A micro dual-arm MZI mode monitor and its preparation method and working principle

Abstract

The present invention provides a micro-double-arm MZI mode monitor and its preparation method and working principle, which belong to the field of optical fiber mode monitoring technology. It solves the technical problems that the structure of the traditional imaging method is not all-optical and is not easy to integrate, and the numerical analysis method cannot analyze complex optical systems. Its technical solution is: including a broadband light source, a spectrum analyzer and a micro-double-arm MZI structure, the micro-double-arm MZI structure includes a single-mode optical fiber, a coreless optical fiber, a beam splitting coupling point, an interference arm, and a reference arm; a micro-double-arm MZI mode monitor and its preparation method, including the following steps: S1, placing two optical fibers in an optical fiber clamp; S2, arc discharge coupling the first point; S3, coupling the second point; S4, respectively connected to a broadband light source and a spectrum analyzer. The beneficial effect is: the present invention understands the mode characteristics involved in interference by analyzing the distribution of the MZI interferometer transmission spectrum and the corresponding Fourier space spectrum diagram, thereby realizing all-optical mode detection.

Description

Technical Field

[0001] The present invention relates to the technical field of optical fiber mode monitoring, and in particular to a micro dual-arm MZI mode monitor and a preparation method and working principle thereof. Background Art

[0002] With the continuous development of optical fiber communication technology, the demand for communication capacity is endless. As an effective method to expand communication capacity, mode division multiplexing systems have been widely studied in the fields of orbital angular momentum, photon integration, and few-mode lasers. Not only in the field of optical communication, mode division multiplexing systems also have broad application prospects in the fields of laser processing, optical sensing, and optical imaging. The use of mode division multiplexing systems can improve the quality of laser beams, increase sensor sensitivity, and reduce the complexity of optical imaging equipment. In the above-mentioned multi-mode transmission process, mode detection in multi-mode transmission becomes particularly important.

[0003] In order to monitor multiple modes during the transmission process, it is necessary to separate the mode to be monitored from the optical signal. Traditional mode monitoring methods include imaging and numerical analysis. However, the structure of the traditional imaging method is not all-fiber and is not easy to integrate, and the numerical analysis method cannot analyze complex optical systems. In recent years, with the rapid development of emerging disciplines such as light field control, the output of light fields in specific modes based on fiber lasers has attracted widespread attention from scientific researchers. Among them, all-fiber mode converters have become a research hotspot in recent years due to their small size and easy integration. This makes the all-fiber structure mode monitor more attractive for monitoring the mode conversion of fiber lasers.

[0004] So far, mode monitoring methods and mode conversion devices are only suitable for processing a small number of high-order modes. There is still a lack of relevant research on the analysis of a large number of high-order modes, especially the monitoring of high-order modes. Summary of the invention

[0005] The purpose of the present invention is to overcome the problems in the background technology and provide a micro dual-arm MZI mode monitor and its preparation method and working principle. It can be prepared by only a fiber fusion splicer. The single-mode optical fiber and the coreless optical fiber are coupled by an arc discharge method to realize an MZI interferometer with a micro dual-arm structure.

[0006] In order to achieve the above-mentioned invention object, the technical solution adopted by the present invention is specifically: a micro-two-arm MZI mode monitor, including a broadband light source and a spectrum analyzer, and also including a micro-two-arm MZI structure, the micro-two-arm MZI structure including a single-mode optical fiber 1, a coreless optical fiber 1, a beam splitting coupling point, an interference arm, a reference arm, a coupling region, a coreless optical fiber 2 and a single-mode optical fiber 2, one end of the single-mode optical fiber 1 and the coreless optical fiber 1 is connected to one side of the beam splitting coupling point, the other side of the beam splitting coupling point is connected to one end of the interference arm and the reference arm, the other end of the interference arm and the reference arm is connected to one side of the coupling region, the other side of the coupling region is connected to one end of the coreless optical fiber 2 and the single-mode optical fiber 2, the other end of the single-mode optical fiber 1 is used as the input end of the micro-two-arm MZI structure, and is connected to the broadband light source, and the other end of the single-mode optical fiber 2 is used as the output end of the micro-two-arm MZI structure, and is connected to the spectrum analyzer.

[0007] Furthermore, the interference arm is made of coreless optical fiber material, and the reference arm is made of single-mode optical fiber material.

