Spectroscopic site determinations in erbium-doped lithium niobate

Rare-earth (eg., Er3+, Nd3+) based, guided wave optical amplification in lithium niobate (LiNbO3) integrated optic systems is anew and important addition to the field of integrated optics. The application of total site selective spectroscopy to rare-earth-doped LiNbO3 provides the most complete spectroscopic characterization of this class of materials to date. In a previous publication we identified six spectroscopic sites in Er:LiNbO3 using total site selective spectroscopy, two of which are cluster sites which upconvert light using nonradiative energy transfer between Er ions within a given site. In this paper Er3+ Site identifications are made based on a consideration of solid solution defect equations in conjunction with an experimental study of the site distribution as a function of dopant concentration (0.4-2.0 mol % Er:LiNbO3) and the Li/Nb ratio in the crystal. The Li/Nb ratio was altered using a vapor phase equilibration technique. Our results indicate that increasing the Li2O content of Er:LiNbO3 not only reduces the cluster site concentration by similar to 30% but also increases the amount of light absorbed in the crystal by similar to 15%. This observation is, to the best of our knowledge, the first report of post growth materials processing in rare-earth-doped LiNbO3 to effect a change in absorption or cluster;site concentration. In addition, increasing the dopant concentration increases Li2O deficiency in Er:LiNbO3 crystals. Simple solid solution defect model calculations agree with these experimental results.