Comparison between the performance of the P-doped and Ge-doped Raman fiber lasers based on numerical simulations

With a published model that describes a nested fiber Raman cavity using FBGs as reflectors, we have made numerical simulations for the comparison between the performance of P-doped and Ge-doped fiber. Although the former fibers are the standard choice for fiber Raman lasers due to the large Raman gain, the latter can be also of interest because they present a large Raman shift so that the configuration of the Raman fiber laser can be simplified. We have considered a two-step Raman laser using a P-doped fiber and a six-step Raman laser using a Ge-doped fiber, both pumped by 1060 nm and emitting at 1480 nm. The effects of the Raman fiber length, output coupler reflectivity and splice loss upon the behavior of both lasers are studied. Simulation results show that the P-doped fiber laser requires a longer fiber length while the Ge-doped fiber laser requires a higher output mirror reflectivity, and the RFL using Ge-doped fiber is more sensitive to the splice loss because of its large Stokes wave number. Finally, by comparison in the optimum configuration, we find that the P-doped fiber laser shows better output characteristics than Ge-doped fiber laser.