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PACS numbers: 42.65.Pc, 42.55.Px, 42.60.Mi ; We report the first experimental observation of multistable states in a single-longitudinal mode semiconductor ring laser. We show how the operation of the device can be steered to either monostable, bistable, or multistable dynamical regimes in a controlled way.We observe that the dynamical regimes are organized in well-reproducible sequences that match the bifurcation diagrams of a two-dimensional model. By analyzing the phase space in this model, we predict how the stochastic transitions between multistable states take place and confirm it experimentally. ; This work has been partially funded by the European Union under Project No. IST-2005-34743 (IOLOS). This work was supported by the Belgian Science Policy Office under Grant No. IAP-VI10. We acknowledge the Research Foundation-Flanders (FWO) for individual support and project funding. ; Peer reviewed

4 pages, 2 figures.-- PACS nrs.: 42.65.-k; 42.55.Px; 42.60.Mi. ; We investigate both theoretically and experimentally the stochastic switching between two counterpropagating lasing modes of a semiconductor ring laser. Experimentally, the residence time distribution cannot be described by a simple one-parameter Arrhenius exponential law and reveals the presence of two different mode-hop scenarios with distinct time scales. In order to elucidate the origin of these two time scales, we propose a topological approach based on a two-dimensional dynamical system. ; This work has been partially funded by the European Union under project IST-2005-34743 (IOLOS). This work was supported by the Belgian Science Policy Office under grant No. IAP-VI10. G.V. is a Postdoctoral Fellow and LG is a PhD Fellow of the Research Foundation - Flanders (FWO). ; Peer reviewed

7 pages, 5 figures. ; We present an analytical, numerical and experimental study of the switching time and jitter of current induced polarization switching in Vertical-Cavity Surface-Emitting Lasers in the presence of spontaneous emission noise. Assuming that the switching is induced by changes in the dichroism, the problem can be reduced to the well-known first passage time problem in gain switched Class-A lasers. The theoretical results obtained in this way show excellent agreement both with numerical simulations based on the full rate equations model, and with experiments performed on oxide-confined Vertical-Cavity Surface-Emitting Lasers. ; This work was supported in part by the Belgian government under the Interuniversity Attraction Pole program (IAP V/18), in part by the Concerted Research Action, and in part by the Research Council of the Vrije Universiteit Brussel. The collaboration between the groups in Brussels, Palma de Mallorca, Ulm, and Florence was made possible through the European RTN network VISTA under Contract HPRN-CT-2000-00034. Additional support from, and discussions within, the framework of the European COST actions 268 and 288 are acknowledged. The work of J. Danckaert, G. Verschaffelt, and B. Nagler was supported by the Fund for Scientific Research—Flanders. ; Peer reviewed