Detecting orbital angular momentum in optical vortex based on ptychographic imaging

Zhaohui Li; Delian Liu

doi:10.1117/12.2579685

7 October 2020 Detecting orbital angular momentum in optical vortex based on ptychographic imaging

Zhaohui Li, Delian Liu

Proceedings Volume 11571, Optics Frontier Online 2020: Optics Imaging and Display; 115710D (2020) https://doi.org/10.1117/12.2579685
Event: Optics Frontiers Online 2020: Optics Imaging and Display (OFO-1), 2020, Shanghai, China

Abstract

A new orbital angular momentum (OAM) model detection approach is proposed by extending the coherent diffraction ptychographic imaging (CDPI) approach. A beam carrying an OAM is a vortex beam which has a doughnut-shape intensity and a helical phase with a topological charge same as the mode index of OAM. To recover its phase helix, a vortex beam radiates a template region-by-region, in grid fashion or scanning way, and the adjacent radiated regions should be overlapped partially. The exit wave field of each radiated region produces a far-field diffraction intensity pattern at the back focal plane of a lens. After recording the intensity patterns, the wavefront of the incident beam can be reconstructed from the patterns via ptychographic iterative engine (PIE). In this paper, we first determine the diffraction intensity recording requirements by analyzing diffraction features of a vortex beam. We second derive the spatial sample requirements in ptychographic OAM detection, for a convergence to the non-ambiguity solution of a helical wavefront, involving two case, with and without a prior knowledge about the template function. Finally, numerical and optical experiments confirm that the helical wavefront of a vortex beam can be accurately recovered by conventional PIE when template is treated as reference. And using a modified regularized PIE (rPIE), the wavefront of incident vortex beam and the unknown transmission function of template can be reconstructed simultaneously.

Citation Download Citation

Zhaohui Li and Delian Liu "Detecting orbital angular momentum in optical vortex based on ptychographic imaging", Proc. SPIE 11571, Optics Frontier Online 2020: Optics Imaging and Display, 115710D (7 October 2020); https://doi.org/10.1117/12.2579685

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KEYWORDS

Diffraction

Wavefronts

Far-field diffraction

Optical vortices

Coherence imaging

Reconstruction algorithms

Spatial frequencies

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