Communication Direct-Buried Optical Cable Manufacturing Process

Direct-buried optical cables are designed with multiple protective layers, including armored steel and polyethylene sheaths, to resist mechanical damage, water ingress, and soil corrosion, and are installed directly in the ground using manual or mechanical methods.Cable Structure and MaterialsDirect-buried optical cables are engineered to withstand harsh underground conditions. The core contains optical fibers housed in loose tubes made of high-modulus plastic and filled with waterproof compounds to prevent moisture ingress. A central strength member, often steel wire, provides tensile strength, while the loose tubes are SZ stranded around this member to reduce stress on the fibers during bending or pulling . The cable core is further protected with cable filling compounds and silica gel to prevent water penetration. For mechanical and rodent protection, corrugated steel tape and high-density polyethylene (HDPE) sheaths are applied as outer layers. In some designs, a double steel tape layer is used for enhanced anti-rodent protection. The cable is typically manufactured according to standards such as G.652D or GR-20, ensuring consistent optical performance and environmental durability .Manufacturing ProcessFiber Preparation: Optical fibers are drawn and coated with protective layers.Loose Tube Formation: Fibers are inserted into loose tubes filled with water-blocking gel.Stranding: Loose tubes are SZ stranded around the central strength member to allow flexibility and reduce stress.Filling and Core Protection: The cable core is filled with water-blocking compounds and silica gel.Armoring and Sheathing: Corrugated steel tape and HDPE sheaths are applied, sometimes with double steel layers for rodent protection.Quality Testing: Attenuation, tensile strength, and water-blocking performance are tested, typically at 1550 nm wavelength .Direct-Buried Cable Laying ProcessDirect-buried optical cables are installed directly in trenches or underground ducts. The laying process can be manual or mechanical:Mechanical Traction Laying: Pulleys are installed along the route to prevent cable dragging. The cable must not be bent below its minimum radius or pulled too tightly .Manual Lifting and Laying: Personnel are trained to lift and place the cable uniformly into the trench, ensuring no twisting or bending. A unified command ensures consistent stress along the cable .Post-Laying Checks: The outer sheath is inspected for damage, and any defects are repaired immediately. The insulation resistance of the cable sheath to ground is tested to ensure electrical continuity and protection . Additional protective measures include burying warning tapes above the cable to prevent accidental excavation damage and ensuring proper burial depth according to environmental conditions, such as frost depth or soil type .Standards and ComplianceDirect-buried optical cables are manufactured and tested according to ITU-T L.101 and IEC 60794-3-11 standards, which define mechanical, environmental, and optical performance requirements for buried applications. Compliance ensures interoperability, durability, and safety in outdoor installations . This combination of robust cable design, protective layers, and careful installation ensures that direct-buried optical cables provide reliable, long-term communication infrastructure even in challenging underground environments.