Current-driven optical response of plasmonic crystal: From dissipation to amplification

We study optical response of a plasmonic crystal based on multi-gated 2D structure with periodic modulation of the electron density in the device channel. In such a structure, the plasma wave velocity is periodically modulated as well. We consider the simplest model of periodically alternating stripes of the electron density and plasma wave velocity: active regions with high plasma wave velocity and passive regions with low plasma wave velocity. Terahertz radiation applied to such a structure excites plasmonic resonances both in the active and passive stripes. The width of the resonances is determined by the momentum relaxation rate. For sufficiently large relaxation rates, the resonances in the passive regions strongly overlap and only “active resonances” survive. In this regime, the plasmonic oscillations in the active regions exponentially decay into the passive regions, so that different active regions are disconnected at plasmonic frequencies but connected at zero dc frequency. We assume that dc current is applied to this plasmonic crystal and calculate radiation-induced correction to the dissipation in the channel. We demonstrate that with increasing the dc current this correction changes sign, which results in amplification of the optical signal.