Soliton supermode transitions and total red shift suppression in multi-core fibers

Soliton propagation in seven-core fibers is studied numerically with the frequency dependence of linear coupling taken into account. It is shown that under certain conditions, solitons can undergo spontaneous supermode transitions upon abrupt red shift, analogous to the recently discovered phenomenon of soliton self-mode conversion in step-index multi-mode fibers. When the core separation is increased, the dynamics change drastically, leading to total suppression of soliton self-frequency shift and the emergence of spatially oscillating solitonic structures with resemblance to solitons in graded-index multi-mode fibers. The observed phenomena are general multi-core effects and not specific to seven-core fibers.