All-fiber converter and method based on the principle of micro double-arm Mach-Zehnder interferometer

Abstract

The present invention provides an all-fiber converter and method based on the principle of a micro double-arm Mach-Zehnder interferometer, which relates to the field of optical fiber communication technology. When the mode conversion is performed by adjusting the curvature, since the transmission paths of the high-order mode and the core mode are different, their own mode changes are relatively independent, thus avoiding the crosstalk problem of different modes in the traditional all-fiber mode converter. In addition, the traditional all-fiber mode converter device often uses special optical fibers or complex operations such as grating etching, and then in the preparation of this structure, a commercial fusion machine and low-cost single-mode optical fibers and multi-mode optical fibers are required, which reduces the manufacturing difficulty and manufacturing cost.

Description

Technical Field

[0001] The present invention relates to the field of optical fiber communication technology, and in particular to an all-optical fiber converter and a method based on the principle of a micro double-arm Mach-Zehnder interferometer. Background Art

[0002] As people's demand for high performance, high bandwidth and high efficiency of optical signals in optical communications increases, mode conversion as an important method of optical information transmission and processing has attracted widespread attention. In the process of optical signal transmission, different optical modes will have different effects on the performance and transmission characteristics of optical signals, so selecting, switching and manipulating the mode of optical signals becomes more critical. Currently, mode converters have been widely used in optical communications, optical sensing, photonic integrated circuits and optical computing.

[0003] Fiber mode converters have low insertion loss, relatively low manufacturing difficulty, and good compatibility with fiber systems, which has attracted great attention. There are currently four main types: mode selective couplers, fiber photon lanterns, fiber Bragg gratings, and long-period fiber gratings. However, they all have their own disadvantages: the design and preparation of mode selective couplers are often complex and the conversion loss for certain specific modes is large, and the performance of fiber photon lanterns is affected by the geometric dimensions of the optical fiber, so the preparation is difficult. In addition, fiber Bragg gratings usually reflect at specific wavelengths, which limits their scope of application. Similar to fiber Bragg gratings, long-period fiber gratings may be limited by wavelength selectivity.

[0004] It is difficult for traditional mode converters to achieve high-order mode conversion and dynamic tunability at the same time. Therefore, a mode converter based on an all-fiber structure that can achieve high-order mode conversion and dynamic tunability at the same time and is easy to prepare is an urgent problem to be solved in the field of this technology. Summary of the invention

[0005] The purpose of the present invention is to provide an all-fiber converter and method based on the principle of a micro double-arm Mach-Zehnder interferometer, which can solve the limitations of traditional all-fiber mode converters on conversion modes and the complexity of conversion methods. At the same time, the manufacturing difficulty is low and it is very suitable for commercial production.

[0006] The present invention is achieved through the following measures: an all-fiber converter based on the principle of a micro double-arm Mach-Zehnder interferometer, comprising: a multimode optical fiber and a single-mode optical fiber, wherein the middle section of the multimode optical fiber and the middle section of the single-mode optical fiber are fused through a beam splitting melting point and a beam combining melting point; the multimode optical fiber section between the beam splitting melting point and the beam combining melting point is an interference arm, and the single-mode optical fiber between the beam splitting melting point and the beam combining melting point is a reference arm; an end of the multimode optical fiber close to the beam splitting melting point is a first multimode optical fiber, and an end of the multimode optical fiber close to the beam combining melting point is a second multimode optical fiber; an end of the single-mode optical fiber close to the beam splitting melting point is a first single-mode optical fiber, and an end of the single-mode optical fiber close to the beam combining melting point is a second single-mode optical fiber.

[0007] Preferably, the first single-mode optical fiber is the input end of the converter, and the first multi-mode optical fiber is suspended in the air; the second single-mode optical fiber is the output end of the converter, and the second multi-mode optical fiber is suspended in the air.

[0008] Preferably, the distance between the beam splitting melting point and the beam combining melting point is 4 cm.

[0009] Preferably, the mode conversion can be performed by changing the curvature of the all-fiber tunable mode converter.

[0010] Preferably, the curvature of the all-fiber adjustable mode converter is changed by fixing the all-fiber adjustable mode converter between two precision displacement platforms, and changing the curvature by adjusting the distance between the precision displacement platforms close to the first single-mode optical fiber and the first multi-mode optical fiber.

