Multiple-wavelength plasmonic nanoantennas.

We propose a type of photonic-plasmonic antennas capable of focusing light into subwavelength focal point(s) at several wavelengths, which are formed by embedding conventional dimer gap or bow-tie nanoantennas into multiple-periodic gratings. Fano-type coupling between localized surface plasmon resonances of dimer antennas and photonic modes in the gratings adds new functionalities, including multiple-wavelength operation and controllable enhancement of the field intensity in the focal point. Multiple-wavelength operation of nanoantennas provides tremendous opportunities for broadband single-molecule fluorescence and Raman sensing, emission enhancement, and near-field imaging.