A single mode hollow core fiber converter

Abstract

The application relates to the technical field of optical communication, in particular to a single-mode hollow optical fiber converter; the converter comprises a double-fiber pigtail, a lens assembly and a mirror, the lens assembly is arranged between the double-fiber pigtail and the mirror, the double-fiber pigtail is provided with a hollow optical fiber and a single-mode optical fiber which are independent of each other, a hollow-core optical fiber is fused to the end of the hollow optical fiber close to the lens assembly, the end of the single-mode optical fiber close to the lens assembly is provided with a beam expansion area, and the equivalent mode field diameter of the beam expansion area is larger than the mode field diameter of the single-mode optical fiber body; an optical signal is incident on the lens assembly through one of the hollow optical fiber or the single-mode optical fiber, is corrected by the lens assembly, is incident on the mirror, is folded back by the mirror, and is coupled into the other one of the hollow optical fiber or the single-mode optical fiber by the lens assembly; the end portions of the hollow optical fiber and the single-mode optical fiber are specially designed, and the space optical path is matched to complete the optical signal interaction between the two optical fibers, so that the coupling loss is low, the anti-pollution capability is strong, the structure is compact, and the development demand of miniaturization is met.

Description

Technical Field

[0001] This invention relates to the field of optical communication technology, and in particular to a single-mode hollow fiber converter. Background Technology

[0002] With the continuous development of high-speed, high-capacity optical communication services, hollow fiber has been gradually applied in communication systems due to its advantages such as low latency, low nonlinear effects, high optical power tolerance, and wide transmission bandwidth. However, the existing optical transmission network is based on traditional solid single-mode fiber and is deployed on a large scale. It is impossible to complete the replacement of the entire network in the short term. During the operation of the system, it is necessary to achieve optical path interconnection between single-mode fiber and hollow fiber.

[0003] Because the mode field diameters of solid single-mode fiber and hollow fiber differ significantly, direct fusion splicing will result in severe mode mismatch, leading to significant coupling loss and a substantial reduction in optical transmission efficiency. Currently, most mainstream fiber optic conversion devices on the market use straight-through optical paths, relying solely on lenses to compensate for mode field differences. Single-lens optical paths have insufficient aberration correction capabilities and limited loss optimization space, restricting their use in high-power scenarios. Furthermore, the axial dimension of the straight-through optical path is long, resulting in large device size, which makes it difficult to meet the development needs of miniaturization and high-density integration of equipment.

[0004] Therefore, designing a single-mode hollow fiber converter with low loss, high coupling stability, adaptability to high-power transmission, and miniaturization is of great importance to those skilled in the art. Summary of the Invention

[0005] This invention provides a single-mode hollow fiber converter with low loss, high coupling stability, adaptability to high-power transmission, and miniaturization, to solve the problems of high optical loss and difficulty in meeting the miniaturization requirements of existing technologies.

[0006] This invention discloses a single-mode hollow fiber converter, comprising: a dual-fiber pigtail, a lens assembly, and a reflector. The lens assembly is disposed between the dual-fiber pigtail and the reflector. The dual-fiber pigtail has an independent first channel and a second channel. The first channel contains a hollow fiber, and a coreless fiber is fused to the end of the hollow fiber near the lens assembly. The second channel contains a single-mode fiber, and a beam-expanding region is provided at the end of the single-mode fiber near the lens assembly. The equivalent mode field diameter of the beam-expanding region is larger than the mode field diameter of the single-mode fiber itself. An optical signal is incident on the lens assembly via either the hollow fiber or the single-mode fiber. After beam collimation and aberration correction by the lens assembly, the signal is incident on the reflector. After reflection and refraction by the reflector, the signal passes through the lens assembly again and is coupled into the other of the hollow fiber or the single-mode fiber via the lens assembly.

[0007] Optionally, the lens assembly includes a short-focal-length lens and a long-focal-length lens, with the short-focal-length lens disposed on the side closer to the dual-fiber pigtail and the long-focal-length lens disposed on the side closer to the reflector.

[0008] Optionally, the beam-expanding region is a radially expanded section integrally formed at one end of the single-mode optical fiber near the lens assembly.

