Implementing achromatic diffractive waveplate optics with thin, uniformly birefringent layers

Abstract

Vector Vortex Coronagraphs can potentially exhibit superior performance in terms of starlight rejection compared to alternative coronagraph technologies aimed at exoplanet detection. Vector Vortex Waveplates (VVWs) acting as coronagraph masks are micrometer-thin with nanometer-smooth continuous structure when fabricated using liquid crystal polymers (LCPs). LCPs allow different architectures for spectrally broadband performance. In this paper, we investigate classical, so-called Pancharatnam, architectures of a system of waveplates, applied to diffractive waveplates, particularly VVWs. These classical architectures involve multiple birefringent layers with angular offsets between each pair of adjacent layers. Along with ensuring high efficiency/contrast with simple structures, they allow manufacturing advantages due to the use of a single material with no additional internal twist angle optimization requirement, and high yield due to separate fabrication of individual films. The technological challenge of combining films with high resolution patterning is overcome by using micromechanical alignment tools which also allow exploring the effects of alignment between the films for controlling optical properties of the system of diffractive waveplates.