Focusing dual-wavelength surface plasmons to the same focal plane by a far-field plasmonic lens

In this Letter, we demonstrate the nanoscale focusing of surface plasmons (SPs) at two different wavelengths to the same focal plane by a far-field plasmonic lens both numerically and experimentally. The far-field plasmonic lens, which consists of an annular slit and a concentric groove and is capable of focusing dual-wavelength SPs to the same focal plane, is characterized by a scanning near-field optical microscope under both linearly and radially polarized illuminations. The demonstrated far-field plasmonic lens can provide immense opportunities for on-chip photonic applications, including dual-wavelength-based super-resolution imaging and ultra-high-density optical data storage.