Optically switchable multi-stopband of non-quarter-wavelength dielectric multilayer using azobenzene polymer liquid crystal

Non-quarter-wave stacked dielectric multilayers including azobenzene polymer liquid crystal layers are investigated in this study. The azobenzene polymer liquid crystal has a photoinduced reversible refractive index based on photoisomerization. By using the reversible refractive-index change, the reflectance of a stopband can be controlled. In this system, the azobenzene molecules change their conformation when they are irradiated with ultraviolet (UV) or visible light. In general, stacking many layers of different thicknesses can produce broadband or multicolor reflections for a dielectric multilayer. However, in a multilayer having thick azobenzene layers, UV or visible light used for controlling photoisomerization hardly reaches the bottom part of the multilayer because the light is mainly absorbed at its top surface. To solve this problem, the dependence on the thickness ratio of the multilayer is investigated and a non-quarter-wave stacked multilayer having RGB reflections is experimentally demonstrated using thin azobenzene layers.