Fiber Bragg grating directional pressure sensor, fiber Bragg grating preparation method and device

Abstract

The present invention is applicable to the field of optical fiber sensing technology, and provides an optical fiber Bragg grating directional pressure sensor, an optical fiber Bragg grating preparation method and an apparatus. The optical fiber Bragg grating directional pressure sensor includes a double-sided hole optical fiber, a load-bearing plate, a force-bearing plate and a spectrum analysis module: the double-sided hole optical fiber includes an optical fiber cladding, an optical fiber core disposed in the optical fiber cladding and two air holes, the two air holes are located at both ends of the optical fiber core, and a directional Bragg grating is also written in the optical fiber core; the diameter of the air hole is larger than the diameter of the optical fiber core and smaller than the radius of the optical fiber cladding; the double-sided hole optical fiber is used to access the measurement light beam, and after being refracted by the Bragg grating, the test light beam is output to the spectrum analysis module; the spectrum analysis module is used to demodulate the spectrum of the test light beam to obtain the magnitude and direction of the force applied to the force-bearing plate. The optical fiber Bragg grating directional pressure sensor provided by the present invention is both directional and can improve sensitivity while reducing the difficulty of production.

Description

Technical Field

[0001] The present invention relates to the field of optical fiber sensing technology, and in particular to an optical fiber grating directional pressure sensor, and an optical fiber grating preparation method and device. Background Art

[0002] As a type of optical fiber sensor, pressure sensors are widely used in the measurement of stresses such as intelligent robot fingers, vehicle-mounted gravity, static water pressure, and surface tension of devices due to their simple principles, strong anti-electromagnetic interference capabilities, and corrosion resistance. At present, pressure sensors mainly use ordinary single-mode optical fibers, polarization-maintaining optical fibers, microstructured optical fibers, and other optical fibers that guide light based on the principle of total internal reflection of optical fibers. External loads are detected by engraving Bragg gratings of various periods in the optical fiber to form lateral pressure sensors.

[0003] However, the pressure sensor made by engraving Bragg grating on ordinary single-mode optical fiber has general sensitivity, the pressure sensor made by engraving Bragg grating on polarization-maintaining optical fiber is not directionally sensitive, and the pressure sensor made by engraving Bragg grating on microstructured optical fiber is affected by scattering due to the large number of holes, and the engraving process is too cumbersome and complicated. In addition, the pressure sensors formed by Bragg grating made in the above three optical fibers do not have the characteristics of directionality. Therefore, it is necessary to design a pressure sensor with high sensitivity, directionality and simple writing procedure. Summary of the invention

[0004] The main purpose of the present invention is to propose a fiber Bragg grating directional pressure sensor, a fiber Bragg grating preparation method and a device to solve the problems that the pressure sensor formed by making a Bragg grating in an optical fiber in the prior art is not directional, has low sensitivity, and has a cumbersome and complicated manufacturing process.

[0005] To achieve the above-mentioned purpose, a first aspect of an embodiment of the present invention provides a fiber Bragg grating directional pressure sensor, comprising a double-sided hole optical fiber, a bearing plate, a force plate and a spectrum analysis module:

[0006] The double-sided hole optical fiber is placed between the load-bearing plate and the force-bearing plate, and the output end of the double-sided hole optical fiber is connected to the spectrum analysis module;

[0007] The double-sided hole optical fiber comprises an optical fiber cladding, an optical fiber core disposed in the optical fiber cladding, and two air holes, wherein the two air holes are located at two ends of the optical fiber core, and a directional Bragg grating is also written in the optical fiber core;

[0008] The diameter of the air hole is larger than the diameter of the optical fiber core and smaller than the radius of the optical fiber cladding;

[0009] The double-sided hole optical fiber is used to receive the measuring light beam, and after being refracted by the Bragg grating, outputs the test light beam to the spectrum analysis module;

[0010] The spectrum analysis module is used to demodulate the spectrum of the test light beam to obtain the magnitude and direction of the force applied to the force-bearing plate.

