Dion–Jacobson Perovskites with a Ferroelectrically Switchable Chiral Nonlinear Optical Response

Electrically switchable second harmonic generation (SHG) is highly valuable in electro-optic modulators, which can be deployed in data communication and quantum optics. Coupling circular dichroism (CD) with an electrically controlled SHG process is advantageous because it enhances the signal transmission bandwidth and security while enabling multiple modulation modes for optical logic. However, ferroelectrically switchable chiral second-order nonlinearity is rarely reported. Here, we demonstrate the electro-optic modulation of SHG based on the multipolar effect in a chiral ferroelectric two-dimensional hybrid perovskite s-(FBDA)CdCl₄ (s-FBDA = (2s)-2-fluorobutane-1,4-diamine). s-(FBDA)CdCl₄ (s-FCC) crystals are highly stable in air, and its SHG response exhibits circular dichroism (i.e., SHG-CD) that can be ferroelectrically switched. The ferroelectrically switchable SHG-CD arises from the reconfiguration of distinct chirality-induced multipolar moments during the ferroelectric switching process. This reconfiguration induces a π/2 circular difference in SHG, leading to a reversal of circularly polarized light sensitivity. As a proof of concept, we demonstrate that the electrically controlled SHG-CD of s-FCC can be used in the transmission of encrypted optical communications.