Efficient side-coupling to photonic crystal nanobeam cavities via state-space overlap

We present design guidelines for realizing side-coupled photonic crystal nanobeam (PCN) cavities with efficient coupling to low-order resonances through adjusting the overlap of the PCN cavity mode and a feeding bus waveguide in both physical and k-space. We show that optimal side-coupled configurations function at a non-zero k-vector offset between the bus waveguide and PCN cavity modes. The straightforward design of side-coupled PCNs with high-contrast resonances opens the door to their practical implementation in multiplexed, on-chip photonic devices.