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Novel low-temperature Er3+ doping of lithium niobate

Low temperature doping procedure is employed to make erbium doped lithium niobate substrates. The doping process is studied for X-, Y- and Z-cuts in both virgin and proton exchanged wafers. The amount as high as 9 weight percent of erbium was found in X-cuts when the doping was performed from a mixture of molten nitrates containing 10 weight percent of erbium slat after 5 hours diffusion at 400 degrees C. The content of erbium in Z- and Y-cuts as well as in the proton exchanged X-cuts was found to be much lower, below 0.5 percent. In-diffused erbium ions concentration is localized in a very thin layer, which can be extended by a subsequent annealing. Annealed proton exchanged waveguides were fabricated in the erbium doped wafers without any deterioration of the samples surfaces.