Co- and counter-propagating second-order-pumped lumped fiber Raman amplifiers

In conclusion, a comparison has been made between co- and counter-propagating first- and second-order pumping in U-band lumped fiber Raman amplifiers. It has been shown that the copropagating pump scheme results in much higher gain increases, which agrees with simulation results. In both the co- and counter-propagating pumps schemes, the noise figure was found to only minimally increase. We believe that second-order Raman pumping can be beneficial in lumped systems as the gain evolution along the fiber can be tailored to specific needs. In addition, undesirable nonlinear effects from a single high-power pump can be suppressed by distributing the pump power between two orders, while still obtaining high Raman gains.