When nanocellulose meets diffraction grating: freestanding photonic paper with programmable optical coupling

Photonic crystals based on plasmonic or dielectric periodic structures have attracted considerable interest owing to their capabilities to control light–matter interactions with tailored precision. By using a nanocellulose derived chiral liquid crystal as a building block, here we demonstrate a bio-inspired dual photonic structure that contains the combination of microscopic periodic 1D surface grating and nanoscopic helical organization, giving rise to programmable colour mixing and polarization rotation. We show that a variation in the photonic band-gap in the bulk matrix leads to simultaneous control over the reflection and diffraction of light with controllable iridescence.