A bending-resistant hollow optical fiber core sea cable and a preparation method thereof

Abstract

The application discloses a kind of anti-bending hollow optical fiber core sea optical cable and its preparation method, the sea optical cable sequentially includes cable core layer, functional isolation layer, inner sheath, armoring layer and outer sheath from inside to outside;Cable core layer includes at least one anti-resonance hollow optical fiber, anti-resonance hollow optical fiber surface is sequentially provided with hexamethyldisiloxane airtight bottom layer, silane coupling agent bridging layer, conductive antistatic layer, stress buffer layer and mechanical reinforcement layer;Armoring layer includes poly-p-phenylene benzobisoxazole fiber winding inner layer and aramid yarn knitted outer layer, form no-metal double-layer fiber armoring structure.The microbending loss and fatigue damage of the application are inhibited by coating layer anti-resonance hollow optical fiber, combined with no-metal fiber armoring to realize the overall light weight of sea optical cable, and avoid electromagnetic coupling and energy loss between metal armoring layer and power supply conductor, suitable for deep sea high pressure and complex laying environment.

Description

Technical Field

[0001] This application relates to the field of submarine optical cable technology, and in particular to a bending-resistant hollow optical fiber core submarine optical cable and its preparation method. Background Technology

[0002] Submarine optical cables are core infrastructure for transoceanic internet backbones, offshore oil and gas platform communications, and coastal broadband networks. With the stringent requirements for transmission latency from artificial intelligence computing power interconnection and high-frequency financial trading, as well as the continuous growth in bandwidth demand from ultra-high-definition video streaming, traditional solid single-mode fiber optic submarine cables are approaching their nonlinear transmission limits.

[0003] Anti-resonant hollow fiber (AR-HCF), as a novel light guiding structure, has an air core, allowing optical signals to propagate through the air. It features low transmission delay, weak nonlinear effects, and a wide usable spectral range. Among these, double-nested anti-resonant nodeless fiber has achieved transmission loss below 0.2 dB / km in the 1550 nm window, with signal propagation speed approximately 30% higher than traditional solid single-mode fiber and nonlinear effects reduced by about two orders of magnitude. It supports high-order modulation formats and ultra-wide bandwidth transmission, providing a potential transmission medium solution for next-generation transoceanic submarine cable systems.

[0004] However, applying hollow optical fibers to submarine cables still faces numerous technical challenges. The quartz capillary wall thickness of anti-resonant hollow optical fibers is only 0.5~2μm, resulting in extremely low cross-sectional stiffness. Existing submarine cables generally employ loose tubes filled with water-blocking grease combined with steel wire armor structures. Under the influence of bending during installation, ocean current vibrations, and deep-sea high pressure, the thin-walled capillaries are highly susceptible to elliptic deformation due to micro-bending and lateral pressure, leading to a shift in the anti-resonance condition and a sharp increase in additional losses. The micro-bending loss of hollow optical fibers is significantly more sensitive to bending and lateral pressure than that of traditional solid optical fibers, making it difficult for conventional submarine cable structures to meet the service requirements of hollow optical fibers.

[0005] Existing submarine optical cables generally employ a phosphated steel wire central reinforcing core and a double-layer steel wire or steel tape armor structure. While this type of structure provides high tensile strength, it significantly increases the cable's weight and bending stiffness, making it unsuitable for deep-sea laying and floating platform applications. Furthermore, the metal components can generate electromagnetic interference in lightning strike environments or near high-voltage power lines, and are prone to electrochemical corrosion in seawater, shortening the service life of the submarine optical cable.

[0006] Submarine optical cables typically employ high-density polyethylene extrusion technology for secondary coating, with processing temperatures reaching 200-240℃. These high temperatures soften or degrade the UV-cured coating and end-sealing structure of the hollow optical fiber, leading to microcracks or interface debonding, creating gas permeation channels. Traditional water-blocking greases are prone to oxidation and deterioration at high temperatures and cannot actively purify the gas components inside the hollow optical fiber. Once external moisture, carbon dioxide, carbon monoxide, and other gases permeate into the hollow core, they will increase light scattering on the capillary walls, raise absorption losses, and cause chemical corrosion. Existing submarine optical cables lack a multi-level airtight barrier design for the hollow core of the optical fiber, making it difficult to meet the requirement of a transoceanic transmission lifespan of over 25 years.

[0007] Transoceanic submarine optical cables require DC power to supply underwater repeaters and optical amplifiers. Traditional structures mix copper conductors for long-distance power supply with steel wire armor, resulting in a complex cable core structure, increased weight, and the electromagnetic field generated by the metal power supply circuit poses potential crosstalk to the ultra-low delay signals of the hollow optical fiber.

