High-Efficiency Erbium-Doped Fiber Amplifier using Mode Field Diameter Adjusting Technique

Abstract

For efficient operation of an Er-doped fiber amplifier (EDFA) at 1.55 µm band it is essential to maximize the pump intensity in the Er-doped region because of the three level system [1], A high NA structure of EDF is effective to reduce the mode field diameter (MFD) of the pump and to achieve strong pump intensity [2], and has resulted in excellent gain performance [3],[4], In practical use, however, such small MFD fibers have a connection/splicing problem due to the mode field diameter mismatching. For example, approximately 1 dB splice loss is expected between an EDF with a 5 µm MFD and a conventional dispersion shifted fiber (DSF) with a 8 µm MFD. The smaller MFD of EDF, the higher splice loss. The increase of splicing loss causes noise figure degradation in pre-amplifiers and decreasing of conversion efficiency in booster amplifiers.