Tunable and selective resonant absorption in vertical nanowires.

We demonstrate that vertical subwavelength diameter nanowires exhibit tunable and selective resonant absorption using numerical simulations and optical waveguide theory. Incident light on vertical nanowires only excites hybrid TM-dominant HE(1m) leaky modes due to symmetry matching requirements. The transverse resonances associated with these hybrid modes result in strong absorption enhancements that may be adjusted by changing the nanowire diameter. In particular, the fundamental HE(11) transverse resonance may be tuned across a wide range of wavelengths and is separated from that of the HE(12) mode by a large spectral gap, which is advantageous for wavelength selectivity. Leaky longitudinal resonances result in weaker absorption peaks at larger wavelengths. We further study the effect of incident light angle on the absorption spectra.