Fano-interference-enhanced optical chirality and helicity-dependent optical forces in dielectric metasurfaces

Kan Yao; Yuebing Zheng

doi:10.1117/12.2568158

20 August 2020 Fano-interference-enhanced optical chirality and helicity-dependent optical forces in dielectric metasurfaces

Kan Yao, Yuebing Zheng

Author Affiliations +

Proceedings Volume 11460, Metamaterials, Metadevices, and Metasystems 2020; 114601U (2020) https://doi.org/10.1117/12.2568158
Event: SPIE Nanoscience + Engineering, 2020, Online Only

Conference Poster

Abstract

Due to the intrinsically weak chirality of biomolecules, discriminating between enantiomers, i.e., chiral molecules of opposite handedness, in low-concentrated solutions by an optical means is one of the unsolved problems in nano-optics. It is even more challenging to separate chiral objects at the nanoscale by optical forces. The key to alleviating the fundamental difficulty of these tasks is to construct an optical field, preferentially in the ultraviolet (UV) region, that carries intense optical chirality with comparable contributions from its electric and magnetic components. However, this requirement has not been met in nanophotonic structures, predominantly because of the lack of magnetic responses in plasmonic materials and the insufficient field enhancement by dielectrics. Innovative designs are highly desired to overcome the limitations from materials. In this work, we systematically investigate the resonance modes in a dielectric metasurface as well as their evolution and interplay as the design variables are engineered. We show that, based on two different mechanisms, 100-fold enhancement of optical chirality can be achieved at near-UV wavelengths with different linewidths. The first one arises from the sharp Fano interference between two distinct magnetic resonances of the unit cell of the metasurface, both of which are enhanced by the coupling across the lattice. The second one originates solely from the magnetic dipole resonance, whereas the chiral hotspots spatially overlap the electric counterparts, forming ideal sites to exert helicity-dependent optical forces on chiral objects at the nanoscale. Our findings pave the way towards practical solutions to the ultimate challenges of chiral optics.

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Kan Yao and Yuebing Zheng "Fano-interference-enhanced optical chirality and helicity-dependent optical forces in dielectric metasurfaces", Proc. SPIE 11460, Metamaterials, Metadevices, and Metasystems 2020, 114601U (20 August 2020); https://doi.org/10.1117/12.2568158

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