70 CHAPTER 2. OPTICAL FIBERS
Figure 2.22: Apparatus used for fiber drawing.in turn changes the photodiode current. This current change acts as a signal for a
servocontrol mechanism that adjusts the winding rate of the fiber. The fiber diameter
can be kept constant to within 0.1% by this technique. A polymer coating is applied to
the fiber during the drawing step. It serves a dual purpose, as it provides mechanical
protection and preserves the transmission properties of the fiber. The diameter of the
coated fiber is typically 250μm, although it can be as large as 900μm when multiple
coatings are used. The tensile strength of the fiber is monitored during its winding
on the drum. The winding rate is typically 0.2–0.5 m/s. Several hours are required
to convert a single preform into a fiber of about 5 km length. This brief discussion
is intended to give a general idea. The fabrication of optical fiber generally requires
attention to a large number of engineering details discussed in several texts [17].
2.7.3 Cables and Connectors.....................
Cabling of fibers is necessary to protect them from deterioration during transportation
and installation [92]. Cable design depends on the type of application. For some