Abstract：Optical fibers designed to support multiple transverse modes offer opportunities to study wave propagation in a setting that is intermediate between single-mode fiber and free-space propagation.

A variety of qualitatively-new phenomena have been observed recently in multimode fibers. Self-cleaning of a multimode beam is observed at a fraction of the critical power for self-focusing, and without loss [1,2]. New instabilities, which are spatiotemporal in nature, occur [3,4,5]. By varying the launched spatial modes, it is possible to generate dispersive waves over an octave in frequency, megawatt pulses in the near infrared, or continua that span multiple octaves [6]. After a tutorial introduction to nonlinear wave propagation, one or two of these phenomena will be presented. Interpretation of the phenomena in terms of the dynamics of multimode solitons can be quite insightful.

Synchronization of transverse and longitudinal modes – spatiotemporal mode-locking – of a multimode fiber laser was recently demonstrated [7]. The basic features of spatiotemporal mode-locking and recent progress in theoretical understanding will be presented. The variety of 3-dimensional lasing states appears to open many opportunities for future study.