2026/06/01 by Shoumik Debnath, Sudipta Saha · 1 voice
Physics and Astronomy · #physics.optics
arxiv published 2026/06/01 · arxiv updated 2026/06/10
We report that the biaxial birefringence of α-MoO3 can activate two spectrally distinct quasi-bound states in the continuum (quasi-BICs) within a single symmetric TiO2 nanobar-pair metasurface, with each resonance governed by a different crystallographic axis pair of the van der Waals crystal. With a full 60 nm α-MoO3 gap fill, a TE resonance at 883.9 nm (Q=92, Fano q=0.090) and a TM resonance at 923.2 nm (Q=31, Fano q=0.393) are obtained. The Q ratio follows the inverse-square permittivity contrast, Q∝(Δε)-2, calibrated across both polarization channels. Oblique-incidence sweeps show that the TE channel acts as a dual-null spatial highpass filter with a broadband stopband (|H|<0.13 for |kx|≤0.63 μm-1, Tbg=0.962), while the TM channel transfers as |H|∝|kx| (R2=0.94), consistent with first-order spatial differentiation. Both operations are verified on a USAF~1951 resolution chart processed in a simulated 4f framework. Channel selection is purely by input polarization angle with no structural modification.