相比与L波段，掺铒光纤放大器(EDFA)在C波段的增益谱平坦必须借助光学滤波器实现。由于带宽非适配，传统的长周期光纤光栅(LPFG)无法有效压缩增益起伏。为改善EDFA的增益平坦度，将LPFG与弱反射率光纤布拉格光栅对(FBG-P)结合构成组合光栅增益平坦器，利用FBG-P的弱谐振特性进一步抑制EDFA的增益谱起伏。通过仿真分析优化了相关重要参数，并实验测试了对应方案的增益平坦特性。数值结果表明，所提方案将EDFA在1520~1560 nm区域内的增益起伏限制在±0.45 dB，与单LPFG结构相比，增益平坦改善达49.31%。

Compared with L band, the gain flattening of erbium doped fiber amplifier (EDFA) in C band should be conducted by optical filter. Due to unmatched bandwidth, the conventional long-period fiber grating (LPFG) cannot efficiently reduce the fluctuation of gain spectrum. Aiming to improve gain flatness of EDFA, a novel scheme named composite fiber grating is proposed which combining LPFG and fiber Bragg grating-pair (FBG-P) with weak reflectivity. Moreover, the key parameters of CFG are optimized by simulation, and its performance of gain flattening is also experimentally tested. The numerical results show that, the proposed scheme achieves controlling the fluctuation within ±0.45 dB in the range from 1520 nm to 1560 nm, and the improvement on gain flattening reaches 49.31% comparing with the scheme based single LPFG.