Optical fiber strain sensor based on vernier effect and manufacturing method thereof

Abstract

The invention belongs to the technical field of optical fiber sensing application, and particularly relates to an optical fiber strain sensor based on a vernier effect and a manufacturing method thereof. The optical fiber strain sensor based on the vernier effect is composed of a one-to-two coupler, a high-sensitivity Fabry-Perot interferometer used for sensing and a low-sensitivity Fabry-Perot interferometer used for reference, wherein the high-sensitivity Fabry-Perot interferometer and the low-sensitivity Fabry-Perot interferometer are connected with the one-to-two coupler in parallel. The high-sensitivity Fabry-Perot interferometer and the low-sensitivity Fabry-Perot interferometer are both made of single-mode fibers, and a cylinder-like bubble is embedded in the center of a conical section of the high-sensitivity Fabry-Perot interferometer; and an ellipsoid-like bubble is embedded in the center of the shuttle-shaped section of the low-sensitivity Fabry-Perot interferometer. The strain sensor can obviously improve the sensitivity of stress measurement, and the strain sensitivity of the strain sensor reaches up to 854.9 pm / mu epsilon. The manufacturing process is simple, and the manufacturing cost is low.

Description

Technical Field

[0001] The present invention belongs to the technical field of optical fiber sensing applications, and in particular relates to an optical fiber strain sensor based on a vernier effect and a manufacturing method thereof. Background Art

[0002] The vernier effect is widely used in interferometric fiber optic sensors due to its excellent sensitivity enhancement capability and simple implementation. This mechanism involves integrating a pair of interferometers, usually referred to as a reference interferometer and a sensing interferometer, in series or parallel, to produce two closely matched free spectral ranges, which in turn simulate a vernier scale. This forms a vernier envelope peak that is highly sensitive to environmental changes, thereby facilitating highly sensitive monitoring of physical parameters such as temperature, strain, and refractive index. However, this method of improving sensitivity can introduce multi-parameter crosstalk and reduce interferometric contrast.

[0003] Fabry-Perot interferometer (FPI) is well known for its reliable free spectral range control capability, simple configuration and extremely low temperature cross-sensitivity, which make it a popular element in fiber optic strain sensors based on the Vernier effect. To produce a stable interference spectrum, specific fiber structures are usually required, including hollow-core photonic crystal fibers, solid-core photonic crystal fibers and silica capillaries. The ability of the Vernier effect to improve sensitivity depends on the product of the free spectral range of the reference interferometer and the sensing interferometer and the difference between the two. Therefore, to obtain a higher extinction ratio and a wider free spectral range, a smaller and specially structured Fabry-Perot cavity is required to improve the sensitivity of the sensor. Summary of the invention

[0004] In order to obtain a highly sensitive stress measurement sensor, the present invention provides an optical fiber strain sensor based on the vernier effect and a manufacturing method thereof. The strain sensor can significantly improve the sensitivity of stress measurement and has low cost.

[0005] The technical solution adopted by the present invention is: an optical fiber strain sensor based on the vernier effect, the optical fiber strain sensor is composed of a one-to-two coupler and a high-sensitivity Fabry-Perot interferometer (FPI) connected in parallel with the one-to-two coupler for sensing. S ) and a low-sensitivity Fabry-Perot interferometer (FPI) used as a reference R 10).

[0006] The high-sensitivity Fabry-Perot interferometer and the low-sensitivity Fabry-Perot interferometer are both made by fusion splicing single-mode optical fibers. A quasi-cylindrical bubble is embedded in the center of the conical section of the high-sensitivity Fabry-Perot interferometer; a quasi-ellipsoidal bubble is embedded in the center of the shuttle section of the low-sensitivity Fabry-Perot interferometer.

[0007] Furthermore, the cladding diameter of the single-mode optical fiber is 125μm, and its core diameter is 8.2μm; the length of the tapered section is 500μm-600μm, and the minimum cladding diameter in the middle of the tapered section is 65μm-70μm; the axial length of the quasi-cylindrical bubble along the optical fiber is 57μm-60μm, and the average wall thickness of the quasi-cylindrical bubble from the edge of the cladding is 1μm-3μm; the length of the shuttle-shaped section is 500μm-600μm, and the maximum cladding diameter in the middle of the shuttle-shaped section is 145μm-165μm, the axial length of the quasi-ellipsoidal bubble along the optical fiber is 2μm-4μm smaller than the axial length of the quasi-cylindrical bubble along the optical fiber, and the average wall thickness of the quasi-ellipsoidal bubble from the edge of the cladding is 20μm-30μm.

