Preparation process and test method of high-sensitivity conical optical fiber sensor

Abstract

The invention relates to the technical field of optical fiber sensors, and discloses a preparation process of a high-sensitivity conical optical fiber sensor, which comprises the following steps of: S1, bending and winding an evanescent coupling region of a conical optical fiber on a customized cylinder mold with the radius of 3.183 mm, fixing a bending position by using a high-temperature-resistant adhesive tape, and fixing the distance and the position of a cylinder by using an acrylic plate; and S2, placing the fixed conical optical fiber and the mold on a constant-temperature heating table for low-temperature heating and shaping. According to the preparation process of the high-sensitivity conical optical fiber sensor, glass fiber heating cloth with a silicone rubber coating is selected as a heat source, the fiber cloth is made into a cylindrical heating part, and nickel-chromium alloy heating wires are uniformly arranged between the two layers of glass fiber cloth, so that a stable, uniform and stable heat source at the temperature of 250 DEG C or below can be provided; the strong temperature change of the polymer fiber at the heating junction can be slowed down, and the risk that the cladding and the fiber core of the fiber are separated and even the cladding is broken can be avoided.

Description

Technical Field

[0001] The invention relates to the technical field of optical fiber sensors, and in particular to a preparation process and a testing method for a high-sensitivity tapered optical fiber sensor. Background Art

[0002] The fused taper method is the main method for preparing quartz tapered optical fibers. The same method can also be applied to prepare tapered polymer optical fibers; however, due to the low softening temperature and narrow softening temperature range of polymer optical fibers, it is difficult to accurately control the heating temperature and stretching force.

[0003] At present, different types of optical fiber taper processes have their own characteristics in preparing tapered optical fibers. For example, the flame taper process is relatively simple and applicable to various materials, but the temperature is difficult to accurately control, which may cause damage to the optical fiber material. The cylindrical optical fiber that is heated unevenly will have different mechanical properties in different directions, affecting the performance of the tapered optical fiber; the electric taper process can quickly prepare fine tapered optical fibers, but requires special equipment and high voltage; the laser taper process has highly precise control and a wide range of material applicability, but requires professional skills and equipment and may cost more. Summary of the invention

[0004] 1. Technical issues to be resolved In view of the deficiencies in the prior art, the present invention provides a preparation process and testing method for a high-sensitivity tapered optical fiber sensor. By selecting a glass fiber heating cloth coated with silicone rubber as a heat source, and making the fiber cloth into a cylindrical heating component, and evenly arranging nickel-chromium alloy heating wires between two layers of glass fiber cloth, a stable, uniform and stable heat source below 250°C can be provided, which can reduce the drastic temperature change of the polymer optical fiber at the heating junction, and avoid the risk of separation of the cladding and the core of the optical fiber or even cladding breakage. This solves the problem of uneven heating of the cylindrical optical fiber by the traditional flame melting tapering method, and the difference in mechanical properties of the cylindrical optical fiber in different directions caused by the uneven heating, which affects the performance of the tapered optical fiber.

[0005] (II) Technical solution To achieve the above-mentioned purpose, the present invention provides the following technical solution: a preparation process of a high-sensitivity tapered optical fiber sensor, comprising the following steps: S1. Bend and wrap the evanescent coupling region of the tapered optical fiber around a customized cylindrical mold with a radius of 3.183 mm, fix the bending position with a high-temperature resistant tape, and fix the distance and position of the cylinder with an acrylic plate; S2. Place the fixed tapered optical fiber and mold on a constant temperature heating table for low temperature heating and shaping. The heating temperature is 90°C and the heating time is 30 minutes. S3. Take out the finalized optical fiber, and heat-press two bent tapered optical fibers and a double layer of 0.4 mm thick TPU at 120°C for 20 seconds to prepare optical fiber sensor samples with different arrangement structures; after the sensor is connected to the light source, it can be seen that the output port of the coupled optical fiber receives light; S4. Encapsulate the extra optical fiber pigtails outside the TPU with a black thermoplastic tube, polish the ends of the two optical fibers and connect them to the FC interface with resin glue to complete the preparation of the optical fiber sensor.

