A low-stress high-density hollow-core fiber cable and a method of manufacturing the same

Abstract

The application discloses a kind of low stress high-density hollow core fiber cable and preparation method thereof, belong to optical communication technical field.To solve the problem of low yield, insufficient integration density and poor environmental stability of hollow core fiber cable in prior art, the manufacturing method of the present application comprises: using multi-stage curing process to make multiple hollow core fibers into fiber ribbon, which forms a flexible intermediate structure before final curing;And using non-contact plastic process to plasticize the fiber ribbon bundle, by establishing a fluid cushion between the fiber ribbon bundle and the plastic mold to avoid physical contact.The cable of the present application comprises: a stress absorbing layer with a Young's modulus of not more than 0.5 MPa directly coated outside the hollow core fiber cladding;The filling polymer of the fiber ribbon contains a thermal expansion coefficient reducing additive;And a multi-layer composite structure loose tube composed of an inner layer providing a low friction interface and an outer layer providing mechanical protection.The present application significantly improves the manufacturing yield, integration density and environmental adaptability through the synergistic innovation of process and structure.

Description

Technical Field

[0001] This invention relates to the field of optical communication technology, specifically to a low-stress, high-density hollow optical fiber cable and its fabrication method. Background Technology

[0002] With the rapid development of next-generation communication networks, data center interconnections, and artificial intelligence computing clusters, unprecedented demands have been placed on the bandwidth, latency, and energy efficiency of data transmission. Hollow-core fiber (HCF), due to its light transmission within an air core, possesses near-vacuum speed of light, ultra-low nonlinear effects, and extremely low scattering loss, and is widely recognized as a key technology for overcoming the transmission bottlenecks of traditional solid-core fiber.

[0003] However, manufacturing high-reliability optical cables capable of large-scale engineering applications from hollow optical fibers, which have a precise structure and fragile mechanical properties, faces severe challenges. Firstly, the integration density is extremely low. To avoid fiber damage, existing hollow optical fiber cables mostly adopt a loosely arranged structure with fewer cores, resulting in a single-core capacity far lower than traditional optical cables. This significantly increases the laying cost per core kilometer, hindering its economic viability and large-scale deployment.

[0004] Secondly, manufacturing stress damage is severe. Traditional solid fiber coloring, ribboning, and molding processes involve high-temperature curing, high-pressure extrusion, and mold-contact traction. When these processes are directly applied to hollow fibers, the resulting radial extrusion pressure and thermal stress easily cause microcracks or deformation in the microstructure of the hollow fiber, leading to a sharp deterioration in additional losses. For example, the shrinkage stress generated by the traditional one-step integral curing process for fiber ribbons far exceeds the safety threshold that hollow fibers can withstand, resulting in generally low manufacturing yields that cannot meet the requirements of commercial production.

[0005] Furthermore, the environmental stability is poor. The loose tube material used in traditional optical cables differs from the quartz material used in hollow optical fibers by nearly three orders of magnitude in terms of thermal expansion coefficient. In a wide temperature range operating environment, the repeated contraction and expansion of the loose tube will apply periodic axial stress to the internal hollow optical fiber, inducing micro-bending loss. As a result, the additional loss of the optical cable in temperature cycling tests is far from meeting the stringent requirements of backbone network projects.

[0006] Therefore, existing technologies are mostly point-based and isolated optimizations, failing to systematically design stress accumulation throughout the entire manufacturing process and stress isolation mechanisms in the multi-layered structure of optical cables. There is an urgent need for a systematic solution that can reduce stress step by step from the source of the process, isolate stress in multiple layers at the structural level, and at the same time take into account high-density integration. Summary of the Invention

[0007] To address the technical problems of low manufacturing yield, insufficient integration density, and poor environmental stability in existing hollow optical fiber cables, this invention provides a manufacturing method for hollow optical fiber cables and a hollow optical fiber cable itself.

[0008] This invention provides a method for manufacturing hollow optical fiber cables, characterized by comprising: using a multi-stage curing process to form an optical fiber ribbon from multiple hollow optical fibers, wherein the multi-stage curing process is controlled to form a flexible intermediate structure before final curing; and using a non-contact molding process to mold the optical fiber ribbon bundle formed from the optical fiber ribbon, wherein the non-contact molding process establishes a fluid pad between the optical fiber ribbon bundle and the molding mold to avoid physical contact between the optical fiber ribbon bundle and the molding mold during the extrusion of the loose tube. This method can significantly reduce the mechanical and thermal stress applied to the fragile hollow optical fibers during manufacturing, thereby greatly improving the manufacturing yield.

