Experimental confirmation of Bragg (gap) solitons in water waves over a periodic bottom

Demonstrate experimentally the existence of Bragg (gap) solitons—long-lived localized packets of standing surface gravity waves corresponding to stationary solutions of the coupled-mode amplitude equations for forward and backward harmonics a_+(x,t) and a_-(x,t)—in the setting of surface gravity waves over a periodic bottom, using realizable experimental excitation methods.

Background

The paper discusses strong interactions between surface gravity waves and bottom inhomogeneities, particularly under the Bragg resonance condition where forward and backward waves couple and a spectral bandgap appears. In prior work, Bragg (gap) solitons—long-lived localized structures described by the coupled-mode equations—were observed in high-precision numerical experiments that employed an idealized initial condition (a flat free surface and a prescribed velocity field), which cannot be implemented with a standard wave-maker.

Because such one-shot excitations are not feasible in laboratory setups, the authors note that there is still no experimental confirmation of the existence of these solitons. The present paper numerically explores a physically realizable scenario (a traveling wave packet approaching a periodic barrier array), but the lack of experimental confirmation remains explicitly highlighted.