Topology optimization of a wavelength-selective Y-junction for 2D photonic crystal waveguides

The topology optimization ( TO) technique has been employed to design a wavelength-selective Y-junction for two-dimensional photonic crystal slab waveguides. The TO design exhibits high-pass and low-pass filtering spectra for two different paths in the Y-junction. Large cross-talk suppression of -20 dB at wavelength separation of 30 nm has also been obtained. These calculated characteristics have been experimentally verified by using a GaAs-based air-bridge-type photonic crystal waveguide. The TO-designed Y-junction contributes to an essential component for a new photonic crystal-based all-optical flip-flop, PC-FF.