A curvature optical fiber sensor based on four-core optical fiber and its preparation method

Abstract

The present invention provides a curvature optical fiber sensor based on a four-core optical fiber and a preparation method, which belongs to the field of optical fiber sensing technology. The technical problem that the longer optical fiber in the traditional Mach-Zehnder interferometer sensor is less sensitive to interference from external factors is solved. It is formed by connecting a broadband light source, a first single-mode optical fiber, a first coupling point, a micro double-arm structure, a second coupling point, a second single-mode optical fiber, and a spectrometer in sequence; the preparation method is: directly welding the single-mode optical fiber with the coreless optical fiber and the four-core optical fiber to form a single-mode optical fiber-coreless optical fiber-four-core optical fiber-coreless optical fiber-single-mode optical fiber online Mach-Zehnder interferometer symmetrical structure; placing a section of single-mode optical fiber with the coating removed in parallel with the single-mode optical fiber in the above-mentioned symmetrical structure in the center of the welding machine, and after discharging twice, the two optical fibers are welded and coupled to form a distance of 8 cm between the two coupling points. The beneficial effects of the present invention are: the four-core optical fiber has the structural characteristics of multiple cores evenly distributed.

Description

Technical Field

[0001] The present invention relates to the field of optical fiber sensing technology, and in particular to a curvature optical fiber sensor based on four-core optical fiber and a preparation method thereof. Background Art

[0002] Among the fiber optic sensors that have been reported, the fiber optic sensor based on Mach-Zehnder interferometer has attracted much attention due to its good sensing characteristics and adaptability. Among them, the precise curvature measurement of Mach-Zehnder interferometer plays an important role in engineering applications such as health monitoring and robotic arms.

[0003] The four-core fiber has a structural feature of multiple cores evenly distributed, which allows it to synchronously transmit different signals in different cores, giving it better sensing performance and enabling multi-parameter measurement. However, in the sensors based on four-core fibers that have been reported, the changes in related physical parameters are detected through one path, and the measurement of the detected parameters is relatively simple. So far, there has been no report on the intensity modulation of the micro double-arm curvature sensor based on four-core fibers. Summary of the invention

[0004] The purpose of the present invention is to provide a micro double-arm Mach-Zehnder interferometer sensor based on four-core optical fiber. The four-core optical fiber has the structural feature of evenly distributed multiple cores, which enables it to synchronously transmit different signals in different cores to achieve multi-parameter measurement. This is the first report of a micro double-arm structure based on intensity detection in a four-core optical fiber sensor.

[0005] In order to achieve the above-mentioned invention object, the technical solution adopted by the present invention is specifically: a curvature optical fiber sensor based on a four-core optical fiber, which is composed of a broadband light source, a first single-mode optical fiber, a first coupling point, a micro double-arm structure, a second coupling point, a second single-mode optical fiber, and a spectrometer connected in sequence;

[0006] Among them, one path in the micro-double-arm is an online Mach-Zehnder interferometer of four-core optical fiber, and the other path is a single-mode optical fiber. One end of the first single-mode optical fiber is connected to a broadband light source through an FC / APC connector, one end of the micro-double-arm structure is connected to the other end of the first single-mode optical fiber through a first coupling point, and the other end of the micro-double-arm structure is connected to one end of the second single-mode optical fiber through a second coupling point. The other end of the second single-mode optical fiber is used as an output end and is connected to the input end of a spectrum analyzer through an FC / APC connector.

[0007] Furthermore, the online Mach-Zehnder interferometer structure is connected by a single-mode optical fiber 1 and one end of a first coreless optical fiber, one end of a four-core optical fiber is connected to the other end of the coreless optical fiber, the other end of the four-core optical fiber is connected to one end of a second coreless optical fiber, and the other end of the coreless optical fiber is connected to a single-mode optical fiber 2, forming a single-mode optical fiber-coreless optical fiber-four-core optical fiber-coreless optical fiber-single-mode optical fiber.

[0008] Furthermore, the four cores of the four-core optical fiber are evenly distributed in the same cladding, and the core diameters are the same, and the spacing between each core is the same. The core diameter of the four-core optical fiber is 8 μm, the core spacing is 42.5 μm, and the cladding diameter is 125 μm.

