Few-mode/single-mode fiber

摘要

The present invention pertains to an optical fiber comprising a transparent core having a maximum refractive index n₁ and a radius a surrounded by a layer of transparent cladding material having a refractive index no which is less than n_1- The refractive indices n₁ and no, the radius a, and the refractive index profile of the core are designed such that:(a) Δτ_j, the difference between |d(Vb)/dV|_j, the normalized delay time of the jth mode and |d(Vb)/dV|0, the normalized delay time of the fundamental mode, is less than about 5 x 10-² over a wide range of V-values where j is equal to 1 or 2 and represents the highest order mode that propagates with a low loss, 0 represents the fundamental mode, b is the propagation constant and V is the normalized frequency, and(b) the normalized waveguide dispersion Vd²(Vb)/dV² is about equal to or less than 0.2 at V-values near Vl, the normalized cutoff frequency of the first higher order mode. A fiber exhibiting characteristics (a) and (b) is capable of providing mode equalized two-mode or three-mode and low dispersion single-mode operation.