Preparation method of F-P optical fiber pressure sensor based on thermoplastic microspheres

Abstract

The invention belongs to the technical field of optical fiber sensing, and particularly relates to a preparation method of an F-P optical fiber pressure sensor based on thermoplastic microspheres, and the preparation method comprises the following steps: S1, removing coating layers of a single-mode optical fiber and a hollow optical fiber, and wiping the single-mode optical fiber and the hollow optical fiber with alcohol; s2, the welding parameters of a welding machine are adjusted in advance, and the single-mode optical fiber and the hollow optical fiber are spliced together; s3, placing the optical fibers spliced in the S2 on an optical fiber precision cutting platform, fixing the optical fibers by using clamps on two sides, and cutting the optical fibers; s4, performing reflecting surface treatment on the spliced optical fibers in the S2 by using a heating device; and S5, moving the heating device to approach the hollow optical fiber, and enabling the molten thermoplastic microspheres to flow into the hollow optical fiber under the action of gravity and capillarity. The F-P thin film can be prepared from the thermoplastic microspheres with low EM, the pressure sensitivity of the sensor can be effectively improved, the reflectivity of the sensor is improved, and the F-P thin film has wide application prospects in the fields of biological medicine, aerospace and the like.

Description

Technical Field

[0001] The invention belongs to the technical field of optical fiber sensing, and in particular relates to a method for preparing an FP optical fiber pressure sensor based on thermoplastic microspheres. Background Art

[0002] In clinical diagnosis and treatment as well as minimally invasive surgery, the measurement of pressure is crucial. With the introduction and promotion of minimally invasive therapies and the extremely narrow space inside the body being detected, the miniaturization of sensors has become more important. So far, many fiber optic pressure sensors based on fiber Mach-Zehnder interferometers (MZIs), long-period fiber gratings (LPFGs), and fiber Fabry-Perot (FP) interferometers have been proposed. They can effectively avoid electromagnetic interference, have the advantages of small size, high precision, and strong biocompatibility, and are highly favored by people in the biological and medical fields.

[0003] Limited by the application environment, the probe-type FP optical fiber sensor has significant advantages such as simple preparation, low cost and small size. However, the pressure sensitivity of the FP sensor prepared based on the thin film structure is limited by the elastic modulus (EM) of the thin film material and the thermal expansion coefficient (TEC) of the air. For the cavity FP, the material properties of the sensitive film will affect the sensing characteristics of the optical fiber sensor. In addition, the film quality of the thin film is also one of the key factors determining the fringe contrast of the FP sensor. Summary of the invention

[0004] The purpose of the present invention is to provide a method for preparing an FP optical fiber pressure sensor based on thermoplastic microspheres. The FP film prepared by thermoplastic microspheres with low EM can effectively improve the pressure sensitivity of the sensor and improve the reflectivity of the sensor, and has broad application prospects in the fields of biomedicine, aerospace, etc.

[0005] The technical solution adopted by the present invention is as follows:

[0006] A method for preparing a FP optical fiber pressure sensor based on thermoplastic microspheres, the preparation method comprising the following steps:

[0007] S1: Remove the coating of a section of single-mode optical fiber and hollow-core optical fiber and wipe them clean with alcohol;

[0008] In S1, the inner diameter of the single-mode optical fiber is 9 microns, and the outer diameter of the optical fiber is 125 microns. The inner diameter of the hollow optical fiber is 75 microns, and the outer diameter of the optical fiber is 75 microns. The single-mode optical fiber is the incident optical fiber, and the hollow optical fiber is the sensing optical fiber.

[0009] S2: pre-adjust the splicing parameters of the splicer to splice the single-mode optical fiber and the hollow-core optical fiber together;

[0010] In S2, the welding strength of the welding machine is 20+bit, and the welding time is 1000ms.