[0008] Furthermore, one end of the single-mode optical fiber 1 away from the beam splitting coupling point is connected to the pigtail interface of the broadband light source through an FC / APC connector, and one end of the single-mode optical fiber 2 away from the coupling area is connected to the pigtail interface of the spectrum analyzer through an FC / APC connector.

[0009] Furthermore, a section of hollow optical fiber is fused between the broadband light source and the single-mode optical fiber.

[0010] The present invention provides a method for preparing a micro dual-arm MZI mode monitor, and the preparation method comprises the following steps:

[0011] S1: After stripping the coating of a single-mode optical fiber and a coreless optical fiber, place them side by side into the optical fiber fusion splicer, and fix the two ends in the optical fiber clamps respectively;

[0012] S2: Adjust the optical fiber fusion splicer to manual mode, control the discharge intensity and discharge time, perform arc discharge on the two optical fibers to fuse them, and obtain the first coupling point by fusion;

[0013] S3: Repeat step S2 and weld to obtain the second coupling point;

[0014] S4: One end of the single-mode optical fiber is connected to the pigtail interface of the broadband light source through an FC / APC connector, and the other end is connected to the pigtail interface of the spectrum analyzer through an FC / APC connector.

[0015] Furthermore, in step S1, the two optical fibers are tightened to make them fit tightly together, and the two optical fibers and the discharge electrode are placed on the same plane.

[0016] Furthermore, in step S2, the discharge intensity is 250 and the discharge time is 250 ms.

[0017] Furthermore, in step S3, the distance between the first welding point and the second welding point is 4.5 cm.

[0018] Furthermore, the core and cladding diameters of the single-mode optical fiber are 8.2 μm and 125 μm respectively, and the diameter of the coreless optical fiber is 125 μm.

[0019] The present invention also provides a working principle of a micro dual-arm MZI mode monitor, and its operating process is as follows: the incident light output by a broadband light source enters a beam splitting coupling point through a single-mode optical fiber and is divided into two parts. One part of the light is transmitted in a fundamental mode in a reference arm made of a single-mode optical fiber, and the other part of the light is transmitted in a multi-mode form in an interference arm made of a coreless optical fiber. Since the transmission paths of the light in the interference arm and the reference arm are different, the two modes of light produce a transmission phase shift. When the optical signal reaches the coupling area, a phase difference is formed due to the different transmission phase shifts of the optical signals of different modes, thereby causing interference. Finally, the light is transmitted to a spectrum analyzer via a single-mode optical fiber 2 to monitor the transmitted light.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] 1. The present invention is based on an all-fiber mode monitor of a micro-double-arm MZI. Since the high-order mode of a coreless optical fiber is easily affected by curvature, by adjusting the curvature of the micro-double-arm MZI, the high-order mode in the coreless optical fiber leaks, causing the transmission spectrum of the MZI to change; by analyzing the change characteristics of the transmission spectrum and spatial spectrum of the MZI (fast Fourier transform of the transmission spectrum), the change characteristics of the transmission mode in the MZI are analyzed; in the verification experiment, the high-order mode is mixed into the input fundamental mode signal, and the high-order mode leaks by bending the micro-double-arm MZI structure, and the transmission spectrum and spatial spectrum are restored to the initial spectrum without mixing the high-order mode. This shows that the high-order mode filtered out in this process is a series of newly added modes, thereby realizing the monitoring of the externally introduced mode. This work is based on the principle of MZI double-arm interference, and uses the transmission spectrum and its spatial spectrum to analyze the mode transmission characteristics of light in the double arms, which opens up new ideas for studying all-fiber mode monitors. At the same time, this micro-double-arm MZI structure provides a new direction for multi-parameter and multi-dimensional MZI applications.

[0022] 2. Compared with the coupling structures prepared by the traditional fused taper method and the side polishing method, we only need to use the fiber fusion splicer for arc discharge welding when preparing the fused coupling point, and do not need to use expensive fiber taper machines and other fiber devices; in addition, for two different types of optical fibers, the fused taper method needs to first model and 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 the curvature and polishing depth of the two optical fibers need to be adjusted 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, thereby controlling the coupling splitting ratio. Furthermore, the strong discharge coupling of the two optical fibers 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 micrometer 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 not only conducive to packaging, but also enables the integration of multiple systems or cascading with other devices. Its easy manufacturing characteristics also make it more suitable for mass production.

