Loose tube cable: small, thin plastic tubes containing as many as a dozen 250 micron buffered fibers used to protect fibers in cables rated for outside plant use. They allow the fibers to be isolated from high pulling tension and can be filled with water-blocking materials to prevent moisture entry.
Loose tube cables are the most widely used cables for outside plant trunks because it offers the best protection for the fibers under high pulling tensions and can be easily protected from moisture with water-blocking gel or tapes.These cables are composed of several fibers together inside a small plastic tube, which are in turn wound around a central strength member, surrounded by aramid strength members and jacketed, providing a small, high fiber count cable. This type of cable is ideal for outside plant trunking applications, as it can be made with the loose tubes filled with gel or water absorbent powder to prevent harm to the fibers from water. It can be used in conduits, strung overhead or buried directly into the ground. Some outdoor cables may have double jackets with a metallic armor between them to protect from chewing by rodents or kevlar for strength to allow pulling by the jackets. Since the fibers have only a thin buffer coating, they must be carefully handled and protected to prevent damage. Loose tube cables with singlemode fibers are generally terminated by spicing pigtails onto the fibers and protecting them in a splice closure. Multimode loose tube cables can be terminated directly by installing a breakout kit, also called a furcation or fan-out kit, which sleeves each fiber for protection.
Loose tube materials for loose tube cables need to possess a relatively high modulus and good processability. During manufacture, optical fiber is fed into the loose tube at a faster rate than it is being produced so that the optical fiber is laid helically within the tube.
To buffer the fibers from each other and from any perturbations on the tube walls, the loose tube is filled with a gel compound similar in composition to the water blocking gels in conventional telecommunication cables. The loose tube material must therefore be compatible with the gel as in conventional cable insulation.
Structure of a Loose Tube Fiber Optic Cable
Elements in a loose tube fiber optic cable:
1. Multiple 250um coated bare fibers (in loose tube)
2. One or more loose tubes holding 250um bare fibers. Loose tubes strand around the central strength member.
3. Moisture blocking gel in each loose tube for water blocking and protection of 250um fibers
4. Central strength member (in the center of the cable and is stranded around by loose tubes)
5. Aramid Yarn as strength member
6. Ripcord (for easy removal of outer jacket)
7. Outer jacket (Polyethylene is most common for outdoor cables because of its moisture resistant, abrasion resistant and stable over wide temperature range characteristics.)
. Good mechanical and temperature performance
. High strength loose tube that is hydrolysis resistant
. Special tube filling compound ensure a critical protection of fiber
. Two parallel steel wires ensure tensile strength
. PE sheath protects cable from ultraviolet radiation
. Small diameter, light weight and friendly installation
. Long delivery length
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