[0006] Preferably, the mold material in S1 is an ABS standard cylinder, and the operating temperature range is 0°C-120°C.

[0007] Preferably, both ends of the TPU in S3 are bonded with double-layer non-elastic fabrics, and the TPU is a highly elastic thermoplastic polyurethane film.

[0008] Preferably, the tapering method of the tapered optical fiber in S1 comprises the following steps: S1. Marking the melt-stretched area of ​​the optical fiber: The tapered optical fiber is prepared by the fixed-length stretching method. First, a 40-cm-long optical fiber is taken, and the 10-cm heating area in the middle is located. Positioning labels are attached to both ends of the heating area, and both ends of the optical fiber are trimmed using optical fiber scissors. S2. At room temperature of 26 degrees, the optical fiber is suspended in the center of the heating cylinder to make the optical fiber in the temperature field heated evenly. Then the two ends of the optical fiber are embedded in the grooves of the magnetic optical fiber flip cover fixture, and one side of the telescopic bracket is fixed on the translation stage; S3, start the temperature controller, heat the heating tube to the set temperature, and after waiting for the predetermined heating time, start the translation stage to stretch at a uniform speed according to the set stretching distance. The stretching speed pulse value is fixed at 2000 Hz and the speed is 0.25 mm / s; S4. After the stretching is completed, turn off the temperature controller, wait for the heating tube to cool to room temperature, open the clamping instrument, and take out the stretched tapered optical fiber.

[0009] Preferably, the optical fiber in S1 is a multimode polymer optical fiber, the core material is polymethyl methacrylate, the refractive index n1 is 1.492, the core diameter is 485±25um, the cladding material is fluororesin, the refractive index n2=1.417, and the cladding diameter is 500±25um.

[0010] A test method for testing a high-sensitivity tapered optical fiber sensor comprises the following steps: S1. After polishing the two end faces of the sensor, connect them to the light source and light detector through a bare fiber adapter; the light source and detector are fixed on a high-precision lifting platform, and the lifting platform at one end is fixed to a high-precision translation platform; the high-precision translation platform is controlled by a motor to control the stretching speed and stretching distance, and the light detector is connected to the computer's optical power meter application software BPM to monitor the optical power change in real time; S2. Fix the optical fiber sensor on a lifting platform with both ends horizontal, keep the optical fiber sensor in a naturally straight but not stretched state, fix the elastic length of the sensor to 5 cm, and record the initial coupled light intensity of the sensor; S3, stretching at a fixed speed through a stepper motor set up by a high-precision translation stage, and recording the sensor output optical power monitored by the optical power software after each stretching, and the test results of the optical fiber sensor can be understood by recording the output optical power; S4. Perform repetitive reciprocating tensile tests on the sensor at a constant speed using a stepper motor in a high-precision translation stage to understand the value of the corresponding tensile strain distance.

[0011] Preferably, the stretching method in S3 is: stretching at a fixed speed of 0.25 mm / s, and the stretching distance increases in units of 1 mm, and the total stretching length is 20 mm.

[0012] Preferably, the S3 medium and high-precision translation stage is set by a stepper motor with a constant speed of 0.25 mm / s and a reciprocating motion for 10 minutes, applying 5%, 10%, 15%, and 20% strain percentages to the sensor respectively, and the corresponding tensile strain distances are 2.5 mm, 5 mm, 7.5 mm, and 10 mm, respectively.

[0013] (III) Beneficial effects Compared with the prior art, the present invention provides a preparation process and testing method for a highly sensitive tapered optical fiber sensor, which has the following beneficial effects: 1. The present invention uses a glass fiber heating cloth coated with silicone rubber as a heat source, and makes the fiber cloth into a cylindrical heating component, which is connected to an intelligent digital temperature controller. The silicone cloth is a high-temperature resistant, corrosion-resistant, and high-strength glass fiber cloth. Nickel-chromium alloy heating wires are evenly arranged between two layers of glass fiber cloth, which can provide a stable, uniform and stable heat source below 250°C, and can slow down the drastic temperature change of the polymer optical fiber at the heating junction, and can avoid the risk of separation of the cladding and the core of the optical fiber or even cladding breakage, and solves the problem of uneven heating of the cylindrical optical fiber by the traditional flame melting taper method. The cylindrical optical fiber subjected to uneven heating will have different mechanical properties in different directions, affecting the performance of the tapered optical fiber.

