The chirality of an object is defined by complete absence of its mirror symmetries. With this property, chiral structures can be divided into two groups of enantiomers representing mirror images of each other. Natural chirality is associated with a microscopic material structure of chiral ions and molecules. The degree of chirality can be probed by circularly polarized light, which allows for distinguishing enantiomers via chiroptical effects arising due to different interaction of light with left and right polarizations and media.¹ In practice, electromagnetic waves with circular polarization are widely employed in a variety of applications in photonics, biology, and chemistry, including ultrafast magnetic imaging² and spectroscopy.³

We demonstrate that chiral response can be achieved in resonant metasurfaces with a monoclinic lattice symmetry (the so-called Bravais oblique lattices) where the mirror symmetry is broken by the lattice asymmetry and also by a substrate, whereas each individual meta-atom remains fully achiral. We describe the underlying physics by introducing a mode chirality parameter as a quantitative measure of the lattice chiral eigenmodes. We confirm experimentally selective linear and nonlinear chiral interaction of resonant silicon metasurfaces with circularly polarized light.

Future technologies underpinning high-performance optical communications, ultrafast computations and compact biosensing will rely on densely packed reconfigurable optical circuitry based on nanophotonics. For many years, plasmonics was considered as the only available platform for nanoscale optics, but the recently emerged novel field of Mie resonant metaphotonics provides more practical alternatives for nanoscale optics by employing resonances in high-index dielectric nanoparticles and structures. In this mini-review we highlight some recent trends in the physics of dielectric Mie-resonant nanostructures with high quality factor (Q factor) for efficient spatial and temporal control of light by employing multipolar resonances and the bound states in the continuum. We discuss a few applications of these concepts to nonlinear optics, nanolasers, subwavelength waveguiding, and sensing.