Meta‐Atom Rotation Unlocks Nonlinear Optical Chirality in Lithium Niobate Metasurfaces

ABSTRACT We propose and experimentally demonstrate a lithium niobate (LN) metasurface that generates significant optical chirality simply by rotating achiral nanorods, thereby breaking mirror symmetry without the need for other complex 3D geometric structures. The chiral response originates from the non‐orthogonal coupling between electric and magnetic dipole moments, which is further enhanced through strong hybridization of transverse electric (TE) and transverse magnetic (TM) modes at specific rotation angles. Theoretical simulations reveal that a rotation angle of 30° leads to a near‐unity circular dichroism (CD) due to robust TE‐TM coupling. Experimentally, we observe a maximum linear CD of −0.37 and a strong nonlinear CD of −0.42 in second‐harmonic generation (SHG). This work presents the first experimental demonstration of intrinsic nonlinear chiroptical effects from an LN metasurface platform. The simple yet effective design, easy to fabricate and extend to other nonlinear optical crystals, establishes LN metasurfaces as a promising candidate for advanced applications in chiral sensing, polarization‑sensitive photonics, and quantum optics.