CN206096413U - Insensitive magnetic field sensor of temperature based on optic fibre microcavity is filled to magnetic current body - Google Patents

Abstract

The utility model provides a temperature-insensitive magnetic field sensor based on the magnetic fluid filling the optical fiber microcavity. The magnetic field sensor includes a sensing head, a fiber optic coupler, a spectrometer and a wide-spectrum light source. The sensing head is composed of a cascaded air cavity and a magnetic fluid cavity, and the absolute value of the difference between the free spectral ranges of the air cavity and the magnetic fluid cavity is less than 1/10 of the magnetic fluid cavity. The wide-spectrum light emitted by the wide-spectrum light source enters the sensor head through the fiber coupler, and the light signal reflected by the sensor head enters the spectrometer through the fiber coupler. The optical signal reflected by the air cavity and the magnetic fluid cavity will produce a vernier effect, thereby greatly improving the measurement sensitivity of the magnetic field. The optical fiber support structure designed by the utility model is fixed on the single-mode optical fiber and the panda optical fiber on both sides of the magnetic fluid cavity, and the thermal expansion effect of the optical fiber support is used to offset the thermo-optical effect of the magnetic fluid, thereby realizing automatic temperature compensation. The magnetic field sensor has the advantages of automatic temperature compensation, compact structure, high sensitivity and large measurement range.

Description

Temperature-insensitive magnetic field sensor based on ferrofluid filled fiber optic microcavity

technical field

This patent relates to an optical magnetic field sensor, and specifically designs a temperature-insensitive magnetic field sensor in which a magnetic fluid fills an optical fiber microcavity.

Background technique

The optical fiber magnetic field sensor has many advantages such as good safety performance, anti-electromagnetic interference, non-contact measurement, real-time telemetry on site and wide dynamic measurement range. In the field of magnetic field measurement and analysis, fiber optic magnetic field sensors have attracted many scholars to conduct research, and will be widely used in the power detection industry.

Magnetic fluid is a kind of superparamagnetic liquid functional material produced in response to the development of modern science. It has almost no hysteresis phenomenon of solid magnetic substances. Its refractive index changes linearly with the external magnetic field within a certain range, and it is easy to combine with optical fiber Combine. The magnetic field sensing technology combining ferrofluid and F-P cavity can make up for the low Wald constant of the magnetic field sensor based on the Faraday effect and the difficulty of overcoming the hysteresis phenomenon of the magnetic field sensor based on the giant magnetostrictive material. However, since the thermo-optic coefficient of ferrofluid is very large, 2 orders of magnitude higher than that of quartz, the magnetic field sensor based on ferrofluid must eliminate the interference of temperature. At present, the method of cascading fiber gratings is usually used to realize the simultaneous measurement of temperature and magnetic field, such as literature 1 (Ri-Qing Lv, Yong Zhao, Dan Wang, and Qi Wang. Magnetic Fluid-Filled Optical Fiber Fabry–Pérot Sensor for Magnetic Field Measurement. IEEE Photonics Technology Letters, 26(3):217-219 (2014)). However, this method is not conducive to the miniaturization and integration of the sensor, the sensitivity is limited by the FBG measurement sensitivity, and it will shorten the measurement range of the interferometric magnetic field sensor. In addition, the invention patent (application number CN 102221679 A) discloses a magnetic field sensor based on a magnetic fluid filled photonic crystal fiber. Although the sensitivity of this sensor to temperature is reduced, it cannot achieve complete temperature compensation, and the sensor has low sensitivity. .

Contents of the invention

A brief overview of the present invention is given below in order to provide a basic understanding of certain aspects of the present invention. It should be understood that this summary is not an exhaustive summary of the invention. It is not intended to identify the key or important part of the present invention, nor is it intended to limit the scope of the present invention. Its purpose is merely to present some concepts in a simplified form as a prelude to the more detailed description that is discussed later.

In view of this, the utility model provides a temperature-insensitive magnetic field sensor based on ferrofluid-filled fiber microcavity to at least solve the problems of temperature cross-sensitivity and low sensitivity of the existing magnetic fluid-based magnetic field sensors.

