Guiding and routing surface plasmons with transformation-invariant metamaterials

Rough metallic surfaces cause severe scattering to surface plasmon polaritons (SPPs), thereby limiting the SPP transmission efficiency. Here, we propose a general scheme to design ultra-compact plasmonic routers that can confine and guide SPPs on arbitrarily shaped rough surface. Our strategy makes use of recently proposed transformation-invariant metamaterials. To illustrate the advantages of this approach, we perform finite-element simulations, showing that the performance of the designed surface-wave router is robust against the change in thickness. As a result, a λ/6-thick transformation-invariant metamaterial layer can significantly suppress scattering from arbitrarily shaped metallic bumps or crevices. We also give a blueprint to implement such ultracompact surface-wave routers based on periodic metal/ epsilon-near-zero (ENZ) material stackings.