Vector Vortex Waveplates with Tunable Spectrum and Switchable Topological Charge

The contrast of astronomical coronagraphs based on vector vortex waveplates (VWs) depends critically on precision of fulfilment of half-wave retardation condition for the desired wavelength range. The structure of VWs designed for operation in broad spectral bands is typically rather complex comprising three-dimensional modulation patterns that in practice are obtained in layer-by-layer deposition of liquid crystal polymers (LCPs). Physical properties of each of those layers - thickness, retardation, and orientation modulation pattern, along with layer integrity and quality - need to be maintained with very high precision to ensure contrast requirements of coronagraphs. This inevitably reduces the yield and affects the quality of high contrast VWs. We discuss opportunities of tuning the retardation values of VWs using electric field for liquid crystal (LC) based VWs as well as temperature and optical radiation for LCPs. LC VWs allow also tuning the spectral range of operation and switching the topological charge of the effective VW system.