[0014] 2. By intercepting the normalized curve of the coupled light power of the sensor in the interval of 30 seconds before and after 10 minutes, it can be seen that the sensor can maintain a relatively stable strain response in the repeated stretching test. With the increase of the reciprocating stretching strain, the amplitude of the response waveform interval increases to a certain extent, which is consistent with the scenario in actual applications that when an individual takes a deep breath, the body circumference changes and the breathing rate slows down. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 A flow chart for making a tapered optical fiber sensor of the present invention; Figure 2 Schematic diagram of sensors with different arrangement combinations of the present invention; Figure 3 It is a schematic diagram of the tapered optical fiber sensor of the present invention; Figure 4 It is an electrically heated fusion taper platform for the tapered optical fiber of the present invention; Figure 5 This is a diagram of the tapered optical fiber taper experiment of the present invention; Figure 6 This is a mutation diagram of the tapered optical fiber sample of the present invention; Figure 7 This is a diagram showing uniform changes in the tapered optical fiber of the present invention; Figure 8 The electron microscope images of the average diameters of the tapered polymer optical fiber at different positions of the present invention are measured; Fig. 9 It is a connection diagram of the tensile measurement device of the present invention; Fig.10 It is the structural stretching-coupling fitting curve diagram in the present invention 4; Fig.11 This is a curve diagram of the repeated stretching amplitude of the optical fiber sensor of the present invention under different strains. DETAILED DESCRIPTION

[0016] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0017] Embodiment 1: Refer to the attached Figure 1-8 , a preparation process of a high-sensitivity tapered optical fiber sensor, comprising the following steps: S1. The evanescent coupling region of the tapered optical fiber, 10 mm at the end of the tapered region, is bent and wound on a customized cylindrical mold with a radius of 3.183 mm. The bending position is fixed with a high-temperature resistant tape, and the distance and position of the cylinder are fixed with an acrylic plate. S2. Place the fixed tapered optical fiber and mold on a constant temperature heating platform for low-temperature heating and shaping. The heating temperature is 90°C and the heating time is 30 minutes. To reduce the influence of external air flow on the temperature, a closed cover is added to the heating platform. S3, take out the finalized optical fiber, and Figure 2As shown in the figure, the tapered optical fiber group arrangement model, two bent tapered optical fibers and a double layer of 0.4 mm thick TPU, 5 cm long and 2.5 cm wide, are hot pressed at 120 ° C for 20 s to prepare optical fiber sensor samples with different arrangement structures, such as Figure 2 As shown; after the sensor is connected to the light source, you can see that the output port of the coupled optical fiber receives light. The placement of the optical fiber can be as follows Figure 2 Set up in the arrangement shown; S4. Use a black thermoplastic tube to encapsulate the extra fiber pigtails outside the TPU, polish the ends of the two optical fibers, and connect them to the FC interface with resin glue to complete the preparation of the optical fiber sensor. Figure 3 shown.

[0018] The two prepared tapered optical fibers are shaped and hot-pressed in turn and embedded into an elastic substrate. In order to reduce the impact of the external environment on the optical fiber pigtail and strengthen the stability of the interface, the optical fiber is thermoplastically encapsulated and the FC interface is welded.

[0019] The mold material in S1 is ABS, acrylonitrile-butadiene-styrene copolymer, a standard cylinder, and the operating temperature range is 0°C-120°C. Compared with the iron mold, the surface of the ABS cylinder is uniform and smooth, and will not cause wear to the surface of the polymer optical fiber during the production process to prevent shape changes during heating.

[0020] In the S3, both ends of the TPU are bonded with double-layer non-elastic fabrics, and the TPU is a highly elastic thermoplastic polyurethane film.

