Multiple-Ring-Core FM-EDF for Weakly-Coupled MDM Amplification With Low Differential Modal Gain

Abstract

Recently weakly-coupled mode-division multiplexing (MDM) transmission systems and networks based on ultralow-modal-crosstalk few-mode fiber (FMF) have attracted much interest, for which optical amplification technologies with low modal crosstalk and twodimension mode-wavelength gain flattening are highly desired. In this paper, we propose for the first time a design method for few-mode Erbium-doped fiber (FM-EDF) with multiring-core (MRC) structures of both index and Erbium doping, which has high compatibility with the transmission MRC-FMF and low differential modal gain (DMG) with simple pump injection requirement. By sharing the boundaries of ring areas for both index and Erbium doping, the design method also helps to reduce the complexity of preform fabrication. We show by simulation that at 1550-nm signal wavelength, a 6-mode MRC-EDF can achieve a minimum DMG of 0.35-dB with only LP 11 pump light injection and a 10-mode MRC-EDF can achieve a minimum DMG of 0.60-dB with LP 01 and LP 03 pump lights injection. Besides, the tolerance of DMG to the variation of fiber parameters induced by fabrication is analyzed. The proposed FM-EDF is beneficial for the practical applications of weakly-coupled MDM transmission systems and networks.

Gain equalization of few-mode fiber amplifier based on particle swarm optimization

“…With the help of the FM-EDF with ring-core [5][6][7][8], multi-layer refractive index [9][10][11] or air-hole [12], both high gains and low DMG are obtained. In the fiber design, the forward fixed variable (FFV) method is mainly applied [7,11], that is, sequentially changin * g one certain parameter within a suitable interval, while the others remain unchanged.…”

Design of Ring-Core Few-Mode-EDFA With the Enhanced Saturation Input Signal Power and Low Differential Modal Gain

“…To realize mode-division multiplexing (MDM) transmission over the long-haul FMF, inline optical amplifiers are indispensable. It has been reported that few-mode erbiumdoped fiber amplifiers (FM-EDFAs) can be applied for the long-haul FMF transmission with good performances [5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21]. One of the most important FM-EDFA characteristics is the differential modal gain (DMG), which needs to be carefully mitigated, for the successful implementation of multiple-input multiple-output (MIMO) signal processing at the receiver side.…”

“…First, the mode profile of the pump laser can be optimized, and the cladding pumping becomes a popular choice because it can provide more uniform pump power distribution over the optical fiber cross section [5]. Secondly, the optimization of the erbium doping distribution is helpful [10][11][12], including the convenient step-index FMF with the ring doping [13] and the doping combination at both ring and central areas [14]. Finally, the corresponding refractive index (RI) profile can be designed in order to manipulate various intensity profiles of guided modes [21].…”