Optical fiber MZI strain sensor based on bending structure and manufacturing and using method thereof

Abstract

The invention belongs to the field of optical fiber interference sensors, and particularly relates to an optical fiber Mach-Zehnder interferometer strain sensor based on a bending structure and a manufacturing and using method of the optical fiber Mach-Zehnder interferometer strain sensor. Comprising a light injection area, a bent optical fiber sensing area and a light receiving area which are sequentially arranged on an optical fiber; the bent optical fiber sensing area is divided into an oxyhydrogen flame heating spiral wave structure and a capillary copper pipe wrapped spring structure; a cladding mode field of the bent optical fiber sensing area deflects to the outer side of the bent structure, and under the action of strain, the strain is concentrated on the inner side of the bent optical fiber sensing area; a cladding mode field offset area and a strain concentration area of the bent optical fiber sensing area are separated in space, the reduction amount of effective refractive index of a cladding mode in the strain process is reduced, and high-sensitivity MZI strain sensing is achieved; the problem that an existing MZI strain sensor is low in sensitivity is solved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of Mach-Zehnder interferometer optical fiber sensor, and particularly relates to a bending structure MZI sensor and a manufacturing and using method thereof. BACKGROUND

[0002] The optical fiber Mach-Zehnder interferometer strain sensor can be used in the fields of medicine, advanced materials and micro-nano manufacturing, and can be used for strain detection of a tooth corrector, internal strain detection of a new material and deformation detection of a precision system.

[0003] During the strain process, the difference between the effective refractive index change of the core mode and the cladding mode caused by the strain is positively correlated with the strain sensitivity. During the strain process, due to the photoelastic effect, the effective refractive index of the core mode and the cladding mode decreases at the same time, and the decrease of the effective refractive index of the core mode is slightly larger than that of the cladding mode, thereby causing a very small change in the difference between the effective refractive index of the core mode and the cladding mode, and thus the sensitivity is low. In recent years, some researchers have carried out research on the strain sensitivity of the optical fiber MZI. Dai et al. proposed a MZI strain sensor with a waved core structure. The bending degree of the core of the sensor gradually decreases during the strain process, thereby increasing the decrease of the effective refractive index of the core mode during the strain process, and the strain sensitivity is improved to 125.5 pm / µε (Dai Z, Mu Z, Su C, et al. A highly sensitive strain fiber sensor based on waved core structure[J]. Optics & Laser Technology, 2024, 169.). However, this kind of sensitivity enhancement method is limited by the bending degree of the fiber core, and the sensitivity is difficult to further improve. In addition, Sun et al. in a single-mode-multimode-single-mode optical fiber sensor, by twisting the multimode fiber to excite high-order cladding modes, the strain sensitivity is improved to 42.5 pm / µε (Sun Y, Liu D, Lu P, et al. High sensitivity optical fiber strain sensor using twisted multimode fiber based on SMS structure[J]. Optics Communications, 2017, 405: 416-420.). Although the effective refractive index of the high-order mode changes less during the strain process, the difference between the effective refractive index changes of different orders of cladding modes during the strain process is small, and it is difficult to realize high-sensitivity strain sensing.

[0004] In summary, although there are some sensitivity enhancement schemes for existing MZI optical fiber strain sensors, the current sensitivity enhancement schemes are difficult to greatly change the difference between the effective refractive index changes of the core mode and the cladding mode during the strain process, and it is difficult to realize a high-sensitivity MZI strain sensor. SUMMARY

[0005] The main purpose of the present application is to provide a MZI strain sensor with a new sensitivity mechanism to solve the technical problem of insufficient sensitivity of the existing MZI strain sensor.

[0006] To address the aforementioned issues, this application provides a curved MZI strain sensor, comprising a light-emitting region, a curved fiber sensing region, and a light-receiving region sequentially arranged on an optical fiber; the curved fiber sensing region is divided into a hydrogen-oxygen flame heated spiral wave structure and a capillary copper tube wrapped spring structure.