[0011] Optionally, the fiber Bragg grating directional pressure sensor further includes a double-sided hole supporting optical fiber;

[0012] The double-sided hole supporting optical fiber and the double-sided hole optical fiber are placed side by side between the load-bearing plate and the force-bearing plate.

[0013] Optionally, the centers of the two air holes and the center of the optical fiber core are on the same straight line.

[0014] Optionally, the length of the Bragg grating is 535 um.

[0015] A second aspect of an embodiment of the present invention provides a method for preparing a fiber Bragg grating, which is applied to the preparation of a fiber Bragg grating directional pressure sensor, comprising:

[0016] Build a grating writing system;

[0017] Writing a directional Bragg grating in a double-sided hole optical fiber by using the grating writing system;

[0018] The double-sided hole optical fiber with Bragg grating is placed between the load-bearing plate and the force-bearing plate, and its output end is connected to the spectrum analysis module.

[0019] Optionally, after constructing the grating writing system, before writing a directional Bragg grating in a double-sided hole optical fiber by using the grating writing system, the method includes:

[0020] The double-sided hole optical fiber is treated with hydrogen.

[0021] Optionally, writing a directional Bragg grating in a double-sided hole optical fiber by using the grating writing system comprises:

[0022] Calibrate the grating processing position in the double-sided hole optical fiber, and calibrate the processing direction of the double-sided hole optical fiber;

[0023] Adjusting the position of the double-sided hole optical fiber so that the grating preparation system can focus on the grating processing position;

[0024] When the grating writing system processes the double-sided hole optical fiber, obtaining a transmission spectrum of the Bragg grating;

[0025] Analyzing changes in spectrum quality and resonance peak position according to the transmission spectrum;

[0026] Whether the Bragg grating is written is determined based on changes in the spectrum quality and the resonance peak position.

[0027] The third aspect of the embodiment of the present invention provides a fiber Bragg grating preparation device, which is used for preparing a fiber Bragg grating directional pressure sensor, including a high-temperature and high-pressure reactor, a charge coupled device image sensor CCD, an ultraviolet laser, a light source, a lens group, a phase mask, an electric rotating fixture, a three-dimensional adjustment frame, a PC module and a transmitted light analysis module;

[0028] The ultraviolet laser, the lens group and the phase mask are connected in sequence;

[0029] A double-sided hole optical fiber is placed in the electric rotating fixture, the electric rotating fixture is placed on the three-dimensional adjustment frame, the PC module is placed on the electric rotating fixture and connected to the CCD;

[0030] The phase mask is placed above the double-sided hole optical fiber to focus the light beam on the double-sided hole optical fiber, the transmitted light analysis module is connected to the output end of the double-sided hole optical fiber, and the light source is connected to the input end of the double-sided hole optical fiber;

[0031] The high temperature and high pressure reactor is used to carry hydrogen to the double-sided hole optical fiber;

[0032] The CCD is used for calibration of the bilateral aperture directions;

[0033] The ultraviolet laser is used to provide coherent light when writing a Bragg grating in the double-sided hole optical fiber;

[0034] The lens group is used to process the coherent light and focus the coherent light;

[0035] The phase mask is used to diffract light beams of different orders onto the double-sided hole optical fiber according to the focused coherent light, and write the Bragg grating according to the calibrated direction;

[0036] The electric rotating fixture is used to fix the position and rotation direction of the optical fiber;

[0037] The three-dimensional adjustment frame is used to adjust the position of the double-sided hole optical fiber;

[0038] The PC module is used to display CCD imaging and control the direction of the electric rotating fixture;

[0039] The transmitted light analysis module is used to collect and analyze the transmitted light signal in the Bragg grating.

[0040] Optionally, the lens group includes a reflector, an aperture and a cylindrical lens arranged in sequence.

