Emission and Absorption Cross-Sections of Mg/Er-Codoped Near-Stoichiometric ${\rm LiNbO}_{3}$ Crystals

De-Long Zhang,Jian Gao,Edwin Yue-Bun Pun,Yu-Heng Xu,Liang Sun,Chao Xu,Juan-Antonio Valles

doi:10.1109/jqe.2010.2050863

Abstract

Near-stoichiometric (NS) (Mg:) Er:LiNbO 3 crystals were grown from melts ([Li 2 O]:[Nb 2 O 5 ] = 1:1) containing 0.0/0.5, 0.5/0.5, and 1.0/0.5 mol%/mol% MgO/Er 2 O 3 . OH absorption study shows that the optical damage threshold Mg concentration of the Er/Mg-codoped NS crystal is just near 1.0 mol%. Polarized visible and near infrared, and unpolarized mid-infrared (2.7 μm, 4 I 11/2 → 4 I 13/2 ) emission spectra of Er 3+ ion in these crystals were measured. From measured emission spectra, the emission and absorption cross-section spectra were calculated based upon McCumber theory, and compared with the data of congruent Er:LiNbO 3 bulk material and/or Ti-diffused Er:LiNbO 3 strip waveguide and the results obtained from the direct unpolarized optical absorption measurements. The 550, 980, and 1530 nm emission lifetimes were also measured, and compared with the Judd-Ofelt theoretical values and the measured values of the congruent material. The results show that the polarized absorption cross-section data derived from the emission spectra are comparable to the unpolarized cross-section data from direct absorption measurements. The emission and absorption cross-sections, their polarization dependences as well as the lifetime all change definitely as the crystal composition shifts from the congruent point to the near-stoichiometry. In the NS crystal, the Er 3+ ion has smaller emission and absorption cross-sections, and longer lifetimes. In contrast, MgO codoping has less effect on the emission and absorption cross-sections, and lifetime.

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