| In 2003, Ahura Company first introduced the high-power incoherent Raman pump, and illustrated the basic property of this pumping is to provide flat gain. After that, no paper relate to incoherent pumping has been published. In this thesis, distributed fiber Raman amplifiers (DFRAs) with incoherent pumping are investigated and the DFRAs performances are compared to those with the conventional coherent pumping for the first time. To achieve accurate modeling, a theoretical model, which includes effects of multiple-path interference (MPI), anti-Stokes, and Rayleigh scattering, is used, and a new Raman gain coefficient scaling method is employed in modeling. Theoretical modeling of incoherent pump is also given. First of all, these models are verified and proved to be accurate. Investigations are based on the above models for DFRAs with one or more incoherent pumps. By comparing the performance between the two types of DFRAs, we confirmed that DFRAs with incoherent pumping can have a much flatter gain than those with coherent pumping, and made the following contributions: (1) The gain ripple, the most important factor in the design of DFRAs, is reduced exponentially in dB with the increase of spectral width of incoherent pumps; while the average Raman gain, for the same pump power as coherent pumping, decreases linearly in dB and noise performance is degraded slightly due to the reduction of the Raman gain. (2) Keeping the spectral width un-changed and increasing the incoherent pump power improves the average Raman gain and noise performance, but noise is still slightly worse than coherent pumping for the same Raman gain level. (3) When multiple pumping is used, the number of pumping wavelengths is reduced significantly for the same gain ripple if incoherent pumping replaces coherent pumping. |
