Fabrication of photonic crystals by three dimensional interference with four waves

我们研究了在折射率随光强变化的材料中利用四个光波的三维干涉图样制备光子晶体的方法。在最初的提议中，我们尝试了使用光敏聚合物的方法。不幸的是，英国的一个研究小组报告了同样的结果，因此，我们略微改变了研究方向。我们选择光折变材料代替光敏聚合物作为三维干涉图样的记录材料。由于折射率的变化可达10^~(-2)~(-2)量级，因此不能实现光子带隙。然而，这种折射率的三维调制产生了一些显著的效应，如反常的群速度，这是未来光子器件的一个很有前途的候选者。当我们考虑三维四波干涉时，我们必须考虑小时波偏振与k矢量方向的关系。从理论上研究了偏振对三维干涉的影响。我们还比较了所有四个波的同时曝光和每组两个波的顺序曝光。我们还研究了光折变晶体中三维折射率图案的非挥发记录。我们尝试了两种方法。一种是使用一个元素的三个能级的方法，另一种是使用两种不同的元素作为杂质。我们用这两种方法对光折变材料中的双光子记录进行了理论和实验研究。我们获得了关于非易失性记录的基础知识。

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.