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A nondestructive method is presented to determine simultaneously the refractive index profile and the cross section geometry of optical fiber preforms. An improved formula for calculating the optical path length from the deflection function is derived. The preform is rotated through 180° and the deflection angle data collected, then the back projection technique and linear interpolation algorithm are used in the computed tomographic two-dimensional (2-D) profile reconstruction for preforms of nonuniform cross section. To minimize the computing time, the spatial Nyquist frequency is analytically used to estimate the angle sampling number of views and the numbers of points per scan in advance. Numerical simulations and experimental results show that using 180° angle of view deflection data, accurate preform index distribution reconstructions are obtained.