Fabrication of photonic crystals by three dimensional interference with four waves

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We investigated the fabrication of the photonic crystals by three dimensional interference pattern with four lightwaves in materials whose refractive index is changed according to the light intensity. At first proposal, we tried the method using photo-sensitive polymers. Unfortunately, an British research group has reported the same results, thus, we changed the research direction slightly. We chose photorefractive materials instead of photo-sensitive polymers as a recording materials of the three dimensional interference pattern. Because the change of the refractive index is up to the order of 10^<-2>, photonic band gap cannot be realized. However, this kind of three dimensional modulation of the refractive index causes several remarkable effects, such as anomalous group velocity, and a promising candidate for the future photonic devices.When we consider the three dimensional four-wave interference, we have to take into account of the relation of the polarization of hour waves as well as the direction of k vectors. We investigated the effect of the polarization on the three dimensional interference theoretically. Also we compared the simultaneous exposure with all four waves and the sequential exposure with each set of two waves.We also studied the non-volatile recording of the three dimensional index patterns in photorefractive crystals. We tried two methods. One is a method using three levels of one element, and the other is that using two different elements as impurities. We studied two photon recording in photorefractive materials with these two methods both theoretically and experimentally. We obtained fundamental knowledge about the non-volatile recording.