[0008] In summary, existing submarine optical cable technologies mostly focus on expanding the capacity of solid optical fibers or optimizing the metal armoring process. No systematic solution has yet been proposed that can simultaneously address issues such as micro-bending protection of hollow optical fibers, deep-sea high-pressure adaptation, non-metallic load-bearing capacity, long-term airtightness maintenance of hollow fibers, and independent power supply for low-voltage applications. Summary of the Invention

[0009] This application addresses the micro-bending sensitivity of anti-resonant hollow optical fibers in existing submarine optical cables due to the extremely thin walls of the quartz capillaries, as well as the problems of heavy weight and high bending stiffness of traditional steel wire armored structures, which are unfavorable for deep-sea laying, and the susceptibility of metal components to electrochemical corrosion and electromagnetic coupling and energy loss between them and the power supply conductor. It proposes a bend-resistant hollow optical fiber core submarine optical cable and its fabrication method. The cable consists of a hexamethyldisiloxane hermetic underlayer, a silane coupling agent bridging layer, a conductive antistatic layer, a stress buffer layer, and a mechanical reinforcement layer sequentially coated on the outer surface of the anti-resonant hollow optical fiber. These coating layers suppress micro-bending loss and fatigue damage of the fiber. The armor layer employs a metal-free double-layer fiber structure consisting of a poly(p-phenylene benzodioxazole) fiber inner layer and an aramid yarn braided outer layer. This achieves cable lightweighting while avoiding electromagnetic coupling and energy loss between the metal armor layer and the power supply conductor, effectively improving the bend resistance, corrosion resistance, and service life of the submarine optical cable in deep-sea high-pressure and complex laying environments. The technical solution provided in this application is as follows: On the one hand, this application provides a bending-resistant hollow optical fiber core submarine optical cable, which includes, from the inside out, a core layer, a functional isolation layer, an inner sheath, an armor layer and an outer sheath; The cable core layer includes: Center reinforcement; At least one fiber optic sub-cable unit is disposed around the central reinforcement member. Each fiber optic sub-cable unit includes a loose tube and at least one anti-resonant hollow fiber sleeved in the loose tube. The outer surface of the anti-resonant hollow fiber is provided with a coating layer, which, from the inside out, includes a hexamethyldisiloxane hermetic bottom layer, a silane coupling agent bridging layer, a conductive antistatic layer, a stress buffer layer, and a mechanical reinforcement layer. A cable core filler is used to fill the gaps in the cable core layer, and a remote power supply conductor is embedded in the cable core filler. The armor layer comprises an inner layer wound with poly(p-phenylene benzodioxazole) fibers and an outer layer woven with aramid yarn.

[0010] In some specific embodiments, the conductive antistatic layer is made of graphene / carbon nanotube composite conductive coating. The stress buffer layer is made of radiation-cured polyurethane acrylate resin containing nano-silica, and the Young's modulus of the stress buffer layer is 0.75~1.2MPa; The mechanical reinforcement layer is made of radiation-cured polyurethane acrylate resin containing nano-inorganic particles, and the Young's modulus of the mechanical reinforcement layer is 700~1000MPa.

[0011] In some specific embodiments, the central reinforcement is a segmented glass fiber reinforced plastic rod with a segment length of 60~100mm and a gap of 3~5mm between segments, the gap being filled with foamed silicone rubber; the outer periphery of the central reinforcement is covered with a layer of foamed silicone rubber.

[0012] In some specific embodiments, the loose tube is a three-layer co-extruded composite structure, consisting of a barrier layer, a foamed buffer layer, and a weather-resistant protective layer from the inside out. The barrier layer is made of polyamide or ethylene-vinyl alcohol copolymer; The foamed buffer layer is made of closed-cell foamed thermoplastic polyurethane; The weather-resistant protective layer is made of weather-resistant polyethylene or seawater-resistant fluorinated thermoplastic polyurethane. The loose sleeve is also provided with a foamed silicone rubber spiral support, which extends spirally along the axial direction of the loose sleeve.

[0013] In some specific embodiments, the loose tube is filled with a thixotropic composite water-blocking gel, which, by weight percentage, comprises the following components: Matrix material: polyalphaolefin or polyether-modified silicone oil; Thixotropic thickener: fumed silica and polyurea compound, wherein the content of fumed silica is 2-5 wt% and the content of polyurea compound is 1-3 wt%. Adsorbent: molecular sieve powder and alkaline earth metal oxide composite, wherein the average particle size of the molecular sieve powder is 2~5μm and the content is 3~5wt%; the alkaline earth metal oxide composite is a mixture of calcium oxide and magnesium oxide and the content is 2~4wt%.

[0014] In some specific embodiments, the functional isolation layer comprises, from the inside out, a semiconducting water-resistant tape wrapping layer, a barrier membrane longitudinal wrapping layer, and a water-resistant adhesive layer. The longitudinal cladding layer of the barrier film is a co-extruded composite film of polyamide and ethylene-vinyl alcohol copolymer; The water-blocking adhesive layer is disposed between the longitudinal wrapping layer of the barrier membrane and the inner sheath.

[0015] In some specific embodiments, the inner sheath is a low-melting-point metallocene polyethylene longitudinal sheath with a melting point of 95~105℃; the outer sheath is a weather-resistant chlorinated polyethylene or thermoplastic polyurethane longitudinal sheath.

[0016] In some specific embodiments, the outer surface of the outer sheath is provided with a V-shaped stress relief groove along the axial direction. The groove depth is 20% to 30% of the thickness of the outer sheath, the groove width is 1.5 to 2.0 mm, and the groove spacing is 15 to 20 mm. A water-blocking expansion strip is embedded in the V-shaped stress relief groove.

[0017] In some specific embodiments, the cable core filler includes a porous honeycomb foamed polyethylene and thermoplastic polyurethane blend filler strip, the filler strip having a closed-cell rate of not less than 70%, and the filler strip having an arc-shaped fitting surface adapted to the outer surface of the optical fiber sub-cable unit.

