Main Parts Of A Fiber Optic Cable

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.

The Common Ways Of Referring To Fibers

The cable buffer is one of two types:loose buffer or tight buffer.The loose buffer uses a hard plastic tube being in an inside diameter several times that of the fiber.One or more fibers lie within the buffer tube.The tube isolates the fiber from the rest of the cable and the mechanical forces operating in it.The tight buffer has a plastic directly applied over the fiber coating.This construction provides better crush and impact resistance.It does not,however,protect the fibre as well from the stresses of temperature variations.

When a table contains several layers of jacketing and protective material,the outer layers are often called the sheath.The jacket becomes the layer directly protecting fibers,and the sheath refers to additional layers.This terminology is particularly common in the telephone industry.

INDOOR CABLES

Cables for indoor applications include the following:

Simplex cables

Duplex cables

Multiplier cables

Hey-,light-,and plenum-duty cables

Breakout cables

Ribbon cables

Although these categories overlap,they represent the common ways of referring to fibers.Figure 7-5 shows cross sections of several typical cable types.

Simplex Fiber Optic Cables

Simplex cables contain single fiber. "Simplex"is a term used in electronics to indicate one-way transmission.Since a fiber carries signals in only one direction,from transmitter to receiver,a simplex cable allows only one-way communication.

Duplex Fiber Optic Cable

Duplex cables contain two optical two optical fibers.Duplex relates to two-way communication.One fiber carries signals in one direction;the other fiber carries signals in the other direction.(Of course,duplex operation is possible with two simplex cables.) Figure compares simplex and duplex operations.

In appearance,duplex cables resemble two simplex cables whose jackets have been bonded together,similar to the jacket of common lamp cords.Ripcord constructions,which allows the two cables to be easily separated,are popular.

Duplex cable is used instead of two simplex cables for aesthetics and convenience, it is easier to handle a single duplex cable,there is less chance of the two channels becoming confused,and the appearance is more pleasing.Remember,the power cord from your lamps is a duplex cable that could easily be two separate wires.Make a single duplex cord in the lamp not make better sense? The same reasoning prevails with fiber optic cables.

Most Outdoor Fiber Optic Cables contain many fibers.The strength member is usually a large steel or fiberglass rod in the center,although small steel strands in the outer sheath are also used, most high-fiber count cables divide the fibers among several buffer tubes.

In cables containing many fibers,not all the fibers are always used at first.Some are kept as spares to replace fibers that fail in the future.Others are saved for future expansion,as the demands for additional capacity dictate,In stalling a cable can be expensive.Having extra fibers in place when they are needed saves future installation costs of additional fibers and cables.It pays to think ahead.