In this work, we consider a wave propagation problem in a two-dimensional (
2-D) waveguide. The problem arises in the study of light in optical fibers.
We construct a transform theory as a framework for studying this problem.
A explicit representation for the solution to problems involving light sour
ces is derived. We derive a decay rate for the nonguided part of the soluti
on in the direction of the core. The approach is also amenable to computati
ons, and we demonstrate this in numerical examples for the case of slab wav
eguides.