Dye-Assisted Gain of Strongly Confined Surface Plasmon Polaritons in Silver Nanowires
Subwavelength confinement and active control of light is essential for nanoscale communication devices at visible frequencies that support large bandwidths.[1-5] Noble-metal nanostructures present an excellent platform for strongly confined optical waveguides [6-13] because of their ability to support surface plasmon polaritons (SPPs). However, SPP propagation suffers from losses that seriously limit their application potential.  Although significant progress toward SPP loss compensation has been reported for various planar 2D waveguide structures,[15-20] as well as lasing involving strongly localized plasmon modes,[21,22] SPP gain in 1D nanoscale waveguides at visible frequencies is yet to be accomplished. Here, we report the first demonstration of gain for deep subwavelength confined SPPs (mode area = λ2/40) in chemically prepared silver nanowires (Ag NWs). We measured a gain coefficient of 270 cm-1 resulting in 14% loss compensation using a continuous-wave (cw) pump laser. These results are an important step toward total loss compensation for highly confined nanowire SPPs.