In erbium doped fiber amplifier (EDFA), erbium
ions act as a three-level system. Therefore, much higher pump
energy is required to achieve the population inversion in an
erbium doped fiber (EDF). This higher pump energy requirement
complicates the efficient design of an EDFA. However, efficient
use of the pump power can improve the EDFA performance. The
improved performance of an EDFA can be obtained by reducing
the doping radius of the EDF. A smaller doping radius increases
pump-dopant interactions and subsequently increases the pumpphoton
conversion efficiency. Decreasing the doping radius allows
a larger proportion of dopant ions, which are concentrated near
the core, to interact with the highest pump intensity. However,
decreasing the doping radius beyond a certain limit will bring
the dopant ions much closer and introduce detrimental ionion
interaction effects. In this paper, we show that an optimal
doping radius in EDF can provide the best gain performance.
Moreover, we have simulated the well-known numerical aperture
(NA) effects on EDFA gain performance to support our claim.