[0011] S3: Place the optical fiber spliced ​​in S2 on the optical fiber precision cutting platform, fix it with clamps on both sides, and cut the optical fiber;

[0012] In S3, the optical fiber cutting steps are as follows:

[0013] S31: Place the spliced ​​optical fiber into the optical fiber precision cutting system and fix it with an optical fiber clamp;

[0014] S32: The cover of the optical fiber cutting knife is opened, and the spliced ​​optical fiber is adjusted to a position perpendicular to the cutting knife using the three-dimensional displacement stage on the platform;

[0015] S33: using a CCD system above the cleaver to observe the melting point of the single-mode fiber-hollow-core fiber of the spliced ​​optical fiber, observing on the screen that the fiber cleaver blade is placed at the melting point position, the fiber cleaver is fixed on one of the three-dimensional displacement stages, and by adjusting the three-dimensional displacement stage, the distance between the cleaver blade and the melting point is adjusted; the preset length of the hollow-core fiber is 50 μm;

[0016] S34: When the distance between the two reaches a preset distance, the optical fiber cutting knife cover is closed, and the optical fiber is cut to obtain a single-mode-hollow-core optical fiber structure.

[0017] S4: Processing the reflection surface of the optical fiber spliced ​​in S2 by using a heating device;

[0018] In S4, the steps of processing the optical fiber reflection surface are as follows:

[0019] S41: Place the spliced ​​optical fiber vertically on a fixed platform and fix it with a clamp, with one side of the hollow-core optical fiber on top, and use tweezers to take a thermoplastic microsphere of appropriate size and place it on top of the hollow-core optical fiber;

[0020] The thermoplastic microspheres are made of polymethyl methacrylate and have a diameter of 75 μm.

[0021] S42: Using a heating device to melt the thermoplastic microspheres close to the optical fiber, the thermoplastic microspheres flow into the core of the coreless optical fiber under the action of capillary phenomenon;

[0022] S43: After cooling, the fusion point between the single-mode optical fiber and the hollow-core optical fiber serves as the first reflection surface of the FP cavity, and the thermoplastic microspheres form a complete surface inside the fiber core, serving as the second reflection surface of the FP cavity.

[0023] S5: Move the heating device close to the hollow optical fiber. After the thermoplastic microspheres are melted, they flow into the hollow optical fiber under the action of gravity and capillary phenomenon, and form a flat surface under the action of internal air pressure. Some microspheres remain outside the hollow optical fiber. After turning off the heating device and cooling, the thermoplastic microsphere material solidifies and is fixed to obtain a fiber optic FP sensor.

[0024] In S5, the heating temperature of the heating device is 150° C., the heating time is 3 minutes, and the cooling time is 1 hour.

[0025] The technical effects achieved by the present invention are:

[0026] The preparation method of the FP optical fiber pressure sensor based on thermoplastic microspheres of the present invention uses thermoplastic microspheres with low EM to prepare the FP film, which can effectively improve the pressure sensitivity of the sensor. At the same time, the micron-sized microspheres with a diameter similar to that of the optical fiber have good ductility on the end face of the optical fiber, and can produce a flat reflective end face after curing. The reflectivity of the sensor is improved. It has broad application prospects in the fields of biomedicine, aerospace, etc.

[0027] The optical fiber FP sensor obtained by the preparation method of the FP optical fiber pressure sensor based on thermoplastic microspheres of the present invention has the advantages of high stability, low manufacturing cost, compact structure and pressure sensitivity, and is more competitive than traditional FP optical fiber pressure sensors; and because the thermoplastic microspheres have a lower Young's modulus, the size of the cavity changes greatly with the increase of ambient pressure, thereby improving the pressure detection sensitivity. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 is a schematic diagram of the overall structure of an embodiment of the present invention;

[0029] Figure 2 is a schematic cross-sectional structural diagram of an embodiment of the present invention;

[0030] Figure 3 is a schematic diagram of an optical fiber splicing device in an embodiment of the present invention;

[0031] Figure 4 Schematic diagram of a heating device for thermoplastic microspheres in an embodiment of the present invention;

[0032] Figure 5 Schematic diagram of the reflection spectrum of the embodiment of the present invention.

[0033] In the accompanying drawings, the components represented by the reference numerals are listed as follows:

[0034] 1. Single-mode optical fiber; 2. Hollow optical fiber; 3. Thermoplastic microspheres; 4. Single-mode optical fiber core; 5. First reflection surface; 6. Second reflection surface; 7. Three-dimensional translation stage; 8. Optical fiber clamp; 9. Optical fiber cutting knife; 10. Display; 11. CCD system; 12. Heating device. DETAILED DESCRIPTION

[0035] In order to make the purpose and advantages of the present invention more clearly understood, the present invention is specifically described below in conjunction with embodiments. It should be understood that the following text is only used to describe one or several specific embodiments of the present invention, and does not strictly limit the scope of protection of the specific claims of the present invention.