[0041] The embodiment of the present invention proposes a fiber Bragg grating directional pressure sensor, the main body of which is a double-sided hole fiber, wherein the double-sided hole fiber includes a fiber cladding, the fiber cladding has only two air holes, and a fiber core placed between the two air holes, and the fiber core is also written with a directional Bragg grating. Therefore, the pressure sensor composed of the double-sided hole fiber written with the directional Bragg grating, a load-bearing plate, a force plate and a spectrum analysis module has directionality; structurally, due to the small number of air holes, large diameter and small influence of scattering, the process of writing the double-sided hole fiber in the fiber core will not be affected by scattering, thereby reducing the difficulty of writing the fiber Bragg grating; in addition, due to the two large air holes, when external force is applied along different directions of the double-sided hole fiber, the double-sided hole fiber has different sensitivities in different directions compared with the polarization-maintaining fiber, and has improved sensitivity compared with the ordinary single-mode fiber. Therefore, the fiber Bragg grating directional pressure sensor provided by the embodiment of the present invention has both directionality and can improve sensitivity while reducing the difficulty of manufacturing. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 A schematic diagram of the structure of a fiber Bragg grating directional pressure sensor provided in Embodiment 1 of the present invention;

[0043] Figure 2 A schematic diagram of the structure of a double-sided hole optical fiber provided in Embodiment 1 of the present invention;

[0044] Figure 3 A schematic diagram of different pressure sensitivities of a fiber Bragg grating directional pressure sensor in different directions provided in the first embodiment of the present invention;

[0045] Figure 4 A schematic diagram of the implementation process of the fiber grating preparation method provided in the second embodiment of the present invention;

[0046] Figure 5 for Figure 4 Detailed implementation flow diagram of step S102;

[0047] Figure 6 The transmission spectrum of the double-sided hole optical fiber provided in the second embodiment of the present invention;

[0048] Figure 7 This is a schematic diagram of the composition structure of the fiber Bragg grating preparation device provided in Example 3 of the present invention.

[0049] The realization of the purpose, functional features and advantages of the present invention will be further explained in conjunction with embodiments and with reference to the accompanying drawings. DETAILED DESCRIPTION

[0050] It should be understood that the specific embodiments described herein are only used to explain the present invention, and are not used to limit the present invention.

[0051] It should be noted that, in this article, the terms "include", "comprises" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, an element defined by the sentence "comprises a ..." does not exclude the existence of other identical elements in the process, method, article or device including the element.

[0052] In this document, suffixes such as "module", "component" or "unit" used to represent elements are only used to facilitate the description of the present invention, and have no specific meanings. Therefore, "module" and "component" can be used interchangeably.

[0053] In the subsequent description, the serial numbers of the invention embodiments are only for description and do not represent the advantages and disadvantages of the embodiments.

[0054] Embodiment 1

[0055] like Figure 1 As shown, an embodiment of the present invention provides a fiber Bragg grating directional pressure sensor 100 , including a double-sided hole optical fiber 10 , a load-bearing plate 20 , a force-bearing plate 30 and a spectrum analysis module 40 .

[0056] In the embodiment of the present invention, the connection relationship of each part of the fiber Bragg grating directional pressure sensor is as follows:

[0057] The double-sided hole optical fiber 10 is placed between the load-bearing plate 20 and the force-bearing plate 30. The double-sided hole optical fiber 10 and the force-bearing plate 30 are both placed on the load-bearing plate 20. The external force to be measured is applied to the force-bearing plate 30, and the output end of the double-sided hole optical fiber 10 is connected to the spectral analysis module 40. The light beam input by the double-sided hole optical fiber 10 is output to the spectral analysis module 40. During measurement, the light beam is refracted in the double-sided hole optical fiber 10, and spectral analysis can be performed in the spectral analysis module 40.

[0058] In a specific application, a double-sided hole optical fiber is placed between a load-bearing plate and a force-bearing plate, and it is difficult to fix the double-sided hole optical fiber while maintaining its natural deformation under force.

[0059] Therefore, if Figure 1 As shown, the fiber Bragg grating directional pressure sensor 100 provided in the embodiment of the present invention further includes a double-sided hole supporting optical fiber 50, which is placed side by side with the double-sided hole optical fiber 10 between the load-bearing plate 20 and the force-bearing plate 30 as a supporting, protective and reference structure.

