Spiral Micropillar Resonator-Based Unidirectional Channel Drop Filters

We report initial numerical simulations of lateral waveguide-coupled spiral micropillar resonator-based channel drop filters. The spiral shape comprises two joint half-circles of slightly different radii with a notch on one side. Our two-dimensional finite-difference time-domain calculations suggest that such spiral microresonator filters are unidirectional - only the preferred sense of lightwave circulation can be dropped. We observe a drop-port intensity ratio of about 18 dB between the resonance lightwave orbiting in the preferred circulation and the other circulation. In the preferred circulation, we find a drop-to-throughput ratio of ~22 dB. However, we find essentially the same spectral features and multimode resonances in the throughput ports of either lightwave circulations. Steady-state time-averaged intensity mode patterns of the resonances are asymmetrical and suggest possibly chaotic ray orbits. Internal intensity is enhanced by exceeding 14 times in the preferred circulation. We also discuss initial device fabrications on silicon nitride-on-silica substrates