According to one aspect of the present invention, a temperature-insensitive magnetic field sensor based on ferrofluid-filled fiber microcavity is provided. The temperature-insensitive magnetic field sensor based on ferrofluid-filled fiber microcavity includes a sensing head, an optical fiber coupler, a spectrometer And a broadband light source; the broadband light emitted by the broadband light source enters the sensor head after passing through the fiber coupler, and the light signal reflected by the sensor head enters the spectrometer through the fiber coupler.

Further, the sensing head includes a first single-mode fiber part, a first hollow-core fiber part, a second single-mode fiber part, a second hollow-core fiber part, a panda fiber part and a fiber holder part; wherein, the first single-mode fiber One end of the part is fused with one end of the first hollow-core fiber part, the other end of the first hollow-core fiber part is fused with one end of the second single-mode fiber part, and the inside of the first hollow-core fiber part is an air cavity; the second The other end of the single-mode fiber part is fused with one end of the second hollow-core fiber part, the other end of the second hollow-core fiber part is fused with the panda fiber part, and the inside of the second hollow-core fiber part is a magnetic fluid cavity; the panda fiber part There is a side hole on the side of the panda fiber part, and the side hole is only connected with one of the two air holes of the panda fiber part; the air hole connected with the side hole on the exposed end face of the panda fiber part is closed.

Further, the length of the first hollow-core fiber part is 50 μm-200 μm, and the wall thickness of the first hollow-core fiber part is 20 μm-50 μm; the length of the second hollow-core fiber part is 50 μm-100 μm, and the wall thickness of the second hollow-core fiber part is The wall thickness is 1 μm-10 μm; the outer diameter of the first single-mode fiber part, the first hollow-core fiber part, the second single-mode fiber part, the second hollow-core fiber part and the panda fiber part are all is 125 μm; the inside of the first hollow-core fiber part is an air cavity, and the inside of the second hollow-core fiber part is a magnetic fluid cavity, and the absolute value of the difference between the free spectral ranges of the air cavity and the magnetic fluid cavity is smaller than that of the magnetic fluid cavity 1/10 of the free spectral range; the diameter of the two air holes in the cladding of the panda fiber part is 10μm-20μm, the distance between the centers of the two air holes is 25μm-60μm, the length of the panda fiber part is 10mm-20mm, and the diameter of the side hole of the panda fiber The size is 5μm-20μm, and the side hole is 2mm-5mm away from the fusion point between the panda fiber part and the second hollow-core fiber part.

Further, one end of the fiber support is fixed on the second single-mode fiber, and the other end is fixed on the panda fiber, and the distance between the two fixed ends and the second hollow-core fiber is 1mm-10mm, and the cross-sectional size of the fiber support is 10mm× 10mm.

Further, the spectral range of the broadband light source is 1300nm-1600nm.

The temperature-insensitive magnetic field sensor based on the magnetic fluid filled optical fiber microcavity of the utility model adopts the cascading mode of the air cavity and the magnetic fluid cavity, and uses the cascaded cursor effect to make the sensor relative to the single magnetic fluid cavity magnetic field sensor (such as the invention patent CN 102221679 A) The sensitivity of magnetic field measurement is improved by 1-2 orders of magnitude. In addition, the magnetic field sensor based on the magnetic fluid filled optical fiber F-P cavity of the present invention designs an optical fiber support structure, which can completely offset the thermo-optical effect of the magnetic fluid by using the thermal expansion effect of the optical fiber support, and solves the problem of the magnetic field sensor based on the magnetic fluid filling type. cross-sensitivity issues. Compared to the method of serial FBG (such as literature 1, Ri-Qing Lv, Yong Zhao, Dan Wang, and QiWang. Magnetic Fluid-Filled Optical Fiber Fabry–Pérot Sensor for Magnetic Field Measurement. IEEE Photonics Technology Letters, 26(3):217 -219 (2014) ), this temperature compensation method has the advantages of compact structure, high sensitivity and large measurement range.

These and other advantages of the utility model will be more apparent through the following detailed description of the preferred embodiments of the utility model in conjunction with the accompanying drawings.

