Prism Excitation of Highly Multimode Deep Planar Waveguides

Abstract

The period-of-propagation length concept for guided modes in planar waveguides is used to derive a simple expression for the coupling length of prism coupler. It is shown that the prism coupling strength for deep multimode waveguides strongly depends on the shape of the refractive index profile as well as-except for the linear profile -on the mode order.Further it is shown that for multimode waveguides simultaneous excitation of several guided modes is typical. Arising interference effects at the waveguide surface are explained and illustrated by experimental results obtained with ion-exchanged waveguides in glass.