Multi‐Stage Tunable Nonlinear Circular Dichroism in 2D NbOCl 2 via Ferroelectric Phase Transition‐Driven Thermal Strain Engineering

ABSTRACT Nonlinear chiroptical effects, such as second‐harmonic generation circular dichroism (SHG‐CD), hold significant application value for chiral sensing, multidimensional optical logic, and polarization‐encrypted communications. To enhance the multi‐scenario adaptability of devices, various active tuning approaches have been developed, including electrical tuning, thermal tuning, and mechanical tuning. However, thermal tuning typically suffers from low sensitivity, limited tuning range, and nonlinear response, limiting its practical performance. In this work, we integrate 2D ferroelectric material NbOCl 2 with a ferroelectric DLATGS crystal. By leveraging the continuous second‐order phase transition of the DLATGS substrate, which generates stage‐dependent thermal expansion mismatch, we effectively overcome the above‐mentioned bottlenecks of thermal tuning. The device preserves the intrinsic linear polarization anisotropy of NbOCl 2 while inducing a pronounced SHG‐CD response, with a nonlinear chiroptical anisotropy factor of 1.246. Crucially, benefiting from the continuous anisotropic variation of the substrate's thermal expansion coefficients during the phase transition, we achieve multi‐stage thermal modulation of the SHG‐CD signal. The device delivers a global modulation depth of 91.7%, a linear tuning range of 81.2%, and a tuning sensitivity of 5.6% K − 1 . This work provides a new and effective strategy for constructing dynamically tunable, ultracompact SHG‐CD devices.