Controlling the distribution of coupling efficiencies of an ultrashort laser pulse to multimode fiber LP_0m modes

Spatiotemporal properties of an ultrashort laser pulse propagating through a multimode optical fiber (MMF) can be manipulated by controlling the coupling efficiency distribution (CED) between the MMF modes. This work proposes a two-arm lens focusing system for controlling the CED. Each arm of the coupling system contains a hybrid diffractive-refractive lens (HL). Two desired CEDs have been selected as examples, and the focal lengths of HLs, their distances from the fiber facet, and the splitting ratio of the input pulse between the two arms are used to obtain the CEDs. Simulation results confirmed the perfect ability to control the CED by this method.