Figure 4

(a,b,e,f) Normalized reflected power, R, for two plasmonic gap metasurfaces of variable TiO₂ [top panels (a) and (b)] and ZnO [bottom panels (e) and (f)] insulating cavity thickness in the range \(H=135{-}550\) nm for both polarizations, i.e, the electric field being normal to the top layer nanowires, E = \(E_x\) [panels (a) and (e)] and the electric field being parallel to the top layer nanowires E = \(E_y\), [panels (b) and (f)]; R\(_x^\mathrm {TiO_{2}}\) in (a), R\(_y^\mathrm {TiO_{2}}\) in (b), R\(_x^\mathrm {ZnO}\) in (e), R\(_y^\mathrm {ZnO}\) in (f). (c) and (g) Extinction ratio of the reflected power between the two polarization, EXT  = 10log\(_{10}(\mathrm {R}_x/\mathrm {R}_y)\) saturated in [0–15] dB for the TiO₂ and ZnO cases with variable cavity thickness in the range \(H=135{-}550\) nm, EXT\(^\mathrm {TiO_{2}}\) in (c) and EXT\(^\mathrm {ZnO}\) in (g). (d) and (h) Wavelength dependence of the extinction ratio in the range \(\lambda\) = [1–4] μm for the thinner TiO₂ (d) and the thicker ZnO (h) case calculated at an optimum cavity thickness H.