Trapezoidal index single-mode fibers for the 1.55 µm band

An analytical study is made of single-mode fibers with a trapezoidal index of refraction profile for low dispersion operation in the 1.55-μm band using Ge doped silica core and pure silica cladding. It is found that certain trapezoid proportions give a fiber with a combination of less Ge doping, larger core diameter, faster decay of the field in the radial direction within the cladding, and smaller rate of change of dispersion with wavelength than is simultaneously possible with either the step index or triangular profiles.