Long-Range Surface Plasmons Along Membrane-Supported Metal Stripes

摘要

Long-range surface plasmon–polaritons propagating along a thin metal stripe on a supporting ultrathin freestanding dielectric membrane (the “membrane-supported metal stripe ”) have been investigated in detail theoretically and experimentally. The materials considered for the structure are Au on a thin Cr or Ti adhesion layer as the stripe, ${{rm Si}_{3}{rm N}_{4}}$ or ${{rm SiO}_{2}}$ as the membrane, and vacuum (air) or ${{rm H}_{2}{rm O}}$ as the background. Three operating wavelengths were considered: $lambda _{0} = hbox{632.8}$, 1310, and 1550 nm. Theoretical results reveal that the long-range mode in this structure has a moderate mode power attenuation (MPA $sim 2$–12 dB/mm at $lambda _{0} = hbox{1310}$ nm), good confinement [ $n_{{rm eff}} - n_{1} sim$ (1–3) $times$$10^{-3}$ ], a good $M_{2}$ figure of merit (10–25), and a reasonable range extension factor ($R_{e} sim 3$–25), when operated in vacuum or in ${{rm H}_{2}{rm O}}$ and for reasonable dimensions. The adhesion layer was found to modestly impact the attenuation. Structures were fabricated as Au/Cr stripes (25 or 20 nm thick) on freestanding (20 or 30 nm thick) large-area ${{rm Si}_{3}{rm N}_{4}}$ membranes clamped around th-n-neir perimeter, and propagation of the long-range mode was observed and characterized in air and in ${{rm H}_{2}{rm O}}$ (and similar optical fluids). The measurements reported include an optical streak, mode outputs, output polarization, and MPA. Errors between measured and theoretical attenuations were below about 7% for all of the structures tested.