[0009] Furthermore, the multi-stage curing process includes: applying a first layer of matrix resin to multiple hollow optical fibers and partially curing it to form the flexible intermediate structure; and applying a subsequent layer of matrix resin to the flexible intermediate structure and completing the final curing. This method avoids the concentrated accumulation of stress on the optical fiber surface by releasing the curing shrinkage stress in stages.

[0010] Optionally, the degree of curing of the partially cured portion is 30% to 40%. This degree of curing can form a flexible intermediate structure with a certain handling strength, while maximizing the preservation of the structure's flexibility to buffer subsequent curing stress.

[0011] In one embodiment, the fluid pad is formed by introducing compressed gas at a pressure of 0.05 MPa to 0.1 MPa into the molding die. This fluid pad stably suspends the fiber ribbon bundle at the center of the die, achieving zero-contact passage throughout the process and fundamentally eliminating contact extrusion stress during molding.

[0012] Furthermore, before fabricating the hollow optical fiber into an optical fiber ribbon, the process includes a low-temperature stepwise coloring and curing step on each individual hollow optical fiber. This low-temperature stepwise coloring and curing is performed at a temperature below 100°C and includes first forming a stress-absorbing layer and pre-curing it, then forming a coloring layer and performing complete curing. This step controls thermal stress and curing stress from the very beginning of the single-fiber processing.

[0013] Furthermore, prior to employing the multi-stage curing process, a step is included in which multiple hollow optical fibers are arranged non-contactly using an air-floating method. This avoids micro-scratches on the fiber surface caused by traditional mechanical guide wheels, thus protecting the initial mechanical properties of the optical fiber.

[0014] Furthermore, prior to the non-contact molding process, a step of segmented annealing is included in the formed fiber ribbon bundle. This step effectively releases the internal stress accumulated in the fiber ribbon during the bundling and lamination process, improving the dimensional stability and stress uniformity of the fiber ribbon bundle.

[0015] This invention also provides a hollow-core optical fiber cable, characterized in that it comprises: a loose tube; and an optical fiber bundle housed within the loose tube; wherein the optical fiber bundle is composed of at least one optical fiber strip, the optical fiber strip being formed by multiple hollow-core optical fibers housed in a filling polymer; the filling polymer contains an additive that reduces the coefficient of thermal expansion; a stress-absorbing layer is directly coated on the outer cladding surface of each hollow-core optical fiber, the stress-absorbing layer having a Young's modulus not greater than 0.5 MPa; the loose tube is a multi-layer composite structure, the multi-layer composite structure comprising: an inner layer configured to provide a low-friction interface to the optical fiber bundle; and an outer layer configured to provide mechanical protection. This structural design, through multi-layer protection and stress isolation, ensures the long-term reliability of the optical cable in complex environments.

[0016] Optionally, the stress-absorbing layer is a soft inner buffer layer that acts as the first stress barrier, effectively absorbing and buffering the microscopic mechanical stress applied to the optical fiber.

[0017] In one embodiment, the coefficient of thermal expansion reducing additive can significantly reduce the coefficient of thermal expansion of the filled polymer, making it more compatible with the thermal behavior of the optical fiber and loose tube, thereby reducing thermal stress caused by temperature changes.

[0018] Furthermore, the inner layer is made of fluoroplastic, and the outer layer is made of thermoplastic polyurethane. The fluoroplastic inner layer provides an extremely low coefficient of friction, ensuring that the fiber bundle can creep freely under temperature changes; the thermoplastic polyurethane outer layer provides excellent mechanical strength and wear resistance.

[0019] Optionally, the loose tube contains multiple layers of the optical fiber ribbons, with a physical buffer gap of 0.05 mm to 0.25 mm between adjacent layers of optical fiber ribbons. This gap effectively prevents stress transfer and accumulation between the stacked optical fiber ribbons, providing structural protection for high-density integration.

[0020] Furthermore, the total number of hollow optical fibers housed within the loose tube is no less than 144. This demonstrates that the present invention can achieve a high-density integration capability far exceeding that of existing technologies.

[0021] Compared with the prior art, the present invention has the following beneficial effects: Significantly improve manufacturing yield and product consistency. By constructing a low-stress process chain from single-fiber coloring to cable coating, the maximum stress applied to hollow optical fibers during manufacturing is reduced by an order of magnitude, resulting in a significant decrease in fiber breakage rate. The geometric accuracy and performance consistency of finished optical cables are greatly improved, and the overall manufacturing yield can be increased to over 95%.

[0022] Achieving ultra-high density integration and reducing deployment costs. Low-stress technology provides the technological prerequisite for high-density stacking. Combined with physical buffer gaps and high-strength composite loose tube structures, the fiber core capacity of a single tube optical cable can reach 144 cores or even higher. The integration density is several to tens of times higher than that of existing technologies, effectively improving the utilization rate of pipeline resources and reducing the laying cost per core kilometer.

