4.4 CABLING OF OPTICAL FIBERS
Early 250-mm outer diameter coated fibers were further protected from the
potential hazards of the cabling process by placement in buffer tubes. The tubes
had an inside diameter many times larger than the diameters of the enclosed fibers.
Fiber length was designed to slightly exceed the length of the buffer tubes, to
introduce fiber slack. This slack was necessary to prevent tensile loading, which
could compromise the optical transmission of the fiber. The buffer tube also con-
tained water-blocking filling compound. The filling compound not only blocked
water from reaching the fiber, but also provided a medium in which the fibers could
freely move past each other during thermal expansions and contractions.Protective