[0018] On the other hand, this application also provides a method for preparing a bend-resistant hollow optical fiber core submarine optical cable, comprising the following steps: The optical fiber preform is heated and drawn into fibers. Hexamethyldisiloxane hermetic underlayer, silane coupling agent bridging layer, and conductive antistatic layer are sequentially deposited on the outer surface of the bare optical fiber. Then, stress buffer layer and mechanical reinforcement layer are formed by UV curing. A loose tube is extruded using a three-layer co-extrusion process, and a foamed silicone rubber spiral support is simultaneously embedded into the loose tube. A thixotropic composite water-blocking gel is then injected into the loose tube. The fiber optic sub-cable units are laid around the central reinforcement, and the cable core filler is laid synchronously with the remote power supply conductor. A functional isolation layer is formed on the outside of the cable core after cabling is completed; The inner sheath is longitudinally wrapped and then hot-melt welded using a process called longitudinal wrapping-hot-melt welding. Poly(p-phenylene benzodioxazole) fibers are spirally wound around the inner sheath, and then aramid yarn is woven to form a double-layer fiber armor layer. The outer sheath is longitudinally wrapped and then hot-air melt-welded using a process.

[0019] By adopting the above technical solution, the bending-resistant hollow optical fiber core submarine optical cable and its preparation method provided in this application have the following beneficial effects: 1. This application comprises a coating layer consisting of a hexamethyldisiloxane hermetic underlayer, a silane coupling agent bridging layer, a conductive antistatic layer, a stress buffer layer, and a mechanical reinforcement layer sequentially disposed on the outer surface of an antiresonant hollow optical fiber. Specifically, the hexamethyldisiloxane hermetic underlayer prevents water molecules from penetrating into the quartz capillary wall; the silane coupling agent bridging layer forms covalent bridges between the hermetic underlayer and subsequent coating layers, improving interlayer bonding; the conductive antistatic layer dissipates static charges generated during fiber drawing and cabling, preventing the antiresonant hollow optical fiber from adhering to the inner wall of the loose tube due to electrostatic adsorption, thus avoiding microbending loss; the stress buffer layer absorbs external stress through low-modulus deformation, preventing stress from being directly transmitted to the antiresonant hollow optical fiber; and the mechanical reinforcement layer resists external friction and impact, protecting the internal structure. Through layer-by-layer functional synergy, these coating layers suppress microbending loss and fatigue damage in the antiresonant hollow optical fiber, improving its structural integrity and optical performance stability under complex loads. Meanwhile, the loose tube is filled with a thixotropic composite water-blocking gel. This gel maintains its shape to block water under static conditions, while its viscosity decreases and its fluidity increases under dynamic laying stress. It can adaptively coat the anti-resonant hollow fiber and fill local gaps, avoiding stress concentration. The coating layer and the loose tube gel support work together to suppress micro-bending loss and fatigue damage, ensuring the long-term transmission stability of the anti-resonant hollow fiber under complex loads.

[0020] 2. In this application, the armor layer adopts a metal-free double-layer fiber structure consisting of a poly(p-phenylene benzodioxazole) fiber-wound inner layer and an aramid yarn-woven outer layer. The poly(p-phenylene benzodioxazole) fiber-wound inner layer provides high modulus tensile strength through a spiral arrangement; the aramid yarn-woven outer layer achieves uniform mechanical protection in all directions through its braided structure, enhancing resistance to lateral pressure and impact. This double-layer fiber armor structure achieves cable lightweighting while enabling the submarine optical cable to withstand bidirectional torsional loads. It also fundamentally avoids electromagnetic coupling and energy loss between the metal armor layer and the power supply conductor, as well as the risk of electrochemical corrosion in the seawater environment. This improves the bending resistance, corrosion resistance, and service life of the submarine optical cable in deep-sea high-pressure and complex laying environments. Attached Figure Description

[0021] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0022] Figure 1 A schematic diagram of the cross-sectional structure of the bend-resistant hollow fiber optic submarine cable provided in this application embodiment.

[0023] The following is supplementary explanation of the attached figures: 10-Cable core layer; 11-Central reinforcement; 12-Anti-resonant hollow optical fiber; 13-Loose tube; 14-Cable core filler; 15-Remote power supply conductor; 20-Functional isolation layer; 30-Inner sheath; 40-Armor layer; 50-Outer sheath. Detailed Implementation

[0024] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application.

[0025] The term "an embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of this application. In the description of this application, it should be understood that the terms "upper," "lower," "top," "bottom," etc., indicating orientation or positional relationships based on the orientation or positional relationships shown in the accompanying drawings, are 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, and therefore should not be construed as a limitation of this application. 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 indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. Moreover, the terms "first," "second," etc., are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of this application described herein can be implemented in orders other than those illustrated or described herein.

[0026] When a numerical range is disclosed herein, the range is considered continuous and includes the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Furthermore, when the range refers to an integer, it includes every integer between the minimum and maximum values ​​of the range. Additionally, when multiple ranges are provided to describe a feature or characteristic, the ranges may be combined. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges to which they are included. For example, a specified range from “1 to 10” should be considered to include any and all subranges between the minimum value 1 and the maximum value 10. Exemplary subranges of the range 1 to 10 include, but are not limited to, 1 to 6.1, 3.5 to 7.8, 5.5 to 10, etc.

[0027] like Figure 1 As shown in the figure, this application embodiment provides a bending-resistant hollow optical fiber core submarine optical cable, which includes, from the inside out, a core layer 10, a functional isolation layer 20, an inner sheath 30, an armor layer 40, and an outer sheath 50.

[0028] The core layer 10 includes a central reinforcement 11, at least one optical fiber sub-cable unit, and a core filler 14.

