Coupling ultrafast laser pulses into few-mode optical fibers: a numerical study of the spatiotemporal field coupling efficiency.

Few-mode optical fibers have been widely used in applications such as data transmission and laser amplification. The coupling of laser beams into such fibers is important because it determines the fiber mode contents, which influence the beam quality, laser amplification efficiency, and appropriate distortion control methods. Ultrafast lasers, as a widely used type of laser source for intense-field applications, can generate pulses with broad spectra and varying phases, adding complexity to the fiber mode coupling problem. In this paper, we numerically study the coupling performance of ultrafast laser pulses into few-mode fibers, investigating the mode coupling efficiency under different launching field conditions. Certain modes can be optimized with their coupling efficiencies in the presence of pulse spatiotemporal couplings, which provides a new perspective toward generating complex waveforms and studying laser matter interactions.