Circularly Polarized Light Emission and Real-Image Projection from Cellulosic Converging Lenses with Adjustable Chiral Photonic Bandgaps

The efficient generation of circularly polarized light (CPL) is crucial in information technologies such as optical communications and three-dimensional displays. In nature, many plants and animals can transform unpolarized light into CPL with chiral helical superstructures, which has inspired the development of CPL-related materials and devices. Herein, by combining the self-assembled chiral nematic liquid crystalline microstructures of cellulose nanocrystals with geometrical configurations of Fresnel lenses, free-standing solid-state cellulosic converging lenses with large sizes, circular polarization features, and adjustable chiral photonic bandgaps were fabricated at low cost, which could produce CPL beams exhibiting dissymmetry factors (<i>g</i> = 2(<i>I</i> _L - <i>I</i> _R)/(<i>I</i> _L+ <i>I</i> _R)) up to -0.61 ± 0.02 by focusing sunlight and generate real images of distant objects. These results may help guide the development of polarized light sources or imaging systems, and also suggest a simple method to construct multifunctional optical devices from photonic crystals.