Local detection of OAM states in weak turbulence with Voronoi-based decision logic: efficiency and intermodal crosstalk

We experimentally study the robustness of local OAM detection under weak turbulence conditions in terms of the induced intermodal crosstalk. We employ a two-port wavefront division interferometer with skewed overlapping light outputs to decouple beam scintillation and local phase distortions. By introducing a Voronoi-based decision logic, we model the turbulent channel as a stochastic displacement within a Voronoi tessellated phase space and evidence a universal behavior for the local intermodal crosstalk, described by master curves of a single dimensionless parameter. Remarkably, such master curves are independent of the specific OAM mode structure and of the turbulence power spectral density. They are determined only by the first-order statistics of optical turbulence. Analytical expressions derived under the Rytov approximation show excellent agreement with experimental data. Finally, we compare our findings with standard approaches relying on full-field OAM modal decomposition. Despite the partial information loss inherent of local sampling, differences in crosstalk probabilities are below the 15% level, thereby validating the robustness of the local OAM detection approach based on Voronoi decision logic for OAM-based FSOC systems in turbulent environments.