Patent ID: 8731358

Claim:
A multi-cladding large-core multimode optical fiber comprising: a longitudinally extending multimode core with low numerical aperture having at least a portion thereof that is rare-earth doped, the core having a core refractive index and a diameter, the diameter being at least 30 μm; a first cladding surrounding the longitudinally extending core, the first cladding having a first cladding refractive index lower than the core refractive index; a second cladding surrounding the first cladding, the second cladding having a second cladding refractive index higher than the first cladding refractive index and lower than the core refractive index; at least one intermediate cladding surrounding the second cladding; and an external cladding surrounding the at least one intermediate cladding, the external cladding having an external cladding refractive index lower than the second cladding refractive index, whereby, for a given diameter of the core, a margin is increased between a first bending radius causing a threshold bending loss in a fundamental mode of the optical fiber and a second bending radius causing the threshold bending loss in higher-order modes of the optical fiber.