Theoretical study of ultra-wideband slow light in dual-stub-coupled plasmonic waveguide

We propose and demonstrate a metal-insulator-metal (MIM) waveguide side coupled double stubs to realize broadband slow surface plasmon polaritons (SPPs) around the telecom frequency 193.5THz. When the depth of single stub is approximately equal to integral multiple of half plasmon wavelength, owing to the constructive interferences between the electromagnetic wave propagating through the MIM waveguide and that reflected from the stubs, wideband slow light effect appears. The improved transmission line theory calculation indicates that the group velocity of SPPs in the plasmonic waveguide system for stub depth 1111nm is 0.1c (c is light speed in vacuum.) over a broad bandwidth of 69THz. Exploiting the finite-difference time-domain (FDTD) numerical simulation, the group velocity of pulse for width 20fs (Full width at half high) is calculated. The result agrees well with that predicted by the transmission line theory. This plasmonic waveguide for slow light effect has important potential application in optical delay lines. •The obviously slow light effect appears around the telecom frequency 193.5THz.•The ultra large bandwidth for slow light effect is 69THz and the high normalized delay-bandwidth product (NDBP) is 3.24.•The transmission of the slow light device is 0.96.