An optical fiber coupling structure and a coupling method

Abstract

The application discloses a kind of optical fiber coupling structure and coupling method.Coupling structure includes solid core optical fiber, hollow core optical fiber and five bushings.The first bushing end face and its axis angle is θ1, inside fixed solid core optical fiber;Solid core optical fiber end face and its axis angle is θ2, and θ1=θ2;Hollow core optical fiber is fixed in the second bushing;Two optical fiber axis coplanar and angle is θ3, satisfy relationship n core cosθ1=cos(θ3‑θ1);By third, fourth bushing respectively fixed first two bushings, and finally loaded into fifth bushing and form sealed whole.Coupling method is using V-shaped groove clamp with specific angle θ3 positioning and packaging.The application does not need lens or bridge fiber, coupling structure process is simple, effectively improve return loss and signal quality, conducive to hollow core optical fiber scale application.

Description

Technical Field

[0001] This invention relates to the field of optical fiber communication technology, and in particular to a coupling structure and coupling method for hollow-core optical fiber and solid-core optical fiber, which is suitable for interconnection scenarios with high return loss and high coupling efficiency between different optical fibers. Background Technology

[0002] Hollow-core fiber is a special type of optical fiber whose core is air or an air-filled cavity. Light primarily propagates within the air core, rather than the silica core of traditional optical fibers. Furthermore, hollow-core fiber exhibits lower nonlinear effects and lower loss, making it more promising for various applications.

[0003] When using hollow-core optical fiber in practice, the following issues arise: Sealing issues: Moisture and dust from the external environment can enter the cavity of the hollow fiber, increasing light transmission loss or even causing it to stop working. Interconnection issue: To realize the application of hollow fiber in current optical communication networks, it is necessary to connect hollow fiber with solid single-mode fiber. Return loss issue: Directly connecting the hollow fiber end face of hollow fiber to the end face of solid single-mode fiber will produce strong Fresnel reflection, resulting in low return loss, which cannot meet the requirements of high-speed transmission.

[0004] To address the above problems, patents CN118348639A, CN119148295A, and CN120370476A have disclosed coupling structures and coupling methods for solving these problems.

[0005] Chinese patent application CN118348639A proposes a coupling structure and method for hollow-core optical fiber and solid-core optical fiber. One end of a bridge fiber (120) is fused to a solid-core optical fiber (110), and the end face of the other end is processed into a bevel. Then, it is coupled to the hollow-core optical fiber (130) by adjusting the coupling platform to find the lowest insertion loss, thereby satisfying the requirements of mode field adaptation, low insertion loss, and high return loss in the coupling of solid-core optical fiber and hollow-core optical fiber. In its coupling method, in order to realize a coupling structure of solid-core optical fiber and hollow-core optical fiber, components such as a first sleeve (120) and a second sleeve (130) are used, and after coupling, they are encapsulated and fixed. The patent has the following shortcomings: a bridge fiber (120) is required between the solid fiber and the hollow fiber. One end of the bridge fiber needs to be fused with the mode field of the solid fiber, while the other end needs to be adjusted to match the mode field diameter of the hollow fiber for coupling. At the same time, the end face needs to be processed into a bevel to achieve high return loss. The patent process is very complex and difficult to implement in actual operation, making mass production difficult. In addition, the patent uses a six-axis fiber coupling platform for coupling and fixing between the hollow fiber and the solid fiber. It does not specify the coupling angle between the solid fiber and the hollow fiber, nor does it specify the steps and methods for adjusting the six-axis coupling platform. It is difficult to achieve efficient coupling in actual operation.

