Abstract
A compact and high-resolution optical orbital angular momentum (OAM) sorter is proposed and demonstrated. The sorter comprises a quadratic fan-out mapper and a dual-phase corrector positioned in the pupil plane and the Fourier plane, respectively. The optical system is greatly simplified compared to previous demonstrations of OAM sorting, and the performance in resolution and efficiency is maintained. A folded configuration is set up using a single reflective spatial light modulator (SLM) to demonstrate the validity of the scheme. The two phase elements are implemented on the left and right halves of the SLM and connected by a right-angle prism. Experimental results demonstrate the high resolution of the compact OAM sorter, and the current limit in efficiency can be overcome by replacing with transmissive SLMs and removing the beam splitters. This novel scheme paves the way for the miniaturization and integration of high-resolution OAM sorters.
Highlights
Light with helical phase fronts is associated with orbital angular momentum (OAM) states denoted as φ(r, φ) = exp(ilφ), where φ is the angular coordinate and l can take any integer value.[1,2]
Efficient separation of light beams based on their OAM quantum number l is of great importance in classical and quantum information systems.[7]
A Mach–Zehnder interferometer with Dove prisms can achieve the separation of OAM states, and it requires N 1 cascaded interferometers to separate N modes.[10]
Summary
The finite size of the unwrapped beam results in overlap between two neighboring OAM states. To reduce the overlap caused by finite size diffraction, a diffractive fan-out element and a corresponding phase corrector can be placed following the two-piece log-polar optics to increase the resolution of the OAM sorter. The first element in our scheme is a quadratic fan-out mapper that simultaneously achieves the log-polar transformation, fanout beam copying, and beam focusing.
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