Rigorous FM-EDF design with an oversized two-layer erbium ion distribution for C-band DMG mitigation

Abstract

We present a rigorous design of few-mode erbium doping fiber (FM-EDF) with an oversized two-layer erbium ion distribution at the central region with effective differential modal gain (DMG) mitigation over the C-band. The proposed erbium doping distribution allows for a similar overlapping integral value among the guided modes, leading to a signal gain equalization over the C-band. When the length of the proposed FM-EDF is 8 m under the cladding pumping power of 2.5 W, our calculated results reveal that four linearly polarized (LP)-modes can achieve an average gain per mode of 24.8 dB and a typical DMG of less than 0.64 dB over the C-band. Meanwhile, we carry out numerical simulations to explore the fabrication tolerance of the oversized two-layer erbium doping distribution with respect to the DMG, indicating stable DMG mitigation over the C-band. We believe that such new manipulation of erbium doping distribution is helpful for the multiple-dimensional multiplexing of fiber optical transmission.