[0011] Preferably, the precision displacement platform is provided with a screw micrometer for changing the distance between the precision translation stages by rotation.

[0012] The present invention also provides a method for preparing the above-mentioned all-fiber converter based on the principle of micro double-arm Mach-Zehnder interferometer, which is characterized by comprising the following steps:

[0013] S1: Select a section of single-mode optical fiber and a section of multi-mode optical fiber and place them side by side in the optical fiber fusion splicer, keeping the single-mode optical fiber and the multi-mode optical fiber in the same plane;

[0014] S2: After the fiber fusion splicer automatically stretches the single-mode fiber and the multi-mode fiber, we set the discharge mode of the fiber fusion splicer to pulse discharge mode;

[0015] S3: Set the fiber fusion splicer to manual mode. After determining the discharge area, perform a single high-intensity discharge to obtain a melting point. Then, take out the optical fiber, adjust the position, and place it in the fiber fusion splicer. During the process, the optical fiber needs to be kept taut, and perform a high-intensity discharge again to obtain another melting point.

[0016] Preferably, in S1, before a section of single-mode optical fiber and a section of multi-mode optical fiber are placed side by side in an optical fiber fusion splicer, the coating layers of the single-mode optical fiber and the multi-mode optical fiber are removed.

[0017] Preferably, when the discharge mode of the optical fiber fusion splicer is set to the pulse discharge mode, the electrode discharge intensity is set to 250 units.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] 1. The output signal of the mode converter of the present invention includes an interference valley formed by mode interference. The corresponding mode conversion is achieved by observing the change of the interference valley and the corresponding spatial spectrum diagram with the curvature adjustment, which solves the limitation of the traditional all-fiber mode converter on the conversion mode and the complexity of the conversion method.

[0020] 2. The present invention is based on a micro dual-arm Mach-Zehnder interferometer structure with direct welding, which combines the advantages of the traditional millimeter-level dual-arm Mach-Zehnder interferometer and the online Mach-Zehnder interferometer, and realizes the innovation of mode conversion technology. Compared with the traditional all-fiber mode converter, we adopt an innovative manufacturing method, that is, parallel welding of single-mode optical fiber with high discharge intensity and multi-mode optical fiber. This method has the advantage of low cost and can be manufactured by simple discharge welding using a fiber fusion splicer. The structure is simple and easy to manufacture, and has the potential to replace expensive optical devices. It has great potential in the promotion of all-fiber mode converters and the expansion of new research fields of all-fiber mode converters.

[0021] 3. The present invention uses simple arc discharge to fuse multimode optical fiber and single-mode optical fiber to form double arms, thereby forming a centimeter-level Mach-Zehnder interferometer. Compared with single-mode optical fiber, due to the sensitivity of the high-order mode of multimode optical fiber to bending, the high-order mode of multimode optical fiber can be adjusted by changing the curvature, thereby realizing the mode conversion function of the Mach-Zehnder interferometer. The transmission spectrum and space-frequency of the Mach-Zehnder interferometer are analyzed to illustrate the mode characteristics involved in the interference. It has opened up an effective path for all-fiber mode conversion and detection, and has good application prospects in the fields of optical communication, optical fiber sensing, optical computing, etc.

[0022] 4. The high-order mode and core mode in the present invention propagate in multi-mode optical fiber and single-mode optical fiber respectively. When we perform mode conversion by adjusting the curvature, since the transmission paths of the high-order mode and the core mode are different, their own mode changes are relatively independent, thus avoiding the crosstalk problem of different modes in the traditional all-fiber mode converter. In addition, traditional all-fiber mode converter devices often use special optical fibers or use complex operations such as grating etching, and then the preparation of this structure requires a commercial fusion splicer and low-cost single-mode optical fiber and multi-mode optical fiber. In general, this structure has low economic cost and low manufacturing difficulty, and is very suitable for commercial production.

