Linear Electro‐Optic Effect in 2D Ferroelectric for Electrically Tunable Metalens

Abstract The advent of 2D ferroelectrics, characterized by their spontaneous polarization states in layer‐by‐layer domains without the limitation of a finite size effect, brings enormous promise for applications in integrated optoelectronic devices. Comparing with semiconductor/insulator devices, ferroelectric devices show natural advantages such as non‐volatility, low energy consumption and high response speed. Several 2D ferrelectric materials have been reported, however, the device implementation particularly for optoelectronic application remains largely hypothetical. Here, we discover the linear electro‐optic effect in 2D ferroelectrics and demonstrate electrically tunable 2D ferroelectric metalens. We verified the linear electric‐field modulation of light in 2D ferroelectric CuInP 2 S 6 . The in‐plane phase retardation can be continuously tuned by a transverse DC electric field, yielding an effective electro‐optic coefficient r c of 20.28 pm/V. The CuInP 2 S 6 crystal exhibits birefringence with the fast axis oriented along its (010) plane. The 2D ferroelectric Fresnel metalens shows efficacious focusing ability with an electrical modulation efficiency of the focusing exceeding 34%. The theoretical analysis uncover the origin of the birefringence and unveil its ultralow light absorption across a wide wavelength range in this non‐excitonic system. The van der Waals ferroelectrics enable room‐temperature electrical modulation of light and offer the freedom of heterogenous integration with silicon and other material system for highly compact and tunable photonics and metaoptics. This article is protected by copyright. All rights reserved