Encoding Hidden Information onto Surfaces Using Polymerized Cholesteric Spherical Reflectors
Yong Geng, Rijeesh Kizhakidathazhath, Jan P. F. Lagerwall
Abstract
Abstract The omnidirectional Bragg reflection of cholesteric liquid crystals molded into spheres turns them into narrow‐band retroreflectors with distinct circular polarization. It is shown that these cholesteric spherical reflectors (CSRs) can encode information onto surfaces for far‐field optical read‐out without false positives, as the selective retroreflectivity allows the background to be easily subtracted. In order to hide the encoding from detection by the human eye, the retroreflection band is tuned to the near‐UV or IR spectra, allowing ubiquitous deployment of CSRs in human‐populated environments. This opens diverse application opportunities, for instance, in supporting safe robotic navigation and in augmented reality. A key breakthrough is our ability to permanently embed CSRs in a binder such that undesired scattering and reflections are minimized. This is achieved by realizing CSRs as shells that are polymerized from the liquid crystalline state. The resulting shrinkage around an incompressible fluid deforms the thinnest region of each shell such that it ruptures at a well‐defined point. This leaves a single small hole in every CSR that gives access to the interior, allowing complete embedding in the binder with optimized refractive index, minimizing visibility.