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Fano resonances in plasmonic nanostructures exhibit sharp resonance and strong light confinement. These properties are very useful for sensing applications, which rely on plasmon line shape engineering. Fano resonances in plasmonic clusters depend on structure symmetry, and this study provides a general understanding of Fano resonances in clusters with D 2h symmetry. We show that, because of the excitation of B3u and B2u dark subradiant modes, four kinds of Fano resonances appear in the spectra for hexamers with D 2h symmetry. When a central particle is introduced to form a heptamer, it is shown that, aside from influence on the resonant behaviors or appearance of an additional Fano resonance for a specific polarization, several hybridized dark subradiant modes are excited for both polarizations, and up to eight kinds of Fano resonances appear in the spectra. Plasmonic clusters with D 2h symmetry are suitable for plasmon line shaping, and it is expected that these structures are useful for multiwavelength sensing applications. This study also reveals that cluster symmetry engineering is a favorable method for generating multiple Fano resonances and tuning spectral features. A similar result is obtained for clusters with other symmetries.

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We propose a tuning filter containing two channels by inserting a defect layer (Air/Si/Air/Si/Air) into a one-dimensional photonic crystal of Si/SiO, which is on the symmetry of the defect. Two transmission peaks (1528.98 and 1564.74 nm) appear in the optical communication S-band and C-band, and the transmittance of these two channels is up to 100%. In addition, this design realizes multi-channel filtering to process large dynamic range or multiple independent signals in the near-infrared band by changing the structure. The tuning range will be enlarged, and the channels can be moved in this range through the easy control of air thickness and incident angle.