[0036] Embodiment 1:

[0037] In this embodiment, the optical fiber cutter 9 and the optical fiber fusion splicer are used to cut and fuse the different types of optical fibers, and the optical fibers are placed vertically on a fixed platform. The thermoplastic microspheres 3 of suitable size are selected and placed on the end face of the optical fiber, and the heating platform is turned on to melt the microspheres at 150°C; the thermoplastic microsphere material flows into the air cavity of the FP under the action of capillary phenomenon. When the cavity air pressure is consistent with the ambient air pressure, the thermoplastic microspheres stop flowing in, and the FP cavity length is jointly adjusted by the viscosity of the microspheres in the molten state, the length of the cut optical fiber, and the size of the microspheres; after the thermoplastic microspheres reach a stable state, the heating platform is adjusted to a cooling mode, and the thermoplastic microspheres gradually solidify and stabilize. Since the elastic modulus of the thermoplastic microspheres 3 is very small, the deformation amount is very large under the action of unidirectional pressure, thereby effectively changing the FP cavity length and improving the pressure sensitivity of the sensor. The optical fiber FP pressure sensor obtained by the proposed preparation method has the advantages of high stability, low manufacturing cost, compact structure and pressure sensitivity, and has greater competitiveness compared with traditional FP optical fiber sensors.

[0038] like Figure 1-Figure 5 As shown, a method for preparing a FP optical fiber pressure sensor based on thermoplastic microspheres 3 comprises the following steps:

[0039] S1: Remove the coating of a section of single-mode optical fiber 1 and hollow-core optical fiber, and wipe them clean with alcohol;

[0040] In S1, the inner diameter of single-mode optical fiber 1 is 9 microns, the outer diameter of optical fiber is 125 microns, the inner diameter of hollow optical fiber is 75 microns, the outer diameter of optical fiber is 75 microns, single-mode optical fiber 1 is the incident optical fiber, the cladding diameter is 125μm, and the core diameter is 9μm; hollow optical fiber 2 is the sensing optical fiber, the cladding diameter is 125μm, and the hollow diameter is 75μm.

[0041] S2: pre-adjust the fusion parameters of the fusion splicer to splice the single-mode optical fiber 1 and the hollow-core optical fiber together;

[0042] In S2, the welding strength of the welding machine is 20+bit, and the welding time is 1000ms.

[0043] S3: Place the optical fibers spliced ​​in S2 on the optical fiber precision cutting platform, fix them with optical fiber clamps 8 on both sides, and cut the optical fibers;

[0044] In S3, the fiber cutting steps are as follows:

[0045] S31: placing the spliced ​​optical fiber into the optical fiber precision cutting system and fixing it with a three-dimensional displacement optical fiber clamp 8;

[0046] S32: The cover of the optical fiber cleaver 9 is opened, and the spliced ​​optical fiber is adjusted to a position perpendicular to the cleaver using the three-dimensional displacement stage 7 on the platform;

[0047] S33: Use the CCD system 11 above the cutter to observe the melting point of the single-mode fiber 1-hollow-core fiber of the spliced ​​optical fiber, and observe on the screen that the blade of the optical fiber cutter 9 is placed at the melting point. The optical fiber cutter 9 is fixed on one of the three-dimensional displacement stages 7. By adjusting the three-dimensional displacement stage, the displacement can be observed on the display 10, and then the distance between the cutter blade and the melting point can be adjusted; the preset length of the hollow-core optical fiber 2 is 50 μm;

[0048] S34: When the distance between the two reaches a preset distance, close the cover of the optical fiber cutting knife 9, cut the optical fiber, and obtain a single-mode-hollow fiber structure.

[0049] S4: Processing the reflection surface of the optical fiber spliced ​​in S2 by using the heating device 12;

[0050] In S4, the steps for processing the optical fiber reflection surface are as follows:

[0051] S41: vertically placing the spliced ​​optical fiber on a fixed platform, fixing it with an optical fiber clamp 8, placing one side of the hollow-core optical fiber on the top, taking a thermoplastic microsphere 3 of an appropriate size with tweezers, and placing it on the hollow-core optical fiber;

[0052] The thermoplastic microspheres 3 are made of polymethyl methacrylate and have a diameter of 75 μm.

