Fig. 2. Generation of single-mode dominated circularly polarized vortex beams.

(A) DONR azimuthal arrangements for generating high-purity circularly polarized vortices with (from top to bottom) diverging spiral, concentric, and converging spiral trajectories, which are colored according to the SPP propagation phase. (B) Simulated intensity and phase distributions of the RCP and LCP contributions for the corresponding configurations. First column: The RCP and LCP intensity profiles with their spatial overlap quantified as 0.3, 1.7, and 6.7%, respectively. Second and third columns: The intensity [numerical aperture (NA) = 0.2] and corresponding phase distributions. The LCP intensity distributions have been enhanced by 100, 50, and 10 times, respectively, to improve their visibility. (C) RCP weight indicating the relative RCP contribution in the total emission for the considered configurations and different chirality thresholds. (D) Enhancement of the RCP emission with respect to the emission without metasurfaces as a function of the collecting objective NA.