Page 138 - Optical Communications Essentials

Connectors and Splices

128 Chapter Eight

The number of abrasives used in this step-down approach depends on the
degree of smoothness that is desired. Fiber inspection and cleanliness are impor-
tant during each step of fiber polishing. This inspection is done visually by the use
of a standard microscope at 200 to 400 times magnification. Figure 8.8 gives an
example of a polishing machine that can prepare several fibers simultaneously.

8.4.2. Controlled fracture
The controlled-fracture techniques are based on score-and-break methods for
cleaving fibers. In this operation, the fiber to be cleaved is first scratched to
create a stress concentration at the surface. The fiber is then bent over a curved
surface while tension is applied simultaneously, as shown in Fig. 8.9. This action
produces a stress distribution across the fiber. The maximum stress occurs at
the scratch point so that a crack starts to propagate through the fiber, resulting
in a highly smooth and perpendicular end face.
A number of different tools based on the controlled-fracture technique are
available commercially for both factory and field uses.

8.4.3. End-face quality
The controlled-fracture method requires careful control of the curvature of the
fiber and of the amount of tension applied. If the stress distribution across the

Figure 8.8. Example of a polishing machine that can prepare several fibers
simultaneously. (Photo courtesy of Domaille Engineering; www.Domaille
Engineering. com.)

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