| 摘要 |
Step index, multimode fiber waveguides are designed according to the disclosed invention with intentional fluctuations of the refractive index of the fiber core, with the aim of reducing dispersion by deliberately enhancing mode coupling in the fiber and, at the same time, minimizing loss in the fiber due to coupling to radiation modes. It is shown that, to avoid radiation losses, conditions should be imposed not only on the axial (z) dependence of the core fluctuations, but also on the azimuthal ( phi ) and radial (r) dependence of the core fluctuations. Specifically, a selection rule is imposed on the coupling in the fiber by providing the core index fluctuations with an azimuthal dependence governed by a function of the form cos p phi , where p is an integer equal to or greater than one. Coupling for a mode of an azimuthal mode number nu is thereby limited by the selection rule DELTA nu =p. Additionally, by limiting the location of the index fluctuations to a region below a certain maximum radius rmax in the core, coupling to modes with large azimuthal mode numbers nu is avoided, and power loss via coupling to radiation modes is held to a minimum.
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