Abstract

Discontinuities formed either by a local change in waveguide depth or by an abrupt change in the effective index of refraction have important effects on the design and operation of optical components in the waveguide. Our work deals with a structure made up of two waveguides with different geometries and material properties that meet at a planar interface. The abrupt discontinuity causes reflection and radiation, and polarization conversion takes place at the discontinuity, leading to mode conversion. Computed values of the power losses and the power converted to a different polarization are presented. Our experimental work involves adjacent double-diffused (deep) and single-diffused (shallow) waveguides made by Ag⁺- Na⁺ ion-exchange in BK-7 glass. By using the prism-coupling technique, we have verified the excitation of all guided modes in the double-diffused region when a single mode impinges on the discontinuity. The intensity profiles of the modes excited in the double-diffused region are displayed by an image-processing system. We have shown experimentally that annealing the waveguide suppresses mode conversion and that a given mode will propagate smoothly across the boundary.

© 1990 Optical Society of America