[0009] Optionally, the cladding diameter of the coreless optical fiber is the same as that of the hollow optical fiber.

[0010] Optionally, it further includes a first sleeve, which is sleeved outside the lens assembly and the dual-fiber pigtail to define the relative position of the lens assembly and the dual-fiber pigtail.

[0011] Optionally, it further includes a second sleeve, which is fitted over the first sleeve and the reflector to define the relative position of the first sleeve and the reflector.

[0012] Optionally, the two ends of the reflector are respectively attached and fixed to the inner walls of the two sides of the end of the second sleeve.

[0013] Optionally, the first sleeve and the second sleeve are fixed together with glue.

[0014] Optionally, the dual-fiber tail is interference-fitted with the first sleeve, and the lens assembly is fixed to the fixing sleeve with glue.

[0015] Optionally, the beam expansion region may employ molten beam expansion or electrode discharge beam expansion.

[0016] The beneficial effects of the single-mode hollow fiber converter provided in this embodiment of the invention are as follows: This invention abandons the traditional scheme of directly splicing hollow fiber and single-mode fiber, and uses a spatial optical path to complete the optical signal interaction between the two fibers, fundamentally avoiding the high coupling loss problem caused by direct splicing due to severe mode field mismatch between the two fibers; the coreless fiber spliced ​​near the end of the hollow fiber close to the lens assembly can, on the one hand, perform mode field shaping on the output beam of the hollow fiber, adjust the output spot, and reduce the mode field difference with the output beam of the single-mode fiber; on the other hand, it can seal the hollow cavity of the hollow fiber, effectively preventing impurities such as glue and dust during the assembly process from entering the hollow fiber, avoiding contamination and damage to the hollow channel, and significantly improving the device's adaptability to high-power optical signal transmission conditions; The beam-expanding region at the end of the single-mode fiber amplifies the output mode field of the single-mode fiber, further reducing the mode field mismatch between the two fiber beams and reducing energy loss in subsequent optical coupling stages. The lens assembly performs collimation and aberration correction on the incident beam, eliminating spherical aberration and astigmatism during optical path transmission, further optimizing beam quality and reducing optical energy loss. The reflector reflects and folds back the beam after it has been shaped by the lens assembly, achieving optical path folding. Without shortening the effective coupling optical path or sacrificing coupling performance, it reduces the overall axial length of the device, improves the device's integration, and facilitates assembly and use in confined spaces. The overall structure enables bidirectional optical signal transmission, featuring low coupling loss, strong anti-pollution capability, and a compact structure, adapting to the miniaturization development needs. Attached Figure Description

[0017] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. In the accompanying drawings:

[0018] Figure 1 This is a schematic diagram of the structure of hollow optical fiber and single-mode optical fiber in the embodiments of the present invention; Figure 2 This is a schematic diagram of the structure of the single-mode hollow fiber converter in this embodiment of the invention. Figure 1 ; Figure 3 This is a schematic diagram of the structure of the single-mode hollow fiber converter in this embodiment of the invention. Figure 2 .

[0019] The labels for the attached figures are as follows: 1. Twin-fiber pigtail; 2. Lens assembly; 3. Reflector; 4. First sleeve; 5. Second sleeve; 11. Hollow fiber; 12. Single-mode fiber; 21. Short focal length lens; 22. Long focal length lens; 111. Coreless fiber; 121. Beam expansion area. Detailed Implementation

[0020] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0021] like Figures 1 to 3 As shown, the present invention provides a specific embodiment of a single-mode hollow fiber converter.

[0022] A single-mode hollow fiber converter, reference Figure 1 and Figure 2 The single-mode hollow fiber converter includes a dual-fiber pigtail 1, a lens assembly 2, and a reflector 3. The lens assembly 2 is disposed between the dual-fiber pigtail 1 and the reflector 3. The dual-fiber pigtail 1 has an independent first channel and a second channel. The first channel contains a hollow fiber 11, and a coreless fiber 111 is fused to the end of the hollow fiber 11 near the lens assembly 2. The second channel contains a single-mode fiber 12, and a beam expansion region 121 is provided at the end of the single-mode fiber 12 near the lens assembly 2. The equivalent mode field diameter of the beam expansion region 121 is larger than the mode field diameter of the single-mode fiber 12 itself.