[0053] S42: Using the heating device 12 to melt the thermoplastic microspheres 3 close to the optical fiber, the thermoplastic microspheres 3 flow into the coreless single-mode optical fiber core 4 under the action of capillary phenomenon;

[0054] S43: After cooling, the fusion point between the single-mode optical fiber 1 and the hollow-core optical fiber serves as the first reflection surface 5 of the FP cavity, and the thermoplastic microspheres 3 form a complete surface inside the fiber core, serving as the second reflection surface 6 of the FP cavity.

[0055] S5: Move the heating device 12 close to the hollow optical fiber. After the thermoplastic microspheres 3 are melted, they flow into the hollow optical fiber under the action of gravity and capillary phenomenon, and form a flat surface under the action of internal air pressure. Some microspheres remain outside the hollow optical fiber. After turning off the heating device 12 and cooling, the thermoplastic microsphere material solidifies and is fixed to obtain a fiber optic FP sensor.

[0056] In S5, the heating temperature of the heating device 12 is 150°C, the heating time is 3 minutes, and the cooling time is 1 hour.

[0057] The working principle of the present invention is as follows: when using the FP optical fiber sensor based on the thermoplastic microspheres 3, the light emitted by the broadband light source propagates in the core through the single-mode optical fiber 1 and enters the hollow-core optical fiber 2. The hollow-core optical fiber 2 serves as a cavity, and the reflection surface on one side is the flat end surface 6 formed by the solidified thermoplastic microsphere 3 material, and the reflection surface on the other side is the junction of the single-mode optical fiber 1 and the hollow-core optical fiber 2. Since the light reflected back and forth between the two parallel reflection surfaces has different optical paths, the light of different optical paths produces an interference effect and finally returns to the single-mode optical fiber 1 to observe the spectrum on the spectrum analyzer. The reflection spectrum is as follows: Figure 5 shown.

[0058] Embodiment 2:

[0059] Embodiment 1 is based on the principle of this embodiment and further defines it;

[0060] For the fiber Fabry-Perot sensor, a cavity is constructed inside the optical fiber, and the two ends of the cavity form two parallel planes at the optical fiber end face and the polymer end face. This cavity is called the FP cavity. When the incident light reaches the FP cavity through the core (4) of the single-mode optical fiber 1, multiple reflections and multiple transmissions occur between the first reflection surface 5 and the second reflection surface 6. In practical applications, when the material reflectivity R is relatively small, the reflected light intensity is mainly affected by the first two beams of reflected light. The reflected light intensity can be expressed as:

[0061]

[0062] In the formula, I i is the incident light intensity, I r is the reflected light intensity, R is the material reflectivity, n is the refractive index of the FP cavity, and L is the cavity length. The reflected light intensity is determined by the material reflectivity, that is, when the material is constant, the smoother the surface, the stronger the reflected light intensity. The reflection spectrum of the FP optical fiber pressure sensor proposed by the present invention is as follows: Figure 5 As shown, it has a fringe contrast greater than 20dB.

[0063] When the phase difference of the reflected light generated by the two reflecting surfaces When k=1,2,3…, the light beams interfere with each other, and peaks and valleys appear in the spectrum lines. The wavelength expression is:

[0064]

[0065] From the interference peak-valley expression, it can be seen that the refractive index of the medium in the cavity and the cavity length will affect the wavelength of the interference peak.

[0066]

[0067] Δn is the change in the refractive index of the medium in the cavity, ΔL is the change in cavity length under the influence of temperature. The material of the sensor thermoplastic microsphere is PMMA. When other parameters do not change and only the change in ambient pressure is considered, the pressure sensitivity S of FPI F The following formula determines:

[0068]

[0069] Where: P is the external pressure, is the change in the refractive index in the cavity caused by external pressure, which is generally a constant. The PMMA deformation caused by pressure changes leads to changes in the FP cavity length. Since PMMA has a lower Young's modulus, when the external pressure environment changes, the PMMA film deforms more and the FP cavity length changes more dramatically, resulting in higher pressure sensitivity.

