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  • Experimental and numerical study of the symbolic dynamics of a modulated external-cavity semiconductor laser

     Aragoneses Aguado, Andres; Sorrentino Amaral, Taciano; Perrone, Sandro; Gauthier, Daniel; Torrent Serra, Maria Del Carmen; Masoller Alonso, Cristina
    Optics express
    Date of publication: 2014-02-21
    Journal article

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    We study the symbolic dynamics of a stochastic excitable optical system with periodic forcing. Specifically, we consider a directly modulated semiconductor laser with optical feedback in the low frequency fluctuations (LFF) regime. We use a method of symbolic time-series analysis that allows us to uncover serial correlations in the sequence of intensity dropouts. By transforming the sequence of inter-dropout intervals into a sequence of symbolic patterns and analyzing the statistics of the patterns, we unveil correlations among several consecutive dropouts and we identify clear changes in the dynamics as the modulation amplitude increases. To confirm the robustness of the observations, the experiments were performed using two lasers under different feedback conditions. Simulations of the Lang-Kobayashi (LK) model, including spontaneous emission noise, are found to be in good agreement with the observations, providing an interpretation of the correlations present in the dropout sequence as due to the interplay of the underlying attractor topology, the external forcing, and the noise that sustains the dropout events.

  • Controlling the likelihood of rogue waves in an optically injected semiconductor laser via direct current modulation

     Perrone, Sandro; Vilaseca Alavedra, Ramon; Zamora-Munt, Jordi; Masoller Alonso, Cristina
    Physical review A
    Date of publication: 2014-03-06
    Journal article

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    Extreme and rare events are nowadays the object of intensive research. Rogue waves are extreme waves that appear suddenly in many natural systems, even in apparently calm situations. Here we study numerically the rogue wave dynamics in an optically injected semiconductor laser with external periodic forcing that is implemented via direct modulation of the laser pump current. In the region of optical injection parameters where the laser intensity is chaotic and occasional ultrahigh pulses occur, our aim is to control the system by applying a weak modulation. We find that for an adequate range of frequency and amplitude parameters, the modulation can completely suppress the extreme pulses. We also show that the interplay between modulation and an external source of noise can significantly modify their probability of occurrence. These results can motivate a range of experimental and theoretical investigations in other natural systems.

  • Exploiting nonlinearity and noise in optical tweezers and semiconductor lasers: from resonant damping to stochastic logic gates and extreme pulses.

     Perrone, Sandro
    Defense's date: 2014-02-07
    Department of Applied Physics, Universitat Politècnica de Catalunya
    Theses

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    El tema central de esta tesis es el estudio de las dinámicas estocásticas y no lineales en sistemas ópticos. En primer lugar, se ha observado experimentalmente la dinámica estocástica de una partícula colloidal en una trampa óptica sometida a una fuerza externa. Los resultados se han relacionado a los efectos de un ruido paramétrico externo agregado a trampas ópticas monoestables y biestables. Específicamente hemos descubierto un nuevo efecto que hemos nombrado resonancia estocástica amortiguada (SRD), que se refiere a la minimización de la varianza de la posición de la partícula atrapada en un potencial harmonico, en funcion de la intensidad de un ruido paramétrico externo, añadido a la fuerza que actua sobre la particula. Se ha comparado la resonancia estocástica clásica con la amortiguada, y hemos demonstrado que se trata de dos fenómenos que coexisten en el mismo sistema, pero en diferentes regímenes. Además, hemos investigado experimentalmente un sistema monoestable, que exhibe un máximo en el cociente señal-ruido, que no se habia observado anteriormente en una trampa optica. Para estas investigaciones, hemos desarrollado una nueva técnica que aumenta 10 veces el rango de detección del fotodiodo, que explota el crosstalk entre canales.En segundo lugar, hemos estudiado la dinámica estocástica de un láser de semiconductor (SCL) de emision vertical (VCSEL), que presenta biestabilidad en las polarización de la luz emitida y fenomenos de histéresis, al variar la corriente inyectada o al variar la potencia óptica inyectada.Hemos demostrado que estas propiedades se pueden utilizar para realizar operaciones lógicas gracias al efecto del ruido de emisión espontánea. Dos señales de entrada lógicas han sido codificadas en tres niveles de potencia inyectada desde un láser guia (llamado master), y la respuesta lógica del laser injectado (slave) fue decodificada a partir de la polarización de la luz emitida. Se ha logrado una respuesta lógica correcta cuando se ajusta la potencia de la injeccion para favorecer, en dos de los niveles de injeccion, a una de las dos polarizaciones, y para favorecer a la otra polarización, en el tercer nivel de injeccion. Hemos demostrado numéricamente que el operador logico basado en la polarizacion emitida por un VCSEL con injeccion optica permite reproducir la tabla de verdad para los operadores lógicos OR y NOR. La extensión a los operadores logicos AND y NAND es de muy simple implementaciòn. Codificando las señales de entrada en forma optica hemos sido capaces de reducir el tiempo mínimo de bit requerido para realizar operaciones logicas correctamente, desde 30 ns, obtenido previamente mediante codificacion optoelectrónica, hasta 5 ns.El tercer objetivo de esta tesis es el estudio de la dinámica no lineal caótica de un SCL inyectado ópticamente en la region de parametros donde se observan esporadicamente picos extremos de intensidad, llamados Rogue Waves (RWs). Nuestros estudios nos permiten concluir que, agregando ruido moderado de intensidad apropiada, el número de pulsos extremos aumenta respecto al caso determinista. Por el contrario, en algunas regiones de parametros, agregar un ruido de baja intensidad da lugar a una significativa disminución de los pulsos extremos. Con el fin de suprimir o inducir estos pulsos extremos, hemos investigado los efectos de una modulación periódica de la corriente del láser. Hemos observado que esta modulacion puede efectivamente suprimir o inducir RWs, dependiendo de la frecuencia de la modulacion.

