High-Q antisymmetric multimode nanobeam photonic crystal cavities in silicon waveguides.

Antisymmetric multimode nanobeam photonic crystal cavities (AM-NPCs) are proposed and demonstrated in this paper. Due to transverse symmetry-breaking of the antisymmetric multimode periodic waveguide, anti-crossing of the fundamental mode and 1st-order mode is realized and confirmed by band structure calculation. Two-mode filtering and reflection-free cavity filters based on this characteristic are demonstrated. Experimental results on silicon-on-insulator platform shows that broadband (> 100 nm) reflection suppression (< -10 dB) and high-Q (7 × 10) AM-NPCs can be achieved using existed design methodology and fabrication facility. We also explain resonance splitting of the measured transmission spectra and find resonance-enhanced mode-conversion phenomena in the AM-NPCs.