[0060] In a specific application, the main body of the fiber Bragg grating directional pressure sensor 100 is a double-sided hole optical fiber 10, and the embodiment of the present invention further describes its structure in detail.

[0061] like Figure 2 The figure shows the end face structure and cross-sectional structure of the double-sided hole optical fiber 10. The double-sided hole optical fiber 10 comprises an optical fiber cladding 11, an optical fiber core 12 disposed in the optical fiber cladding 11, and two air holes 13, the two air holes 13 are located at both ends of the optical fiber core 12, and a directional Bragg grating 14 is also written in the optical fiber core 12.

[0062] In a specific application, the double-sided hole optical fiber 10 is used to receive the measurement beam, and after being refracted by the Bragg grating, the test beam is output to the spectrum analysis module;

[0063] The spectrum analysis module 40 is used to demodulate the spectrum of the test light beam to obtain the magnitude and direction of the force applied to the force-bearing plate.

[0064] In one embodiment, the centers of the two air holes 13 are on the same straight line as the center of the optical fiber core 12; by setting the positional relationship between the air holes and the optical fiber core, the double-sided hole optical fiber has a symmetrical structure inside and outside, thereby increasing the measurement accuracy of the double-sided hole fiber Bragg grating pressure sensor.

[0065] In one embodiment, the length of the Bragg grating 14 is 535 um. The grating serves as a modulation and demodulation functional structure of the optical fiber, and its submicron size determines that the fiber Bragg grating directional pressure sensor has a submicron resolution.

[0066] like Figure 2 In the double-sided hole optical fiber 10 shown, the diameter of the air hole 13 is larger than the diameter of the optical fiber core 12 and smaller than the radius of the optical fiber cladding 11 .

[0067] In a specific application, the value of the diameter of the air hole is greater than four times the value of the optical fiber core diameter.

[0068] In a pressure sensor, if there are a large number of air holes in the optical fiber, the light beam will be scattered when propagating in the optical fiber. However, in the fiber grating directional pressure sensor provided by the embodiment of the invention, the double-sided hole optical fiber has a small number of air holes, a large diameter, and a small scattering effect. Therefore, the process of writing the double-sided hole optical fiber in the optical fiber core will not be affected by scattering.

[0069] In addition, when the diameter of the air hole is set to a larger diameter, if external forces are applied along different directions of the double-sided hole fiber, the double-sided hole fiber will have different sensitivities in different directions compared with the polarization-maintaining fiber, and the sensitivity is improved compared with the ordinary single-mode fiber.

[0070] like Figure 3As shown, the embodiment of the present invention also provides a fiber Bragg grating directional pressure sensor with different pressure sensitivities in different directions. Figure 3 The scale in represents the ratio of the difference between the propagation peaks when the light beam propagates in the fiber Bragg grating to the external force applied to the force plate, and the unit is nm / N. Figure 3 In the figure, points close to 0° to 180° indicate low sensitivity, and points close to 90° to 270° indicate high sensitivity.

[0071] The fiber Bragg grating directional pressure sensor provided by the embodiment of the present invention has a main body of a double-sided hole fiber, wherein the double-sided hole fiber includes a fiber cladding, in which there are only two air holes, and a fiber core placed between the two air holes, and a directional Bragg grating is also written in the fiber core. Therefore, the pressure sensor composed of the double-sided hole fiber written with the directional Bragg grating, a load-bearing plate, a force plate and a spectrum analysis module has directionality; structurally, due to the small number of air holes, large diameter and small influence of scattering, the process of writing the double-sided hole fiber in the fiber core will not be affected by scattering, thereby reducing the difficulty of writing the fiber Bragg grating; in addition, due to the two large air holes, when external force is applied along different directions of the double-sided hole fiber, the double-sided hole fiber has different sensitivities in different directions compared with the polarization-maintaining fiber, and has improved sensitivity compared with the ordinary single-mode fiber. Therefore, the fiber Bragg grating directional pressure sensor provided by the embodiment of the present invention has both directionality and can improve sensitivity under the premise of reducing the difficulty of production.

