Dispersion flattening in a W fiber.

An exhaustive and simple method for dispersion flattening in double-clad single-mode fibers is presented. The idea is to generate all such fibers with a certain cutoff wavelength and then find, by one-dimensional minimization and direct inspection, fibers yielding minimum dispersion. As examples, the root mean square chromatic dispersion over the wavelength range (1.25, 1.60 µm) is minimized for a W fiber and also for a triangular-index fiber with a depressed inner cladding. The material dispersion is included through a Sellmeier refractive-index formula. The full vector solution of Maxwell's equations is used. It is found, as is well known, that the W fiber is capable of dispersion flattening. The validity of the numerical results presented depends on the validity of the approximate refractive-index model used.