[0006] Chinese patent application CN119148295A proposes a coupling structure and coupling method for hollow-core optical fiber and single-mode optical fiber. The light-collecting part (20) of this patent is formed by burning one end of the single-mode optical fiber (3) into a ball, which acts as a lens and couples with the hollow-core optical fiber. The disadvantage of this patent is that, in order to ensure that the outer diameter of the light-collecting part (20) formed by burning the ball is not greater than the cladding diameter of the single-mode optical fiber, the single-mode optical fiber needs to be stripped of its outer coating layer, etched to thin it, and then heated to burn the ball. Optical fibers made of quartz glass generally need to be etched with hydrofluoric acid, which is dangerous and difficult to control the etching thickness precisely. Moreover, immersion etching also requires a long process time, making it difficult to achieve a consistent, fast and efficient coupling.

[0007] Chinese patent application CN120370476A discloses a single-lens coupling assembly, a single-lens mode field converter, and a connector for coupling hollow-core optical fibers and solid-core optical fibers. This patent discloses the use of a single lens (4) between solid-core optical fibers (1) and hollow-core optical fibers (2) to achieve mode field adaptation between them. To achieve high return loss, both the lens (4) and the tilted end face of the optical fiber are coated with anti-reflection films. The shortcomings of this patent are that it requires customizing the lens assembly for both hollow-core and solid-core optical fibers. In particular, hollow-core optical fibers are not yet standardized, and the geometric dimensions and optical properties of hollow-core optical fibers from different manufacturers vary. Different lenses must be customized to complete the coupling, resulting in insufficient flexibility. Furthermore, the presence of the lens increases the cost of the coupling device. Summary of the Invention

[0008] In view of this, the present invention addresses the deficiencies of existing technologies, and its main objective is to provide an optical fiber coupling structure and method that is simple in structure, easy to assemble, highly efficient in coupling, and has high return loss. Specifically, it solves the following technical problems: 1) Simplifying the coupling structure by eliminating complex optical components such as bridge fibers and lenses; 2) Providing a precise and repeatable coupling alignment method to reduce manufacturing complexity; 3) Achieving high return loss through structural design to meet the requirements of high-speed optical communication systems; 4) Achieving reliable sealing of the coupling parts to protect the hollow fiber end face from environmental contamination.

[0009] To achieve the above objectives, the present invention adopts the following technical solution: An optical fiber coupling structure, comprising: The first sleeve has an angle θ1 between its end face and its axis. A solid optical fiber is inserted into and fixed to the first sleeve. The angle between the end face of the solid optical fiber and the axis of the solid optical fiber is a second specific angle θ2, and θ2=θ1. The end face of the solid optical fiber coincides with the end face of the first sleeve. Second casing; A hollow optical fiber is inserted into and fixed to the second sleeve. The end face of the hollow optical fiber is flush with or extends beyond the end face of the second sleeve. The axis of the hollow optical fiber is coplanar with the axis of the solid optical fiber, and the angle between the axis of the hollow optical fiber and the axis of the solid optical fiber is a third specific angle θ3, which satisfies the following relationship: n core cosθ1 = cos(θ3 - θ1); Where, n core The refractive index of the solid fiber core; The third sleeve has an angle of θ4 between its end face and its axis, where θ4 = 90° - (θ3 / 2); the first sleeve is inserted into the third sleeve and fixed together by adhesive. The fourth sleeve has an angle of θ5 between its end face and its axis, where θ5 = θ4; the second sleeve is inserted into the fourth sleeve and fixed together by adhesive. The third sleeve and the end face of the fourth sleeve are bonded together as one piece. The axis of the third sleeve and the axis of the fourth sleeve are coplanar, and the angle between the axis of the third sleeve and the axis of the fourth sleeve is a sixth specific angle θ6, where θ6 = θ3. The fifth sleeve is formed by inserting the first sleeve and the second sleeve into the third sleeve and fixing them together by adhesive.

[0010] As a preferred embodiment, the value of θ1 ranges from 80° to 87°, and the value of θ3 ranges from 1.35° to 4.6°.

[0011] As a preferred embodiment, the distance between the center of the end face of the hollow optical fiber and the center of the end face of the solid optical fiber is 5 micrometers to 20 micrometers.

