Novelty Design in Gain Flattening Filter of ASE Source Based on Fat Ultra-Long Period Fiber Grating

A new type of gain flattening filter for amplified spontaneous emission （ASE） source based on erbium doped fiber （EDF） is proposed and demonstrated by fabricating and writing two series ultra-long period fiber grating （ULPFG） on single mode fiber （SMF-28）. The novelty method in this research is based on writing the two ULPFGs as fat gratings. The LPG is written by a simple and available arc-discharge method. The pump power based on single-pass backward pump configuration is around 100mW, and the average wavelength is near to 974nm. The gain flattening profile is obtained by 3.4 （±1.7）dB ripple in the wavelength range between 1524nm and 1565nm with 41-nm band width.