Electrooptic coefficient variation in proton exchanged and annealed lithium niobate samples

A new technique to measure relative changes in the electrooptic (EO) coefficient of a material is presented. It is used to measure the spatial variation of the EO coefficient in x-cut lithium niobate caused by the annealed proton exchange technique. The lithium niobate samples are proton exchanged at different temperatures for varying times. The measurements presented indicate significant degradation of the EO coefficient immediately after the proton exchange process. The samples are annealed at 375°C to enable recovery of the EO coefficient. Samples processed in benzoic acid for 30 min at a temperature of 240°C show immediate recovery of the EO coefficient upon thermal annealing. Samples processed in benzoic acid for 5 h at a temperature of 180°C show a slower recovery of the EO coefficients requiring longer periods of thermal annealing even though the diffusion depth is the same as in the previous case. Samples processed in benzoic acid for 5 h at a temperature of 240°C exhibit significant cracking which worsens progressively upon thermal annealing. The EO coefficient cannot be restored in all areas even after a long 8-h anneal step