Photonic metacrystal cavities with dual taper design for higher Q-factor

We report a design approach for achieving higher quality (Q) factor photonic crystal nanobeam cavities by exploiting design freedoms available in photonic metacrystal unit cells. By tapering the unit cells between the central cavity and end mirrors using two different tapering strategies in series, a larger band gap is obtainable, and consequently, a higher Q cavity can be designed. We show that a silicon nitride bowtie photonic metacrystal nanobeam (PhMCNB) cavity in water designed with unit cells that first taper in nanobeam width and then in rotation angle achieves more than an eight-fold increase in Q compared to a similar PhMCNB cavity designed only with tapering of the nanobeam width using the same total number of tapering unit cells. The dual taper design approach could also be employed to reduce the footprint of a PhMCNB cavity by more than 25% compared to a nanobeam width-tapered PhMCNB cavity that has a similar Q.