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    Multidimensional subwavelength position sensing using a semiconductor laser with optical feedback  Open access

     Cohen, Seth; Aragoneses Aguado, Andres; Rontani, Damien; Torrent Serra, Maria Del Carmen; Masoller Alonso, Cristina; Gauthier, Daniel
    Optics letters
    Date of publication: 2013-11-01
    Journal article

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    We demonstrate experimentally how to harness quasi-periodic dynamics in a semiconductor laser with dual optical feedback for measuring subwavelength changes in each arm of the cavity simultaneously. We exploit the multifrequency spectrum of quasi-periodic dynamics and show that independent frequency shifts are mapped uniquely to two-dimensional displacements of the arms in the external cavity. Considering a laser diode operating at telecommunication wavelength ¿¿1550¿¿nm, we achieve an average nanoscale resolution of approximately 9.8 nm (~¿/160).

    We demonstrate experimentally how to harness quasi-periodic dynamics in a semiconductor laser with dual optical feedback for measuring subwavelength changes in each arm of the cavity simultaneously. We exploit the multifrequency spectrum of quasi-periodic dynamics and show that independent frequency shifts are mapped uniquely to two-dimensional displacements of the arms in the external cavity. Considering a laser diode operating at telecommunication wavelength λ≈1550nm, we achieve an average nanoscale resolution of approximately 9.8 nm (∼λ∕160).

  • Two-parameter study of square-wave switching dynamics in orthogonally delay-coupled semiconductor lasers

     Masoller Alonso, Cristina; Sciamanna, Marc; Gavrielides, Athanasios Tom
    Philosophical transactions of the Royal Society A. Mathematical physical and engineering sciences
    Date of publication: 2013-09
    Journal article

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    We perform a detailed numerical analysis of square-wave (SW) polarization switching in two semiconductor lasers with time-delayed, orthogonal mutual coupling. An in-depth mapping of the dynamics in the two-parameter plane coupling strength versus frequency detuning shows that stable SWs occur in narrow parameter regions that are localized close to the boundary of stability of the pure-mode solution. In this steady state, the two coupled lasers emit orthogonal polarizations. We also show that there are various types of SW forms and that stable switching does not need the inclusion of noise or nonlinear gain in the model. As these narrow regions of deterministic and stable SWs occur for quite different combinations of parameters, they could potentially explain the waveforms that have been observed experimentally. However, on the other hand, these regions are narrow enough to be in fact considered as experimentally unreachable. Therefore, our results indicate that further experimental statistical studies are needed in order to distinguish deterministic and stationary square waveforms from long transients because of noise.

