Artificial wave plates made from sub-wavelength structures

Current and finished studies on the fabrication of polarisation elements made from Si3N4 sub-wavelength gratings will be presented. The form birefringence of a dielectric material is achieved by structuring the surface in the nano meter range. The structure of the presented half wave plates is based on sub-wavelength gratings with period 300 nm. The depth and the duty cycle are optimised to introduce a retardation of π to light at a wavelength of 633nm. The design of a radial polariser is based on sub-wavelength silicon nitride structures introducing a retardation of π, with a space variant orientation of the optical axis. The first results of a transformation of linear polarised light into a radial polarised one will be shown.