Hollow core fiber optical cable and method of manufacturing the same

Abstract

The application belongs to the field of optical fiber cables, and specifically discloses a hollow-core optical fiber cable and a preparation method thereof. The hollow-core optical fiber cable comprises a central reinforcing member, at least one optical unit and an outer sheath. The at least one optical unit is twistedly arranged at the periphery of the central reinforcing member. The optical unit comprises a loose tube and at least one hollow-core optical fiber arranged in the loose tube. The loose tube has a structure of at least two layers, and the friction coefficient of the inner surface of the innermost layer is lower than that of the outer surface of the outermost layer. The outer sheath wraps the central reinforcing member and the optical unit. Through the application, the problem of micro-bending loss of the hollow-core optical fiber cable can be effectively solved.

Description

Technical Field

[0001] This application belongs to the field of optical fiber and cable, and more specifically, relates to a hollow optical fiber and cable and its manufacturing method. Background Technology

[0002] Hollow-core fiber is a groundbreaking optical waveguide technology. Its core characteristic is that optical signals are primarily transmitted within an air-filled core, rather than the solid glass core of traditional optical fibers. This unique structure allows it to operate independently of traditional total internal reflection. Instead, it utilizes the precise microstructures of the cladding to confine light within an air channel, including photonic bandgap fibers utilizing the photonic bandgap effect and anti-resonant microstructure fibers employing the principle of anti-resonant reflection. Thanks to the faster propagation speed and lower loss of light in air, hollow-core fiber can significantly reduce signal transmission delay by approximately 30% and minimize signal attenuation. Therefore, it is considered a key technological direction for solving bottleneck problems in future high-speed communications and high-power laser transmission.

[0003] During cabling, hollow optical fibers are primarily subjected to two types of bending stress: macrobending and microbending. Macrobending is mainly caused by loose tube stranding and excess fiber length; microbending is mainly caused by fiber adhesion and stacking due to friction, static electricity, high and low temperature changes causing polymer material shrinkage, or localized stress. Due to the complex internal structure of hollow optical fibers and their non-symmetrical circular cross-section, they experience higher stress and are more sensitive to microbending than ordinary optical fibers. Currently, to address microbending loss, the inner diameter of the tube is typically increased to reduce the probability of fiber adhesion and stacking. However, the size of current hollow optical fibers is already larger than that of conventional optical fibers, and further increasing the tube size is extremely detrimental to the laying of hollow optical cables. Summary of the Invention

[0004] In view of the deficiencies or improvement needs of the existing technology, this application provides a hollow optical fiber cable and its manufacturing method, aiming to solve the problem of micro-bending loss in hollow optical fiber cables.

[0005] Firstly, the hollow-core optical fiber cable provided in this application specifically includes:

[0006] Center reinforcement;

[0007] At least one optical unit is stranded around the periphery of the central reinforcing member. The optical unit includes a loose tube and at least one hollow optical fiber disposed within the loose tube. The loose tube has at least two layers, and the coefficient of friction of its innermost inner surface is lower than the coefficient of friction of its outermost outer surface.

[0008] An outer sheath covers the central reinforcement and the at least one optical unit.

[0009] As a further preferred embodiment, the outer surface of the hollow optical fiber is subjected to plasma treatment and grafted with fluorinated carbon or silicon groups.

[0010] As a further preferred embodiment, the outermost layer of the loose sleeve is extruded from a mixture of polybutylene terephthalate and inorganic additives, wherein the mass ratio of polybutylene terephthalate to inorganic additives is (90-95):(1-10).

[0011] As a further preferred embodiment, the innermost layer of the loose sleeve is extruded from a polybutylene terephthalate modified material. The polybutylene terephthalate modified material is a mixture of polybutylene terephthalate, polytetrafluoroethylene, silicone, and an antistatic agent. The mass ratio of polybutylene terephthalate, polytetrafluoroethylene, silicone, and antistatic agent is (80-95):(1-5):(1-5):(1-3).

[0012] As a further preferred embodiment, the outermost surface of the loose sleeve is subjected to surface roughening treatment.

[0013] As a further preferred embodiment, the outer surface of the central reinforcement is subjected to surface roughening treatment.