[0008] Furthermore, the cladding diameter of the single-mode optical fiber is 125μm, and its core diameter is 8.2μm; the length of the tapered section is 500μm, and the minimum cladding diameter in the middle of the tapered section is 65μm; the axial length of the quasi-cylindrical bubble along the optical fiber is 57μm, and the average wall thickness of the quasi-cylindrical bubble from the edge of the cladding is 1μm; the length of the shuttle-shaped section is 500μm, and the maximum cladding diameter in the middle of the shuttle-shaped section is 145μm; the axial length of the quasi-ellipsoidal bubble along the optical fiber is 55μm, and the average wall thickness of the quasi-ellipsoidal bubble from the edge of the cladding is 20μm.

[0009] Furthermore, the cladding diameter of the single-mode optical fiber is 125μm, and its core diameter is 8.2μm; the length of the tapered section is 550μm, and the minimum cladding diameter in the middle of the tapered section is 67.5μm; the axial length of the quasi-cylindrical bubble along the optical fiber is 58.5μm, and the average wall thickness of the quasi-cylindrical bubble from the edge of the cladding is 2μm; the length of the shuttle-shaped section is 550μm, and the maximum cladding diameter in the middle of the shuttle-shaped section is 155μm; the axial length of the quasi-ellipsoidal bubble along the optical fiber is 55.5μm, and the average wall thickness of the quasi-ellipsoidal bubble from the edge of the cladding is 25μm.

[0010] Furthermore, the cladding diameter of the single-mode optical fiber is 125μm, and its core diameter is 8.2μm; the length of the tapered section is 600μm, and the minimum cladding diameter in the middle of the tapered section is 70μm; the axial length of the quasi-cylindrical bubble along the optical fiber is 60μm, and the average wall thickness of the quasi-cylindrical bubble from the edge of the cladding is 3μm; the length of the shuttle-shaped section is 600μm, and the maximum cladding diameter in the middle of the shuttle-shaped section is 165μm; the axial length of the quasi-ellipsoidal bubble along the optical fiber is 56μm, and the average wall thickness of the quasi-ellipsoidal bubble from the edge of the cladding is 30μm.

[0011] Furthermore, the conical section is a double cone with a small size in the middle and large sizes in two sections.

[0012] Furthermore, the single-mode optical fiber model is G.652 single-mode optical fiber.

[0013] The preparation method of the high-sensitivity Fabry-Perot interferometer comprises the following steps: Step 1: Cut the end faces of two single-mode optical fibers into flat end faces and place them in a fiber optic fusion splicer. Control the stepper motor of the fiber optic fusion splicer so that the flat end faces are placed at the discharge center of the fiber optic fusion splicer.

[0014] Step 2: Control the optical fiber fusion splicer to discharge the two flat end faces to melt them into spherical end faces. The discharge time is 800ms and the discharge power is standard power.

[0015] Step 3: Take out the two single-mode optical fibers processed in step 2, dip glycerin on the spherical end faces and put them into the optical fiber fusion splicer. Control the stepper motor of the optical fiber fusion splicer to make the spherical end faces of the two single-mode optical fibers contact at the discharge center of the optical fiber fusion splicer.

[0016] Step 4: Control the optical fiber fusion splicer to perform discharge fusion splicing on two single-mode optical fibers. The discharge time is 800 ms and the discharge power is standard power. During the fusion splicing process, a micro bubble is formed at the connection of the two spherical end faces.

[0017] Step 5: Slightly stretch the optical fiber by controlling the stepper motor of the optical fiber fusion splicer and keep the microbubbles at the discharge point of the optical fiber fusion splicer. The microbubbles are expanded by long-term high-power discharge and form a conical section at the fusion point of the single-mode optical fiber. The discharge time is 1400ms and the discharge power is +20 power. The expanded microbubbles are round bubbles.