[0012] As a preferred embodiment: the inner diameter of the first sleeve is larger than the outer diameter of the cladding of the solid optical fiber; the inner diameter of the second sleeve is larger than the outer diameter of the cladding of the hollow optical fiber; and the outer diameters of the first sleeve and the second sleeve are the same.

[0013] As a preferred embodiment, the first sleeve and the second sleeve are optical fiber ceramic ferrules.

[0014] An optical fiber coupling method applied to the aforementioned optical fiber coupling structure includes the following steps: The solid optical fiber is inserted into the first sleeve and fixed. The end faces of the first sleeve and the solid optical fiber are ground so that the end faces of the two coincide and form a first specific angle θ1 with the axis of the first sleeve. Insert the hollow optical fiber into the second sleeve and fix it so that the end face of the hollow optical fiber is flush with the end face of the second sleeve, or extends out of the end face of the second sleeve. Insert the first sleeve into the third sleeve, and the second sleeve into the fourth sleeve; Place the fifth sleeve in the coupling fixture; Place the first sleeve and the second sleeve in the corresponding V-groove of the coupling fixture, and adjust the positions of the first sleeve and the second sleeve so that the axis of the solid fiber and the axis of the hollow fiber are coplanar, and the angle between their axes is θ3. Adjust the positions of the third and fourth sleeves so that the end faces of the two sleeves fit together and the included angles θ6 and θ3 between their axes are equal.

[0015] The fifth sleeve is fitted onto the end joint of the first, second, third, and fourth sleeves and fixed together by adhesive bonding to form a sealed coupling structure.

[0016] As a preferred embodiment: the coupling fixture includes a first V-groove and a second V-groove, the first V-groove being used to constrain the first sleeve, the second V-groove being used to constrain the second sleeve, and there is an angle between the extension directions of the first V-groove and the second V-groove, which is configured as θ3 to achieve control of the axial angle between the solid fiber and the hollow fiber.

[0017] As a preferred embodiment: when adjusting the positions of the first sleeve and the second sleeve, an optical adjustment stage and clamp with displacement and rotation combined functions are used to clamp the first sleeve and the second sleeve respectively for adjustment.

[0018] As a preferred option, the solid fiber can also be thermally expanded before coupling to match its mode field diameter with that of the hollow fiber.

[0019] As a preferred option, an antireflection coating can also be deposited on the end face of the solid optical fiber.

[0020] Compared with existing technologies, this invention has significant advantages and beneficial effects. Specifically, as can be seen from the above technical solution, by precisely controlling the grinding angle of the solid fiber end face and the relative angle between the hollow fiber and the solid fiber, and using a specially designed coupling fixture for rapid and accurate assembly and alignment, a stable and sealed whole is finally formed through sleeve encapsulation. This invention eliminates the need for additional lenses or bridge fibers and other complex optical components, effectively simplifying the structure, reducing insertion loss and return loss, and facilitating the large-scale application of hollow fiber.

[0021] Compared with the prior art, the present invention has the following advantages: High return loss: This is achieved by grinding the end face of solid fiber into a specific large-angle bevel, combined with a specific tilt angle of hollow fiber (satisfying n...). core cosθ1= cos(θ3-θ1)), causing the reflected light to deviate from its original path, achieving a high return loss of over 60dB without the need for coating.

[0022] Low insertion loss: By precisely controlling the included angle θ3 of the two optical fibers and the end-face alignment (contact or micro-distance), efficient mode field matching and optical power transmission are achieved, with typical insertion loss below 0.5dB. Simple structure and high reliability: It eliminates the need for additional optical components such as lenses and bridge fibers, and adopts a mechanical structure with sleeves and clamps, simplifying the device and improving mechanical stability and environmental adaptability.

[0023] Excellent sealing performance: The encapsulation of the third sleeve and the curing adhesive effectively isolates external moisture and dust, protecting the delicate optical fiber coupling interface.

