Tailored modal gain in a multi-mode erbium-doped fiber amplifier based on engineered ring doping profiles

摘要

Various space division multiplexing (SDM) schemes are currently investigated as a way to overcome the capacity limit of data links. We here focus on mode division multiplexing (MDM) in a multi-mode fiber (MMF). Towards long-haul data transmission, for which signal amplification is a key enabling component, we investigate a simple approach to precisely control the mode-dependent gain (MDG) between the co-propagating LP_(01) and LP_(11) modes of an erbium-doped few-mode fiber amplifier (MM-EDFA) by engineering a multi-ring doping profile. In practice, the mode dependent loss of the few-mode transmission fiber must be taken into account in order to equalize the gain for all modal channels. In a step towards practical implementation of MM-EDFA for long-haul SDM, we extend the single ring doping approach to incorporate multi-ring and multi-level doping. Through numerical simulations we study the optimization of the width and doping level of each ring so as to control the MDG. We further discuss the possibility of modal gain equalization through zero-differential modal gain (ZDMG) points in a single stage MM-EDFA, or via tuning of pump powers in a dual-stage MM-EDFA configuration.