Spatial Dimension Expansion of Incoherent Optical Field in a Multimode Fiber Scheme for Speckle Suppression

•A scheme for decoherence of an optical field in 2D for MMFs based framework is developed by combining an MMF, retardation plate, and a pair of microlens arrays, and a theoretical analysis model is developed to describe the 2D decoherence mechanism.•The experimental results show that the proposed method can significantly improve speckle suppression efficiency when the numerical aperture and length of the MMF are limited. The experimental results were generally consistent with the theoretical expectations.•This study specifically investigated the speckle elimination mechanism in the framework of MMFs, and the incoherent areas distribution of the optical field at the distal end of the MMF shifts from 1D to 2D as the length of the MMF increases, which is significant for understanding the evolution of a partially coherent light field within an MMF.