Manipulating multiple plasmon modes by coupling fields for broadband filtering in terahertz metamaterials

Multiple modes resonance provides the possibility of broadband filtering and has great potential applications in terahertz devices, including miniaturized spectrometers, hyperspectral imagers and optical switches in communication systems. However, it is difficult to further expand the bandwidth range due to the inability to stack an infinite number of resonant structures in a finite space. Here, an innovative method is reported for manipulating two localized surface plasmon polaritons (LSPP) modes by multiscale-coupled plasmonic fields to realize broadband filtering at terahertz (THz) frequencies. The interaction between two LSPP modes was verified theoretically and experimentally, exhibiting a prominent Rabi splitting and two peaks with high transmittance. Particularly, broadband filtering is accomplished by utilizing a double-layer structure that can be regarded as a cavity for inducing far-field interference. Experimental result demonstrates that the maximum transmission range of the bilayer metamaterial reaches 0.63 THz. Besides, the two wide bands can be integrated into one broadband through near-field coupling effects. The integration of strong coupling and far-field interference expands the transmission range of the double-layer metamaterial, further enhancing its capability for broadband filtering. This unique approach for manipulating multi-mode plasmonic coupling forges a convenient route for realizing broadband filtering.