Patent ID: 7899294

Claim:
A double-clad optical fiber comprising a core, a glass inner cladding and a glass outer cladding wherein: the glass core (i) comprises a first index of refraction n 1 and (ii) does not contain any active rare-earth dopants; the glass inner cladding surrounds the glass core and comprises: (i) a radial thickness t, (ii) a numerical aperture greater than the numerical aperture of the core, (iii) and a second index of refraction n 2 such that n 2 <n 1 , wherein a relative refractive index percent (Δ%) of the core relative to the inner cladding is greater than about 0.1%; the glass outer cladding surrounds the glass inner cladding and comprises a radial thickness at least 10 μm and a third index of refraction n 3 such that n 3 <n 2 ; and the core, the inner cladding and the outer cladding are formed from silica-based glass.