Bloch mode selection in silicon photonic crystal microring resonators.

A novel method of selecting a subset of Bloch modes in silicon-based photonic crystal microring resonators (PhCR)s is demonstrated. Bloch modes in the PhCR are calculated, and their intensity beating patterns are analyzed. Based on the different spatial intensity distribution for each resonance, a subset of resonances is out-coupled using an output coupler waveguide (CWG) which is positioned at an angle θ=90° with respect to the input CWG. As shown in theory and experiment, resonances with an even mode number are selected, while resonances with an odd mode number are rejected. The highest contrast between mode selection and mode rejection is ∼9  dB in the experiments. This approach opens another design freedom for ring resonator-based devices and could potentially reduce the footprint of microring resonator-based multiplexers and add-drop filters.