Asymmetric light transmission via Sb2S3-enhanced nonreciprocal gratings on a glass substrate

Abstract

We propose and demonstrate a compact, high-performance optical isolator utilizing nonreciprocal gratings enhanced by antimony trisulfide (Sb₂S₃) deposited on a glass substrate. The vertical asymmetry created by layered materials and the amorphous silicon (a-Si) grating enables direction-dependent optical transmission behavior in the near-infrared spectral range. Rigorous coupled-wave analysis (RCWA) simulations reveal that the introduction of Sb₂S₃ significantly boosts nonreciprocal transmission contrast, enabling an isolation ratio of 22.28 dB for an a-Si surface grating with a period p of 1 μm, a fill factor f of 0.5, and a groove depth h of 0.36 μm on a Sb₂S₃/glass stack. Breaking mirror symmetry yields polarization-selective optical isolation, supporting both transverse-electric (TE) and transverse-magnetic (TM) polarizations. Calculated and measured transmittance spectra match closely for both TE and TM at normal incidence, confirming the grating model and fabrication fidelity. Transitioning Sb₂S₃ to the crystalline phase substantially elevates asymmetric transmission for both polarizations, as captured by the model. This work provides a promising route toward scalable, efficient, and broadband nonreciprocal photonic devices based on cost-effective and versatile material platforms.