Fibre core profile characterization by measuring group velocity equalization wavelengths

When operated at shorter wavelengths, fibers that are single mode at telecommunications wavelengths of 1.3 and 1.55 mu m become few mode. Relative values of the group velocity equalization wavelengths for the different mode pairs existing down to visible wavelengths are quite sensitive to the refractive-index profile. Their measurement by few-mode interferometry provides simple, fast, and accurate characterization of fiber core refractive-index profile parameters: numerical aperture, core radius, central dip, and dopant diffusion. The method is attractive as a complement or alternative to standard refracted-near-field and preform measurements.<
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