High-order Photonic Cavity Modes Enabled 3D Structural Color

TL;DR

This paper introduces a novel method for 3D printing of structural colors using high-order photonic cavity modes in woodpile photonic crystals, enabling vivid, angle-independent colors without post-processing.

Contribution

The authors developed a new side-illumination strategy to support high-order modes in WPCs, allowing one-step 3D printing of structural colors with commercial TPL.

Findings

Achieved vivid colors with ~25 nm FWHM reflectance peaks.

Demonstrated voxel-level color control in arbitrary 3D shapes.

Produced colors with ~85% sRGB gamut and large viewing angles.

Abstract

It remains a challenge to directly print three-dimensional arbitrary shapes that exhibit structural colors at the micrometer scale. Woodpile photonic crystals (WPCs) fabricated via two-photon lithography (TPL) are promising as building blocks to produce 3D geometries that generate structural colors due to their ability to exhibit either omnidirectional or anisotropic photonic stopbands. However, existing approaches have focused on achieving structural colors when illuminating WPCs from the top, which necessitates print resolutions beyond the limit of commercial TPL and/or post-processing techniques. Here, we devised a new strategy to support high-order photonic cavity modes upon side-illumination on WPCs that surprisingly generate large reflectance peaks in the visible spectrum. Based on that, we demonstrate one-step printing of 3D photonic structural colors without requiring post-processing or subwavelength features. Vivid colors with reflectance peaks exhibiting a full width at half maximum of ~25 nm, a maximum reflectance of 50%, gamut of ~85% of sRGB, and large viewing angles, were achieved. In addition, we also demonstrated voxel-level manipulation and control of colors in arbitrary-shaped 3D objects constituted with WPCs as unit cells, which has great potential for applications in dynamic color displays, colorimetric sensing, anti-counterfeiting, and light-matter interaction platforms.