[0023] For details, please refer to Figure 1 and Figure 2 The single-mode hollow fiber converter consists of three core optical components arranged along the optical axis: a dual-fiber pigtail 1, a lens assembly 2, and a reflector 3. The lens assembly 2 is positioned between the dual-fiber pigtail 1 and the reflector 3. The fiber output end face of the dual-fiber pigtail 1 faces one side of the lens assembly 2, and the other side of the lens assembly 2 faces the reflection plane of the reflector 3. The centers of the three components are aligned with the same principal optical axis.

[0024] The dual-fiber pigtail 1 is arranged at the front end of the entire optical path, located on the side of the lens assembly 2 away from the reflector 3. The internal structure of the dual-fiber pigtail 1 is divided into two independent and non-connected channels, namely the first channel and the second channel. The first channel is equipped with a hollow fiber 11, and the second channel is equipped with a single-mode fiber 12. The end faces of the hollow fiber 11 and the single-mode fiber 12 facing the lens assembly 2 are coplanar and flush.

[0025] A coreless fiber 111 is fused to the end of the hollow fiber 11 facing the lens assembly 2. The coreless fiber 111 serves as the entry and exit channel for external optical signals of the hollow fiber 11, covering the hollow inner cavity opening on the side of the hollow fiber 11 facing the lens assembly 2. On the one hand, the coreless fiber 111 can block colloids and dust from entering the inner cavity during the assembly and dispensing process of the coreless fiber, making it suitable for high-power optical transmission scenarios. On the other hand, the coreless fiber 111 can perform mode field shaping on the beam emitted from the hollow fiber 11, adjust the spot size of the output beam of the hollow fiber 11, reduce the mode field difference with the single-mode beam, and reduce coupling loss from the source.

[0026] Furthermore, the end of the single-mode fiber 12 facing the lens assembly 2 is integrally formed with a beam expansion region 121. The beam expansion region 121 is a solid structure formed by radial expansion of the fiber body. The equivalent mode field diameter of the beam expansion region 121 is larger than the mode field diameter of the middle section of the single-mode fiber 12. The output mode field of the single-mode fiber 12 is amplified by the end beam expansion region 121 to match the spot size of the hollow fiber 11 after being shaped by the coreless fiber 111, thereby reducing the degree of mode field mismatch between the two beams and reducing subsequent optical coupling loss.

[0027] The dual-fiber pigtail 1 carries two optical fibers, hollow fiber 11 and single-mode fiber 12, serving as a relay carrier for optical signal communication between hollow fiber 11 and single-mode fiber 12. After the optical signal is shaped into a mode field by either hollow fiber 11 or single-mode fiber 12 and emitted, it is incident on lens assembly 2. The beam is collimated and aberration corrected by lens assembly 2 and then transmitted to mirror 3. It is then reflected and refracted by mirror 3. The refracted beam passes through lens assembly 2 again and is converged and coupled by lens assembly 2 before entering the other of hollow fiber 11 or single-mode fiber 12 to complete the output. Optical signal transmission between hollow fiber 11 and single-mode fiber 12 is achieved by relying on the spatial optical path, replacing the existing direct fusion splicing method of single-mode fiber 12 and hollow fiber 11, and avoiding the high coupling loss caused by mode field mismatch in direct fusion splicing.

[0028] Lens assembly 2 is located between the dual-fiber pigtail 1 and the reflector 3, and is the core component for optical path correction. Lens assembly 2 includes a short focal length lens 21 and a long focal length lens 22. The short focal length lens 21 is located on the side closer to the dual-fiber pigtail 1, and the long focal length lens 22 is located on the side closer to the reflector 3. The short focal length lens 21 and the long focal length lens 22 are coaxially coupled to form an aberration-correcting optical combination, which is used to receive the diverging beam emitted from either the hollow fiber 11 or the single-mode fiber 12, and to complete the beam collimation and aberration correction. The processed beam is then transmitted to the reflector 3. When the beam is reflected back by the reflector 3 and passes through the long focal length lens 22 and the short focal length lens 21 again, the long focal length lens 22 and the short focal length lens 21 can converge the reflected beam, so that the beam can be accurately coupled to the other of the hollow fiber 11 or the single-mode fiber 12.