[0014] As a further preferred embodiment, the friction coefficient of the innermost inner surface is 0.05-0.15, and the friction coefficient of the outermost outer surface is 0.4-0.8.

[0015] As a further preferred embodiment, the coefficient of friction of the outer surface of the central reinforcing member is 0.4-0.8.

[0016] As a further preferred embodiment, the thickness of the innermost layer of the loose sleeve is 0.05-0.3 mm, and the thickness of the outermost layer is 0.05-0.3 mm.

[0017] As a further preferred embodiment, the outer sheath is provided with a reinforcing structure evenly distributed along the inner circumferential direction.

[0018] Secondly, this application provides a method for manufacturing the hollow-core optical fiber cable, comprising the following steps:

[0019] S1. A loose tube is extruded and formed on the outside of at least one hollow optical fiber to form an optical unit, wherein the loose tube has at least two layers and the friction coefficient of the innermost inner surface is lower than the friction coefficient of the outermost outer surface.

[0020] S2. The optical unit is twisted around the periphery of the central reinforcing member;

[0021] S3. An outer sheath is extruded around the optical unit.

[0022] As a further preferred embodiment, before step S1, the outer surface of the hollow optical fiber is first subjected to plasma treatment to graft fluorinated carbon or silicon groups to reduce the friction coefficient of the outer surface of the hollow optical fiber.

[0023] As a further preferred option, before step S2, the outermost surface of the loose sleeve is subjected to surface roughening treatment.

[0024] As a further preferred embodiment, before step S2, the outer surface of the central reinforcement is subjected to surface roughening treatment.

[0025] In summary, compared with the prior art, the technical solutions conceived in this application have the following main technical advantages:

[0026] 1. This application designs a loose tube with at least two layers of varying friction coefficients (i.e., the inner layer has a low friction coefficient and the outer layer has a high friction coefficient) to reduce fiber adhesion and accumulation on the inner wall of the loose tube through the low friction coefficient inner layer, thereby reducing microbending caused by fiber adhesion and accumulation in the loose tube, and reducing microbending caused by temperature changes through the high friction coefficient outer layer.

[0027] 2. At the same time, this application effectively reduces the surface friction coefficient of the optical fiber by grafting the surface of the optical fiber. Combined with the loose tube inner layer with a low friction coefficient, the microbending caused by the optical fiber adhering to the wall and accumulating inside the tube is further reduced.

[0028] 3. Secondly, this application uses a loose tube outer layer with a high coefficient of friction to cooperate with a central reinforcement and a surface roughening treatment of the loose tube outer layer, which further increases the friction between the loose tube outer layer and the surface of the central reinforcement. When the ambient temperature changes, the shrinkage tension of the loose tube is resisted by the central reinforcement, reducing the state change of the hollow fiber in the loose tube when the ambient temperature changes, and reducing the microbending of the fiber under high and low temperatures.

[0029] 4. In addition, the present application provides reinforcement members evenly distributed around the outer sheath, which can effectively reduce the cable core shrinkage caused by the shrinkage of the outer sheath and further reduce the micro-bending of the optical fiber. Attached Figure Description

[0030] Figure 1 This is a schematic diagram of the structure of a hollow optical fiber cable provided in an embodiment of this application;

[0031] Figure 2 This is a schematic diagram of the two-layer loose tube structure provided in the embodiments of this application;

[0032] Figure 3 This is a schematic diagram of another hollow optical fiber cable provided in the embodiments of this application.

[0033] In all the accompanying drawings, the same reference numerals are used to denote the same elements or structures, wherein:

[0034] 1-Central reinforcement, 2-Hollow fiber, 3-Outer sheath, 4-Loose tube, 5-Reinforcing structure, 6-Filling rope, 41-Inner layer, 42-Outer layer. Detailed Implementation

[0035] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0036] like Figure 1 As shown, this application provides a hollow-core optical fiber cable, comprising a central reinforcing member 1, at least one optical unit, and an outer sheath 3. The optical unit is stranded around the central reinforcing member 1, and the outer sheath 3 encloses the central reinforcing member 1 and the optical unit. The central reinforcing member 1, located at the center of the optical cable, serves as the core mechanical support component, primarily responsible for bearing tensile stress, maintaining structural integrity, and resisting lateral pressure and impact. Regarding bearing tensile stress, during cable laying (e.g., aerial, duct pulling, direct burial) and use, it resists external tension, preventing fiber breakage due to tension or excessive stress, thus ensuring stable optical transmission performance. Regarding maintaining structural integrity, as the central axis of the cable core stranding, it ensures the loose tubes, fiber bundles, and other components are evenly stranded, maintaining the overall roundness of the optical cable and preventing deformation and flattening. Regarding resisting lateral pressure and impact, its rigidity disperses external squeezing, collision, and other mechanical forces, reducing direct damage to the internal optical fibers and improving the cable's resistance to lateral pressure and impact.

