Biomedical subjects

Pere Colet

Publications and source records attributed to Pere Colet.

10 recordsLinked to original sources

PubMed2005

Chaos-based communications at high bit rates using commercial fibre-optic links.

Chaotic signals have been proposed as broadband information carriers with the potential of providing a high level of robustness and privacy in data transmission. Laboratory demonstrations of chaos-based optical communications have already shown the potential of this technology, but a field experiment using commercial optical networks has not been undertaken so far. Here we demonstrate high-speed long-distance communication based on chaos synchronization over a commercial fibre-optic channel. An optical carrier wave generated by a chaotic laser is used to encode a message for transmission over 120 km of optical fibre in the metropolitan area network of Athens, Greece. The message is decoded using an appropriate second laser which, by synchronizing with the chaotic carrier, allows for the separation of the carrier and the message. Transmission rates in the gigabit per second range are achieved, with corresponding bit-error rates below 10(-7). The system uses matched pairs of semiconductor lasers as chaotic emitters and receivers, and off-the-shelf fibre-optic telecommunication components. Our results show that information can be transmitted at high bit rates using deterministic chaos in a manner that is robust to perturbations and channel disturbances unavoidable under real-world conditions.

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PubMed2005

Chaotic breathers in delayed electro-optical systems.

We show that in integro-differential delayed dynamical systems, a hybrid state of simultaneous fast-scale chaos and slow-scale periodicity can emerge subsequently to a sequence of Hopf bifurcations. The resulting time trace thereby consists in chaotic oscillations "breathing" periodically at a significantly lower frequency. Experimental evidence of this type of dynamics in delayed dynamical systems is achieved with a Mach-Zehnder modulator optically fed by a semiconductor laser and is subjected to a delayed nonlinear electro-optical feedback. We also propose a theoretical understanding of the phenomenon.

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PubMed2005

Excitability mediated by localized structures in a dissipative nonlinear optical cavity.

We find and characterize an excitability regime mediated by localized structures in a dissipative nonlinear optical cavity. The scenario is that stable localized structures exhibit a Hopf bifurcation to self-pulsating behavior, that is followed by the destruction of the oscillation in a saddle-loop bifurcation. Beyond this point there is a regime of excitable localized structures under the application of suitable perturbations. Excitability emerges from the spatial dependence since the system does not exhibit any excitable behavior locally. We show that the whole scenario is organized by a Takens-Bogdanov codimension-2 bifurcation point.

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PubMed2004

Phase synchronization and polarization ordering of globally coupled oscillators.

We introduce a prototype model for globally coupled oscillators in which each element is given an oscillation frequency and a preferential oscillation direction (polarization), both randomly distributed. We found two collective transitions: to phase synchronization and to polarization ordering. Introducing a global-phase and polarization order parameters, we show that the transition to global-phase synchrony is found when the coupling overcomes a critical value and that polarization order enhancement cannot take place before global-phase synchrony. We develop a self-consistent theory to determine both order parameters in good agreement with numerical results.

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PubMed2004

Effect of parameter mismatch on the synchronization of chaotic semiconductor lasers with electro-optical feedback.

We investigate the detrimental effects of parameter mismatch on the synchronization of semiconductor lasers with electro-optical feedback, whose intensity dynamics can display a hyperchaotic behavior. Analytical techniques are developed to study the statistical properties of the synchronization error as a function of the various types of mismatches. The multiple mismatch case, which is of high experimental interest, is also studied and some compensation conditions allowing the improvement of the synchronization are derived. The analytical predictions are confirmed by numerical simulations and by some experimental measurements.

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PubMed2004

Secondary bifurcations of hexagonal patterns in a nonlinear optical system: alkali metal vapor in a single-mirror arrangement.

Secondary bifurcations of hexagonal patterns are analyzed in a model of a single-mirror arrangement with an alkali metal vapor as the nonlinear medium. A stability analysis of the hexagonal structures is performed numerically. Different instabilities are predicted in dependency on the wave number of the hexagons. Some of the instabilities take place at a finite wave number and result in the formation of structures with 12 spatial modes. These structures are compared with those observed experimentally.

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PubMed2003

All-optical image processing with cavity type II second-harmonic generation.

The possibilities offered by type II intracavity second-harmonic generation for all-optical parallel processing of images are investigated. By injecting an image in a linearly polarized pump beam and a homogeneous field with orthogonal polarization, we obtain, according to the value of the latter, either frequency and polarization transfer or contrast enhancement and contour recognition. Noise-filtering effects are also predicted.

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PubMed2003

Synchronization of vectorial noise-sustained structures.

The synchronization of vectorial, noise-sustained structures in nonlinear optical systems is discussed. In particular, the analysis is made for nondegenerate optical parametric oscillators with walk off. The interplay between walk off and noise fluctuations leads to the formation of noise-sustained transverse patterns in both the signal and idler fields. Despite the fact that both patterns are stochastic macroscopic structures driven by independent sources of noise, their correlation grows with time, finally leading to a spatially distributed time synchronization of noise-sustained structures. A physical explanation of this phenomenon is found by analyzing the linear instability process and the existence of exact nonlinear solutions that show the same correlation.

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PubMed2002

Fluctuations and correlations in hexagonal optical patterns.

We analyze the influence of noise in transverse hexagonal patterns in nonlinear Kerr cavities. The near-field fluctuations are determined by the neutrally stable Goldstone modes associated to translational invariance and by the weakly damped soft modes. However, these modes do not contribute to the far-field intensity fluctuations that are dominated by damped perturbations with the same wave vectors than the pattern. We find strong correlations between the intensity fluctuations of any arbitrary pair of wave vectors of the pattern. Correlation between pairs forming 120 degrees is larger than between pairs forming 180 degrees, contrary to what a naive interpretation of emission in terms of twin photons would suggest.

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PubMed2002

Patterns arising from the interaction between scalar and vectorial instabilities in two-photon resonant Kerr cavities.

We study pattern formation associated with the polarization degree of freedom of the electric field amplitude in a mean field model describing a nonlinear Kerr medium close to a two-photon resonance, placed inside a ring cavity with flat mirrors and driven by a coherent x-polarized plane-wave field. In the self-focusing case, for negative detunings the pattern arises naturally from a codimension two bifurcation. For a critical value of the field intensity there are two wave numbers that become unstable simultaneously, corresponding to two Turing-like instabilities. Considered alone, one of the instabilities would originate a linearly polarized hexagonal pattern whereas the other instability is of pure vectorial origin and would give rise to an elliptically polarized stripe pattern. We show that the competition between the two wave numbers can originate different structures, the detuning being a natural selection parameter.

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