Phonon-enhanced polarization conversion and circular dichroism in monoclinic CdWO ₄ films

Abstract Polarization conversion and chiral optical responses are important aspects of optical-field manipulation, yet achieving them in compact and continuously tunable devices remains challenging. In this work, we propose to use natural low-symmetry CdWO 4 thin films to achieve strong gyrotropic and chiral optical responses. We derive and simulate the complex Kerr and Faraday angles, and circular dichroism of the CdWO 4 film under oblique incidence conditions. The results show strong gyrotropic and significant chiral responses in Reststrahlen frequency band. Crucially, these strong chiroptical responses can be dynamically and continuously tuned simply by adjusting the material’s azimuth angle and incident angle. These giant gyrotropic and chiral responses originate from the synergistic effect of the strong anisotropy caused by the hyperbolic dispersion of CdWO 4 and the intrinsic off-diagonal dielectric elements introduced by its monoclinic lattice. This work provides new physical ideas for the development of dynamic polarization control devices.