| In this dissertation we have studied photorefractive phenomena in a nonlinear LiNbO3 crystal doped with Fe as the main focus. Specifically, we investigated recording and permanent fixing of two holographic grating patterns with slightly different periods. Our gratings were designed to serve as Bragg reflectors for different wavelengths around 1550 nm. In the process we employed two variations to the thermal fixing technique, and studied evolution of the holograms during recording, optical erasure, and revealing. Our fixed gratings had the same strength as a result of developed exposure schedule for recording phase. The estimated amplitude of refractive index modulation was of the order of 10-5 limited by the concentration of Fe in the crystal used. We have compared our results with previously published ones and find them in good agreement. Therefore, the work performed in this dissertation can be viewed as the proof-of-principle demonstration on recording and fixing of a pair of the index gratings. We have provided theoretical calculations and discussions on the possibility of increasing the magnitude of the index modulation. A pair of the index gratings with the larger index modulation may eventually be used to implement the recently proposed traveling-wave electro-optic modulator based on cascaded Bragg gratings. |