[0018] Step 6. Control the stepper motor of the fiber fusion splicer to slightly squeeze the single-mode optical fiber and keep the circular bubble at the discharge point of the fiber fusion splicer. The circular bubble is repaired into a quasi-cylindrical bubble through short-time low-power discharge. The discharge time is 600ms and the discharge power is standard power. The single-mode optical fiber with a quasi-cylindrical bubble embedded in the center of the tapered section is a high-sensitivity Fabry-Perot interferometer.

[0019] Furthermore, the preparation method of the low-sensitivity Fabry-Perot interferometer comprises the following steps: Step 1: Cut the end faces of two single-mode optical fibers into flat end faces and place them in a fiber optic fusion splicer. Control the stepper motor of the fiber optic fusion splicer so that the flat end faces are placed at the discharge center of the fiber optic fusion splicer.

[0020] Step 2: Control the optical fiber fusion splicer to discharge the two flat end faces to fuse them into spherical end faces. The discharge time is 800ms and the discharge power is standard power.

[0021] Step 3: Take out the two single-mode optical fibers processed in step 2, dip glycerin on the spherical end faces and put them into the optical fiber fusion splicer. Control the stepper motor of the optical fiber fusion splicer to make the spherical end faces of the two single-mode optical fibers contact at the discharge center of the optical fiber fusion splicer.

[0022] Step 4: Control the optical fiber fusion splicer to perform discharge fusion splicing on two single-mode optical fibers. The discharge time is 800 ms and the discharge power is standard power. During the fusion splicing process, a micro bubble is formed at the connection of the two spherical end faces.

[0023] Step 5: Slightly stretch the optical fiber by controlling the stepper motor of the optical fiber fusion splicer, and keep the microbubbles at the discharge position of the optical fiber fusion splicer. Expand the microbubbles through long-term high-power discharge. The expanded microbubbles are round bubbles. The discharge time is 1400ms and the discharge power is +20 power.

[0024] Step 6. Control the stepper motor of the fiber fusion splicer to slightly squeeze the single-mode optical fiber and keep the circular bubble at the discharge point of the fiber fusion splicer. The circular bubble is repaired into an ellipsoidal bubble through short-time low-power discharge. At this time, the cladding of the ellipsoidal bubble is a shuttle-shaped segment. The discharge time is 600ms and the discharge power is standard power. The single-mode optical fiber with an ellipsoidal bubble embedded in the center of the shuttle-shaped segment is a low-sensitivity Fabry-Perot interferometer.

[0025] Furthermore, by precisely controlling the motor of the optical fiber fusion splicer to apply axial tension or pressure, and using arc discharge technology to precisely control and adjust the discharge time and discharge power, cylindrical and ellipsoidal bubbles of different sizes have been obtained.

[0026] Beneficial effects of the invention: The invention provides an optical fiber strain sensor based on the vernier effect and a manufacturing method thereof. The strain sensor can significantly improve the sensitivity of stress measurement, and its strain sensitivity is as high as 854.9pm / με. The manufacturing process is simple, the manufacturing cost is low, and the difficulty of obtaining the vernier effect phenomenon is reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 is a schematic diagram of the structure of the optical fiber strain sensor in Example 1; Figure 2 is a schematic structural diagram of a high-sensitivity Fabry-Perot interferometer in Embodiment 1; Figure 3 is a schematic structural diagram of a low-sensitivity Fabry-Perot interferometer in Embodiment 1; Figure 4 is a microscope image of the high-sensitivity Fabry-Perot interferometer in Example 1; Figure 5 It is a microscope picture of a low-sensitivity Fabry-Perot interferometer; Figure 6 It is a schematic diagram of the first step of the method for manufacturing the Fabry-Perot interferometer in the fourth embodiment and the fifth embodiment; Figure 7 is a schematic diagram of the second step of the method for manufacturing the Fabry-Perot interferometer in the fourth and fifth embodiments; Figure 8 is a schematic diagram of the third step of the method for manufacturing the Fabry-Perot interferometer in Embodiment 4 and Embodiment 5; Fig. 9 is a schematic diagram of the fourth step of the method for manufacturing the Fabry-Perot interferometer in the fourth and fifth embodiments; Fig.10 is a schematic diagram of the fifth step of the method for manufacturing the Fabry-Perot interferometer in the fourth and fifth embodiments; Fig.11 is a schematic diagram of the sixth step of the method for manufacturing a high-sensitivity Fabry-Perot interferometer in Example 4; Fig.12 Schematic diagram of the sixth step of the method for manufacturing a low-sensitivity Fabry-Perot interferometer in Example 5 Fig.13 Spectral diagram of the interference curve of the optical fiber strain sensor in the range of 0-300με as the strain changes.

