Optical fiber fusion splicing protection tube and fusion-spliced optical fiber

Abstract

An optical fiber fusion splicing protection tube (10), comprising a heat-shrink tube (11), a heat-fusible tube (12), and a supporting tube (13). The heat-fusible tube (12) is sleeved on the outer periphery of the supporting tube (13), the heat-shrink tube (11) is sleeved on the outer periphery of the heat-fusible tube (12), and the supporting tube (13) is provided with several liquid injection through holes (131). Compared with an optical fiber fusion splice protection tube in the existing technology, the supporting tube (13) in the optical fiber fusion splicing protection tube (10) provides a dedicated space for an optical fiber, and the dedicated space only allows flowing liquid substances to enter, which can protect against damage from any direction within the full 360-degree circumference, thereby providing more reliable and more symmetrical support and protection performance. In addition, when the heat-shrink tube (11) shrinks upon heating, the heat-shrink tube wraps only around the exterior of the supporting tube (13) without directly transmitting pressure to the optical fiber, thereby preventing the optical fiber from bending or breaking. Compared with the solutions using thinner support rods and flat strips in the existing technology, the optical fiber is protected by the distributed supporting tube (13) on the outer periphery of the optical fiber, resulting in a smaller size after fusion splicing.

Description

A fiber optic fusion splice protection tube and a fusion splice fiber Technical Field

[0001] This invention relates to the field of optical fiber communication technology, specifically to an optical fiber fusion splice protection tube and an optical fiber. Background Technology

[0002] With the rapid development of communication technology, the reliability and high-speed transmission capability of optical fiber communication have made it occupy a core position in the modern communication field.

[0003] Fiber optic communication relies on fiber optic interconnections, which can be categorized into two types: active connections and fixed connections. Active connections primarily rely on fiber optic connectors for mating. Fixed connections, on the other hand, create a permanent splice between two fibers. Currently, the most commonly used fixed connection method in fiber optic communication is fiber optic fusion splicing.

[0004] Fiber optic fusion splicing requires stripping the protective layer of the optical fiber before splicing. After splicing, the protective layer is removed from the spliced ​​area, leaving only the fragile glass fiber exposed, making it highly susceptible to breakage from external influences. Therefore, fiber optic fusion splice protection tubing is essential. Currently available protection methods for single-core and multi-core fiber fusion splices are as follows.

[0005] As shown in Figure 1(a), the existing single-core fiber optic fusion splice protection tube includes: an inner sleeve A12, an outer sleeve A13, and a support A11, which is a thin support rod, disposed between the inner and outer sleeves. The outer sleeve is a heat-shrink tubing, and the inner sleeve is a heat-fusion tubing. At a certain temperature, the inner sleeve melts, and under the external force of the outer sleeve's thermal shrinkage, it wraps around the fused fiber. At this time, the thin support rod embedded in the melted inner sleeve provides support, preventing the fusion splice from bending under stress and breaking.

[0006] However, such single-core fiber optic splice protection tubes have the following problems:

[0007] 1) Fiber optic cables do not have dedicated space.

[0008] Although the thin support rod is isolated from the optical fiber by the inner sleeve before the inner sleeve melts, the outer sleeve contracts due to heat after the inner sleeve melts to form a molten material. This forces the molten material to flow, and during this flow, the thin support rod may come into contact with the optical fiber, causing the fiber to bend or even break the splice on the fiber.

[0009] 2) Asymmetrical support structure

[0010] In a single-core fiber optic fusion splice protection tube, the support consists of only a single thin support rod, located on one side of the fiber. When the outer tube contracts due to heat, the fiber at the center experiences uneven force, which can easily cause the fiber inside the protection tube to move without direction, resulting in bending and arching. This bending and arching can create shear stress at the fusion splice point, potentially leading to splice breakage.

[0011] 3) Insufficient protection of optical fibers by the support structure

[0012] The support is just a single support rod, not a rigid shell, which makes it unable to withstand collisions and impacts on the optical fiber from all directions, resulting in insufficient protection.

