A broadband quarter-wave plate enabled by a dual-aluminium metastructure with process-realistic SiO 2 geometry

morphology suppresses reflectance and improves polarization conversion efficiency compared with planar dielectric layers. Experimental results confirm the QWP operation with discrepancies within 5% at representative wavelengths of 520, 632, 785, and 1550 nm. This approach provides a robust and practical route toward fabrication-tolerant broadband polarization-control devices for integrated photonic and imaging platforms.