Description of drawings

The present invention can be better understood by referring to the following description given in conjunction with the accompanying drawings, wherein the same or similar reference numerals are used throughout the drawings to denote the same or similar components. The accompanying drawings, together with the following detailed description, are included in and form a part of this specification, and are used to further illustrate preferred embodiments of the utility model and explain principles and advantages of the utility model. In the attached picture:

Fig. 1 is a schematic structural view showing an example of a temperature-insensitive magnetic field sensor based on a magnetic fluid filled fiber microcavity of the present invention;

Fig. 2 is a schematic diagram showing a possible structure of the sensing head shown in Fig. 1;

Fig. 3 is a flow chart showing an exemplary process of the fabrication method for fabricating the sensor head of the present invention;

Fig. 4 shows the cascaded four-beam interference model of the air cavity and the magnetic fluid cavity;

Fig. 5 shows the variation of the spectral envelope of the cascaded interference between the air cavity and the magnetic fluid cavity.

It will be appreciated by those skilled in the art that elements in the figures are illustrated for simplicity and clarity only and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the drawings may be exaggerated relative to other elements to help to improve understanding of the embodiments of the present invention.

detailed description

Exemplary embodiments of the present utility model will be described below with reference to the accompanying drawings. In the interest of clarity and conciseness, not all features of an actual implementation are described in this specification. It should be understood, however, that in developing any such practical embodiment, many implementation-specific decisions must be made in order to achieve the developer's specific goals, such as meeting those constraints related to the system and business, and those Restrictions may vary from implementation to implementation. Moreover, it should also be understood that development work, while potentially complex and time-consuming, would at least be a routine undertaking for those skilled in the art having the benefit of this disclosure.

Here, it should also be noted that, in order to avoid obscuring the utility model due to unnecessary details, only the device structure and/or processing steps closely related to the solution according to the utility model are shown in the drawings, Other details that have little relationship with the utility model are omitted.

The embodiment of the utility model provides a temperature-insensitive magnetic field sensor based on a magnetic fluid-filled optical fiber microcavity. The temperature-insensitive magnetic field sensor based on a magnetic fluid-filled optical fiber microcavity includes a sensing head, an optical fiber coupler, a spectrometer and a wide Spectrum light source; the wide-spectrum light emitted by the wide-spectrum light source enters the sensor head after passing through the fiber coupler, and the light signal reflected by the sensor head enters the spectrometer through the fiber coupler.

An example of a temperature-insensitive magnetic field sensor 100 based on a magnetic fluid-filled fiber microcavity of the present invention will be described below in conjunction with FIG. 1 . As shown in FIG. 1 , the temperature-insensitive magnetic field sensor based on ferrofluid-filled optical fiber microcavity of the present invention includes a broadband light source 1-1, an optical fiber coupler 1-2, a sensor head 1-3 and a spectrometer 1-4. The broadband light source 1-1 is connected to the fiber coupler 1-2 through the fiber, the fiber coupler 1-2 is connected to the sensing head 1-3 through the fiber, and the spectrometer 1-4 is also connected to the fiber coupler 1-2 through the fiber. In this way, the broadband light emitted by the broadband light source 1-1 enters the sensor head 1-3 after passing through the fiber coupler 1-2, and the light signal reflected by the sensor head 1-3 enters the spectrometer 1 through the fiber coupler 1-2 -4. Wherein, the spectral range of the broadband light source 1-1 is, for example, 1300nm-1600nm.

According to one implementation, as shown in FIG. 2 , the sensing head 1-3 may include a first single-mode fiber part 2-1, a first hollow-core fiber part 2-2, a second single-mode fiber part 2-3, The second hollow-core fiber part 2-4, the panda fiber part 2-5 and the fiber holder part 2-6; wherein, one end of the first single-mode fiber part 2-1 is in phase with one end of the first hollow-core fiber part 2-2 Fusion splicing, the other end of the first hollow-core fiber part 2-2 is fused with one end of the second single-mode fiber part 2-3; the other end of the second single-mode fiber part 2-3 is connected to the second hollow-core fiber part 2- One end of 4 is fused, and the other end of the second hollow fiber part 2-4 is fused with the panda fiber part 2-5; there is a hole on the side of the panda fiber part 2-5, as the panda fiber part 2-5 Side hole, which only communicates with one of the two air holes of the panda fiber part 2-5; the exposed end of the panda fiber part 2-5 (that is, the end that is not fused with the second hollow-core fiber part 2-4 ) on the end face, the air hole connected to the side hole is closed (for example, the air hole is blocked by resin glue); the inside of the first hollow-core optical fiber part 2-2 is an air cavity, and the second hollow-core optical fiber part 2-4 The inside of the magnetic fluid cavity is a magnetic fluid cavity, and the absolute value of the difference between the free spectral range of the air cavity and the magnetic fluid cavity is less than 1/10 of the free spectral range of the magnetic fluid cavity; one end of the fiber support part 2-6 is fixed on the second single The other end of the mode fiber part 2-3 is fixed on the panda fiber part 2-5, and the distance between the two fixed ends and the second hollow-core fiber part 2-4 is 1mm-10mm.

