FIBEROPTIC SENSOR TECHNOLOGY HANDBOOK

Two cables manufactured in Japan by SUMITOMO
for underground and indoor telecommunication applications
are shown in Figs. 3.26a and 3.26b, respectively.
In the cable designed for underground installations a
set of four multimode fibers, separated by plastic
strings are spaced uniformly around a cushioned central
strength member and surrounded first by a cushioning
sheath and then a second high-strength outer polyethylene
jacket. This cable has an outer diameter of only
18 millimeters. The multifiber cable designed for indoor
test is even smaller. As shown in Fig. 3.25b, it
has an outer polyvinylchloride (PVC) jacket only 8 mm
in outer diameter, and an inner cushioning sheath that
surrounds a set of plastic-jacketed graded-index optical
fibers.
used, especially for relatively short-run applications
where microbend losses introduced by cabling are not
excessive. For low-loss long-run applications, unique
designs aimed at eliminating random bending and the
effects of cabling and environmental disturbances have
been developed that are capable of preventing the addition
of more than 1 or 2 dB/km to the original optical
power losses in the uncabled optical fibers.
Discussions of fiberoptic cable risetime budgets,
power budgets, bussing schemes, design parameters,
environmental factors, and their use in connection with
fiberoptic sensor arrays and telemetry systems is given
in Chapter 6.
PLASTIC STR
PLASTIC TAPE
ISmmOD ~ PESHEATH
mO.D
STRENGTHM
A. underground CABLE B. INDOOR CABLE
Fig. 3.26
Two fiberoptic cables produced by SUMITOMO
of Japan.
A somewhat different cable design is employed
by HITACHI to reduce losses induced by cabling and installation.
As shown in Fig. 3.27, channels are formed
in the outer periphery of a plastic spacer that is reinforced
with a central high-strength metal or plastic
tension member. The individual plastic-jacketed optical
fibers, and copper wires if some are required, fit
loosely in the channels and are held in by a thin outer
sheath. Thus, each fiber is well isolated from both
external and internal stress.
CU WIRE
16mm
SPACER \
O.D
NONMETALLIC CABLE
co MPOUNDCASLE
Fig. 3.27
A fiberoptic cable produced by HITACHI of
Japan.
3.3.3 Summary
From the above brief discussion of current
fiberoptic cabling procedures, it should be clear that
in some cases conventional cabling techniques are being
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