Dual-stage EDFA for improving the performance of long-haul optical systems

A cascade of single-stage erbium doped fiber amplifiers (SS-EDFAs) are known to improve the signal strength and system reach in long-haul optical systems. However, such a cascade introduces an amplified spontaneous emission (ASE) noise accumulation, which results in system performance degradation. To reduce this ASE noise accumulation, we propose the incorporation of a dual-stage EDFA (DS-EDFA) with a narrow bandwidth (typically 3 nm or even smaller depending on the system under consideration) bandwidth optical bandpass filter (OBPF) in the system. We analyze the role of a DS-EDFA, which is formed using two identical SS-EDFAs, for its effectiveness in improving the overall system performance. The gain vs input power characteristic comparison is provided for the DS-EDFA (without interstage OBPF) modelled in OptSim and MATLAB. A system-level numerical model in MATLAB matching the OptSim parameters has been presented to validate the OptSim results. For a cascade incorporating DS-EDFA with interstage OBPF, a system-level analysis is presented with results obtained from a simulated model designed using OptSim. The results demonstrate the effectiveness of DS-EDFA in improving the optical signal-to-noise ratio (OSNR) and bit error rate (BER) performance of the long-haul optical system under consideration. From the obtained results, the optimum placement of a DS-EDFA at the start of the amplifier chain/cascade is recommended for practical implementation in a long-haul optical communication system.