US Patent 8000576 Double-clad optical fibers and devices with double-clad optical fibers

A double-clad optical fiber includes a core, an inner cladding and an outer cladding of silica-based glass. The core may have a radius of less than about 5 μm, a first index of refraction n1 and does not contain any active rare-earth dopants. The inner cladding may surround the core and includes a radial thickness of at least about 25 μm, a numerical aperture of at least about 0.25, and a second index of refraction n2 such that n2<n1. The relative refractive index percent (Δ%) of the core relative to the inner cladding may be greater than about 0.1%. The outer cladding may surround the inner cladding and include a radial thickness from about 10 μm to about 50 μm and a third index of refraction n3 such that n3<n2. The relative refractive index percent (Δ%) of the inner cladding relative to the outer cladding may be greater than about 1.5%.