Multi-parameter enhanced optical encryption with biphasic chiral photonic crystals.

Encoding information across multiple degrees of light, including spin, wavelength, amplitude, and phase into the multi-level structures of a stimuli-responsive material, presents a highly promising strategy for optical encryption. Here, we present a biphasic chiral photonic crystal platform that addresses the intrinsic coupling among photonic spin, wavelength, and functions, thus providing a multi-parameter security framework that substantially enhances encryption complexity. By integrating two separately photopatternable chiral photonic crystals with opposite handedness into a single cell, independent geometric phase modulation for orthogonal spins and discrete wavelengths is fully released. The near-field polarization interference imaging and far-field spin-multiplexed holography with partly temperature-robust and partly thermally responsive information are demonstrated. Furthermore, we concealed the latitude and longitude coordinates of a destination across two separate far-field images, which are only revealed at the correct combination of temperature, optical spin, and wavelength. This biphasic system fully harnesses light's potential for advanced encryption, which will drastically enhance the security of secure logistics, anti-counterfeiting, and hardware authentication.