Optical-Fiber Packaging and Its Influence on Fiber Straightness and Loss

Surprisingly small external forces can cause lateral deformations, mode coupling, and optical loss in clad fibers. For example, minute irregularities in the machined surface of a metal drum suffice to cause substantia] loss in fibers wound on this drum with only a few grams of tension. 1 (An interesting and valuable study of this subject is described by W. B. Gardner. 2 ) The pressure exerted on the individual fiber in a cable will almost certainly be considerably stronger and less uniform. The concern with this effect has heightened recently with the notion that lowest loss values are measured almost invariably in connection with extremely small mode coupling and after carefully eliminating external forces on the fiber.3-r> Maintaining these loss values in a cable may require better fiber and, more importantly, effective jackets designed to optimally shield against external forces. This paper addresses the latter problem. After gaining some insight into fiber deformation, we compute the excess transmission loss6 resulting from statistical surface variations and lateral pressures affecting the fiber. The reader who is mainly interested in the results of this theory may wish to turn to Sections V or VI immediately, where practical examples and suggestions for an improved jacket design are discussed. We show that some care in this 245