Reconfigurable photonic crystals with optical bistability enabled by "cold" programming and thermo-recoverable shape memory polymers

Recently, reconfigurable photonic crystals that can reversibly change and recover their optical properties (e.g. photonic stopbands) in response to external stimuli have aroused much attention. However, developing a photonic crystal with a dynamically tunable nanostructure that can memorize and maintain different nanostructures and related optical properties is still a challenge. Based on capillary pressureinduced "cold" programming and heat-triggered recoverable shape memory polymers, reconfigurable 3D photonic crystal membranes with optical bistability, which show two reversibly tunable stable equilibrium states, are reported in this work. During shape memory programming and recovery processes, capillary pressure created by water evaporation induces "cold" programming of photonic crystal membranes with a disordered temporary state without diffractive peaks at room temperature. The permanent ordered photonic crystal nanostructures with apparent characteristic diffraction peaks can be recovered by heating. The reversible transition of photonic crystals between an ordered permanent state and a disordered temporary state during the cyclical programming and recovery results in a tremendous change in appearance and a large and stable shift of diffraction peaks different from conventionally tunable photonic crystals. This disorder-to-order transition and the tremendous shift of photonic bandgaps enable the photonic crystals to serve as a sensitive optical tool to the probe shape memory effect at the nanoscale. Importantly, a large difference in optical transmittances is shown as no stopband exists in the disordered temporary state, which provides a unique alternative in developing photonic crystal photoswitches with higher contrast and optical switching effect, as well as rewritable photonic devices and displays etc.