Characterization and performance estimates for polymer, step-index, multi-mode, channel waveguides requires simulation of light propagation in models requiring large numbers of spatial samples using the method of finite-difference time-domain methods (FDTD). As noted in [1], full 3-D solutions for multi-mode waveguides with a cross-section of tens of microns are nontrivial. In many instances, designers are forced to use a ray-tracing model to characterize the channel. However, ray-tracing is not intended to characterize spectral and modal properties. Approximation of Helmholtz equation for slowly varying field in the propagation plane, termed beam propagation methods (BPM), has proved efficient for modeling optical waveguides [2–4]; however, these are primarily intended for modeling waveguides with slowly varying axes of propagation.
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