Observation of double Fano interference in metal-insulator block arrays

The coexistence of double Fano interference originating from anti-phased and in-phased lattice resonances is observed in a novel plasmonic lattice array, which being consists of a horizontal double-stacked rectangular metal-insulator block. Based on a classic model analysis of coupled harmonic oscillators, the observed double Fano interference is revealed as a result of the interaction between a bright broad resonance and a dark narrow one as well as the coupling of narrow and broad spectral lines. This allows for active tuning of the double Fano resonance to a desired spectral position by a controlled size variation of the metal-insulator block arrays. After optimizing the parameters, they display two narrow absorbance peaks with high-quality factors of 84.92 and 214.1, respectively. This is because of the utmost enhancements of local electric fields in the gap between two opposing rectangular metal blocks. We expect that double Fano interference character may gain more significant potential applications in biomedical sensing.