Patent ID: 7215858

Claim:
Optical apparatus, comprising: a length of a first optical fiber having a wavelength of operation, said first optical fiber comprising a first region comprising a first index of refraction; a core comprising a second index of refraction that is greater than said first index of refraction, said core disposed about said first region and comprising a rare earth material for providing energy having the wavelength of operation responsive to absorbing pump energy having a wavelength different than the wavelength of operation, said core being multimode at said wavelength of operation; a first cladding for receiving pump light, said first cladding disposed about said multimode core and comprising a third index of refraction that is less than said second index of refraction; and a second optical fiber comprising a core and a cladding disposed about said core, said core of said second optical fiber being connected to only a part of the cross section of said core of said first optical fiber.