[0023] Environmental adaptability is significantly enhanced. Through the triple synergistic mechanism of stress-absorbing layer, low thermal expansion coefficient filler, and low friction composite loose tube, stress caused by temperature changes and external mechanical forces is effectively isolated and buffered, significantly reducing the additional loss of optical cable in harsh environments such as wide temperature range cycling and lateral pressure resistance, reaching or even exceeding the level of traditional solid core optical fiber cables.

[0024] The optical cable produced by this invention exhibits excellent combined optical and mechanical properties. It also boasts extremely low additional cabling loss, good engineering splicing performance, and long-term service reliability, providing a high-performance and economical physical layer solution for the large-scale deployment of next-generation optical communication networks. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the cross-sectional structure of a hollow optical fiber cable provided in an embodiment of the present invention.

[0026] Markings: 12 - Physical buffer gap, 20 - Loose sleeve of composite structure, 21 - Inner layer, 22 - Outer layer, 30 - Reinforcing member, 40 - Outer sheath.

[0027] Figure 2 This is a cross-sectional schematic diagram of a single hollow optical fiber cladding structure provided in an embodiment of the present invention.

[0028] Markings: 101-Hollow fiber, 102-Stress absorption layer, 103-Stress relief layer (coloring layer).

[0029] Figure 3 This is a structural cross-sectional schematic diagram of a special mold for low-temperature coloring provided in an embodiment of the present invention.

[0030] Markings: 201-tapered fiber guide hole, 202-diamond-like friction-reducing layer, 203-pressure gradient control cavity.

[0031] Figure 4This is a schematic diagram of the arc-shaped diversion channel layout with mold provided in the multi-stage curing process of the present invention.

[0032] Markings: 301 - Arc-shaped diversion channel, 302 - Buffer and pressure stabilizing chamber.

[0033] Figure 5 This is a schematic diagram illustrating the center positioning principle of a non-contact plastic mold provided in an embodiment of the present invention.

[0034] Markings: 401-Fiber optic ribbon bundle, 402-Fluid pad, 403-Compressed air inlet, 404-Annular flow channel.

[0035] Figure 6 This is an overall flowchart of the low-stress manufacturing method provided in an embodiment of the present invention.

[0036] Markings: S10 - Low temperature stepwise coloring and curing, S20 - Air flotation non-contact arrangement, S30 - Multi-stage curing process with tape, S40 - Segmented annealing, S50 - Non-contact plastic coating, S60 - Cable and sheath extrusion. Detailed Implementation

[0037] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are for illustrative purposes only and are not intended to limit the scope of protection of this invention. Without conflict, the embodiments and features described in this application can be combined with each other.

[0038] This invention aims to address the core challenges in the manufacturing process of hollow optical fibers into optical cables, such as low manufacturing yield, insufficient integration density, and poor environmental stability caused by mechanical and thermal stress. To this end, this invention proposes a systematic solution that synergistically innovates a "low-stress process chain" and a "high-reliability structural system." Starting from two dimensions—stress control throughout the entire manufacturing process and stress isolation in the multi-layered structure of the optical cable—it achieves high performance, high density, and high reliability for hollow optical fiber cables.

[0039] In the description of this invention, a series of core terms will be used. "Multi-stage curing process" refers to a process for forming fiber ribbons from multiple hollow optical fibers, characterized by not completing the curing in one go, but rather through multiple controlled stages to form a flexible, stress-buffered intermediate structure before final curing; this intermediate structure is referred to as the "flexible intermediate structure" in this invention. "Non-contact cladding process" refers to a process for extruding loose tubes outside the fiber ribbon bundle, eliminating contact stress by forming a "fluid cushion layer" between the fiber ribbon bundle and the mold to prevent physical contact between the two. Furthermore, "stress-absorbing layer" refers to a material directly covering the outer surface of the hollow optical fiber cladding, with a low Young's modulus, whose main function is to absorb and buffer external mechanical stress applied to the fiber. "Coefficient of thermal expansion reducing additive" refers to a material added to the filler polymer of the fiber ribbon to reduce the polymer's coefficient of thermal expansion. "Physical buffer gap" refers to a gap or separator of physical thickness between adjacent fiber ribbon layers in a multilayer fiber ribbon stack structure, used to prevent interlayer stress transmission.