[0009] Furthermore, the curvature measuring device includes a broadband light source, a fiber optic sensor, two precision displacement platforms, and a spectrometer placed on a horizontal workbench. The sensor is fixed on the two precision displacement platforms by using clamps on the two precision displacement platforms. SMF2 in the fiber optic sensor is connected to the BBS port of the broadband light source, and SMF6 in the fiber optic sensor is connected to the spectrometer with a resolution of 0.02nm. The curvature is indirectly changed by changing the distance between the two precision displacement platforms and changing the curvature radius.

[0010] In order to better achieve the above-mentioned object of the invention, the present invention also provides a method for preparing a curvature optical fiber sensor based on a four-core optical fiber, comprising the following steps:

[0011] S1. In the process of making the symmetrical structure of the online Mach-Zehnder interferometer, the welding machine is first selected to the SM-MM discharge mode, the automatic welding method is adopted, the discharge intensity is 150, and the discharge number is 1;

[0012] S2, after removing the coating layer of the first single-mode optical fiber and the first coreless optical fiber by an appropriate length, place them in a fusion splicer for discharge fusion splicing;

[0013] S3, splice the four-core optical fiber with the other end of the first coreless optical fiber;

[0014] S4, repeating the above steps S3 and S2, fusing the other end of the four-core optical fiber with the second coreless optical fiber, and then fusing the other end of the second coreless optical fiber with the second single-mode optical fiber to form a symmetrical structure of single-mode optical fiber-coreless optical fiber-four-core optical fiber-coreless optical fiber-single-mode optical fiber;

[0015] S5. Adjust the discharge mode of the welding machine to MM-MM and use manual welding, and the discharge intensity is 220;

[0016] S6. The preparation of the micro dual-arm Mach-Zehnder interferometer sensor is to place a section of single-mode optical fiber with the coating removed parallel to the single-mode optical fiber in the symmetrical structure of the above-mentioned online Mach-Zehnder interferometer at the center of the fusion splicer, discharge the two optical fibers twice to make them fusion-coupled, and form a dual-arm coupling point image of the fusion splicer;

[0017] S7. Move the two optical fibers in parallel, place the second single-mode optical fiber in the symmetrical structure in the center of the fusion splicer again, and perform fusion splicing again with the same parameters to obtain a coupling point. During the fusion splicing process, the length interval between the two coupling points is 8 cm.

[0018] The optical path propagation sequence of the curvature sensor of the present invention is:

[0019] The incident light output by the broadband light source enters the coupling point through the first single-mode optical fiber. The light is divided into two paths, passing through an in-line Mach-Zehnder interferometer sensing structure and a single-mode optical fiber respectively. The two paths of light have an optical path difference due to the different paths they have traveled through, and interference occurs at the coupling point. When the light propagates from the single-mode optical fiber-coreless optical fiber segment to the four-core optical fiber, the mode field mismatch between the single-mode optical fiber and the coreless optical fiber will cause the fundamental mode to be excited and generate higher-order modes. Part of the light will be coupled to the four cores of the four-core optical fiber, and part of the light will be transmitted in the cladding of the four-core optical fiber and cause loss. Since the light produces a phase difference along different paths in the four-core optical fiber, it is converged and coupled to the single-mode optical fiber in the coreless optical fiber to generate interference. Finally, the optical signal is transmitted to the single-mode optical fiber, which is the output end of the system. The optical signal continues to be transmitted from here and can eventually be connected to a spectrometer for detection and analysis.

[0020] Implementation process of the present invention: The curvature sensor of the proposed micro dual-arm Mach-Zehnder interferometer can be formed by coupling an online Mach-Zehnder interferometer sensor based on four-core optical fiber through a fiber fusion splicer and a single-mode optical fiber through direct arc discharge, wherein the online Mach-Zehnder interferometer sensor structure is single-mode optical fiber-coreless optical fiber-four-core optical fiber-coreless optical fiber-single-mode optical fiber, and the manufacturing process is as follows. First, prepare an online Mach-Zehnder interferometer sensor based on four-core optical fiber. After removing the coating layer of the single-mode optical fiber and the coreless optical fiber of appropriate length, place them in a fusion splicer for discharge welding. Then, the four-core optical fiber is fused with the previous section of coreless optical fiber, and the above operation is repeated to form a symmetrical structure of single-mode optical fiber-coreless optical fiber-four-core optical fiber-coreless optical fiber-single-mode optical fiber. In the process of making the symmetrical structure of the online Mach-Zehnder interferometer, we selected the SM-MM discharge mode, adopted the automatic fusion method, the discharge intensity was 150, and the number of discharges was 1. Secondly, the preparation of the micro dual-arm Mach-Zehnder interferometer sensor is to place a section of single-mode optical fiber with the coating removed parallel to the optical fiber of the symmetrical structure of the online Mach-Zehnder interferometer in the center of the fusion machine, adjust the discharge mode to MM-MM, the discharge intensity to 220, and use the manual mode to discharge twice to make the two optical fibers fusion-coupled. Finally, move the two optical fibers in parallel, place the other point in the center of the fusion machine again, and fusion-couple again with the same parameters to obtain the second coupling point. During the fusion process, the length interval between the two coupling points is 8cm.