[0029] The central stiffener 11 is located at the center of the core layer 10, providing longitudinal tensile strength and lateral pressure resistance for the submarine optical cable. The central stiffener 11 is a segmented glass fiber reinforced plastic rod, with segments ranging from 60 to 100 mm in length and gaps of 3 to 5 mm between segments, filled with foamed silicone rubber. This segmented structure allows for localized micro-rotations between segments during bending, preventing the continuous rigid core from resisting bending and thus reducing the overall cable's bending stiffness. The outer periphery of the central stiffener 11 is covered with a layer of foamed silicone rubber to buffer radial pressure and protect adjacent fiber optic sub-cable units. Glass fiber reinforced plastic is lightweight, high-strength, corrosion-resistant, and non-magnetic. Compared to traditional phosphated steel wire, it avoids electromagnetic interference and electrochemical corrosion while significantly reducing cable weight.

[0030] At least one fiber optic sub-cable unit is disposed around the central reinforcing member 11. Each fiber optic sub-cable unit includes a loose tube 13 and at least one anti-resonant hollow optical fiber 12 sleeved within the loose tube 13. The loose tube 13 has a three-layer co-extruded composite structure, consisting of a barrier layer, a foamed buffer layer, and a weather-resistant protective layer from the inside out. The barrier layer is made of polydodecyl lactam or ethylene-vinyl alcohol copolymer, with a thickness of 0.10~0.15mm, exhibiting low water vapor permeability and superior barrier properties against gases such as CO2 and CO compared to polyethylene. The foamed buffer layer is made of closed-cell foamed thermoplastic polyurethane, with a thickness of 0.60~0.90mm, a micropore diameter of 20~80μm, a foaming ratio of 2~3 times, and a closed-cell rate of not less than 85%. Under deep-sea high pressure, the closed-cell microporous structure absorbs external water pressure through controllable elastic compression, recovering its original thickness after unloading, thus preventing stress from being directly transmitted to the anti-resonant hollow optical fiber 12. The weather-resistant protective layer is made of weather-resistant polyethylene or seawater-resistant fluorinated thermoplastic polyurethane, with a thickness of 0.20~0.30mm, which can effectively resist seawater erosion and external mechanical damage.

[0031] The loose tube 13 is filled with a thixotropic composite water-blocking gel. By weight percentage, the thixotropic composite water-blocking gel comprises the following components: Matrix material: polyalphaolefin or polyether-modified silicone oil; when polyalphaolefin is used as the matrix, a small amount of polyether-modified silicone oil can be added, preferably 1~3wt%. This polyether-modified silicone oil acts as an antistatic lubricant. The polyether segments are hydrophilic and hygroscopic, forming microscopic conductive channels at the contact interface between the gel and the antiresonant hollow optical fiber 12 and the foamed silicone rubber spiral support to dissipate static charge accumulation and reduce the friction coefficient between the surface of the antiresonant hollow optical fiber 12 and the foamed silicone rubber spiral support. When polyether-modified silicone oil is used as the matrix, it itself has the functions of matrix filling and antistatic lubrication, and no additional antistatic lubricant is required.

[0032] Thixotropic thickener: Fumed silica and polyurea compound, with fumed silica content of 2-5 wt% and polyurea compound content of 1-3 wt%. The polyurea compound can be generated by reacting diisocyanate with amine compounds. In a static state, the silanol groups on the surface of fumed silica and the urea groups of the polyurea compound form a three-dimensional network framework through hydrogen bonding, locking the matrix material within it to form a gel state. During construction and pouring, the hydrogen bond network undergoes reversible breakage under shear force, reducing the system viscosity and increasing fluidity, making it easier to fill voids. After the external force is removed, the hydrogen bond network gradually rebuilds, the system viscosity recovers, and the gel is fixed and does not leak.

[0033] Adsorbent: Molecular sieve powder and alkaline earth metal oxide composite. The molecular sieve powder is preferably 3A / 4A type molecular sieve powder with an average particle size of 2~5μm and a content of 3~5wt%. It selectively captures water molecules and small molecule gases through physical adsorption. The alkaline earth metal oxide composite is a mixture of calcium oxide and magnesium oxide, with a preferred mass ratio of calcium oxide to magnesium oxide of 1:1 and a content of 2~4wt%. It absorbs moisture through chemical reaction and works synergistically with the physical adsorption of the molecular sieve powder to form a long-lasting low-humidity microenvironment inside the tube.

[0034] The volume filling rate of the thixotropic composite water-blocking gel in the loose tube 13 is not less than 95%.

[0035] The thixotropic properties of the composite water-blocking gel enable it to maintain its gel morphology under static conditions to block water penetration. Under dynamic laying conditions and shear stress, its viscosity decreases and its fluidity increases, allowing it to fully spread and fill the micro-irregular gaps caused by the contact between the optical fiber and the support. After the stress is removed, it returns to its gel state and achieves uniform and tight coverage of the anti-resonant hollow optical fiber 12, avoiding stress concentration caused by insufficient or uneven filling, and ensuring the long-term stability and optical performance of the optical fiber under complex service conditions.

[0036] The outer surface of the anti-resonant hollow optical fiber 12 is provided with a coating layer, which includes, from the inside out: Hexamethyldisiloxane gas-tight bottom layer: A dense Si-O-Si network layer formed on the surface of optical fiber by low-pressure plasma polymerization process, with a thickness of 2~3μm; the water vapor permeability coefficient of this layer is reduced by 1~2 orders of magnitude compared with the bare quartz surface, effectively blocking water molecules from penetrating into the quartz capillary wall of the optical fiber.

