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

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.