Cladding rectangular groove filled liquid Bragg fiber grating magnetic field probe

Abstract

The present invention belongs to the field of fiber grating sensing technology, and specifically relates to a Bragg fiber grating magnetic field probe with a rectangular groove engraved on the cladding and filled with liquid, which includes a broadband light source, a connecting optical fiber, an optical fiber circulator, a sensing probe, a matching liquid, a 1×2 optical fiber coupler 1, a filter LPG1, a wavelength division multiplexer, a 1×2 optical fiber coupler 2, a filter LPG2, a photodetector and a signal processor; the optical fiber cladding at the left end of the sensing probe is coated with a silver metal film on the surface of the optical fiber cladding by vacuum sputtering coating technology to form a sensing FBG1; the optical fiber cladding at the right end of the sensing probe is processed into a rectangular groove by femtosecond laser micromachining technology, and filled with magnetic fluid to form a sensing FBG2. The advantages of the present invention are simple structure, manufacturing process and working principle, the magnetic fluid changes its own refractive index as the magnetic field intensity changes, so that the resonant wavelength of the Bragg fiber grating changes, and the measurement of the magnetic field intensity is achieved by demodulating the change of the resonant wavelength.

Description

Technical Field

[0001] The invention belongs to the technical field of optical fiber grating sensing, and in particular relates to an optical fiber Bragg grating magnetic field probe with a cladding-carved rectangular groove filled with liquid. Background Art

[0002] Fiber Bragg grating is a classic fiber passive device, which is essentially a periodic modulation of the refractive index of the fiber core to form a transmission or reflection narrowband filter. According to the period of the refractive index modulation, the fiber Bragg grating with a grating period less than 1μm is called a short-period fiber Bragg grating (FBG); the fiber Bragg grating with a grating period of tens or hundreds of microns is called a long-period fiber Bragg grating (LPFG). With the continuous improvement of the understanding of fiber Bragg grating, fiber Bragg grating not only has the advantages of low cost, strong anti-electromagnetic interference ability, good stability and small size, but can also be designed into sensors for measuring different physical quantities based on relevant physical foundations, such as magnetic field, temperature, liquid level and strain.

[0003] Most of the traditional magnetic field sensors, such as Hall sensors, fluxgate sensors and induction coil sensors, have the disadvantages of large size, complex structure and susceptibility to complex environmental influences, making them difficult to apply in special fields. Fiber Bragg grating magnetic field sensors not only have the advantages of fiber Bragg gratings mentioned above and can be applied in complex environments, but also can design different magnetic field sensors according to different sensing mechanisms to meet the needs. For example, the fiber Bragg grating can be combined with magnetic fluid, grooves can be cut in the fiber cladding and filled with magnetic fluid, and the refractive index of the magnetic fluid can be changed under an external magnetic field. When the direction of the magnetic field is perpendicular to the direction of the transmitted light, the refractive index decreases with the increase of the external magnetic field, thereby causing the wavelength of the output light to change. The signal is demodulated by edge filtering and demodulation technology to achieve the measurement of magnetic field strength.

[0004] The present invention uses a short-period Bragg fiber grating, and then uses femtosecond laser micromachining technology to remove part of the fiber cladding, and then silver metal film is plated on the surface of the fiber cladding area where the fiber cladding is not removed, and then it is packaged with a quartz glass capillary, and a syringe is used to fill the cladding with magnetic fluid to make a sensor probe, and finally the edge filter demodulation technology is used to demodulate the output light wave intensity and wavelength size changes to achieve the measurement of the magnetic field strength. Summary of the invention

[0005] The invention aims to realize the measurement of magnetic field intensity and designs a Bragg fiber grating magnetic field probe with rectangular grooves engraved on the cladding and filled with liquid.