[0007] The Mach-Zehnder interferometer (MZI) follows the principle of two-beam interference, and its interference wavelength can be expressed as: (1) in For the core mode effective refractive index, Let L be the effective refractive index of the cladding mode and L be the length of the interferometer arm. During strain changes, the difference in effective refractive index between the core mode and the cladding mode, as well as the length of the interferometer arm, will change, causing a change in the wavelength of the interference valley, thus achieving strain sensing. During strain, the change in sensor length has a relatively small impact on the wavelength of the interference valley. The change in the wavelength of the interference valley is mainly caused by the change in the effective refractive index between the core mode and the cladding mode. Therefore, the influence of the change in the effective refractive index between the core mode and the cladding mode on the interference wavelength is mainly considered here. The strain sensitivity of the sensor can be expressed as shown in equation (2).

[0008] (2) During the straining process, due to the elasto-optic effect, the effective refractive index of both the core mode and the cladding mode decreases simultaneously in MZI. However, the decrease in the effective refractive index of the core mode is slightly greater than that of the cladding mode, resulting in a very small change in the difference between the effective refractive indices of the core mode and the cladding mode, and thus its sensitivity is low.

[0009] To increase the strain sensitivity of the sensor, the bending structure separates the cladding mode field from the strain space, reducing the decrease in the effective refractive index of the cladding mode and increasing the change in the effective refractive index difference between the core mode and the cladding mode during strain, thus achieving high-sensitivity strain sensing. The sensor is a spiral wave structure heated by an oxyhydrogen flame, heat-formed by an oxyhydrogen flame fiber processing system. The bending structure changes the refractive index distribution of the fiber cladding, increasing the refractive index on the outer side of the bend. Therefore, the cladding mode field of the sensor will be biased towards the outer side of the bending structure. After the fiber is bent, the refractive index distribution can be expressed as shown in equation (3), where... This indicates the refractive index of the optical fiber material after bending. This represents the refractive index of the optical fiber when it is not bent. This represents the distance from the fiber neutral plane to the cladding, with positive values ​​on the stretched side and negative values ​​on the compressed side along the bending radius. When the fiber is bent, the refractive index increases on the outer side of the wave structure, i.e., the stretched side, causing the cladding optical field to shift to the outer side of the wave structure fiber.

[0010] (3) Simulation studies show that during strain, strain concentrates on the inner side of the curved structure, at which point the cladding mode field separates from the strain space. For traditional fiber MZI strain sensors, the change in the effective refractive index of the cladding mode is due to strain on the fiber in the cladding mode optical field region. However, in the curved structure fiber MZI strain sensor of this application, because the fiber is curved, the strain on the cladding mode optical field region and the strain on the fiber are not in the same region. Therefore, the decrease in the effective refractive index of the cladding mode in the curved structure MZI sensor during strain is very small, while the change in the difference between the effective refractive indices of the core mode and the cladding mode increases, enabling highly sensitive strain sensing. The longitudinal amplitude of the wave structure is 223μm-311μm, the transverse period is 2500μm, and the number of wave structures is 1-2. The longitudinal amplitude of the hydrogen-oxygen flame-heated spiral wave structure is proportional to the sensor's sensitivity and insertion loss; the sensor's strain sensitivity and insertion loss are adjusted by selecting the longitudinal amplitude of the wave structure.

[0011] When the sensor is a capillary copper tube wrapped around a spring structure, an optical fiber is inserted into the capillary copper tube, and the capillary copper tube is bent into a spring shape. The pitch between each coil of the spring is 3 mm, the bending radius of the spring structure is 3-5 mm, and the number of spring bends is 2-4. The number of capillary copper tubes wrapped around the spring structure and the radius of curvature are directly proportional to the sensor sensitivity and insertion loss. The sensor strain sensitivity and insertion loss can be adjusted by selecting the number of spring structures and the radius of curvature.

[0012] When the capillary copper tube encasing the spring structure is subjected to strain and tension, the pitch between the spring coils increases, causing a synchronous increase in the pitch of the internal optical fiber. This leads to a gradual increase in the fiber's bending radius, resulting in a significant decrease in fiber curvature and a substantial change in the effective refractive index difference between modes, achieving high-sensitivity sensing. Simultaneously, the spring structure converts strain into a change in fiber curvature, providing a wide detection range. The change in fiber curvature during strain is influenced by two factors: firstly, there is an inverse proportional relationship between fiber curvature and bending radius (…). According to the inverse proportional function property, when the bending radius is small, the same change in bending radius will cause a larger change in curvature. Secondly, the change in fiber curvature is cumulative within the sensing region, manifesting as the superposition of curvature changes in each bent fiber segment. The more bent fibers in the sensing region, the greater the change in curvature during strain. During strain, these two factors jointly affect the change in curvature of the sensor, thus influencing the movement of the interference valley. The wavelength of the interference valley as a function of strain can be expressed as: (4) in For the effective elastic coefficient, For the cladding mode effective refractive index, The distance by which the cladding mode deviates from the fiber neutral plane. The bending radius of the optical fiber. For the number of bends, The length of a single bend. From equation (4), it can be seen that during the strain process, the smaller the bending radius and the greater the number of bends in the spring structure sensor, the greater the change in fiber curvature during the strain process, thus increasing... By measuring the change in the quantity of change, highly sensitive strain sensing can be achieved.