[0024] Good processability and conducive to mass production: The use of a special coupling fixture with a V-groove at a predetermined angle enables rapid and accurate pre-positioning of the fiber angle, which greatly simplifies the complex active optical alignment process and improves production efficiency and product consistency.

[0025] High flexibility and compatibility: By adjusting the sleeve size and angle parameters, and with optional thermal expansion or coating processes, it can flexibly adapt to hollow and solid optical fibers of different models and optical properties.

[0026] To more clearly illustrate the structural features and effects of the present invention, a detailed description is provided below in conjunction with the accompanying drawings and specific embodiments. Attached Figure Description

[0027] Figure 1 This is a cross-sectional view of the coupling structure between hollow-core optical fiber and solid-core optical fiber of the present invention; Figure 2 This is an enlarged schematic diagram of the coupling and connection point between the hollow-core optical fiber and the solid-core optical fiber of the present invention; Figure 3 This is a schematic diagram of the coupling fixture of the present invention; Explanation of reference numerals in the attached diagram: To make the differences between the present invention and the prior art clearer, the reference numerals in the accompanying drawings of the present invention will be described below: Figure 1-3 The attached figures are labeled as follows: 101, first sleeve; 102, second sleeve; 103, third sleeve; 104, fourth sleeve; 105, fifth sleeve; 201, solid fiber; 202, hollow fiber; 301, coupling fixture base; 302, coupling fixture top cover; 303, coupling fixture; 304, first V-groove; 305, second V-groove; 306, through hole; θ1, angle between the end face of the first sleeve and its own axis; θ2, angle between the end face of the solid fiber and its own axis; θ3, angle between the axis of the hollow fiber and the axis of the solid fiber; θ4, angle between the end face of the third sleeve and its own axis; θ5, angle between the end face of the fourth sleeve and its own axis; θ6, angle between the axis of the third sleeve and the axis of the fourth sleeve. Detailed Implementation An optical fiber coupling structure and coupling method, wherein: The optical fiber coupling structure provided by this invention mainly includes a first sleeve 101, a solid optical fiber 201, a second sleeve 102, a hollow optical fiber 202, a third sleeve 103, a fourth sleeve 104, and a fifth sleeve 105. The first sleeve 101 is a slender cylindrical component, and its end face is machined into an inclined surface with an angle θ1 between it and the axis of the first sleeve 101. The solid optical fiber 201 is inserted into and bonded to the first sleeve 101, and its end face is also ground into an inclined surface. The angle between this inclined surface and the axis of the solid optical fiber 201 is a second specific angle θ2, and the grinding process ensures that θ2 = θ1, while simultaneously ensuring that the end face of the solid optical fiber 201 precisely coincides with the inclined end face of the first sleeve 101. The structure of the second sleeve 102 is similar to that of the first sleeve 101. The hollow optical fiber 202 is inserted into and fixed inside the second sleeve 102. The end face of the hollow optical fiber 202 can be made flush with the end face of the second sleeve 102, or slightly protrude from the end face. In the final coupling structure, the axis of the hollow optical fiber 202 needs to be in the same plane as the axis of the fixed solid optical fiber 201, and the included angle between the two axes forms a third specific angle θ3.

[0028] The angle θ3 satisfies the following relationship: n core cosθ1 = cos(θ3 - θ1); n core is the refractive index of the 201 solid fiber core.

[0029] This relationship ensures that the light energy emitted from the inclined surface of the solid fiber 201 is coupled into the hollow fiber 202 with high efficiency, while suppressing the reflected light from returning to the fiber core to the maximum extent, thereby achieving high return loss.

[0030] In a preferred embodiment, the value of θ1 ranges from 80° to 87° (e.g., 82°), and the value of θ3 ranges from 1.35° to 4.6° (e.g., 3.6°).