[0037] Silane coupling agent bridging layer: γ-methacryloyloxypropyltrimethoxysilane (KH-570) coupling agent layer, used to improve the interfacial bonding strength between the hermetic underlayer and the subsequent coating layer.

[0038] Conductive and antistatic layer: The material is graphene / carbon nanotube composite conductive coating with a thickness of 0.5~1μm. It is used to eliminate the micro-bending caused by electrostatic adsorption during the drawing and cabling process, and to prevent the anti-resonant hollow optical fiber 12 from adhering to the inner wall of the loose tube 13 due to electrostatic adsorption.

[0039] Stress buffer layer: The material is radiation-cured polyurethane acrylate resin containing nano-silica, with a Young's modulus of 0.75~1.2MPa and a thickness of 25~35μm. This low-modulus layer absorbs energy through its own deformation when under stress, reducing the stress concentration acting on the anti-resonant hollow optical fiber 12 thin-walled capillary structure and preventing stress from being directly transmitted to the quartz capillary wall.

[0040] Mechanical reinforcement layer: Made of radiation-cured polyurethane acrylate resin containing nano-inorganic particles, with a Young's modulus of 700~1000MPa and a thickness of 30~50μm; used to resist external friction and impact, protecting the internal structure. The stress buffer layer and the mechanical reinforcement layer together form a gradient coating structure that is tough inside and hard outside. The two work together to effectively resist complex loads such as deep-sea high pressure, laying bending and wear.

[0041] This application provides a coating layer on the outer surface of the anti-resonant hollow optical fiber 12. The layers work together to suppress the micro-bending loss and fatigue damage of the optical fiber, and improve its structural integrity and optical performance stability under complex loads.

[0042] The core filler 14 fills the voids within the core layer 10 to maintain the roundness of the core and provide radial support for the fiber optic sub-units. The core filler 14 comprises a porous honeycomb foamed polyethylene and thermoplastic polyurethane blend filler strip. The filler strip has an arc-shaped contact surface adapted to the outer surface of the fiber optic sub-unit to provide uniform radial support and avoid localized stress concentration. A remote power supply conductor 15 is embedded within the core filler 14, used only for low-voltage power supply to the repeater / optical amplifier and not for transmitting high-power electricity externally.

[0043] A functional isolation layer 20 is disposed between the cable core layer 10 and the inner sheath 30 to prevent external moisture and gas from penetrating into the cable core layer 10. The functional isolation layer 20 comprises, from the inside out: Semiconducting resistive water tape wrapping layer: It consists of 1 to 2 layers of semiconducting resistive water tape wrapped in a wrapping manner, with an overlap rate of 20% to 30%. It is used to absorb the trace amounts of water vapor that seep in and to achieve radial water blocking, while also having buffering and antistatic functions.

[0044] The longitudinal cladding layer of the barrier membrane is a co-extruded composite membrane of polyamide and ethylene-vinyl alcohol copolymer with an overlap width of 3~5mm. It is wrapped longitudinally along the cable core axis, and the overlap edges are hot-melt bonded to effectively prevent gas and water vapor from penetrating into the cable core layer 10.

[0045] Water-blocking adhesive layer: Located between the longitudinal wrapping layer of the barrier membrane and the inner sheath 30, the material is nylon 6 / 66 / 1010 or nylon 6 / 66 / 12 ternary copolymer hot melt adhesive, with a thickness of 0.1~0.2mm. It is used to bond the longitudinal wrapping layer of the barrier membrane and the inner sheath 30, and form a water-blocking sealing ring at the interface to prevent water vapor from penetrating longitudinally along the interlayer interface.

[0046] The inner sheath 30 is a longitudinally wrapped layer of low-melting-point metallocene polyethylene with a melting point of 90~105℃ and a thickness of 0.8~1.0mm, formed by a longitudinal wrapping-hot-melt welding process. Low-melting-point metallocene polyethylene has a low melting processing temperature, enabling lap edge fusion welding at a welding temperature of 120~140℃, thereby avoiding the thermal impact of high temperature on the internal functional isolation layer 20 and the coating layer of the anti-resonant hollow optical fiber 12.

[0047] The armor layer 40 is disposed between the inner sheath 30 and the outer sheath 50, comprising a poly(p-phenylene benzodioxazole) fiber-wound inner layer and an aramid yarn braided outer layer. The poly(p-phenylene benzodioxazole) fiber-wound inner layer is spirally wound at a winding angle of 15°~25°, utilizing the high modulus properties of PBO fibers to provide axial tensile stiffness. The aramid yarn braided outer layer disperses lateral concentrated loads and absorbs impact energy through a circumferential braided structure, enhancing circumferential restraint and impact resistance. The double-layer fiber armor layer 40 features a metal-free design, achieving cable lightweighting while enabling the submarine optical cable to withstand bidirectional torsional loads. It fundamentally avoids electromagnetic coupling and energy loss between the metal armor layer 40 and the power supply conductor, as well as the risk of electrochemical corrosion in the seawater environment, thereby improving the submarine optical cable's bending resistance, corrosion resistance, and service life in deep-sea high-pressure and complex laying environments.

[0048] The outer sheath 50 is a longitudinally wrapped layer of weather-resistant chlorinated polyethylene or thermoplastic polyurethane with a thickness of 1.5~2.0mm; wherein the chlorine content of the weather-resistant chlorinated polyethylene is 25%~35%. It is formed by longitudinal wrapping-hot melt welding process, with a longitudinal wrapping overlap width of 3~5mm. The overlap edge is fused and welded through a hot air channel at 120~130℃, and the overall heating temperature does not exceed 140℃. This low-temperature welding process avoids thermal damage to the internal functional layer and the coating layer of the anti-resonant hollow optical fiber 12.