[0013] 4) Large volume after installing protective pipe

[0014] After the single-core fiber fusion splice protection tube is installed, the support rod is set on one side of the fiber, which greatly increases the size and affects the use of the fusion splice fiber in confined environments.

[0015] As shown in Figure 1(b), the existing multi-core fiber optic splice protection tube includes: an outer sleeve A13, an inner sleeve A12, and supports A11. The two supports A11 are respectively positioned above and below the fiber optic cable. These supports are flat strips, and the multi-core fiber optic cable is arranged in a ribbon shape. The outer sleeve is a heat-shrink tubing, and the inner sleeve is a heat-fusion tubing. At a certain temperature, the inner sleeve melts, and under the external force of the outer sleeve's thermal shrinkage, it wraps around the spliced ​​fiber optic cable. The flat strips positioned above and below the fiber optic cable provide support and protection, preventing the splice from breaking due to external forces.

[0016] The flat plates of the multi-core fiber optic splice protection tube are symmetrically arranged, which reduces the problem of the fiber easily bending and arching during the melting process of the inner sleeve. However, the following problems still exist:

[0017] 1) Glass optical fibers are bent or collide with each other.

[0018] As shown in Figure 2(a), the coating layer of the ribbon fiber A17 is stripped off, exposing the glass fiber A15. There is a fusion splice A16 on the glass fiber A15. The protective tube A14 is sleeved on the outside of the glass fiber A15 and the head of the ribbon fiber A17.

[0019] When the inner sheath melts to form a molten material, the outer sheath contracts due to heat, forcing the molten material to flow towards the center, as shown in Figure 2(b). Multiple glass optical fibers A15 will converge towards the center under the influence of the molten material. During this convergence process, the outer optical fibers undergo severe bending, resulting in microbending loss or even breakage of the splice A16. At the same time, collisions between optical fibers are inevitable, and the splice A16 on the optical fibers may also break as a result.

[0020] 2) Multi-core optical fibers do not have dedicated space.

[0021] Since the upper and lower flat strips are not isolated from the multi-core optical fiber, the freely positioned upper and lower flat strips can still easily come into contact with the optical fiber during the flow of the fusion material, causing the optical fiber to bend or even break the fusion splice on the optical fiber.

[0022] 3) The flat sheet does not adequately protect the optical fiber.

[0023] Although the flat strip can cover the top and bottom of the fiber optic strip, it is still unable to withstand impacts from the side.

[0024] 4) Large volume after installing protective pipe

[0025] To ensure sufficient strength, the flat fiber is typically designed as a solid arch. After installing the multi-core fiber optic splice protection tube, the originally flat fiber will essentially become cylindrical, significantly increasing its volume.

[0026] There is an urgent need for a welding protection sleeve that can solve the above problems. Summary of the Invention

[0027] This invention provides an optical fiber fusion splice protection tube to solve the problems of existing fusion splice protection sleeves that extrude optical fibers, have large dimensions, and provide insufficient protection for optical fibers.

[0028] In a first aspect, the present invention provides an optical fiber splice protection tube, which includes a heat shrink tube, a heat fusion tube, and a support tube. The heat fusion tube is sleeved on the outer periphery of the support tube, the heat shrink tube is sleeved on the outer periphery of the heat fusion tube, and the support tube has a plurality of liquid injection through holes.

[0029] Furthermore, the injection port can be circular, triangular, prismatic, or polygonal.

[0030] Furthermore, the support tube has an upper flat portion and a lower flat portion, and the injection through hole is only provided on the upper flat portion and the lower flat portion and / or near the upper flat portion and the lower flat portion.

[0031] Furthermore, the support tube is a metal tube.

[0032] Furthermore, the support tube is made of rolled metal sheet.

[0033] Furthermore, the heat-fusion tube is bonded and fixed together with the heat-shrink tube and the support tube.

