Hollow core fiber low return loss fusion splice assembly compatible with single mode or multi mode fiber interfaces and methods of making the same

Abstract

The application discloses a hollow optical fiber low-return-fusion connecting assembly compatible with single-mode or multi-mode optical fiber interfaces and a preparation method thereof, and particularly relates to the technical field of optical fiber device packaging, and comprises a hollow optical fiber transmission section, a first protected conversion module, a second protected conversion module, a first tail fiber, a second tail fiber, a first optical fiber connecting end and a second optical fiber connecting end; the two ends of the hollow optical fiber transmission section are respectively connected with the first protected conversion module and the second protected conversion module; the first protected conversion module is connected with the first optical fiber connecting end through the first tail fiber; and the second protected conversion module is connected with the second optical fiber connecting end through the second tail fiber. Most of the energy is coupled into the low-loss fundamental mode, and the high-order mode is effectively suppressed, so that the output light field of the mode field adaptation section is injected in a phase and amplitude distribution conforming to the hollow optical fiber fundamental mode incidence condition, and the insertion loss caused by mode mismatch and non-target mode excitation is reduced.

Description

Technical Field

[0001] This application relates to the field of optical fiber device packaging technology, and more specifically, to a hollow fiber low-return fusion splice assembly compatible with single-mode or multi-mode optical fiber interfaces and its preparation method. Background Technology

[0002] Hollow-core optical fiber uses air or a low-refractive-index gas region as the primary light-guiding channel. Compared to traditional solid-core silica fiber, it offers advantages such as low latency, low nonlinearity, low thermo-optical sensitivity, high power handling capability, low Rayleigh scattering, and broadband transmission potential. It holds significant application value in high-speed communication, data center interconnection, quantum links, high-power lasers, gas sensing, and precision interferometry. Currently, many optical communication devices, test instruments, and system ports utilize standard single-mode or multimode fiber interfaces. To integrate hollow-core optical fiber into existing fiber optic systems, it is necessary to maintain its transmission advantages while achieving a low-loss, low-return, and mechanically reliable connection between hollow-core optical fiber and standard single-mode or multimode fiber.

[0003] A search revealed that publication number CN100570416C discloses an optical fiber, a method for connecting optical fibers, and an optical connector. The optical fiber has multiple openings around its core, and the openings near the connector end are filled with a light-transmitting material such as resin or glass with a refractive index lower than that of quartz-based materials. The connector of this optical fiber connects an optical fiber with multiple openings within the cladding surrounding its core to other optical fibers, wherein the optical fiber is aligned with the other optical fibers via a refractive index matching agent with a refractive index lower than that of the core at the lowest temperature in actual use. The inventors discovered the following problems with the prior art during the development of this application: Existing hollow-core optical fibers differ from standard single-mode or multimode optical fibers in mode field size, phase distribution, and light guiding mechanism. Simple direct splicing or fusion splicing can easily generate large coupling losses. Furthermore, due to the refractive index difference between glass core and air core, Fresnel echo reflections are easily introduced at the connection interface, which can lead to multipath interference, increased system noise, or laser instability. In addition, the microstructure at the end of hollow-core optical fibers is sensitive to heat input, mechanical stress, end-face contamination, and repeated insertion and removal. Ordinary end-face treatment or excessive fusion heat may cause microstructure deformation, local collapse, or mode perturbation. Therefore, to address the above issues, a hollow fiber low-echo fusion splice assembly compatible with single-mode or multi-mode fiber interfaces and its fabrication method are proposed. Summary of the Invention

[0004] In order to overcome the above-mentioned defects of the prior art, this application provides a hollow fiber low-echo fusion splice connection component compatible with single-mode or multi-mode fiber interfaces and its preparation method, so as to solve the problems mentioned in the background art.

