Page 28 - Optical Switching And Networking Handbook

Introduction to Optical Communications 13

in the early 1980s, the carriers built national backbone systems of
single-mode fiber with 1300-nanometer sources.This technology has
spread into other telecommunications applications and remains the
standard for most fiberoptic systems.
However, a new generation of single-mode systems found applica-
tion in submarine cables and systems serving large numbers of sub-
scribers. They operate at 1.55 microns. Fiber loss is 0.2 to 0.3 decibel
per kilometer, enabling even longer repeater spacing. More impor-
tantly, erbium-doped optical fibers serve as optical amplifiers at this
wavelength, avoiding the need for electro-optical regenerators.
Submarine cables with optical amplifiers operate at speeds up to
5 gigabits per second (Gbps). These can be upgraded from lower
speeds simply by changing terminal electronics. Optical amplifiers
also are attractive for fiber systems delivering the same signals to
many terminals because the fiber amplifiers can compensate for
losses in dividing the signals among many terminals.
The biggest challenge remaining for fiberoptics is economic.Today,
telephone and cable television companies can cost-justify installing
fiber links to remote sites serving tens to a few hundred customers.
Terminal equipment remains too expensive to justify installing fiber
all the way to the home, at least for now. Instead, cable and phone
companies run twisted-pair wire or coaxial cable from optical net-
work units along the side of the road to individual homes. Time will
see how long this lasts, although many people believe that fiber to
the home (FFTH) is already upon us.

Fiber Justification

Many reasons exist for the initial introduction of fiber, but some of
the strongest reasons are as follows:

Bandwidth compared with copper Taken in bulk, it
would take 33 tons of copper to transmit the same amount
of information handled by 1/4 pound of optical fiber.
Strength The tinsel strength of the fiber is greater than that
of steel.