System Performance Analysis of Distributed Raman Amplification With Dual-Order Forward Pumping

Performance of distributed Raman amplification (DRA) system with dual order forward (FW) pumping is analyzed with the consideration of both pump relative intensity noise (RIN) to signal phase noise transfer and signal nonlinear interference. The efficiencies of pump RIN to signal phase noise transfer are theoretically analyzed and experimentally verified by measuring signal phase noise introduced by small index intensity modulations applied on the pump lasers. The results indicate that the efficiency of 2nd order pump RIN to signal phase noise transfer can be more than 2 orders of magnitude higher than that from the 1st order pump. Although dual order FW Raman pumping corresponds to a slight increase of amplified spontaneous emission (ASE) compared to using only a 1st order pump, its major advantage comes from the reduction of nonlinear interference noise in a dense wavelength-division multiplexing (DWDM) system. Because pump RIN to signal phase noise transfer has lowpass characteristics, systems at high baud rates, such as 100 Gbaud, are less susceptible to the impact of pump laser RIN.