Full-colour nanoprint-hologram synchronous metasurface with arbitrary hue-saturation-brightness control

The colour gamut, a two-dimensional (2D) colour space primarily comprising hue and saturation (HS), lays the most important foundation for the colour display and printing industries. Recently, the metasurface has been considered a promising paradigm for nanoprinting and holographic imaging, demonstrating a subwavelength image resolution, a flat profile, high durability, and multi-functionalities. Much effort has been devoted to broaden the 2D HS plane, also known as the CIE map. However, the brightness (B), as the carrier of chiaroscuro information, has long been neglected in metasurface-based nanoprinting or holograms due to the challenge in realising arbitrary and simultaneous control of full-colour HSB tuning in a passive device. Here, we report a dielectric metasurface made of crystal silicon nanoblocks, which achieves not only tailorable coverage of the primary colours red, green and blue (RGB) but also intensity control of the individual colours. The colour gamut is hence extruded from the 2D CIE to a complete 3D HSB space. Moreover, thanks to the independent control of the RGB intensity and phase, we further show that a single-layer silicon metasurface could simultaneously exhibit arbitrary HSB colour nanoprinting and a full-colour hologram image. Our findings open up possibilities for high-resolution and high-fidelity optical security devices as well as advanced cryptographic approaches. Structural colours with hue-saturation-brightness (HSB) control and independent integration with full-colour hologram open up possibilities for optical security devices and advanced cryptographic approaches. Researchers from China and Singapore propose a crystalline-silicon nanoblock metasurface that is able to control the intensity and phase of transmitted red, green, blue (RGB) lights independently. By mixing the three RGB nanoblocks with different intensity proportions together, it is possible to control the HSB value of the transmitted light, pushing the metasurface structural colour from conventional two-dimensional hue-saturation space to a real three-dimensional HSB space. Furthermore, arbitrary HSB colour printing and full-colour hologram images can be integrated in one single metasurface structure. That makes a drastic leap for singlet multifunctional metasurfaces, instead of cascading multiple metasurfaces with one for colourprinting and the other for hologram respectively.