Modal Analysis of Light Propagation, Polarization and Diffraction by Cholesteric Liquid Crystal Layers

Chiral liquid crystals (CLCs) are widely explored for polarization‐selective photonic applications due to their photonic bandgap and strong Bragg reflection, yet a predictive framework linking bulk eigenmodes to external wave propagation remains underdeveloped. Here, we introduce a Floquet‐based theoretical framework that rigorously describes electromagnetic eigenstates in periodic helicoidal media and establishes a direct mapping between bulk 3D modes and their emission into external media. This approach enables quantitative prediction of key optical phenomena, including Bragg reflection, total internal reflection, and polarization‐selective mode routing, in both planar and tilted CLC configurations. We experimentally validate these predictions through angular‐resolved measurements, demonstrating excellent agreement with theory. Beyond visualization of dispersion relations, our framework provides a unified and predictive tool to engineer light transport in chiral photonic media. These results establish a predictive design framework for cholesteric photonic devices and highlight their potential for advanced diffractive optics, including emerging AR/XR applications.