Dynamic Controls of Second‐Harmonic Generations in Both Forward and Backward Modes Using Reconfigurable Plasmonic Metawaveguide

Second‐harmonic generation (SHG) has recently been explored in plasmonic metamaterials, but real‐time tunability of the nonlinear process still remains a challenge and has not been reported. Here, an ultrathin spoof surface plasmon polariton (SSPP) waveguide loaded with varactor diodes is proposed to achieve high conversion efficiencies of SHGs in both forward and backward phase‐matching conditions in the same frequency band. The dispersion behaviors of SSPPs can be manipulated by adjusting the capacitance of the varactor diodes loaded on the unit structure, allowing forward and backward phase‐matching for both fundamental and second‐harmonic waves. Experiments are demonstrated in the microwave frequency to observe the dynamic controls of the forward/backward SHGs in a single SSPP platform, showing good agreement with theoretical predictions. It is expected that the reconfigurable SHGs may find many applications in nonlinear plasmonic metamaterials, wireless communication systems, and microwave integrated circuits.