“…The dispersion represents one of the main impairments for optical communications. The study and the tailoring of different refractive index profiles aim at a desirable manipulation of the dispersion (as well as of several other transmission characteristics, e.g., [25,28,29]). Fibers with the dispersion parameter reduced at a certain wavelength, flattened for a wide range of wavelengths or even made highly negative are used for applications concerning long-haul communications, wavelength division multiplexing and dispersion compensation, among others (see, e.g., [3], [26, chapter 4]).…”