Optimization of pumping schemes for 160-Gb/s single-channel Raman amplified systems

Three different distributed Raman amplification schemes-backward pumping, bidirectional pumping, and second-order pumping-are evaluated numerically for 160-Gb/s single-channel transmission. The same longest transmission distance of 2500 km is achieved for all three pumping methods with a 105-km span composed of superlarge effective area fiber and inverse dispersion fiber. For longest system reach, second-order pumping and backward pumping have larger pump power tolerance than bidirectional pumping, while the optimal span input signal power margin of second-order pumping is the largest and gets 5-dB improvement compared to backward pumping. Span loss tolerance increased to 140 km with more than 2000-km reach. Optimal signal power variation at both ends of the span can provide about 6-dB positive net gain.