Cascaded plasmon-induced transparency in spoof surface plasmon polariton waveguide

Manipulating spoof surface plasmon polaritons (SPPs) effectively has promising applications in developing ultracompact plasmonic circuits. Research on versatile components in planar spoof SPP waveguides has attracted widespread attention over the decades. In particular, cascaded chip-scale devices play an important role in enhancive buffering, highly-sensitive sensing and nonlinear interaction. Herein, we propose a novel strategy to manipulate the switching and slow wave features of spoof SPPs on the basis of plasmon-induced transparency (PIT) spectral responses. A combined module consisting of split square-ring resonators and electric-LC resonators is loaded with a spoof SPP waveguide along the propagating trajectory, where the destructive interference between the two resonators contributes to the PIT behavior and the group delay of the spoof SPPs. A modulation contrast of up to 16.2 dB is achieved for the spoof SPP transmission at the PIT peak frequency. The measurements are consistent with both full-wave simulations and theoretical calculations. Cascaded capabilities performed by installing multiple PIT modules at an interval of an equivalent wavelength are accomplished in the planar spoof SPP waveguide. The proposed strategy opens up fascinating prospects on highly integrated plasmonic circuits and networks.