[0031] In the coupled state, the end face of the hollow fiber 202 and the end face of the solid fiber 201 remain in a stable relative position. In some embodiments, their end faces can be completely fitted and coplanar to achieve optimal coupling; in other embodiments, a small distance, such as 5 to 20 micrometers, can be maintained between the centers of their end faces to still ensure low insertion loss. The outer diameters of the first sleeve 101 and the second sleeve 102 are preferably the same, while their inner diameters are slightly larger than the cladding outer diameter of the fiber they house. Preferably, the first sleeve 101 and the second sleeve 102 are fiber ceramic ferrules.

[0032] The third sleeve 103 is a cylindrical component with an inner diameter slightly larger than the outer diameter of the first sleeve 101. Its end face is machined into an inclined plane at a specific angle θ4 with its own axis, where θ4 = 90° - (θ3 / 2). When the first sleeve 101 is inserted into the third sleeve 103, the axes of the two sleeves coincide.

[0033] The fourth sleeve 104 is a cylindrical component with an inner diameter slightly larger than the outer diameter of the second sleeve 102. Its end face is machined into an inclined plane at a specific angle θ5 with its own axis, where θ5 = θ4 = 90° - (θ3 / 2). When the second sleeve 102 is inserted into the fourth sleeve 104, the axes of the two sleeves coincide. Preferably, the outer diameters of the fourth sleeve 104 and the third sleeve 103 are the same.

[0034] The fifth sleeve 105 has an inner diameter larger than the outer diameters of the third sleeve 103 and the fourth sleeve 104. The sleeves are firmly bonded and fixed together by injecting thermosetting adhesive or UV-curing adhesive into the gaps between the first sleeve 101, the second sleeve 102, the third sleeve 103, the fourth sleeve 104, and the fifth sleeve 105 and then curing it, ensuring a reliable airtight seal.

[0035] Accordingly, the optical fiber coupling method provided by the present invention includes the following steps: First, prepare and grind the solid fiber optic assembly. Insert the solid fiber 201 into the first sleeve 101 and initially fix it, then clamp it onto the grinding device and grind its end face until it coincides with the end face of the first sleeve 101, with the coincident end face forming a first specific angle θ1 with the axis. Next, prepare the hollow fiber optic assembly. Insert the hollow fiber 202 into the second sleeve 102, adjusting its end face to be flush with or slightly protruding from the sleeve end face, then fix it. Next, pre-fit the third sleeve 103 onto the first sleeve 101, pre-fit the fourth sleeve 104 onto the second sleeve 102; and pre-place the fifth sleeve 105 into the through hole 306 of the special coupling fixture. Then, perform assembly and rough positioning. The first sleeve 101 and the second sleeve 102 are respectively placed into the corresponding first V-groove 304 and second V-groove 305 on the coupling fixture 303 (including the coupling fixture base 301 and the coupling fixture cover 302 that cooperate with each other). The assembly of the first sleeve 101 and the third sleeve 103 and the assembly of the second sleeve 102 and the fourth sleeve 104 are pushed towards the center, so that their end portions pass into the already positioned fifth sleeve 105. The first V-groove 304 and the second V-groove 305 of the coupling fixture 303 have an angle θ3 that is precisely configured between their extending directions, thereby constraining the two fiber axes to be automatically coplanar with an angle of θ3. Then, fine adjustments and alignment are performed. Using a fine-tuning mechanism, such as two precision optical adjustment stages with translation and rotation functions and an auxiliary clamp, the first sleeve 101 and the second sleeve 102 are clamped and fine-tuned to make the end face of the hollow fiber 202 in physical contact with the end face of the solid fiber 201. Then, the third sleeve 103 and the fourth sleeve 104 are rotated until their end faces fit together seamlessly.

[0036] Finally, fixation and encapsulation are performed. After confirming the optimal coupling position, adhesive is injected into the sleeve gap and cured to firmly fix and seal the first sleeve 101, the second sleeve 102, the third sleeve 103, the fourth sleeve 104, and the fifth sleeve 105 into a whole, thus completing the fabrication of the coupling device.

