Metasurface Measuring Twisted Light in Turbulence

Practical free-space communication systems suffer from turbulence-induced phase distortions to propagating beams, destroying the orthogonality of orbital angular momentum (OAM) modes used for space-division multiplexing and introducing modal crosstalk. Here we present the design and use of an ultrathin OAM mode-sorting metasurface for investigating the deterioration of OAM orthogonality under different turbulence conditions, offering a compact, fast and efficient way to measure the OAM spectrum.