  • All-optical stochastic logic gate based on a VCSEL with tunable optical injection

     Salvide, Matias Fernando; Masoller Alonso, Cristina; Torre, Maria Susana
    IEEE journal of quantum electronics
    Date of publication: 2013-10
    Journal article

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    We study the dynamics of a vertical-cavity surface-emitting laser with continuous-wave orthogonal optical injection from a tunable laser. We use the dynamical properties of polarization bistability and the interplay with internal or external noise to demonstrate numerically a reliable logic output to two logic inputs encoded in the optical frequency of the injected light. This all-optical configuration is more than ten times faster than the electro-optical implementation and has the advantage of operating at constant injection power. © 1965-2012 IEEE.

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    Extreme intensity pulses in a semiconductor laser with a short external cavity  Open access

     Reinoso, Jose A.; Zamora Munt, Jordi; Masoller Alonso, Cristina
    Physical review E: statistical, nonlinear, and soft matter physics
    Date of publication: 2013-06
    Journal article

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    We present a numerical study of the pulses displayed by a semiconductor laser with optical feedback in the short-cavity regime, such that the external cavity round-trip time is shorter than the laser relaxation oscillation period. For certain parameters there are occasional pulses, which are high enough to be considered extreme events. We characterize the bifurcation scenario that gives rise to such extreme pulses and study the influence of noise. We demonstrate intermittency when the extreme pulses appear and hysteresis when the attractor that sustains these pulses is destroyed. We also show that this scenario is robust under the inclusion of noise.

    We present a numerical study of the pulses displayed by a semiconductor laser with optical feedback in the short-cavity regime, such that the external cavity round-trip time is shorter than the laser relaxation oscillation period. For certain parameters there are occasional pulses, which are high enough to be considered extreme events. We characterize the bifurcation scenario that gives rise to such extreme pulses and study the influence of noise. We demonstrate intermittency when the extreme pulses appear and hysteresis when the attractor that sustains these pulses is destroyed. We also show that this scenario is robust under the inclusion of noise.

  • Characterizing the dynamics of coupled pendulums via symbolic time series analysis

     de Polsi, G.; Cabeza, C.; Marti, A.C.; Masoller Alonso, Cristina
    European physical journal. Special topics
    Date of publication: 2013-06
    Journal article

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    We propose a novel method of symbolic time-series analysis aimed at characterizing the regular or chaotic dynamics of coupled oscillators. The method is applied to two identical pendulums mounted on a frictionless platform, resembling Huygens' clocks. Employing a transformation rule inspired in ordinal analysis [C. Bandt and B. Pompe, Phys. Rev. Lett. 88, 174102 (2002)], the dynamics of the coupled system is represented by a sequence of symbols that are determined by the order in which the trajectory of each pendulum intersects an appropriately chosen hyperplane in the phase space. For two coupled pendulums we use four symbols corresponding to the crossings of the vertical axis (at the bottom equilibrium point), either clock-wise or anti-clock wise. The complexity of the motion, quantified in terms of the entropy of the symbolic sequence, is compared with the degree of chaos, quantified in terms of the largest Lyapunov exponent. We demonstrate that the symbolic entropy sheds light into the large variety of different periodic and chaotic motions, with different types synchronization, that cannot be inferred from the Lyapunov analysis.

  • Extreme optical pulses: origin, predictability and suppression

     Masoller Alonso, Cristina
    Workshop on Instabilities and Non-equilibrium Structures
    Presentation's date: 2013-12
    Presentation of work at congresses

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    Distinguishing signatures of determinism and stochasticity in spiking complex systems  Open access

     Aragoneses Aguado, Andres; Rubido, Nicolás; Tiana Alsina, Jordi; Torrent Serra, Maria Del Carmen; Masoller Alonso, Cristina
    Scientific reports
    Date of publication: 2013-05-07
    Journal article

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  • Rogue waves in optically injected lasers: origin, predictability, and suppression

     Zamora Munt, Jordi; Garbin, Bruno; Barland, Stéphane; Giudici, Massimo; Rios Leite, José R.; Masoller Alonso, Cristina; Tredicce, Jorge R.
    Physical review A
    Date of publication: 2013-03-07
    Journal article

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    Rogue waves are devastating extreme events that occur in many natural systems, and a lot of work has focused on predicting and understanding their origin. In optically injected semiconductor lasers rogue waves are rare ultra-high pulses that sporadically occur in the laser chaotic output intensity. Here we show that these optical rogue waves can be predicted with long anticipation time, that they are generated by a crisis-like process, and that noise can be employed to either enhance or suppress their probability of occurrence. By providing a good understanding of the mechanisms triggering and controlling the rogue waves, our results can contribute to improve the performance of injected lasers and can also enable new experiments to test if these mechanisms are also involved in other natural systems where rogue waves have been observed.