[0005] To achieve the above objectives, this application provides the following technical solution: a hollow-core fiber low-return fusion splice assembly compatible with single-mode or multi-mode fiber interfaces, comprising a hollow-core fiber transmission segment, a first protected conversion module, a second protected conversion module, a first pigtail, a second pigtail, a first fiber connector, and a second fiber connector; the first protected conversion module and the second protected conversion module are respectively connected to both ends of the hollow-core fiber transmission segment; the first protected conversion module is connected to the first fiber connector via the first pigtail; the second protected conversion module is connected to the second fiber connector via the second pigtail. The first protected conversion module includes a solid core mode field adapter section, an end face coupling compensation area, a controlled fusion splice area, a stress relief component, and an external protective component; the solid core mode field adapter section, the end face coupling compensation area, and the hollow fiber end are optically coupled in sequence, and the first protected conversion module and the second protected conversion module have the same structure; The end-face coupling compensation area is located between the solid-core mode field adapter section and the hollow-core fiber end, used to reduce echo reflection at the connection interface and suppress non-target mode excitation; the controlled fusion splice connection area is located at the fusion splice connection point of the hollow-core fiber end, used to achieve mechanical fixation while maintaining the basic integrity of the microstructure at the hollow-core fiber end; the external protective component is used to isolate the influence of environmental stress on the connection point. The solid core mode field adaptation section, end face coupling compensation area, and controlled fusion connection area are encapsulated inside the external protective component. The structural parameters of the three are adapted in a coordinated manner to achieve synergistic optimization between low echo reflection and high fundamental mode coupling efficiency.

[0006] Preferably, the solid-core mode field adapter section is used to adjust the output optical field of a single-mode or multi-mode fiber to a suitable optical field for coupling into the fundamental mode of a hollow-core fiber. The solid-core mode field adapter section can be any of the following solid-core fiber structures that can achieve equivalent mode field conversion: graded-index fiber, thermally expanded fiber, tapered fiber, and reverse tapered fiber. One end of the solid-core mode field adapter section is fused with a pigtail, and the solid-core mode field adapter section and the pigtail are pre-fused to form an integrated single-mode side structure.

[0007] Preferably, the end-face coupling compensation area is adjusted by a combination of end-face angle, lateral relative position, axial spacing, and fusion hot zone position, so that the optical field after mode field adaptation is coupled into the hollow fiber in a state that meets the incident conditions of the hollow fiber fundamental mode.

[0008] Preferably, the controlled fusion splice region is specifically formed under heat-affected zone conditions, the fusion is applied to the fiber cladding region, and the core microstructure at the end of the hollow fiber remains in a state without thermal collapse.

[0009] Preferably, the stress relief component and the external protective component are sequentially wrapped around the outside of the controlled fusion splice area 8 to isolate the effects of bending, tension, vibration and temperature stress on the connection point; the end face of the hollow fiber is located inside the first protected conversion module and is not exposed as an external plug-in end face.

[0010] Preferably, the length of the hollow fiber transmission segment is adjustable, and the hollow fiber transmission segment can be used as a hollow transmission unit in an optical fiber delay line, an intra-module interconnect component, a high-power transmission component, or a low-nonlinear transmission link.

[0011] Preferably, a method for fabricating a hollow-core fiber low-return fusion splice assembly compatible with single-mode or multimode fiber interfaces includes the following steps: S1. Based on the working wavelength, target hollow fiber length, interface type and target connection performance, select the hollow fiber transmission segment, pigtail and solid mode field adapter segment with corresponding parameters. S2. Connect the solid core mode field adapter section and the pigtail, and preprocess the solid core mode field adapter section to make its output optical field meet the coupling requirements of the target hollow fiber. S3. Place the solid core mode field adapter section and the hollow fiber end on the fusion splicing platform to complete the alignment and adjustment. Monitor the optical performance parameters in real time during the alignment process. S4. After reaching the target coupling state, a heat-affected fusion splicing method is used to form a fusion connection, maintaining the stability of the microstructure at the end of the hollow fiber and forming a connection point with mechanical strength. S5. Stress relief components and external protective components are sequentially installed on the outside of the controlled fusion splicing area 8 to connect the outer end of the pigtail and the standard optical fiber connection end into one unit. S6. Perform optical and mechanical performance tests on the finished components to verify the connection performance.

