The University of British Columbia

Here we point out that in their comment Bastiaansen et al. {[}Appl. Opt, 33, this issue (1994)] overlooked both the context of and the assumptions in Jaeger and Lai's paper {[}Appl. Opt, 31, 7183-7190 (1992)]. This omission appears to have resulted in their applying the Jaeger and Lai method inappropriately to a particular rib waveguide structure, yielding strange results. Therefore we present the underlying theory and ad hoc a simple and theoretically consistent method for applying it to rib waveguides. We demonstrate that good results may be obtained for a weakly guiding rib waveguide structure when field separability may be assumed, i.e., one that better meets the assumptions; this structure was chosen because numerical results were available for comparison.