  • Neuronal oscillations: from single-unit activity to emergent dynamics and back  Open access

     De Sancristobal Alonso, Belen
    Defense's date: 2013-07-22
    Department of Physics and Nuclear Engineering, Universitat Politècnica de Catalunya
    Theses

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    L’objectiu principal d’aquesta tesi és avançar en la comprensió del processament d’informació en xarxes neuronals en presència d’oscil lacions subumbrals. La majoria de neurones propaguen la seva activitat elèctrica a través de sinapsis químiques que són activades, exclusivament, quan el corrent elèctric que les travessa supera un cert llindar. És per aquest motiu que les descàrregues ràpides i intenses produïdes al soma neuronal, els anomenats potencials d’acció, són considerades la unitat bàsica d’informació neuronal, és a dir, el senyal mínim i necessari per a iniciar la comunicació entre dues neurones. El codi neuronal és entès, doncs, com un llenguatge binari que expressa qualsevol missatge (estímul sensorial, memòries, etc.) en un tren de potencials d’acció. Tanmateix, cap funció cognitiva rau en la dinàmica d’una única neurona. Circuits de milers de neurones connectades entre sí donen lloc a determinats ritmes, palesos en registres d’activitat colectiva com els electroencefalogrames (EEG) o els potencials de camp local (LFP). Si els potencials d’acció de cada cèl lula, desencadenats per fluctuacions estocàstiques de les corrents sinàptiques, no assolissin un cert grau de sincronia, no apareixeria aquesta periodicitat a nivell de xarxa. Per tal de poder entendre si aquests ritmes intervenen en el codi neuronal hem estudiat tres situacions. Primer, en el Capítol 2, hem mostrat com una cadena oberta de neurones amb un potencial de membrana intrínsecament oscil latori filtra un senyal periòdic arribant per un dels extrems. La resposta de cada neurona (pulsar o no pulsar) depèn de la seva fase, de forma que cada una d’elles rep un missatge filtrat per la precedent. A més, cada potencial d’acció presinàptic provoca un canvi de fase en la neurona postsinàptica que depèn de la seva posició en l’espai de fases. Els períodes d’entrada capaços de sincronitzar les oscil lacions subumbrals són aquells que mantenen la fase d’arribada dels potencials d’acció fixa al llarg de la cadena. Per tal de què el missatge arribi intacte a la darrera neurona cal, a més a més, que aquesta fase permeti la descàrrega del voltatge transmembrana. En segon cas, hem estudiat una xarxa neuronal amb connexions tant a veïns propers com de llarg abast, on les oscil lacions subumbrals emergeixen de l’activitat col lectiva reflectida en els corrents sinàptics (o equivalentment en el LFP). Les neurones inhibidores aporten un ritme a l’excitabilitat de la xarxa, és a dir, que els episodis en què la inhibició és baixa, la probabilitat d’una descàrrega global de la població neuronal és alta. En el Capítol 3 mostrem com aquest ritme implica l’aparició d’una bretxa en la freqüència de descàrrega de les neurones: o bé polsen espaiadament en el temps o bé en ràfegues d’elevada intensitat. La fase del LFP determina l’estat de la xarxa neuronal codificant l’activitat de la població: els mínims indiquen la descàrrega simultània de moltes neurones que, ocasionalment, han superat el llindar d’excitabilitat degut a un decreixement global de la inhibició, mentre que els màxims indiquen la coexistència de ràfegues en diferents punts de la xarxa degut a decreixements locals de la inhibició en estats globals d’excitació. Aquesta dinàmica és possible gràcies al domini de la inhibició sobre l’excitació. En el Capítol 4 considerem acoblament entre dues xarxes neuronals per tal d’estudiar la interacció entre ritmes diferents. Les oscil lacions indiquen recurrència en la sincronització de l’activitat col lectiva, de manera que durant aquestes finestres temporals una població optimitza el seu impacte en una xarxa diana. Quan el ritme de la població receptora i el de l’emissora difereixen significativament, l’eficiència en la comunicació decreix, ja que les fases de màxima resposta de cada senyal LFP no mantenen una diferència constant entre elles. Finalment, en el Capítol 5 hem estudiat com les oscil lacions col lectives pròpies de l’estat de son donen lloc al fenomen de coherència estocàstica. Per a una intensitat òptima del soroll, modulat per l’excitabilitat de la xarxa, el LFP assoleix una regularitat màxima donant lloc a un període refractari de la població neuronal. En resum, aquesta Tesi mostra escenaris d’interacció entre els potencials d’acció, característics de la dinàmica de neurones individuals, i les oscil lacions subumbrals, fruit de l’acoblament entre les cèl lules i ubiqües en la dinàmica de poblacions neuronals. Els resultats obtinguts aporten funcionalitat a aquests ritmes emergents, agents sincronitzadors i moduladors de les descàrregues neuronals i reguladors de la comunicació entre xarxes neuronals.