[0037] To enable those skilled in the art to better understand and implement the present invention, three specific embodiments are provided below.

[0038] Example 1: Taking a 1310nm communication window as an example. A ceramic ferrule with an outer diameter of 1.25 mm is selected as the first sleeve 101 and the second sleeve 102. The solid fiber 201 is a G.657A2 single-mode fiber, which is fixed to the first sleeve 101 and then ground so that the end face forms an 82° angle with the axis (θ1=θ2=82°). The hollow fiber 202 is a type with a cladding of 125 micrometers and a mode field diameter of approximately 9.1 micrometers at 1310nm, and is fixed to the second sleeve 102. The third sleeve 103 and the fourth sleeve 104 are both glass tubes with an inner diameter of 1.26 mm and an outer diameter of 1.66 mm, and their end faces are ground to form an inclined surface with an angle of θ4=θ5=88.2° with the axis. The coupling fixture 303 is made of a substrate with V-grooves, and the angle between the extension directions of the first V-groove 304 and the second V-groove 305 is θ3=3.6°. Assemble and align all components in the fixture as described above (ensuring the two fiber end faces are in contact and coplanar), and then seal them with thermosetting adhesive. Measured coupling insertion loss is less than 0.5 dB, and return loss is better than 60 dB.

[0039] Example 2: Based on Example 1, taking the 1550nm window as an example, a thermal expansion process is introduced. The end of the G.652D fiber fixed in the first sleeve 101 is thermally expanded to increase its mode field diameter at 1550nm wavelength to approximately 20 micrometers. A hollow-core fiber 202 with a cladding of 210 micrometers and a mode field diameter of approximately 20 micrometers at 1550nm is selected, and a ceramic ferrule with an inner diameter of 211 micrometers is used as the second sleeve 102. The angle between the extension directions of the first V-groove 304 and the second V-groove 305 of the coupling fixture 303 remains 3.6°, and the assembly alignment method is the same as in Example 1. The measured coupling insertion loss is approximately 0.5dB.

[0040] Example 3: Based on Example 1, an antireflection coating is deposited on the 82° bevel of the polished solid-core fiber 201, and subsequent steps remain unchanged. The measured coupling insertion loss can be further reduced to below 0.34dB.

[0041] Through the above-described specific embodiments, this invention achieves high return loss exceeding 60dB without coating by employing a specific angle relationship design; it achieves low insertion loss below 0.5dB by precisely controlling the included angle and end face alignment; it eliminates complex components such as lenses and bridge fibers, resulting in a simple and reliable structure; it forms a reliable hermetically sealed package through a third sleeve and adhesive encapsulation; it simplifies the alignment process by using a dedicated fixture for angle pre-positioning, ensuring good consistency and facilitating mass production; and it can flexibly adapt to different types of optical fibers by selecting different parameters or supplementing with thermal expansion and coating processes.

[0042] The above description is merely a preferred embodiment of the present invention and does not constitute any limitation on the technical scope of the present invention. Therefore, any minor modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention shall still fall within the scope of the technical solution of the present invention.

