Surface States on Photonic Crystals As Hybrid Dielectric Metasurface Bound States of the Termination Layer

Dark resonant surface states on photonic crystals are of great technological interest for providing easily accessible, very high Q-factor concentration of light into subwavelength volumes and for their ability to help control and direct radiation emitted from photonic crystal surfaces. However, in general, photonic crystals require specific surface corrugations in order to support dark surface states, that is, states localized to the surface that do not radiate into either a photonic crystal or the surrounding free space. On the other hand, single layers of photonic crystals can form dielectric metasurfaces that support dark bound states. We develop a theory and demonstrate numerically and experimentally that corrugation-induced surface states on photonic crystals can be interpreted as hybrid modes arising from coupling between the dark bound states of the dielectric metasurface formed by the isolated corrugation layer and the bulk photonic crystal. We investigate the interaction and hybridization of the various possible surface modes and how their dispersion properties can be controlled. We show the emergence of a photonic crystal without surface states, but with independent dark bound states of the isolated corrugation layer for weak coupling, and show how the metasurface dark states disappear for strong coupling in the limit of an uncorrugated photonic crystal. Our theory for the semi-infinite photonic crystal is demonstrated to also apply to the discretized, resonant surface states of a finite photonic crystal