Manipulation of the photorefractive properties of ferroelectric waveguides by ion-beam implantation
This thesis presents the results of a study of ion-beam implantation (IBI) and the effect it has on the photorefractive properties of ferroelectric waveguides. IBI was used to create waveguides in strontium barium niobate (SBN) and lithium niobate in addition to modifying the properties of annealed proton exchanged (APE) channel waveguides fabricated in lithium niobate. Low loss SBN planar waveguides were fabricated by ion-beam implantation. These waveguides represent the first reported in this material to have preserved their photorefractive properties. Two-beam coupling was used as a technique to measure the photorefractive gain and response time in the waveguides; it was observed that unlike IBI waveguides in BaTiO3 and KNbO3, the gain direction had not reversed and the response time had decreased by two orders of magnitude. Evidence of a nonlinear dependence of the response time on intensity indicates that these results are due to oxygen vacancies, induced by the implant, which act as shallow traps. This hypothesis was strengthened when IBI was used as a post-processing technique on APE LiNbO3 channel waveguides. It was observed that for a high enough implant dose of H+ ions, the photorefractive effect was dramatically reduced. This is attributed to the formation of oxygen vacancies due to the implant which reduce the photovoltaic currents within the material; this procedure is thought to be similar to the mechanism responsible for reducing the photorefractive effect in MgO doped LiNbO3. These effects were not observed in planar Fe:LiNbO3 waveguides formed by ion-beam implantation. KTP channel waveguides were fabricated using ion-exchange. The photorefractive susceptibility of these waveguides was assessed and compared to APE LiTaO3 channel waveguides. It was observed that the photorefractive susceptibility of KTP was appreciably lower than that of LiTaO3.