Transmission efficiency of surface plasmon polaritons across gaps in gold waveguides

A far-field microscopy approach is introduced that measures the transmittance of surface plasmon polaritons across gaps in plasmonic waveguides. Local plasmon intensity is monitored through radiation scattered from discontinuities placed before and after the gap. An unusually broad range of gap sizes, 30 nm to 16 mu m, is reported for optically thick, 5 mu m wide Au stripe-waveguides excited at 860 nm wavelength. Transmittances approach 100% for a 30 nm gap and remain as high as 50% for a 1 mu m gap. Finite-element analysis yields transmittances in agreement with experiment and finds gap losses are dominated by radiation scattered into the substrate and air.