[0021] Embodiment 2: Based on embodiment 1, the difference is that; Refer to the attached Figures 4 to 8 As shown, the tapered optical fiber taper method in S1 comprises the following steps: S1. Marking the melt-stretched area of ​​the optical fiber: The tapered optical fiber is prepared by the fixed-length stretching method. First, a 40-cm-long optical fiber is taken, and the 10-cm heating area in the middle is located. Positioning labels are attached to both ends of the heating area, and both ends of the optical fiber are trimmed using optical fiber scissors. S2. At room temperature of 26 degrees, the optical fiber is suspended in the center of the heating cylinder to make the optical fiber in the temperature field heated evenly. Then the two ends of the optical fiber are embedded in the grooves of the magnetic optical fiber flip cover fixture, and one side of the telescopic bracket is fixed on the translation stage. Figure 5 As shown; S3, start the temperature controller, heat the heating tube to the set temperature, and after waiting for the predetermined heating time, start the translation stage to stretch at a uniform speed according to the set stretching distance. The stretching speed pulse value is fixed at 2000 Hz and the speed is 0.25 mm / s; The set temperature of the heating tube is 100-150°C, preferably 115°C, and the predetermined heating time is 10-25 seconds, preferably 20 seconds; S4. After the stretching is completed, turn off the temperature controller, wait for the heating tube to cool to room temperature, open the clamping instrument, and take out the stretched tapered optical fiber; By building a small electric heating melting stretching platform, using a local uniform electric heating cylinder and a high-precision translation stage to stretch and produce polymer tapered optical fibers, the effects of heating temperature, heating time and stretching distance on the forming of tapered optical fibers were explored. Different types of fiber taper processes have their own characteristics in preparing tapered optical fibers. The flame taper process is relatively simple and applicable to a variety of materials, but it is difficult to accurately control the temperature, which may cause damage to the optical fiber material. The electric taper process can quickly prepare fine tapered optical fibers, but requires special equipment and high voltage. The laser taper process has highly precise control and wide material applicability, but requires professional skills and equipment, and may require higher costs. In comparison, the fusion taper process has significant process advantages, but the traditional flame fusion taper method heats the cylindrical optical fiber unevenly. The mechanical properties of the cylindrical optical fiber subjected to uneven heating will be different in different directions, affecting the performance of the tapered optical fiber. By designing an annular heat source to uniformly heat the optical fiber, it helps to make the tapered optical fiber structure prepared under axial tension symmetrical and uniform.

[0022] Therefore, this study proposes a tapered optical fiber processing method based on electric heating annular heat source melting, and its platform is mainly composed of an electric heating melting module and a high-precision translation stretching module; Electric heating melting module: In order to build a uniform physical field that is stable internally and isolated from the influence of the external environment, a glass fiber heating cloth coated with silicone rubber is selected as the heat source, and the fiber cloth is made into a cylindrical heating component and connected to an intelligent digital temperature controller. The silicone cloth is a high-temperature resistant, corrosion-resistant, and high-strength glass fiber cloth. The nickel-chromium alloy heating wire is evenly arranged between the two layers of glass fiber cloth, which can provide a stable, uniform and stable heat source below 250°C; This document tests the effect of heating cylinders with radii of 0.5cm, 1cm, and 1.5cm on the forming of tapered optical fibers at the same temperature and heating time. It is found that the opening of the heating cylinder with a radius of 1cm can allow the internal temperature field to have a certain gradient distribution, which slows down the strong temperature change of the polymer optical fiber at the heating junction and avoids the risk of separation of the cladding and the core of the optical fiber or even cladding breakage. Therefore, this document selects a heating sleeve with a radius of 1cm; High-precision translation stretching module: In order to accurately control the distance and speed of each fiber taper, this document uses MTS302 high-precision heavy-duty electric control translation stage and SC100 displacement control stepper motor; the control motor sets the minimum unit of the translation stage to 0.001 mm, and its platform composition is as follows Figure 4 shown.

