RFA pump-initiated gain augmented spectrum linearization of ASE re-injected EDFA-RFA hybrid amplifier for ultra-dense WDM systems

Wavelength Division Multiplexing (WDM) has gained considerable interest as a promising means to address the demand-driven transmission capacity increase. For proper use of this technology, optical amplification requirement along the transmission line needs to be explored. Amplified Spontaneous Emission (ASE) re-injection technique to enhance the overall Erbium-doped Fiber Amplifier (EDFA) gain spectrum characteristics has been re-examined, and its utility has been favorably extended to Hybrid Optical Amplifiers (HOA) in this work. We analyze the performance of EDFA, ASE re-injected EDFA (EDFA(ase)), and ASE re-injected EDFA and Raman Fiber Amplifier (RFA) based HOA (ER-HOA(ase)) in an ultra-dense high capacity WDM system. The performance is evaluated and compared in terms of Gain (G) and Differential Gain ( increment G) for the optical amplifier configurations mentioned above. This paper investigates the effect of Input Power (P-in) on the performance of these three configurations. Wavelength selection of the RFA pump is also explored since it plays a crucial role in augmenting the gain. Here, the inherent gradient in the RFA gain spectrum is well exploited in achieving spectrum linearization with reduced slope and hence decreasing increment G in the ER-HOA(ase) configuration. After identifying optimal input power, RFA pump wavelength, and RFA length, it is observed that ER-HOA(ase) outperforms both EDFA(ase), and EDFA based configurations where G and increment G is concerned. The ER-HOA(ase) offers a flat gain of 45.19 dB with a minor variation of +/- 0.25 dB. An insight to the processing of ASE spectrum, as it traverses through various units, is also provided. The gain capability of each amplifying unit will have an equal impact on both the signal and ASE spectrum. This is followed by comparing the Quality factor performance of the configurations in a 128 x 10 Gbps, 0.05 nm spaced ultra-dense WDM system, wherein it is observed that ER-HOA(ase) performs the best amongst all. For ER-HOA(ase,) it is observed that Q >= 6 till a distance of 280 km.