Refractive index profile and modal dispersion in single mode optical fibers are computed from the measured expansion coefficients of the near field, which is expanded in a series of Gauss Laguerre functions. The coefficients of the series are measured from the correlation intensity between the near field of single mode fibers and the Gauss Laguerre mode of filter fabricated by computer generated holograms. The main advantage of the proposed method lies in its inherent insensitivity against random measurement errors and low optical dynamic range of a detector.