A magnetic field and temperature sensor based on a three-core hollow optical fiber filled with magnetic fluid

Abstract

The present invention proposes a three-core hollow optical fiber magnetic field and temperature sensor based on magnetic fluid filling, with a three-core optical fiber sensing module as a sensitive element, the three-core optical fiber sensing module includes an outer cladding, an inner cladding, a first hollow core, a second hollow core, and a third hollow core, the three hollow cores are arranged at 120 degrees in space, the magnetic liquid and the glycerol liquid are respectively filled into the first hollow core and the third hollow core to obtain two liquid waveguides, the second hollow core is not filled, the detection light output by the two liquid waveguides interferes with the reference light output by the second hollow core, two interference spectra are obtained by a spectrum analyzer, and the magnetic field sensitivity characteristics of the magnetic fluid and the temperature sensitivity characteristics of glycerol are used to detect the drift of the interference image to infer the changes in the magnetic field and temperature. The optical fiber sensor not only achieves the purpose of simultaneous measurement of the dual parameters of magnetic field and temperature, but also has temperature compensation capability, thereby improving the accuracy of magnetic field measurement.

Description

Technical Field

[0001] The present invention belongs to the technical field of optical fiber sensing. A three-core hollow optical fiber magnetic field and temperature sensor based on magnetic fluid filling is designed. The hollow optical fiber is filled with magnetic fluid and glycerol. The magnetic field sensitivity characteristics of the magnetic fluid and the temperature sensitivity characteristics of glycerol are utilized to realize the simultaneous measurement of dual parameters. Background Art

[0002] Magnetic fields or information related to magnetic fields exist in many places in nature and human social life. Magnetic sensors are devices that can convert various magnetic fields and their changing quantities into electrical signal outputs. Therefore, the tasks of detecting, collecting, storing, converting, and monitoring various magnetic fields and various information carried in magnetic fields are also very important. In recent years, with the rapid development of informatization, industrialization, transportation, electronic technology, etc., magnetic field sensors have been developed and applied more. At present, with the increasingly low prices and types of optical fiber devices, and the increasingly mature optical fiber communication technology, a new type of sensor technology has emerged, namely optical fiber sensing technology. Combining the two forms a new type of sensor, namely optical fiber magnetic field sensor, which inherits the advantages of both, and has outstanding advantages such as small size, corrosion resistance, strong anti-electromagnetic interference ability, convenience for distributed multi-point detection, and all-optical transmission. It has become a research hotspot in the field of magnetic field sensing.

[0003] Magnetic fluid is mainly composed of nanomagnetic particles, base fluid and surfactant. It is a new type of intelligent material with both fluidity and strong magnetism. It has rich optical properties, such as tunable refractive index, tunable transmittance, birefringence effect and thermal lens effect. At present, many optical devices based on magnetic fluid have been studied on the basis of experiments. The optical sensing principle and application based on magnetic fluid are a hot research topic at home and abroad.

[0004] In today's production applications and life, most optical sensors use ordinary optical fibers. The optical fiber sensors made with ordinary optical fibers as basic components can generally only measure a single variable, and there will be cross-sensitivity problems when measuring dual parameters, which greatly limits the performance improvement of optical fiber sensors in applications. In response to the above-mentioned problems, the present invention proposes a three-core hollow optical fiber magnetic field and temperature sensing structure based on magnetic fluid filling, which not only realizes the dual parameter measurement of magnetic field and temperature, but also has temperature compensation capability, thereby improving the measurement accuracy of the magnetic field. Summary of the invention

[0005] In response to the above-mentioned problems, the present invention proposes a three-core hollow optical fiber magnetic field and temperature sensor based on magnetic fluid filling. The sensor not only realizes the dual parameter measurement of magnetic field and temperature, but also has temperature compensation capability, thereby improving the accuracy of magnetic field measurement.

[0006] To achieve the above object, the present invention adopts the following technical solution:

[0007] like Figure 1 As shown, a three-core hollow fiber magnetic field and temperature sensor based on magnetic fluid filling includes an LD light source (1), a 1×3 coupler (2), a first optical path matching module (3), a three-core optical fiber sensing module (4), a second optical path matching module (5), an optical path interference module (6), a first receiver (7-1), a second receiver (7-2), and a spectrum analyzer (8). Figure 2 and Figure 3 As shown, the three-core optical fiber sensing module (4) comprises an outer cladding (4-1), an inner cladding (4-2), a first hollow core (4-3), a second hollow core (4-4), and a third hollow core (4-5), wherein the first hollow core (4-3) is filled with magnetic fluid, the second hollow core (4-4) is not filled, and the third hollow core (4-5) is filled with glycerol, and the spatial positions of the three hollow optical fibers are 120° to each other.

