Fabrication of tunable photonic crystals

Tunable photonic crystals were prepared by the infiltration of photoresponsive liquid crystals into inverse opal structure films. The inverse opal structure was fabricated and the voids were infiltrated with liquid crystals, which was a mixture of 4-pentyl-4'-cyanobiphenyl (5CB) and 4-buthyl-4'-methoxyazobenzene (AzoLC) with a volume ratio of 97:3. Tuning of their optical properties could be realized by means of photoinduced phase transition of liquid crystals. The materials could store and display images that were created by the irradiation with UV light through a photo mask. A great advantage of this technique is that the films themselves can display an image without the use of polarizers or other assistant materials, and they can also render a color display that can be selected by varying the lattice distance of the inverse opal structure. In addition, we achieved the control of their optical properties by the application of an electric field. Because the state induced by the electric field is different from that engendered by a photoinduced phase transition, it is now possible to switch between three states by a combination of these two techniques. The materials that we have developed have possibilities for practical applications in optical devices.