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 L P 01 and L P 11e modes, and about 2.5 dB for L P 11o mode, and the theoretical model is more useful for the FM-EDFA design in the presence of fiber bending.