Wherein, the length of the first hollow-core fiber part 2-2 is 50 μm-200 μm, and the wall thickness is 20 μm-50 μm, the length of the second hollow-core fiber part 2-4 is 50 μm-100 μm, and the wall thickness is 1 μm-10 μm; the first Single-mode fiber part 2-1 outer diameter, first hollow-core fiber part 2-2 outer diameter, second single-mode fiber part 2-3 outer diameter, second hollow-core fiber part 2-4 outer diameter, and panda fiber part 2 -5 have the same outer diameter, both 125 μm; the diameter of the two air holes in the cladding of the panda optical fiber part 2-5 is 10 μm-20 μm, and the distance between the centers of the two air holes is, for example, 25 μm-60 μm, and the length of the panda optical fiber part 2-5 is, for example, 10mm-20mm; the diameter of the side hole of the panda fiber is 5μm-20μm, and the distance from the side hole of the panda fiber to the fusion point of the panda fiber part 2-5 and the second hollow fiber part 2-4 is 2mm-5mm; the fiber holder 2-6 The section size is 10mm×10mm.

The temperature-insensitive magnetic field sensor based on the magnetic fluid filled optical fiber microcavity of the utility model adopts the cascading mode of the air cavity and the magnetic fluid cavity, and uses the cascade vernier effect to make the sensor relative to the single magnetic fluid cavity magnetic field sensor (for example, the invention patent CN 102221679 A) Magnetic field measurement sensitivity increased by 1-2 orders of magnitude. In addition, the magnetic field sensor based on the magnetic fluid filling the optical fiber F-P cavity of the utility model designs a fiber micro-stent structure, which uses the thermal expansion effect of the optical fiber support to offset the thermo-optical effect of the magnetic fluid, and solves the problem of the magnetic field sensor based on the magnetic fluid filling the F-P cavity. temperature cross-sensitivity issues.

The processing flow 300 of an example of the manufacturing method for manufacturing the sensor head of the present invention will be described below with reference to FIG. 3 .

As shown in FIG. 3 , after the processing flow 300 starts, step S310 is executed.

In step S310, the target first single-mode fiber is fused with the target first hollow-core fiber, using the same discharge intensity as when two single-mode fibers are fused. Then step S320 is executed.

In step S320, starting from the fusion point between the target first single-mode fiber and the target first hollow-core fiber, a section of hollow-core fiber is cut from the target first hollow-core fiber, and the free end of this section of hollow-core fiber is connected to the target The second single-mode fiber fusion splicing adopts 1/3 to 2/3 of the discharge intensity when splicing two single-mode fibers to form an air cavity between the target first single-mode fiber and the target second single-mode fiber. Then step S330 is executed.

In step S330, the target second single-mode optical fiber is fused with the target second hollow-core optical fiber, using the same discharge intensity as when two single-mode optical fibers are fused. Then step S340 is executed.

In step S340, starting from the fusion splicing point between the target second single-mode fiber and the target second hollow-core fiber, cut a section of hollow-core fiber on the target second hollow-core fiber, and connect the free end of this section of hollow-core fiber to the target For Panda fiber splicing, the discharge intensity used is 1/3 to 2/3 of that when splicing two single-mode fibers; move the fiber so that the electrode of the fusion splicer is aligned with the center of the second hollow-core fiber part, discharge 3-5 times, and use The discharge intensity is 1/3 to 2/3 of that when splicing two single-mode fibers, so that the wall thickness of the second hollow-core fiber is reduced to 1 μm-10 μm. Then step S350 is executed.

