Hybrid unidirectional meta-coupler for vertical incidence to a high-refractive-index waveguide in telecom wavelength

Unidirectional optical manipulation, especially the coupling from a vertical light beam to a waveguide unidirectionally, is desirable in photonic integration. We first propose a hybrid unidirectional meta-coupler for vertical incidence to a high-refractive-index waveguide in telecom wavelength, a periodic plasmonic metasurface composed of metal-insulator-metal unit cells is used for phase matching. Three designs are given for devices working around wavelengths 0.85, 1.31, and 1.55 μm. The simulated coupling efficiencies are all around 70%, and the 1 dB coupling bandwidths are 29, 82, and 105 nm, respectively. Our approach paves the way for the applications of optical metasurfaces to planar lightwave circuits.