Highly efficient single-pass second harmonic generation in a periodically poled MgO:LiNbO₃ waveguide pumped by a fiber laser at 1111.6 nm

A green light at 556 nm is generated by direct frequency doubling of a fiber laser at 1111.6 nm with a periodically poled MgO:LiNbO3 waveguide. We have investigated optical inhomogeneities by measuring the temperature tuning curve of second harmonic generation, and the obtained parameters are used for identifying the uniformity of the waveguide. The thermal dephasing could be diminished by adjusting the crystal temperature, and the conversion efficiency was maximized. Finally, an output power of 111.8 mW at 556 nm was generated with 213 mW of coupled fundamental light under optimum conditions, which corresponds to 52.5% conversion efficiency.