Optical fiber amplifiers for WDM optical networks

In recent years, tremendous progress has been made in the development of br oadband erbium-doped fiber amplifiers (EDFAs) which form the backbone of hi gh-capacity lighwave communication systems. Initially, the use of gain equa lization filters increased the bandwidth of amplifiers by a factor of three (relative to first-generation amplifiers deployed in the field). Subsequen tly, 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 t he bandwidth. In addition, this amplifier provides high output power and lo w 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 Gbls are currently avai lable, and terabit systems have been demonstrated in the laboratory. The re cently discovered phenomenon of fast power transients in chains of EDFAs co nstituting an optical network has been shown to impair the performance of p ropagating channels in the event of channel failure or network reconfigurat ion. Several schemes to control the gain of EDFAs have been devised to miti gate the degradation caused by the fast power transient effect. Practical b roadband amplifiers incorporating these and other control schemes, such as internal attenuation to control gain tilt, will enable future terabit and h igher capacity networks.