[0037] Specifically, the central reinforcing member 1 in this application can be a metal reinforcing member, such as stainless steel wire or galvanized steel wire. Of course, it can also be a non-metallic reinforcing member, such as glass fiber reinforced plastic (FRP), aramid fiber reinforced plastic (KFRP), carbon fiber reinforced plastic (CFRP), etc. The appropriate reinforcing member can be selected according to actual needs.

[0038] Furthermore, the optical unit includes a loose tube 4 and at least one hollow optical fiber 2 disposed within the loose tube 4. The loose tube 4 has at least two layers, i.e., a multi-layer structure with two or more layers. The friction coefficient of the innermost surface of the loose tube 4 is lower than that of the outermost surface. This reduces microbending caused by wall adhesion and accumulation by the inner layer with a low friction coefficient working in conjunction with the optical fiber, and reduces microbending caused by shrinkage by the outer layer with a high friction coefficient working in conjunction with the central reinforcement. In other words, the loose tube 4 has a non-uniform friction coefficient (variable friction coefficient) structure, meaning that the friction coefficient of the entire loose tube 4 is not the same, with the inner layer having a lower coefficient than the outer layer. This allows the same loose tube 4 to have different friction coefficients, reducing microbending caused by wall adhesion and accumulation of the optical fiber within the loose tube, and also reducing microbending of the optical fiber caused by shrinkage under high and low temperature environments.

[0039] In a preferred embodiment, the friction coefficient of the innermost inner surface of the loose tube 4 is 0.05-0.15, and the friction coefficient of the outermost outer surface of the loose tube 4 is 0.4-0.8. This minimizes the friction between the inner layer and the optical fiber, reducing micro-bending caused by the fiber's adhesion to the wall, while maximizing the friction between the outer layer and the reinforcing member, so that the shrinkage tension of the tube is resisted by friction, reducing the shrinkage of the tube at high and low temperatures. In another preferred embodiment, the friction coefficient of the innermost inner surface of the loose tube 4 is 0.6 lower than that of the outermost outer surface. Specifically, the friction coefficient can be measured using existing detection techniques, and this application is not limited to this.

[0040] In a preferred embodiment, the outer surface of the hollow optical fiber 2 is subjected to plasma treatment to graft fluorocarbon-containing or silicon-containing groups onto the outer surface of the hollow optical fiber 2, thereby reducing the friction coefficient of the optical fiber surface. The combination of the low-friction optical fiber and the low-friction inner layer of the loose tube further reduces the microbending caused by the fiber adhering to and accumulating within the loose tube. Specifically, an active gas composed of nitrogen, oxygen, and fluorocarbon unsaturated hydrocarbons is introduced into a vacuum chamber. The plasma is then activated, and the introduction of the active gas is stopped. A reactive gas is then introduced into the vacuum chamber. Under plasma conditions, a deposition and copolymerization reaction occurs on the substrate surface (i.e., the outer surface of the hollow optical fiber 2), forming a surface layer containing fluorocarbon or silicon groups through chemical bonding. The specific grafting process is existing technology and will not be described in detail here.

[0041] Furthermore, the innermost and outermost layers of the loose sleeve 4 are made of the same main material. The innermost layer uses a modified version of the main material, while the outermost layer uses the main material combined with inorganic additives. This ensures the preparation of an innermost layer with a low coefficient of friction and an outermost layer with a rough surface (high coefficient of friction). Specifically, the inorganic additives can be silicon dioxide or aluminum oxide.