Claims

1. An optical fiber coupling structure, characterized in that... include: Solid fiber, hollow fiber, first sleeve, second sleeve, third sleeve, fourth sleeve, fifth sleeve; The angle between the end face of the first sleeve and the axis of the first sleeve is a first specific angle θ1; The solid optical fiber is inserted into and fixed to the first sleeve. The angle between the end face of the solid optical fiber and the axis of the solid optical fiber is a second specific angle θ2, and θ2=θ1. The end face of the solid optical fiber coincides with the end face of the first sleeve. The hollow-core optical fiber is inserted into and fixed to the second sleeve. The end face of the hollow-core optical fiber is flush with the end face of the second sleeve, or extends out of the end face of the second sleeve. The axis of the hollow-core optical fiber is coplanar with the axis of the solid-core optical fiber, and the angle between the axis of the hollow-core optical fiber and the axis of the solid-core optical fiber is a third specific angle θ3, which satisfies the following relationship: n core cosθ1= cos(θ3-θ1), where, n core The refractive index of the solid fiber core is θ1, which ranges from 80° to 87°, and the refractive index of θ3 ranges from 1.35° to 4.6°. The angle between the end face of the third sleeve and the axis of the third sleeve is a fourth specific angle θ4, where θ4 = 90° - (θ3 / 2); the first sleeve is inserted into the third sleeve and fixed together by adhesive. The angle between the end face of the fourth sleeve and the axis of the fourth sleeve is a fifth specific angle θ5, where θ5 = θ4; the second sleeve is inserted into the fourth sleeve and fixed together by adhesive. The end faces of the third sleeve and the fourth sleeve are bonded together as one piece. The axis of the third sleeve and the axis of the fourth sleeve are coplanar, and the angle between the axis of the third sleeve and the axis of the fourth sleeve is a sixth specific angle θ6, where θ6 = θ3. The third and fourth sleeves are inserted into the fifth sleeve and fixed together by adhesive.

2. The fiber coupling structure according to claim 1, characterized in that, The distance between the center of the end face of the hollow optical fiber and the center of the end face of the solid optical fiber is 5 micrometers to 20 micrometers.

3. The fiber coupling structure according to claim 1, characterized in that, The inner diameter of the first sleeve is larger than the outer diameter of the cladding of the solid optical fiber; the inner diameter of the second sleeve is larger than the outer diameter of the cladding of the hollow optical fiber; the outer diameters of the first sleeve and the second sleeve are the same.

4. The fiber coupling structure according to claim 1, characterized in that, The first sleeve and the second sleeve can be optical fiber ceramic ferrules, optical fiber metal ferrules, glass tubes or metal tubes.

5. A fiber coupling method applied to the fiber coupling structure as described in any one of claims 1-4, characterized in that, Includes the following steps: The solid optical fiber is inserted into the first sleeve and fixed. The end faces of the first sleeve and the solid optical fiber are ground so that their end faces coincide and form a first specific angle θ1 with the axis of the first sleeve. Insert the hollow optical fiber into the second sleeve and fix it so that the end face of the hollow optical fiber is flush with the end face of the second sleeve, or extends out of the end face of the second sleeve. Insert the first sleeve into the third sleeve, and the second sleeve into the fourth sleeve; Place the fifth sleeve in the coupling fixture; Place the first sleeve and the second sleeve in the corresponding V-groove of the coupling fixture, and adjust the positions of the first sleeve and the second sleeve so that the axis of the solid fiber and the axis of the hollow fiber are coplanar, and the angle between their axes is θ3. Adjust the positions of the third sleeve and the fourth sleeve so that the end faces of the two sleeves fit together and the included angle θ6 between their axes is equal to θ3. The fifth sleeve is fitted onto the end joint of the first, second, third, and fourth sleeves and fixed together by adhesive bonding to form a sealed coupling structure.

6. The fiber coupling method according to claim 5, characterized in that, The coupling fixture includes a first V-groove and a second V-groove. The first V-groove is used to constrain the first sleeve, and the second V-groove is used to constrain the second sleeve. The first V-groove and the second V-groove have an angle between their extending directions, which is configured as θ3 to control the axial angle between the solid fiber and the hollow fiber.

7. The fiber coupling method according to claim 5, characterized in that, When adjusting the positions of the first sleeve and the second sleeve, an optical adjustment stage and clamp with displacement and rotation functions are used to clamp the first sleeve and the second sleeve respectively for adjustment.

8. The fiber coupling method according to claim 5, characterized in that, Another step is to perform a thermal expansion process on the solid fiber before coupling so that its mode field diameter matches the mode field of the hollow fiber.

9. The fiber coupling method according to claim 5, characterized in that, The end face of the solid optical fiber is coated with an anti-reflection film to reduce insertion loss in the coupling structure.

Images