Q-plate
A q-plate is an optical device which can generate light beams with orbital angular momentum of light (OAM) from a beam with well-defined Spin angular momentum of light (SAM). It is currently realized using liquid crystals, polymers or sub-wavelength gratings. A method for generating orbital angular momentum of light (OAM) is based on the SAM-OAM coupling that may occur in a medium which is both anisotropic and inhomogeneous. In the case of the q-plate, the OAM sign is controlled by the input polarization.