[0042] In a preferred embodiment, the outermost layer of the loose sleeve 4 is extruded from a mixture of PBT (polybutylene terephthalate, also known as tetramethyl terephthalate) and inorganic additives to increase the coefficient of friction of the outer layer of the loose sleeve. Preferably, the mass ratio of PBT to inorganic additives is (90-95):(1-10). This ratio can effectively improve the coefficient of friction of the material, have little impact on the physical processing and mechanical properties of the main material, and form a rough surface. Specifically, the above raw materials can be blended according to the above ratio, stirred at high speed, and then extruded and granulated by twin screw extruder to obtain a mixed material for subsequent preparation of the outer layer of the loose sleeve. The specific preparation process is prior art and will not be described in detail in this application.

[0043] In a preferred embodiment, the innermost layer of the loose tube 4 is extruded using a PBT-modified material to prepare an inner layer with a low coefficient of friction. Preferably, the PBT-modified material is a mixture of PBT, PTFE (polytetrafluoroethylene), silicone, and an antistatic agent. Preferably, the mass ratio of PBT, PTFE, silicone, and antistatic agent is (80-95):(1-5):(1-5):(1-3), where PTFE and silicone act as lubricants, providing synergistic lubrication, and the antistatic agent reduces adhesion and buildup caused by electrostatic adsorption between the optical fiber and the inner surface of the loose tube. Through the combination of the above-mentioned components, the friction between the inner surface of the tube and the optical fiber is significantly reduced. Specifically, the PBT-modified material can be obtained by mixing the above-mentioned raw materials according to the above ratio, high-speed stirring, and then extruding and granulating using a twin-screw extruder for subsequent preparation of the inner layer of the loose tube. The specific preparation process is existing technology and will not be elaborated in this application.

[0044] In addition, the other layers of the loose sleeve 4 can be any one of PBT, PC (polycarbonate), PP (polypropylene), and PA (polyamide), and this application does not limit them.

[0045] In a preferred embodiment, the innermost layer of the loose sleeve 4 has a thickness of 0.05-0.3 mm, and the outermost layer has a thickness of 0.05-0.3 mm, thus balancing processing performance and mechanical properties. The thicknesses of the inner and outer layers can be the same or different, and this application does not limit this. In a preferred embodiment, the loose sleeve is preferably a two-layer structure to reduce micro-bending while lowering manufacturing costs, such as... Figure 2 As shown, the loose tube 4 with a two-layer structure includes an inner layer 41 and an outer layer 42.

[0046] In a preferred embodiment, the outermost surface of the loose tube 4 is roughened to further improve the friction coefficient of the outer layer of the loose tube. In a preferred embodiment, the outer surface of the central reinforcement 1 is roughened to improve the friction coefficient of the central reinforcement surface (to 0.4-0.8). The combination of the high friction coefficient of the loose tube outer layer and the high friction coefficient of the central reinforcement increases the friction between the surfaces of the loose tube and the central reinforcement, effectively resisting the shrinkage tension caused by changes in ambient temperature and reducing fiber micro-bending at high and low temperatures.

[0047] Specifically, the surface roughening treatment of the loose sleeve 4 and the central reinforcing member 1 can be achieved through physical-mechanical methods (such as sandblasting, mechanical grinding, laser etching, etc.), chemical methods (acid etching, alkaline etching, etc.), plasma methods (plasma etching, etc.). Further, the acid etching treatment involves preparing the required etching solution (e.g., concentrated sulfuric acid, potassium dichromate, and deionized water in the required proportions), etching at 60-80°C for 10-60 seconds, neutralizing with a reducing agent such as sodium bisulfite, and then thoroughly washing and drying. Existing methods can be used for the specific surface roughening treatment; this application is not limited to any particular method, as long as it can create a rough surface.

[0048] In a preferred embodiment, a reinforcing structure 5 is uniformly provided circumferentially inside the outer sheath 3 to effectively reduce the cable core shrinkage caused by the shrinkage of the outer sheath, and further reduce fiber micro-bending. Specifically, the reinforcing structure 5 can be FRP, steel wire, etc.

[0049] Of course, the hollow fiber optic cable also has a water-blocking structure. Specifically, the water-blocking structure is filled between the innermost layer of the hollow fiber 2 and the loose tube 4, between the outermost layer of the loose tube 4 and the central reinforcing member 1, and between the outermost layer of the loose tube 4 and the outer sheath 3. The water-blocking structure can be grease, water-blocking yarn, etc. The design location and specific type of the water-blocking structure are existing technologies and are not limited in this application.