[0049] The outer surface of the outer sheath 50 is provided with V-shaped stress relief grooves along the axial direction. The depth of the V-shaped stress relief grooves is 20% to 30% of the thickness of the outer sheath 50, the groove width is 1.5 to 2.0 mm, and the groove spacing is 15 to 20 mm. Water-blocking expansion strips are embedded in the V-shaped stress relief grooves. The water-blocking expansion strips are water-swellable rubber strips. After expanding when exposed to water, they fill and block the longitudinal channel of the V-shaped groove, achieving local longitudinal water blocking. The geometric configuration of the V-shaped groove provides stress relief space when the cable is laid in a bending manner. Under normal conditions, the water-blocking expansion strip keeps the groove tightly filled, preventing seawater from forming a longitudinal flow channel in the groove.

[0050] This application also provides a method for preparing a bend-resistant hollow optical fiber core submarine cable.

[0051] The optical fiber preform is heated in a furnace with a power of 50-65 kW, and then cooled and solidified in an 8-m long cooling cylinder to form a bare optical fiber. During the fiber drawing process, a hexamethyldisiloxane hermetic underlayer, a silane coupling agent bridging layer, and a conductive antistatic layer are sequentially deposited on the outer surface of the bare optical fiber. Then, a stress buffer layer and a mechanical reinforcement layer are sequentially formed by UV curing. The hexamethyldisiloxane hermetic underlayer is deposited using a low-pressure plasma polymerization process with a plasma power of 30-50 W, a chamber pressure of 20-50 Pa, a hexamethyldisiloxane flow rate of 10-30 sccm, an argon carrier gas flow rate of 20-50 sccm, and a deposition time of 60-90 s, forming a dense Si-O-Si network layer with a thickness of 2-3 μm, effectively blocking water molecules from penetrating into the quartz capillary wall of the optical fiber. The silane coupling agent bridging layer is formed by immersing the optical fiber in an ethanol solution of γ-methacryloxypropyltrimethoxysilane for 10-20 seconds, followed by drying at 80°C for 5 minutes. The conductive antistatic layer is formed by spraying or dipping a graphene / carbon nanotube composite conductive coating followed by UV pre-curing for 1-2 seconds. This layer is used to eliminate micro-bending caused by electrostatic adsorption during fiber drawing and cabling. The mass ratio of graphene to carbon nanotubes is 3:1 to 5:1, the solid content of the coating is 5-10 wt%, and the coating thickness is 0.5-1 μm.

[0052] The stress-relief coating is prepared according to the following proportions: 50-90 parts by weight of polyurethane oligomer, 5-45 parts by weight of monofunctional monomer, 0-2 parts by weight of polyfunctional monomer, 0.5-15 parts by weight of photoinitiator, and 0.5-2 parts by weight of nano-silica modified with silane coupling agent. The polyurethane oligomer is a reaction product of aliphatic polyester glycol or polyether glycol with hexamethylene diisocyanate and / or isophorone diisocyanate, with a molecular weight of 2000-4000; the monofunctional monomer is selected from isooctyl acrylate or isobornyl acrylate; the polyfunctional monomer is 1,6-hexanediol diacrylate; the photoinitiator is selected from 1-hydroxycyclohexylphenyl ketone or 2-phenylbenzyl-2-dimethylamine-1-(4-morpholinobenzylphenyl)butanone; and the average primary particle size of the nano-silica is 30-70 nm. Nano-silica was pre-treated by ultrasonic dispersion and ball milling. The ultrasonic dispersion power was 200~400W for 30 min, and the ball milling speed was 300 rpm for 2 h. Zirconia balls were used as the grinding media. Polyurethane oligomers, monofunctional monomers and polyfunctional monomers were mixed evenly and heated to 40℃. The pre-treated nano-silica was added and stirred at 1000 rpm for 60 min. After adding a photoinitiator, stirring was continued for 30 min. After filtering through a 1500-mesh filter, the mixture was degassed in a 40℃ oven for 1 day to obtain a homogeneous coating with a viscosity of 4000~5500 mPa·s at 25℃ and a Young's modulus of 0.75~1.2 MPa. The preparation method of the mechanical reinforcement layer coating is the same as that of the stress buffer layer coating. The difference is that polyester diol hard segments with a molecular weight of 1000~2000 are selected, and nano-silica and / or nano-alumina modified by silane coupling agent are added. The total addition amount is 1~5 parts by mass, wherein the average primary particle size of nano-silica is 30~70nm, and the average primary particle size of nano-alumina is 20~50nm. The dispersion process is the same as that of the stress buffer layer coating, and the viscosity is controlled at 6500~7500mPa·s at 25℃. The Young's modulus of the coating film is 700~1000MPa.

