 125 μm, the diameter of the first fiber core (4-2) is 9.6 μm, the diameter of the second fiber core (4-3) is 6 μm, and the third fiber core (4-4) is written with FBG, with a diameter of 9.6 μm. The FBG is directly written by femtosecond laser, with a period of 0.5 μm and a length of 500 μm. The angle formed by the first fiber core (4-2) and the third fiber core (4-4) and the second fiber core (4-3) is 120°, and the spacing between the first fiber core (4-2) and the third fiber core (4-4) and the second fiber core (4-3) is 35.3 μm. The outer diameter of the quartz glass capillary (4-6) is 1 mm, and the inner diameter is 0.3mm; the second coupling module (5) comprises a fourth optical waveguide (5-1), a fifth optical waveguide (5-2), and a sixth optical waveguide (5-3), which are 3mm long, 1mm wide, and 3mm high; the 3×1 coupler (6) comprises a first input optical fiber (6-1), a second input optical fiber (6-2), a third input optical fiber (6-3), and an output optical fiber (6-4); the broadband light source (1) is coupled to the input optical fiber (2-1), the first output optical fiber (2-2) is coupled to the front end of the first optical waveguide (3-1), the second output optical fiber (2-3) is coupled to the second optical waveguide (3-4), and the third input optical fiber (6-5) is coupled to the output optical fiber (6-6). The front end of the first optical waveguide (3-2) is coupled to the front end of the third optical waveguide (3-2), the third output optical fiber (2-4) is coupled to the front end of the third optical waveguide (3-3), the rear end of the first optical waveguide (3-1) is coupled to the front end of the first fiber core (4-2), the rear end of the second optical waveguide (3-2) is coupled to the front end of the second fiber core (4-3), the rear end of the third optical waveguide (3-3) is coupled to the front end of the third fiber core (4-4), the rear end of the first fiber core (4-2) is coupled to the front end of the fourth optical waveguide (5-1), the rear end of the second fiber core (4-3) is coupled to the front end of the fifth optical waveguide (5-2), and the third fiber core (4-4) is coupled to the front end of the fifth optical waveguide (5-2). ) is coupled with the front end of the sixth optical waveguide (5-3), the rear end of the fourth optical waveguide (5-1) is coupled with the first input optical fiber (6-1), the rear end of the fifth optical waveguide (5-2) is coupled with the second input optical fiber (6-2), the rear end of the sixth optical waveguide (5-3) is coupled with the third input optical fiber (6-3), and the output optical fiber (6-4) is coupled with the detector (7); the decladding region (4-5) filled with magnetic fluid is obtained by etching above the first fiber core (4-2) using a femtosecond laser, and has a depth of 22.4 μm, a length of 100 μm, and a diameter of 96 μm; the The quartz glass capillary (4-6) is used to encapsulate the three-core optical fiber sensing structure (4). The light in the first fiber core (4-2) is used as the detection light, the light in the second fiber core (4-3) is used as the reference light, and another light enters the third fiber core (4-4). The three beams of light are combined through the 3×1 coupler (6) to interfere with each other. The first fiber core (4-2), the second fiber core (4-3) and the decladding area (4-5) filled with magnetic fluid form an MZI structure. The adjustable refractive index characteristics of the magnetic fluid can be used to measure the magnetic field. The third fiber core (4-4) is sensitive to temperature and can measure the temperature.

[0009] The front ends of the first optical waveguide (3-1) and the second optical waveguide (3-2) are 0.5 mm apart, and the rear ends are 35.3 μm apart; the front ends of the third optical waveguide (3-3) and the second optical waveguide (3-2) are 0.5 mm apart, and the rear ends are 35.3 μm apart; and the angle formed by the rear ends of the first optical waveguide (3-1) and the third optical waveguide (3-3) and the rear end of the second optical waveguide (3-2) is 120°.

[0010] The front ends of the fourth optical waveguide (5-1) and the fifth optical waveguide (5-2) are 35.3 μm apart, and the rear ends are 0.5 mm apart. The front ends of the sixth optical waveguide (5-3) and the fifth optical waveguide (5-2) are 35.3 μm apart, and the rear ends are 0.5 mm apart. The angle formed by the front ends of the fourth optical waveguide (5-1) and the sixth optical waveguide (5-3) and the front end of the fifth optical waveguide (5-2) is 120°. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] FIG1( a ) is a schematic structural diagram of a magnetic fluid and side-decladding three-core optical fiber magnetic field and temperature sensing structure according to the present invention;

[0012] FIG1( b ) is a schematic diagram of a three-core optical fiber sensing structure according to the present invention;

[0013] Figure 2 This is a cross-sectional view of a magnetic fluid and side-decladding three-core optical fiber magnetic field and temperature sensing structure according to the present invention. DETAILED DESCRIPTION

[0014] The specific implementation of the present invention will be further described below with reference to FIG. 1( a ) and FIG. 1( b ).

