Patent ID: 6959022

Claim:
A high damage threshold multi-clad optical fiber suitable for use as a high power fiber/fiber amplifier, comprising: a rare-earth-doped active core with index of refraction n 1 ; wherein said active core is selected from the group consisting of near-single mode and single mode; a pump core with index of refraction n 2 , surrounding said active core; a glass inner cladding layer with index of refraction n 3 , surrounding said pump core, said inner cladding preventing damage to a layer surrounding said glass inner cladding layer during high power use; a protective coating, surrounding said glass inner cladding layer, with an index of refraction n 4 , and wherein n 1 is greater than n 2 , n 2 is greater than n 3 , and n 3 is greater than n 4 .