Fig. 2: Spatiotemporal response of multimode optical fiber.

a, c, e Measured iso-intensity surfaces of the pulsed field when we excite individually each one of the first three supported modes \(\left({{HG}}_{00},{{HG}}_{01},{{HG}}_{10}\right)\). b, d, f Color-coded modal decomposition maps after projecting the field onto a set of Laguerre–Gaussian (\({LG}\)) modes, in this map each ‘pixel’ corresponds to the spatial distribution of the amplitude and phase, measured at a specific time and wavelength. Each mode of this basis is associated with an \({CMY}\) color (\({{\ell}}_{-1}=-1\,\)(yellow), \({{\ell}}_{0}=0\) (magenta), and \({{\ell}}_{1}=1\) (cyan)). Note that the presence of only one color in each panel indicates mode purity. We observe that the spatial mode with vorticity \({\ell}{=}0\) is the fastest, followed by the modes with OAM \({\ell}{=}{{{\mathscr{+}}}}1\) and \({\ell}{=}{{{\mathscr{-}}}}1\), respectively. Chromatic dispersion produces a delay in the spectral components of the pulse, which appears as a positive slope in the shape. In the insets, we present a detailed view of the spatial structure of the propagated pulses.