3 years ago

Free-space propagation of high-dimensional structured optical fields in an urban environment

Martin P. J. Lavery, Peter Banzer, Gerd Leuchs, Kevin Günthner, Christian Peuntinger, Christoph Marquardt, Miles J. Padgett, Dominique Elser, Robert W. Boyd

Spatially structured optical fields have been used to enhance the functionality of a wide variety of systems that use light for sensing or information transfer. As higher-dimensional modes become a solution of choice in optical systems, it is important to develop channel models that suitably predict the effect of atmospheric turbulence on these modes. We investigate the propagation of a set of orthogonal spatial modes across a free-space channel between two buildings separated by 1.6 km. Given the circular geometry of a common optical lens, the orthogonal mode set we choose to implement is that described by the Laguerre-Gaussian (LG) field equations. Our study focuses on the preservation of phase purity, which is vital for spatial multiplexing and any system requiring full quantum-state tomography. We present experimental data for the modal degradation in a real urban environment and draw a comparison to recognized theoretical predictions of the link. Our findings indicate that adaptations to channel models are required to simulate the effects of atmospheric turbulence placed on high-dimensional structured modes that propagate over a long distance. Our study indicates that with mitigation of vortex splitting, potentially through precorrection techniques, one could overcome the challenges in a real point-to-point free-space channel in an urban environment.

Publisher URL: http://advances.sciencemag.org/cgi/content/short/3/10/e1700552

DOI: 10.1126/sciadv.1700552

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