Femtosecond laser-written quasi-phase-matched waveguides in lithium niobate

We report on thermally stable optical waveguides written in periodically poled lithium niobate with a femtosecond laser using a two line approach. Both fundamental and second harmonic light at 1064 and 532 nm are guided with low damping losses. In a 10-mm-long sample a conversion efficiency of 58% was achieved.