Abstract

If optical fiber losses of a few dB/km are to be realized in fiber cables, considerable care will have to be taken in packaging these fibers. Microscopic thickness variations of the coating or filler material in between the fibers, for example, cause lateral deformations (microbending), mode coupling, and loss, when the fibers are pressed against each other in the cable. The deformations are usually of a random nature and certain spectral components are most critical in causing coupling and loss.¹ Our analysis reveals that the best cure for this problem is a cable design which exploits and reinforces the inherent stiffness of the fiber to keep it in its naturally straight condition. We describe various implementations of this idea and compute the resulting excess loss. We also model the physical environment which the fiber finds in such a cable by a microscopically rough drum surface onto which the fiber is wound with a controlled tensile winding force. In this case, the drum surface elasticity should equal that of the coating material in the cable; the surface statistics should be equivalent to the thickness statistics of the coating; and the ratio of tensile winding force to drum radius should equal the pressure (lateral force per unit length of fiber) to which each fiber is subjected in the cable.

© 1975 Optical Society of America