[0006] A Bragg fiber grating magnetic field probe with rectangular grooves in the cladding and filled with liquid, the structure of which comprises a broadband light source (1), a connecting optical fiber (2), an optical fiber circulator (3), a sensing probe (4), a matching liquid (5), a 1×2 optical fiber coupler 1 (6), a filter LPG1 (7), a wavelength division multiplexer (8), a 1×2 optical fiber coupler 2 (9), a filter LPG2 (10), a photodetector (11) and a signal processor (12), characterized in that: light emitted by the broadband light source (1) passes through the connecting optical fiber (2), enters the optical fiber circulator (3) from port 1, and then enters the sensing probe (4) from port 2 of the optical fiber circulator, a part of the light wave is reflected back to the optical fiber circulator (3) from port 2, and another part of the light wave enters the matching liquid. The light waves are absorbed in the liquid (5), and the reflected light waves enter the wavelength division multiplexer (8) from the port 3, and then are divided into two beams of light, respectively passing through the 1×2 optical fiber coupler 1 (6) and the 1×2 optical fiber coupler 2 (9), and then passing through the filter LPG1 (7) and the filter LPG2 (10), respectively. The light signals are detected by the photodetector (11), and finally the signal is analyzed by the signal processor (12); the structure of the sensing probe (4) includes an optical fiber core (4-1), an optical fiber cladding (4-2), a cladding region filled with liquid (4-3), a quartz glass capillary (4-4), a liquid filling channel (4-5), a sensing FBG1 (4-6), a silver metal film (4-7) and a sensing FBG2 (4-8). The diameter of the optical fiber core (4-1) is 8 μm, and the core is engraved with a Bragg grating. The diameter of the optical fiber cladding (4-2) is 125 μm. The cladding region (4-3) filled with liquid has a depth of 40 μm, a length of 5 mm, and a width of 60 μm. The quartz glass capillary (4-4) is used to encapsulate the sensor probe (4), and has an inner diameter of 135 μm and an outer diameter of 1000 μm. The liquid-filled channel (4-5) is formed by femtosecond laser processing technology. The silver metal film (4-7) is plated by vacuum sputtering and has a thickness of 200 nm.

[0007] The total length of the sensing probe (4) is 1 cm, and its structure includes a sensing FBG1 (4-6) whose optical fiber cladding is plated with a silver metal film (4-7) and a sensing FBG2 (4-8) whose optical fiber cladding is removed and filled with a magnetic sensitive liquid, each of which is 5 mm in length, and the optical fiber core Bragg grating period is 520 nm, the core refractive index is 1.465, and the central wavelength is 1523 nm.

[0008] The liquid in the liquid-filled cladding area (4-3) is a magnetic fluid, and there are two liquid filling channels (4-5) on the surface processed by femtosecond laser micromachining technology. The magnetic fluid is filled into the cladding area through one liquid filling channel (4-5) using a syringe, and when liquid overflows from the other liquid filling channel (4-5), it indicates that it is full. Finally, UV glue is applied to the port of the liquid filling channel (4-5), and then ultraviolet light is used for packaging. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1 This is a schematic diagram of the working structure of the cladding rectangular groove filled with liquid Bragg fiber grating magnetic field probe of the present invention;

[0010] Figure 2 The figure is a schematic diagram of the specific structure of the sensing probe described in the present invention. DETAILED DESCRIPTION

[0011] The following is a further detailed description of the present invention in conjunction with the accompanying drawings and specific implementation steps.

[0012] like Figure 1 As shown, a broadband light source (1), a connecting optical fiber (2), an optical fiber circulator (3), a sensor probe (4), a matching liquid (5), a 1×2 optical fiber coupler 1 (6), a filter LPG1 (7), a wavelength division multiplexer (8), a 1×2 optical fiber coupler 2 (9), a filter LPG2 (10), a photodetector (11) and a signal processor (12) are connected as shown in FIG. Figure 1 .

[0013] like Figure 2 As shown, the optical fiber core (4-1), the optical fiber cladding (4-2), the liquid-filled cladding region (4-3), the quartz glass capillary (4-4), the liquid-filled channel (4-5), the sensing FBG1 (4-6), the silver metal film (4-7) and the sensing FBG2 (4-8).

