Inhomogeneously broadened fiber-amplifier cascades for transparent multiwavelength lightwave networks

The emergence of practical fiber-amplifier chains has swiftly raised the prospect of transparent lightwave networks, in which signals travel from source to destination through a sequence of intermediate nodes without optoelectronic conversion. When such networks employ multiple wavelengths, however, some of the most substantial new research challenges are those posed by the amplifier chains themselves. Such networks suffer from accumulating interchannel power spread, from sensitivity to interamplifier loss variations, and from transient cross saturation, as the network undergoes reconfiguration. All of these difficulties effectively vanish in a chain of saturated lightwave amplifiers whose per-channel gains are decoupled by, e.g., inhomogeneous broadening. Unlike conventional, homogeneously broadened systems, saturated fiber-amplifier chains with decoupled gain dynamics provide automatic channel-by-channel power regulation, tolerance to interamplifier loss variations, and immunity to transient cross saturation. Thus, if amplifiers with such decoupled gain dynamics can be implemented in a practical way, they promise to solve-in a single stroke-several of the most substantial technological challenges facing transparent multiwavelength lightwave networks