On the Analysis and Comparison of Decoupled Modal Gain Equalization Systems for Four-Mode (4M)-EDFAs

Abstract

SpaceDivision Multiplexing (SDM) has gained considerable interest as a promising means to increase transmission capacity per fiber. For proper use of this technology, optical components of transmission line including Erbium-Doped Fiber Amplifiers (EDFAs) need to be re-examined. In this work we analyze modal gain equalization systems obtained from extended Giles model for 4M-EDFA. We introduced a simpler method of calculation of two radial overlap factors extracted from the model using standard B–V curve thus proposing two decoupled systems for Modal Gain Equalization. In Decoupled Mode Specific Pump Combination (MSPC) system so obtained, Differential Modal Gain (DMG) was reduced to 1.55 dB with mean gain of about 28.72 dB. For Modified Erbium Doped Profile (MEDP) system we obtained an optimum Multi-Well Profile. The DMG here showed further reduction to 1.3254 dB with mean gain of about 24.24 dB. Further we report investigation on evolution of ASE for 4M-EDFA for the first time with new performance metric namely ASE ratio to indicate the deviation of noise between four modes. The ASE levels reached in MEDP are smaller than MSPC system thus enabling reduction in Noise Figure. Simulation results and comparison indicated that in MEDP, DMG is more sensitive to variation in length, concentration and wavelength. Each spatial channel in our designed MEDP and MSPC system as well as simple 4M-EDFA system gave good pre-amplification performance for data rates upto 15 Gb/s.