[0021] Different types of fiber lengths affect the sensing characteristics of the online Mach-Zehnder interferometer. In order to select the appropriate length of coreless fiber, the transmission spectra of coreless fibers with lengths of 0.5 cm, 1 cm and 2 cm are given when the length of the four-core fiber is 5 cm. The clear transmission spectra show that coreless fibers with different lengths present different free spectral ranges and extinction ratios. The extinction ratios of the transmission spectra of 2 cm, 1 cm and 0.5 cm are 4.9 dB, 16.72 dB and 12.1 dB respectively. It can be clearly seen that the extinction ratio of the transmission spectrum of the coreless fiber with a length of 1 cm is the highest, and the free spectral range is more uniform. The spatial spectrum of the online Mach-Zehnder interferometer obtained by fast Fourier transform (FFT) shows that the three online Mach-Zehnder interferometers with different lengths can excite the dominant high-order mode and several weaker high-order modes in spatial frequency. When the length of the coreless fiber is 1 cm, the fundamental mode excites more high-intensity high-order modes, indicating that the sensing characteristics of the sensing arm are relatively good. Based on the above considerations, this paper uses a coreless optical fiber with a length of 1 cm to study the curvature sensing characteristics.

[0022] Working principle of the present invention:

[0023] When light enters the first coupling point through a single-mode fiber, the light is divided into two paths. The two paths of light have an optical path difference due to the different paths, and interference occurs at the second coupling point. When light propagates from the single-mode fiber-coreless fiber section to the four-core fiber, the mode field mismatch between the single-mode fiber and the coreless fiber causes the fundamental mode to be excited and generate higher-order modes. Part of the light will be coupled to the four cores of the four-core fiber, and part of the light will be transmitted in the cladding of the four-core fiber and cause loss. Since the light produces a phase difference along different paths in the four-core fiber, it is coupled to the single-mode fiber through convergence in the next coreless fiber to generate interference. Since a large number of high-order modes excited by the coreless fiber exist in the four-core fiber, when the external environment changes, the effective refractive index of the four-core fiber will change, causing the interference fringes of the linear Mach-Zehnder interferometer sensor to change, which also causes the interference fringes of the micro double-arm Mach-Zehnder interferometer sensor to change. By observing the changes in the interference fringes, the external environment of the sensor can be detected.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] 1. The present invention proposes a fiber curvature sensor with intensity demodulation based on a combination of a quad-core fiber and a coreless fiber, which has a micro double-arm structure. By designing a coreless fiber, the light of the single-mode fiber is more easily excited and coupled to the four cores of the quad-core fiber, so that the light is coupled and converged in the coreless fiber and interferes in the single-mode fiber.

[0026] 2. Since a large number of high-order modes excited by the coreless optical fiber exist in the four-core optical fiber, when the external environment changes, the effective refractive index of the four-core optical fiber will change, and the interference fringes will change. By observing the changes in the interference fringes, the external environment of the sensor can be detected. The results show that when the curvature changes from 0m-1 to 0.1045m-1, its curvature sensitivity can reach up to 108.29dB / m-1. Compared with other curvature sensors, the sensor we proposed has the advantages of high sensitivity and simple manufacturing, especially the detection of intensity environmental parameters, which makes the sensor more advantageous in demodulation. The double-arm structure of the sensor is realized through simple arc discharge of the welding machine to improve the sensor sensitivity, and it provides a new method for the preparation of high-sensitivity sensors with simple structure, small size and low cost.

