A nanophotonic all-optical diode for non-reciprocal transmission of circularly polarized lights

All optical diodes (AODs) play an important role in quantum optics and information processing, in which the information is encoded by photons. Only circularly polarized lights are able to carry the spin states of photons, which has been intensively used in quantum computing and information processing and enable new research fields, such as chiral quantum optics. An ideal AOD should be able to work with arbitrary polarizations states, including circularly polarized lights, which has not been demonstrated yet. In this paper, we theoretically demonstrate for the first time a nanophotonic AOD that is able to work with circularly polarized lights. The AOD nanostructure is based on a heterostructure of two-dimension silica and silicon photonic crystals (PhCs). By controlling the effective refractive indices of the PhCs and using an inclined interface, we are able to exploit generalized total reflection principle to achieve non-reciprocal transmission of circularly polarized lights. In addition, the nanophotonic AOD is able to achieve high forward transmittance greater than 0.6 and high contrast ratio close to 1 in a broad wavelength range of 1497 nm to 1666 nm. The designed nanophotonic AOD will find broad applications in optical quantum information processing and computing.