Reflectionless Linear Polarization Rotators with Angular Robustness

An open challenge in integrated polarization optics is creating compact, alignment-free rotators that maintain low reflection at a constant thickness. This capability is essential for compatibility with scalable wafer-level fabrication. In this work, we numerically design a terahertz chiral bilayer metasurface that uses 4-fold rotational (<i>C</i> ₄) symmetry to achieve prescribed linear-polarization rotations with near-zero reflection over a wide range of incident angles. The <i>C</i> ₄ symmetry inherently removes cross-polarized reflection across the spectrum, while a destructive interference eliminates the copolarized reflectivity at a target resonance. A key novelty of our approach is that reflectionless response is maintained across diverse rotation angles without need to change the device thickness. Simulations further show that the structure remains reflectionless for incidence angles up to ∼20°, confirming strong angular robustness. Our design surpasses natural optical rotators, such as quartz, which require bulky thickness, and existing metasurfaces that rely on multilayer stacks or thickness variations to achieve reflectionless operation across varied rotation angles. The potential applications include integrated secure optical communications, parallel photonic processing, and advanced imaging systems.