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We predict a new kind of ring-profile solitary wave in nonlinear optical media, with finite orbital angular momentum. During propagation these fragment into fundamental solitons. Like free Newtonian particles, these fly off tangential to the ring, vividly demonstrating conservation of orbital angular momentum in soliton motion. [S0031-9007(97)

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

Analytic and numerical investigations of a cavity containing a Kerr medium are reported. The mean field equation with plane-wave excitation and diffraction is assumed. Stable hexagons are dominant close to threshold for a self-focusing medium. Bistable switching frustrates pattern formation for a self-defocusing medium. Under appropriate parametric conditions that we identify, there is coexistence of a homogeneous stationary solution, of a hexagonal pattern solution and of a large (in principle infinite) number of localized structure solutions which connect the homogeneous and hexagonal state. Further above threshold, the hexagons show defects, and then break up with apparent turbulence. For Gaussian beam excitation, the different symmetry leads to polygon formation for narrow beams, but quasihexagonal structures appear for broader beams.

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.

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We demonstrate that, in contrast with what was previously believed, multi-hump solitary waves can be stable. By means of linear stability analysis and numerical simulations, we investigate the stability of two-and three-hump solitary waves governed by incoherent beam interaction in a saturable medium, providing a theoretical background for the experimental results reported by M. Mitchell, M. Segev, and D. Christodoulides [Phys. Rev. Lett. 80, 4657 (1998)].