Abstract: The invention pertains to W-profile single-mode silica-based optical fiberguide, and to communication systems employing these fiberguide. Such guides can be designed to have large bandwidth over a wide wavelength region, and, in particular, to have minimal chromatic dispersion at two different wavelengths, e.g., about 1.3 .mu.m and about 1.55 .mu.m, the wavelengths of loss minima in silica. Disclosed are ranges of fiber parameters that can yield these and other advantageous fiberguide characteristics. In particular, in fibers according to the invention the difference between core and outer cladding refractive index is between about 0.1% and 0.4% of the outer cladding index, the difference between the inner cladding and the outer cladding index is between about 1 times and about 3 times the difference between core and outer cladding, the core radius is between about 0.5 and 0.8 times the outer radius of the inner cladding, and the outer radius of the inner cladding is at least about 5 .mu.m.