Most often ,an optical fiber must be packaged before it is used is used Packaging involves cabling the fiber,Cabling is an outer protective structure surrounding one or more fibers.It is analogous to the insulation or other materials surrounding a copper wire.Cabling protects copper and fibers environmentally and mechanically from being damaged or degraded in performance.(The additional protection against electrical shock,shorts,and the possibility of fire important to copper is not an issue with dielectric fibers.) The purpose of this chapter is to describe some typical cable structures.
Like their copper counterparts,fiber-optic cables come in a great variety of configurations. Important considerations in any cable are tensile strength,ruggedness,durability,flexibility,environmental resistance,temperature extremes,and even appearance.
The figure shows the main parts of a simplex single-fiber cable.Even though cables come in many varieties,most have the following parts in common:optical fiber; strength member;jacket.
Number Of Optical Fibers
Yet another difference between fiber optic cables is the number of individual optical fibers within them.The number depends on the intended used of the cable and can increase the cable’s size,cost and capacity.because the focus of this book is network cabling and the majority of fiber optic cables you will encounter for networking are tight buffered,we will limit our disccussions here to tight buffered cables.These cables can be divided into three categories based on the number of optical fibers: simplex cables;duplex cables;multifiber cables.
A Simplex Fiber Optic Cables has only one tight -buffered optical fiber inside cable jacket.An example of a simplex cable was shown earlier in this chapter in figure 8.8 becayse simplex cables have only one fiber inside them,only aramid yarn is used for strength and flexibility;the crimped directly to a mechanical connector.simplex fiber optic cables are typically categorized as interconnect cables and are used to make interconnections in front of the patch panel.
Duplex cables,in contrast,have two tight buffered optical fibers inside a single jacket.The most popular use for Duplex Fiber Optic Cable is as a fiber optic LAN backone cable,because all LAN connections need a transmission fiber and a reception fiber.Duplex cable have both inside a Single cable,and running a single cable is of course easier than running two.
Outdoor Fiber Optic Cables
Cables used outside a building must withstand harsher environmental conditions than most indoor cables,outdoor cables are used in applications such as the following:
- Overhead:cable are strung from telephone poles.
- Direct burial:cables are placed directly in a trench dug in the ground and covered
- Indirect burial:this is similar to direct burial,but the cable is inside a duct or conduit.
- Submarine:the cable is underwater,including transoceanic applications.
Such cables must obviously be rugged and durable,since they will be exposed to various extremes.Most cables have additional protective sheaths,for example,a layer of steel armoring protects against rodents that might chew through plastic jackets and into the fiber.Other constructions use a gel compound to fill the cables and eliminate air within the cable.Loose tube buffers,for example ,are so filled to prevent water from seeping into the cable, where it will freeze,expand,and damage the cable.The fibers “float ” in the gel that will not freeze and damage the fiber.