Multimode optical fiber

Claim 1

Glass transmission line for the transmission of electromagnetic radiation centering about a wavelength within the range of from 0.5 to 2.0 μm, said line comprising a core member manifesting a radially decreasing refractive index for said radiation from the axial core composition to the peripheral core composition, together with a cladding about said core, in which the said core consists essentially of SiO 2 and at least one refractive index modifying ingredient, in which the gradient within the said core is due at least in part to a radially increasing concentration of boron oxide, B 2 O 3 , to an ultimate peripheral core composition which is essentially borosilicate containing from 10 mole percent B 2 O 3 to 20 mole percent B 2 O 3 , the said gradient approximating the form: n = n.sub.1 [1-2Δ(r/a).sup.α].sup.1/2, in which the n 1 is the index maximum, r is the distance from the fiber axis, a is the core radius, Δ is the relative index difference between core center and cladding and α is a power law exponent which characterizes the profile, characterized in that Δ is equal to n 1 - (n 2 - 0.007)/n 1 , n 1 and n 2 are index values as measured in bulk samples of glass of the compositions represented, respectively, by the axial core composition and the peripheral core composition.