Photonic crystal-based smart window design for seasonal solar energy management in Beni-Suef City, Egypt

This paper presents a broadband optical short-wave pass (OSWP) multilayer filter optimized for smart-window integration to enhance building energy efficiency in Beni-Suef, Egypt. The structure comprises <i>C</i><i>a</i><i>F</i>₂, <i>S</i><i>i</i>₃<i>N</i>₄, and ZnS dielectric stacks in a dual-laminate configuration designed using the transfer matrix method (TMM). The optimized design achieves high visible transmittance (∼86<i>%</i> at 400-700 nm) while strongly suppressing near-infrared (NIR) radiation across 800-1500 nm. A well-defined photonic band gap (PBG) is confirmed through spectral and phase analyses, showing strong angular sensitivity. With increasing incidence angle, the PBG exhibits an ∼100<i>n</i><i>m</i> blue shift, enabling passive seasonal modulation of solar heat: effective NIR blocking for summer cooling and enhanced NIR transmission for winter heating. Compared with conventional low-E glazing and previously reported photonic crystal filters, the proposed smart-window design offers superior spectral selectivity and climate-responsive performance without electrical power or active control. These results highlight a practical passive solution for reducing energy demand in buildings located in hot-arid regions.