A method for producing an optical fiber is provided. The method includes the steps of drawing an optical fiber from a heated glass source in a furnace and introducing index perturbations to the optical fiber via a plurality of perturbation sources arranged at a plurality of different azimuthal locations. The index perturbations are introduced synchronously at different locations along the axial length of the fiber by the plurality of perturbation sources in a generally helical pattern on the outside surface of the fiber in one embodiment. According to another embodiment, the index perturbations are introduced by the plurality of perturbation sources at different frequencies.