Gain-assisted light guiding at the subwavelength scale in a hybrid dielectric-loaded surface plasmon polariton waveguide based on a metal nanorod

Hybrid dielectric-loaded plasmonic waveguide consisting of an inverted U-shaped high-index ridge covering atop a low-index polymer coated metal nanorod is proposed and numerically investigated. Through incorporating a gain medium either in the ridge or the buffer layer, the loss of the supported plasmonic mode can be effectively compensated. For a typical configuration comprising a 450 nm × 160 nm InGaAsP ridge with a 5-40 nm thick PMMA layer and a 30 nm wide Ag nanorod, the necessary gain required in InGaAsP for lossless propagation of the quasi-TE type symmetric hybrid mode can be as low as 3.45-9.85 cm ^-1, along with a subwavelength mode area (λ²/60- λ²/148) attainable simultaneously. The configuration potentially offers a promising solution to enable lossless light transport at the sub-diffraction-limited scale with low compensation gain, thereby opening venues for ultra-compact active plasmonic devices and circuits.