Full Geometric Control of Hidden Color Information in Diffraction Gratings under Angled White Light Illumination

TL;DR

This study demonstrates full geometric control of hidden color information in diffraction gratings using advanced nanofabrication, enabling secure information encoding with minimal crosstalk under white light illumination.

Contribution

It introduces a versatile nanofabrication method to encode hidden color information by varying all geometric parameters of gratings, surpassing previous limitations.

Findings

All geometric parameters can be varied to encode information.

Two design approaches successfully hide color information.

Crosstalk is minimized with sector separation >= 10°.

Abstract

Under white light illumination, gratings produce an angular distribution of wavelengths dependent on the diffraction order and geometric parameters. However, previous studies of gratings are limited to at least one geometric parameter (height, periodicity, orientation, angle of incidence) kept constant. Here, we vary all geometric parameters in the gratings using a versatile nanofabrication technique, two-photon polymerization lithography, to encode hidden color information through 2 design approaches. The first approach hides color information by decoupling the effects of grating height and periodicity under normal and oblique incidence. The second approach hides multiple sets of color information by arranging gratings in sectors around semi-circular pixels. Different images are revealed with negligible crosstalk under oblique incidence and varying sample rotation angles. Our analysis shows that an angular separation >= 10{\deg} between adjacent sectors is required to suppress crosstalk. This work has potential applications in information storage and security watermarks.