[0013] As a preferred embodiment, the light-emitting and light-receiving areas of the sensor are composed of single-mode optical fiber with a core diameter of 9 μm, a cladding diameter of 125 μm, and a coating diameter of 250 μm; when the bending optical fiber sensing area is a spring structure wrapped in a capillary copper tube, the outer diameter of the copper tube is 0.4 mm and the inner diameter is 0.3 mm. As a preferred embodiment, the bending optical fiber sensing region can be composed of two types of optical fibers, including single-mode optical fiber and few-mode optical fiber; the single-mode optical fiber has a core diameter of 9μm, a cladding diameter of 125μm, and a coating diameter of 250μm; the few-mode optical fiber has a core diameter of 20μm, a cladding diameter of 125μm, and a coating diameter of 250μm. As a preferred embodiment, when the curved fiber sensing region is a helical wave structure heated by an oxyhydrogen flame, the larger the longitudinal amplitude of the wave structure, the more the sensor cladding mode field is biased towards the outside of the wave structure. It should be concentrated on the inside of the wave structure. At the same time, the insertion loss of the sensor is greater. In order to obtain a clear interference spectrum, the longitudinal amplitude of the wave structure can be set to 223μm-311μm. The sensor sensitivity can be adjusted by adjusting the longitudinal amplitude of the wave structure. In order to obtain a stable interference spectrum in the 1510nm-1610nm band, the number of wave structures can be set to 1-2. The free spectral range of the sensor can be adjusted by adjusting the number of wave structures within this range. As a preferred embodiment, when the bent fiber sensing area is a spring structure wrapped in a capillary copper tube, the smaller the bending radius of the spring structure, the greater the curvature change during sensor strain, and the greater the sensor insertion loss. The bending radius of the spring structure can be set to 3-5 mm, and the sensitivity of the sensor can be adjusted by adjusting the bending radius of the spring structure. The number of spring bends determines the free spectral range of the sensor. In order to produce a stable interference spectrum in the 1510nm-1610nm band, the number of spring bends can be set to 2-4, and the free spectral range of the sensor can be adjusted by adjusting the number of spring bends.

[0014] As a preferred embodiment, the optical fibers used in the light-injecting and light-receiving areas are single-mode optical fibers. The single-mode optical fiber used in the light-receiving area at the left end of the sensor is connected to a spectrometer, which is a YOKAGAWA AQ6370D. The single-mode optical fiber used in the light-injecting area at the right end is connected to a light source, which is a HOYATEK HY-ASE-CL-17-NB-FP. Light is injected into the light-injecting area of ​​the sensor through the light source, interference is achieved through the sensor, and finally the light is input to the spectrometer through the light-receiving area. Strain is applied to the sensor by moving the displacement stages on both sides of the sensor through a strain controller. A set strain, such as 10 με, is applied to the sensor each time. After each strain stretching, the interference spectrum in the spectrometer is recorded. Finally, the interference wavelengths under different strains are linearly fitted. In subsequent use, the strain magnitude of the sensor can be solved by inversely applying the linear fitting formula based on the interference wavelength.

[0015] Another objective of this invention is to provide a method for fabricating and using a fiber optic MZI strain sensor with a bent structure.

