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Metasurfaces have provided a promising approach to enhance the nonlinearity at subwavelength scale, but usually suffer from a narrow bandwidth as imposed by sharp resonant features. Here, we counterintuitively report a broadband, enhanced second-harmonic generation, in nanopatterned hyperbolic metamaterials. The nanopatterning allows the direct access of the mode with large momentum, rendering the rainbow light trapping, i.e. slow light in a broad frequency, and thus enhancing the local field intensity for boosted nonlinear light-matter interactions. For a proof-of-concept demonstration, we fabricated a nanostructured Au/ZnO multilayer, and enhanced second harmonic generation can be observed within the visible wavelength range (400-650 nm). The enhancement factor is over 50 within the wavelength range of 470-650 nm, and a maximum conversion efficiency of 1.13×10−6 is obtained with a pump power of only 8.80 mW. Our results herein offer an effective and robust approach towards the broadband metasurface-based nonlinear devices for various important technologies. Though metamaterials enhance nonlinear light-matter interactions due to their resonant features, these materials typically show a narrow spectral bandwidth. Here, the authors report broadband enhanced second-harmonic generation in patterned multilayer hyperbolic metamaterial arrays. [ABSTRACT FROM AUTHOR]

[Display omitted] The rapid development of metamaterials offers a new avenue to achieve exotic electromagnetic properties, such as perfect absorption for important stealth engineering applications. So far, there are few demonstrations of wide-angle broadband absorption, due to the stringent impedance matching requirement. Here, inspired by the concept of log-periodic dipole antenna (LPDA) for broadband emission, we propose a wide-angle broadband absorption based on both indium tin oxide (ITO) material and judiciously engineered metapyramid geometry. The strip ITO arrays on the sidewalls of metapyramid follow the quasi-LPDA strategy for gradient impedance and expands significantly both angular and spectral operating bandwidth by a cascading of multiple electric and magnetic resonances, as revealed by the rigorous characteristic mode analysis. Our experimental results show that the exotic absorption reaches above 0.9 at 45° tilted incidence for both transverse electric and transverse magnetic polarizations across the band of 8 ∼ 18 GHz. Our strategy circumvents the issues of limited-angle operation, high costs and high weight raised by metal structures, providing a new paradigm toward wide-angle broadband metadevices. [ABSTRACT FROM AUTHOR]