Mode coupling in FM-EDFAs caused by fiber bending: theory and experiments

Refractive index perturbation caused by erbium-doped fiber (EDF) bending is inevitable in the fabrication of erbium-doped fiber amplifiers (EDFAs). The resulting mode coupling might bring about the deviation of theoretical results from experimental data. We present a theoretical model of FM-EDFAs with mode coupling due to fiber bending and carry out a proof-of-concept experiment by a 3.2-m-long EDF stretcher. Our experiments show that the fluctuation of modal gain due to fiber bending is about 1.5 dB for LP01 and LP11e modes, and about 2.5 dB for LP11o mode, and the theoretical model is more useful for the FM-EDFA design in the presence of fiber bending.