Significant enhancement of broadband optical limiting behavior using off-resonant sub-wavelength coupled plasmonic waves

We present the numerical investigation of the optical limiting behavior based on coupled nonlinear plasmonic waveguides. Exploiting the strong localization of the electromagnetic fields at metal-dielectric interfaces, significant enhancement of the nonlinear absorption was achieved. Two types of optical limiters (OLs), one based on the enhanced optical Kerr (OK) effect and the other based on the enhanced two-photon absorption (TPA), are proposed. Their transmission characteristics at off-resonant band of Au are investigated. The simulation results reveal that the linear transmittances in both cases are higher than 85%, and the limiting thresholds are 250 GW/cm² and 42.69 GW/cm² for the OK and TPA based OLs, respectively. As compared with the non-structured slab waveguides, the optical limiting thresholds are greatly reduced. Wideband operation over 200 nm was confirmed and TPA induced free carrier absorption (FCA) discussed.