Surface polaritons in a negative-index metamaterial with active Raman gain

Abstract

We propose a scheme to realize stable propagation of linear and nonlinear surface polaritons (SPs) by placing a $N\ensuremath{-}\text{type}$ four-level quantum emitters at the interface between a dielectric and a negative-index metamaterial (NIMM). We show that in linear propagation regime SPs can acquire an active Raman gain (ARG) from a pump field and a gain doublet appears in the gain spectrum of a signal field induced by the quantum interference effect from a control field. The ARG can be used not only to completely compensate the Ohmic loss in the NIMM but also to acquire a superluminal group velocity for the SPs. We also show that in the nonlinear propagation regime a huge enhancement of the Kerr nonlinearity of the SPs can be obtained. As a result, ARG-assisted $(1 + 1)\ensuremath{-}$ and $(2 + 1)\ensuremath{-}$ dimensional superluminal surface polaritonic solitons with extremely low generation power may be produced based on the strong confinement of the electric field at the dielectric-NIMM interface.