[0050] In another embodiment, this application also provides a method for preparing the aforementioned hollow-core optical fiber cable, specifically including the following steps:

[0051] S1. A loose tube 4 with at least two layers, in which the friction coefficient of the innermost outer surface is lower than that of the outermost outer surface, is extruded on the outside of at least one hollow optical fiber 2 to form an optical unit. Each layer of the loose tube 4 is extruded simultaneously. Specifically, the hollow optical fiber 2 is released through a pay-off frame and enters an extruder. A double-layer or multi-layer extrusion die is used to extrude PBT modified material in the inner layer and unmodified PBT material (i.e., a mixture of PBT and inorganic additives) in the outer layer. The corresponding materials are extruded in other layers. After cooling in a cooling water tank, a loose tube 4 with at least two layers, in which the friction coefficient of the innermost outer surface is lower than that of the outermost outer surface, is prepared. The whole consisting of the hollow optical fiber 2 and the loose tube 4 is an optical unit.

[0052] S2. Twisting the optical unit around the center reinforcing member 1 and binding it to form the cable core;

[0053] Specifically, the optical unit can be individually twisted around the periphery of the central reinforcing member 1, or it can be twisted together with the filling rope 6 around the periphery of the central reinforcing member 1, such as... Figure 1 As shown, multiple optical units are twisted together around the central reinforcing member 1; as Figure 3As shown, the optical unit is twisted with the filling rope 6 around the central reinforcing member 1. The filling rope 6 can be made of plastics such as polyethylene (PE) and polypropylene (PP). This application does not limit the material. The number of optical units and the way they are matched with the filling rope 6 can be designed according to actual needs. This application does not limit the material.

[0054] S3. An outer sheath 3 is extruded and formed around the optical unit (i.e., outside the cable core).

[0055] In a preferred embodiment, before preparing the loose tube (i.e., before step S1), the outer surface of the hollow fiber 2 is first subjected to plasma treatment to graft fluorocarbon or silicon groups, thereby reducing the friction coefficient of the hollow fiber surface. Specifically, the plasma treatment can be performed after the hollow fiber 2 is colored.

[0056] In a preferred embodiment, before step S2 (i.e., before stranding), the outermost surface of the loose sleeve 4 is roughened to further increase the friction between the loose sleeve 4 and the central reinforcing member 1. In a preferred embodiment, before step S2 (i.e., before stranding), the outer surface of the central reinforcing member 1 is also roughened to improve its coefficient of friction.

[0057] In summary, the hollow-core optical fiber cable designed in this application, by designing a loose tube inner layer with a low coefficient of friction and a loose tube outer layer with a high coefficient of friction, and by having the low coefficient of friction inner layer cooperate with the low coefficient of friction optical fiber surface, and the high coefficient of friction outer layer cooperate with the high coefficient of friction central reinforcement, can effectively reduce the microbending caused by the fiber adhering to the wall and accumulating inside the loose tube, and resist the shrinkage tension caused by changes in ambient temperature. This reduces the microbending of the fiber at high and low temperatures, and solves the microbending problem without increasing the size of the loose tube. In other words, the overall size of the hollow-core optical fiber cable will not increase, which is very beneficial for the subsequent laying of the optical cable.

[0058] This application is applicable to various types of hollow optical fibers, especially anti-resonant hollow optical fibers. Since anti-resonant hollow optical fibers are composed of anti-resonant units, cladding and coating, and the anti-resonant units are composed of multiple sets of resonant rings, their internal structure is more complex than that of solid optical fibers. Therefore, the additional attenuation when the fiber is bent is more significant. The design of this application can effectively reduce its attenuation.

[0059] In addition, this application also provides a hybrid optical cable formed by combining hollow-core optical fiber cable and solid-core optical fiber cable. The hollow-core optical fiber cable can adopt the structure of the hollow-core optical fiber cable described above, and the solid-core optical fiber cable can include at least one solid-core optical fiber unit. The solid-core optical fiber unit includes a loose tube and multiple solid-core optical fibers wrapped in the loose tube. The solid-core optical fibers can be G.652D, G.654E or G.655, etc.