[0012] Preferably, in step S2, the preprocessing of the solid core mode field adaptation section includes the control of the end face state, length state and equivalent optical length, so that the mode field size and phase distribution of the output light field are close to the corresponding parameters of the target hollow fiber fundamental mode.

[0013] Preferably, in step S3, the alignment of the solid core mode field adapter segment and the hollow core fiber end on the fusion splicing platform includes multi-dimensional alignment in terms of lateral direction, axis, and angle; during the alignment process, one or more parameters among the transmitted power, echo reflection, and output mode are monitored in real time, and the alignment state is adjusted according to the monitoring results until the target coupling state is achieved.

[0014] Preferably, in step S4, the heat-affected fusion splicing method includes pulsed discharge fusion splicing, offset discharge fusion splicing, or low-current long-time fusion splicing, and the fusion splicing parameters are optimized according to the hollow fiber structure, mode field size, and working wavelength. In step S6, the performance tests include insertion loss test, echo reflection test, mode stability test, mechanical strength test, temperature cycling test, bending test, and long-term stability test.

[0015] The technical effects and advantages of this application are as follows: 1. Compared with existing technologies, this hollow-core fiber low-echo fusion splice component and its fabrication method, compatible with single-mode or multi-mode fiber interfaces, physically disrupts the vertical reflection condition by making a small-angle bevel on the solid-core side end face, preventing the reflected light from returning along the original path and thus significantly suppressing echo. However, the beveled end face inevitably causes refraction and deflection of the outgoing beam. If directly aligned, it will excite higher-order modes in the hollow-core fiber, causing energy loss and mode dispersion. To address this, the present invention introduces a lateral optical axis offset compensation mechanism. By setting the relative position of the axes of the solid-core fiber and the hollow-core fiber, the refracted beam is realigned with the center of the hollow-core fiber's fundamental mode, ensuring that most of the energy is coupled into the low-loss fundamental mode while effectively suppressing higher-order modes. This injects the output optical field of the mode field adaptation section with a phase and amplitude distribution that conforms to the incident conditions of the hollow-core fiber's fundamental mode, reducing insertion loss caused by mode mismatch and excitation of non-target modes.

[0016] 2. Compared with existing technologies, this hollow-core fiber low-return fusion splice connection component and its fabrication method, compatible with single-mode or multi-mode fiber interfaces, restricts heat input to the fiber cladding region through various heat-affected zone control methods such as fusion splicing. This ensures that the core microstructure at the hollow-core fiber end remains in its original state without thermal collapse, forming a strong mechanical connection only at the cladding. This allows the connection point to obtain sufficient strength to withstand tension, bending, and vibration while retaining the light-guiding mechanism of the hollow-core fiber, avoiding optical performance degradation due to thermal deformation. Furthermore, stress relief components and external protective components are sequentially arranged outside the controlled fusion splice connection area, forming a layered protection structure: the stress relief components absorb and buffer local strain caused by temperature changes, mechanical bending, or assembly stress, preventing stress from directly acting on the fusion splice point; the external protective components provide rigid encapsulation, isolating external contaminants, moisture, and accidental impacts. All hollow-core fiber end faces are built into the protection module, preventing external insertion / removal of the end faces and reducing the risk of end face contamination, scratches, and damage from repeated insertion / removal. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the overall structure of the connection component in this application; Figure 2 This is a schematic diagram of the structure of the first protected conversion module of this application; Figure 3 This is a schematic diagram of the optical axis compensation principle of this application; Figure 4 This is a schematic diagram of the preparation method of this application.

