Biomedical subjects

Salvador Balle

Publications and source records attributed to Salvador Balle.

9 recordsLinked to original sources

PubMed2006

Passive mode locking of lasers by crossed-polarization gain modulation.

We report on a novel approach for inducing passive mode locking of lasers without using any saturable absorber but exploiting the polarization degree of freedom of light. In our scheme, passive mode locking is achieved by crossed-polarization gain modulation caused by the reinjection of a polarization-rotated replica of the laser output after a time delay. The reinjection time delay defines resonance tongues that correspond to mode-locking operation. Numerical continuation reveals that the cw solution is destabilized through a Hopf bifurcation that defines the onset of multimode operation which evolves sharply into a mode-locked solution. Our approach can be applied to a large variety of laser systems. For vertical-cavity surface-emitting lasers, we demonstrate stable mode-locked pulses at repetition rates in the GHz range and pulse widths of few tens of picoseconds.

Journal Article↗

PubMed2006

Multiplicative noise in the longitudinal mode dynamics of a bulk semiconductor laser.

We analyze theoretically and experimentally the influence of current noise on the longitudinal mode hopping dynamics of a bulk semiconductor laser. It is shown that the mean residence times on each mode have different sensitivity to external noise added to the bias current. In particular, an increase of the noise level enhances the residence time on the longitudinal mode that dominates at low current, evidencing the multiplicative nature of the stochastic process. A two-mode rate equation model for a semiconductor laser is able to reproduce the experimental findings. Under a suitable separation of the involved time scales, the model can be reduced to a one-dimensional bistable potential system with a multiplicative stochastic term related to the current noise strength. The reduced model clarifies the influence of the different noise sources on the hopping dynamics.

Journal Article↗

PubMed2005

Excitable optical waves in semiconductor microcavities.

We demonstrate experimentally and theoretically the existence of excitable optical waves in semiconductor microcavities. Although similar to those observed in biological and chemical systems, these excitable optical waves are self-confined. This is due to a new dynamical scenario, where a stationary Turning pattern controls the propagation of waves in an excitable medium, thus bringing together the two paradigms of dynamical behavior (waves and patterns) in active media.

Models, Theoretical↗

PubMed2004

Dynamical mechanism of anticipating synchronization in excitable systems.

We analyze the phenomenon of anticipating synchronization of two excitable systems with unidirectional delayed coupling which are subject to the same external forcing. We demonstrate for different paradigms of excitable system that, due to the coupling, the excitability threshold for the slave system is always lower than that for the master. As a consequence the two systems respond to a common external forcing with different response times. This allows us to explain in a simple way the mechanism behind the phenomenon of anticipating synchronization in excitable systems.

Journal Article↗

PubMed2004

Thermo-optical "canard orbits" and excitable limit cycles.

We demonstrate experimentally and theoretically the existence of canard orbits and excitable quasiharmonic limit cycles in the thermo-optical dynamics of semiconductor optical amplifiers. We also observe the phase locking of the noise-induced spikes to the small-amplitude Hopf quasiharmonic oscillations, recently predicted by Makarov, Nekorkin, and Velarde [Phys. Rev. Lett. 86, 3431 (2001)]].

Biological Clocks↗

PubMed2003

Experimental evidence of van der Pol-Fitzhugh-Nagumo dynamics in semiconductor optical amplifiers.

Thermo-optical pulsing in semiconductor amplifiers is experimentally shown to correspond to a very common excitable scenario (the van der Pol-Fitzhugh-Nagumo system). Self-sustained oscillations appear in the sequence predicted by this simple dynamical model as we change either the injection level or the bias current. Periodic modulation of these parameters leads to the characteristic phase-locking structure. Furthermore, coherence resonance is observed when external noise is added to the system.

Journal Article↗

PubMed2002

Cavity solitons as pixels in semiconductor microcavities.

Cavity solitons are localized intensity peaks that can form in a homogeneous background of radiation. They are generated by shining laser pulses into optical cavities that contain a nonlinear medium driven by a coherent field (holding beam). The ability to switch cavity solitons on and off and to control their location and motion by applying laser pulses makes them interesting as potential 'pixels' for reconfigurable arrays or all-optical processing units. Theoretical work on cavity solitons has stimulated a variety of experiments in macroscopic cavities and in systems with optical feedback. But for practical devices, it is desirable to generate cavity solitons in semiconductor structures, which would allow fast response and miniaturization. The existence of cavity solitons in semiconductor microcavities has been predicted theoretically, and precursors of cavity solitons have been observed, but clear experimental realization has been hindered by boundary-dependence of the resulting optical patterns-cavity solitons should be self-confined. Here we demonstrate the generation of cavity solitons in vertical cavity semiconductor microresonators that are electrically pumped above transparency but slightly below lasing threshold. We show that the generated optical spots can be written, erased and manipulated as objects independent of each other and of the boundary. Numerical simulations allow for a clearer interpretation of experimental results.

Journal Article↗

PubMed2002

Coupled optical excitable cells.

In this work we investigate experimentally the dynamics of two coupled optical excitable cells, namely, two semiconductor lasers with optical feedback. We analyze the dynamics observed in terms of the statistical properties of the time series and in terms of the phase space reconstruction from the data. We build a model based on a simple set of deterministic equations (on a two torus) plus noise in order to capture the essential features of the dynamics observed. We discuss the validity of our theoretical results in terms of families of excitable systems and coupling terms.

Journal Article↗

PubMed2002

Experimental evidence of stochastic resonance in an excitable optical system.

Experimental evidence of stochastic resonance in an excitable optical system is reported. We apply a sinusoidal forcing to the system and, for a finite external noise level, we find a frequency for which the excitable pulsing occurs periodically at the frequency imposed by the modulation. This resonant frequency matches the inverse of the average escape time of the stochastically driven system (i.e., without forcing). The same resonance is found by varying the noise level for fixed forcing frequencies. We discuss different indicators in order to describe quantitatively the degree of resonance.

Journal Article↗