[0023] The optical fiber in S1 is a multimode polymer optical fiber, the core material is polymethyl methacrylate, the refractive index n1 is 1.492, the core diameter is 485±25um, the cladding material is fluororesin, the refractive index n2=1.417, and the cladding diameter is 500±25um.

[0024] Before the formal experiment, the tapered optical fiber needs to be pre-tested to test the upper limit of the optical fiber melting deformation temperature, and then explore the relationship between the heating temperature, heating time, stretching distance and the optical fiber tapered area formation by continuously adjusting the parameter range; Preparation and measurement of tapered optical fibers: The multimode polymer optical fiber taper process is explored by adjusting parameters such as heating temperature, heating time, and stretching distance; the appearance morphology analysis and size measurement of tapered optical fibers made with different parameters are performed; Experimental results analysis: When the heating temperature is higher than 130°C, the polymer optical fiber melts rapidly in the melting heating zone, and abnormal melting bending is likely to occur at the tapered transition.

[0025] At about 115°C, the fiber taper changes evenly, the heating time has a significant effect on the taper, and the taper length increases with the stretching length.

[0026] When the heating temperature is lower than 110℃, the change of the fiber taper region is not obvious.

[0027] If the heating time is less than 10 seconds, the material inside and outside the optical fiber is uneven, and bending and diameter thickening may occur. Figure 6 Schematic diagram of a in the figure, Figure 6 a and b in the figure are respectively the tapered fiber bending and the tapered region mutation; Figure 7 The a and b optical fibers change in the heating section between 30 and 35 mm, and the c, d, e and f optical fibers change in the heating section between 35 and 40 mm.

[0028] Increasing the stretching distance can improve the uniformity of the appearance of the cone area to a certain extent. If the stretching distance is too long and the temperature is insufficient, a mutation will occur in the micro-nano cone area, such as Figure 6 Schematic diagram b in the figure. At the same time, it will also reduce the speed at which the fiber diameter becomes thinner, and the taper required for simulation cannot be achieved within a certain taper length range; After many experimental adjustments, the target parameters for fiber taper drawing in this document are set to heating temperature 115℃, heating time 20s, and stretching distance 20mm. This parameter can ensure that the drawn fiber has good beam characteristics. Under this parameter, the length of the fiber taper area can reach 20mm.

[0029] The 3D profilometer was used to observe the forming of 10 tapered optical fibers made under the parameters mentioned above. The diameter was measured every 5 mm starting from the heating positioning mark point. The positions where the tapered area began to change and the minimum taper were marked respectively. The size data is shown in the attached Figure 6 As shown; Since the device uses a heating tube with open ends, it is conducive to forming a certain temperature gradient. In the central area of ​​the heating tube, the optical fiber is subjected to the highest temperature and reaches the molten state first. When subjected to uniform external force stretching, the diameter change is reflected on the polymer optical fiber as gradually becoming thinner from the "opening area" to the "central heating area"; the optical fiber diameter within the first 30 mm near the opening is basically unchanged, and in the area after 30 mm, the optical fiber diameter begins to decrease significantly, and reaches the minimum in the central heating area.