[0072] Embodiment 2

[0073] like Figure 4 As shown, an embodiment of the present invention provides a method for preparing a fiber Bragg grating, which is applied to the preparation of a fiber Bragg grating directional pressure sensor, including but not limited to the following steps:

[0074] S101, constructing a grating writing system.

[0075] In the above step S101, the grating writing system utilizes the light-induced refractive index change characteristics of the fiber core and uses special processes, such as ultraviolet light thermal processing, to make the refractive index of the fiber core undergo permanent periodic changes to form a specific grating; the characteristics of the grating are similar to a wavelength selector, which can reflect incident light whose wavelength meets the Bragg reflection condition.

[0076] In an embodiment of the present invention, the grating writing system is used to write a Bragg grating, the central wavelength of which satisfies: λB=2neffΛ, where 2neff is the effective refractive index of the optical fiber core, and Λ is the grating period.

[0077] S102, writing a directional Bragg grating in a double-sided hole optical fiber by using the grating writing system.

[0078] In the above step S102, the Bragg grating is a diffraction grating formed by axial periodic modulation of the refractive index of the optical fiber core, and the directivity of the Bragg grating is manifested as the lateral stress of the double-sided hole optical fiber.

[0079] like Figure 5 As shown, the embodiment of the present invention shows the detailed implementation process of the above step S102, including:

[0080] S1021, calibrating the grating processing position in the double-sided hole optical fiber, and calibrating the processing direction of the double-sided hole optical fiber.

[0081] In the above step S1021, the proceeding direction of the double-sided hole fiber is the direction from the input position to the output position of the light beam in the double-sided hole fiber.

[0082] In a specific application, before calibrating the grating processing position, the double-sided hole fiber is first fixed at a specified position, and the specified position is referenced to the grating preparation system, that is, the double-sided hole fiber is fixed at the specified position of the grating preparation system.

[0083] S1022, adjusting the position of the double-sided hole optical fiber so that the grating preparation system can focus at the grating processing position.

[0084] In the above step S1022, the grating preparation system uses ultraviolet light thermal processing to achieve grating writing. The main process is: first connect the ultraviolet laser and process it, focus the processed ultraviolet laser on the double-sided hole optical fiber to change the refractive index of the optical fiber core, and complete the grating preparation.

[0085] S1023. When the grating writing system processes the double-sided hole optical fiber, obtain a transmission spectrum of the Bragg grating.

[0086] S1024, analyzing changes in spectrum quality and resonance peak position according to the transmission spectrum;

[0087] S1025, judging whether the Bragg grating is written successfully according to the changes in the spectrum quality and the resonance peak position.

[0088] In the above steps S1023 to S1025, the optical parameters of the light beam after passing through the Bragg grating can be analyzed through the transmission spectrum.

[0089] like Figure 6 As shown, the embodiment of the present invention also shows the transmission spectrum of the double-sided hole optical fiber, wherein the horizontal axis represents the wavelength value in nm, and the vertical axis represents the transmission value in dB. Figure 6 In the method, after the processed ultraviolet laser passes through the double-sided hole optical fiber, the wavelength of the light beam passing through the double-sided hole optical fiber is between 1553nm and 1554nm.

[0090] S103, placing the double-sided hole optical fiber with Bragg grating written on it between the load-bearing plate and the force-bearing plate, and connecting its output end to the spectrum analysis module.

[0091] In a specific application, in order to increase the photosensitivity of the optical fiber, after constructing the grating writing system, before writing a directional Bragg grating in the double-sided hole optical fiber through the grating writing system, the double-sided hole optical fiber may be subjected to hydrogen loading treatment.

[0092] Among them, the hydrogen loading treatment of double-sided hole optical fiber can be carried out in a high-temperature and high-pressure reactor.

