Optical fiber amplifiers for WDM optical networks

In recent years, tremendous progress has been made in the development of broadband erbium-doped fiber amplifiers (EDFAs), which form the backbone of high-capacity lighwave communication systems. Initially, the use of gain equalization filters increased the bandwidth of amplifiers by a factor of three (relative to first-generation amplifiers deployed in the field). Subsequently, the introduction of a two-band architecture, which includes amplifier sections for the C-band and the L-band, resulted in a further doubling of the bandwidth. In addition, this amplifier provides high output power and low noise figure to support the ever-increasing capacity demand on lightwave systems. Commercial systems with up to 80 wavelength division multiplexing (WDM) channels having a total capacity of up to 400 Gb/s are currently available, and terabit systems have been demonstrated in the laboratory. The recently discovered phenomenon of fast power transients in chains of EDFAs constituting an optical network has been shown to impair the performance of propagating channels in the event of channel failure or network reconfiguration. Several schemes to control the gain of EDFAs have been devised to mitigate the degradation caused by the fast power transient effect. Practical broadband amplifiers incorporating these and other control schemes, such as internal attenuation to control gain tilt, will enable future terabit and higher capacity networks.