[0015] The present invention is a magnetic field and temperature sensing structure of a magnetic fluid and a side-decladding three-core optical fiber that can detect magnetic fields. The specific implementation steps are as follows:

[0016] Step 1: Fiber end face pretreatment

[0017] Use a fiber optic cutter to cut the upper and lower end faces of the three-core optical fiber flat, and then use an ultrasonic cleaner to clean the optical fiber.

[0018] Step 2: Prepare the coupling module

[0019] Two coupling modules with the same specifications were prepared by semiconductor micromachining technology. They were 3 mm long, 1 mm wide and 3 mm high. They were composed of three optical waveguides with the same diameter of 9 μm. At the end coupled with the three-core optical fiber with side decladding, the two outer optical waveguides were 35.3 μm away from the middle optical waveguide, and the angle formed by the two outer optical waveguides and the middle optical waveguide was 120°; at the end coupled with the coupler, the two outer optical waveguides were 0.5 mm away from the middle optical waveguide.

[0020] Step 3: Femtosecond laser writing FBG

[0021] Fix the processed three-core optical fiber on a three-dimensional mechanical platform, adjust the parameter settings of the femtosecond laser, and then focus the femtosecond laser. The focus of the femtosecond laser focused by the objective lens is incident on a core on the side of the three-core optical fiber. At the same time, move the optical fiber parallel to form a waveguide structure with a period of 0.5μm and a length of 500μm inside the core.

[0022] Step 4: Remove the cladding from the side of the three-core optical fiber

[0023] The processed three-core optical fiber is fixed on a three-dimensional mechanical platform, and the computer is used to control the high-precision movement in the three-dimensional direction. The parameters of the femtosecond laser are adjusted, and then the light spot is focused to keep the position of the light spot unchanged, and the movement of the platform is controlled to drive the optical fiber to move relative to the light spot, so that the focused femtosecond laser scans the other side of the optical fiber to remove the cladding and form a plane, which is the decladding area, with a length of 100μm, a depth of 22.4μm, and a diameter of 96μm.

[0024] Step 5: Filling the magnetic fluid

[0025] Under an optical microscope, the three-core optical fiber was placed in a quartz glass capillary with an inner diameter of 0.3 mm and an outer diameter of 1 mm. One end of the three-core optical fiber with side decladding was fixed in the quartz glass capillary with UV glue. Then, a syringe was used to fill the magnetic fluid into the quartz glass capillary. Finally, the other end of the quartz glass capillary was sealed with UV glue. In this way, the three-core optical fiber with side decladding immersed in the magnetic fluid was sealed in the quartz glass capillary.

[0026] The basic principle of the present invention for detecting magnetic field is as follows: a three-core optical fiber with side cladding removed, wherein the core with side cladding removed and the middle core form an MZI structure, the core with FBG written thereon is used as a temperature compensation structure, the light of a broadband light source is divided into three paths through a 1×3 coupler and enters the three cores of the three-core optical fiber respectively, the light in the core with side cladding removed is modulated by the magnetic field due to the refractive index characteristics of the magnetic fluid and is used as the detection light, the light in the middle core is used as the reference light, the light in the core with FBG written thereon is sensitive to temperature and is only modulated by temperature, the three paths of light are merged through a 3×1 coupler to cause interference, since both the magnetic field and temperature will change the refractive index of the magnetic fluid, thereby changing the output light intensity, and the FBG is only modulated by temperature, so the wavelength change of the output light is only related to the temperature, and the dual parameter measurement of the magnetic field and temperature can be realized by demodulating the changes of the output light intensity and the light wavelength.