[0093] Embodiment 3

[0094] The embodiment of the present invention provides a fiber Bragg grating preparation device 200, which is used for the preparation of a fiber Bragg grating directional pressure sensor, including a high-temperature and high-pressure reactor 201, a charge coupled device image sensor CCD202, an ultraviolet laser 203, a light source 204, a lens group 205, a phase mask 206, an electric rotating fixture 207, a three-dimensional adjustment frame 208, a PC module 209 and a transmitted light analysis module 210.

[0095] The fiber grating preparation device 200 provided in the embodiment of the present invention is used to prepare a Bragg grating in a double-sided hole optical fiber. In a specific application, after the Bragg grating is prepared in the double-sided hole optical fiber by the fiber grating preparation device, it is also necessary to prepare a fiber grating directional pressure sensor according to the fiber grating preparation method in Example 2.

[0096] like Figure 7 As shown, the connection relationship of each part of the above-mentioned fiber grating preparation device is as follows:

[0097] The ultraviolet laser 203, the lens group 205 and the phase mask 206 are connected in sequence. The ultraviolet laser 203 provides laser light and processes the laser light through the lens group 205 and the phase mask 206. The double-sided hole optical fiber 10 is placed in the electric rotating fixture 207. The electric rotating fixture 207 is placed on the three-dimensional adjustment frame 208. The PC module 209 is placed on the electric rotating fixture 207 and connected to the CCD 202. The phase mask 206 is placed above the double-sided hole optical fiber 10 to focus the light beam on the double-sided hole optical fiber 10. The transmitted light analysis module 210 is connected to the output end of the double-sided hole optical fiber 10. The light source 204 is connected to the double-sided hole optical fiber 10. The input end of the optical fiber 10 is connected; wherein, the electric rotating clamp 207 and the three-dimensional adjustment frame 208 fix the double-sided hole optical fiber 10, but the three-dimensional rotating frame 208 can be rotated horizontally to adjust the position of the double-sided hole optical fiber 10; since the incident azimuth of the treated ultraviolet laser is unchanged, the electric rotating clamp 207 can be used to adjust the double-sided hole optical fiber 10 to make it rotate axially and change the action position of the treated ultraviolet laser. Although the transmitted light analysis module 210 is connected to the output end of the double-sided hole optical fiber 10, it actually analyzes the light beam passing through the Bragg grating that has been written or not written in the double-sided hole optical fiber 10.

[0098] In the embodiment of the present invention, the high temperature and high pressure reactor 201 is used to carry hydrogen to the double-sided hole optical fiber;

[0099] CCD202, used for calibration of bilateral hole directions;

[0100] The ultraviolet laser 203 is used to provide coherent light when writing a Bragg grating in a double-sided hole optical fiber;

[0101] A lens group 204 is used to process the coherent light and focus the coherent light;

[0102] In the embodiment of the present invention, the lens group 204 includes a reflector, an aperture, and a cylindrical lens arranged in sequence.

[0103] The phase mask 205 is used to diffract light beams of different orders onto the double-sided hole optical fiber according to the focused coherent light, and write the Bragg grating according to the calibrated direction;

[0104] An electric rotating fixture 206, used to fix the position and rotation direction of the optical fiber;

[0105] Three-dimensional adjustment frame 207, used to adjust the position of the double-sided hole optical fiber;

[0106] PC module 208, used to display CCD imaging and control the direction of the electric rotating fixture;

[0107] The transmitted light analysis module 209 is used to collect and analyze the transmitted light signal in the Bragg grating.

[0108] In the embodiment of the present invention, two electric rotating fixtures are provided to make the parts of the double-sided hole optical fiber rotate synchronously. Meanwhile, a PC module is provided on each electric rotating fixture, and one of the PC modules is connected to a CCD for direction calibration and monitoring.

[0109] Embodiment 4

[0110] The embodiment of the present invention shows the preparation process of the fiber Bragg grating directional pressure sensor to illustrate the implementation process of the fiber Bragg grating preparation method provided in the second embodiment and the working principle of the fiber Bragg grating preparation device provided in the third embodiment.

