Spatiotemporally synchronized pure high-even-order dispersion solitons in multimode fiber lasers

Soliton solutions of nonlinear wave equations continue to attract broad scientific interest across diverse physical settings. Currently, the study of pure high-even-order dispersion (PHEOD) solitons and multimode spatiotemporal dynamics represents two compelling frontiers in ultrafast photonics. The intersection of these domains is theoretically rich; however, the realization of PHEOD solitons in multimode fibers has been difficult due to the challenge of independently managing dispersion for different transverse modes. Here, we report the first experimental generation of synchronized PHEOD solitons in a multimode fiber laser. By employing a transverse mode division control technique, we physically decouple the modes, which enables control of both modal and chromatic dispersions. We systematically demonstrate the generation of spatiotemporally synchronized PHEOD solitons in four transverse modes, with fourth-, sixth-, or eighth-order dispersion. These multimode pulsed states self-organize through nonlinear coupling among the transverse modes. Numerical simulations account for the main experimental observations and illuminate the nonlinear multimode dynamics that underlie the laser operation. This work bridges the scientific gap between PHEOD engineering and multimode fiber lasers, and opens new possibilities for the development of sources of multidimensionally structured ultrafast light.