[0028] Figure numerals: 1. high-sensitivity Fabry-Perot interferometer; 2. low-sensitivity Fabry-Perot interferometer; 3. one-to-two coupler; 4. conical section; 5. quasi-cylindrical bubble; 6. shuttle-shaped section; 7. quasi-ellipsoidal bubble; 8. flat end face; 9. spherical end face; 10. glycerol; 11. microbubble; 12. round bubble. DETAILED DESCRIPTION Example

[0029] like Figure 1 As shown, the optical fiber strain sensor based on the vernier effect is composed of a one-to-two coupler 3, a high-sensitivity Fabry-Perot interferometer 1 used for sensing and a low-sensitivity Fabry-Perot interferometer 2 used for reference connected in parallel with the one-to-two coupler 3.

[0030] like Figure 2-Figure 5 As shown, the high-sensitivity Fabry-Perot interferometer 1 and the low-sensitivity Fabry-Perot interferometer 2 are both made by fusion splicing single-mode optical fibers, and a quasi-cylindrical bubble 5 is embedded in the center of the conical section 4 of the high-sensitivity Fabry-Perot interferometer 1; and a quasi-ellipsoidal bubble 7 is embedded in the center of the shuttle section 6 of the low-sensitivity Fabry-Perot interferometer 2.

[0031] The cladding diameter of the single-mode optical fiber is 125μm, and its core diameter is 8.2μm; the length of the conical section 4 is 500μm, and the minimum cladding diameter in the middle of the conical section 4 is 65μm; the axial length of the quasi-cylindrical bubble 5 along the optical fiber is 57μm, and the average wall thickness of the quasi-cylindrical bubble 5 from the edge of the cladding is 1μm; the length of the shuttle-shaped section 6 is 500μm, and the maximum cladding diameter in the middle of the shuttle-shaped section 6 is 145μm; the axial length of the quasi-ellipsoidal bubble 7 along the optical fiber is 55μm, and the average wall thickness of the quasi-ellipsoidal bubble 7 from the edge of the cladding is 20μm. Example

[0032] On the basis of the technical solution of Example 1, the cladding diameter of the single-mode optical fiber is 125μm, and its core diameter is 8.2μm; the length of the conical section 4 is 550μm, and the minimum cladding diameter in the middle of the conical section 4 is 67.5μm; the axial length of the quasi-cylindrical bubble 5 along the optical fiber is 58.5μm, and the average wall thickness of the edge of the quasi-cylindrical bubble 5 from the cladding is 2μm; the length of the shuttle section 6 is 550μm, and the maximum cladding diameter in the middle of the shuttle section 6 is 155μm; the axial length of the quasi-ellipsoidal bubble 7 along the optical fiber is 55.5μm, and the average wall thickness of the edge of the quasi-ellipsoidal bubble 7 from the cladding is 25μm. Example

[0033] On the basis of the technical solution of Example 1, the cladding diameter of the single-mode optical fiber is 125μm, and its core diameter is 8.2μm; the length of the conical section 4 is 600μm, and the minimum cladding diameter in the middle of the conical section 4 is 70μm; the axial length of the quasi-cylindrical bubble 5 along the optical fiber is 60μm, and the average wall thickness of the edge of the quasi-cylindrical bubble 5 from the cladding is 3μm; the length of the shuttle section 6 is 600μm, and the maximum cladding diameter in the middle of the shuttle section 6 is 165μm; the axial length of the quasi-ellipsoidal bubble 7 along the optical fiber is 56μm, and the average wall thickness of the edge of the quasi-ellipsoidal bubble 7 from the cladding is 30μm. Example

[0034] like Figure 6-Figure 11 As shown, the preparation method of the high-sensitivity Fabry-Perot interferometer includes the following steps: Step 1: Cut the end faces of two single-mode optical fibers into flat end faces 8 and place them in a fiber optic fusion splicer. Control the stepper motor of the fiber optic fusion splicer so that the flat end faces 8 are placed at the discharge center of the fiber optic fusion splicer.