[0111] The preparation process of fiber Bragg grating directional pressure sensor can be divided into the preparation of fiber Bragg grating and the preparation of fiber Bragg grating directional pressure sensor.

[0112] When preparing the fiber Bragg grating, firstly, a double-sided hole fiber is selected and subjected to a high-temperature and high-pressure hydrogen loading treatment in a high-temperature and high-pressure reactor to increase the photosensitivity of the fiber.

[0113] Then, construct the grating writing system. The structure of the grating writing system can be found in Figure 7 , including a light path constructed by a charge coupled device image sensor CCD, an ultraviolet laser, a light source, a lens group, a phase mask, an electric rotating fixture, a three-dimensional adjustment frame, a PC module and a transmitted light analysis module, wherein the lens group includes a reflector, an aperture and a cylindrical lens.

[0114] The realization of the fiber Bragg grating preparation method and the working principle of the fiber Bragg grating preparation device can be expressed as follows:

[0115] The ultraviolet laser of the above-mentioned grating writing system provides a laser with a wavelength of 266nm, which is reflected by the reflector and then shot into the aperture. The spot size can be controlled by the aperture; the laser exiting the aperture passes through the cylindrical lens to converge the circular spot into a linear spot, increasing the energy density of the laser spot, wherein the focal length of the cylindrical lens is 50.2mm; finally, the laser is diffracted into different orders through the phase mask, and the energy is mainly concentrated on ±1, wherein the period of the phase mask is 1070nm; at a position close to the phase mask, the distance is about 150-200um, and the light of ±1 will undergo interference phenomenon of light intensity distribution. After the construction of the grating writing system is completed, the double-sided hole optical fiber loaded with hydrogen is placed on an electric rotating fixture, and the direction and processing position are calibrated through CCD106 imaging. The rotation angle is controlled through CCD106 imaging, and the CCD imaging and the direction of the electric rotating fixture are obtained through the PC module. Then the three-dimensional adjustment frame is adjusted to make the double-sided hole optical fiber in the best focusing state. The ultraviolet laser passes through the lens group and the phase mask and acts on the processing position. The fiber grating is written on the core of the double-sided hole optical fiber by utilizing the interference phenomenon of the light intensity distribution. At the same time, the output end of the light source is connected to the input end of the double-sided hole optical fiber, and the output end of the double-sided hole optical fiber is connected to the transmitted light analysis module. The transmitted light analysis module is used for real-time recording and monitoring to determine the preparation degree of the fiber grating.

[0116] In the embodiment of the present invention, the grating written by the optical fiber writing system in the double-sided hole optical fiber is a Bragg grating, and the length of the Bragg grating is 535 um.

[0117] When preparing a fiber Bragg grating directional pressure sensor, after the Bragg grating has been prepared in the double-sided hole fiber, the double-sided hole fiber and the double-sided hole supporting fiber are placed parallel to each other on a load-bearing plate and covered with a force plate. When the required external measurement force is applied, the spectral change and demodulation are analyzed by the spectral analysis module to obtain the magnitude and direction of the external force.

[0118] The embodiments described above are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the foregoing embodiments describe the present invention in detail, those skilled in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or replace some of the technical features therein by equivalents. Such modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention, and should all be included in the protection scope of the present invention.

Claims

1. A fiber Bragg grating directional pressure sensor, characterized in that: Including double-sided hole optical fiber, load-bearing plate, force-bearing plate and spectrum analysis module: The double-sided hole optical fiber is placed between the load-bearing plate and the force-bearing plate, and the output end of the double-sided hole optical fiber is connected to the spectrum analysis module; The double-sided hole optical fiber comprises an optical fiber cladding, an optical fiber core disposed in the optical fiber cladding, and two air holes, wherein the two air holes are located at two ends of the optical fiber core, and a directional Bragg grating is also written in the optical fiber core; The diameter of the air hole is larger than the diameter of the optical fiber core and smaller than the radius of the optical fiber cladding, and the value of the diameter of the air hole is larger than four times the value of the diameter of the optical fiber core; The double-sided hole optical fiber is used to receive the measuring light beam, and after being refracted by the Bragg grating, outputs the test light beam to the spectrum analysis module; The spectrum analysis module is used to demodulate the spectrum of the test light beam to obtain the magnitude and direction of the force applied to the force-bearing plate; The fiber Bragg grating directional pressure sensor also includes a double-sided hole supporting optical fiber; The double-sided hole supporting optical fiber and the double-sided hole optical fiber are placed side by side between the load-bearing plate and the force-bearing plate.

