High-Q chiral metasurfaces have emerged as an exciting platform for diverse applications including chiral photoluminescence, chiral lasing, optical vortex generation, and chiral biochemical sensing. How to actively tune the chiroptical responses of metasurfaces while maintaining high quality factors is important for these applications but remains challenging, since conventional approaches based on tunable materials such as VO₂, Ge₂Sb₂Te₅ and ITO suffer from intrinsic absorption losses.

In this work, Liu and coauthors propose a concept of stably and fast tunable chiral metasurfaces. They make use of bound states in the continuum in silicon metasurfaces to realize high Q-factors and strong circular dichroism (CD). In order to dynamically tune the resonance wavelength of high-Q CD spectra, they adopt a graphene layer as the ultrafast heating source, which in theory takes only 10 μs at a low voltage of 2 V to heat the metasurface from room temperature to 550 K. They numerically demonstrate stable and linear spectral tuning of 0.06 nm/K. These findings open new avenues for active high-Q chiral metasurfaces and will significantly extend their applications.

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