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Cavity solitons (CS) are single peak localized structures which form over a homogeneous background in the section of broad-area non linear resonator driven by a coherent holding beam. They can be switched on and off by shining a writing/ erasing local laser pulse into the optical cavity. Moreover, when a phase or amplitude gradient is introduced in the holding beam, CS are set in motion along the gradient with a speed that depends on gradient strength. The ability to address CS and to control their location as well as their motion makes them interesting for alloptical processing units. In this chapter we report on several functionalities of CS that have been experimentally implemented in a Vertical Cavity Surface Emitting Laser (VCSEL) biased below threshold. We show that CS positions in the transverse section of the resonator can be reconfigured according to a phase landscape introduced in the holding beam. CS drifting propelled by a phase gradient in the holding beam can be used for realizing an all-optical delay line. Information bits are written in form of CS at a point of the device and a time delayed version of the written information can be read elsewhere along the gradient direction. CS existence and functionalities are deeply affected by presence of device defects generated during the fabrication process and randomly distributed through the device section. The sensitivity of CS to parameters gradients can be used to probe these defects, otherwise not detectable, and mapping their positions. Finally, a periodic flow of moving CS can be obtained by the interplay between a device defect and an external parameter gradient. This suggests the possibility of engineering a CS source directly onto the device. [ABSTRACT FROM AUTHOR]

In this Chapter we intend to make a review on our work on cavity solitons in semiconductor lasers with saturable absorbers, with a special attention to the most recent results.We study theoretically a broad-area vertical cavity surface emitting laser (VCSEL) with a saturable absorber, and show numerically the existence of cavity solitons in the system: they exist as solitary structures superposed on a background with zero intensity. Therefore, this system can work as a cavity soliton laser, ensuring maximum contrast and compactness of the device, in comparison with other systems supporting cavity solitons. In particular, in absence of a holding beam, these solitons do not rely on a proper phase of the addressing pulses to be either created or deleted.We also show that the properties of the system are deeply influenced by the radiative recombination of carriers. Taking into account this process, the existence of solitons is shown numerically for a choice of parameters suitable to describe real devices, where the same material is used for the active and the passive parts. Furthermore, we compare three different switching techniques for the control of cavity solitons in a VCSEL based cavity soliton laser, one incoherent and the other two semicoherent with different injection frequencies. We show that the switching dynamics and energies can be very different depending on the type of injection. Finally, we show that in a cavity soliton laser based on a VCSEL with a saturable absorber the solitons can spontaneously move if the ratio of the carrier lifetimes in the amplifier and in the absorber takes appropriate values. The direction of the motion is arbitrary, while its velocity is determined by the parameters of the system. In devices with a finite cross section the CS describes different trajectories depending on the shape of the boundary of the pumped region. For a circular pump the CS moves on circular trajectories along the boundary. This dynamical regime can be exploited to create controllable trains of pulses, together with frequency and amplitude modulation. [ABSTRACT FROM AUTHOR]