Patent ID: 7006752

Claim:
A waveguide configuration comprising: a core having an index of refraction and a shear velocity, the core being doped with Al, Yb, wherein the respective amount Yb in the divalent state is such that any indirect and direct losses of Yb in the divalent state are exceeded by the gain attributable to Yb in the trivalent state; a first cladding extending about the core having a shear velocity which is less than that of the core and an index of refraction which is less than the core; a second cladding extending about the first cladding, the second cladding having a shear velocity which is greater than that of the first cladding, wherein an optical mode has an index of refraction greater than that of the second cladding; third cladding extending about the second cladding, the third cladding having an index of refraction less than that of each of the core, first cladding and second cladding; and a buffer extending about the third cladding.