[0018] The attached figures are labeled as follows: 1. Hollow-core fiber transmission segment; 2. First protected conversion module; 3. Second protected conversion module; 4. First pigtail; 5. Second pigtail; 6. First fiber connector; 7. Second fiber connector; 8. Controlled fusion splice area; 9. Solid core mode field adaptation segment; 10. End face coupling compensation area; 11. Hollow-core fiber end; 12. Stress relief component; 13. External protection component. Detailed Implementation

[0019] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0020] Example 1 As attached Figures 1 to 4 The hollow-core fiber low-return fusion splice assembly shown is compatible with single-mode or multimode fiber interfaces and includes a hollow-core fiber transmission segment 1, a first protected conversion module 2, a second protected conversion module 3, a first pigtail 4, a second pigtail 5, a first fiber connector 6, and a second fiber connector 7. The first protected conversion module 2 and the second protected conversion module 3 are respectively connected to the two ends of the hollow-core fiber transmission segment 1. The first protected conversion module 2 is connected to the first fiber connector 6 through the first pigtail 4. The second protected conversion module 3 is connected to the second fiber connector 7 through the second pigtail 5. The standard connector can adopt common fiber optic connector types such as LC, SC, and FC, which can be directly adapted to the ports of existing optical communication systems. The first protected conversion module 2 includes a solid core mode field adapter section 9, an end face coupling compensation area 10, a controlled fusion splice connection area 8, a stress relief component 12, and an external protection component 13; the solid core mode field adapter section 9, the end face coupling compensation area 10, and the hollow fiber end 11 are optically coupled in sequence, and the first protected conversion module 2 and the second protected conversion module 3 have the same structure. The end-face coupling compensation region 10 is located between the solid-core mode field adapter section 9 and the hollow-core fiber end 11. By making a small-angle oblique cut on the solid-core side end face, the vertical reflection condition can be destroyed, and Fresnel echo reflection can be greatly reduced. At the same time, in response to the beam refraction and deflection caused by the oblique end face, the lateral axis offset between the solid-core side and the hollow-core side is pre-set so that the deflected beam is re-aligned with the center of the hollow-core fiber fundamental mode, avoiding the excitation of higher-order modes and achieving a balance between low echo and high coupling efficiency. This region can be adjusted by combining the end face angle, lateral offset, axial micro-gap, and fusion hot zone position to adapt to hollow optical fibers with different structural parameters. It is used to reduce echo reflection at the connection interface and suppress non-target mode excitation. The controlled fusion connection area 8 is set at the connection point of the fusion splice at the end 11 of the hollow optical fiber. When the optical fiber is heated, the fusion heat is mainly concentrated in the cladding area of ​​the optical fiber. The microstructure of the core area is not affected by heat and does not collapse or deform. While ensuring the mechanical connection strength, the light guiding performance of the hollow optical fiber is maintained and the microstructure at the end 11 of the hollow optical fiber is basically intact to achieve mechanical fixation. The external protective component 13 is used to isolate the influence of environmental stress on the connection point. The solid core mode field adaptation section 9, the end face coupling compensation area 10, and the controlled fusion connection area 8 are encapsulated inside the external protective component 13. The structural parameters of the three are adapted in a coordinated manner to achieve synergistic optimization between low echo reflection and high fundamental mode coupling efficiency.

[0021] In a preferred embodiment, the solid-core mode field adapter section 9 is used to adjust the output optical field of a single-mode or multi-mode fiber to a suitable optical field for coupling into the fundamental mode of a hollow-core fiber. The solid-core mode field adapter section 9 can be any of the following solid-core fiber structures that can achieve equivalent mode field conversion: graded-index fiber, thermally expanded fiber, tapered fiber, and reverse tapered fiber. One end of the solid-core mode field adapter section 9 is fused with a pigtail, which is a structure at the outward extension of the first or second pigtail, referred to as a pigtail. The solid-core mode field adapter section 9 is made of graded-index fiber. The solid-core mode field adapter section 9 and the pigtail are pre-fused to form an integrated single-mode side structure. The core refractive index of the graded-index fiber is parabolically distributed radially, which can perform graded beam expansion and shaping on the incident optical field, smoothly converting the small mode field output of the standard single-mode fiber into a large mode field output that matches the fundamental mode size of the hollow-core fiber, while maintaining the continuity of the phase distribution and reducing coupling loss caused by mode field mismatch.