[0016] When the bending fiber sensing region is a spiral wave structure heated by an oxyhydrogen flame, the fabrication process of the wave junction is as follows: S1: Remove a 4cm long coating layer from the middle of the single-mode or few-mode fiber and place the fiber in the fiber clamps at both ends of the hydrogen-oxygen flame fiber processing system. S2: Adjust the fiber optic clamps at both ends so that the height difference between the clamps at the left and right ends is h, and set the hydrogen flow rate to 180 SCCM. S3: The flame of the hydrogen-oxygen flame is ignited, and the optical fiber forms an S-shaped bending structure under the action of gravity. S3: Set the clamp motors at both ends of the optical fiber to spiral the optical fiber. The speed of the right motor is 12000μm / s, and the spiraling time is set to 3s. S4: Turn on the motor and twist the optical fiber. After passing through the spiral, the S-shaped structure is made into a wave structure. S5: After the wave structure is made, peel off 2cm of coating from the left and right ends of the wave structure, use a cleaver to cut the fiber end faces of the left and right ends of the wave structure flat, and use a fusion splicer to fusion splice the left and right ends of the wave structure to the single-mode fiber of the light injection area and the light receiving area respectively. When the bending fiber sensing area is a spring structure wrapped in a capillary copper tube, the fabrication process of the spring structure is as follows: S1: Remove 13cm of coating from single-mode or few-mode optical fiber; S2: Insert the area where the fiber optic sensor coating has been removed into the capillary copper tube; S3: Pre-bend the capillary copper tube into a spring shape, set the pitch between each coil of the spring to 3 mm, the bending radius of the spring structure sensor to be 3-5 mm, and the number of spiral bends to be 2-4. S4: After the spring structure is made, peel off 2cm of coating from both ends of the spring structure, use a cleaver to cut the fiber end faces of both ends of the spring structure flat, and use a fusion splicer to fusion splice the left and right ends of the spring structure to the single-mode fiber in the light injection area and the light receiving area respectively. The beneficial effects of the technical solution of this invention application are as follows: 1. When the sensing region of the bent optical fiber is a spiral wave structure, the cladding mode field coupled from the fiber core to the fiber cladding is biased to the outside of the bent structure through the wave bending structure, resulting in uneven distribution of the cladding mode field on both sides of the sensor. At the same time, the strain will concentrate on the inside of the wave structure, causing the cladding mode field offset area to be spatially separated from the strain concentration area. The strain experienced by the cladding mode during the strain process is very small, thereby reducing the change in the effective refractive index of the cladding mode during the strain process and increasing the change in the effective refractive index of the fiber core mode and the cladding mode during the strain process, thus achieving highly sensitive strain sensing.

[0017] 2. When the bending fiber sensing region is a capillary copper tube wrapped around a spring structure, the spring structure, constrained by the capillary copper tube, causes the optical fiber to form a spring structure with a small bending radius and a large number of bends. When strain is applied to the sensor, the pitch between the coils of the spring structure increases, which in turn drives the pitch of the optical fiber inside the capillary copper tube to increase synchronously. This significantly reduces the fiber curvature, enhances the change in effective refractive index difference between modes, and achieves high-sensitivity sensing. The spring structure converts strain changes into changes in fiber curvature. During the strain process, the optical fiber is more easily stretched, enabling wide-range detection based on high-sensitivity monitoring.

[0018] 3. The MZI strain sensor fabricated in this application can be formed into a curved structure by micro-bending of single-mode or few-mode optical fiber, which eliminates the need for expensive special optical fibers or processing equipment, thus reducing the manufacturing cost of the sensor. 4. The MZI strain sensor fabricated in this application has stronger tensile resistance due to its bending structure, making it less prone to breakage during strain detection. Attached Figure Description

[0019] To make the objectives, technical solutions, and beneficial effects of this invention clearer, the following figures are provided for illustration: Figure 1 This is a schematic diagram of the overall composition of the fiber optic MZI strain sensor based on a curved structure of the present invention, which includes a hydrogen-oxygen flame heated spiral wave structure and a capillary copper tube wrapped spring structure. Figure 2 This is a schematic diagram of the strain calibration device of the present invention; Figure 3 Simulation diagram of the cladding mode field distribution of the sensor when the sensing region of the bent optical fiber is a spiral wave structure heated by an oxyhydrogen flame. Figure 4Simulation diagram of strain distribution of the sensor under strain when the sensing area of ​​the bent optical fiber is a spiral wave structure heated by an oxyhydrogen flame. Figure 5 The strain detection data of the sensor when the bending fiber sensing area is heated by an oxyhydrogen flame to a spiral wave structure. Figure 6 The linear fitting relationship between strain and wavelength of the sensor when the sensing area of ​​the bent optical fiber is a spiral wave structure heated by an oxyhydrogen flame. Figure 7 The strain detection data of the sensor when the bending fiber sensing area is a spring structure wrapped in a capillary copper tube; Figure 8 The linear fitting relationship between strain and wavelength of the sensor is shown when the sensing area of ​​the bent optical fiber is a spring structure wrapped in a capillary copper tube. Detailed Implementation