2. The fiber Bragg grating directional pressure sensor according to claim 1, characterized in that: The centers of the two air holes and the center of the optical fiber core are on the same straight line.

3. The fiber Bragg grating directional pressure sensor according to claim 1, characterized in that: The length of the Bragg grating is 535 um.

4. A method for preparing a fiber Bragg grating, characterized in that: The preparation of a fiber Bragg grating directional pressure sensor as claimed in any one of claims 1 to 3 comprises: Build a grating writing system; Writing a directional Bragg grating in a double-sided hole optical fiber by using the grating writing system; The double-sided hole optical fiber with Bragg grating is placed between the load-bearing plate and the force-bearing plate, and its output end is connected to the spectrum analysis module.

5. The method for preparing a fiber Bragg grating according to claim 4, characterized in that: After constructing the grating writing system, before writing a directional Bragg grating in a double-sided hole optical fiber by using the grating writing system, the method includes: The double-sided hole optical fiber is treated with hydrogen.

6. The method for preparing a fiber Bragg grating according to claim 4, characterized in that: The grating writing system is used to write a directional Bragg grating in a double-sided hole optical fiber, comprising: Calibrate the grating processing position in the double-sided hole optical fiber, and calibrate the processing direction of the double-sided hole optical fiber; Adjusting the position of the double-sided hole optical fiber so that the grating writing system can focus on the grating processing position; When the grating writing system processes the double-sided hole optical fiber, obtaining a transmission spectrum of the Bragg grating; Analyzing changes in spectrum quality and resonance peak position according to the transmission spectrum; Whether the Bragg grating is written is determined based on changes in the spectrum quality and the resonance peak position.

7. A fiber Bragg grating preparation device, characterized in that: The method for preparing a fiber Bragg grating directional pressure sensor according to any one of claims 1 to 3 comprises a high temperature and high pressure reactor, a charge coupled device image sensor CCD, an ultraviolet laser, a light source, a lens group, a phase mask, an electric rotating fixture, a three-dimensional adjustment frame, a PC module and a transmitted light analysis module; The ultraviolet laser, the lens group and the phase mask are connected in sequence; A double-sided hole optical fiber is placed in the electric rotating fixture, the electric rotating fixture is placed on the three-dimensional adjustment frame, the PC module is placed on the electric rotating fixture and connected to the CCD; The phase mask is placed above the double-sided hole optical fiber to focus the light beam on the double-sided hole optical fiber, the transmitted light analysis module is connected to the output end of the double-sided hole optical fiber, and the light source is connected to the input end of the double-sided hole optical fiber; The high temperature and high pressure reactor is used to carry hydrogen to the double-sided hole optical fiber; The CCD is used for calibration of the bilateral aperture directions; The ultraviolet laser is used to provide coherent light when writing a Bragg grating in the double-sided hole optical fiber; The lens group is used to process the coherent light and focus the coherent light; The phase mask is used to diffract light beams of different orders onto the double-sided hole optical fiber according to the focused coherent light, and write the Bragg grating according to the calibrated direction; The electric rotating fixture is used to fix the position and rotation direction of the optical fiber; The three-dimensional adjustment frame is used to adjust the position of the double-sided hole optical fiber; The PC module is used to display CCD imaging and control the direction of the electric rotating fixture; The transmitted light analysis module is used to collect and analyze the transmitted light signal in the Bragg grating.

8. The fiber Bragg grating preparation device according to claim 7, characterized in that: The lens group includes a reflector, an aperture and a cylindrical lens which are arranged in sequence.

Images