In step S350, starting from the fusion splicing point between the target second hollow-core fiber and the target panda fiber, cut a section of panda fiber on the target panda fiber. Then execute step S360.

In step S360, a side hole is opened on the side of the target panda optical fiber, so that the side hole communicates with only one of the two air holes of the target panda optical fiber. Then execute step S370.

In step S370, the free end face of the target panda optical fiber is enlarged under a microscope, and the air hole of the target panda optical fiber connected to the side hole is blocked. Then execute step S380.

In step S380, the free end of the target panda fiber is inserted into the magnetic fluid, and the side hole of the target panda fiber is exposed to the air, and the magnetic fluid is filled into the second hollow-core fiber part by capillary phenomenon, making it a magnetic fluid. fluid cavity. Then execute step S390.

In step S390, one end of the fiber holder is fixed to the second single-mode fiber, and the other end is fixed to the panda fiber. The processing flow 300 ends.

According to an implementation, the length of a section of hollow-core fiber cut from the target first hollow-core fiber is 50 μm-200 μm, the wall thickness is 20 μm-50 μm, and the length of the air cavity is 50 μm-200 μm; The length of a section of hollow-core optical fiber intercepted above is 50 μm-100 μm, the wall thickness is 1 μm-10 μm, and the length of the magnetic fluid cavity is 50 μm-100 μm; the optical path difference between the air cavity and the magnetic fluid cavity is less than 10 wavelengths; the outer surface of the target panda fiber The diameter and the outer diameter of the target first single-mode fiber, the outer diameter of the second single-mode fiber, the outer diameter of the first hollow-core fiber, and the outer diameter of the second hollow-core fiber are all 125 μm; the length of the target panda fiber is 10mm- 20mm, the diameter of the two pores in the cladding of the target panda fiber is 10μm-20μm, and the distance between the centers of the two pores is 25μm-60μm; the diameter of the side hole of the panda fiber is 5μm-20μm, and the distance between the side hole and the target Panda fiber is the second The splicing point of the hollow core fiber is 2mm-5mm.

The experimental data show that the sensor head made by the above method can not only improve the measurement sensitivity of the magnetic field, but also can compensate the influence of temperature on the magnetic field measurement.

Application example 1

An application example of the temperature-insensitive magnetic field sensor 100 based on the magnetic fluid filled fiber microcavity of the present invention is described below.

Under the action of a magnetic field, the magnetic fluid will produce a magnetorefractive effect, and its refractive index will change with the change of the magnetic field, which will lead to a change in the optical path of the fiber microcavity, thereby causing the interference spectrum of the fiber microcavity to translate. By detecting the interference spectrum The magnitude of the translation can obtain the magnitude of the measured magnetic field.

Broad-spectrum light source 1-1 adopts ASE light source, and its spectral range is 1300nm-1600nm. The broad-spectrum light emitted passes through 1×2 fiber coupler (as an example of fiber coupler 1-2) and then enters sensor head 1-3. (air cavity and magnetic fluid cavity), the optical signal reflected by the sensor head 1-3 enters the spectrometer 1-4 through the above-mentioned 1×2 fiber coupler, and then the signal is processed by the computer.

The temperature-insensitive magnetic field sensor 100 based on the magnetic fluid filled optical fiber microcavity of the present utility model is realized based on the four-beam interference principle of the air cavity and the magnetic fluid cavity cascaded, and the interference model is shown in Figure 4. Therefore, the spectrometer 1-4 The received interference spectrum signal can be expressed as:

Formula one:

In Formula 1, E ₁ , E ₂ , E ₃ and E ₄ are the complex amplitudes of the reflected light of the incident light on the reflecting surfaces E ₁ , E ₂ , E ₃ and E ₄ respectively, and I is the light intensity of the four-beam interference spectrum. When the free spectral range Δ λ FSR 1 of the air cavity and the free spectral range Δ λ _{FSR 2 of} the ferrofluid cavity satisfy Δ λ _{FSR 1} ≈ Δ λ _{FSR 2} , the four-beam interference spectrum presents a peak envelope phenomenon as shown in Figure 5, And the peak envelope moves with the change of the refractive index of the magnetic fluid. The relationship between the peak envelope shift Δ λ _BL and the refractive index of the magnetic fluid is

Formula two:

In formula 2, λ _i is the oscillation wavelength of the magnetic fluid cavity, and Δn _MF is the variation of the magnetic fluid refractive index. Compared with a single magnetic fluid cavity, the sensitivity of the cascaded air cavity and magnetic fluid cavity is increased by M times, and the value of M is generally 10≤M≤40 .