[0035] Step 2: Control the optical fiber fusion splicer to perform discharge processing on the two flat end faces 8 to fuse the flat end faces 8 into spherical end faces 9. The discharge time is 800ms and the discharge power is standard power.

[0036] Step 3: Take out the two single-mode optical fibers processed in step 2, dip glycerol 10 at the spherical end faces 9 and put them into the optical fiber fusion splicer. Control the stepper motor of the optical fiber fusion splicer to make the spherical end faces 9 of the two single-mode optical fibers contact at the discharge center of the optical fiber fusion splicer.

[0037] Step 4: Control the optical fiber fusion splicer to perform discharge fusion splicing on two single-mode optical fibers. The discharge time is 800 ms and the discharge power is standard power. During the fusion splicing process, a micro bubble 11 is formed at the connection of the two spherical end faces 9 .

[0038] Step 5: Control the stepper motor of the optical fiber fusion splicer to slightly stretch the optical fiber and keep the microbubble 11 at the discharge point of the optical fiber fusion splicer. The microbubble 11 is expanded by high-power and long-term discharge to form a conical section 4 at the fusion point of the single-mode optical fiber. The discharge time is 1400ms, the discharge power is +20 power, and the expanded microbubble 11 is a round bubble 12.

[0039] Step six, control the stepper motor of the optical fiber fusion splicer to slightly squeeze the single-mode optical fiber, and keep the circular bubble 12 at the discharge point of the optical fiber fusion splicer, and repair the circular bubble 12 into a quasi-cylindrical bubble 5 through a short-time low-power discharge, the discharge time is 600ms, and the discharge power is standard power; the single-mode optical fiber with a quasi-cylindrical bubble 5 embedded in the center of the tapered section 4 is a high-sensitivity Fabry-Perot interferometer 1. Example

[0040] like Figure 6-Figure 10 and Fig.12 As shown, the preparation method of the low-sensitivity Fabry-Perot interferometer comprises the following steps: Step 1: Cut the end faces of two single-mode optical fibers into flat end faces 8 and place them in a fiber optic fusion splicer. Control the stepper motor of the fiber optic fusion splicer so that the flat end faces 8 are placed at the discharge center of the fiber optic fusion splicer.

[0041] Step 2: Control the optical fiber fusion splicer to perform discharge processing on the two flat end faces 8 to fuse the flat end faces 8 into spherical end faces 9. The discharge time is 800 ms and the discharge power is standard power.

[0042] Step 3, take out the two single-mode optical fibers processed in step 2, dip glycerol 10 at the spherical end faces 9 and put them into the optical fiber fusion splicer, control the stepper motor of the optical fiber fusion splicer, and make the spherical end faces 9 of the two single-mode optical fibers contact at the discharge center of the optical fiber fusion splicer.

[0043] Step 4: Control the optical fiber fusion splicer to perform discharge fusion splicing on two single-mode optical fibers. The discharge time is 800 ms and the discharge power is standard power. During the fusion splicing process, a micro bubble 11 is formed at the connection of the two spherical end faces 9 .

[0044] Step 5: Control the stepper motor of the fiber fusion splicer to slightly stretch the optical fiber and keep the microbubble 11 at the discharge position of the fiber fusion splicer. Expand the microbubble 11 through long-term high-power discharge. The expanded microbubble 11 is a round bubble 12. The discharge time is 1400ms and the discharge power is +20 power.

[0045] Step 6, control the stepper motor of the optical fiber fusion splicer to slightly squeeze the single-mode optical fiber, and keep the circular bubble 12 at the discharge point of the optical fiber fusion splicer, and repair the circular bubble 12 into an ellipsoidal bubble 7 through low-power short-time discharge. At this time, the cladding of the ellipsoidal bubble 7 is a shuttle-shaped segment 6, the discharge time is 600ms, and the discharge power is standard power; the single-mode optical fiber with the ellipsoidal bubble 7 embedded in the center of the prepared shuttle-shaped segment 6 is a low-sensitivity Fabry-Perot interferometer 2. Example

[0046] The optical fiber strain sensor based on the vernier effect obtained in the above embodiment is applied in the field of strain measurement.