[0027] 3. The micro double-arm Mach-Zehnder interferometer curvature sensor proposed in the present invention has the highest curvature sensitivity in the current four-core optical fiber curvature measurement. The double-arm structure of the sensor is realized through simple arc discharge of a fusion splicer to improve the sensor sensitivity, and provides a new method for the preparation of high-sensitivity sensors with simple structure, small size and low cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The accompanying drawings are used to provide further understanding of the present invention and constitute a part of the specification. They are used to explain the present invention together with the embodiments of the present invention and do not constitute a limitation of the present invention.

[0029] Figure 1 It is a schematic diagram of the structure of the micro double-arm curvature sensor in the present invention.

[0030] Figure 2 It is a schematic diagram of the structure of the online Mach-Zehnder interferometer based on four-core optical fiber in the present invention.

[0031] Figure 3 This is the geometric structure of the cross section of the four-core optical fiber in the present invention.

[0032] Figure 4 These are the fusion imaging diagrams of the micro double-arm curvature sensor in the present invention; wherein, (a) is the direct fusion diagram of coreless optical fiber and four-core optical fiber; (b) is the fusion point diagram of coreless and four-core optical fiber under a microscope; (c) is the image of the double-arm coupling point of the fusion splicer; and (d) is the double-arm coupling point diagram under a microscope.

[0033] Figure 5 This is a diagram of the curvature sensing system of the micro dual-arm curvature sensor in the present invention.

[0034] Figure 6 (a) is the transmission spectrum of the linear Mach-Zehnder interferometer as the curvature changes; (b) is the linear fitting curve of intensity and curvature; (c) is the transmission spectrum of the micro double-arm Mach-Zehnder interferometer as the curvature changes; (d) is the linear fitting curve of intensity and curvature.

[0035] Among them, the figure markings are: 1. broadband light source; 2. the first single-mode optical fiber; 3. the first coupling point; 4. micro double-arm structure; 5. the second coupling point; 6. the second single-mode optical fiber; 7. spectrometer; 8. single-mode optical fiber one; 9. the first coreless optical fiber; 10. four-core optical fiber; 11. the second coreless optical fiber; 12. single-mode optical fiber two; 2-6, optical fiber sensor; 16. two precision displacement platforms; 17. spectrometer. DETAILED DESCRIPTION

[0036] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. Of course, the specific embodiments described here are only used to explain the present invention and are not used to limit the present invention.

[0037] Example 1

[0038] See also Figure 1As shown, the technical solution provided by this embodiment is a curvature optical fiber sensor based on a four-core optical fiber, which is composed of a broadband light source 1, a first single-mode optical fiber 2, a first coupling point 3, a micro double-arm structure 4, a second coupling point 5, a second single-mode optical fiber 6, and a spectrometer 7 connected in sequence;

[0039] Among them, one path in the micro double arm 4 is an inline Mach-Zehnder interferometer of four-core optical fiber, such as Figure 2 , the other path is a single-mode optical fiber. One end of the first single-mode optical fiber 2 is connected to a broadband light source 1 through an FC / APC connector. One end of the micro-double-arm structure 4 is connected to the other end of the first single-mode optical fiber 2 through a first coupling point 3. The other end of the micro-double-arm structure 4 is connected to one end of a second single-mode optical fiber 6 through a second coupling point 5. The other end of the second single-mode optical fiber 6 is used as an output end and is connected to the input end of an optical spectrum analyzer 7 through an FC / APC connector.

[0040] Further, Figure 2 In the structure of the online Mach-Zehnder interferometer, a single-mode optical fiber 8 is connected to one end of a first coreless optical fiber 9, one end of a four-core optical fiber 10 is connected to the other end of the first coreless optical fiber 9, the other end of the four-core optical fiber 10 is connected to one end of a second coreless optical fiber 11, and the other end of the coreless optical fiber 11 is connected to a single-mode optical fiber 2 12, forming a single-mode optical fiber-coreless optical fiber-four-core optical fiber-coreless optical fiber-single-mode optical fiber.

[0041] Furthermore, the four cores of the quad-core optical fiber 10 are evenly distributed in the same cladding, and have the same core diameters and the same spacing between each core. The core diameter of the quad-core optical fiber is 8 μm, the core spacing is 42.5 μm, and the cladding diameter is 125 μm.

