All-dielectric Metasurface System for Sorting and Shaping of Orbital Angular Momentum Modes

A light beam with orbital angular momentum (OAM) has a helical phase front where the phase increases with the azimuthal angle, giving a donut-shaped intensity profile [1], [2]. These OAM beams have been of great interest in optical communications due to their innate property of orthogonality, allowing OAM beams with different OAM topological charge <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$l$</tex> to be combined by multiplexing, propagated through an optical fiber and separated again into the original beams [2]. The separation of the beams can be done by the use of phase masks which can apply a phase shift on an incoming beam [3]. The phase masks can be realized as silicon nanopillar metasurfaces, and through design a system of three metasurfaces in series can be created that can sort an OAM-multiplexed beam passively, efficiently and with a small footprint.