Optically switchable photonic crystals based on inverse opals partially infiltrated by photoresponsive liquid crystals

We demonstrate optically switchable photonic crystals based on SiO ₂ inverse opals infiltrated with photoresponsive liquid crystals. The optical properties of the hybrid organic/inorganic structure were characterized by measuring reflectance spectra. The Bragg reflection of the photonic crystal, i.e. photonic band gap, can be switched upon UV photoirradiation. The physical mechanism underlying this switchable behavior is the nematic-isotropic phase transition of the liquid crystals inside the opals triggered by the trans-cis isomerization of the photochromic liquid crystal molecules, resulting in a change of the refractive index contrast between the liquid crystal and the SiO ₂ inverse opal. The experimental results are in excellent agreement with the analytical calculations. With advantages in cost-effective fabrication, easy integration, and all-optical control, this kind of photonic crystals could find many active photonic applications.