Optimization of Biased PT-Symmetric Plasmonic Directional Couplers

We study a plasmonic directional coupler with a metallic cladding and dielectric core in the presence of balanced gain and loss, and demonstrate that such a photonic structure can possess the parity-time (PT) symmetry even when optical losses in metal are taken into account. We analyze the modal dispersion of the coupler when losses in metal are negligible and then study how substantially increased losses modify the modal dispersion and coupler's properties. For realistic parameters, we demonstrate a novel approach for recovering the property of the PT-symmetry by introducing unbalanced loss and gain in both cores of the coupler.