ELECTROOPTIC COEFFICIENT VARIATION IN PROTON-EXCHANGED AND ANNEALED LITHIUM-NIOBATE SAMPLES

A new technique to measure relative changes in the electrooptic (EO) c oefficient of a material is presented. It is used to measure the spati al variation of the EO coefficient in x-cut lithium niobate caused by the annealed proton exchange technique. The lithium niobate samples ar e proton exchanged at different temperatures for varying times. The me asurements presented indicate significant degradation of the EO coeffi cient immediately after the proton exchange process. The samples are a nnealed at 375 degrees C to enable recovery of the EO coefficient. Sam ples processed in benzoic acid for 30 min at a temperature of 240 degr ees C show immediate recovery of the EO coefficient upon thermal annea ling. Samples processed ire benzoic acid for 5 h at a temperature of 1 80 degrees C shaw a slower recovery of the EO coefficients requiring l onger periods of therman annealing even though the diffusion depth is the same as in the previous case. Samples processed in benzoic acid fo r 5 h at a temperature of 240 degrees C exhibit significant cracking w hich worsens progressively upon thermal annealing. The EO coefficient cannot be restored in all areas even after a long 8-h anneal step.