[0040] In one aspect of the invention, a method for manufacturing a hollow-core optical fiber cable is provided. (See also...) Figure 6 The core of this method lies in constructing a complete low-stress process chain. Key steps include using a multi-stage curing process to fabricate fiber ribbons from multiple hollow optical fibers, and using a non-contact coating process to coat the fiber ribbon bundles formed from the fiber ribbons. The multi-stage curing process releases and controls the curing shrinkage stress in stages during ribbon fabrication, avoiding the instantaneous accumulation of stress on the fiber surface during traditional one-step curing. The non-contact coating process completely eliminates physical contact between the mold and the fiber ribbon bundle during the coating process, fundamentally preventing contact compression stress. The combination of these two core processes forms the basis of the low-stress manufacturing method of this invention, significantly reducing the maximum radial force applied to the hollow optical fibers during manufacturing from 10-12 MPa in traditional processes to below 3 MPa.

[0041] Furthermore, the multi-stage curing process includes applying a first layer of matrix resin to multiple hollow optical fibers and partially curing it to form the flexible intermediate structure; subsequently, applying a subsequent layer of matrix resin to the flexible intermediate structure and completing the final curing. By first forming an intermediate state that still retains flexibility, this process decomposes the huge shrinkage stress generated by one-time curing into multiple stages of small stress release. This flexible intermediate structure acts as a buffer layer, effectively absorbing the stress generated by the subsequent curing process and preventing the stress from being directly transmitted to the fragile hollow optical fibers.

[0042] In a preferred embodiment, the degree of curing of the partially cured portion is precisely controlled between 30% and 40%. When the degree of curing is below 30%, the flexible intermediate structure is too soft and difficult to maintain the precise alignment of the optical fibers; while when the degree of curing is above 40%, its flexibility decreases, the buffering effect weakens, and its own shrinkage stress increases. Controlling the degree of curing within the range of 30% to 40% can maximize its stress buffering capacity while ensuring the pre-shape of the structure, creating an ideal low-stress foundation for subsequent final curing.

[0043] In the non-contact coating process, the fluid pad is formed by introducing compressed gas at a pressure of 0.05 MPa to 0.1 MPa into the coating mold. This pressure range has been precisely calculated and experimentally verified to generate sufficient lifting force to stably suspend the fiber ribbon bundle at the center of the mold, avoiding any physical contact with the inner wall of the mold, while also preventing disturbance or pressure on the fiber ribbon bundle due to excessive gas pressure. Therefore, the radial force on the fiber ribbon bundle during the coating process is controlled below 0.5 MPa, almost completely eliminating mechanical stress damage during the coating process.

[0044] Building upon the aforementioned approach, to control stress from the very beginning of the process chain, a low-temperature, stepwise coloring and curing step is included before fabricating the hollow fiber into an optical fiber ribbon. This step is performed at temperatures below 100°C and involves first forming a stress-absorbing layer and pre-curing it, followed by forming a coloring layer and completing the curing process. Compared to the traditional one-step coloring process at temperatures above 120°C, this low-temperature process significantly reduces the impact of thermal shock on the microstructure of the hollow fiber, while the stepwise curing further disperses the curing shrinkage stress, providing a "healthy" fiber with extremely low initial stress for all subsequent processes.

[0045] Furthermore, prior to the multi-stage curing process, a non-contact alignment step is included using an air-floating method to align multiple hollow optical fibers. This step utilizes positive pressure gas to form an air film between the optical fiber and the guiding device, allowing the fibers to be precisely aligned without any mechanical contact. This design eliminates, from the outset, the micro-scratches and stress concentration points that traditional V-groove or comb-tooth guiding devices may cause to the fiber surface, which is crucial for ensuring the long-term mechanical reliability and fatigue resistance of the hollow optical fiber.

[0046] In addition, prior to the non-contact coating process, a segmented annealing step is included in the forming of the fiber ribbon bundle. Residual internal stress is inevitably introduced during the ribbon bonding and lamination processes. Segmented annealing, through precise "heating-holding-slow cooling" heat treatment of the fiber ribbon bundle, promotes the rearrangement and relaxation of polymer molecular chains, thereby effectively releasing these accumulated internal stresses. This step ensures that the fiber ribbon bundle entering the coating process is in an ideal state of dimensional stability and uniform stress, further improving the performance consistency and long-term reliability of the final optical cable product.

[0047] In another aspect of the invention, a highly reliable hollow-core optical fiber cable is provided. For example... Figure 1 As shown, the optical cable generally includes a loose tube 20, an optical fiber ribbon bundle housed therein, and optional reinforcing members 30 and an outer sheath 40. Its core design concept lies in systematically isolating and buffering mechanical and thermal stresses from the external environment through multi-level, multi-functional structural synergy. Specifically, the optical fiber ribbon bundle of the cable consists of at least one optical fiber ribbon, which is formed by multiple hollow optical fibers 101 housed in a filling polymer. The structural innovation of this invention is reflected in three aspects: first, the filling polymer contains additives that reduce the coefficient of thermal expansion; second, such as... Figure 2 As shown, each hollow fiber 101 has a stress-absorbing layer 102 directly coated on its outer cladding surface; finally, the loose tube 20 that houses the fiber bundle is a multi-layer composite structure.