[0029] The reflector 3 is located at the end of the lens assembly 2 away from the dual-fiber pigtail 1. The reflecting surface is perpendicular to the main optical axis of the lens assembly 2, and the mirror surface is facing the end face of the telephoto lens 22. It is used to receive the light beam output by the lens assembly 2 and reflect the light beam back, thereby folding the overall optical path and reducing the axial length of the device.

[0030] The optical signal transmitted from inside the hollow fiber 11 can be shaped by the coreless fiber 111 at one end of the hollow fiber 11 and emitted outward, and then incident on the lens assembly 2. After entering the lens assembly 2, the beam collimation and aberration correction are completed. The corrected beam continues to propagate forward and is incident on the reflector 3. After the beam contacts the reflector 3, it is reflected and returns along the original path. The returned beam passes through the lens assembly 2 again along the original path. The lens assembly 2 converges the returned beam and couples it to the single-mode fiber 12, thus completing the optical signal transmission from the hollow fiber 11 to the single-mode fiber 12.

[0031] The optical signal transmitted from inside the single-mode fiber 12 can be amplified in the mode field by the beam expansion region 121 at one end of the single-mode fiber 12 and then emitted outward and incident on the lens assembly 2. After the beam enters the lens assembly 2, the beam collimation and aberration correction are completed. The corrected beam continues to propagate forward and is incident on the reflector 3. After the beam contacts the reflector 3, it is reflected and returns along the original path. The returned beam passes through the lens assembly 2 again along the original path. The lens assembly 2 performs convergence processing on the returned beam and couples the beam into the hollow fiber 11, finally completing the optical signal transmission from the single-mode fiber 12 to the hollow fiber 11.

[0032] In one embodiment, the beam expansion region 121 is a radially expanded section integrally formed at the end of the single-mode fiber 12 near the lens assembly 2, and is expanded by fusion beam expansion or electrode discharge beam expansion. During processing, a high temperature is locally applied to the end of the single-mode fiber 12 facing the lens assembly 2, and the fiber cladding and core are melted and softened by the heat effect. The fiber end expands radially outward, and after cooling and shaping, a radially expanded solid beam expansion region 121 is formed. The beam expansion region 121 formed by processing is a continuous integral structure of the single-mode fiber 12 body and the single-mode fiber 12 body, without additional fusion splices, which can avoid additional losses and reflection problems caused by splices. The equivalent mode field diameter of the beam expansion region 121 is larger than the mode field diameter of the single-mode fiber 12 body. When the optical signal transmitted inside the single-mode fiber 12 propagates to the position of the beam expansion region 121, the mode field is broadened outward, realizing beam mode field amplification, thereby reducing the mode field difference between the beam and the beam after the hollow fiber 11 is shaped by the coreless fiber 111, thereby reducing the optical energy loss in the subsequent spatial optical path coupling process.

[0033] Among them, the process controllability of melt beam expansion and electrode discharge beam expansion is good, which can stably control the expansion diameter and length of the beam expansion region 121, facilitate precise control of the mode field size, reduce processing costs, and facilitate mass production of devices.

[0034] In one embodiment, the cladding diameter of the coreless optical fiber 111 is the same as that of the hollow optical fiber 11; the coreless optical fiber 111 and the hollow optical fiber 11 are fused together and fixed to the end face of the lens assembly 2, and the outer diameter of their claddings is consistent. After fusion, the outer circle of the cladding can achieve a flush transition without any radial steps.

