Chip-Integrated Geometric Metasurface As a Novel Platform for Directional Coupling and Polarization Sorting by Spin–Orbit Interaction

The focus of the research in metasurfaces has mainly been on the manipulation of the electromagnetic waves in free space during the past few years, which generally require thousands of subwavelength meta-atoms or even more. In this paper, we propose a conceptually new approach that chip-integrated metasurface can behave as a promising compact platform to control the propagation of guided waves when it is integrated with optical waveguide. As a proof of the concept, geometric metasurfaces consisting of only seven rotating anisotropic antennas, both metallic and dielectric, are integrated with silicon-on-insulator waveguide. Benefiting from the geometric phase shift stemming from spin-orbit interaction in metasurfaces, linearly gradient wavefront is generated along the waveguide, which is equivalent to introduce a unidirectional effective wavevector and thus leads to directional coupling. Inspired by the spin dependent gradient wavefront, opposite light flow is excited in the integrated waveguide by switching the handedness of incidence, which may provide a potential pathway to integrated polarization sorters and switchers.