A Multi-Layer Erbium-Doped Air-Hole-Assisted Few-Mode Fiber with Ultra-Low Differential Modal Gain

The air-hole assisted few-mode fiber (AH-FMF) enables modal intensity balance and offers a profound prospect in gain equalization with the combination of adaptive ion doping. In this paper, we proposed an AH-FM-EDF multi-layered erbium doping profile. AH-FM-EDF, due to central air hole, only first radial order modes (LP01, LP11, LP21, LP31) are supported, all confined same high refractive index core region. differential (DMG) is highly reduced by optimizing proportion each layer. Compared uniform doping, DMG from 4 dB 0.14 as triple-layer deployed. Additionally, erbium-doped performs well flattening fabrication tolerance over whole C-band.