Fiber designs with significantly reduced nonlinearity for very long distance transmission

A class of low-nonlinearity dispersion-shifted fibers based on depressed-core multistep index profiles is investigated. A systematic approach for designing these fibers in which a reference W-index profile is used to initiate the design is presented. Transmission properties, including effective area, mode-field diameter, dispersion, dispersion slope, and cutoff wavelength, are evaluated for several design examples. The effects of varying fiber dimensions and indices on effective area and mode-field diameter are assessed. It is shown that there is a trade-off between these two properties and, generally, larger effective areas are associated with larger mode-field diameters. Dispersion-shifted single-mode fiber designs with effective areas of from 78 to 210 microm2 and the corresponding mode-field diameter of from 8.94 to 14.94 microm, dispersion less than 0.07 ps/nm km, and dispersion slope of approximately 0.05 ps/nm2 km are presented.