    The main objective of this thesis is to better understand information processing in neuronal networks in the presence of subthreshold oscillations. Most neurons propagate their electrical activity via chemical synapses, which are only activated when the electric current that passes through them surpasses a certain threshold. Therefore, fast and intense discharges produced at the neuronal soma (the action potentials or spikes) are considered the basic unit of neuronal information. The neuronal code is understood, then, as a binary language that expresses any message (sensory stimulus, memories, etc.) in a train of action potentials. Circuits of thousands of interconnected neurons give rise to certain rhythms, revealed in collective activity measures such as electroencephalograms (EEG) and local field potentials (LFP). Synchronization of action potentials of each cell, triggered by stochastic fluctuations of the synaptic currents, cause this periodicity at the network level.To understand whether these rhythms are involved in the neuronal code we studied three situations. First, in Chapter 2, we showed how an open chain of neurons with an intrinsically oscillatory membrane potential filters a periodic signal coming from one of its ends. The response of each neuron (to spike or not) depends on its phase, so that each cell receives a message filtered by the preceding one. Each presynaptic action potential causes a phase change in the postsynaptic neuron, which depends on its position in the phase space. Those incoming periods that are able to synchronize the subthreshold oscillations, keep the phase of arrival of action potentials fixed along the chain. The original message reaches intact the last neuron provided that this phase allows the discharge of the transmembrane voltage.I the second case, we studied a neuronal network with connections to both long range and close neighbors, in which the subthreshold oscillations emerge from the collective activity apparent in the synaptic currents. The inhibitory neurons provide a rhythm to the excitability of the network. When inhibition is low, the likelihood of a global discharge of the neuronal population is high. In Chapter 3 we show how this rhythm causes a gap in the discharge frequency of neurons: either they pulse single spikes or they fire bursts of high intensity. The LFP phase determines the state of the neuronal network, coding the activity of the population: its minima indicate the simultaneous discharge of many neurons, while its maxima indicate the coexistence of bursts due to local decreases of inhibition at global states of excitation. In Chapter 4 we consider coupling between two neural networks in order to study the interaction between different rhythms. The oscillations indicate recurrence in the synchronization of collective activity, so that during these time windows a population optimizes its impact on a target network. When the rhythm of the emitter and receiver population differ significantly, the communication efficiency decreases as the phases of maximum response of each LFP signal do not maintain a constant difference between them.Finally, in Chapter 5 we studied how oscillations typical of the collective sleep state give rise to stochastic coherence. For an optimal noise intensity, modulated by the excitability of the network, the LFP reaches a maximal regularity leading to a refractory period of the neuronal population.In summary, this Thesis shows scenarios of interaction between action potentials, characteristics of the dynamics of individual neurons, and the subthreshold oscillations, outcome of the coupling between the cells and ubiquitous in the dynamics of neuronal populations . The results obtained provide functionality to these emerging rhythms, triggers of synchronization and modulator agents of the neuronal discharges and regulators of the communication between neuronal networks.

  • ESTOCASTICIDAD EN SISTEMAS COMPLEJOS NOLINEALES

     Pons Rivero, Antonio Javier; Torrent Serra, Maria Del Carmen; Masoller Alonso, Cristina; Pigolotti, Simone; Ramirez de La Piscina Millan, Laureano; Peñaranda Ayllon, Angelina; Malagarriga Guasch, Daniel; Dies Miracle, Marta; Aragoneses Aguado, Andres; Deza, Juan Ignacio; Garcia Ojalvo, Jorge
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    Detecting long-range teleconnections in the climate network via ordinal pattern time-series analysis  Open access

     Deza, Juan Ignacio; Barreiro, Marcelo; Masoller Alonso, Cristina
    Congreso de Física Estadística
    Presentation's date: 2012-10-19
    Presentation of work at congresses

