Abstract

Review of the effects of different perturbations of optical fibers shows that their physical effects are generally identical: that usually is the transfer of the lower-order modes (as measured in the far field) to the higher-order modes of the fiber. This is so for the general classes of microbends, macrobends, pressure variations, temperature variations, and chemical changes. This means that rather than being truly different perturbations, they are physically really the same thing. Each represents a true gauge-invariant perturbation plus a piece that is merely a gauge transformation. Each perturbation is then transformable, and their apparent differences are physically trivial. We take as our points of departure the perturbed fiber discussions of Snyder and Love¹ and Hill’s² analysis of differential equations from their group invariance properties. We analyze the modal structure of unperturbed fiber in terms of the invariance group of the wave equation for the appropriate fiber geometries and boundary conditions and then show how their perturbations consist of a true physical piece and insignificant parts that are just gauge transformations of each other.

© 1987 Optical Society of America