Patent ID: 7526167

Claim:
An apparatus comprising: a fiber amplifier including one or more amplification stages, at least one of which contains a cladded gain fiber having: a primary core doped with a rare-earth lasing species; a pump cladding surrounding the primary core, wherein the pump cladding conducts pump light along and into the core to provide energy for amplification of light of a signal wavelength within a gain bandwidth of the rare-earth lasing species; an outer cladding surrounding the pump cladding, wherein the outer cladding is used to contain the pump light within the pump cladding; a doped secondary region outside the core and inside the pump cladding that absorbs light of the signal wavelength and is configured to provide attenuation of undesired modes within the gain bandwidth of the primary core; and one or more grating perturbations configured to couple light from the core into the pump cladding.