Spectral Condensing of All‐Dielectric Structural Colors via Cascaded Formation of Self‐Similar Beams

Abstract

ABSTRACT Achieving strongly saturated structural coloring in pixels made entirely of low‐index dielectrics, such as polymers or glass, is a challenging task as they lack the index contrast for narrowband resonances. Forming gratings or photonic crystals is an alternative, but their large footprints often degrade the printing resolution. Recently, standalone low‐index pixels have been demonstrated in the form of microscale ridges (MRs). Although they are compact and easy to fabricate, their color purity trails behind that of resonator‐ or periodic pattern‐based counterparts. In this work, we spectrally condense the MR‐generated color by “cascading” the MR's coloring mechanism, i.e., spectrally selective self‐similar beam formation. To that end, we optimize the multi‐stage cascaded MR design computationally, fabricate the optimal designs through 3D‐nanoprinting of polymer, and characterize the spectra and profiles of the self‐similar beams. The results show that a 3‐stage cascading can narrow the transmission's spectral bandwidth from >300 to ∼100 nm and boost its peak‐to‐valley ratio from <2.0 to 3.7–6.2, while maintaining the cost‐effectiveness and manufacturability of polymer. With a wide color tuning range and sub‐10‐micrometer pixels, this scheme provides a viable pathway for high‐resolution, high‐saturation structural coloring.