[0042] In order to better achieve the above-mentioned purpose of the invention, this embodiment also provides a method for preparing a curvature optical fiber sensor based on a four-core optical fiber, which is prepared by using an optical fiber fusion splicer. First, an online Mach-Zehnder interferometer sensor based on a four-core optical fiber is prepared;

[0043] In the first step, in the process of making the symmetrical structure of the online Mach-Zehnder interferometer, we first select the SM-MM discharge mode of the welding machine, adopt the automatic welding method, the discharge intensity is 150, and the number of discharges is 1.

[0044] In the second step, after removing the coating of the single-mode optical fiber and the coreless optical fiber of appropriate length, they are placed in a fusion splicer for discharge fusion splicing.

[0045] The third step is to fuse the four-core optical fiber with the previous section of coreless optical fiber. The schematic diagram of the fusion is as follows: Figure 4 (a) is shown, and (b) is the coreless and four-core welding point diagram under a microscope.

[0046] Step 4: Repeat the above operations to form a symmetrical structure of single-mode fiber-coreless fiber-quad-core fiber-coreless fiber-single-mode fiber.

[0047] The fifth step is to adjust the welding machine discharge mode to MM-MM and use manual welding with a discharge intensity of 220.

[0048] The sixth step is to prepare the micro dual-arm Mach-Zehnder interferometer sensor by placing a section of single-mode optical fiber with the coating removed parallel to the SMF of the above-mentioned symmetrical structure of the online Mach-Zehnder interferometer in the center of the fusion splicer, and then discharge the two optical fibers twice to form a fusion coupling. Figure 4 (c) Image of the double-arm coupling point of the welding machine. The double-arm coupling point under the microscope is shown in Figure 2. Figure 4 (d).

[0049] Step 7: Move the two optical fibers in parallel, place the other symmetrical SMF in the center of the fusion splicer again, and perform fusion splicing again with the same parameters to obtain the coupling point. During the fusion splicing process, the length interval between the two coupling points is 8 cm.

[0050] This embodiment also provides a curvature measuring device of a curvature optical fiber sensor based on a four-core optical fiber. The entire experimental device includes a broadband light source 1, optical fiber sensors 2-6, two precision displacement platforms 16, and a spectrometer 7 placed on a horizontal workbench. The optical fiber sensor is fixed on the two precision displacement platforms 16 by using clamps on the two precision displacement platforms 16. The SMF2 in the optical fiber sensor is connected to the BBS port of the broadband light source 1, and the SMF6 in the optical fiber sensor is connected to the spectrometer 7 with a resolution of 0.02nm. The curvature is indirectly changed by changing the distance between the two precision displacement platforms 16 and changing the curvature radius.

[0051] like Figure 5 The figure shows the curvature measurement device of the sensor in this experiment. The sensor is placed on a horizontal workbench, the input port is connected to the BBS port of the broadband light source 1, and the output port is connected to the spectrometer 7 (OSA) with a resolution of 0.02nm. The MZI is tightened and straightened using a fixed fixture and a displacement platform 12. During the measurement process, the position of the precision displacement platform 16 on the right is fixed, and the position of the precision displacement platform 16 on the left is moved to achieve the curvature change of the sensor. When the curvature changes, Figure 6 (a) It can be observed that the intensity of the transmission spectrum of the online Mach-Zehnder interferometer sensor decreases by 5.65dB as the curvature changes. Figure (b) is the linear fitting curve of its intensity and curvature. The curvature sensitivity is 57.29dB / m -1 , the linear fit is 0.987. Figure 6(c) is the transmission spectrum of the micro double-arm Mach-Zehnder interferometer as the curvature changes. The light intensity in the trough decreases from 43.47dB to 32.69dB, a decrease of 10.78dB. (d) is the linear fitting curve of intensity and curvature. It can be seen that the curvature sensitivity of the sensor is 108.29dB / m -1 , the linear fit is 0.996.

