Clusters of metallic nanoparticles are known to be able to support complex optical Fano resonances as a result of interactions between multiple modes. Now Wei-Shun Chang and colleagues from Rice University, USA have shown a simple way of switching between optical responses of different polarizations simply by turning on a voltage of 6 V. The team fabricated a ring (several hundred nanometres in diameter) composed of seven gold disks, each about 30 nm in size. An eighth larger and semicircular-shaped disk is located inside the ring and introduces structural and polarization asymmetry. For one polarization the authors report an optical Fano resonance with two peaks (at red and near-infrared wavelengths), whereas for another polarization a simple single-peak resonance (red wavelength) is observed. However, by embedding the system in a liquid crystal and applying a voltage of about 6 V (alternating at a frequency of 1 kHz), the transition from a homogeneous nematic phase to a twisted phase can be induced, and the polarization rotated by 90°. As a result, the authors were able to use the voltage to switch the Fano resonance reversibly off for one polarization and on for another.
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Pile, D. Switching resonances. Nature Photon 6, 716 (2012). https://doi.org/10.1038/nphoton.2012.287
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DOI: https://doi.org/10.1038/nphoton.2012.287
