Detailed study of four-wave mixing in Raman DFB fiber lasers.

We both experimentally and numerically studied the ultra-compact wavelength conversion by using the four-wave mixing (FWM) process in Raman distributed-feedback (R-DFB) fiber lasers. The R-DFB fiber laser is formed in a 30 cm-long commercially available Ge/Si standard optical fiber. The internal generated R-DFB signal acts as the pump wave for the FWM process and is in the normal dispersion range of the fiber. Utilizing a tunable laser source as a probe wave, FWM frequency conversion up to ~40 THz has been demonstrated with conversion efficiency > -40 dB. The principle of such a wide bandwidth and high conversion efficiency in such a short R-DFB cavity has been theoretically analyzed. The simulation results match well with the experimental data.