Frequency Down-Conversion of Dual-Wavelength Raman Fiber Laser in PPLN-Based Optical Parametric Oscillator

We report on frequency down-conversion of dual-wavelength (DW) Raman fiber laser in a periodically poled lithium niobate-based optical parametric oscillator. The DW pump source was fixed at 1060 and 1111 nm that was obtained based on stimulated Raman scattering effect by combining a home-made linearly polarized 1060-nm fiber laser and 137-m-long polarization-maintaining passive fiber. The total pump power went through three stages, in the latter two of which the 1111-nm wave appeared. In the entire experiment, the 1060-nm pump beam achieved parametric oscillation and generated 1626-nm signal beam and 3056-nm idler beam. The 1111-nm pump beam generated 3503-nm idler beam based on difference frequency generation (DFG) between itself and 1626-nm signal beam in the second stage. With power enhancement, it built independent parametric oscillation in the third stage and generated 1621-nm signal beam as well as 3530-nm idler beam. The DW idler power ranged from 3.94 to 7.78 W in the latter two stages. The power and efficiency characteristics in frequency conversion processes of 1060- and 1111-nm pump beams were also analyzed separately.