[0008] The three-core optical fiber sensing module (4) has a length of 6 to 8 cm, wherein the diameter of each hollow core is 50 to 100 μm.

[0009] The magnetic fluid filled in the first hollow optical fiber (4-3) is a water-based magnetic fluid, with Fe3O4 nanoparticles as magnetic particles and linoleic acid as a surfactant.

[0010] The length of the two ends of the first hollow core (4-3) and the third hollow core (4-3) not filled with liquid is 1 to 2 mm.

[0011] The present invention designs a three-core hollow optical fiber magnetic field and temperature sensor based on magnetic fluid filling, wherein the sensing probe is based on a customized three-core hollow optical fiber, the three cores have the same diameter, and the spatial positions are 120° to each other. A double cladding structure is used to reduce transmission loss, and magnetic liquid and glycerol liquid are respectively filled into the first hollow core and the third hollow core, and the output light of the two liquid waveguides is used as detection light one and detection light two to interfere with the reference light output by the second hollow core. When the temperature and magnetic field act together, the interference spectrum generated by the interference of the detection light one and the reference light responds to both the external magnetic field change and the temperature change. The change of the magnetic field causes the change of the refractive index of the magnetic fluid, thereby bringing about the change of the optical path difference and causing the interference peak to drift. At the same time, the change of temperature will also affect the change of the refractive index of the magnetic fluid, which will also cause the interference peak to drift. However, the interference peak generated by the detection light two and the reference light does not respond to the change of the external magnetic field, but only responds to the temperature change. The temperature change causes the refractive index of glycerol to change, which in turn causes the change of the optical path difference between the detection light two and the reference light, and finally causes the interference peak generated by the detection light two and the reference light to drift. Therefore, the temperature change can be calculated by detecting the drift of the interference peak generated by the detection light 2 and the reference light, and the temperature compensation can be further performed for the interference spectrum generated by the detection light 1 and the reference light, thereby reducing the influence of temperature on the magnetic field measurement. The sensor not only achieves the purpose of simultaneous measurement of the magnetic field and temperature, but also has the ability of temperature compensation, thus improving the accuracy of magnetic field measurement.

[0012] The formula for the optical path difference between the detection light 1 and detection light 2 and the reference light is:

[0013] δ1=(n1-n0)L

[0014] δ2=(n2-n0)L

[0015] Where n0 is the refractive index of air, n1 is the refractive index of magnetic fluid, n2 is the refractive index of glycerol, and L is the sensitive length of the three-core optical fiber. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 Schematic diagram of a three-core hollow optical fiber magnetic field and temperature sensor filled with magnetic fluid;

[0017] Figure 2 This is a schematic diagram of the three-core optical fiber sensing module of the present invention;

[0018] Figure 3 A cross-sectional view of a three-core hollow fiber magnetic field and temperature sensor filled with magnetic fluid. DETAILED DESCRIPTION

[0019] The present invention will be described in further detail below in conjunction with the accompanying drawings.

[0020] In the accompanying drawings, there are an LD light source (1), a 1×3 coupler (2), a first optical path matching module (3), a three-core optical fiber sensor module (4), a second optical path matching module (5), an optical path interference module (6), a first receiver (7-1), a second receiver (7-2), and a signal demodulator (8). The LD light source (1) is connected to the 1×3 coupler (2) through an output optical fiber (2-1), the right end of the 1×3 coupler (2) is connected to the left end of the first optical path matching module (3), the left and right ends of the three-core optical fiber sensor module (4) are fused to the first optical path matching module (3) and the second optical path matching module (5), the right end of the second optical path matching module (5) is connected to the left end of the optical path interference module (6), the right end of the optical path interference module (6) is connected to the first receiver (7-1) and the second receiver 2 (7-2), and the signals output by the first receiver and the second receiver are transmitted to the spectrum analyzer (8) for processing.

[0021] The specific implementation steps are as follows:

[0022] Step 1: Fiber end face pretreatment

[0023] Select a three-core optical fiber of appropriate length, cut its upper and lower end faces flat with a fiber optic cutter, and then clean the optical fiber with an ultrasonic cleaner.