[0030] Embodiment 3: Based on embodiment 1, the difference is that; See attached Figures 9 to 11 , a test method for testing a high-sensitivity tapered optical fiber sensor, comprising the following steps: S1. After polishing the two end faces of the sensor, connect them to the light source and light detector through a bare fiber adapter; the light source and detector are fixed on a high-precision lifting platform, and the lifting platform at one end is fixed to a high-precision translation platform; the high-precision translation platform is controlled by a motor to control the stretching speed and stretching distance, and the light detector is connected to the computer's optical power meter application software BPM to monitor the optical power change in real time; S2. Fix the optical fiber sensor on a lifting platform with both ends horizontal, keep the optical fiber sensor in a naturally straight but not stretched state, fix the elastic length of the sensor to 5 cm, and record the initial coupled light intensity of the sensor; S3, the stepper motor set by the high-precision translation stage is stretched at a fixed speed of 0.25mm / s, and the stretching distance is increased in units of 1mm, and the total stretching length reaches 20mm. After each stretching, the sensor output optical power monitored by the optical power software is recorded, and a total of 21 output optical powers with different stretching amounts are recorded; As attached Fig. 9 and 10 As shown, three independent tensile test results are retained for each sample, and the three tensile data of each sample are fitted to obtain its change trend. As shown in the figure are the tensile change curves of the sensor elements of four arrangement modes; The initial evanescent light intensity is A>B>C>D, Fig. 9 It can be seen from the optical fiber sensor connected to the light source that in the A arrangement, the evanescent light of the tapered optical fiber is more easily received by the coupled optical fiber along the light propagation direction, and the experimental results are consistent with the simulation analysis; The trinomial fitting was performed on the strain coupling data of the four structures. The coefficients of the fitting function represent the linear relationship between the strain and the coupling data. Comprehensive analysis of the coefficients of the trinomials shows that the absolute value of the comprehensive fitting coefficient of structure A is larger, indicating that the structure is more sensitive to the change to coupled data; By observing the change in the curve amplitude within the stretching distance of 0-20mm, it can be seen that the A structure has the largest drop, and the curve is more sensitive to the change in distance. In summary, the A arrangement is the easiest arrangement structure to form coupling, and has the best sensitivity within the coupling distance of 0-20mm.

[0031] S4. Perform repetitive reciprocating tensile tests on the sensor at a constant speed through the stepper motor in the high-precision translation stage to understand the value of the corresponding tensile strain distance. The high-precision translation stage is set by the stepper motor at a constant speed of 0.25 mm / s, and the reciprocating motion lasts for 10 minutes. The strain percentages of 5%, 10%, 15%, and 20% are applied to the sensor respectively, and the corresponding tensile strain distances are 2.5 mm, 5 mm, 7.5 mm, and 10 mm respectively. Repeatability refers to the ability of the strain sensor to recover its original state during the reciprocating stretching and straining process. In actual applications, breathing drives the human chest and abdomen to expand and contract cyclically, and the fiber optic sensor will also perform repetitive reciprocating stretching. The dimensional differences in the body fluctuations of different individuals during breathing are also different. The sensor principle of this application is based on the evanescent field and bending loss of a bent tapered optical fiber, and has higher sensitivity to small changes; To this end, this section conducts repeatable experiments on the designed optical fiber sensor with different stretching amounts. The sensor is also Fig. 9 The experimental system constructed as shown is used for repeated tensile tests; The test structure is as follows Fig.11 As shown in the figure, under the four strain conditions, the normalized curves of the coupled optical power of the sensor in the 30s interval before and after 10 minutes (10s-30s, 560s-590s) were respectively intercepted. It can be seen that the sensor can maintain a relatively stable strain response in the repeated tensile test. With the increase of the reciprocating tensile strain, the amplitude of the response waveform interval increases to a certain extent, which is consistent with the scenario in actual applications that when an individual takes a deep breath, the body circumference changes and the breathing rate slows down.

[0032] It should be noted that the term "comprises" or any other variation thereof is intended to cover non-exclusive inclusion, so that a process, method, article, or device that includes a series of elements includes not only those elements, but also includes other elements that are 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 presence of other identical elements in the process, method, article, or device that includes the element.

[0033] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A preparation process of a highly sensitive tapered optical fiber sensor. It is characterized in that The following steps are involved: S1. Bend and wrap the evanescent coupling region of the tapered optical fiber around a customized cylindrical mold with a radius of 3.183 mm, fix the bending position with a high-temperature resistant tape, and fix the distance and position of the cylinder with an acrylic plate; S2. Place the fixed tapered optical fiber and mold on a constant temperature heating table for low temperature heating and shaping. The heating temperature is 90°C and the heating time is 30 minutes. S3. Take out the finalized optical fiber, and heat-press two bent tapered optical fibers and a double layer of 0.4 mm thick TPU at 120°C for 20 seconds to prepare optical fiber sensor samples with different arrangement structures; after the sensor is connected to the light source, it can be seen that the output port of the coupled optical fiber receives light; S4. Encapsulate the extra optical fiber pigtails outside the TPU with a black thermoplastic tube, polish the ends of the two optical fibers and connect them to the FC interface with resin glue to complete the preparation of the optical fiber sensor.

