Gain-forming effect on optical signal-to-noise ratio in Raman fiber amplifier.

We have introduced the comprehensive optical-to-noise ratio (OSNR) to investigate simultaneously the effects of all three major linear noise sources in distributed Raman fiber amplifier (DRFA). The total noise power contains double Rayleigh backscattering (DRB) noise, amplified spontaneous emission (ASE) noise, and relative intensity noise (RIN). Also, we have introduced an approximated gain profile approach, which helps in evaluating the OSNR for higher-order pumping (HOP) configuration for backward, forward, and bidirectional DRFA schemes. Finally, by applying the dynamic and static full-numerical computations on a system of eight wavelength division multiplexing (WDM) channels (for amplifier lengths of 70, 140, and 210 km), we demonstrated that for RIN frequencies greater than 100 kHz, the higher-order bidirectional pumping scheme exceeds the backward schemes by 12 dB. [ABSTRACT FROM AUTHOR]