Second harmonic generation in reverse-proton-exchanged waveguides fabricated in periodically-poled stoichiometric lithium tantalate

In this paper, we will examine second harmonic generation in buried waveguides created through reverse-proton-exchange in periodically-poled stoichiometric lithium tantalate. Waveguides of various widths were fabricated on a 2.5cm long SLT sample provided with 5 poling periods ranging from 17.7 to 18.5μm. The fabrication parameters were chosen according to the modelling guidelines recently proposed, in order to obtain single-mode propagation at 1.55μm with good fiber mode-matching. The proton-exchange was performed in pure benzoic acid at 280°C for 1h 45m, followed by annealing in air at 350°C for 3h. The burying step was achieved by a reverse-exchange process involving the immersion of the sample for 25h at 350°C in an euthectic melt composed by LiNO₃, KNO₃ and NaNO₃. The nonlinear characterization was performed by measuring the second harmonic generation efficiency as a function of the wavelength.