Light-driven plasmonic color filters by overlaying photoresponsive liquid crystals on gold annular aperture arrays.

Plasmonics paves the way for manipulating optical signals at the nanoscale level by coupling light to coherent electronic excitations (known as surface plasmon resonances) at the dielectric/ metal interface. [ 1 ] The strong confi nement of light associated with surface plasmon resonances has led to the development of various subwavelength photonic components, such as waveguides, [ 2–4 ] switches, [ 5–7 ] lenses, [ 8–11 ] antennas, [ 12–15 ] and spasers. [ 16–19 ] The conversion effi ciency between photons and plasmons plays the most important role in all the aforementioned components. By exploiting plasmonic nanostructures, coupling between photons and plasmons can be effi ciently controlled at the subwavelength scale. [ 20–22 ] Several types of nanostructures, such as nanohole arrays, [ 23–26 ] metal–insulator–metal (MIM) structures, [ 26–29 ] and nanoslits combined with periodic grooves [ 30 ] have been used in tuning the resonant transmission peak in the visible range for potential color fi ltering, a crucial component for color display applications. However, issues related to these fi lters are low transmission due to the high loss of metals and relatively broad pass bands, which do not satisfy the requirement for the multiband spectral imaging. Recently, noble metallic annular aperture arrays (AAAs)— plasmonic coaxial nanostructures—have drawn considerable attention due to their peculiar properties and great potential for ultracompact optical applications. Baida and coworkers have theoretically investigated the properties of the waveguiding modes in such AAAs. [ 31 , 32 ] The plasmon dispersion of a single coaxial structure can be conveniently engineered for various applications by controlling its coaxial geometry, composition, and surrounding dielectrics. [ 33 , 34 ] Atwater et al. have shown that such a single-layer coaxial nanostructure can also form metamaterials with negative refractive index in the visible range. [ 35 , 36 ]