Dynamically adjustable astigmatic transformations for OAM mode identification under atmospheric turbulence

The success of free-space optical communication links employing orbital angular momentum (OAM) shift-keying techniques depends on receiver architectures that can successfully recover the input OAM state under atmospheric turbulence. A method for OAM mode identification under turbulent conditions is selected for resistance to turbulence. Monte-Carlo phase screens are generated using the subharmonic method and modified Von Kármán power spectral density to simulate turbulence. Using spatial light modulators configured for phase modulation that display phase screens made up of superimposed cylindrical and spherical lens phase terms, a method believed to be novel is proposed for generating and customizing interference patterns for OAM mode identification. OAM mode identification based on this method showed low sensitivity to beam alignment and offered reliable performance under strong turbulence. Very high detection accuracy is demonstrated for OAM states between 7 and 63, even under strong turbulence, when using an optimized astigmatic interference pattern generated from these phase screens.