Polarization Reflector/Color Filter at Visible Frequencies via Anisotropic α-MoO₃

2D van der Waals materials have attracted increasing attention in recent years due to their exciting physical properties and offer new opportunities for creating devices with enhanced or novel functionalities. In particular, α-MoO₃ is an emerging member of the fast-growing 2D family with strong natural anisotropic optical properties. However, anisotropic optical properties of -MoO₃ in the visible frequency range remain elusive. Here, α-MoO₃ is investigated as an optical material at the visible frequency (450–750 nm), which exhibits a polarization-dependent complex refractive index due to the anisotropic crystal structure. As a proof of concept, polarization-sensitive photonic devices including polarization reflectors and polarization color filters are designed and realized by constructing metal–insulator–metal Fabry–Perot cavities. It is observed that resonance frequencies for designed transmission and reflection filters change up to 25 nm with incident polarization which stems from the polarization-dependent complex refractive indices of α-MoO₃. The largest contrasts are observed for two orthogonal polarization states parallel to the two orthogonal in-plane crystal directions. The approach in this study offers new directions for potential applications in the development of polarization-dependent devices based on 2D van der Waals materials for visible frequencies.