Patent ID: 6990277

Claim:
Article comprising at least one optical fiber suitable for multimode operation at a system operating wavelength in the wavelength range of 800-1700 nm, the fiber including a core of radius “a” and a cladding and having a guide strength, “Δ”, the core including a first core portion having a continuous α relationship between value of refractive index and radial position such that the maximum change in index over a radial distance of 2 μm is less than 5% Δ, with all wavelength-dependent values determined at a wavelength of 850 nm as measured in free space, in which all radius-dependent values of index of refraction disregard deviations extending radially for distance of less than 850 nm, and in which the said fiber includes a plurality of spaced perturbations, each perturbation constituting an interruption in fiber transmission properties for at least one bound mode in the core, CHARACTERIZED IN THAT the first core portion is enclosed within an annular, alpha-profiled second core portion, of radial dimension, 20-50% a, within which values of index of refraction are at least 5% Δ less than extrapolated values prescribed by extension of the said continuous relationship, and in that the said first core portion is of radial dimension 50-80% a, and wherein said first and second core portions have a discontinuous interface therebetween.