The magnetic fluid has a magnetostrictive property, and the magnetic field sensor 100 utilizes this property of the magnetic fluid to realize magnetic field sensing. Under the action of a magnetic field, the magnetic fluid will produce a magnetorefractive effect, and its refractive index will change with the change of the magnetic field, which will lead to the change of the optical path of the magnetic fluid cavity, so that the interference spectrum of the cascaded air cavity and the magnetic fluid cavity will shift , the magnitude of the measured magnetic field can be obtained by detecting the magnitude of the interference spectrum translation. The method of cascading the air cavity and the magnetic fluid cavity greatly improves the magnetic field measurement sensitivity, and the magnetic field measurement sensitivity is improved by 1-2 orders of magnitude compared with a single magnetic fluid cavity magnetic field sensor (such as the invention patent CN 102221679 A).

Application example 2

The temperature compensation principle of the sensor head of the temperature-insensitive magnetic field sensor 100 based on the magnetic fluid filled fiber microcavity of the present invention will be described below.

The sensor head structure is shown in Fig. 2. Both ends of the rectangular fiber holder are respectively fixed on the second single-mode fiber and the panda fiber, and both fixed ends are at a certain distance from the second hollow-core fiber.

The thermo-optic coefficient of ferrofluid is two orders of magnitude higher than that of quartz. Therefore, the magnetic field sensor based on ferrofluid cavity must consider the interference of temperature. This patent designs an optical fiber support structure, which uses the thermal expansion effect of the optical fiber support to offset the thermo-optical effect of the magnetic fluid. The principle of temperature compensation is analyzed as follows:

The change of the optical path length of the magnetic fluid cavity caused by the thermo-optic effect of the magnetic fluid is

Formula three:

In Equation 3, Δn is the change in the refractive index of the magnetic fluid caused by temperature, d is the length of the magnetic fluid cavity, α is the thermo-optic coefficient of the magnetic fluid, and ΔT is the change in temperature.

The metal whose thermal expansion is much larger than quartz is selected as the fiber support. When the temperature increases, the fiber support will pull the fiber to make it elongate. Since the wall thickness of the second hollow-core fiber is very thin (between 1µm and 10µm), its elastic modulus is much smaller than that of the Panda fiber. Therefore, under the tension of the fiber holder, the second hollow-core fiber The strain is much larger than the second single-mode fiber part and the panda fiber part, resulting in the change of the optical path length of the magnetic fluid cavity as

Formula four:

In Formula 4, n is the refractive index of the magnetic fluid, Δ d is the elongation of the magnetic fluid cavity under tension, γ is the thermal expansion coefficient of the fiber support material, and a< 1 is the elastic modulus of the single-mode fiber and the hollow-core fiber ratio, b< 1 is the ratio of the elastic modulus of the panda fiber to the hollow core fiber, and D is the inner length of the fiber holder.

When the thermal expansion effect and the thermo-optical effect of the magnetic fluid cancel each other out, the change of the optical path of the magnetic fluid cavity is zero, that is

Formula five:

Substitute formula 3 and formula 4 into formula 5 to get:

Formula six:

As long as Formula 6 is satisfied, automatic temperature compensation can be realized. By controlling the wall thickness of the second hollow-core optical fiber and the inner length of the optical fiber holder, it can be ensured that the sensing head satisfies Formula 6.

