Spoof Surface Plasmons
Double-Fano and Slow Light
Fano resonances in plasmonic nanostructures are analogues to that in the atomic systems, but with the energy levels defined by the structure designs instead of the orbit levels. The resonances occur as a result of interference between the super- and sub-radiant modes. Advantages of Fano resonances in plasmonics include tunable resonant frequencies, controllability over the interference, spectral selectivity, and also significant near-field enhancement, making them promising in applications ranging from slow-light buffering to index sensing and biomolecule detection.
Our interest in Fano resonance lies in both fundamental and application aspects. Under the framework of the group theory, the Fano resonances can be categorized according to whether the super- and sub-radiant modes are under the same representation. These two situations respond differently when symmetry breakings are introduced to the structures, providing different schemes for controlling the interference. We also investigated the so-called double-continuum Fano resonances and. By introducing two super-radiant modes, a peculiar dispersion is formed when both interferences are turned on. Topological features, namely, the absence of band-gap near the resonance, can be utilized to construct broad-band slow-light buffers.
In the application aspect, we constructed an array of frequency selective interfaces with Fano resonances. With this array, we were able to identify proteins using their amide vibrational modes with mono-layer accuracy, as well as determine the optical thickness of the proteins. Binding to additional proteins can also be identified, and orientation of secondary structures can be obtained by comparing different proteins.