[0035] On the one hand, matching cladding diameters can improve the bonding quality of the fusion interface, reduce deformation and bubbles at the fusion point, and reduce additional optical loss at the fusion point. On the other hand, consistent outer diameters facilitate fusion processing and positioning, allowing for direct alignment and clamping in fiber optic fusion splicing equipment, reducing assembly difficulty. Simultaneously, the coreless fiber 111 can cover the hollow inner cavity opening on the side of the hollow fiber 11 facing the lens assembly 2, preventing impurities such as glue and dust from intruding into the hollow channel of the hollow fiber 11, meeting the requirements for high-power optical transmission. After the optical signal is output from the hollow fiber 11, it enters the coreless fiber 111 for propagation. The coreless fiber 111 performs mode field shaping on the beam, adjusting the size of the output beam spot and reducing the mode field difference between the beam and the beam output from the expansion region 121 of the single-mode fiber 12, which helps reduce coupling loss in the subsequent spatial optical path. The same cladding diameter can also avoid edge diffraction caused by mismatched outer diameters, further improving the beam output quality.

[0036] In one embodiment, reference Figures 1 to 3 The single-mode hollow fiber optic converter also includes a first sleeve 4, which is sleeved on the outside of the lens assembly 2 and the dual-fiber pigtail 1 to fix the relative position of the lens assembly 2 and the dual-fiber pigtail 1.

[0037] Specifically, refer to Figures 1 to 3 The first sleeve 4 is a hollow cylindrical component, and a part of the dual-fiber pigtail 1 and the lens assembly 2 are housed together inside the cavity of the first sleeve 4. During the assembly process, the inner wall of the first sleeve 4 is used to achieve radial positioning, ensuring the coaxiality and axial spacing between the optical fiber output end face of the dual-fiber pigtail 1 and the lens assembly 2, and preventing radial offset or axial movement between the two. By integrating the dual-fiber pigtail 1 and the lens assembly 2 into a sub-assembly through the sleeve, the coupling alignment and adhesive curing of the two can be completed in advance, and then the whole assembly can be assembled with the reflector 3. This reduces the difficulty of the whole assembly, reduces the optical alignment error caused by the assembly process, improves the consistency of the optical path in mass production of the device, suppresses the positional offset of the lens assembly 2 and the dual-fiber pigtail 1 caused by vibration and temperature changes, and ensures the stable coupling loss performance of the device.

[0038] In one embodiment, reference Figures 1 to 3The single-mode hollow fiber optic converter also includes a second sleeve 5, which is sleeved on the outside of the first sleeve 4 and the reflector 3 to fix the relative position of the first sleeve 4 and the reflector 3. The second sleeve 5 is a hollow cylindrical structure. The first sleeve 4, together with the dual-fiber pigtail 1 and the lens assembly 2 assembled inside it, is housed in the inner cavity of the second sleeve 5. The reflector 3 is installed inside the second sleeve 5 at the end away from the first sleeve 4.

[0039] The inner wall of the second sleeve 5 forms a radial limit on the first sleeve 4, and at the same time provides positioning support for the reflector 3, thereby ensuring the coaxiality and axial working distance between the lens assembly 2 and the reflector 3, and preventing radial misalignment and axial movement between the first sleeve 4 and the reflector 3. During assembly, the dual-fiber tail 1 and the lens assembly 2 can be pre-aligned and cured inside the first sleeve 4 to form a pre-assembled sub-component. Then, the pre-assembled sub-component is installed into the second sleeve 5, and the reflector 3 is aligned and fixed. This structure does not require complex adjustment tooling, which can reduce the difficulty of overall assembly, effectively resist the component position displacement caused by vibration and temperature changes, stabilize the incident attitude of the beam emitted from the lens assembly 2 to the reflector 3, ensure the accuracy of the beam reflection path, and facilitate the consistency of device coupling performance under mass production conditions.

[0040] The two ends of the reflector 3 are respectively attached and fixed to the inner walls of the two sides of the end of the second sleeve 5. The reflector 3 and the second sleeve 5 can be assembled and fixed by interference fit or by adhesive bonding. The first sleeve 4 and the second sleeve 5 are fixed by adhesive bonding. The dual-fiber tail 1 is positioned by interference fit with the first sleeve 4. The lens assembly 2 is fixed by adhesive bonding with the first sleeve 4.

