Refractive-index modulation by change in alignment of liquid crystals (LCS) has been explored: order to disorder phase transition of LCs by photochemical reactions of photoresponsive molecules, order to order alignment change of LCs in the LC phases induced by photochemical reactions. In the order to disorder phase transition of LCs, the refractive index can be changed very quickly while the change in the refractive index is smaller than those induced by the order to order alignment change of LC molecules. In-plane (2 D) and out-of-plane (3 D) alignment change of LCs have been studied. With the out-of-plane alignment change of LC molecules, refractive-index modulation not only to linearly polarized light but also to unpolarized light can be achieved. The alignment change of LCs without photochemical processes is also discussed.