Abstract

Orbital angular momentum (OAM) mode division multiplexing and encoding have been widely investigated for achieving higher information capacity and performance in both classical and quantum communication systems [1]. A critical component in such systems is an OAM mode sorter that can efficiently sort different OAM modes exp(ilθ) according to the mode index l. To this end, an elegant scheme is to transform the vortex phase exp(ilθ) of OAM modes to a linear phase exp(ilv / β) of tilted plane waves through geometrical transformations, so that they can be separated in the focal plane of a lens. A log-polar transformation was firstly employed [2] and recently a spiral transformation has been proposed to achieve high-resolution OAM mode sorting by the authors [3].

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