[0024] Step 2: Fill the first hollow core with magnetic fluid

[0025] Due to the high viscosity of magnetic fluid, the first hollow core is filled with a syringe. Under an optical microscope, the optical fiber is first placed at an angle, the syringe is inserted into the first hollow core, and the magnetic fluid is then poured into the syringe. By pressurizing the syringe, the magnetic fluid is injected into the core to obtain the filled optical fiber, and then the first hollow core is sealed with high-transmittance ultraviolet glue. During the filling process, it cannot be carried out too quickly to prevent bubbles from entering the fiber core due to excessive squeezing, which will cause discontinuous filling of the fiber core liquid column.

[0026] Step 3: Fill the third hollow core with glycerin

[0027] Under an optical microscope, first seal the two ends of the second hollow core with high-transmittance UV glue, then insert one end of the three-core optical fiber vertically into the bottle containing glycerin, and use the capillary action of the air inside the optical fiber and the external space to absorb the glycerin into the third hollow core. Then, seal the two end ports of the third hollow core with high-transmittance UV glue, and clean it with alcohol after curing is completed.

[0028] Step 4: Prepare the optical path matching module

[0029] Two optical path matching modules with the same specifications are prepared by semiconductor micromachining technology. One end has three interfaces connected to three optical fibers, and the other end has an end face structure consistent with the three-core hollow optical fiber.

[0030] Step 5: Coupling the three-core hollow fiber with the optical path matching module

[0031] The first optical path matching module and the three-core hollow optical fiber are coaxially fused. The fusion is carried out using the manual mode of the optical fiber fusion splicer to firmly fuse the liquid-filled three-core optical fiber and the first optical path matching module to ensure that the liquid does not leak. The other end is fused to the second optical path matching module in the same way.

[0032] The working principle of the present invention is as follows: the laser light emitted by the LD light source is divided into three paths through a 1×3 coupler and enters the three cores of the three-core optical fiber respectively; when outputting, the light in the first hollow core (4-3) is used as the detection light 1, the light in the second hollow core (4-4) is used as the reference light, and the light in the third hollow core (4-5) is used as the detection light 2; the three paths of light enter the optical path interference module, the detection light 1 is superimposed on the reference light and interferes with it, and the detection light 2 is superimposed on the reference light and interferes with it; the optical signals after interference are respectively received by the first receiver and the second receiver; finally, the signals output by the first receiver and the second receiver are transmitted to the spectrum analyzer (8) for processing; by monitoring the movement of the two interference peaks, the changes of the magnetic field and the temperature can be calculated; and the magnetic field measurement result can be temperature compensated by software calculation to reduce the influence of temperature on the magnetic field measurement.

Claims

1. A three-core hollow fiber magnetic field and temperature sensor based on magnetic fluid filling, comprising an LD light source (1), a 1×3 coupler (2), a first optical path matching module (3), a three-core optical fiber sensing module (4), a second optical path matching module (5), an optical path interference module (6), a first receiver (7-1), a second receiver (7-2), and a spectrum analyzer (8), characterized in that: The three-core optical fiber sensing module (4) is 6 to 8 cm long and comprises an outer cladding (4-1), an inner cladding (4-2), a first hollow core (4-3), a second hollow core (4-4), and a third hollow core (4-5). The diameter of each hollow core is 50 to 100 μm. The first hollow core (4-3) is filled with magnetic fluid, the second hollow core (4-4) is not filled, and the third hollow core (4-5) is filled with glycerol. The spatial positions of the three hollow optical fibers are 120° to each other, and the center of each hollow core is located at half the radius of the three-core optical fiber. The first hollow core (4-3) is filled by a syringe, and the output light of the first hollow core (4-3) is The output light of the second hollow core (4-4) interferes, and the adjustable refractive index characteristic of the magnetic fluid can be used to measure the magnetic field. The third hollow core (4-5) is filled by capillary action, and the output light of the third hollow core (4-5) interferes with the output light of the second hollow core (4-4). The temperature sensitivity of glycerol can be used to measure the temperature. The magnetic fluid filled in the first hollow core (4-3) is a water-based magnetic fluid, with Fe3O4 nanoparticles as magnetic particles and linoleic acid as a surfactant. The length of the first hollow core (4-3) and the third hollow core (4-5) that is not filled with liquid is 1 to 2 mm.

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