Claims

1. A magnetic fluid and side-decladding three-core optical fiber magnetic field and temperature sensing structure, comprising a broadband light source (1), a 1×3 coupler (2), a first coupling module (3), a three-core optical fiber sensing structure (4), a second coupling module (5), a 3×1 coupler (6), and a detector (7), characterized in that: The 1×3 coupler (2) comprises an input optical fiber (2-1), a first output optical fiber (2-2), a second output optical fiber (2-3), and a third output optical fiber (2-4); the first coupling module (3) comprises a first optical waveguide (3-1), a second optical waveguide (3-2), and a third optical waveguide (3-3), which are 3 mm long, 1 mm wide, and 3 mm high; the three-core optical fiber sensing structure (4) comprises a cladding (4-1), a first fiber core (4-2), a second fiber core (4-3), a third fiber core (4-4), a decladding region (4-5) filled with a magnetic fluid, and a quartz glass capillary (4-6); the diameter of the cladding (4-1) is 125 μm, the diameter of the first fiber core (4-2) is 9.6 μm, and the diameter of the second fiber core (4-3) is 9.6 μm. The diameter of the fiber core (4-3) is 6 μm, the third fiber core (4-4) is written with FBG, and the diameter is 9.6 μm, the FBG is directly written by femtosecond laser, the period is 0.5 μm, the length is 500 μm, the angle formed by the first fiber core (4-2) and the third fiber core (4-4) and the second fiber core (4-3) is 120°, the spacing between the first fiber core (4-2) and the third fiber core (4-4) and the second fiber core (4-3) is 35.3 μm, the outer diameter of the quartz glass capillary (4-6) is 1 mm, and the inner diameter is 0.3 mm; the second coupling module (5) includes a fourth optical waveguide (5-1), a fifth optical waveguide (5-2), and a sixth optical waveguide (5-3), which are 3 mm long, 1 mm wide, and 3 mm high; the The 3×1 coupler (6) comprises a first input optical fiber (6-1), a second input optical fiber (6-2), a third input optical fiber (6-3), and an output optical fiber (6-4); the broadband light source (1) is coupled to the input optical fiber (2-1), the first output optical fiber (2-2) is coupled to the front end of the first optical waveguide (3-1), the second output optical fiber (2-3) is coupled to the front end of the second optical waveguide (3-2), the third output optical fiber (2-4) is coupled to the front end of the third optical waveguide (3-3), the rear end of the first optical waveguide (3-1) is coupled to the front end of the first fiber core (4-2), the rear end of the second optical waveguide (3-2) is coupled to the front end of the second fiber core (4-3), the rear end of the third optical waveguide (3-3) is coupled to the front end of the third fiber core (4-4 ), the rear end of the first fiber core (4-2) is coupled to the front end of the fourth optical waveguide (5-1), the rear end of the second fiber core (4-3) is coupled to the front end of the fifth optical waveguide (5-2), the rear end of the third fiber core (4-4) is coupled to the front end of the sixth optical waveguide (5-3), the rear end of the fourth optical waveguide (5-1) is coupled to the first input optical fiber (6-1), the rear end of the fifth optical waveguide (5-2) is coupled to the second input optical fiber (6-2), the rear end of the sixth optical waveguide (5-3) is coupled to the third input optical fiber (6-3), and the output optical fiber (6-4) is coupled to the detector (7); the decladding region (4-5) filled with magnetic fluid is obtained by etching above the first fiber core (4-2) using a femtosecond laser, and the depth is 22.The quartz glass capillary (4-6) is used to encapsulate a three-core optical fiber sensing structure (4), the light in the first fiber core (4-2) is used as detection light, the light in the second fiber core (4-3) is used as reference light, and another light path enters the third fiber core (4-4), the first fiber core (4-2), the second fiber core (4-3) and the decladding region (4-5) filled with magnetic fluid form an MZI structure, the adjustable refractive index characteristics of the magnetic fluid can be used to measure the magnetic field, the third fiber core (4-4) is sensitive to temperature, and can measure the temperature; the first optical waveguide (3-1) and the second optical waveguide (3-2) are 0.5 mm apart at the front end and 3 mm apart at the rear end. 5.3μm, the front ends of the third optical waveguide (3-3) and the second optical waveguide (3-2) are 0.5mm apart, and the rear ends are 35.3μm apart, and the angle formed by the rear ends of the first optical waveguide (3-1) and the third optical waveguide (3-3) and the rear end of the second optical waveguide (3-2) is 120°; the front ends of the fourth optical waveguide (5-1) and the fifth optical waveguide (5-2) are 35.3μm apart, and the rear ends are 0.5mm apart, the front ends of the sixth optical waveguide (5-3) and the fifth optical waveguide (5-2) are 35.3μm apart, and the rear ends are 0.5mm apart, and the angle formed by the front ends of the fourth optical waveguide (5-1) and the sixth optical waveguide (5-3) and the front end of the fifth optical waveguide (5-2) is 120°. .

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