Low‐Symmetry α‐MoO₃ Heterostructures for Wave Plate Applications in Visible Frequencies

Abstract Low‐symmetry van der Waals materials are promising candidates for the next generation of polarization‐sensitive on‐chip photonics since they do not require lattice matching for growth and integration. Due to their low‐symmetry crystal behavior, such materials exhibit anisotropic and polarization‐dependent optical properties for a wide range of optical frequencies. Here, depolarization characteristics of orthorhombic α‐MoO₃ is studied in the visible range. Using polarizers and analyzers, it is demonstrated that α‐MoO₃ has negligible loss and that birefringence values as high as 0.15 and 0.12 at 532 nm and 633 nm, respectively, are achievable. With such a high birefringence, quarter‐ and half‐wave plate actions are demonstrated for a 1400 nm α‐MoO₃ flake at green (532 nm) and red (633 nm) wavelengths, and polarizability as high as 90% is reported. Furthermore, a system of double α‐MoO₃ heterostructure layer is investigated that provides the possibility of tuning polarization as a function of rotation angle between the α‐MoO₃ layers. These findings pave the way to the promising future of on‐chip photonic heterostructures and twist‐optics that can dictate the polarization state of light.