[0048] Specifically, the stress-absorbing layer 102 serves as the first stress barrier, with a Young's modulus of no more than 0.5 MPa. This extremely low modulus makes it act like a soft "mattress," effectively absorbing and dissipating the microscopic compressive and bending stresses applied to the optical fiber during subsequent manufacturing processes or in the usage environment, preventing stress concentration and transmission to the fragile quartz microstructure.

[0049] Furthermore, the additive that reduces the coefficient of thermal expansion is preferably hollow glass microspheres. The quartz material of hollow optical fibers differs significantly in its coefficient of thermal expansion from the polymer materials used in traditional optical cables. By doping the filled polymer with this additive that reduces the coefficient of thermal expansion, its overall coefficient of thermal expansion can be reduced from approximately (1.8-2.2) × 10⁻⁻⁻⁶. 4 / ℃ decreased significantly to (5.0-6.0)×10⁻ 5 / ℃, making it more compatible with the thermal behavior of the loose tube material. This design effectively reduces the periodic axial stress on the optical fiber caused by material mismatch contraction or expansion in a wide temperature range (e.g., -40℃ to +70℃), thereby significantly improving the temperature stability of the optical cable.

[0050] In a preferred embodiment, the loose tube 20 has a multilayer composite structure comprising an inner layer 21 and an outer layer 22. The inner layer 21 is configured to provide a low-friction interface to the fiber bundle and is preferably made of fluoroplastic (such as FEP); the outer layer 22 is configured to provide mechanical protection and is preferably made of thermoplastic polyurethane (TPU). The extremely low coefficient of friction (≤0.2) of the fluoroplastic inner layer 21 allows the fiber bundle to freely "creep" within the loose tube 20 to release axial stress caused by temperature changes, while the high-strength TPU outer layer 22 provides excellent resistance to compression, impact, and abrasion, protecting the internal fibers from external mechanical damage. This functionally separated design addresses both the internal stress relief and external mechanical protection requirements.

[0051] In a high-density integrated implementation, such as Figure 1 As shown, the loose tube 20 contains multiple layers of optical fiber ribbons, with a physical buffer gap 12 between adjacent layers. The size of this physical buffer gap 12 is preferably between 0.05 mm and 0.25 mm. During high-density stacking, the weight of the upper optical fiber ribbons and external pressure are transmitted to the lower layers. The presence of the physical buffer gap 12, whether through an insulating material or a simple void, effectively blocks the transmission and accumulation of this interlayer pressure, ensuring that even the bottommost fiber does not suffer performance degradation due to pressure. This is a key structural guarantee for achieving high-density integration.

[0052] To achieve high-density integration, the optical cable structure design of this invention allows for a total number of hollow optical fibers 101 housed within the loose tube 20 to be no less than 144, and even up to 288 or more. This is thanks to the synergistic effect of the aforementioned low-stress process and high-reliability structure, which together make high-density stacking possible. This enables the integration density of the hollow optical fiber cable to reach a level comparable to that of traditional solid optical fiber cables for the first time, significantly improving the utilization rate of pipeline resources and reducing the laying cost per core kilometer.

[0053] The method of the present invention will be described in more detail below through a general manufacturing process embodiment. Figure 6 As shown, the overall process of this low-stress manufacturing method includes, in sequence: low-temperature stepwise coloring and curing S10, air-float non-contact arrangement S20, multi-stage curing process and strip S30, lamination and segmented annealing S40, non-contact plastic coating S50, and cable and sheath extrusion S60.

[0054] The first step of this process is low-temperature stepwise coloring and curing of S10, in which the following is used: Figure 3The specialized coloring mold shown is used to coat a single hollow optical fiber. The mold's entrance end has a tapered, tapered fiber guide hole 201 with a taper angle of 20° to 40° to guide the fiber smoothly into the fiber. The inner wall of the fiber guide hole is coated with a diamond-like carbon anti-friction layer 202 with a friction coefficient not greater than 0.1 to prevent scratches. A pressure gradient control chamber 203 is located in the middle of the mold, which can control the radial pressure exerted by the resin on the fiber during the coating process to below 0.3N. The specific process is as follows: First, a layer of UV-curable acrylate resin with a thickness of 5-8μm is coated and pre-cured at 75-85℃ to a curing degree of 60%-70%, forming a stress-absorbing layer 102 with a modulus of 0.3-0.5MPa. Then, a layer of coloring ink with a thickness of 2-5μm is coated and fully cured at the same low temperature to a total curing degree ≥95%, forming a stress-relieving layer (coloring layer) 103.

