Ultra-low noise figure in optical fiber amplifier by tailoring the mode field profile of erbium-doped fiber

We present a numerical analysis of noise performance improvement of the erbium-doped fiber amplifier by flatting the mode field intensity distribution within the interaction region of erbium ions. Three different refractive index types of erbium-doped fiber were used to study the effect of the pump mode intensity distribution on noise performance. The results show that taking advantage of the depressed refractive index erbium-doped fiber which has a flat mode distribution in the fiber core, the maximum reduction of nearly 0.53 dB for noise figure was achieved across the full C-band. Based on the center depressed refractive index profile, the noise figure was further decreased by about 0.1 dB by reducing the doping radius to 0.71 m. Finally, maintaining the same gain level of ~38.3 dBa NF reduction of ~0.63 dB was realized by introducing the center depressed index profile and narrowing the erbium doping region. It is suggested that our investigation shows great potential for improving the noise performance of the erbium-doped fiber amplifier.