RECOVERY OF 2ND-ORDER OPTICAL NONLINEARITY IN ANNEALED PROTON-EXCHANGED LINBO3

The second-order nonlinear coefficients in proton-exchanged LiNbO3 have been measured for the first time as a function of annealing time. Measurements of reflected second harmonic power indicate that the second-order nonlinear coefficient d33 is reduced to 60% of the bulk value as a result of proton exchange in pure benzoic acid. We also show 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 thick proton-exchanged layer, annealed for 10 h at 350-degrees-C.