Green up-conversion and near-infrared luminescence of femtosecond-laser-written waveguides in Er3+, MgO co-doped nearly stoichiometric LiNbO3 crystal.

Abstract

We report on the green up-conversion and near-infrared (NIR) emission in Er3+, MgO co-doped nearly stoichiometric LiNbO3 waveguides fabricated by femtosecond laser writing. The waveguides with so-called Type I geometry by laser writing support nearly single-mode propagation of light at NIR wavelength of 1.55 μm. In addition, it has been found that the guidance is only along the vertical (i.e., TM) polarization, which is due to the laser-induced positive changes of extraordinary index in the guiding core. The green up-conversion at 550 nm and 528 nm, corresponding to the transitions of 4S3/2 → 4I15/2, 2H11/2 → 4I15/2, as well as the NIR luminescence emission at C-band centered at 1550 nm under 4I13/2 → 4I15/2 transition have been realized in the waveguides, respectively. Our results have shown that the intensities of the guided-wave green up-conversion and NIR emissions are higher than those obtained from the bulk, which may be owing to the enhanced intracavity optical intensities of the waveguide with respect to the bulk.