[0053] The loose tube 13 is extruded using a three-layer co-extrusion process. The inner layer is made of polydodecyl lactam or ethylene-vinyl alcohol copolymer, with an extrusion temperature of 180~200℃ and a thickness of 0.10~0.15mm. It has a low water vapor permeability and better barrier properties against gases such as CO2 and CO than polyethylene. The middle layer is made of closed-cell foamed thermoplastic polyurethane, with an extrusion temperature of 190~210℃ and a thickness of 0.60~0.90mm. The foamed micropore diameter is 20~80μm, the foaming ratio is 2~3 times, and the closed-cell rate is not less than 85%. This middle layer absorbs external water pressure under deep-sea high pressure through controllable elastic compression of the closed-cell microporous structure. After unloading, it can return to its original thickness, thereby avoiding direct stress transmission to the optical fiber. The outer layer is made of weather-resistant polyethylene or seawater-resistant fluorinated thermoplastic polyurethane, with an extrusion temperature of 170~190℃ and a thickness of 0.20~0.30mm. It is used to resist seawater erosion and external mechanical damage. Simultaneously with the extrusion of the loose tube 13, a foamed silicone rubber spiral support is embedded within the loose tube 13 to support the anti-resonant hollow optical fiber 12 at its center. This maintains a radial gap between the optical fiber and the tube wall, preventing the anti-resonant hollow optical fiber 12 from adhering to the wall and piling up due to friction, electrostatic adsorption, and high / low temperature shrinkage. After extrusion, a thixotropic composite water-blocking gel is injected into the loose tube 13. This gel maintains its shape to block water under static conditions, but its viscosity increases and its fluidity decreases under dynamic laying stress or deep-sea pressure, allowing it to better encapsulate the anti-resonant hollow optical fiber 12 and fill local gaps, thereby preventing stress concentration.

[0054] During cabling, multiple fiber optic sub-cable units are laid around the central reinforcing member 11 in an SZ twisted configuration, with a twist pitch of 100-150mm. Simultaneously, the cable core filler 14 and the remote power supply conductor 15 are laid, with the remote power supply conductor 15 embedded within the cable core filler 14. The remote power supply conductor 15 is a pair of annealed tin-plated copper wires, with a cross-linked polyethylene insulation layer covering the conductor, used to provide DC power to underwater repeaters or optical amplifiers.

[0055] A functional isolation layer 20 is formed outside the cable core after cabling. Specifically, 1 to 2 layers of semi-conductive water-resistant tape are wrapped around the cable core with an overlap rate of 20% to 30%, forming a semi-conductive water-resistant tape wrapping layer; then, a polydodecylamine / ethylene-vinyl alcohol copolymer co-extruded barrier film is longitudinally wrapped around the semi-conductive water-resistant tape wrapping layer with an overlap width of 3 to 5 mm, and fixed by hot-melt bonding to form a barrier film longitudinal wrapping layer; then, a water-blocking adhesive layer with a thickness of 0.1 to 0.2 mm is set outside the barrier film longitudinal wrapping layer to make the layers tightly bonded and form a continuous multi-level radial water-blocking barrier.

[0056] The low-melting-point metallocene polyethylene inner sheath 30 is longitudinally wrapped using a hot air channel at 110~120℃ and then melt-welded. The overlap width is 3~5mm, forming an inner sheath 30 with a thickness of 0.8~1.0mm.

[0057] Poly(p-phenylene benzodioxazole) fiber is spirally wound around the inner sheath 30 at a winding angle of 15°~25° to form the inner layer of poly(p-phenylene benzodioxazole) fiber winding; then, para-aramid yarn is woven to form the outer layer of aramid yarn weaving. This double-layer fiber armor structure achieves cable lightweighting while giving the submarine optical cable bidirectional torsional load resistance. It also fundamentally avoids electromagnetic coupling and energy loss between the metal armor layer and the power supply conductor, as well as the risk of electrochemical corrosion in the seawater environment. This improves the submarine optical cable's bending resistance, corrosion resistance, and service life in deep-sea high-pressure and complex laying environments.

[0058] A longitudinal wrapping-thermal fusion welding process is employed. After longitudinally wrapping a weather-resistant chlorinated polyethylene or thermoplastic polyurethane outer sheath 50, it is fused and welded through a 120-130°C hot air channel, with an overlap width of 3-5mm, forming an outer sheath 50 with a thickness of 1.5-2.0mm. Throughout the entire manufacturing process, the overall heating temperature of the cable core does not exceed 140°C, avoiding thermal damage to the outer surface coating layer and functional isolation layer 20 of the anti-resonant hollow optical fiber 12 caused by traditional high-temperature extrusion above 220°C. After welding, the outer sheath 50 is rolled to form a V-shaped stress relief groove. The groove depth is 20%-30% of the outer sheath 50 thickness, the groove width is 1.5-2.0mm, and the groove spacing is 15-20mm. A water-blocking expansion strip is embedded in the groove and fixed by thermal fusion. Upon contact with water, it expands and can block the longitudinal channel, providing both bending stress relief and longitudinal water blocking functions.

[0059] Unless otherwise specified, all the above layers can be prepared using existing methods in the art, such as extrusion molding, coating, wrapping, and braiding. The specific process can be selected according to the material properties and structural requirements of each layer, and this application does not impose any specific limitations on it. Those skilled in the art, with a full understanding of the above technical solutions and in conjunction with conventional techniques in the art, can realize the preparation of the cable of this application.

Claims

1. A bend-resistant hollow optical fiber core submarine optical cable, characterized in that, From the inside out, it includes the core layer, functional isolation layer, inner sheath, armor layer and outer sheath; The cable core layer includes: Center reinforcement; At least one fiber optic sub-cable unit is disposed around the central reinforcement member. Each fiber optic sub-cable unit includes a loose tube and at least one anti-resonant hollow fiber sleeved in the loose tube. The outer surface of the anti-resonant hollow fiber is provided with a coating layer. The coating layer includes, from the inside out, a hexamethyldisiloxane hermetic bottom layer, a silane coupling agent bridging layer, a conductive antistatic layer, a stress buffer layer, and a mechanical reinforcement layer. A cable core filler is used to fill the gaps in the cable core layer, and a remote power supply conductor is embedded in the cable core filler. The armor layer comprises an inner layer wound with poly(p-phenylene benzodioxazole) fibers and an outer layer woven with aramid yarn.

