We review the properties of optical spatial dissipative solitons (SDS). These are stable, self-localized optical excitations sitting on a uniform, or quasi-uniform, background in a dissipative environment like a nonlinear optical cavity. Indeed in optics they are often termed 'cavity solitons'. We discuss their dynamics and interactions in both ideal and imperfect systems, making comparison with experiments. SDS in lasers offer important advantages for applications. We review candidate schemes and the tremendous recent progress in semiconductor-based cavity soliton lasers. We examine SDS in periodic structures, and we show how SDS can be quantitatively related to the locking of fronts. We conclude with an assessment of potential applications of SDS in photonics, arguing that best use of their particular features is made by exploiting their mobility, e.g. in all-optical delay lines.

The rapidly developing field of optomechanics aims at the com- bined control of optical and mechanical modes1–3. In cold atoms, the spontaneous emergence of spatial structures due to opto- mechanical back-action has been observed in one dimension in optical cavities3–8 or highly anisotropic samples9. Extensions to higher dimensions that aim to exploit multimode configurations have been suggested theoretically10–16. Here, we describe a simple experiment with many spatial degrees of freedom, in which two continuous symmetries—rotation and translation in the plane orthogonal to a pump beam axis—are spontaneously broken. We observe the simultaneous long- range spatial structuring (with hexagonal symmetry) of the density of a cold atomic cloud and of the pump optical field, with adjustable length scale. Being based on coherent phenom- ena (diffraction and the dipole force), this scheme can poten- tially be extended to quantum degenerate gases

The realization of a cavity soliton laser using a vertical-cavity surface-emitting semiconductor gain structure coupled to an external cavity with a frequency-selective element is reported. Alloptical control of bistable solitonic emission states representing small microlasers is demonstrated by injection of an external beam. The control scheme is phase-insensitive and hence expected to be robust for all-optical processing applications. The motility of these structures is also demonstrated.

We report on the observation and interaction of dissipative localized structures in an optical pattern-forming system. Single localized structures are found to have oscillatory decaying tails originating from diffraction. We observe bound states of two or more constituents. These clusters contain several preferred mutual distances. Numerical simulations show that the corresponding interactions are mediated by the oscillatory tails.

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