Wavelength division multiplexed optical communication systems employing uniform gain optical amplifiers

Claim 1

A wavelength division multiplexed optical communication system comprising: a plurality of optical transmitters for outputting a plurality of optical signals, each optical signal having a particular wavelength; an optical combiner optically communicating with each of the optical transmitters for combining the optical signals and outputting the optical signals onto an output path to create a wavelength division multiplexed optical communication signal; an optical transmission line optically communicating with the output path of the optical combiner and configured to carry a wavelength division multiplexed optical communication signal; at least one optical amplifier positioned in the optical transmission line for substantially uniformly amplifying the wavelength division multiplexed optical communication signal and having at least first and second amplifier stages, the first amplifier stage including a first length of rare-earth doped optical fiber, the second amplifier stage including a second length of rare-earth doped optical fiber, the optical amplifier including at least one optical component positioned between the first and second amplifier stages selected from optical isolators, optical filters, optical circulators, Bragg gratings, and wavelength division multiplexers; a first optical pump for outputting a first pump signal at a first wavelength; a first optical pump path positioned between the first optical pump and the first stage of the optical amplifier for transporting pump energy to the first stage of the optical amplifier; a second optical pump for outputting a second pump signal at a second wavelength; a second optical pump path positioned between the second optical pump and the second stage of the optical amplifier for transporting pump energy to the second stage of the optical amplifier; wherein the first and second lengths of the rare-earth-doped optical fiber and the first and second optical pump signals are selected such that the gain of the first amplifier stage has a first gain slope within the spectral region from approximately 1540 nm to 1560 nm and the second amplifier stage has a second gain slope different from the first gain slope within the spectral region from approximately 1540 nm to 1560 nm, the first and second gain slopes being configured such that the composite of the first gain slope and the second gain slope yields a substantially constant amplifier gain within a spectral region from 1540 nm to 1560 nm.