[0055] The second step of the process is the air-floating non-contact arrangement S20, which uses an air-floating fiber guide wheel assembly to arrange multiple colored hollow optical fibers. Positive pressure dry air or nitrogen at 0.02-0.05 MPa is introduced into the guide wheel surface, forming a stable air film with a thickness of 10-50 μm between the optical fiber and the guide wheel surface, allowing the optical fiber to levitate throughout the process. This method allows for precise control of the fiber center distance within 280-320 μm, with an arrangement error of no more than ±5 μm, and completely avoids mechanical contact damage.

[0056] The third step of the process is a multi-stage curing process with S30, which uses, for example... Figure 4 The mold shown is a dedicated component. This mold has an arc-shaped flow diversion channel 301 and a buffer voltage stabilizing cavity 302 to ensure uniform coating of the matrix resin. The core process involves two-step curing: First, a first layer of matrix resin is extruded onto the fiber bundle and blown with nitrogen at room temperature to achieve a curing degree of precisely 30%-40%, forming a flexible intermediate structure with minimal shrinkage stress (≤0.2MPa). Second, a second layer of high-modulus matrix resin is extruded onto this structure and cured using a stepped UV curing process (first low light intensity 300-500mW / cm², then high light intensity 1000-1400mW / cm²) to complete the final curing (total curing degree ≥95%). Preferably, the matrix resin used for filling is premixed with a 5%-10% by mass additive that reduces the coefficient of thermal expansion (such as hollow glass microspheres) with a particle size of 10-30 micrometers.

[0057] The fourth step in the process is lamination and segmented annealing (S40), in which multiple prepared optical fiber ribbons are laminated, and a polyester film separator with a thickness of 0.05-0.25 mm is inserted between adjacent layers to form a physical buffer gap (12). Subsequently, the laminated optical fiber ribbon bundle undergoes segmented annealing: it is heated to 75-85℃ and held for 30-60 seconds, then slowly cooled to room temperature at a rate not exceeding 2℃ / minute. This step can reduce the overall residual stress value of the optical fiber ribbon bundle by 40%-50%.

[0058] The fifth step in the process is non-contact S50 molding, which uses, for example... Figure 5 The mold shown is a composite tube. Compressed air at a pressure of 0.05-0.1 MPa is introduced into the mold's compressed air inlet 403, and through the annular flow channel 404 and microporous throttling ring, a stable fluid pad 402 is formed between the fiber optic ribbon bundle 401 and the inner wall of the mold, allowing the fiber optic ribbon bundle 401 to suspend and pass through. Simultaneously, a loose tube 20 with a composite structure is extruded using a co-extrusion process. Its inner layer 21 is a 0.15-0.25 mm thick fluorinated ethylene propylene copolymer (FEP), and its outer layer 22 is a 0.35-0.45 mm thick thermoplastic polyurethane (TPU).

[0059] Finally, in the cabling and sheath extrusion step S60, the prepared loose tube 20 and the reinforcing member 30 (such as phosphated steel wire) are twisted together by SZ, and the outer sheath 40 is extruded on the outermost layer, thus completing the manufacturing of the hollow optical fiber cable.

[0060] To further illustrate the technical solution of the present invention, verify the preferred range of key parameters, and demonstrate its significant beneficial effects compared with the prior art, several preferred embodiments will be provided below, and comparative examples will be set for comprehensive performance comparison.

[0061] Example 1: 144-core high-density hollow fiber optic cable In one embodiment, a high-density hollow-core optical fiber cable with 144 cores (composed of six 24-core fiber ribbons stacked together) is manufactured in a single tube. This embodiment strictly follows the general process described above and selects preferred parameters. Specifically, the stress-absorbing layer 102 has a thickness of 6 μm, a modulus of 0.4 MPa, a pre-curing temperature of 80°C, and a degree of curing of 65%. The air pressure for air flotation arrangement is 0.035 MPa, and the fiber center spacing is 300 ± 5 μm. When using a multi-stage curing process, the degree of curing of the first resin layer is 35%, and the amount of thermal expansion coefficient reducing additive (hollow glass microspheres) added to the second resin layer is 8%. The segmented annealing temperature is 80°C, with a dwell time of 40 seconds. The air pressure for non-contact cladding is 0.08 MPa, the thickness of the FEP inner layer 21 is 0.20 mm, and the thickness of the TPU outer layer 22 is 0.40 mm. The final product structure is as follows. Figure 1 and Figure 2 As shown, the outer diameter of the finished product is 14.5mm.

