Page 35 - Optical Switching And Networking Handbook

20 Chapter 1

applications.The standard single-mode fiber core is approximately 8
to 10 microns in diameter. Because of its greater information-carrying
capacity, single-mode fiber typically is used for longer distances and
higher-bandwidth applications.
Although it may appear that multimode fibers have higher infor-
mation-carrying capacity, this is not the case. Single-mode fibers
retain the integrity of each light pulse over a longer distance, which
enables more information to be transmitted. This is why multimode
fibers are used for shorter distances and more often in premises at
corporate locations (such as, high-rise offices, campus environments,
and so on).

An Application of Fiberoptics

How are fiberoptics used in every day life? A basic telephone conver-
sation can be used as an analogy for this discussion. In the North
American telecommunications system, a call is transmitted from one
end through an electric cable (copper) to an encoder, which transmits
a signal through a fiberoptic (glass) cable. It then travels through a
repeater, back through the cable, into a decoder and through an elec-
tric cable (copper) into the phone line on the other end. This transi-
tion is shown in Figure 1-10 for the flow of communications.
The sound waves that your voice generates become waves of elec-
tricity in the mouthpiece of your telephone. Rather than electricity
flowing through copper wire to the final destination, fiberoptics
enables electricity to pass through the encoder, which measures the
waves of electricity 8000 times each second. The encoder then con-
verts these waves into on/off pulses of light (operating as invisible
infrared light). The pulses are digitized, enabling them to be read by
the telephone system. The digitized message is received at the
decoder. The decoder converts the laser light back into electricity.
These electrical waves are changed into the sound that you hear on
the phone. This same process works not only for the telephone but
also for other sources that transmit data (such as, computers, televi-
sions, and so on).