Abstract
<title>Abstract</title> <p>In this paper we present detailed numerical study of the spatial gain dynamics, ASE (amplified spontaneous emission) evolution and NF (noise figure) characteristics of erbium-doped-fiber-amplifiers (EDFAs) operating in the pre-amplifier regime with input signal power − 40 dBm. We first perform parametric analysis of signal gain under bidirectional (1480 nm and 980 nm) and hybrid (1480 nm forward + 980 nm backward and 980 nm forward + 1480 nm backward) pumping configurations for four different EDFA lengths of 5, 10, 15 and 20 m. We solve two-level rate equation EDFA model using the fourth-order Runge-Kutta method (RK4) with iterative forward-backward ASE and pump integration. The results validate that 20 m long EDFA with 1480 nm forward pumping provides optimum gain. Our results reveal 15 m as threshold length beyond which hybrid scheme outperforms bidirectional configuration for 35% to 80% 1480 nm forward pump fraction. This is attributed to the higher ASE build up beyond 15 m causes gain saturation for bidirectional pumping. However for 80% and above pump fraction, both hybrid and bidirectional schemes show nearly identical gain performance. This is because of rapid absorption of the 980 nm backward pump in the first 5 m creates asymmetric pump distribution that suppresses ASE buildup in the latter half of the fiber. The 980 nm forward pumping is suitable for 10 m long EDFA though it performs poorly for 20 m length due to rapid pump depletion and signal reabsorption. These results provide practical guidelines for EDFA operation in optical communication system.</p>