Low-loss waveguides in a single-crystal lithium niobate thin film

We report low-loss channel waveguides in a single-crystal LiNbO3 thin film achieved using the annealed proton exchange process. The simulation indicated that the mode size of the alpha phase channel waveguide could be as small as 1.2 mu m(2). Waveguides with several different widths were fabricated, and the 4 mu m-wide channel waveguide exhibited a mode size of 4.6 mu m(2). Its propagation loss was accurately evaluated to be as low as 0.6 dB/cm at 1.55 mu m. The single-crystal lattice structure in the LiNbO3 thin film was preserved by a moderate annealed proton exchange process (5 min of proton exchange at 200 degrees C, followed by 3 h annealing at 350 degrees C), as revealed by measuring the extraordinary refractive index change and x ray rocking curve. A longer proton exchange time followed by stronger annealing would destroy the crystal structure and induce a high loss in the channel waveguides. (C) 2015 Optical Society of America