We have proposed, designed, simulated and fabricated a holographic, low loss focusing lens with engineered nano-scaled features. This metastructure was designed to converge off-axis infrared (IR) radiation and created by patterning a dielectric surface. To leverage previous efforts for baseline data, we chose an array of nano-pillars which varied in widths although were fixed in both height and periodicity. We achieved the desired Gradient Index (GRIN) and resulting focus length, by engineering the effective index of refraction across the metasurface which was achieved from varying the material-to-air ratio. This allowed us to create a parabolic phase gradient, thereby generating an effective optical density that peaks in the appropriate sector of the lens while gradually degrading towards the perimeter of the lens in Figure 1. Lenslets with varying patterns, dependent upon their position in the array, were designed, simulated and fabricated.
Plasmonic metasurface lenses based on polarization conversion are inherently limited in efficiency, and as a result, they have been given sparse attention in favor of higher-performing dielectric variants. However, recent proposals for expanding the design beyond a single interface offer hope for efficient plasmonic structures. Before developing these multi-layer structures, we wish to better understand dependencies of 2D plasmonic designs. Here we demonstrate the spectral, polarization and geometrical sensitivities of nine large-scale variants of the original V-antenna lens design at λ0 = 8μm. We show that the spectral response oscillates rapidly within a span as small as λ0/320, and that strong focusing can occur at both the designed polarization state, and its orthogonal state–and with differing focal distances. Additionally, we determine that the lens performance is only weakly tied to the size of the discretization, offering only marginal improvement as the discretization approaches a continuum.