[0034] Secondly, the present invention provides a fusion splicing optical fiber, comprising an optical fiber with fusion splices, the fusion splicing optical fiber further comprising a support tube, a hot-melt material, and a fastening material, the support tube having a plurality of liquid injection holes, the support tube being fitted around the outer periphery of the optical fiber, the hot-melt material being formed by the hot-melt tube being melted and flowing to fill it, at least filling the interior of the support tube and wrapping the optical fiber, the fastening material being formed by the heat-shrinkable tube being shrunk by heat, the fastening material wrapping around the hot-melt material and / or the outer periphery of the support tube.

[0035] Furthermore, the injection port can be circular, triangular, prismatic, or polygonal.

[0036] Furthermore, the support tube is a metal tube.

[0037] Furthermore, the support tube is made of rolled metal sheet.

[0038] Beneficial effects

[0039] Compared to existing fiber optic splice protection tubes, the support tube in the fiber optic splice protection tube of this invention acts like a protective cage, set on the outer periphery of the fiber, providing the fiber with a dedicated space that only allows flowing liquid substances to enter. The protective cage can protect against damage from any angle within the 360-degree circumference, providing more reliable and symmetrical support and protection performance.

[0040] Furthermore, the injection holes on the support tube facilitate the melting process. After the heat-shrinkable tube melts, the heat-shrinkable material flows evenly into the support tube under the pressure generated by the thermal shrinkage of the heat-shrinkable tube. This ensures uniform stress on the optical fiber within the support tube and prevents severe bending of the optical fiber due to irregular flow of the heat-shrinkable material. Simultaneously, as the heat-shrinkable tube shrinks under heat, it wraps around the outside of the support tube, slowing down the shrinkage. This slows the flow of the heat-shrinkable material, reducing its impact on the optical fiber and lowering the possibility of severe bending and breakage.

[0041] Finally, compared to the existing technology that uses thinner support rods and flat sheets, using distributed support tubes around the fiber to protect the fiber results in a smaller size after splicing. Attached Figure Description

[0042] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the description of the embodiments of the present invention will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0043] Figure 1 is a schematic diagram of the structure of single-core fiber fusion splice protection tube and multi-core fiber fusion splice protection tube in the prior art;

[0044] Figure 2 shows the state of the multi-core optical fiber after the multi-core optical fiber splice protection tube is melted and formed in the prior art.

[0045] Figure 3 is a three-dimensional structural diagram of the support tube of the single-core optical fiber fusion splice protection tube in Example 1;

[0046] Figure 4 is a three-dimensional structural diagram of the single-core optical fiber fusion splice protection tube in Example 1;

[0047] Figure 5 is a schematic diagram of the end face of the single-core fiber fusion splice protection tube in Example 1;

[0048] Figure 6 is a schematic cross-sectional view of the single-core optical fiber after fusion splicing in Example 1;

[0049] Figure 7 is a schematic diagram of the support tube structure of another single-core optical fiber fusion splice protection tube in Example 2;

[0050] Figure 8 is a three-dimensional structural diagram of the support tube in the multi-core optical fiber fusion splice protection tube in Example 3;

[0051] Figure 9 is a three-dimensional structural diagram of the multi-core optical fiber fusion splice protection tube in Example 3;

[0052] Figure 10 is a schematic diagram of the end face of the multi-core optical fiber fusion splice protection tube in Example 3;

[0053] Figure 11 is a schematic cross-sectional view of the multi-core optical fiber spliced ​​in Example 3;

[0054] Figure 12 is a schematic diagram of the three-dimensional structure of the support tube of another multi-core optical fiber fusion splice protection tube in Example 3.

[0055] Explanation of reference numerals in the attached figures:

[0056] A11, Support; A12, Inner sleeve; A13, Outer sleeve; A14, Protective tube; A15, Glass optical fiber; A16, Fusion splice; A17, Ribbon optical fiber;

[0057] 10. Fiber optic splice protection tube; 11. Heat shrink tubing; 12. Heat fusion tube; 13. Support tube; 131. Liquid injection through hole;

[0058] 20. Fusion splicing of optical fiber; 21. Optical fiber; 22. Hot melt material; 23. Fastening material. Detailed Implementation

[0059] To make the technical problems solved, technical solutions, and beneficial effects of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0060] In the description of this invention, it should be understood that the terms "longitudinal," "radial," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicating orientation or positional relationships, are based on the orientation or positional relationships shown in the accompanying drawings and are only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the invention. In the description of this invention, unless otherwise stated, "a plurality of" means two or more.

