Recovery of second-order optical nonlinearity in annealed proton-exchanged LiNbO/sub x/

The second-order nonlinear coefficients measured in proton-exchanged LiNbO/sub 3/ as a function of annealing time are discussed. Measurements of reflected second-harmonic power indicate that the second-order nonlinear coefficient d/sub 33/ is reduced to 60% of the bulk value as a result of proton exchange in pure benzoic acid. It is also shown that annealing restores the d-coefficients to almost the original value of the virgin crystal. For example, recovery to approximately 90% of the bulk value was obtained for a sample with a 0.3- mu m-bulk proton-exchanged layer, annealed for 10 h at 350 degrees C.>