[0022] In a preferred embodiment, the end-face coupling compensation region 10 is adjusted by combining the end-face angle, lateral relative position, axial spacing, and fusion hot zone position, so that the optical field after mode field adaptation is coupled into the hollow fiber in a state that meets the incident conditions of the hollow fiber fundamental mode. The synergistic effect of the solid core mode adaptation section 9 and the end-face coupling compensation region 10 expands the mode field size or adjusts the morphology of the output optical field from the single-mode or multi-mode pigtail, so that its mode field diameter, wavefront curvature, phase distribution and other characteristics match the corresponding characteristics of the fundamental mode of the target hollow fiber, thereby maximizing the excitation of the hollow fiber fundamental mode and suppressing higher-order modes and echo reflection.

[0023] In a preferred embodiment, the controlled fusion splice region 8 is specifically formed under heat-affected conditions, and the fusion splice is used in the cladding region of the optical fiber, so that the core microstructure of the hollow fiber end 11 remains in a state without thermal collapse.

[0024] In a preferred embodiment, the stress relief component 12 and the external protection component 13 are sequentially wrapped around the outside of the controlled fusion splice area 8 to isolate the effects of bending, stretching, vibration and temperature stress on the connection point; the end face of the hollow fiber is located inside the first protected conversion module 2 and is not exposed as an external plug-in end face.

[0025] In a preferred embodiment, the length of the hollow fiber transmission segment 1 is adjustable, and the hollow fiber transmission segment 1 can be used to connect prefabricated patch cords, fiber delay lines, interconnect components within modules, high-power transmission components, or hollow transmission units in low nonlinear transmission links.

[0026] The optical signal is input from the first fiber connector 6, enters the first protected conversion module 2 via the first pigtail 4, and undergoes gradual beam expansion and shaping of the incident light field in the solid core mode field adaptation section 9, so that the mode field size and phase distribution gradually match the hollow fiber fundamental mode. Subsequently, the light field is coupled into the hollow fiber transmission section 1 in the end face coupling compensation area 10 under low echo conditions, and is transmitted along the air core with low loss and low delay. After the optical signal is transmitted to the other end, it is coupled back to the second pigtail 5 via the second protected conversion module 3 in the reverse process, and finally output from the second fiber connector 7. The component has consistent forward and reverse transmission performance, supports bidirectional optical signal transmission, and all hollow fiber end faces are encapsulated inside the external protective component 13, presenting only the standard solid fiber connector to the outside.

[0027] Example 2 Based on Example 1, the solution in Example 1 will be further described in detail below with reference to the specific working method, such as... Figures 1 to 4 As shown below, see details: A method for fabricating a hollow-core fiber low-return fusion splice assembly compatible with single-mode or multimode fiber interfaces includes the following steps: S1. Based on the working wavelength, target hollow fiber length, interface type and target connection performance, select hollow fiber transmission segment 1, pigtail and solid mode field adapter segment 9 with corresponding parameters. S2. Connect the solid core mode field adapter section 9 to the pigtail, and preprocess the solid core mode field adapter section 9 so that its output optical field meets the coupling requirements of the target hollow fiber. S3. Place the solid core mode field adapter section 9 and the hollow core fiber end 11 on the fusion splicing platform to complete the alignment and adjustment. Monitor the optical performance parameters in real time during the alignment process. S4. After reaching the target coupling state, a heat-affected fusion splicing method is used to form a fusion splice connection, keeping the microstructure of the hollow fiber end 11 stable and forming a connection point with mechanical strength. S5. Stress relief component 12 and external protection component 13 are sequentially installed on the outside of the controlled fusion splicing area 8 to connect the outer end of the pigtail and the standard optical fiber connection end into one unit. S6. Perform optical and mechanical performance tests on the finished components to verify the connection performance.