[0023] 3. Compared with the complex optical devices used in traditional mode monitoring methods, our mode monitor is an all-fiber structure, which makes it naturally possess the advantages of anti-electromagnetic interference, high temperature resistance, and easy integration in the characteristics of optical fibers. In recent years, the research on high-order mode characteristics based on mode conversion and mode filtering devices has been limited to the conversion or suppression of a small number of known high-order modes. There is currently no relevant research on the analysis of a large number of high-order modes, especially the monitoring of high-order modes. When analyzing multiple modes, we qualitatively analyze the characteristics and changes of the modes through the transmission spectrum and FFT output by the micro dual-arm MZI structure.

[0024] 4. The present invention proposes an all-fiber mode monitor based on a micro-dual-arm MZI, which can be prepared by only a fiber fusion splicer. The single-mode fiber and the coreless fiber are coupled by an arc discharge method to realize an MZI interferometer with a micro-dual-arm structure. When the curvature of the micro-dual-arm MZI changes, the high-order mode in the coreless fiber is more susceptible to leakage due to the change in curvature than the fundamental mode in the single-mode fiber, thereby causing the interference spectrum of the MZI to change. By analyzing the distribution of the transmission spectrum and the spatial spectrum of the MZI interferometer, the mode characteristics involved in the interference are understood, thereby realizing all-fiber mode detection. After inducing a high-order mode in the input light, the externally introduced mode can be monitored by bending the micro-dual-arm MZI structure. This study has opened up a direction for the feasibility study of the mode monitor, provided new ideas and approaches for all-fiber mode monitoring and digital mode monitoring, and has important theoretical and practical significance.

[0025] 5. This study proposed a centimeter-level all-fiber mode monitor based on a micro dual-arm MZI, which opened up a direction for the feasibility study of mode monitors and has important theoretical and practical significance. In general, the mode monitor proposed in this study has the advantages of small size, high robustness, easy preparation and low cost, and has broad application prospects in various fields such as optical communication, laser processing, optical sensing and imaging. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] 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.

[0027] Figure 1 This is a schematic diagram of the structure of the monitor in this mode.

[0028] Figure 2 This is a schematic diagram of the device when the monitor of this mode performs curvature adjustment.

[0029] Figure 3 This is a structural diagram of the verification experiment for this mode monitor.

[0030] Figure 4 (a) is the transmission spectrum before and after the high-order mode is excited by the hollow-core fiber. Figure 4 (b) Yes Figure 4 (a) Spatial spectrum after Fourier transform.

[0031] Figure 5 is the transmission spectrum of the mode monitor in its initial state and after it is connected to the hollow-core fiber and bent. Figure 5 (b) Yes Figure 5 (a) Spatial spectrum after Fourier transform.

[0032] Figure 6 This is a comparison chart of the shape changes of the welding coupling point before and after the production process.

[0033] Among them, the figure markings are: 1. broadband light source; 2. coreless optical fiber 1; 3. single-mode optical fiber 1; 4. beam splitting coupling point; 5. interference arm; 6. reference arm; 7. coupling region; 8. coreless optical fiber 2; 9. single-mode optical fiber 2; 10. spectrum analyzer; 11. translation stage; 12. micrometer; 13. hollow optical fiber. DETAILED DESCRIPTION

[0034] 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.

[0035] Embodiment: This embodiment provides a micro dual-arm MZI mode monitor, a micro dual-arm MZI mode monitor, including a broadband light source 1 and a spectrum analyzer 10, and also includes a micro dual-arm MZI structure, such as Figure 1 As shown, the micro dual-arm MZI structure includes a broadband light source 1, a coreless optical fiber 2, a single-mode optical fiber 3, a beam splitting coupling point 4, an interference arm 5, a reference arm 6, a coupling region 7, a coreless optical fiber 8, a single-mode optical fiber 9 and a spectrum analyzer 10;

