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In this paper we address the problem of controlling chaos by using a selective filter inserted in a negative feedback loop. This has been achieved in driven double-well Duffing oscillator in a parameter region exhibiting both a boundary crisis and generalized bistability. The optimization of the filter response allows us to improve the reduction of the control signal when the periodic solution competing with the chaotic attractor is approached. The advantage in using a selective frequency approach with respect to the Pyragas's method mainly resides in the tunability of the maximum of its amplitude response and zero phase condition. Numerical simulations performed in the temporal domain match with the experiment and make us glimpse the potential of an automatic adaptive strategy adopting filter parameter variations in order to reach an optimal feedback signal reduction.

International audience; We revisit the laser model with cavity loss modulation, from which evidence of chaos and generalized multistability was discovered in 1982. Multistability refers to the coexistence of two or more attractors in nonlinear dynamical systems. Despite its relative simplicity, the adopted model shows us how the multistability depends on the dissipation of the system. The model is then tested under the action of a secondary sinusoidal perturbation, which can remove bistability when a suitable relative phase is chosen. The surviving attractor is the one with less dissipation. This control strategy is particularly useful when one of the competing attractors is a chaotic attractor.

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Photopolymerization of customized materials became a well-established technique for micro- and nano-fabrication of photonic structures, and their optical properties as the refractive index should be precisely tailored to design specific photonic features. For this purpose, the refractive index determination in macroscopic samples is not exhaustive, and an in situ characterization is thus necessary at both the macro- and microscale to point out how different polymerization processes differently modulate the optical properties. In particular, we focus our attention on liquid crystalline networks (LCNs) that have been studied as birefringent materials whose tunable response is of interest for applications in different fields such as in robotics, biomedicine, and photonics. By tuning the molecular composition of LCN mixtures, e.g., modifying the cross-linker and dye amount inside the polymer network, the refractive index and the optical anisotropy of microscopic and macroscopic samples have been engineered and measured by a refractometer method under temperature variation or light actuation stimuli. Monitoring the refractive index at different length scales showed that two-photon polymerization increases the birefringence in microscopic structures, and the maximum variation of the optical anisotropy is achieved by a remote laser light stimulus.

International audience; We revisit the model of the laser with feedback and the minimal nonlinearity leading to chaos. Although the model has its origin in laser physics, with peculiarities related to the [Formula: see text] laser, it belongs to the class of the three-dimensional paradigmatic nonlinear oscillator models giving chaos. The proposed model contains three key nonlinearities, two of which are of the type [Formula: see text], where [Formula: see text] and [Formula: see text] are the fast and slow variables. The third one is of the type [Formula: see text], where [Formula: see text] is an intermediate feedback variable. We analytically demonstrate that it is essential for producing chaos via local or global homoclinic bifurcations. Its electronic implementation in the range of kilo Hertz region confirms its potential in describing phenomena evolving on different time scales.

International audience; In 1976, Leon Chua showed that a thermistor can be modeled as a memristive device. Starting from this statement we designed a circuit that has four circuit elements: a linear passive inductor, a linear passive capacitor, a nonlinear resistor and a thermistor, that is, a nonlinear "locally active" memristor. Thus, the purpose of this work was to use a physical memristor, the thermistor, in a Muthuswamy-Chua chaotic system (circuit) instead of memristor emulators. Such circuit has been modeled by a new three-dimensional autonomous dynamical system exhibiting very particular properties such as the transition from torus breakdown to chaos. Then, mathematical analysis and detailed numerical investigations have enabled to establish that such a transition corresponds to the so-called route to Shilnikov spiral chaos but gives rise to a "double spiral attractor". Michael Faraday (1791-1867) is generally well known for his contributions to the study of electromagnetism and electrochemistry. However, according to Orton 1 , while investigating the effect of temperature on the conductivity of "sulphuret of silver" (silver sulfide) in 1833 he discovered what is now considered as a thermistor 2. Thermistor, i.e., thermal resistor, is thus an electrical-resistance element made of a semiconducting material the resistance of which varies with temperature. Thermistor production was then difficult, and applications were limited. One century had to pass before thermistors became commonly used by commercial manufacturers. In the 1930s, Samuel Ruben (1900-1988) invented the first commercial thermistor that he called "electrical pyrometer resistance" (Patents N o 2,021,491). He explained that: This invention relates to an electrical pyrometer and specifically to one utilizing the resistance change of a metallic compound with heat to indicate temperature changes. The characteristic property of the material employed for the temperature indicating resistance element is one having a high negative resistance coefficient.

A communication scheme based on the synchronization of two chaotic quantum dot light emitting diodes (QD-LEDs) is theoretically examined. The Chaos in the QD-LED is generated by means of an optical feedback. Synchronization of the chaos is achieved by varying coupling strength between the transmitter and the receiver as unidirectional coupling. The proposed communication schemes is test a by successfully transmitting messages.

This research reports a theoretical investigation on the role of filtered optical feedback (FOF) in the quantum dot light emitting diode (QD-LED). The underlying dynamics is affected by a sidle node, which returns to an elliptical shape when the wetting layer (WL) is neglected. Both filter width and time delay change the appearance of different dynamics (chaotic and mixed mode oscillations ,MMOs). The results agrees with the experimental observations. Here, the fixed point analysis for QDs was done for the first time. For QD-LED with FOF, the system transits from the coherence collapse (CC) case in conventional optical feedback (COF) to a coherent case with a filtered mode in FOF. It was found that the WL washes out the modes which is an unexpected result. This may attributed to the longer capture time of WL compared with that between QD states. Thus, WL reduces the chaotic behavior.

We report the experimental evidence coherence and stochastic resonance in a dynamics of fast chaotic spiking of a semiconductor laser with optical feedback using an external nonwhite noise in the pumping current. We characterize both coherence and stochastic resonance in the time and frequency domain. We show that the regularity of the chaotic pulses in the intensity of laser diod increases when adding noise and it is optimal for some intermediate value of the noise intensity. We find that the power spectrum of the signal develops a peak at a finite frequency at intermediate values of the noise. The results show that noise may help in extracting the periodic signal without synchronization in chaotic communication. Then we reported the effect of external noise numerically on a single system by using bifurcation diagram. Finally, we considered Chaos synchronization in a network of 28 distinct chaotic systems with independent initial conditions when a normal Gaussian noise is added. The transition between non-synchronization to synchronization states using a suitable spatio-temporal representation has been reported. The role of coherence has also been considered. Keywords: Coherence resonance, Stochastic resonance, Control, Noise