Switching waves (SWs) are walls that connect two homogeneous stable states of a multistable system. They are typically transient: a single SW will travel until the more stable state invades completely the less stable one. A single SW is only ever stationary at the so-called Maxwell point, a set of parameters where the two states have the same marginal stability. For parameters close to the Maxwell point, two approaching SWs can form a stable stationary structure provided that they have oscillatory tails through which they interlock. Such structures have recently been observed in the normal dispersion regime of microresonators and are known to correspond to dark pulse Kerr frequency combs. However, the small physical size of microresonators means that quantitative study of the transient dynamics that leads to their formation is difficult.
In this contribution, we overcome this challenge by performing systematic experiments and simulations in a synchronously-driven macroscopic fiber ring resonator, and report on observations of transient SW dynamics. Our resonator is made of normal dispersion fiber, which allows for the coexistence of two homogeneous steady states and their connection through a SW. We have measured the SW velocities across a wide range of parameters, and close to the identified Maxwell point, observed interlocked SWs persisting for 100’s of resonator photon lifetimes. Our results provide significant experimental insights on the transient dynamics of SWs that have been theoretically predicted to underpin the formation of Kerr frequency combs in normally dispersive microresonators.