2. The bend-resistant hollow optical fiber core submarine optical cable according to claim 1, characterized in that, The conductive antistatic layer is made of graphene / carbon nanotube composite conductive coating. The stress buffer layer is made of radiation-cured polyurethane acrylate resin containing nano-silica, and the Young's modulus of the stress buffer layer is 0.75~1.2MPa; The mechanical reinforcement layer is made of radiation-cured polyurethane acrylate resin containing nano-inorganic particles, and the Young's modulus of the mechanical reinforcement layer is 700~1000MPa.

3. The bend-resistant hollow optical fiber core submarine optical cable according to claim 1, characterized in that, The central reinforcing member is a segmented glass fiber reinforced plastic rod with a segment length of 60~100mm and a gap of 3~5mm between segments, the gap being filled with foamed silicone rubber; the outer periphery of the central reinforcing member is covered with a layer of foamed silicone rubber.

4. The bend-resistant hollow optical fiber core submarine optical cable according to claim 1, characterized in that, The loose sleeve has a three-layer co-extruded composite structure, consisting of a barrier layer, a foamed buffer layer, and a weather-resistant protective layer from the inside out. The barrier layer is made of polyamide or ethylene-vinyl alcohol copolymer; The foamed buffer layer is made of closed-cell foamed thermoplastic polyurethane; The weather-resistant protective layer is made of weather-resistant polyethylene or seawater-resistant fluorinated thermoplastic polyurethane. The loose sleeve is also provided with a foamed silicone rubber spiral support, which extends spirally along the axial direction of the loose sleeve.

5. The bend-resistant hollow optical fiber core submarine optical cable according to claim 4, characterized in that, The loose tube is filled with a thixotropic composite water-blocking gel, which comprises the following components by weight percentage: Matrix material: polyalphaolefin or polyether-modified silicone oil; Thixotropic thickener: fumed silica and polyurea compound, wherein the content of fumed silica is 2-5 wt% and the content of polyurea compound is 1-3 wt%. Adsorbent: molecular sieve powder and alkaline earth metal oxide composite, wherein the average particle size of the molecular sieve powder is 2~5μm and the content is 3~5wt%; the alkaline earth metal oxide composite is a mixture of calcium oxide and magnesium oxide and the content is 2~4wt%.

6. The bend-resistant hollow optical fiber core submarine optical cable according to claim 1, characterized in that, The functional isolation layer, from the inside out, includes a semi-conductive water-resistant tape wrapping layer, a barrier membrane longitudinal wrapping layer, and a water-resistant adhesive layer. The longitudinal cladding layer of the barrier film is a co-extruded composite film of polyamide and ethylene-vinyl alcohol copolymer; The water-blocking adhesive layer is disposed between the longitudinal wrapping layer of the barrier membrane and the inner sheath.

7. The bend-resistant hollow optical fiber core submarine optical cable according to claim 1, characterized in that, The inner sheath is a longitudinal sheath of low-melting-point metallocene polyethylene with a melting point of 95~105℃; the outer sheath is a longitudinal sheath of weather-resistant chlorinated polyethylene or thermoplastic polyurethane.

8. The bend-resistant hollow optical fiber core submarine optical cable according to claim 7, characterized in that, The outer surface of the outer sheath is provided with a V-shaped stress relief groove along the axial direction. The groove depth is 20% to 30% of the thickness of the outer sheath, the groove width is 1.5 to 2.0 mm, and the groove spacing is 15 to 20 mm. A water-blocking expansion strip is embedded in the V-shaped stress relief groove.

9. The bend-resistant hollow optical fiber core submarine optical cable according to claim 1, characterized in that, The cable core filler includes a porous honeycomb foamed polyethylene and thermoplastic polyurethane blend filler strip, the closed-cell rate of the filler strip is not less than 70%, and the filler strip has an arc-shaped fitting surface adapted to the outer surface of the optical fiber sub-cable unit.

10. A method for preparing a bend-resistant hollow optical fiber core submarine optical cable as described in any one of claims 1 to 9, characterized in that, Includes the following steps: The optical fiber preform is heated and drawn into fibers. Hexamethyldisiloxane gas-tight underlayer, silane coupling agent bridging layer, and conductive antistatic layer are sequentially deposited on the outer surface of the bare optical fiber. Then, the stress buffer layer and the mechanical reinforcement layer are formed by UV curing in sequence; A loose tube is extruded using a three-layer co-extrusion process, and a foamed silicone rubber spiral support is simultaneously embedded into the loose tube. A thixotropic composite water-blocking gel is then injected into the loose tube. The fiber optic sub-cable units are laid around the central reinforcement, and the cable core filler is laid synchronously with the remote power supply conductor. A functional isolation layer is formed on the outside of the cable core after cabling is completed; The inner sheath is longitudinally wrapped and then hot-melt welded using a process called longitudinal wrapping-hot-melt welding. Poly(p-phenylene benzodioxazole) fibers are spirally wound around the inner sheath, and then aramid yarn is woven to form a double-layer fiber armor layer. The outer sheath is longitudinally wrapped and then hot-air melt-welded using a process.

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