Ultra-Wideband Dielectric Mirrors via Digitally Chirped Nanoporous Silica Bragg Reflectors

In this work, we introduce a novel approach to dielectric mirrors with user-selectable ultrawide reflectance through digitally chirped nanoporous silica Bragg reflectors (DBRs). Unlike traditional continuously chirped mirrors, our design features a monolithic series of discrete DBRs, each precisely engineered to reflect specific wavelengths and angles, resulting in broader spectral and angular reflectance bands. This digitally chirped design provides enhanced flexibility and simplifies the fabrication process compared to conventional approaches. We demonstrate digitally chirped mirrors for visible and near-IR light by stacking up to nine digitally tuned nanoporous silica DBRs, utilizing electrochemical etching and thermal oxidation of nanoporous silicon. Our experimental results demonstrate reflectance exceeding 95% over a broad visible spectrum, with omnidirectional performance for unpolarized light between 485 and 625 nm across incident angles from 0 to 45°. This innovative mirror architecture can be adapted to a variety of dielectric materials and is suitable for applications requiring tailored omnidirectional reflectance with minimal optical losses, such as high-power lasers, radiative heat barriers, and energy-harvesting systems.