[0020] The following embodiments are used to illustrate this application, but are not intended to limit the scope of this application. Where specific techniques or conditions are not specified in the embodiments, they should be performed in accordance with the techniques or conditions described in the literature in this field, or in accordance with the product manual.

[0021] In the description of this application, unless otherwise stated, the terms "upper" and "lower" indicate the orientation or state relationship based on the orientation or state relationship shown in the drawings, and are only for the convenience of describing this application and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this application.

[0022] In the following embodiments, all instruments and equipment used, unless otherwise specified, are conventional products that can be purchased through legitimate channels. Unless otherwise stated, all methods described are conventional methods, and all raw materials used are commercially available. like Figure 1 As shown, the fiber MZI strain sensor based on the bending structure in this embodiment includes a light-emitting area 1, a bending fiber sensing area 2, and a light-receiving area 3 sequentially arranged on the fiber. The bending fiber sensing area is divided into a hydrogen-oxygen flame heated spiral wave structure 2-1 and a capillary copper tube wrapped spring structure 2-3. The refractive index distribution on the fiber in the bending fiber sensing area changes, the cladding mode field is biased to the outside of the bending structure, and the strain is concentrated on the inside of the bending structure during the strain process. like Figure 1As shown, the hydrogen-oxygen flame-heated spiral wave structure is heat-formed using a hydrogen-oxygen flame optical fiber processing system. The longitudinal amplitude of the wave structure is 311 μm, the transverse period is 2500 μm, and there are two wave structures. The sensor is composed of single-mode optical fiber with a core diameter of 9 μm, a cladding diameter of 125 μm, and a coating diameter of 250 μm. The longitudinal amplitude of the hydrogen-oxygen flame-heated spiral wave structure is proportional to the sensitivity and insertion loss of the sensor. The strain sensitivity and insertion loss of the sensor can be adjusted by selecting the longitudinal amplitude of the wave structure. The specific fabrication steps for a fiber optic MZI strain sensor based on a bent structure, where the bent fiber sensing region is a helical wave structure heated by an oxyhydrogen flame, are as follows: S1: Remove a 4cm long coating layer from the middle of the single-mode or few-mode fiber and place the fiber in the fiber clamps at both ends of the hydrogen-oxygen flame fiber processing system. S2: Adjust the fiber optic clamps at both ends so that the height difference between the clamps at the left and right ends is h, and set the hydrogen flow rate to 180 SCCM. S3: The flame of the hydrogen-oxygen flame is ignited, and the optical fiber forms an S-shaped bending structure under the action of gravity. S3: Set the clamp motors at both ends of the optical fiber to spiral the optical fiber. The speed of the right motor is 12000μm / s, and the spiraling time is set to 3s. S4: Turn on the motor and twist the optical fiber. After passing through the spiral, the S-shaped structure is made into a wave structure. The longitudinal amplitude of the wave structure is set to 311μm and the transverse period is set to 2500μm. S5: After the wave structure is made, peel off 2cm of coating from the left and right ends of the wave structure, use a cleaver to cut the fiber end faces of the left and right ends of the wave structure flat, and use a fusion splicer to fusion splice the left and right ends of the wave structure to the single-mode fiber of the light injection area and the light receiving area respectively. like Figure 2 As shown, the usage method of the MZI strain sensor is as follows: Strain testing experimental apparatus such as Figure 2 As shown, the light-emitting area 1 of the sensor is connected to the light source, and the light-receiving area 3 is connected to the spectrometer. After the connection is completed, the two ends of the sensor are clamped in the fiber optic clamps at both ends of the strain table. The strain table is moved to both sides by the strain controller to apply strain to the sensor. The interference wavelength under different strain states is recorded, and the actual strain magnitude is obtained by demodulation based on the interference wavelength.

