General model of signal propagation in a Raman amplified single-mode fiber based coherent optical communication system

• A model governing the signal propagation under Raman amplification is proposed.
• The numerical approach for solving the coupled equations is illustrated in detail.
• An example of using the model to do system characterization is shown.
• Through comparison, we found that the coarse-step method is inaccurate.
• The model can be used to characterize the Raman amplified transmission systems.

The distributed Raman amplifier (DRA) has been widely utilized in state-of-the-art coherent optical communication systems using multi-level modulation formatted signals in order to improve transmission performance. A general model based on Jones vector notation governing the signal propagation under Raman amplified link is proposed. Primary physics including both linear and nonlinear effects have been taken into account. The numerical approach for solving the equations is illustrated in detail. Using the model, system characterization and optimization can be easily performed. We also compare our model with the commonly used coarse-step method. It is found that the coarse-step method will exaggerate the cross-polarization modulation induced impairments by over 6 dB and will become unusable when the pump power is as high as several Watts. The proposed model provides a guideline for the simulation of Raman amplified coherent transmission systems.