Lithography-free polarization-dependent absorber based on α-MoO3

As a natural biaxial hyperbolic material, α-phase molybdenum trioxide (α-MoO₃) exhibits dielectric and metallic properties in the plane, rendering it an exceptional candidate for polarization-dependent devices. In this work, we design a lithography-free polarization-dependent absorber consisting of an α-MoO₃ film, a germanium layer, and a silver substrate. The results show that a narrowband absorption of up to 0.99 is achieved at a wavelength of 12.2 µm for transverse magnetic polarization. In contrast, the absorption is only 0.06 at this wavelength for transverse electric polarization. This remarkable polarization-dependent absorption performance is attributed to the coupling of epsilon-near-zero modes and Fabry-Perot resonances, which is confirmed by the electric field and power dissipation density distributions. Furthermore, strong polarization-dependent performance could also be achieved when the crystal axis of α-MoO₃ is rotated in the out-of-plane. This work demonstrates that in-plane anisotropic α-MoO₃ has the potential for designing high polarization-dependent devices.