Electrical tuning of three-dimensional photonic crystals using polymer dispersed liquid crystals

Electrically tunable three-dimensional photonic crystals with a tunable wavelength range of over 70 nm of stop gaps between 3 and 4 µm have been generated in a liquid crystal-polymer composite. The photonic crystals were fabricated by femtosecond-laser direct writing of void channels in an inverse woodpile configuration with 20 layers providing an extinction of infrared light transmission of 70% in the stacking direction. Stable structures could be manufactured up to a liquid crystal concentration of 24%. Applying a direct voltage of several hundred volts in the stacking direction of the photonic crystal changes the alignment of the liquid crystal directors and hence the average refractive index of the structure. This mechanism permits the direct tuning of the photonic stop gap.