The temperature-insensitive magnetic field sensor based on the magnetic fluid filled optical fiber microcavity of the utility model completely offsets the thermo-optic effect of the magnetic fluid by the thermal expansion effect of the optical fiber bracket, and solves the problem of temperature cross sensitivity of the magnetic fluid filled magnetic field sensor. Compared to the method of serial FBG (such as literature 1, Ri-Qing Lv, Yong Zhao, Dan Wang, and Qi Wang. Magnetic Fluid-Filled Optical Fiber Fabry–Pérot Sensor for Magnetic Field Measurement. IEEE Photonics Technology Letters, 26(3): 217-219(2014) ), the temperature compensation method has compact structure, high sensitivity and large measurement range.

Application example 3

An application example for making a sensor head of the temperature-insensitive magnetic field sensor 100 based on ferrofluid-filled fiber microcavity of the present invention is described below.

First, splice common single-mode fiber (as an example of the target first single-mode fiber) with a hollow-core fiber (as an example of the target first hollow-core fiber), and the arc intensity used for fusion splicing is the same as that of splicing two common single-mode fibers under normal conditions. The strength of the fiber is the same.

Then, starting from the fusion point of ordinary single-mode fiber and hollow-core fiber, cut a section of hollow-core fiber with a length between 50 μm and 200 μm on the hollow-core fiber, and connect the free end of this section of hollow-core fiber to the ordinary single-mode fiber (Example as target second single-mode fiber) splicing. Starting from the fusion splicing point between the hollow core fiber and the ordinary single-mode fiber, cut a section of ordinary single-mode fiber with a length between 1mm and 10mm on the ordinary single-mode fiber.

Then, the common single-mode fiber is spliced to the hollow-core fiber (as an example of the target second hollow-core fiber) with the same arc intensity as that used to splice two common single-mode fibers under normal circumstances.

Then, move the optical fiber so that the electrode of the fusion splicer is aligned with the center of the second hollow-core optical fiber, and discharge 3-5 times. The wall thickness of the second hollow-core fiber is reduced to 1 μm-10 μm.

Then, starting from the fusion splicing point between the ordinary single-mode fiber and the second hollow-core fiber, cut off a section of hollow-core fiber with a length between 50 μm and 100 μm on the hollow-core fiber, and connect the free end of this section of hollow-core fiber to the panda fiber (as an example of a target Panda fiber) fusion splice. Among them, the outer diameter of Panda fiber, ordinary single-mode fiber and hollow core fiber is the same, all of which are 125 μm. The diameter of the double hole in the cladding of Panda fiber is 10 μm-20 μm, and the center-to-center distance of the double hole is 25 μm-60 μm. The discharge intensity used for fusion splicing of hollow core fiber and Panda fiber is 1/3 to 2/3 of the discharge intensity of splicing two common single-mode fibers under normal circumstances. In this way, a fiber microcavity with a length of 50 μm-100 μm (as an example of a target magnetic fluid cavity) will be formed between the ordinary single-mode fiber and the Panda fiber.

Then, starting from the fusion point of ordinary single-mode fiber and Panda fiber, cut a section of Panda fiber with a length of 10mm-20mm on the Panda fiber, and then cut it at a distance of 2mm-5mm from the fusion point of ordinary single-mode fiber and Panda fiber A small hole (which can be drilled by a femtosecond laser) is made on the side of the panda fiber, so that it is only connected to one of the two air holes of the panda fiber.

Then, enlarge the end face of the panda fiber under a microscope, and use resin glue to block the air hole of the panda fiber connected to the side hole.

Then, insert the free end of the panda fiber into the ferrofluid, ensure that the side hole of the panda fiber is exposed to the air, and use the capillary phenomenon to fill the ferrofluid into the fiber microcavity.

Finally, fix one end of the fiber holder (as an example of the target fiber holder) to the second single-mode fiber, and fix the other end to the panda fiber, and ensure that the distance between the two fixed ends is L and the two fixing points are to the second The distance of the hollow core fiber section is the same.

The resulting sensing head has a structure as shown in Figure 2. As shown in Figure 2, in the manufactured sensing head, the part of the target first single-mode optical fiber corresponds to the first single-mode optical fiber shown in Figure 2 The single-mode fiber part 2-1, the part of the target first hollow-core fiber corresponds to the first hollow-core fiber part 2-2 shown in Figure 2, and the part of the target second single-mode fiber corresponds to the second part shown in Figure 2 The single-mode fiber part 2-3, the part of the target second hollow-core fiber corresponds to the second hollow-core fiber part 2-4 shown in Figure 2, and the part of the target panda fiber corresponds to the part of the panda fiber shown in Figure 2- 5, and the part of the target fiber holder corresponds to the part 2-6 of the fiber holder shown in FIG. 2 .

