Gain flattening and clamping in L-band ring EDFA incorporating fiber Bragg grating

A new design of long wavelength band erbium-doped fiber amplifier (L-band EDFA) is experimentally demonstrated based on ring laser cavity to obtain better gain flatness as well as gain clamping characteristics. It uses a fibre Bragg grating (FBG) to provide laser feedback, which is arranged to propagate in the opposition to the signal in the amplifier by a pair of circulators. A flat-gain spectrum with less than 1.1 dB variation between 1568 nm and 1604 nm was observed with the laser wavelength at 1560 nm. A gain-clamping effect also was observed with this configuration, which provided a constant gain for all tested input signal powers from -40 dBm until 0 dBm.