High-performance nanoscale polarizers enabled by transparent birefringence of layered α-MoO3.

We demonstrate a high-performance linear polarizer based on layered α-MoO3 that achieves simultaneous high extinction ratio (ER) and optical reflectivity via cavity-enhanced transparent birefringence. The layered α-MoO3 shows transparent in-plane birefringence in the visible wavelength range due to its large bandgap above 3.0 eV, which enables the precise tuning of the ERs and optical reflectivity by simply tailoring the resonance conditions of the optical cavities to achieve narrowband polarization selectivity with both markedly high extinction ratios (ERs) and optical reflectivity. Using layered α-MoO3 on a Si/SiO2 substrate as an example, systematic analysis based on the scattering matrix method shows that a high-performance polarizer with an ER > 10 dB and an optical reflectivity > 0.5 can be obtained in the wavelength range of 400-490 nm. The central polarization wavelength can be tuned by varying the thickness of the α-MoO3 layer. Experimental results validate the proposed design strategy, demonstrating the feasibility of constructing high-performance, miniaturized polarizers using transparent anisotropic van der Waals crystals. This approach shows strong potential for applications in on-chip photonic integration, polarization optics, and next-generation optical communication systems.