[0060] It should be understood that expressions such as "comprising" and "may include" as used in this application indicate the existence of the disclosed functions, operations, or constituent elements, and do not limit one or more additional functions, operations, and constituent elements. In this application, terms such as "comprising" and / or "having" may be interpreted as indicating a specific characteristic, number, operation, constituent element, component, or combination thereof, but should not be interpreted as excluding the existence or possibility of adding one or more other characteristics, numbers, operations, constituent elements, components, or combinations thereof.

[0061] It should be understood that the terms “center,” “upper,” “lower,” “front,” “rear,” “left,” “right,” “vertical,” “horizontal,” “inner,” “outer,” “clockwise,” “counterclockwise,” “axial,” “radial,” and “circumferential” indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this application 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. Therefore, they should not be construed as limitations on this application.

[0062] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this application, "multiple" means two or more, unless otherwise explicitly specified.

[0063] In this application, unless otherwise expressly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., 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 between two components. Those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances.

[0064] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A hollow core fiber optical cable characterized by, The application relates to a kind of optical cables, comprising: a central strength member (1); at least one optical unit is stranded to the periphery of the central strength member (1), the optical unit comprises a loose tube (4) and at least one hollow core optical fiber (2) arranged in the loose tube (4), the loose tube (4) is at least two layers structure, and the friction coefficient of the inner surface of the innermost layer is lower than the friction coefficient of the outer surface of the outermost layer; and an outer sheath (3) wrapping the central strength member (1) and the at least one optical unit.

2. The hollow-core fiber optic cable of claim 1, wherein, The outer surface of the hollow core optical fiber (2) is plasma treated to graft fluorine-containing or silicon groups.

3. The hollow-core fiber optic cable of claim 1, wherein, The outermost layer of the loose tube (4) is extruded by a mixture of polybutylene terephthalate and inorganic additives, and the mass ratio of polybutylene terephthalate and inorganic additives is (90-95):(1-10).

4. The hollow-core fiber optic cable of claim 1, wherein, The innermost layer of the loose tube (4) is extruded by polybutylene terephthalate modified material, and the polybutylene terephthalate modified material is a mixture of polybutylene terephthalate, polytetrafluoroethylene, silicone and antistatic agent, and the mass ratio of polybutylene terephthalate, polytetrafluoroethylene, silicone and antistatic agent is (80-95):(1-5):(1-5):(1-3).

5. The hollow-core fiber optic cable of claim 1, wherein, The outer surface of the outermost layer of the loose tube (4) is subjected to surface roughening treatment; and / or the outer surface of the central strength member (1) is subjected to surface roughening treatment.

6. The hollow-core fiber optic cable of claim 1, wherein, The friction coefficient of the inner surface of the innermost layer is 0.05-0.15, the friction coefficient of the outer surface of the outermost layer is 0.4-0.8, and / or the friction coefficient of the outer surface of the central strength member (1) is 0.4-0.

8.

7. The hollow-core fiber optic cable of claim 1, wherein, The thickness of the innermost layer of the loose tube (4) is 0.05-0.3 mm, and the thickness of the outermost layer is 0.05-0.3 mm.

8. The hollow-core fiber optic cable of claim 1, wherein, The outer sheath (3) is uniformly provided with a reinforcing structure (5) along the circumference.

9. A method of manufacturing a hollow-core fiber optical cable according to any one of claims 1-8, characterized in that, The application also discloses a kind of optical cable manufacturing method, comprising the following steps: S1, extruding a loose tube (4) on the outside of at least one hollow core optical fiber (2) to form an optical unit, wherein the loose tube (4) is at least two layers structure, and the friction coefficient of the inner surface of the innermost layer is lower than the friction coefficient of the outer surface of the outermost layer; S2, stranding the optical unit to the periphery of the central strength member (1); S3, extruding an outer sheath (3) on the periphery of the optical unit.

10. The production method according to claim 9, wherein Before step S1, the outer surface of the hollow core optical fiber (2) is subjected to plasma treatment to graft fluorine-containing or silicon groups to reduce the friction coefficient of the outer surface of the hollow core optical fiber (2); and / or, before step S2, the outer surface of the outermost layer of the loose tube (4) is subjected to surface roughening treatment; and / or, before step S2, the outer surface of the central strength member (1) is subjected to surface roughening treatment.

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