While the invention has been described in terms of a limited number of embodiments, it will be apparent to a person skilled in the art having the benefit of the above description that other embodiments are conceivable within the scope of the invention thus described. In addition, it should be noted that the language used in the specification has been chosen primarily for the purpose of readability and teaching rather than to explain or define the subject matter of the present invention. Accordingly, many modifications and alterations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the appended claims. Regarding the scope of the present utility model, the disclosure of the present utility model is illustrative rather than restrictive, and the scope of the present utility model is defined by the appended claims.

Claims (5)

1. based on the temperature insensitive magnetic field sensor of magnetic fluid filling fiber microcavity, it is characterized in that, described based on the temperature insensitive magnetic field sensor of magnetic fluid filling fiber optic microcavity comprises sensor head, optical fiber coupler, spectrometer and wide-spectrum light source; Wherein, the sensing head includes a first single-mode fiber part, a first hollow-core fiber part, a second single-mode fiber part, a second hollow-core fiber part, a panda fiber part and a fiber support part; one end of the fiber support fixed on the second single-mode fiber part, the other end of the fiber holder is fixed on the panda fiber part, and the distance between the two fixed ends and the second hollow-core fiber part is 1mm-10mm ; Wherein, the inside of the first hollow-core fiber part is an air cavity, the inside of the second hollow-core fiber part is a magnetic fluid cavity, and the absolute value of the difference between the free spectral ranges of the air cavity and the magnetic fluid cavity is smaller than the 1/10 of the free spectral range of the magnetic fluid cavity; Wherein, the broadband light emitted by the broadband light source enters the sensing head after passing through the optical fiber coupler, and the light signal reflected by the sensing head enters the spectrometer through the optical fiber coupler. 2. The temperature-insensitive magnetic field sensor based on ferrofluid-filled fiber microcavity according to claim 1, wherein one end of the first single-mode fiber part is fused with one end of the first hollow-core fiber part , the other end of the first hollow-core fiber part is fused with one end of the second single-mode fiber part, and the inside of the first hollow-core fiber part is an air cavity; the other end of the second single-mode fiber part It is fused with one end of the second hollow-core fiber part, and the other end of the second hollow-core fiber part is fused with the panda fiber part, and the inside of the second hollow-core fiber part is a magnetic fluid cavity; There is a side hole on the side of the panda fiber part, which only communicates with one of the two air holes of the panda fiber part; the exposed end surface of the panda fiber part communicates with the side hole The pores are closed. 3. The temperature-insensitive magnetic field sensor based on ferrofluid filled fiber microcavity according to any one of claims 1-2, wherein the length of the first hollow-core fiber part is 50 μm-200 μm, and the The wall thickness of the first hollow-core fiber part is 20 μm-50 μm; the length of the second hollow-core fiber part is 50 μm-100 μm, and the inner diameter of the second hollow-core fiber part is 1 μm-10 μm; the first hollow-core fiber part The outer diameter of the optical fiber portion, the outer diameter of the second hollow-core optical fiber portion, the outer diameter of the first single-mode optical fiber portion, the outer diameter of the second single-mode optical fiber portion, and the outer diameter of the panda optical fiber portion Both are 125 μm; the length of the panda optical fiber part is 10mm-20mm, the diameter of the two air holes in the cladding of the panda optical fiber part is 10 μm-20 μm, and the distance between the centers of the two air holes is 25 μm-60 μm; the panda optical fiber The diameter of the side hole is 5 μm-20 μm, and the side hole is 2 mm-5 mm away from the fusion point between the panda fiber part and the hollow core fiber part. 4 . The temperature-insensitive magnetic field sensor based on ferrofluid-filled fiber microcavity according to claim 1 , wherein the cross-sectional size of the fiber holder is 10 mm×10 mm. 5 . The temperature-insensitive magnetic field sensor based on ferrofluid-filled fiber microcavity according to claim 1 , wherein the spectral range of the broadband light source is 1300nm-1600nm.