Localized Structures in Dissipative Nonlinear Systems - Abstract
Panajotov, Krassimir
Cavity Solitons (CS), i.e. localized spots of light in the transverse plane of a broad area nonlinear cavity or laser, have recently been demonstrated in broad area Vertical-Cavity Surface-Emitting Lasers (VCSELs). Typically the VCSEL diameter is d 150 − 200µm in order to guarantee an independence on the transverse boundaries. In medium size VCSELs (d 40-50 µm) emission of a single high order mode or a combination of several such modes prevents the existence of localized structures. We however, demonstrate hereby that a spontaneous pattern and localized structures in the nonlasing, orthogonal linear polarization can still exist. Due to current crowding, the laser emission in medium size VCSELs starts at threshold in a linearly polarized ?flower mode? concentrated at the laser aperture periphery. Introducing a holding beam with orthogonal liner polarization we observe localized structure in the center of the device in the orthogonal polarization while the VCSEL keeps lasing in the same flower-mode. We support theoretically our experimental findings using two different VCSEL models, which account for both polarization and spatial dynamics.
We next consider theoretically the impact of optical feedback on cavity soliton behaviour. To this aim we introduce a rate equation model describing broad area VCSELs subject to injection and to time-delayed optical feedback. We show that the inclusion of an external cavity affects dramatically the space-time behavior of this system by modifying the instability threshold as well as the wavelength of the Turing instability. We show also that the delayed feedback is responsible for the appearance of traveling wave instability. Finally, we demonstrate that a single cavity soliton exhibits a spontaneous motion with a constant velocity.