Mumbai University > Electronics and Telecommunication > Sem7 > Optical Communication and Networks

Marks: 5M

Year: May 2012

• Cabling of fibers is necessary to protect them from deterioration during transportation and installation.

• Cable design depends on the type of application. For some applications it may be enough to buffer the fiber by placing it inside a plastic jacket (light duty cables).

• For others the cable must be made mechanically strong by using strengthening elements such as steel rods (heavy duty cables).

• A light-duty cable is made by surrounding the fiber by a buffer jacket of hard plastic. A tight jacket can be provided by applying a buffer plastic coating of 0.5–1 mm thickness on top of the primary coating applied during the drawing process.

• In an alternative approach the fiber lies loosely inside a plastic tube. Microbending losses are nearly eliminated in this loose-tube construction, since the fiber can adjust itself within the tube. This construction can also be used to make multifiber cables by using a slotted tube with a different slot for each fiber.

• Heavy-duty cables use steel or a strong polymer such as Kevlar to provide the mechanical strength.

• In the loose-tube construction, fiber glass rods embedded in polyurethane and a Kevlar jacket provide the necessary mechanical strength (left drawing).

• The same design can be extended to multifiber cables by placing several loose-tube fibers around a central steel core (middle drawing).

• When a large number of fibers need to be placed inside a single cable, a ribbon cable is used (right drawing). The ribbon is manufactured by packaging typically 12 fibers between two polyester tapes. Several ribbons are then stacked into a rectangular array which is placed inside a polyethylene tube. The mechanical strength is provided by using steel rods in the two outermost polyethylene jackets. The outer diameter of such fiber cables is about 1–1.5 cm.