Effects of profile deformations on fiber bandwidth.

Any deviation of the refractive-index profile of an optical fiber from its optimum shape dramatically lowers the fiber bandwidth. In this paper we study the influence on bandwidth of a number of refractive-index deformations commonly encountered in preform manufacture. The deformations include sinusoidal ripples near the fiber axis, a central dip, and a departure from optimum shape near the core-cladding boundary. We also consider a deformation in the shape of a sinusoidal half-period whose length covers one fifth of the core radius. Placing this bulge deformation at five different radial positions between the axis and the core-cladding interface we investigate how the position of an index deformation affects the bandwidth on the assumption that all modes are equally excited. It is demonstrated that the theoretically realizable bandwidth of about 11,000 MHz.km is reduced to several hundred MHz.km for many of these deviations. Comparison is made with an experimentally measured profile.