[0014] The sensor probe (4) of the present invention is combined with Figure 2 The structure shown in the figure, the specific production process is as follows:

[0015] Step 1: Fiber end face pretreatment

[0016] The present invention selects a common Bragg fiber grating with a core diameter of 8 μm, a cladding diameter of 125 μm, a Bragg grating period of 520 nm, a central wavelength of 1523 nm and a total length of 1 cm. The coating layer on the surface of the Bragg fiber grating is removed, and then the single-mode optical fiber is cleaned with an ultrasonic cleaning machine.

[0017] Step 2: Femtosecond laser removes part of the fiber cladding

[0018] Fix the Bragg fiber grating in step 1 onto the four-dimensional precision moving platform to ensure that it is placed parallel to the platform; set the relevant parameters of the femtosecond laser; then use a computer to control the movement of the moving platform to make the surface of the optical fiber cladding of the sensor probe move parallel to the platform, so as to remove the 5mm long optical fiber cladding at the right end of the optical fiber, and form a rectangular groove with a depth of 40μm, a length of 5mm, and a width of 60μm in the optical fiber cladding, such as Figure 2The structure is shown.

[0019] Step 3: Metal coating on the surface of optical fiber cladding

[0020] The Bragg fiber grating in step 2 is coated with a silver metal film on the left end surface of the optical fiber of the sensor probe by vacuum sputtering coating technology, and the right end of the optical fiber cladding of the sensor probe is covered with a high temperature resistant tape. The vacuum sputtering coating is performed four times. After each coating, the sensor probe is rotated 90° and then re-coated to achieve the purpose of uniform coating. The thickness of the silver metal film is 200nm and the length is 5mm.

[0021] Step 4: Encapsulating the Fiber and Cladding Filling Liquid

[0022] First, fix the quartz glass capillary and the sensor probe parallel to the platform surface on a four-dimensional precision moving platform, and use the computer-controlled platform to slowly insert the Bragg fiber grating processed in step three into the quartz glass capillary. After the insertion is completed, apply UV glue to the left and right ends, and then irradiate with ultraviolet light for packaging. Using femtosecond laser micromachining technology, a filling liquid channel is processed on the surface of the quartz glass capillary just above the rectangular groove area, 1 mm close to the right edge, and then move 3 mm to the left parallel to this filling liquid channel to process a second filling liquid channel. The two processed filling liquid channels serve as channels for filling magnetic fluid. Finally, use a syringe to inject magnetic fluid into the rectangular groove from any filling liquid channel. When magnetic fluid overflows from the other filling liquid channel, it indicates that the filling is complete. Finally, apply UV glue to the two gaps and irradiate with ultraviolet light for packaging. The inner diameter of the quartz glass capillary is 135μm and the outer diameter is 1000μm. After the above manufacturing process steps are successfully completed, the sensor probe is prepared. According to Figure 1 Structure to connect devices.

[0023] The resonant wavelength formula of the Bragg fiber grating is:

[0024] λ0=2n eff Λ

[0025] where n eff is the effective refractive index of the Bragg fiber grating, Λ is the period of the Bragg fiber grating, and λ0 is the central resonant wavelength. The surface of the optical fiber cladding of the sensor FBG1 is coated with a silver metal film. When the external temperature changes, the silver metal film expands and contracts, causing the Bragg fiber grating period of the sensor FBG1 to change, and the resonant wavelength will also change accordingly. The change in the resonant wavelength can reflect the size of the external temperature.

[0026] The filling liquid is a magnetic fluid, which is sensitive to changes in the external magnetic field. Its refractive index will change with changes in the magnetic field strength. The resonant wavelength of the sensor FBG2 whose optical fiber cladding is filled with magnetic fluid will change according to changes in the magnetic field strength.

[0027] The wavelength division multiplexer is specially designed. Two different transmission windows are designed according to the resonant wavelengths of the sensor FBG1 and the sensor FBG2, so that the resonant wavelength λ1 and the resonant wavelength λ2 can enter different demodulation systems respectively.

[0028] The resonant wavelength λ1 passes through the 1×2 fiber coupler 1 and is then divided into two beams of light. One beam of light directly enters the photodetector as a reference optical path; the other beam of light passes through the filter LPG1, so that the resonant wavelength λ1 falls on the right linear part of the transmission spectrum of the filter LPG1 and is subjected to linear filtering. The processing of the resonant wavelength λ2 is similar to that of the resonant wavelength λ1.

