Double-sided and omnidirectional absorption of visible light in tapered dielectric nanostructure coated with non-noble metal

The common complex architecture constitutes the major bottleneck of optical absorber operating on broadband spectrum. Here we demonstrate a super absorber consisting of tapered dielectric nanostructure coated with a thin-layer of non-noble metal chromium on flexible poly(ethylene terephthalate) substrate. The proposed device yields double-sided, omnidirectional, and polarization-independent absorption over the entire visible spectrum with an average efficiency more than 90% at normal incidence, and 80% at a tilt incident angle of 60°. It can be easily realized by nanoimprinting lithography combined with physical vapor deposition technique. Theoretical analysis demonstrates that the superior optical performance is ascribed to the non-resonant light absorption by using the metal-covered, closed-packed tapered nanostructure via adiabatic nanofocusing of the metal-dielectric-metal (MDM) guided modes excited by scattering of the gradually changing nanostructure. For the cost-effective fabrication and material strategy, the super absorber has potential applications in a wide range of passive and active photonic devices, including inkless printing, harvesting solar energy, as well as thermal emitter and optical detector.