Abstract

The WKB method has been widely used to obtain approximate solutions of the guided mode propagation constants for optical waveguides with slowly varying graded-index profiles. One of the key features of the standard method, which is properly applied only to problems with isolated turning points, is the assumption of a constant phase shift (π/4) at a turning point. However, it has long been known that when turning points are not isolated, but are instead near some other transition points, the phase shift is no longer constant [1]. Here, we consider the presence of an index discontinuity near or at a turning point in an optical waveguide and present analytical expressions of the improved phase shift.

© 1992 Optical Society of America