Reflectionless perfect linear polarization rotator

Creating polarization rotators that are all reflectionless at the same layer thickness is a nontrivial challenge in integrated polarization optics. In most existing approaches, reflection suppression relies on interference effects that require thickness tuning for each target rotation angle. Such thickness-dependent designs are incompatible with large-scale wafer-level fabrication and limit applications that require spatially varying polarization manipulation with high efficiency. Here, we numerically demonstrate a polarization-rotator devices based on fourfold rotational (C4) symmetry that overcomes this limitation. The proposed devices convert incident linear polarization to prescribed output angles with linear polarzaition while remaining near-reflectionless at a single, fixed layers and device thickness. The structure consists of a chiral bilayer metasurface in which each individual layer possesses C4 symmetry. Chirality is introduced by twisting one layer relative to the other, while the overall structure retains the rotational symmetry. This C4 symmetry-enforced configuration intrinsically suppresses cross-polarized reflection, and a designed interference condition eliminates co-polarized reflection at an operating resonance. As a result, multiple polarization rotation angles can be realized without modifying the physical thickness or layer stack. Compared to conventional optical rotators and thickness-tuned metasurfaces, this approach provides a compact, planar, and fabrication-friendly route to reflectionless polarization control.