Design of double-pass dispersion-compensated Raman amplifiers for improved efficiency: guidelines and optimizations

In this paper, an intensive theoretical and experimental investigation is conducted on the dispersion-compensating Raman amplification module configured in double-pass geometry. An analytical model is developed to study the gain/pump efficiency improvement and the noise performance in a novel double-pass discrete-Raman-amplifier (DCRA) system. This paper demonstrates that the gain and pump efficiency can be improved significantly by using the double-pass configuration and the pump light reflector. The impairments of multipath-interference (MPI) noise due to the Rayleigh scattering and the external reflection are analyzed in order to balance the high gain efficiency and the enhanced MPI noise in the double-pass DCRA. Furthermore, the nonlinear penalty in the DCRA system is investigated and a 10-Gb/s nonreturn-to-zero (NRZ) signal transmission in a 4 /spl times/ 100-km fiber system is simulated. The signal quality and bit-error rate are examined, and the optimization is done with reference to the input signal level and Raman gain; hence, the impact of double-pass DCRA on the dispersion-compensated optical communication systems is explored.