[0023] 5. Compared with the coupling structures prepared by the traditional melt taper method and the side polishing method, the present invention only needs to use an optical fiber fusion splicer for arc discharge welding when preparing the melt coupling point, and does not need to use expensive optical fiber devices such as optical fiber taper machines; in addition, for two different types of optical fibers, the melt taper method needs to first simulate the two optical fibers to obtain the relationship curve between the core radius and the mode effective refractive index, and then pre-tap to meet the phase matching conditions. The side polishing method needs to prepare the corresponding refractive index matching liquid, and needs to adjust the curvature and polishing depth of the two optical fibers respectively. The preparation process is very cumbersome. We only need to simply adjust the discharge intensity, discharge time and discharge number to control the length of the coupling zone and the size of the equivalent refractive index of the core therein, thereby controlling the coupling splitting ratio.

[0024] 6. The strong discharge coupling of the two optical fibers of the present invention makes the refractive index of the optical fiber core in the coupling zone homogenized, that is, the refractive index distribution of the two optical fibers is relatively uniform after discharge. This homogenization of the core refractive index ensures that light can be split by the micro-double-arm optical fiber through the micron-level coupling length. At the same time, the length of the coupling zone is controlled at the micron level, which also enables the size of the entire MZI to be controlled at the centimeter level; compared with the traditional meter-level MZI, the smaller volume is conducive to packaging, and can also realize the integration of multiple systems or cascade with other devices. Its easy manufacturing characteristics also make it more suitable for mass production. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] 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.

[0026] Figure 1 is a schematic structural diagram of the converter of the present invention;

[0027] Figure 2 Schematic diagram of a device for studying mode conversion characteristics of the converter of the present invention;

[0028] Figure 3 It is a manufacturing flow chart of the converter of the present invention;

[0029] Figure 4 is the initial transmission spectrum of the mode converter of the present invention;

[0030] Figure 5 is the initial spatial spectrum of the mode converter of the present invention;

[0031] Figure 6 is the transmission spectrum of different curvatures during the first mode conversion of the present invention;

[0032] Figure 7 is the spatial spectrum of the initial curvature and the terminal curvature of the first mode conversion of the present invention;

[0033] Figure 8 is the transmission spectrum of different curvatures during the second mode conversion of the present invention;

[0034] Fig. 9 is the spatial spectrum of the initial curvature and the terminal curvature of the second mode conversion of the present invention;

[0035] Fig.10 is the transmission spectrum of different curvatures during the third mode conversion of the present invention;

[0036] Fig.11 is the spatial spectrum of the initial curvature and the terminal curvature of the third mode conversion of the present invention;

[0037] Fig.12 This is a physical picture of the double ball structure of the present invention;

[0038] Fig.13 is the transmission spectrum of the present invention after connecting the double-ball structure;

[0039] Fig.14 It is the transmission spectrum after the curvature is adjusted after connecting the double-ball structure of the present invention;

[0040] Fig.15 The present invention Fig.14 and Fig.15 Comparison of transmission spectra of the two;

[0041] Fig.16 It is the spatial spectrum comparison before and after the curvature adjustment of the double-ball structure of the present invention;

[0042] Among them, the figure markings are: 1. broadband light source; 2. first multimode optical fiber; 3. first single-mode optical fiber; 4. beam splitting melting point; 5. interference arm; 6. reference arm; 7. beam combining melting point; 8. second multimode optical fiber; 9. second single-mode optical fiber; 10. spectrum analyzer; 11. precision displacement platform; 12. micrometer. DETAILED DESCRIPTION

[0043] 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.

[0044] Example 1

[0045] See also Figures 1 to 8 The present invention provides a technical solution, which is an all-fiber converter based on the principle of a micro double-arm Mach-Zehnder interferometer, comprising: a multimode optical fiber and a single-mode optical fiber, wherein the middle section of the multimode optical fiber and the middle section of the single-mode optical fiber are fused through a beam splitting melting point 4 and a beam combining melting point 7; the multimode optical fiber section between the beam splitting melting point 4 and the beam combining melting point 7 is an interference arm 5, and the single-mode optical fiber between the beam splitting melting point 4 and the beam combining melting point 7 is a reference arm 6; the end of the multimode optical fiber close to the beam splitting melting point 4 is a first multimode optical fiber 2, and the end of the multimode optical fiber close to the beam combining melting point 7 is a second multimode optical fiber 8; the end of the single-mode optical fiber close to the beam splitting melting point 4 is a first single-mode optical fiber 3, and the end of the single-mode optical fiber close to the beam combining melting point 7 is a second single-mode optical fiber 9.

