Patent ID: 7724422

Claim:
Optical apparatus for providing light having a selected linear polarization having a polarization ratio, said apparatus comprising a length of optical fiber and comprising a rare earth for providing light having a first wavelength responsive to said optical fiber receiving pump light having a second wavelength that is different than said first wavelength, wherein when said length of optical fiber is placed in a first position wherein said length of fiber is substantially linearly oriented said fiber supports at said first wavelength a fundamental mode and a plurality of higher order modes and said apparatus provides light having a first polarization ratio for the selected linear polarization and an parameter, said optical apparatus being configured such that said length of fiber is positioned in a second position that increases the bend loss of said fiber relative to said first position such that, responsive to said increased bend loss, said apparatus provides light having a reduced M 2 parameter relative to said M 2 parameter as well as a second polarization ratio for the selected linear polarization that is increased relative to said first polarization ratio such that said second polarization ratio is at least 6 dB greater than said first polarization ratio, and wherein when said length of fiber is in said second position the apparatus provides a slope efficiency that is at least 50% of the ratio of said second wavelength to said first wavelength.