Gain Equalization for Erbium-Doped Fiber Amplifiers by the Synthesis of a Long-Period Fiber Grating

We present a method for the synthesis of long-period fiber gratings (LPFGs) which is based on a genetic algorithm (GA). The method is applied in the design of LPFG-based gain equalizers for erbium-doped fiber amplifiers (EDFAs). Differently from other works, gain equalizers designed by our method require only one nonuniform LPFG. The magnitude and phase profiles of the coupling coefficient of the LPFG are optimized by the GA. Also, unlike other designs, our synthesized LPFG couples the fundamental core mode to only one cladding mode across the whole EDFA bandwidth. Comparison with the results obtained in previous works shows that our gratings have a smaller range of variation of the coupling coefficient magnitude. This simplifies the fabrication of practical devices.