[0041] By employing the aforementioned multiple assembly and fitting methods, reliable positioning between components can be achieved. When the reflector 3 is clamped and fixed by the squeezing force of the inner wall at the end of the second sleeve 5 through an interference fit, the risk of adhesive volatiles contaminating the optical reflective surface of the reflector 3 can be reduced. Using adhesive bonding provides a larger assembly tolerance and facilitates compensation for component processing tolerances. The first sleeve 4 and the second sleeve 5 are bonded together by adhesive, which can fix the first sleeve 4 sub-assembly, pre-installed with the dual-fiber pigtail 1 and lens assembly 2, as a whole inside the second sleeve 5, locking the axial and radial alignment of the first sleeve 4 and the reflector 3. Position; the dual-fiber pigtail 1 and the first sleeve 4 are interference-fitted, which can ensure the radial position accuracy of the dual-fiber pigtail 1, limit the radial wobble of the dual-fiber pigtail 1, and reduce the risk of glue overflow to the optical fiber output end face during the dispensing process; the lens assembly 2 and the first sleeve 4 are glued together, which can be applied and cured after the optical path is aligned, to compensate for the processing tolerance of the lens assembly 2 and ensure the coaxiality of the lens assembly 2 and the dual-fiber pigtail 1; the combination of multiple fixing methods can not only ensure the alignment accuracy between optical components, but also adapt to batch assembly processes, improve the device's resistance to vibration and temperature changes, and maintain the long-term stability of device coupling loss.

[0042] It should be understood that the above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit them. Those skilled in the art can modify the technical solutions described in the above embodiments, or make equivalent substitutions for some of the technical features; and all such modifications and substitutions should fall within the protection scope of the appended claims of the present invention.

Claims

1. A single-mode hollow fiber converter, characterized in that, include: The system comprises a dual-fiber pigtail, a lens assembly, and a reflector. The lens assembly is disposed between the dual-fiber pigtail and the reflector. The dual-fiber pigtail has an independent first channel and a second channel. The first channel contains a hollow fiber, and a coreless fiber is fused to the end of the hollow fiber near the lens assembly. The second channel contains a single-mode fiber, and a beam-expanding region is provided at the end of the single-mode fiber near the lens assembly. The equivalent mode field diameter of the beam-expanding region is larger than the mode field diameter of the single-mode fiber itself. An optical signal is incident on the lens assembly via either the hollow fiber or the single-mode fiber. After beam collimation and aberration correction by the lens assembly, the signal is incident on the reflector. After reflection and refraction by the reflector, the signal passes through the lens assembly again and is coupled into the other of the hollow fiber or the single-mode fiber via the lens assembly.

2. The single-mode hollow fiber converter according to claim 1, characterized in that, The lens assembly includes a short-focal-length lens and a long-focal-length lens, with the short-focal-length lens positioned on the side closer to the dual-fiber pigtail and the long-focal-length lens positioned on the side closer to the reflector.

3. The single-mode hollow fiber converter according to claim 1, characterized in that, The expanded beam region is a radially expanded section integrally formed at one end of the single-mode optical fiber near the lens assembly.

4. The single-mode hollow fiber converter according to claim 1, characterized in that, The cladding diameter of the coreless optical fiber is the same as that of the hollow optical fiber.

5. The single-mode hollow fiber converter according to claim 1, characterized in that, It also includes a first sleeve, which is sleeved on the outside of the lens assembly and the dual-fiber pigtail, and is used to define the relative position of the lens assembly and the dual-fiber pigtail.

6. The single-mode hollow fiber converter according to claim 5, characterized in that, It also includes a second sleeve, which is fitted over the first sleeve and the reflector to define the relative position of the first sleeve and the reflector.

7. The single-mode hollow fiber converter according to claim 6, characterized in that, The two ends of the reflector are respectively attached and fixed to the inner walls of the two sides of the end of the second sleeve.

8. The single-mode hollow fiber converter according to claim 6, characterized in that, The first sleeve and the second sleeve are fixed together with glue.

9. The single-mode hollow fiber converter according to claim 5, characterized in that, The dual-fiber tail is interference-fitted with the first sleeve, and the lens assembly is fixed to the fixing sleeve with glue.

10. The single-mode hollow fiber converter according to claim 1, characterized in that, The beam expansion region employs either molten beam expansion or electrode discharge beam expansion.

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