INHOMOGENEOUSLY BROADENED FIBER-AMPLIFIER CASCADES FOR TRANSPARENT MULTIWAVELENGTH LIGHTWAVE NETWORKS

The emergence of practical fiber-amplifier chains has swiftly raised t he prospect of transparent lightwave networks, in which signals travel from source to destination through a sequence of intermediate nodes w ithout optoelectronic conversion. When such networks employ multiple w avelengths, however, some of the most substantial new research challen ges are those posed by the amplifier chains themselves. Such networks suffer from accumulating interchannel power spread, from sensitivity t o interamplifier loss variations, and from transient cross saturation, as the network undergoes reconfiguration. All of these difficulties e ffectively vanish in a chain of saturated lightwave amplifiers whose p er-channel gains are decoupled by, e.g., inhomogeneous broadening. Unl ike conventional, homogeneously broadened systems, saturated fiber-amp lifier chains with decoupled gain dynamics provide automatic channel-b y-channel power regulation, tolerance to interamplifier loss variation s, and immunity to transient cross saturation. Thus, if amplifiers wit h such decoupled gain dynamics can be implemented in a practical way, they promise to solve-in a single stroke-several of the most substanti al technological challenges facing transparent multiwavelength lightwa ve networks.