DEPTH PROFILING OF PROTON-EXCHANGED LINBO3 WAVE-GUIDES BY MICRO-RAMAN SPECTROSCOPY

Z-cut LiNbO3 wafers were proton exchanged (PE) with pyrophosphoric acid. The polished edges provided a side view of the exchanged region. The region was probed by micro-Raman spectroscopy by stepping a 488.0 nm laser at intervals as small as 0.2 mum across the edge face starting below the exchanged region and moving towards the wafer surface, thereby traversing the PE region. Profiling revealed significant changes, in the 125-800 cm-1 and 3200-3600 cm-1 frequency ranges. The PE region expanded after annealing at 300-degrees-C indicating proton penetration into the wafer. Continued annealing resulted in the progressive recovery of spectral characteristics resembling unexchanged lithium niobate. Micro-Raman profiles provide spectroscopic information regarding which vibrational modes are affected by the exchange and the annealing processes as a function of depth.