[0062] Example 2: 288-core ultra-high density hollow fiber optic cable To verify the density expansion capability of the present invention, a 288-core ultra-high-density hollow-core optical fiber cable was manufactured in another embodiment. This embodiment uses 12 stacked 24-core fiber ribbons, with the fiber ribbon thickness reduced to 0.28 mm and the physical buffer gap 12 reduced to 0.08 mm. Testing showed that the additional cable loss at 1550 nm wavelength was 0.032 dB / km, the additional loss due to temperature cycling was 0.042 dB / km, and the additional loss due to lateral pressure was 0.07 dB / km. All indicators remained excellent, demonstrating that the present invention has outstanding high-density integration and expansion capabilities.

[0063] Example 3: Composite loose-sleeve pipes with different material combinations This invention is not limited to the above-described material combinations. In another embodiment, the materials of the composite loose-sleeve tube were verified. The inner layer 21 was replaced with polytetrafluoroethylene (PTFE), and the outer layer 22 was replaced with nylon 12 (PA12). Test results showed that this combination was comparable to the FEP+TPU combination in terms of lateral pressure resistance, but its flexibility at low temperatures (-40°C) was slightly worse, with a temperature loss of 0.05 dB / km, indicating that FEP+TPU is the preferred combination that balances various performance aspects.

[0064] Example 4: Effect of different stress-absorbing layer moduli To determine the optimal parameters for the stress-absorbing layer, the effect of different moduli of the stress-absorbing layer 102 was investigated in another embodiment. Samples were prepared at four modulus levels: 0.2 MPa, 0.4 MPa, 0.5 MPa, and 0.8 MPa. The results showed that at a modulus of 0.2 MPa, the buffer layer was too soft, affecting process stability; at a modulus of 0.8 MPa, it exceeded the upper limit of 0.5 MPa specified in this invention, resulting in a deterioration in the buffering effect and an increase in temperature-induced loss to 0.09 dB / km. The optimal balance between stress buffering and process stability was achieved within the modulus range of 0.3 MPa to 0.5 MPa, especially at 0.4 MPa, with the lowest cable loss of 0.028 dB / km.

[0065] Example 5: The effect of different coefficients of thermal expansion on reducing additive content To determine the optimal content of the additive for reducing the coefficient of thermal expansion, the effect of the mass fraction of the additive (hollow glass microspheres) in the filled polymer was investigated in another embodiment. Optical fiber ribbon samples with addition amounts of 0%, 3%, 5%, 8%, 10%, and 12% were prepared, and their relevant properties were tested. The results are shown in Table 2. When the addition amount was 0% (blank control), the coefficient of thermal expansion was as high as 195 × 10⁻⁻⁻⁶. 6 / ℃, with an additional loss due to temperature change of 0.19 dB / km. As the addition amount increases, both the coefficient of thermal expansion and the loss due to temperature change decrease significantly. When the addition amount is 8%, the coefficient of thermal expansion drops to 58 × 10⁻ 6 / ℃, the temperature-dependent additional loss decreases to 0.035dB / km. Further increasing to 12%, although the coefficient of thermal expansion decreases further, the tensile strength of the fiber ribbon drops from 28.5MPa to 20.0MPa, affecting mechanical reliability. Therefore, 5% to 10% is the preferred range, and 8% is the optimal value balancing thermal and mechanical properties.

[0066] Table 2 Comparison of fiber ribbon performance under different addition amounts

[0067] To fully verify the overall superiority of the technical solution of this invention, two comparative optical cables were prepared for comparison.

[0068] Comparative Example 1 (Traditional Process): Manufactured using traditional processes, including high-temperature one-step coloring, contact guide wheel arrangement, one-step full curing with belt and contact extrusion molding.

[0069] Comparative Example 2 (only process optimization, no structural optimization): All the low-stress processes of this invention are adopted, but the optical cable structure is a traditional structure, that is, a single-layer PBT loose tube is used, and no additives to reduce the coefficient of thermal expansion are added to the filling polymer, and no physical buffer gaps are set between the layers.

[0070] The 144-core embodiment (Example 1) and 288-core embodiment (Example 2) of the present invention were compared with these two comparative examples in a comprehensive performance comparison. The test results are summarized in Table 1.

[0071] Table 1 Comparison of key performance indicators of different optical cable samples

[0072]

[0073] Comprehensive data analysis shows that: Comparing Example 1 and Comparative Example 1, after adopting the low-stress process chain of the present invention, the maximum fiber stress during manufacturing was reduced from 11.8 MPa to ≤3.2 MPa, the fiber ribbon breakage rate was reduced from 4.7% to 0.28%, and the additional cable loss was reduced from 0.21 dB / km to 0.028 dB / km. This strongly demonstrates the significant effectiveness of the low-stress process chain of the present invention in reducing manufacturing damage and improving yield.