[0070] The above is only a preferred embodiment of the present invention. It should be noted that, for those skilled in the art, several improvements and modifications can be made without departing from the principles of the present invention, and these improvements and modifications should also be considered as the protection scope of the present invention. The structures, devices and operating methods not specifically described and explained in the present invention shall be implemented according to the conventional means in the art unless otherwise specified and limited.

Claims

1. A method for preparing a FP optical fiber pressure sensor based on thermoplastic microspheres, Features: The preparation method comprises the following steps: S1: Remove the coating of a section of single-mode optical fiber and hollow-core optical fiber and wipe them clean with alcohol; S2: pre-adjust the splicing parameters of the splicer to splice the single-mode optical fiber and the hollow-core optical fiber together; S3: Place the optical fiber spliced ​​in S2 on the optical fiber precision cutting platform, fix it with clamps on both sides, and cut the optical fiber; S4: Processing the reflection surface of the optical fiber spliced ​​in S2 by using a heating device; S5: Move the heating device close to the hollow optical fiber. After the thermoplastic microspheres are melted, they flow into the hollow optical fiber under the action of gravity and capillary phenomenon, and form a flat surface under the action of internal air pressure. Some microspheres remain outside the hollow optical fiber. After turning off the heating device and cooling, the thermoplastic microsphere material solidifies and is fixed to obtain a fiber optic FP sensor.

2. The method for preparing a FP optical fiber pressure sensor based on thermoplastic microspheres according to claim 1, Features: In S1, the single-mode optical fiber is the incident optical fiber, and the hollow optical fiber is the sensing optical fiber.

3. The method for preparing a FP optical fiber pressure sensor based on thermoplastic microspheres according to claim 1, Features: In S2, the welding strength of the welding machine is 20+bit, and the welding time is 1000ms.

4. The method for preparing a FP optical fiber pressure sensor based on thermoplastic microspheres according to claim 1, Features: In S3, the optical fiber cutting steps are as follows: S31: Place the spliced ​​optical fiber into the optical fiber precision cutting system and fix it with an optical fiber clamp; S32: The cover of the optical fiber cutting knife is opened, and the spliced ​​optical fiber is adjusted to a position perpendicular to the cutting knife using the three-dimensional displacement stage on the platform; S33: using a CCD system above the cleaver to observe the melting point of the single-mode fiber-hollow-core fiber of the spliced ​​optical fiber, observing on the screen that the fiber cleaver blade is placed at the melting point position, the fiber cleaver is fixed on one of the three-dimensional translation stages, and the distance between the cleaver blade and the melting point is adjusted by adjusting the three-dimensional translation stage; S34: When the distance between the two reaches a preset distance, the optical fiber cutting knife cover is closed, and the optical fiber is cut to obtain a single-mode-hollow-core optical fiber structure.

5. The method for preparing a FP optical fiber pressure sensor based on thermoplastic microspheres according to claim 4, Features: The preset length of the hollow optical fiber is 50 μm.

6. The method for preparing a FP optical fiber pressure sensor based on thermoplastic microspheres according to claim 1, Features: In S4, the steps of processing the optical fiber reflection surface are as follows: S41: Place the spliced ​​optical fiber vertically on a fixed platform and fix it with a clamp, with one side of the hollow-core optical fiber on top, and use tweezers to take a thermoplastic microsphere of appropriate size and place it on top of the hollow-core optical fiber; S42: Using a heating device to melt the thermoplastic microspheres close to the optical fiber, the thermoplastic microspheres flow into the core of the coreless optical fiber under the action of capillary phenomenon; S43: After cooling, the fusion point between the single-mode optical fiber and the hollow-core optical fiber serves as the first reflection surface of the FP cavity, and the thermoplastic microspheres form a complete surface inside the fiber core, serving as the second reflection surface of the FP cavity.

7. The method for preparing a FP optical fiber pressure sensor based on thermoplastic microspheres according to claim 1, Features: The thermoplastic microspheres are made of polymethyl methacrylate and have a diameter of 75 μm.

8. The method for preparing a FP optical fiber pressure sensor based on thermoplastic microspheres according to claim 1, Features: In S5, the heating temperature of the heating device is 150° C., the heating time is 3 minutes, and the cooling time is 1 hour.

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