Topology optimization of a photonic crystal waveguide termination to maximize directional emission

Topology optimization based on nonlinear programming techniques and design sensitivity analysis are used to maximize directional emission from a waveguide termination in a two-dimensional square lattice rods-in-air photonic crystal. Maximizing directional emission from a photonic crystal waveguide termination is desirable since a horn antenna style termination of comparable functionality is very large, while small simple terminations show strong angular spread. The optimized waveguide termination designed here is compact and exhibits a fivefold increase in power incident upon the target area over the simple termination. This improvement is achieved by creating surface modes that interfere to produce highly directional emission. (C) 2005 American Institute of Physics.