Analysis of doped layer step waveguides using dark modes

Results for the analysis of index profiles in steplike waveguide layers formed by proton exchange in LiNbO/sub 3/ and epitaxially grown Ge-doped quartz are presented. Modeling of the profile with real modes is difficult unless many modes propagate. However, an analysis which includes the substrate modes recorded in dark mode measurements greatly increases the data and hence the confidence in the model of the index profile. Analysis using a reflectivity function provides the required precision. The data demonstrate that the epitaxial GeO/sub 2/-doped layer has an index variation with depth.>