[0047] like Fig.13 As shown, Fig.13 This is a spectrum of the interference curve of a low-cost optical fiber strain sensor based on the vernier effect in the range of 0-300με as the strain changes. By measuring the wavelength change of the envelope peak of the interference curve, it can be obtained that the strain sensitivity of the sensor is as high as 854.9pm / με. The manufacturing process is simple and the manufacturing cost is low, which reduces the difficulty of obtaining the vernier effect phenomenon.

Claims

1. An optical fiber strain sensor based on vernier effect, characterized in that: The optical fiber strain sensor comprises a one-to-two coupler (3), a high-sensitivity Fabry-Perot interferometer (1) used for sensing and a low-sensitivity Fabry-Perot interferometer (2) used for reference connected in parallel with the one-to-two coupler (3); The high-sensitivity Fabry-Perot interferometer (1) and the low-sensitivity Fabry-Perot interferometer (2) are both made by fusion splicing single-mode optical fibers; a quasi-cylindrical bubble (5) is embedded at the center of the conical section (4) of the high-sensitivity Fabry-Perot interferometer (1); and a quasi-ellipsoidal bubble (7) is embedded at the center of the shuttle section (6) of the low-sensitivity Fabry-Perot interferometer (2).

2. The optical fiber strain sensor based on the vernier effect according to claim 1, characterized in that: The cladding diameter of the single-mode optical fiber is 125 μm, and the core diameter is 8.2 μm; the length of the tapered section (4) is 500 μm-600 μm, and the minimum cladding diameter at the middle of the tapered section (4) is 65 μm-70 μm; the axial length of the quasi-cylindrical bubble (5) along the optical fiber is 57 μm-60 μm, and the average wall thickness of the quasi-cylindrical bubble (5) from the edge of the cladding is 1 μm-3 μm; the length of the shuttle section (6) is 500 μm-600 μm, and the maximum cladding diameter at the middle of the shuttle section (6) is 145 μm-165 μm; the axial length of the quasi-ellipsoidal bubble (7) along the optical fiber is 2 μm-4 μm shorter than the axial length of the quasi-cylindrical bubble (5) along the optical fiber, and the average wall thickness of the quasi-ellipsoidal bubble (7) from the edge of the cladding is 20 μm-30 μm.

3. The optical fiber strain sensor based on the vernier effect according to claim 2, characterized in that: The length of the conical section (4) is 500 μm, and the minimum cladding diameter in the middle of the conical section (4) is 65 μm; the axial length of the quasi-cylindrical bubble (5) along the optical fiber is 57 μm, and the average wall thickness of the quasi-cylindrical bubble (5) from the edge of the cladding is 1 μm; the length of the shuttle section (6) is 500 μm, and the maximum cladding diameter in the middle of the shuttle section (6) is 145 μm; the axial length of the quasi-ellipsoidal bubble (7) along the optical fiber is 55 μm, and the average wall thickness of the quasi-ellipsoidal bubble (7) from the edge of the cladding is 20 μm.

4. The optical fiber strain sensor based on the vernier effect according to claim 2, characterized in that: The length of the conical section (4) is 550 μm, and the minimum cladding diameter in the middle of the conical section (4) is 67.5 μm; the axial length of the quasi-cylindrical bubble (5) along the optical fiber is 58.5 μm, and the average wall thickness of the quasi-cylindrical bubble (5) from the edge of the cladding is 2 μm; the length of the shuttle section (6) is 550 μm, and the maximum cladding diameter in the middle of the shuttle section (6) is 155 μm; the axial length of the quasi-ellipsoidal bubble (7) along the optical fiber is 55.5 μm, and the average wall thickness of the quasi-ellipsoidal bubble (7) from the edge of the cladding is 25 μm.

5. The optical fiber strain sensor based on the vernier effect according to claim 2, characterized in that: The length of the conical section (4) is 600 μm, and the minimum cladding diameter in the middle of the conical section (4) is 70 μm; the axial length of the quasi-cylindrical bubble (5) along the optical fiber is 60 μm, and the average wall thickness of the quasi-cylindrical bubble (5) from the edge of the cladding is 3 μm; the length of the shuttle section (6) is 600 μm, and the maximum cladding diameter in the middle of the shuttle section (6) is 165 μm; the axial length of the quasi-ellipsoidal bubble (7) along the optical fiber is 56 μm, and the average wall thickness of the quasi-ellipsoidal bubble (7) from the edge of the cladding is 30 μm.

