Rays, Modes and Flux

Abstract

The ray approach, the mode approach and where appropriate a flux approach are briefly reviewed for many guided wave concepts or applications. These comprise eigenvalues, transforms in the angle domain, mode filtering, cycle distance and time, phase and group velocity, attenuation, arrival time, transmission loss, interference patterns, range-dependent environments and horizontal refraction. For example the interference patterns show fuzzy rays, from both the source and the complementary source position, which combine to produce a series of focal points. The duality or trinity of descriptions is shown to be very widely useful and by no means restricted to the angle domain. It is helpful to distinguish between source distances that are finite and those that are infinite. There are many interesting symmetries in definitions, eg phase and group velocity correspond to different kinds of beam displacement at boundaries.