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Dynamic EDFA gain-flattening filter using two LPFGs with divided coil heaters

We introduce a new type of dynamic erbium-doped fiber amplifier (EDFA) gain-flattening filter using two long-period fiber gratings (LPFGs) equipped with divided coil heaters. By individually controlling each of the 64 segments of coil heaters over the grating, we adjusted the temperature distribution of LPFGs piecewise-uniformly, thus, to maintain optimum gain-flatness for different EDFA operation conditions. By controlling the different cladding modes for each LPFGs, we also achieve enhanced controllability/flexibility for the filter spectrum of dynamic LPFG. Wide dynamic-range gain/power control with less than 0.8-dB signal ripples, over 30 nm was demonstrated.