Broadband omnidirectional visible spectral metamaterials

Abstract

Optical metamaterials offer the possibility of controlling the behavior of photons similarly to what has been done about electrons in semiconductors. However, most optical metamaterials are narrowband, and they achieve negative refraction within a small window of incident angles, making them impractical for common visible light systems that operate effectively over a wide range of frequencies and directions. Considerable resistive loss at the resonant frequency of these metamaterials further prevents them from being deployed in the real world. Here, we develop a novel metamaterial randomly assembled by a list of narrowband, omnidirectional, and ultralow-loss meta-cluster systems using a bottom-up approach. Weak interactions among numerous meta-cluster sets greatly broaden the effective bandwidth of the overall structure, exhibiting frequency selectivity and spatial modulation when responding to white-light illumination. We observe negative refraction in the 490–730 nm band, and observe an inverse Doppler effect at green, yellow, and red frequencies, across most of the visible spectrum. Our method allows for low-cost fabrication of sizable broadband omnidirectional three-dimensional metamaterial samples, which opens the door to the rapid development of optical metamaterials, micro–nano assembly and preparation, tunable optical device engineering, etc.