[0023] like Figure 3As shown, when the sensing region of the bent optical fiber is a spiral wave structure heated by an oxyhydrogen flame, the sensor is simulated using Rsoft software to determine the cladding mode field distribution. The fiber cladding diameter is 125 μm, the core diameter is 9 μm, the cladding refractive index is 1.443, and the core refractive index is 1.451. The longitudinal amplitude of the sensor is set to 311 μm, and the transverse period is set to 2500 μm. The simulation results are as follows: Figure 3 As shown, the cladding mode field of the sensor is more concentrated on the outside of the curved structure, while the energy of the cladding mode field near the inside of the curved fiber is very weak. like Figure 4 As shown, when the bending fiber sensing region is a spiral wave structure heated by an oxyhydrogen flame, the strain distribution experienced by the sensor is analyzed using steady-state mechanical simulation analysis with COMSOL software. The sensor material is set to have a density of 2203 kg / m³. 3 The Poisson's ratio is 0.17, and the Young's modulus is 73.1 GPa; the longitudinal amplitude of the sensor is set to 311 μm, and the transverse period is set to 2500 μm; the simulation results are as follows. Figure 4 As shown, when the sensor is subjected to strain, the strain will concentrate on the inside of the bent optical fiber, while the strain on the outside of the optical fiber is very small. like Figure 5 As shown, the usage method of the MZI strain sensor is as follows: When the bending fiber sensing area is a helical wave structure heated by an oxyhydrogen flame, the specific usage method of the MZI strain sensor is as follows: The applied strain is increased from 0µε to 100µε, with a step size set to 10µε. The sensor's resonant wavelength changes as shown in the figure. Figure 5 As shown, by fitting the applied strain to the resonant wavelength, the calculated strain sensitivity is 166.64 pm / µε, which is more than 80 times the sensitivity of a typical MZI strain sensor. Figure 6 As shown.

[0024] When the bent fiber optic sensing area is replaced with a capillary copper tube wrapped spring structure, the fabrication process of the capillary copper tube wrapped spring structure is as follows: S1: Remove 13cm of coating from single-mode or few-mode optical fiber; S2: Insert the area where the fiber optic sensor coating has been removed into the capillary copper tube; S3: Pre-bend the capillary copper tube into a spring shape, set the pitch between each coil of the spring to 3 mm, the bending radius of the spring structure sensor to 3 mm, and the number of spiral bends to 4. S4: After the spring structure is made, peel off 2cm of coating from both ends of the spring structure, use a cleaver to cut the fiber end faces of both ends of the spring structure flat, and use a fusion splicer to fusion splice the left and right ends of the spring structure to the single-mode fiber in the light injection area and the light receiving area respectively. likeFigure 7 As shown, the usage method of the MZI strain sensor is as follows: When the sensing area of ​​the bent optical fiber is a capillary copper tube wrapped around a spring structure, the specific usage method of the MZI strain sensor is as follows: the applied strain is increased from 0µε to 300µε, the step size is set to 20µε, and the sensor's resonant wavelength changes as shown in the figure. Figure 7 As shown, by fitting the applied strain to the resonant wavelength, the calculated strain sensitivity is 91.1 pm / µε, which is more than 40 times the sensitivity of a typical MZI strain sensor. Figure 8 As shown.

[0025] The performance adjustment method of the sensor is to adjust the sensor's sensitivity and insertion loss by selecting the bending radius of the elastic structure, and to change the sensor's free spectral range by selecting the number of spring bends.

[0026] The above descriptions are merely embodiments of this application. Commonly known structures, properties, and reactant ratios are not described in detail here. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application. For example, simply adjusting the parameter selection within or near a specified parameter range should also be considered within the scope of protection of this application, and these will not affect the effectiveness of the application or the practicality of the patent. The scope of protection claimed in this application should be determined by the content of its claims, and the specific embodiments described in the specification can be used to interpret the content of the claims.

Claims

1. A fiber MZI strain sensor based on a bending structure, characterized in that: It comprises a light injection area, a curved fiber sensing area and a light receiving area arranged on the optical fiber in sequence. The spiral wave structure is formed by heat setting of a hydrogen-oxygen flame fiber processing system, and the cladding mode field is deviated to the outside of the curved structure, and the strain is concentrated on the inside of the curved structure during the strain process; the longitudinal amplitude of the spiral wave structure is directly proportional to the sensitivity and insertion loss of the sensor, and the strain sensitivity and insertion loss of the sensor are adjusted by selecting the longitudinal amplitude of the wave structure; The number and curvature radius of the spring structure wrapped by the capillary copper tube are directly proportional to the sensitivity and insertion loss of the sensor, and the strain sensitivity and insertion loss of the sensor are adjusted by selecting the number and curvature radius of the spring structure.