[0036] Among them, one end of the single-mode optical fiber 3 is connected to the broadband light source 1 through an FC / APC connector, and the other end is connected to the beam splitting coupling point 4. One end of the coreless optical fiber 3 is connected to the beam splitting coupling point 4, and the other end is a free end. The other side of the beam splitting coupling point 4 is connected to one end of the interference arm 5 and the reference arm 6. At the same time, the other ends of the interference arm 5 and the reference arm 6 are connected to one side of the coupling region 7. The other side of the coupling region 7 is connected to one end of the coreless optical fiber 2 8 and the single-mode optical fiber 2 9. The other end of the coreless optical fiber 2 8 is a free end. The single-mode optical fiber 2 9 The other end of the single-mode optical fiber 1 is connected to the spectrum analyzer 10 through an FC / APC connector, the other end of the single-mode optical fiber 1 is used as the input end of the micro-double-arm MZI structure, and is connected to the broadband light source 1, and the other end of the single-mode optical fiber 1 is used as the output end of the micro-double-arm MZI structure, and is connected to the spectrum analyzer 10; that is, the coreless optical fiber 1 and the single-mode optical fiber 1 are located on the same side of the beam splitting coupling point 4, the interference arm 5 and the reference arm 6 are both located between the beam splitting coupling point 4 and the coupling region 7, and the coreless optical fiber 1 and the single-mode optical fiber 1 are located on the same side of the coupling region 7.

[0037] like Figure 2As shown in FIG. 1 , it is a diagram of the curvature measuring device of this example. The mode monitor of this embodiment is fixed on two translation stages 11 by using a screw micrometer 12. The screw micrometer 12 on the translation stage is rotated to change the distance between the two translation stages. The curvature is precisely controlled by adjusting the radius of curvature. Since the high-order modes of the coreless optical fiber are easily affected by the curvature, by adjusting the curvature of the micro dual-arm MZI, the high-order modes in the coreless optical fiber are leaked, causing the transmission spectrum of the MZI to change. By analyzing the changing characteristics of the transmission spectrum and spatial spectrum of the MZI, the changing characteristics of the transmission mode in the MZI are analyzed.

[0038] like Figure 3 As shown in FIG. 1 , it is a schematic diagram of the verification experiment structure of this example. A hollow-core optical fiber 13 is fused between the light source and the micro-double-arm MZI structure. The optical signal passes through the hollow-core optical fiber 13 before entering the micro-double-arm MZI structure, which will excite the high-order mode. Figure 4 (a) It can be seen that after mixing the high-order mode into the input light, dense wavelets will be superimposed on the original interference spectrum. Figure 4 (b) is the corresponding space-frequency diagram. It can be seen that compared with the initial space-frequency diagram, two main high-order modes are added to the MZI space spectrum after the hollow-core fiber 13 is connected. When the MZI is bent to a certain extent, the high-order modes leak, and the high-order sub-peaks on the transmission spectrum gradually disappear. The transmission spectrum is basically restored to the initial transmission spectrum without the addition of the hollow-core fiber 13. Figure 5 (a), the corresponding space-frequency distribution is also the same as Figure 5 (b); Therefore, the high-order modes filtered out in this process are a series of newly added modes. If we can perform statistical analysis on all the modes of the MZI, then we can quantitatively analyze the main modes involved in the interference in the MZI through the transmission spectrum and space-frequency diagram output from the micro-double-arm MZI structure, so as to realize the monitoring of the unknown modes mixed into the input signal by the structure.

[0039] The optical path propagation order of the curvature sensor in this embodiment is:

[0040] The incident light output by the broadband light source 1 enters the beam splitting coupling point 4 through the single-mode optical fiber 3 and is divided into two parts. One part of the light is transmitted in the reference arm 6 made of the single-mode optical fiber in the form of a fundamental mode, and the other part of the light is transmitted in the interference arm 5 made of the coreless optical fiber in the form of a multi-mode. Since the transmission paths of the light in the reference arm 6 and the interference arm 5 are different, the two modes of light will produce a transmission phase shift; when the optical signal reaches the coupling region 7, due to the different transmission phase shifts of the optical signals of different modes, a phase difference is formed, thereby interfering, and finally the light is transmitted to the spectrum analyzer 10 via the single-mode optical fiber 2 9 to monitor the transmitted light.

