Analytical investigation and numerical modelling of optimum EDFA-RFA hybrid optical amplifier for augmented gain and reduced differential spectral gain in ultra-dense WDM environment

Erbium-Doped Fiber Amplifier (EDFA) system is analysed by using coupled mode equations and subsequently through simulations. We aim reduction in differential spectral gain (∆G) while maintaining high gain (G). Analytical elucidation explores pivotal gain influencing parameters which include input signal power ( P S q , 01 z ), EDFA parameters like erbium doping radius to Erbium-Doped Fiber (EDF) core radius ( r d / r c ) ratio, EDF length ( L EDF ) and pump power ( P p , 01 z ). The propagation behaviour of input signal, pump signal, Amplified Spontaneous Emission (ASE), population inversion criteria, G and ∆G observed trends are analysed. Modified Giles model is extended to extract transverse overlap factor confirming gain influencing behaviour of r d . For gain enhancement, ASE re-injection and its utility as a secondary pump source has been exploited. To ensure optimum G and ∆G in the trending research window (C + L band), an ultra-dense ASE re-injected EDFA and Raman Fiber Amplifier (RFA) based Hybrid Optical Amplifier (ER-HOA ase ) setup is investigated. The proposed optimum setup offers high G (> 44.5 dB), low NF (~ 4 dB), reduced ∆G = ± 0.19 dB for 128 WDM channels from 1561.8 to 1568.15 nm spaced 0.05 nm apart. Four hybrid systems are compared: ASE re-injected systems (ER-HOA ase-initial , ER-HOA ase-opt ) and systems without ASE re-injection (ER-HOA initial , ER-HOA opt ). It is observed that the performance of the proposed ER-HOA ase-opt is the highest, followed by ER-HOA ase-initial , ER-HOA opt, and ER-HOA initial . Also, Quality factor performance with initial and optimum parameters is evaluated. Consequently, it is observed that the best performing setup, ER-HOA ase-opt maintains Q ≥ 6 over 290 km of fiber length.