Aperiodic metalenses: intrinsically near-achromatic visible focusing with identical nanocylinders

Abstract: Conventional metalenses control light by varying meta-atom geometry, a design strategy that inherently couples phase modulation to structural dimensions and exacerbates chromatic dispersion. Here, we break this paradigm by decoupling phase control from meta-atom geometry. We introduce an aperiodic metalens architecture composed exclusively of structurally identical dielectric nanorods, where full 2π phase coverage is achieved solely through local periodicity modulation. We theoretically demonstrate that this geometric invariance yields a linear effective-refractive-index scaling that intrinsically satisfies the dispersive condition required for near-achromatic focusing. Operating in the visible spectrum, our aperiodic designs (moderate and high numerical apertures of 0.4 and 0.8) reveal a passive suppression of chromatic aberration. Compared to conventional size-variant designs, our aperiodic approach reduces longitudinal chromatic focal shift by nearly 42% and maintains superior spectral efficiency, yielding tighter, diffraction-limited focal spots. By relying on a single, fabrication-tolerant nanostructural building block, this approach offers a highly simplified and scalable route toward next-generation broadband metasurfaces.