[0028] In a preferred embodiment, step S2 includes the preprocessing of the solid core mode field adaptation segment 9, which includes the control of the end face state, length state, and equivalent optical length, so that the mode field size and phase distribution of the output light field are close to the corresponding parameters of the target hollow fiber fundamental mode.

[0029] In a preferred embodiment, in step S3, the alignment of the solid core mode field adapter segment 9 and the hollow core fiber end 11 on the fusion splicing platform includes multi-dimensional alignment in the lateral, axial and angular directions; during the alignment process, one or more parameters among the transmission power, echo reflection and output mode are monitored in real time, and the alignment state is adjusted according to the monitoring results until the target coupling state is achieved.

[0030] As a preferred embodiment, in step S4, after the target coupling state is reached, a heat-affected fusion splicing method is used to form a fusion connection. The heat-affected fusion splicing method includes pulsed discharge fusion splicing, offset discharge fusion splicing, or low current long-time fusion splicing. The fusion splicing parameters are optimized according to the hollow fiber structure, mode field size, and working wavelength. In step S6, the performance tests include insertion loss test, echo reflection test, mode stability test, mechanical strength test, temperature cycling test, bending test, and long-term stability test.

Claims

1. A hollow-core fiber low-return fusion splice assembly compatible with single-mode or multimode fiber interfaces, characterized in that, It includes a hollow-core optical fiber transmission segment (1), a first protected conversion module (2), a second protected conversion module (3), a first pigtail (4), a second pigtail (5), a first optical fiber connector (6), and a second optical fiber connector (7); the two ends of the hollow-core optical fiber transmission segment (1) are respectively connected to the first protected conversion module (2) and the second protected conversion module (3); the first protected conversion module (2) is connected to the first optical fiber connector (6) through the first pigtail (4); the second protected conversion module (3) is connected to the second optical fiber connector (7) through the second pigtail (5); The first protected conversion module (2) includes a solid core mode field adapter section (9), an end face coupling compensation area (10), a controlled fusion splice connection area (8), a stress relief component (12), and an external protection component (13); the solid core mode field adapter section (9), the end face coupling compensation area (10), and the hollow fiber end (11) are optically coupled in sequence, and the first protected conversion module (2) and the second protected conversion module (3) have the same structure; The end-face coupling compensation area (10) is disposed between the solid core mode field adaptation section (9) and the hollow fiber end (11) to reduce the echo reflection at the connection interface and suppress the excitation of non-target modes; the controlled fusion splice connection area (8) is disposed at the fusion splice connection of the hollow fiber end (11). The solid core mode field adaptation section (9), the end face coupling compensation area (10), and the controlled fusion connection area (8) are encapsulated inside the external protective component (13). The structural parameters of the three are adapted in a coordinated manner to achieve synergistic optimization between low echo reflection and high fundamental mode coupling efficiency.

2. The hollow-core fiber low-return fusion splice assembly compatible with single-mode or multimode fiber interfaces according to claim 1, characterized in that, The solid core mode field adapter section (9) is used to adjust the output optical field of a single-mode or multi-mode fiber to a suitable optical field for coupling into the fundamental mode of a hollow fiber. One end of the solid core mode field adapter section (9) is fused with a pigtail. The solid core mode field adapter section (9) and the pigtail are pre-fused to form an integrated single-mode side structure.

