A wave guide amplifier is presented which has a relatively flat gain over a band of wavelengths. In some embodiments, the amplifier is an erbium doped amplifier and the gain is flat to within 2.5 dB across the C-band. Gain flattening can be accomplished by adjusting the concentration of ground state...http://www.google.ca/patents/US20030174391?utm_source=gb-gplus-sharePatent US20030174391 - Gain flattened optical amplifier
