Giant second-harmonic generation efficiency and ideal phase matching with a double ε-near-zero cross-slit metamaterial

Efficient second-harmonic generation may be induced based on the anomalous tunneling properties of double zero-permittivity narrow cross-slit nonlinear channels. Ideal phase matching conditions, large coherence length, combined with uniform field enhancement entail the ideal conditions to achieve giant second-harmonic conversion efficiencies for backward and forward signals. It is shown that these conditions are particularly well suited to enhance nonlinear effects over a wide range of frequencies, leading to efficient electromagnetic wave mixers and parametric amplifiers.