Active Control of Anisotropic van der Waals Optics.

Atomically thin van der Waals materials with low in-plane symmetry offer a versatile platform where inherent anisotropy governs polarization-dependent optical properties. While early studies relied on passive observations, recent advancements have shifted toward strategies that enable active, reversible, and tunable modulation of this anisotropy. In this Mini-Review, we highlight representative demonstrations of dynamic modulation via electrical gating, magnetic fields, ultrafast optical excitation, strain engineering, and pressure tuning. We discuss how electrical methods exploit carrier injection and field-induced symmetry breaking to reconfigure excitons, plasmons, and nonlinear optical responses. Similarly, magnetic control in antiferromagnetic layered semiconductors manipulates excitonic resonances via spin reorientation, while ultrafast optical pulses provide transient polarization-selective modulation of carrier dynamics. Furthermore, strain and pressure serve as robust mechanical knobs to tune excitons, nonlinearities, and photocurrents in an orientation-dependent manner. Collectively, these strategies illustrate how dynamic modulation bridges fundamental crystalline anisotropy with advanced device-level functionality, paving the way for hybrid reconfigurable approaches in polarization-sensitive photonics and quantum technologies.