[0029] The basic working principle of the cladding rectangular groove filled liquid Bragg fiber grating magnetic field probe of the present invention is: the light emitted by the broadband light source enters the optical fiber circulator from port 1, and then enters the sensing probe from port 2 of the optical fiber circulator, the sensing FBG1 is sensitive to the external temperature and the sensing FBG2 is sensitive to the external magnetic field and reflects specific wavelengths respectively, the reflected light returns to the optical fiber circulator from port 2, and then enters the wavelength division multiplexer from port 3 of the optical fiber circulator, is divided into two beams of light and enters different demodulation systems, linear filtering is performed on the resonant wavelength λ1 and the resonant wavelength λ2 respectively, and finally passes through the photoelectric detector, and then the signal processor performs signal processing and analysis to achieve the purpose of measuring the magnetic field intensity.

Claims

1. A Bragg fiber grating magnetic field probe with rectangular grooves in the cladding and filled with liquid, comprising a broadband light source (1), a connecting optical fiber (2), an optical fiber circulator (3), a sensing probe (4), a matching liquid (5), a 1×2 optical fiber coupler 1 (6), a filter LPG1 (7), a wavelength division multiplexer (8), a 1×2 optical fiber coupler 2 (9), a filter LPG2 (10), a photodetector (11) and a signal processor (12), characterized in that: Light emitted by a broadband light source (1) passes through a connecting optical fiber (2), enters an optical fiber circulator (3) from port 1, and then enters a sensor probe (4) from port 2 of the optical fiber circulator. A portion of the light wave is reflected back to the optical fiber circulator (3) from port 2, and another portion of the light wave enters a matching liquid (5) and is absorbed. The reflected light wave enters a wavelength division multiplexer (8) from port 3, and then is divided into two beams of light, which respectively pass through a 1×2 optical fiber coupler 1 (6) and a 1×2 optical fiber coupler 2 (9), and then pass through a filter LPG1 (7) and a filter LPG2 (10), respectively. The optical signal is detected by a photodetector (11), and finally is transmitted by a signal The sensor probe (4) is structured to include an optical fiber core (4-1), an optical fiber cladding (4-2), a cladding region filled with liquid (4-3), a quartz glass capillary (4-4), a liquid-filled channel (4-5), a sensing FBG1 (4-6), a silver metal film (4-7) and a sensing FBG2 (4-8). The diameter of the optical fiber core (4-1) is 8 μm, and a Bragg grating is engraved on the core. The diameter of the optical fiber cladding (4-2) is 125 μm. The depth of the cladding region (4-3) filled with liquid is 40 μm, the length is 5 mm, and the width is 60 μm. The quartz glass capillary (4-4) is used to encapsulate the sensor probe (4), and has an inner diameter of 135 μm and an outer diameter of 1000 μm. The filling liquid channel (4-5) is formed by femtosecond laser processing technology. The silver metal film (4-7) is plated by vacuum sputtering and has a thickness of 200 nm. The sensor FBG1 (4-6) can measure the size of the external temperature and perform temperature compensation on the parameters of the magnetic field strength measured by the sensor FBG2 (4-8). The total length of the sensor probe (4) is 1 cm. Its structure includes a 5 mm sensor FBG1 (4 -6) and 5mm sensing FBG2 (4-8), the optical fiber cladding of the sensing FBG1 (4-6) is plated with a silver metal film (4-7), the optical fiber cladding of the sensing FBG2 (4-8) is removed and filled with a magnetic sensitive liquid, the Bragg grating period is 520nm, the core refractive index is 1.465, and the central wavelength is 1523nm, the liquid in the cladding area (4-3) filled with liquid in the sensing probe (4) is a magnetic fluid, and there are two filling liquid channels (4-5) on the surface processed by femtosecond laser micromachining technology, and the magnetic fluid is filled into the cladding area through the filling liquid channel (4-5) using a syringe.

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