Flat-top drop filter based on a single topology optimized photonic crystal cavity

Outperforming conventional design concepts, a flat-top drop filter has been designed by applying 3D topology optimization to a single waveguide-coupled L3 photonic crystal cavity. Measurements on the design fabricated in silicon-on-insulator material reveal that the pass-band of the drop channel is flat within 0.44 dB over a wavelength range of 9.7 nm with an insertion loss lower than 0.85 dB.