Role of resonances in tapered bi-modal plasmonic nanoslit metasurfaces for multi-functional nonlocal spatial filtering

In this paper, the roles of multiple resonances in a tapered bi-modal plasmonic nanoslit metasurface for multi-functional and efficient nonlocal spatial frequency filtering are rigorously studied. The physical mechanisms and design guidelines to engineer wavelength-dependent multiple transfer functions in a single plasmonic metasurface are suggested by analyzing vertical waveguiding and resonance, transversal momentum-matching, and incidence angle and wavelength-dependent light funneling phenomena. In particular, the interplay between multiple resonances enables multi-functional and efficient spatial filtering such as wavelength-dependent low-pass or high-pass filtering in a single nonlocal metasurface. The numerical results obtained from electromagnetic full-field simulations are explained phenomenologically based on the harmonic oscillator model. It is envisioned that the proposed results would provide fruitful insight for developing advanced nonlocal metasurfaces and their applications to analog optical computing and computational imaging.