Estimating index profiles of 1.3-µm single-mode fibers by near-field measurements at blue wavelengths

Near-field intensity measurements are obtained at the wavelength of 0.45 μm for fibers designed to operate in a single mode at 1.3 μm. At blue wavelengths, the fibers are sufficiently multimode so the near-field scan gives an approximation to the index profile. Near-field scans from six fibers are compared to actual index profiles as determined by the refracted ray method. Experimental near-field scans are also compared to theoretical predictions from a model using numerical solutions to the scalar-wave equation.