Wide-band gain-flattened fibre amplifiers

Wide-band and gain-flattened fibre amplifiers are indispensable for multiwavelength and long-distance wavelength-division-multiplexed (WDM) optical network systems around 1500 nm. We review the configurations and amplification characteristics of fibre amplifiers featuring flat gain and high gain-bandwidth product. Different approaches resulting in wide-band and gain-flattened amplification in the third communication window are reviewed.