2. The preparation process of a highly sensitive tapered optical fiber sensor according to claim 1, Features: The mold material of S1 is ABS standard cylinder, and the operating temperature range is 0℃-120℃.

3. The preparation process of a high-sensitivity tapered optical fiber sensor according to claim 1, Features: In the S3, both ends of the TPU are bonded with double-layer non-elastic fabrics, and the TPU is a highly elastic thermoplastic polyurethane film.

4. A process for preparing a highly sensitive tapered optical fiber sensor according to any one of claims 1 to 3, Features: The method for tapering a tapered optical fiber in S1 comprises the following steps: S1. Marking the melt-stretched area of ​​the optical fiber: The tapered optical fiber is prepared by the fixed-length stretching method. First, a 40-cm-long optical fiber is taken, and the 10-cm heating area in the middle is located. Positioning labels are attached to both ends of the heating area, and both ends of the optical fiber are trimmed using optical fiber scissors. S2. At room temperature of 26 degrees, the optical fiber is suspended in the center of the heating cylinder to make the optical fiber in the temperature field heated evenly. Then the two ends of the optical fiber are embedded in the grooves of the magnetic optical fiber flip cover fixture, and one side of the telescopic bracket is fixed on the translation stage; S3, start the temperature controller, heat the heating tube to the set temperature, and after waiting for the predetermined heating time, start the translation stage to stretch at a uniform speed according to the set stretching distance. The stretching speed pulse value is fixed at 2000 Hz and the speed is 0.25 mm / s; S4. After the stretching is completed, turn off the temperature controller, wait for the heating tube to cool to room temperature, open the clamping instrument, and take out the stretched tapered optical fiber.

5. The preparation process and testing method of a highly sensitive tapered optical fiber sensor according to claim 4, Features: The optical fiber in S1 is a multimode polymer optical fiber, the core material is polymethyl methacrylate, and the refractive index is n 1 is 1.492, the core diameter is 485±25um, the cladding material is fluororesin, and the refractive index is n 2 =1.417, cladding diameter 500±25um.

6. A method for testing a highly sensitive tapered optical fiber sensor as claimed in any one of claims 1 to 3, It is characterized in that The following steps are involved: S1. After polishing the two end faces of the sensor, connect them to the light source and light detector through a bare fiber adapter; the light source and detector are fixed on a high-precision lifting platform, and the lifting platform at one end is fixed to the high-precision translation platform; The high-precision translation stage is controlled by a motor to control the stretching speed and stretching distance, and the light detector is connected to the computer's optical power meter application software BPM to monitor the optical power changes in real time; S2. Fix the optical fiber sensor on a lifting platform with both ends horizontal, keep the optical fiber sensor in a naturally straight but not stretched state, fix the elastic length of the sensor to 5 cm, and record the initial coupled light intensity of the sensor; S3, stretching at a fixed speed through a stepper motor set up by a high-precision translation stage, and recording the sensor output optical power monitored by the optical power software after each stretching, and the test results of the optical fiber sensor can be understood by recording the output optical power; S4. Perform repetitive reciprocating tensile tests on the sensor at a constant speed using a stepper motor in a high-precision translation stage to understand the value of the corresponding tensile strain distance.

7. A method for testing a high-sensitivity tapered optical fiber sensor according to claim 6, Features: The stretching method in S3 is: stretching at a fixed speed of 0.25 mm / s, and the stretching distance increases in units of 1 mm, and the total stretching length is 20 mm.

8. A method for testing a high-sensitivity tapered optical fiber sensor according to claim 6, Features: The S3 medium-to-high-precision translation stage is set by a stepper motor at a constant speed of 0.25 mm / s and a reciprocating motion for 10 minutes, applying 5%, 10%, 15%, and 20% strain percentages to the sensor respectively, and the corresponding tensile strain distances are 2.5 mm, 5 mm, 7.5 mm, and 10 mm, respectively.

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