Turbulence-Invariant Polarization Readout via Spin-Dependent Angular Mapping

Abstract Atmospheric turbulence disrupts spatial coherence in free-space optical (FSO) systems, fundamentally limiting the reliable extraction of optical information encoded in intensity, phase, or spatial degrees of freedom. While polarization is intrinsically immune to scalar turbulence, its robust detection remains challenging due to the lack of turbulence-invariant observables. Here, we establish a general spin-dependent phase-difference-to-angle (PDA) mapping mechanism that converts polarization states into global angular intensity modulations, forming a class of turbulence-invariant observables accessible via intensity-only detection. This mapping, enabled by spin–orbit coupling in a vortex waveplate, eliminates the need for wavefront reconstruction and preserves information integrity under strong turbulence. We experimentally validate turbulence-invariant polarization readout over an equivalent long-distance FSO link under both weak and strong turbulence, achieving error rates below 2%. Leveraging this invariant readout, we further demonstrate a 100-Gbps-class orbital angular momentum polarization shift keying (OAMPolSK) communication scheme, with a 12.43-dB reduction in the required optical power compared with PAM-6 at a reference SER of 0.1 under the implemented experimental configurations. Our results demonstrate a turbulence-resilient optical information extraction strategy, in which polarization information is mapped onto a robust angular observable, offering a potential approach for optical communication and sensing in complex environments.