Directional and singular surface plasmon generation in chiral and achiral nanostructures demonstrated by leakage radiation microscopy

Chiral plasmonic nanostructures have received considerable attention due to their peculiar responses such as asymmetric transmission and optical vortex generation, arising from the spin−orbit interactions of light via... [ view full abstract ]

Chiral plasmonic nanostructures have received considerable attention due to their peculiar responses such as asymmetric transmission and optical vortex generation, arising from the spin−orbit interactions of light via plasmonic nanostructures. Owing to the additional degree of freedom added by the incident spin, chiral plasmonic couplers, such as T-shaped aperture arrays, have been reported to induce surface plasmons (SP) emission with spin-controlled directionality, opening new possibilities in manipulation of light at the nanoscale. Due to the inherently confinement of the SP, near-field optical detection has been widely employed in the past to image SP propagation. In the present work, we propose a complementary and versatile far-field approach based on leakage radiation microscopy (LRM) allowing quantitative and polarization analysis in both direct and Fourier spaces. We report on the quantitative characterization and comparison of the directional coupling associated with a chiral and an achiral plasmonic coupler made of T- and Λ- shaped apertures array, respectively. Both spin-driven propagation as well as vortex generation of SP is demonstrated. This study allows clarifying the role of the phase and symmetry breaking in the directional SP launching mechanism which is analytically described in terms multidipolar model. We expect our method to bring an important contribution in future characterization and design optimization of new directional couplers for integrated optics.