A Metasurface-Based Scalar Vortex Phase Mask Design

The technique best suited for direct imaging of exoplanets is high contrast direct imaging using a coronagraph. In particular, the vortex coronagraph has proven to be one of the most promising approaches for imaging Earth-like planets with future space-based optical/infrared telescopes. However, differential polarization aberrations become difficult to control at the high contrasts required for this goal, requiring careful wavefront control in both polarizations independently. While the well-established vector vortex coronagraph is polarization-sensitive, a polarization-independent (scalar) vortex coronagraph circumvents this issue since it imprints the same phase ramp regardless of polarization [1]. Metasurfaces provide a promising approach for implementing a scalar vortex with relatively simple microfabrication techniques. The freedom introduced by different design topologies makes them a prime candidate for achieving achromatic performance.