Advances in nanotechnology have led to many new achievements in fields ranging from electronics to medicine. The general trend of “smaller is better” also applies to the world of optics, where optical elements designed at the micro- and nano-scales are now being used in areas like lithography, fiber optics, and particle trapping. When you shrink a lens down to the scale of one optical wavelength, however, you must account for sub-wavelength effects during its design. If considered carefully, though, phenomena like plasmonic resonance and metamaterial-like feedback can actually be used to enhance optical performance. In this work, M. Naserpour and colleagues consider how an appropriately designed sub-wavelength pattern across the surface of a small lens may improve its ability to focus light. Previous work has already identified how lenses made from so-called negative index materials – bulk materials patterned with periodic structures at the nanometer scale – can create sharper focal spots than normal glass lenses. Here, M. Naserpour et al. show that normal lenses that include sub-wavelength structures along their front and back surface (termed “metacoatings”) also achieve a similar focusing enhancement. This is important for two reasons. First, it is currently challenging to fabricate sub-wavelength features throughout a volume, whereas surface patterning is much easier. Second, metacoatings may enable a thinner lens design than their bulk counterparts, which may allow them to squeeze into the ever smaller spaces that new applications require.
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