What type of fiber optic cable is used in the tunnel

Armored, water-blocking fiber optic cables designed for duct and tunnel installations are typically used to ensure durability, mechanical protection, and reliable data transmission.Tunnel-Specific Fiber Optic Cable CharacteristicsFiber optic cables installed in tunnels are engineered to withstand harsh environmental and mechanical conditions. They are generally armored to resist physical damage from construction vibrations, accidental impacts, or rodent attacks. Common armoring materials include stainless steel wire armor or aluminum tape, which provide high tensile strength and protection against crushing forces . To prevent moisture ingress, tunnel cables often incorporate water-blocking mechanisms, such as gel-filled cores or superabsorbent tapes, ensuring long-term reliability even in damp or wet conditions . The outer jacket is typically made of PE (polyethylene) or other durable materials rated for a wide temperature range, often from -40°C to +85°C, to handle extreme environmental conditions .Compliance with StandardsThe ITU-T L.100 Recommendation specifies the technical requirements for optical fiber cables installed in ducts and tunnels. This standard outlines mechanical, optical, and environmental performance criteria, including tests for tensile strength, bending, and electrical continuity for metallic elements within the cable . Compliance ensures that the cable can be safely pulled through ducts or tunnels without compromising signal integrity.Common Cable TypesDepending on the tunnel environment, different cable designs are used:GYXTW cables: Double steel armored cables suitable for urban tunnels with high construction activity .GYFTY cables: Reinforced with FRP (fiber-reinforced plastic) for rural or less accessible tunnels .GYTS cables: Water-blocking cables with aluminum composite tape, ideal for marshy or high-moisture tunnels . These cables can be single-mode or multimode, depending on the required transmission distance and bandwidth. Single-mode fibers are preferred for long-distance, high-speed communication, while multimode fibers are suitable for shorter distances with high data rates .SummaryIn tunnels, armored, water-blocking fiber optic cables compliant with ITU-T L.100 standards are used to ensure durability, environmental protection, and reliable high-speed data transmission. The choice of specific cable type—such as GYXTW, GYFTY, or GYTS—depends on the tunnel's environmental conditions, mechanical stress, and network requirements .