6. A method for preparing a high-sensitivity Fabry-Perot interferometer, characterized in that: The preparation method comprises the following steps: Step 1: Cut the end faces of two single-mode optical fibers into flat end faces (8) and place them in an optical fiber fusion splicer, and control the stepper motor of the optical fiber fusion splicer so that the flat end faces (8) are placed at the discharge center of the optical fiber fusion splicer; Step 2: Controlling the optical fiber fusion splicer to perform discharge processing on the two flat end surfaces (8), so as to fuse the flat end surfaces (8) into spherical end surfaces (9); Step 3, take out the two single-mode optical fibers processed in step 2, dip glycerol (10) at the spherical end surfaces (9), and put them into an optical fiber fusion splicer, and control the stepper motor of the optical fiber fusion splicer so that the spherical end surfaces (9) of the two single-mode optical fibers are in contact at the discharge center of the optical fiber fusion splicer; Step 4: Control the optical fiber fusion splicer to perform discharge fusion splicing on the two single-mode optical fibers. During the fusion splicing process, a micro bubble (11) is formed at the connection of the two spherical end faces (9); Step 5: Controlling the stepper motor of the optical fiber fusion splicer to stretch the optical fiber and keep the microbubble (11) at the discharge position of the optical fiber fusion splicer. The microbubble (11) is expanded by long-term discharge and forms a conical section (4) at the fusion position of the single-mode optical fiber. The expanded microbubble (11) is a round bubble (12). Step 6: Control the stepper motor of the optical fiber fusion splicer to squeeze the single-mode optical fiber and keep the circular bubble (12) at the discharge position of the optical fiber fusion splicer. The circular bubble (12) is repaired into a quasi-cylindrical bubble (5) through short-time discharge. The single-mode optical fiber with the quasi-cylindrical bubble (5) embedded in the center of the conical section (4) is a high-sensitivity Fabry-Perot interferometer (1).

7. A method for preparing a low-sensitivity Fabry-Perot interferometer, characterized in that: The preparation method comprises the following steps: Step 1, cutting the end faces of two single-mode optical fibers into flat end faces (8) and placing them in an optical fiber fusion splicer, and placing the flat end faces (8) at the discharge center of the optical fiber fusion splicer by controlling the stepper motor of the optical fiber fusion splicer; Step 2, controlling the optical fiber fusion splicer to perform discharge processing on the two flat end surfaces (8), so as to fuse the flat end surfaces (8) into spherical end surfaces (9); Step 3, take out the two single-mode optical fibers processed in step 2, dip glycerol (10) at the spherical end faces (9), and put them into an optical fiber fusion splicer, and control the stepper motor of the optical fiber fusion splicer so that the spherical end faces (9) of the two single-mode optical fibers are in contact at the discharge center of the optical fiber fusion splicer; Step 4, controlling the optical fiber fusion splicer to perform discharge fusion splicing on the two single-mode optical fibers, during which a micro bubble (11) is formed at the connection of the two spherical end faces (9); Step 5, stretching the optical fiber by controlling the stepper motor of the optical fiber fusion splicer, and keeping the microbubble (11) at the discharge position of the optical fiber fusion splicer, and expanding the microbubble (11) by long-term discharge, and the expanded microbubble (11) is a round bubble (12); Step 6, control the stepper motor of the optical fiber fusion splicer to squeeze the single-mode optical fiber, and keep the circular bubble (12) at the discharge position of the optical fiber fusion splicer, and repair the circular bubble (12) into a quasi-ellipsoidal bubble (7) through short-time discharge. At this time, the cladding of the quasi-ellipsoidal bubble (7) is a shuttle-shaped segment (6), and the single-mode optical fiber with the quasi-ellipsoidal bubble (7) embedded in the center of the shuttle-shaped segment (6) is a low-sensitivity Fabry-Perot interferometer (2).

8. Application of the optical fiber strain sensor based on vernier effect as claimed in claim 1 in strain measurement.

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