Loose tube construction, tubes jelly filled, elements (tubes and filler rods) and water blocking yarns laid up around non-metallic central strength member, polyester yarns used to bind the cable core, water blocking tape and mica tape, dry core, then LSZH outer sheath with. Loose tube construction, tubes jelly filled, elements (tubes and filler rods) and water blocking yarns laid up around non-metallic central strength member, polyester yarns used to bind the cable core, water blocking tape and mica tape, dry core, then LSZH outer sheath with. In fiber-optic communication, a single-mode optical fiber, also known as fundamental- or mono-mode, is an optical fiber designed to carry only a single mode of light - the transverse mode. Fiber. A 4-core fiber optic cable is a type of cable that contains four individual optical fibers within a single protective jacket. These fibers are used to transmit data as light signals, offering high-speed data transfer capabilities over long distances with minimal loss. It supports long-haul transmissions over a single light path and has low loss for one mode while having much higher losses for all other modes.