[0074] Comparing Example 1 and Comparative Example 2, under the premise of completely identical processes, the temperature cycling additional loss (0.18 dB / km) and lateral pressure resistance additional loss (0.18 dB / km) of Comparative Example 2 are far inferior to those of Example 1 (0.035 dB / km and 0.05 dB / km, respectively) only due to structural differences. This clearly shows that low-stress processes alone cannot guarantee the reliability of optical cables in complex environments. A high-reliability structural system proposed in this invention (including a stress-absorbing layer, low thermal expansion filling material, composite loose tube, and physical buffer gaps) is necessary to achieve comprehensive environmental adaptability, demonstrating the irreplaceable nature of synergistic innovation combining "process + structure".

[0075] Embodiments 1 and 2 of this invention simultaneously achieve all the objectives of high manufacturing yield, low additional cable loss, good temperature stability, and high-density integration (144-288 cores / tube). Their dynamic fatigue parameters (Nd value) reach over 22, and their expected service life is extended by more than 30% compared to existing solutions. These data fully demonstrate that this invention, through systematic collaborative design, has successfully overcome the core technical challenges of engineered cabling of hollow-core optical fibers, paving the way for the large-scale application of high-density, low-cost, and high-reliability hollow-core optical fiber cables.

[0076] The above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of protection of the present invention. For those skilled in the art, the present invention can have various modifications and variations. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for fabricating a low-stress, high-density hollow-core optical fiber cable, characterized in that, include: A multi-stage curing process is used to form an optical fiber ribbon from multiple hollow optical fibers, wherein the multi-stage curing process forms a flexible intermediate structure in a controlled manner before final curing. as well as A non-contact molding process is used to mold the fiber ribbon bundle formed by the fiber ribbon. The non-contact molding process establishes a fluid pad between the fiber ribbon bundle and the molding mold to avoid physical contact between the fiber ribbon bundle and the molding mold during the extrusion of the loose tube.

2. The method according to claim 1, characterized in that, The multi-stage curing process includes: A first layer of matrix resin is applied to multiple hollow optical fibers and partially cured to form the flexible intermediate structure, wherein the flexible intermediate structure is a pre-shaped structure; and Subsequent layers of matrix resin are applied to the predetermined structure and then cured.

3. The method according to claim 2, characterized in that, The degree of curing of the partially cured portion is 30% to 40%.

4. The method according to claim 1, characterized in that, The fluid cushion is an air cushion formed by introducing compressed gas at a pressure of 0.05 MPa to 0.1 MPa into the molding die.

5. The method according to claim 1, characterized in that, Before the hollow optical fiber is made into an optical fiber ribbon, the process includes a step of low-temperature step-by-step coloring and curing of a single hollow optical fiber. The low-temperature step-by-step coloring and curing is carried out at a temperature below 100°C and includes first forming an inner buffer layer and pre-curing it, and then forming a coloring layer and fully curing it.

6. The method according to claim 1, characterized in that, Before employing the multi-stage curing process, the process also includes a step of arranging multiple hollow optical fibers in a non-contact manner using an air-floating method.

7. The method according to claim 1, characterized in that, Prior to the non-contact molding process, the process also includes a step of segmented annealing of the formed optical fiber bundle.

8. A hollow-core optical fiber cable, characterized in that, include: Loosen the sleeve; as well as A bundle of optical fibers contained within the loose tube; The fiber ribbon bundle consists of at least one fiber ribbon, which is formed by multiple hollow optical fibers housed in a filled polymer. The filled polymer contains additives that reduce the coefficient of thermal expansion; Each hollow optical fiber has a stress-absorbing layer directly coated on its outer cladding surface, and the Young's modulus of the stress-absorbing layer is not greater than 0.5 MPa. The loose sleeve is a multi-layer composite structure, which includes: An inner layer configured to provide a low-friction interface to the fiber optic bundle; and An outer layer is configured to provide mechanical protection.

9. The hollow-core optical fiber cable according to claim 8, characterized in that, The stress-absorbing layer is a polymer inner buffer layer, the thermal expansion coefficient reducing additive is hollow glass microspheres, the inner layer is made of fluoroplastics, and the outer layer is made of thermoplastic polyurethane.

10. The hollow-core optical fiber cable according to claim 8, characterized in that, The loose tube contains multiple layers of optical fiber ribbons, and a physical buffer gap with a size of 0.05 mm to 0.25 mm is provided between adjacent layers of optical fiber ribbons.

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