[0061] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0062] The fiber optic splice protection tube and the spliced ​​fiber in this invention will be described below.

[0063] It should be noted that "heat shrink tubing" in the following description refers to tubing that can shrink when heated, while "heat melt tubing" refers to tubing that can melt when heated.

[0064] Example 1

[0065] In a first aspect, this embodiment provides an optical fiber splicing protection tube for splicing a single-core tight-buffered optical fiber with a diameter of 0.9 mm. The single-core tight-buffered optical fiber with a diameter of 0.9 mm contains a 0.25 mm optical fiber and an outer plastic protective layer.

[0066] As shown in Figures 3-5, the fiber optic splice protection tube 10 includes a heat-shrink tubing 11, a heat-fusion tubing 12, and a support tube 13. The heat-fusion tubing 12 is sleeved around the support tube 13, and the heat-shrink tubing 11 is sleeved around the heat-fusion tubing 12. The support tube 13 has several liquid injection holes 131, through which the optical fiber to be protected can pass. In this embodiment, the support tube is a circular tube.

[0067] When using the fiber optic fusion splice protection tube, it is fitted onto the outside of the fused fiber. The splice area of ​​the fused fiber is placed inside the protection tube, and then the fused fiber with the protection tube is placed in the heater of the fusion splicer. The heater generates a high-temperature environment of 70-150°C, melting the heat shrink tubing inside the fiber optic fusion splice protection tube. Under the pressure of the heat shrink tubing shrinking due to heat, the melt flows from the injection port into the support tube. This completes the fusion splicing of the optical fiber.

[0068] As shown in Figure 6, the fusion splice optical fiber 20 in this embodiment includes an optical fiber 21 with a fusion splice point. The fusion splice optical fiber 20 also includes a support tube 13, a hot melt material 22, and a fastening material 23. The support tube 13 has several liquid injection holes 131 and is fitted around the outer periphery of the optical fiber 21. The hot melt material 22 is formed by the hot melt tube 12 being heated and melted to fill the tube. It fills at least inside the support tube 13 and wraps around the optical fiber 21. The fastening material 23 is formed by the heat shrink tube 11 being heated and shrunk. The fastening material 23 wraps around the hot melt material 22 and / or the outer periphery of the support tube 13.

[0069] Compared to existing fiber optic splice protection tubes, the support tube in the fiber optic splice protection tube of this invention acts like a protective cage, set on the outer periphery of the fiber, providing the fiber with a dedicated space that only allows flowing liquid substances to enter. The protective cage can protect against damage from any angle within the 360-degree circumference, providing more reliable and symmetrical support and protection performance.

[0070] Furthermore, the injection holes on the support tube facilitate the uniform flow of liquid into the support tube after the heat-shrinkable tubing melts, under the pressure generated by the thermal shrinkage of the heat-shrinkable tubing. This ensures uniform stress on the optical fiber within the support tube, preventing severe bending of the fiber due to irregular flow of the heat-shrinkable material. Simultaneously, as the heat-shrinkable tubing shrinks under heat, it wraps around the outside of the support tube, slowing down the shrinkage process. This further slows the flow of the heat-shrinkable material, reducing its impact on the optical fiber and lowering the possibility of severe bending and breakage.

[0071] In this embodiment, the outer diameter of the fiber optic fusion splice protection tube is 2.1 mm. After fusion splicing onto the fiber, the outer diameter is slightly reduced to 2.05 mm. Compared to the 3.8 mm diameter of the thin support rod solution, the fiber optic fusion splice protection tube in this embodiment, compared to the thinner support rod and flat sheet solutions in the prior art, uses distributed support tubes on the outer periphery of the fiber to protect the fiber, resulting in a smaller size after fusion splicing.

[0072] In this embodiment, the injection holes are all circular with uniform dimensions. Of course, the injection holes can also be other shapes, such as triangles, quadrilaterals, or other polygons, etc.

