Multiple fano resonances in spatially compact and spectrally efficient spoof surface plasmon resonators with composite textures.

Spoof surface plasmons derive their properties from structure resonance rather than from electronic resonance, enabling an extremely high degree of freedom for tuning and modulating different resonances. Here, a composite resonator based on multiscale textured metal surface of different grooves is presented, and spoof localized surface plasmons (LSPs) are shown to emerge and interact coherently. Each band of the spoof LSPs resembles those generated by the homogenously textured surface with the corresponding groove. By adjusting the geometry and filling medium of each substructure in the composite system, we find that the multipole resonant modes sustained by one substructure can couple with those in the other, giving rise to multi-band Fano resonances. Such multiple-Fano resonance structures are spatially more compact while spectrally more comprehensive than usual spoof structures. They can be used for unique resonant devices such as microwave antennas and metasurfaces.