As the key transmission medium of the "last mile" of fiber-to-the-home, outdoor covered optical cable ftth needs to operate stably in complex outdoor environments such as strong winds, temperature differences, and human pulling. The optimization of its mechanical properties such as tensile strength and bending resistance is directly related to the reliability and service life of the communication network, and requires comprehensive efforts from multiple dimensions such as materials, structures, and processes.
The application of high-performance reinforcement materials is the core of improving tensile performance. Outdoor covered optical cable ftth usually has high-strength Kevlar fiber (Kevlar) or glass fiber reinforced plastic (FRP) built-in as reinforcement. Kevlar fiber has a density of only one-fifth of steel, but has a tensile strength five times higher than steel, which can effectively resist common external forces in the outdoors, such as construction collisions and tree branches. FRP reinforcements have good corrosion resistance. In harsh environments such as high salt fog and industrial pollution along the coast, they can avoid the strength loss caused by material corrosion and ensure the long-term and stable operation of the optical cable. In addition, some new optical cables use aramid yarn braided layers, which further disperse the tension through the spiral winding process, and improve the tensile performance by 20% - 30%.
Scientific structural design provides guarantee for anti-bending performance. FTTH sheathed optical cables often use flat or 8-shaped structures. Compared with traditional round optical cables, the flat structure can reduce stress concentration during bending. For example, in the double-layer sheath structure, the inner layer is highly elastic polyvinyl chloride (PVC) or low-smoke zero halogen (LSZH) material, which can buffer external pressure; the outer layer is made of polyolefin (PO) material with excellent tear resistance to protect the internal fiber core. At the same time, a buffer layer, such as aramid cotton or polyurethane foam, is set between the fiber core and the reinforcement. When the optical cable is bent, the buffer layer can absorb the deformation energy and prevent the fiber core from breaking due to excessive extrusion. Some high-end products also introduce microbend-insensitive fiber (MIF) to reduce the bending loss to one-tenth of traditional optical fiber, and can maintain stable signal transmission even in frequent bending scenarios.
Process optimization further enhances mechanical properties. In the production process of optical cables, a secondary sheathing process is used to accurately coat the fiber core and reinforcements to ensure that the positions of each component are fixed and to prevent the performance from being affected by structural dislocation caused by external forces. At the same time, by optimizing parameters such as extrusion temperature and pulling speed, the sheath is closely fitted to the internal structure to avoid stress concentration caused by looseness. For example, when producing in a high-temperature environment, appropriately lowering the extrusion temperature can reduce the internal stress caused by thermal expansion of the material; while in a low-temperature environment, the pulling speed is adjusted to prevent the sheath from cracking due to excessive cooling. In addition, the finished optical cables are subjected to strict mechanical performance tests, including tensile tests, repeated bending tests, and flattening tests. Unqualified products are screened by simulating extreme outdoor working conditions to ensure factory quality.
Special environmental adaptability design expands the application boundaries. For long-distance overhead laying scenarios such as mountainous areas and across rivers, R&D personnel will increase the diameter or number of reinforcements and use more weather-resistant materials, such as galvanized steel wire and Kevlar fiber composite reinforcements, to significantly increase tensile strength while ensuring lightweight. In areas with frequent strong winds, the optical cable will also be equipped with windproof hooks or pre-twisted wires to reduce fatigue damage caused by shaking through multi-point fixation. When laying underground pipelines, the outer sheath of the optical cable will be added with special coatings to prevent rat bites and termites to avoid mechanical performance failure due to biological damage.
Installation and maintenance specifications ensure long-term mechanical performance. During the construction process, the laying standards must be strictly followed to avoid excessive bending, knotting or strong pulling of the optical cable. For example, the bending radius at the bend must be greater than 20 times the diameter of the optical cable to prevent damage to the fiber core; when laying overhead, appropriate sag is reserved to buffer the impact of external forces such as wind, ice and snow. In daily maintenance, regularly check whether the optical cable fixing points are loose and whether the outer sheath is damaged, and replace the damaged section in time to ensure that the optical cable is always in good mechanical performance.
Intelligent monitoring technology escorts mechanical performance. By installing optical fiber sensors at key nodes of outdoor covered optical cable ftth, real-time monitoring of parameters such as tension and strain is carried out, and immediate warning is issued once abnormalities are found. For example, distributed fiber optic sensing technology (DFOS) can accurately capture tiny deformations along the optical cable and predict the risk of signal attenuation caused by mechanical damage in advance. Combined with big data analysis, operation and maintenance personnel can quickly locate the fault point and optimize the maintenance strategy based on historical data, realizing the transition from passive maintenance to active protection.
Through the application of high-performance materials, scientific structural design, process optimization, special environment adaptation, standardized construction and maintenance, and intelligent monitoring, the mechanical properties of outdoor covered optical cable ftth, such as tensile strength and bending resistance, have been significantly improved, so as to calmly cope with the challenges of complex outdoor environments and provide solid guarantees for the stable operation of fiber-to-the-home networks.
