Fig. 1

Acceleration of intermodal collisions in a tapered multimode fiber. a Schematic of a core-decreasing parabolic multimode fiber. As the fiber core is reduced in size, the spacing between the propagation eigenvalues increases, leading to an acceleration in intermodal collisions and energy exchange. b Evolution of the spot-size as a function of the propagation distance in a 4-cm tapered fiber when its core decreases from 40 to 10 µm. In this example, the input spot-size was chosen to be 1.5 times larger than that of the fundamental mode. As shown in b, the oscillations in the optical beam diameter experience an acceleration along the propagation direction