Dual-Material Metastructure for Simultaneous Filtering and Focusing of Incoherent White Light

Microlenses integrated with color filters continue to be of great interest for sensors, light-emitting diodes, three-dimensional (3D) imaging, and 3D display applications. Many techniques have been investigated to reduce the thickness and the size of the total devices, and microlenses with hybrid functions have been developed. However, traditional hybrid microlenses usually work under coherent illumination due to the single material used and the lack of effective diffraction elements for incoherent illumination. Here, we demonstrate a new flat optics device based on a dual-material 3D metastructure that achieves simultaneous color filtering and focusing under spatially incoherent white light illumination. Our device comprises a nanocone array fabricated by 3D direct laser writing at the interface with a Fresnel metalens based on a typical two-dimensional (2D) material: graphene oxide-reduced graphene oxide. The unique spatial arrangement of the nanocone array enables us to double the acceptable spatial coherence of the illumination compared with conventional nanopillar-based structural color. The chemical and optical stabilities of the metalens under the laser fabrication conditions allow for the successful integration with the nanocone array (∼200 nm diameter) and diffraction-limited focusing (within 50 μm). The dual-material 3D metastructure enables simultaneous filtering and focusing for selected wavelengths within a distance of 20 μm under incoherent white light illumination. Our results show promise for expanding the degrees of freedom of light manipulation in flat optics and the implementation of hybrid and multifunctional photonic devices in CCD and CMOS-compatible, high-resolution light field prints for 3D display.