[0073] In addition, forming liquid injection through holes on small-sized support tubes is a relatively difficult process to facilitate the mass production of fiber optic splice protection tubes.

[0074] The R&D team tried various precision machining solutions and finally found several feasible options, such as using precision injection molding to form a plastic support tube, or precision stamping to form a liquid injection through hole on a metal extrusion capillary tube, or first forming a liquid injection through hole on a metal sheet and then rolling it into a tube.

[0075] After numerous experiments and comparisons, it was determined that metal support tubes made from rolled sheet metal are the best choice, considering both cost and ease of processing.

[0076] In one specific embodiment, the heat-fusion tube 12 is bonded and fixed to the heat-shrink tube 11 and the support tube 13. The advantage of this is that only a slight heating of the heat-fusion tube is needed to use its melting function to fix the heat-shrink tube and the support tube, thus avoiding the problem of parts being lost due to the lack of any constraint between the three tubes.

[0077] Example 2

[0078] Example 2 improves upon Example 1 by modifying the shape of the injection through hole to allow the hot melt tube to flow into and fully fill the support tube after melting.

[0079] Both this embodiment and Embodiment 1 involve protecting 0.9mm diameter optical fibers after fiber fusion splicing, and the similarities will not be repeated here.

[0080] In this embodiment, the liquid injection through hole 131 on the support tube 13 is prismatic in shape, as shown in Figure 7. The manufacturing process of the support tube 13 is to first form the liquid injection through hole on the metal substrate by chemical etching, and then roll the metal substrate to form a circular support tube.

[0081] Researchers discovered that the shape and distribution of the injection holes have a significant impact on the inflow of hot-melt material after melting. Through comparative experiments on the melting and inflow effects of hot-melt tubes with the same number and distribution of circular and rhomboid injection holes, the results show that the rhomboid injection holes provide a significantly better filling effect than the circular ones. Analysis of the melting process revealed that, for the same area, rhomboid injection holes occupy a larger axial dimension in the support tube compared to circular ones. This results in a smaller distance between two adjacent rhomboid injection holes, making it easier for the hot-melt material to fill into a single unit.

[0082] Example 3

[0083] This embodiment provides an optical fiber splice protection tube for protecting a 12-core multi-core optical fiber, which contains an array of 12 0.25mm optical fibers with a width of 3.0mm.

[0084] As shown in Figures 8-10, the fiber optic splice protection tube 10 includes a heat-shrink tubing 11, a heat-fusion tubing 12, and a support tube 13. The heat-fusion tubing 12 is fitted around the support tube 13, and the heat-shrink tubing 11 is fitted around the heat-fusion tubing 12. The support tube 13 has several liquid injection holes 131, through which the optical fiber to be protected can pass. Because this embodiment requires protection of a multi-core fiber array, the support tube is shaped into an oval tube.

[0085] Of course, to ensure symmetrical protection of the ribbon-shaped multi-core fiber array, the support tube is designed with a symmetrical shape. Depending on the specific circumstances, the cross-section of the support tube can be not only waist-shaped, but also rectangular, prismatic, or other shapes.

[0086] The method of use is the same as in Example 1. The fiber optic fusion splice protection tube is fitted over the outside of the fused fiber. The splice area of ​​the fiber is placed inside the protection tube, and then the fiber with the protection tube in place is placed in the heater of the fusion splicer. The heater generates a high-temperature environment of 70-150°C, causing the heat-shrink tubing in the fiber optic fusion splice protection tube to melt. Under the pressure of the heat-shrink tubing shrinking due to heat, the melt flows from the injection hole into the support tube. This results in a fully fused fiber.

[0087] As shown in Figure 11, the fusion splice optical fiber 20 in this embodiment includes an optical fiber 21 with a fusion splice point. The fusion splice optical fiber 20 also includes a support tube 13, a hot melt material 22, and a fastening material 23. The support tube 13 has several liquid injection holes 131 and is fitted around the outer periphery of the optical fiber 21. The hot melt material 22 is formed by the hot melt tube 12 being heated and melted to fill the tube. It fills at least inside the support tube 13 and wraps around the optical fiber 21. The fastening material 23 is formed by the heat shrink tube 11 being heated and shrunk. The fastening material 23 wraps around the hot melt material and / or the outer periphery of the support tube.