[0041] In order to better achieve the above-mentioned invention effect, this embodiment also provides a preparation method of a micro dual-arm MZI structure: in the production process, we only use a fiber fusion splicer (FURUKAWA S178C) to obtain this structure, which consists of a section of coreless optical fiber, a section of single-mode optical fiber and two fusion coupling points; in the first step, after stripping the coating layer of the single-mode optical fiber and the coreless optical fiber respectively, they are placed in the fiber fusion splicer side by side, and the two ends are fixed in the fiber clamps respectively. In order to obtain a better coupling effect, it is necessary to tighten the two optical fibers to make them fit tightly, and make the two optical fibers and the discharge electrode in the same plane; in the second step, adjust the fiber fusion splicer to manual mode, control the discharge intensity to 250, and the discharge time to 250ms, perform arc discharge on the two optical fibers to couple them, and obtain the first fusion point , repeat the same operation, and then fuse at a distance of 4.5 cm from the first fusion point to obtain a second fusion point; wherein the length of the coupling region is 500 μm, the length of the interference arm is 4.5 cm, the core and cladding diameters of the single-mode optical fiber are 8.2 μm and 125 μm respectively, and the diameter of the coreless optical fiber is 125 μm. One end of the single-mode optical fiber in the micro-double-arm MZI structure is connected to the pigtail interface of the broadband light source (1) through an FC / APC connector, and the other end is connected to the pigtail interface of the spectrum analyzer (10) through an FC / APC connector, thereby forming the micro-double-arm MZI mode monitor.

[0042] The operation process of this embodiment is as follows:

[0043] After the incident light enters the beam splitting coupling point 4 through the single-mode optical fiber 3, it is divided into two parts. One part of the light is transmitted in the reference arm 6 made of the single-mode optical fiber in the fundamental mode, and the other part of the light is transmitted in the interference arm 5 made of the coreless optical fiber in the form of multimode. Since the transmission paths of the light in the interference arm 5 and the reference arm 6 are different, the two modes of light produce a transmission phase shift. When the optical signal reaches the coupling region 7, the different transmission phase shifts of the optical signals of different modes form a phase difference, thereby causing interference. Since the interference fringes passing through the coupling region 7 are caused by the interference of different mode lights, the mode characteristics and high-order mode characteristics of the optical signal involved in the interference can be known by analyzing the transmission spectrum and spatial frequency characteristics of the MZI. When the double-arm structure is bent, the fundamental mode in the single-mode optical fiber arm basically does not change due to the small bending curvature, while the high-order mode in the coreless optical fiber is sensitive to bending, and bending will cause the high-order mode in the coreless optical fiber to leak and lose. Therefore, as the bending curvature of the MZI increases, the high-order modes participating in the interference of the coupling region 7 decrease accordingly. By analyzing the transmission spectrum and spatial spectrum of the output light, the mode change characteristics in the transmission arm can be monitored.

[0044] This embodiment proposes an all-fiber mode monitor based on a micro-dual-arm MZI, which can be prepared by only a fiber fusion splicer. The single-mode fiber and the coreless fiber are coupled by an arc discharge method to realize an MZI interferometer with a micro-dual-arm structure. When the curvature of the micro-dual-arm MZI changes, the high-order mode in the coreless fiber is more susceptible to leakage due to the change in curvature than the fundamental mode in the single-mode fiber, thereby causing the interference spectrum of the MZI to change. By analyzing the distribution of the transmission spectrum and the spatial spectrum diagram of the MZI interferometer, the mode characteristics involved in the interference are understood, thereby realizing all-fiber mode detection. After inducing a high-order mode in the input light, the externally introduced mode can be monitored by bending the micro-dual-arm MZI structure. This study has opened up a direction for the feasibility study of the mode monitor, provided new ideas and approaches for all-fiber mode monitoring and digital mode monitoring, and has important theoretical and practical significance.

[0045] 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 micro dual-arm MZI mode monitor, comprising a broadband light source (1), a spectrum analyzer (10), a translation stage (11) and a micrometer screw (12), characterized in that: The invention also comprises a micro double-arm MZI structure, wherein the micro double-arm MZI structure comprises a single-mode optical fiber (3), a coreless optical fiber (2), a beam splitting coupling point (4), an interference arm (5), a reference arm (6), a coupling region (7), a coreless optical fiber (8) and a single-mode optical fiber (9), wherein one end of the single-mode optical fiber (3) and the coreless optical fiber (2) are connected to one side of the beam splitting coupling point (4), and the other side of the beam splitting coupling point (4) is respectively connected to one end of the interference arm (5) and the reference arm (6), and the interference arm (5) and the reference arm (6) are connected to one end of the interference arm (5) and the reference arm (6). The other end of the arm (6) is connected to one side of the coupling region (7), and the other side of the coupling region (7) is respectively connected to one end of the coreless optical fiber 2 (8) and the single-mode optical fiber 2 (9). The other end of the single-mode optical fiber 1 (3) is used as the input end of the micro-double-arm MZI structure and is connected to the broadband light source (1). The other end of the single-mode optical fiber 2 (9) is used as the output end of the micro-double-arm MZI structure and is connected to the spectrum analyzer (10). The micro-double-arm MZI structure is fixed on two translation stages (11) via a screw micrometer (12).

