Nonlinear Chiral Metasurfaces Based on the Optical Kerr Effect

Chiral nanostructures have immense potential for complete polarization control of light. Given the intrinsic 3D structure of circularly polarized light, nanoarchitectures with structural chirality in 3D space are usually required to achieve "full" chiroptical response. On the other hand, due to the lack of available active materials at optical wavelengths, examples of chiral photonic devices that can be tuned in an active manner remain rare. Here, based on the large Kerr nonlinearities of silicon, the nonlinear chiroptical response from a planar Si metasurface supporting high quality (Q)-factor guided mode resonances (GMRs) at near-infrared wavelengths, are numerically demonstrated. In the linear regime, the optical anisotropy of the C-2-symmetric structure associated with the observed GMRs leads to a pair of chiral resonance modes, enabling pronounced cross-polarization transmission circular dichroism and a strong handedness-dependent field enhancement effect. Owing to the nonlinear Kerr effect, such Si metasurfaces are seen to exhibit prominent chiral-selective optical nonlinearity. Importantly, a pronounced co-polarization transmission circular dichroism is observed, suggesting that the circularly polarized waves in the nonlinear regime possess asymmetric Jones matrices. Dielectric chiral metasurfaces with Kerr nonlinearities can be utilized to facilitate polarization-state modulators with simple planar structures.