2. The curved structure MZI strain sensor according to claim 1, characterized in that: The light injection area and the light receiving area are composed of single-mode optical fibers, the core diameter of the single-mode optical fiber is 9 μm, the cladding diameter is 125 μm, and the coating layer diameter is 250 μm; The curved fiber sensing area is composed of single-mode optical fibers or few-mode optical fibers.

3. The curved structure MZI strain sensor of claim 1, wherein: The longitudinal amplitude of the wave structure is 223 μm-311 μm, the transverse period is 2500 μm, and the number of wave structures is 1-2.

4. The curved structure MZI strain sensor of claim 1, wherein: The outer diameter of the copper tube of the spring structure wrapped by the capillary copper tube is 0.4 mm, the inner diameter is 0.3 mm, the pitch between the coils of the spring is 3 mm, the bending radius of the spring structure is 3-5 mm, and the number of spring bending is 2-4.

5. A method of fabricating a sensor as claimed in claim 1, characterized by: The curved fiber sensing area is a spiral wave structure, and the manufacturing method of the spiral wave structure is as follows: S1: remove the coating layer of a certain length from the middle of the single-mode optical fiber or few-mode optical fiber, and place the optical fiber in the optical fiber clamps at both ends of the hydrogen-oxygen flame fiber processing system; S2: adjust the optical fiber clamps at both ends to make the heights of the clamps at both ends different by h; S3: ignite the hydrogen-oxygen flame, and the optical fiber forms an S-shaped curved structure under the action of gravity; S3: set the optical fiber clamps at both ends to twist the optical fiber; S4: turn on the motor and twist the optical fiber, and the S-shaped structure is made into a wave structure after twisting; S5: after the wave structure is made, remove the coating layer of a certain length from the left and right ends of the wave structure, cut the end faces of the optical fiber at both ends of the spiral wave structure, and fuse them to the single-mode optical fibers of the light injection area and the light receiving area, respectively.

6. A method of fabricating a sensor as claimed in claim 1, characterized by: The curved fiber sensing area is a spring structure wrapped by a capillary copper tube, and the manufacturing method of the spring structure is as follows: S1: remove the coating layer of a certain length from the single-mode optical fiber or few-mode optical fiber; S2: insert the coating layer removal area of the optical fiber sensor into the capillary copper tube; S3: pre-bend the capillary copper tube into a spring shape; S4: after the spring structure is made, remove the coating layer of a certain length from the left and right ends of the spring structure, cut the end faces of the optical fiber at both ends of the spring structure, and fuse them to the single-mode optical fibers of the light injection area and the light receiving area, respectively.

7. A method of using the sensor of claim 1, wherein The steps include: S1: inject light into the sensor light injection area through the light source, and the sensor realizes interference; S2: input the light into the spectrometer through the light receiving area. S3: moving displacement tables on both sides of the sensor through a strain controller to apply strain to the sensor; each time a sensor is applied to a set size of strain; S4: after the strain is stretched, record the interference spectrum in the spectrometer; S5: linear fitting of the interference wavelengths under different strains; S6: according to the interference wavelength, the linear fitting formula is used to inversely solve the strain size of the sensor.

8. A method of adjusting the performance of a sensor as claimed in claim 1, characterized by: When the bending fiber sensing area is a hydrogen-oxygen flame heating spiral wave structure, the longitudinal amplitude of the wave structure is 223 μm -311 μm, the sensitivity and insertion loss of the sensor are adjusted by selecting the longitudinal amplitude of the wave structure; the number of the wave structure is 1-2, the insertion loss and the interference free spectral range of the sensor are adjusted by selecting the number of the wave structure; when the bending fiber sensing area is a spring structure wrapped by a capillary copper tube, the bending radius of the spring structure is 3-5 mm, the sensitivity and insertion loss of the sensor are adjusted by selecting the bending radius of the spring structure, the number of spring bending is 2-4, the free spectral range of the sensor is changed by selecting the number of spring bending.

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