Spin-directional coupling in hyperbolic shear metasurfaces

Optical spin angular momentum defines the polarization properties of light. There is a robust connection between the directions of wave propagation and optical spin angular momentum. Here, we investigate the hyperbolic shear metasurface, a recently introduced type of metasurface with axial dispersion, in the context of optical spin and polarization control of surface electromagnetic waves. We show that shear metasurfaces provide greater control over optical spin than conventional anisotropic and hyperbolic metasurfaces, enabling more possible polarization states and spatial orientations of spin angular momentum with respect to wave propagation direction. It enables on-chip routing of surface waves with reconfigurable polarization paving a way towards compact planar polarizers, couplers, sensors and other photonic devices.