Ring dark solitons

Self-defocusing nonlinear media can support dark solitary waves with ring symmetry that are robust but slowly change their parameters. This alternative type of optical dark soliton is investigated numerically and analytically, and it is shown that in the small-amplitude limit such solitons are described by the so-called cylindrical Korteweg–de Vries equation known, e.g., from plasma physics. Ring dark solitons may coexist with other types of dark solitons, displaying almost an elastic interaction.