[0088] Compared to existing fiber optic splice protection tubes, the support tube in the fiber optic splice protection tube of this invention acts like a protective cage, providing a dedicated space for the optical fiber. This dedicated space only allows flowing liquid substances to enter, and the protective cage can protect against damage from any direction within the 360-degree circumference, providing more reliable and symmetrical support and protection performance.

[0089] In this embodiment, after the fiber optic fusion splice protection tube is fused onto the fiber, the splice remains flat, with a length of approximately 5.0 mm in the longest direction. Compared to the dual-flat-plate solution where the splice is a cylinder with a diameter of 5.8 mm, the fiber optic fusion splice protection tube in this embodiment uses distributed support tubes around the fiber to protect it, resulting in a smaller size after fusion, compared to the thinner support rods and flat plates used in the prior art.

[0090] In one specific embodiment, the support tube is shown in FIG12. The support tube has an upper flat portion and a lower flat portion, and the liquid injection through hole 131 is only provided on the upper flat portion and the lower flat portion.

[0091] The reason for this design is that researchers found that if liquid injection holes are provided on the upper flat part, lower flat part, and left and right sides of the relatively flat waist-shaped support tube, and it is used to protect the fusion spliced ​​optical fiber, the pressure of the molten hot melt material flowing into the left and right sides is relatively large. This causes the optical fibers located on both sides of the multi-core optical fiber to bend towards the middle.

[0092] After the injection holes on the left and right sides of the support tube are removed, the hot melt material flows into the support tube only from the upper and lower flat parts. This prevents the hot melt material from squeezing the optical fiber from both sides, thus eliminating the possibility of the optical fiber bending severely inward and breaking.

[0093] In addition, providing liquid injection holes 131 near the upper and lower flat portions can also alleviate the bending of the optical fibers on both sides towards the middle in a multi-core optical fiber to some extent.

[0094] The above-described embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention, and should all be included within the protection scope of the present invention.

Claims

1. A fusion splice protection tube, characterized by, It includes a heat shrink tubing, a heat fusion tubing, and a support tube. The heat fusion tubing is sleeved around the outer periphery of the support tube, and the heat shrink tubing is sleeved around the outer periphery of the heat fusion tubing. The support tube has several injection holes.

2. The optical fiber fusion splice protector of claim 1, wherein, The injection port can be circular, triangular, prismatic, or polygonal.

3. The optical fiber fusion splice protector of claim 2, wherein, The support tube has an upper flat portion and a lower flat portion, and the injection through hole is only provided on the upper flat portion and the lower flat portion and / or near the upper flat portion and the lower flat portion.

4. The optical fiber fusion splice protector of claim 1, wherein, The support tube is a metal tube.

5. The optical fiber fusion splice protector of claim 4, wherein, The support tube is made of rolled metal sheet.

6. The optical fiber fusion splice protector of claim 1, wherein, The heat-fusion tube is bonded and fixed together with the heat-shrink tube and the support tube.

7. A fusion spliced optical fiber comprising an optical fiber, the optical fiber having a fusion splice thereon, wherein, It also includes a support tube, a hot melt material, and a fastening material. The support tube has several liquid injection holes and is fitted around the outer periphery of the optical fiber. The hot melt material is formed by the hot melt tube being heated and melted, and it fills at least the interior of the support tube and wraps the optical fiber. The fastening material is formed by the heat shrink tube being heated and shrunk, and it wraps around the hot melt material and / or the outer periphery of the support tube.

8. The fused optical fiber according to claim 7, wherein, The injection port can be circular, triangular, prismatic, or polygonal.

9. The fused optical fiber according to claim 7, wherein, The support tube is a metal tube.

10. The fusion spliced optical fiber as claimed in claim 9, wherein, The support tube is made of rolled metal sheet.

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