Overview

Optical fibers, ideally, would be immune to environmental influences, mechanical stresses, and other effects. As is always the case, the system designer cannot ignore these issues. This chapter is included to provide some insight into the practical problems that can develop with these very long, thin slivers of glass. Finally, fibers have been deployed in telecom cables for decades, and statistics and lessons learned about the real-world mechanical properties are brought to light (pun intended) herein.

The rules in this chapter provide some information on how fibers react to mechanical stress from bending or cleaving, exposure to humidity, and other effects. For example, stress or temperature change in a fiber can change the wavelength properties of gratings built into the fiber. The interested reader will note that this topic is also discussed in other chapters of the book. Another factor in the performance of fiber optics includes the mechanical history of the installed system. One of our rules advises that a requirement for testing should be to ensure that "in-field" use conditions will be within the expected guidelines. We include in this topic the maximum stress that the fiber should experience before, during, and after installation. Interestingly, the strength of the fiber is affected by its stress history.

Most fiber mechanical failures derive from crack propagation and interaction of the fiber with the strength members in the cable. We address these issues, concentrating on quantitative expressions for the relationship between stress and a reduction in component life. At the...