[0046] In this embodiment, the first single-mode optical fiber 3 is the input end of the converter, and the first multi-mode optical fiber 2 is suspended in the air; the second single-mode optical fiber 9 is the output end of the converter, and the second multi-mode optical fiber 8 is suspended in the air.

[0047] In this embodiment, the distance between the beam splitting melting point 4 and the beam combining melting point 7 is 4 centimeters.

[0048] like Figure 1 As shown, one end of the first single-mode optical fiber 3 is connected to the broadband light source 1 through the FC / APC connector, and the second single-mode optical fiber 9 is connected to the spectrum analyzer 10 through the FC / APC connector. When the light is transmitted from the core of the single-mode optical fiber to the beam splitting melting point 4, the high-order mode will be significantly excited, and then part of the light will be split into the multi-mode optical fiber for propagation, and the rest of the light will continue to propagate in the single-mode optical fiber. When passing through the beam combining melting point 7, the light originally transmitted in the multi-mode optical fiber and the single-mode optical fiber will converge together, thereby causing interference, and finally continue to propagate in the single-mode optical fiber.

[0049] In this embodiment, mode conversion can be performed by changing the curvature of the all-fiber tunable mode converter.

[0050] In this embodiment, the method for changing the curvature of the all-fiber adjustable mode converter is to fix the all-fiber adjustable mode converter between two precision displacement platforms 11, and change the curvature by adjusting the distance between the precision displacement platforms 11 close to the first single-mode optical fiber 3 and the first multi-mode optical fiber 2.

[0051] In this embodiment, the precision displacement platform 11 is provided with a screw micrometer 12 for changing the distance between the precision translation stages by rotating.

[0052] like Figure 2 As shown, the converter of this embodiment is fixed on two precision displacement platforms 11 by using a screw micrometer 12, and the screw micrometer 12 on the precision displacement platform 11 is rotated to change the distance between the two precision displacement platforms 11, and the curvature is indirectly changed by changing the radius of curvature, and the corresponding mode conversion is realized by observing the change of the interference valley and the corresponding spatial spectrum diagram with the curvature adjustment; according to theoretical analysis, the strain variable is proportional to the curvature of the optical fiber. When the precision displacement platform 11 is fixed, the curvature of the MZI mode converter can be changed by adjusting the distance of the left precision displacement platform 11. The input port of the converter is connected to the broadband light source 1, and the output port is connected to the spectrometer.

[0053] The curvature of the mode converter can be expressed as:

[0054]

[0055] Where x is the displacement of the left translation stage; L0 is the initial distance between the two precision translation stages; R is the radius of curvature; and C is the curvature.

[0056] Figure 4 The initial transmission spectrum and spatial spectrum of the MZI mode converter are shown. Figure 5 It can be seen that in addition to the fundamental mode, two main higher-order modes are excited, and several weak higher-order modes are also excited.

[0057] According to the experimental results, as the curvature is continuously adjusted, the mode converter in this paper can achieve three different mode conversions. The first mode conversion process occurs at a curvature of 0.4961m. -1 To 0.6265m -1 In, by Figure 6 The overall trend of the transmission spectrum shows that dip 1 and dip 6 have small changes, while dip 3 and dip 5 gradually become shallower as the curvature increases. At the same time, the peak near the wavelength of 1570nm gradually changes to the trough dip 3, and a new trough dip 4 appears near the wavelength of 1666nm. The initial curvature and the final curvature in the curvature adjustment process are compared, that is, the curvature is 0.4961m -1 and 0.62651m -1 The spatial spectrum of Figure 7 It can be seen that the curvature is 0.4961m -1 Compared with the spatial spectrum, the curvature is 0.6265m -1When a new weak high-order mode appeared in its spatial spectrum, the original curvature was 0.4961m -1 Some weak higher-order modes disappear, and the curvature is 0.6265m -1 The energy of the main high-order mode region is significantly lower than that of the curvature of 0m -1 The energy of the main higher-order modes when .