[0052] The optical path propagation sequence of the curvature sensor of the present invention is:

[0053] The incident light output by the broadband light source 1 enters the coupling point 3 through the first single-mode optical fiber 2. The light is divided into two paths, passing through an in-line Mach-Zehnder interferometer sensing structure and a single-mode optical fiber respectively. The two paths of light have an optical path difference due to the different paths, and interference occurs at the coupling point 5. When the light propagates in the direction of the four-core optical fiber 10 from the single-mode optical fiber 8 to the coreless optical fiber 9, the mode field mismatch between the single-mode optical fiber 8 and the coreless optical fiber 9 will cause the fundamental mode to be excited and generate higher-order modes. Part of the light will be coupled into the four cores of the four-core optical fiber 10, and part of the light will be transmitted in the cladding of the four-core optical fiber and cause loss. Since the light generates a phase difference along different paths in the four-core optical fiber, it is coupled to the single-mode optical fiber 12 through convergence in the coreless optical fiber 11 to generate interference. Finally, the optical signal is transmitted to the single-mode optical fiber 6, which is the output end of the system. The optical signal continues to be transmitted from here and can eventually be connected to the spectrometer 7 for detection and analysis.

[0054] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A curvature optical fiber sensor based on four-core optical fiber, characterized in that: It is composed of a broadband light source (1), a first single-mode optical fiber (2), a first coupling point (3), a micro double-arm structure (4), a second coupling point (5), a second single-mode optical fiber (6), and a spectrometer (7) connected in sequence; One path in the micro double-arm structure (4) is an online Mach-Zehnder interferometer of a four-core optical fiber, and the other path is a single-mode optical fiber. One end of the first single-mode optical fiber (2) is connected to a broadband light source (1) via an FC / APC connector. One end of the micro double-arm structure (4) is connected to the other end of the first single-mode optical fiber (2) via a first coupling point (3). The other end of the micro double-arm structure (4) is connected to one end of a second single-mode optical fiber (6) via a second coupling point (5). The other end of the second single-mode optical fiber (6) is used as an output end and is connected to an input end of a spectrometer (7) via an FC / APC connector.

2. The curvature optical fiber sensor based on four-core optical fiber according to claim 1, characterized in that: The online Mach-Zehnder interferometer structure is composed of a single-mode optical fiber (8) connected to one end of a first coreless optical fiber (9), a four-core optical fiber (10) connected to the other end of the first coreless optical fiber (9), the other end of the four-core optical fiber (10) connected to one end of a second coreless optical fiber (11), and the other end of the coreless optical fiber (11) connected to a single-mode optical fiber (12), thereby forming a single-mode optical fiber-coreless optical fiber-four-core optical fiber-coreless optical fiber-single-mode optical fiber.

3. The curvature optical fiber sensor based on four-core optical fiber according to claim 2, characterized in that: The four cores of the four-core optical fiber (10) are evenly distributed in the same cladding, and have the same core diameters and the same spacing between each core. The core diameter of the four-core optical fiber is 8 μm, the core spacing is 42.5 μm, and the cladding diameter is 125 μm.

4. The method for preparing a curvature optical fiber sensor based on a four-core optical fiber according to any one of claims 1 to 3, characterized in that: The following steps are involved: S1. In the process of making the symmetrical structure of the online Mach-Zehnder interferometer, the welding machine is first selected to the SM-MM discharge mode, the automatic welding method is adopted, the discharge intensity is 150 a.u., and the number of discharges is 1; S2, after removing a proper length of coating layer from the first single-mode optical fiber (2) and the first coreless optical fiber (9), place them in a fusion splicer for discharge fusion splicing; S3, fusing the four-core optical fiber to the other end of the first coreless optical fiber (9); S4, repeating the above steps S3 and S2, fusing the other end of the quad-core optical fiber (10) with the second coreless optical fiber (11), and then fusing the other end of the second coreless optical fiber (11) with the second single-mode optical fiber (6) to form a symmetrical structure of single-mode optical fiber-coreless optical fiber-quad-core optical fiber-coreless optical fiber-single-mode optical fiber; S5. Adjust the discharge mode of the welding machine to MM-MM and use manual welding, and the discharge intensity is 220a.u.; S6. The preparation of the micro dual-arm Mach-Zehnder interferometer sensor is to place a section of single-mode optical fiber with the coating removed parallel to the single-mode optical fiber in the symmetrical structure of the above-mentioned online Mach-Zehnder interferometer at the center of the fusion splicer, discharge the two optical fibers twice to make them fusion-coupled, and form a dual-arm coupling point image of the fusion splicer; S7. Move the two optical fibers in parallel, place the second single-mode optical fiber (6) in the symmetrical structure in the center of the fusion splicer again, and perform fusion splicing again with the same parameters to obtain a coupling point. During the fusion splicing process, the length interval between the two coupling points is 8 cm.

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