“…In the context of fluid flow, undular bores have been observed, studied and modelled in the atmosphere [7,8,9], on the continental shelf in the internal tide [10], 20 in stratified fluids [11], in magma flow in geophysics [12, 13,14], in Fermi gases [15] and BoseEinstein condensates [16]. Of relevance to the present work, there have been experimental and theoretical studies of DSWs in nonlinear optical media such as photorefractive crystals [17,18,19], nonlinear optical fibres [20,21,22] and nonlinear thermal optical media [23,24]. While the terms DSW and undular bore refer to the same phenomenon and, in principle, are interchangeable, the 25 first term will be used in the present work.…”