Dependence of refractive index on hydrogen concentration in proton exchanged LiNbO3

The nonlinear relationship between refractive index and hydrogen concentration has been experimentally determined for proton exchanged LiNbO3, incorporating the effects of partial and full annealing. Complete annealing results in low-loss waveguides in the alpha phase with small surface index changes (less than 0.02). The anneal conditions needed to reach the alpha phase can be estimated using the measured temperature dependence of the anneal diffusion coefficient. A model is presented which attributes the index change in the alpha phase to the addition of hydrogen and the loss of lithium, which is consistent with experimental results. (I.E.)