[0058] The second mode conversion process occurs at the curvature of 0.8348m -1 To 1.1465m -1 In. By Figure 8 It can be seen from the transmission spectrum that when the curvature gradually increases, a new trough dip 1 appears at the wavelength of 1526nm, dip 2 gradually becomes flat, and dip 3 gradually becomes deeper. Fig. 9 The curvature is 0.1465m -1 Three weak high-order modes appear in the spatial spectrum at 0.6265 m, and the number of main high-order modes is also increasing. However, the energy proportion of each main high-order mode is relatively small compared with the curvature of 0.6265 m. -1 time is significantly reduced.

[0059] The third mode conversion process occurs at the curvature of 1.1724m -1 To 1.2759m -1 In. By Fig.10 It can be seen that in the transmission spectrum, as the curvature increases, the peak near the wavelength of 1579nm and the trough near the wavelength of 1582nm gradually merge into a new dip 2, and dip 1 and dip 3 gradually become steeper. Fig.11 The curvature is 1.2759m -1 The spatial spectrum at 0.4961 m shows the emergence of new main high-order modes and the weak high-order modes are closely related to 0.4961 m. -1 There are also certain differences.

[0060] In addition, in order to verify the effectiveness of the mode conversion characteristics of the structure proposed in this paper, we also conducted a self-consistent experiment. In the experiment to verify the mode conversion function, we connected the structure proposed in this paper with the double-ball structure (keeping the curvature at 0 at this time). The actual picture of the double-ball structure is shown in Fig.12 As shown in , it has the effect of exciting the fundamental mode into higher-order modes. The generated higher-order modes will affect the transmission spectrum of the device, such as Fig.13 As shown in the figure, many continuous and dense wavelets appear in the transmission spectrum of the original device. When we adjust the curvature, the high-order mode generated by the double-sphere structure will gradually leak out. In this experiment, the curvature is adjusted to 0.8088m. -1 When , the transmission spectrum of the original device is almost completely restored, such as Fig.14As shown in , the wavelet completely dissipates at this time. From the comparison of the transmission spectra, it can be seen that after the curvature adjustment, the smoothness of the device transmission spectrum is significantly improved, and the envelope of the overall spectrum has not changed, as shown in Fig.15 shown. Fig.16 The spatial spectrum comparison of the three is shown, from which it can be clearly seen that the energy occupied by the mode close to the fundamental frequency has increased significantly, while at the same time the energy share of the mode far from the fundamental frequency has decreased, and the mode has been effectively converted.

[0061] It can be seen that in the experiment, we can achieve the tunability of the mode by simply changing the curvature of the structure. In addition, we introduced higher-order modes by connecting the device to a double-sphere structure, and then restored the initial transmission spectrum of the original device by adjusting the curvature, successfully achieving the theoretical self-consistency of mode conversion.

[0062] Embodiment 2:

[0063] like Figure 3 As shown, the present invention also provides a method for preparing an all-fiber converter based on the principle of a micro double-arm Mach-Zehnder interferometer, comprising the following steps:

[0064] S1: Select a section of single-mode optical fiber and a section of multi-mode optical fiber and place them side by side in the optical fiber fusion splicer, keeping the single-mode optical fiber and the multi-mode optical fiber in the same plane;

[0065] S2: After the fiber fusion splicer automatically stretches the single-mode fiber and the multi-mode fiber, we set the discharge mode of the fiber fusion splicer to pulse discharge mode;

[0066] S3: Set the fiber fusion splicer to manual mode. After determining the discharge area, perform a single high-intensity discharge to obtain a melting point. Then, take out the optical fiber, adjust the position, and place it in the fiber fusion splicer. During the process, the optical fiber needs to be kept taut, and perform a high-intensity discharge again to obtain another melting point.

[0067] In this embodiment, in S1, a section of single-mode optical fiber and a section of multi-mode optical fiber are placed side by side in front of an optical fiber fusion splicer to remove the coating layers of the single-mode optical fiber and the multi-mode optical fiber.

[0068] In this embodiment, when the discharge mode of the optical fiber fusion splicer is set to the pulse discharge mode, the electrode discharge intensity is set to 250 units.