3. The hollow-core fiber low-return fusion splice assembly compatible with single-mode or multimode fiber interfaces according to claim 1, characterized in that, The end face coupling compensation area (10) is adjusted by a combination of end face angle, lateral relative position, axial spacing and fusion hot zone position, so that the optical field after mode field adaptation is coupled into the hollow fiber in a state that meets the incident conditions of the hollow fiber fundamental mode.

4. The hollow-core fiber low-return fusion splice assembly compatible with single-mode or multi-mode fiber interfaces according to claim 1, characterized in that, The controlled fusion splice region (8) is specifically formed under heat-affected conditions. The fusion splice is used in the cladding region of the optical fiber, and the core microstructure of the hollow fiber end (11) remains in a state of no thermal collapse.

5. A hollow-core fiber low-return fusion splice assembly compatible with single-mode or multimode fiber interfaces according to claim 1, characterized in that, The stress relief component (12) and the external protection component (13) are sequentially wrapped around the outside of the controlled fusion splice area (8), and the end face of the hollow fiber is located inside the first protected conversion module (2).

6. The hollow-core fiber low-return fusion splice assembly compatible with single-mode or multimode fiber interfaces according to claim 1, characterized in that, The length of the hollow fiber transmission segment (1) is adjustable, and the hollow fiber transmission segment (1) can be used to connect to the hollow transmission unit in the prefabricated patch cord.

7. A method for fabricating a hollow-core fiber low-return fusion splice assembly compatible with single-mode or multimode fiber interfaces, characterized in that, Includes the following steps: S1. Based on the working wavelength, target hollow fiber length, interface type and target connection performance, select the hollow fiber transmission segment (1), pigtail and solid mode field adapter segment (9) with corresponding parameters. S2. Connect the solid core mode field adapter section (9) and the pigtail, and preprocess the solid core mode field adapter section (9) so that its output optical field meets the coupling requirements of the target hollow fiber. S3. Place the solid core mode field adapter section (9) and the hollow core fiber end (11) on the fusion splicing platform to complete the alignment and adjustment. Monitor the optical performance parameters in real time during the alignment process. S4. After reaching the target coupling state, a heat-affected fusion splicing method is used to form a fusion splice connection, keeping the microstructure of the hollow fiber end (11) stable and forming a connection point with mechanical strength. S5. Stress relief component (12) and external protection component (13) are sequentially installed on the outside of the controlled fusion splicing area (8) to connect the outer end of the pigtail and the standard optical fiber connection end into one unit. S6. Perform optical and mechanical performance tests on the finished components to verify the connection performance.

8. The method for preparing a hollow-core fiber low-return fusion splice assembly compatible with single-mode or multimode fiber interfaces according to claim 7, characterized in that, In step S2, the preprocessing of the solid core mode field adaptation segment (9) includes the control of the end face state, length state and equivalent optical length, so that the mode field size and phase distribution of the output optical field are close to the corresponding parameters of the target hollow fiber fundamental mode.

9. The method for preparing a hollow-core fiber low-return fusion splice assembly compatible with single-mode or multimode fiber interfaces according to claim 7, characterized in that, In step S3, the alignment of the solid core mode field adapter segment (9) and the hollow fiber end (11) on the fusion splicing platform includes multi-dimensional alignment in the lateral, axial and angular directions. During the alignment process, one or more parameters in the transmission power, echo reflection and output mode are monitored in real time, and the alignment state is adjusted according to the monitoring results until the target coupling state is achieved.

10. The method for preparing a hollow-core fiber low-return fusion splice assembly compatible with single-mode or multi-mode fiber interfaces according to claim 7, characterized in that, In step S4, the heat-affected fusion splicing method includes pulsed discharge fusion splicing, offset discharge fusion splicing, or low-current long-time fusion splicing, and the fusion splicing parameters are optimized according to the hollow fiber structure, mode field size, and working wavelength. In step S6, the performance tests include insertion loss test, echo reflection test, mode stability test, mechanical strength test, temperature cycling test, bending test, and long-term stability test.

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