2. A micro dual-arm MZI mode monitor according to claim 1, characterized in that: The interference arm (5) is made of coreless optical fiber material, and the reference arm (6) is made of single-mode optical fiber material.

3. A micro dual-arm MZI mode monitor according to claim 2, characterized in that: One end of the single-mode optical fiber 1 (3) away from the beam splitting coupling point (4) is connected to the pigtail interface of the broadband light source (1) through an FC / APC connector, and one end of the single-mode optical fiber 2 (9) away from the coupling region (7) is connected to the pigtail interface of the spectrum analyzer (10) through an FC / APC connector.

4. A micro dual-arm MZI mode monitor according to claim 1, characterized in that: A section of hollow optical fiber (13) is fused between the broadband light source (1) and the single-mode optical fiber (3).

5. A method for preparing a micro dual-arm MZI mode monitor, characterized in that: The preparation method is based on the micro dual-arm MZI mode monitor according to any one of claims 1 to 4, and comprises the following steps: S1: After stripping the coating of a single-mode optical fiber and a coreless optical fiber, place them side by side into the optical fiber fusion splicer, and fix the two ends in the optical fiber clamps respectively; S2: Adjust the optical fiber fusion splicer to manual mode, control the discharge intensity and discharge time, perform arc discharge on the two optical fibers to fuse them, and obtain the first coupling point by fusion; S3: Repeat step S2 and weld to obtain the second coupling point; S4: One end of the single-mode optical fiber is connected to the pigtail interface of the broadband light source (1) through an FC / APC connector, and the other end is connected to the pigtail interface of the spectrum analyzer (10) through an FC / APC connector.

6. The method for preparing a micro dual-arm MZI mode monitor according to claim 5, characterized in that: In the step S1, the two optical fibers are tightened to make them fit tightly together, and the two optical fibers and the discharge electrode are placed in the same plane.

7. The method for preparing a micro dual-arm MZI mode monitor according to claim 5, characterized in that: In step S2, the discharge intensity is 250 and the discharge time is 250 ms.

8. The method for preparing a micro dual-arm MZI mode monitor according to claim 5, characterized in that: In step S3, the distance between the first welding point and the second welding point is 4.5 cm.

9. The method for preparing a micro dual-arm MZI mode monitor according to claim 5, characterized in that: The core and cladding diameters of the single-mode optical fiber are 8.2 μm and 125 μm respectively, and the diameter of the coreless optical fiber is 125 μm.

10. A working principle of a micro dual-arm MZI mode monitor, the working principle is based on the micro dual-arm MZI mode monitor according to any one of claims 1 to 4, characterized in that: The incident light output by the broadband light source (1) enters the beam splitting coupling point (4) through the single-mode optical fiber (3) and is divided into two parts. One part of the light is transmitted in the reference arm (6) made of the single-mode optical fiber in the form of a fundamental mode, and the other part of the light is transmitted in the interference arm (5) made of the coreless optical fiber in the form of a multi-mode. Since the transmission paths of the light in the interference arm (5) and the reference arm (6) are different, the two modes of light will produce a transmission phase shift. When the light signal reaches the coupling region (7), due to the different transmission phase shifts of the light signals of different modes, a phase difference is formed, interference occurs, and the light signal is transmitted to the spectrum analyzer (10) through the single-mode optical fiber (9). The transmitted light is monitored, and the screw micrometer (12) on the translation stage is rotated to change the distance between the two translation stages (11) to adjust the curvature of the micro dual-arm MZI, and the change characteristics of the transmission spectrum and spatial spectrum of the MZI are analyzed, thereby analyzing the change characteristics of the transmission mode in the MZI.

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