[0069] The mode converter based on the principle of micro two-arm Mach-Zehnder interferometer is obtained by direct fusion discharge of a fiber fusion splicer. Through simple arc discharge, multimode fiber and single-mode fiber are fused to form two arms, forming a centimeter-level Mach-Zehnder interferometer. Compared with the coupling structure prepared by the traditional fusion taper method and side-throwing method, we only need to use a fiber fusion splicer for arc discharge fusion when preparing the fusion coupling point, and do not need to use expensive fiber devices such as fiber taper machines; the structure is simple and easy to manufacture, and it has the potential to replace expensive optical devices. It has great potential in the promotion of all-fiber mode converters and the expansion of new research fields of all-fiber mode converters.

[0070] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. An all-fiber converter based on the principle of micro double-arm Mach-Zehnder interferometer, characterized in that: include: A multimode optical fiber and a single-mode optical fiber, wherein the middle section of the multimode optical fiber and the middle section of the single-mode optical fiber are fused through a beam splitting melting point (4) and a beam combining melting point (7); the multimode optical fiber section between the beam splitting melting point (4) and the beam combining melting point (7) is an interference arm (5), and the single-mode optical fiber section between the beam splitting melting point (4) and the beam combining melting point (7) is a reference arm (6); an end of the multimode optical fiber close to the beam splitting melting point (4) is a first multimode optical fiber (2), and an end of the multimode optical fiber close to the beam combining melting point (7) is a second multimode optical fiber (8); an end of the single-mode optical fiber close to the beam splitting melting point (4) is a first single-mode optical fiber (3), and an end of the single-mode optical fiber close to the beam combining melting point (7) is a second single-mode optical fiber (9); The first single-mode optical fiber (3) is the input end of the converter, and the first multi-mode optical fiber (2) is suspended in the air; the second single-mode optical fiber (9) is the output end of the converter, and the second multi-mode optical fiber (8) is suspended in the air; The distance between the beam splitting melting point (4) and the beam combining melting point (7) is 4 cm.

2. The all-fiber converter based on the principle of micro double-arm Mach-Zehnder interferometer according to claim 1, characterized in that: Mode conversion is performed by changing the curvature of an all-fiber tunable mode converter.

3. The all-fiber converter based on the principle of micro double-arm Mach-Zehnder interferometer according to claim 2, characterized in that: The method for changing the curvature of the all-fiber adjustable mode converter is to fix the all-fiber adjustable mode converter between two precision displacement platforms (11), and to change the curvature by adjusting the distance between the precision displacement platforms (11) close to the first single-mode optical fiber (3) and the first multi-mode optical fiber (2).

4. The all-fiber converter based on the principle of micro double-arm Mach-Zehnder interferometer according to claim 3 is characterized in that: The precision displacement platform (11) is provided with a screw micrometer (12) for rotating and changing the distance between the precision translation stages.

5. A method for preparing an all-fiber converter based on the principle of a micro double-arm Mach-Zehnder interferometer as claimed in any one of claims 1 to 4, characterized in that: The following steps are involved: S1: Select a section of single-mode optical fiber and a section of multi-mode optical fiber and place them side by side in the optical fiber fusion splicer, keeping the single-mode optical fiber and the multi-mode optical fiber in the same plane; S2: After the fiber fusion splicer automatically stretches the single-mode fiber and the multi-mode fiber, we set the discharge mode of the fiber fusion splicer to pulse discharge mode; S3: Set the fiber fusion splicer to manual mode. After determining the discharge area, perform a single high-intensity discharge to obtain a melting point. Then, take out the optical fiber, adjust the position, and place it in the fiber fusion splicer. During the process, the optical fiber needs to be kept taut, and perform a high-intensity discharge again to obtain another melting point.

6. The method for preparing an all-fiber converter based on the principle of a micro double-arm Mach-Zehnder interferometer according to claim 5, characterized in that: In S1, a section of single-mode optical fiber and a section of multi-mode optical fiber are placed side by side in front of an optical fiber fusion splicer to remove the coating layers of the single-mode optical fiber and the multi-mode optical fiber.

7. The method for preparing an all-fiber converter based on the principle of a micro double-arm Mach-Zehnder interferometer according to claim 5, characterized in that: When the discharge mode of the optical fiber fusion splicer is set to the pulse discharge mode, the electrode discharge intensity is set to 250 units.

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