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  • Exploiting bistability, time delay and noise for obtaining all-optically square-wave switching

     Masoller Alonso, Cristina
    International Conference on Delayed Complex Systems
    Presentation's date: 2012-06
    Presentation of work at congresses

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  • Hopf bifurcation to square-wave switching in mutually coupled semiconductor lasers

     Sciamanna, Marc; Virte, V; Masoller Alonso, Cristina; Gavrielides, Athanasios Tom
    Physical review E: statistical, nonlinear, and soft matter physics
    Date of publication: 2012
    Journal article

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  • Stochastic logic gate that exploits noise and polarization bistability in an optically injected VCSEL

     Perrone, S.; Vilaseca Alavedra, Ramon; Masoller Alonso, Cristina
    Optics express
    Date of publication: 2012-09-24
    Journal article

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    We study numerically the dynamics of a vertical-cavity surface-emitting laser (VCSEL) with optical injection and show that the interplay of polarization bistability and noise yields a reliable logic output to two logic inputs. Specifically, by encoding the logic inputs in the strength of the light injected into the suppressed polarization mode of the VCSEL (the so-called 'orthogonal' injection), and by decoding the output logic response from the polarization state of the emitted light, we demonstrate an all-optical stochastic logic gate that exploits the ubiquitous presence of noise. It gives the correct logic output response for as short as 5 ns bit times when the dimensionless spontaneous emission coefficient, ß(sp), is within the range 10(-4)-10(-1). Considering that typical values of ß(sp) in semiconductor lasers are in the range 10(-5)-10(-4), the VCSEL-based logic gate can be implemented with nowadays commercially available VCSELs, exploiting either their intrinsic noise, or external and background noise sources.

  • Concept Design, Analysis, and Integration of the New U.P.C. Multispectral Lidar System  Open access

     Kumar, Dhiraj
    Defense's date: 2012-07-16
    Department of Signal Theory and Communications, Universitat Politècnica de Catalunya
    Theses

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    The increasing need for range-resolved aerosol and water-vapour atmospheric observation networks worldwide has given rise to multi-spectral LIDARs (Light Detection and Ranging, a synonym of laser radar) as advanced remote sensing sensors. This Ph.D. presents the design, integration and analysis of the new 6-channel multispectral elastic/Raman LIDAR for aerosol and water-vapour content monitoring developed at the Remote Sensing Lab. (RSLAB) of the Universitat Politècnica de Catalunya (UPC). It is well known that the combination of at least three elastic and two Raman nitrogen channels are sufficient to enable retrieval of the optical and microphysical properties of aerosols with a key impact on climate change variables. The UPC lidar is part of the EARLINET (European Aerosol Research Lidar Network) -GALION (Global Atmospheric Watch Atmospheric Lidar Observation Network), a ground-based continental network including more than 28 stations. Currently, only 8 of the 28 EARLINET stations are of such advanced type. This Ph.D. specifically focuses on: (1) Concept link-budget instrument design and overlap factor assessment. The former includes opto-atmospheric parameter modelling and assessment of backscattered power and SNR levels, and maximum system range for the different reception channels (3 elastic, and 2 aerosol and 1 water-vapour Raman channels, ultraviolet to near-infrared bands). The latter studies the laser-telescope crossover function (or overlap function) by means of a novel ray-tracing Gaussian model. The problem of overlap function computation and its near-range sensitivity for medium size aperture (f/10, f/11) bi-axial tropospheric lidar systems using both detector and fiber-optics coupling alternatives at the telescope focal-plane is analysed using this new ray-tracing approach, which provides a much simpler solution than analytical-based methods. Sensitivity to laser divergence, field-lens and detector/fiber positions, and fiber¿s numerical aperture is considered. (2) Design and opto-mechanical implementation of the 6-channel polychromator (i.e., the spectrally selective unit in reception). Design trade-offs concerning light collimation, end-to-end transmissivity, net channel responsivity, and homogeneous spatial light distribution onto the detectors¿ active area discussed. (3) System integration and validation. This third part is two fold: On one hand, first-order backscatter-coefficient error bounds (a level-1 data product) for the two-component elastic lidar inversion algorithm are estimated for both random (observation noise) and systematic error sources (user¿s uncertainty in the backscatter-coefficient calibration, and user¿s uncertainty in the aerosol extinction-to-backscatter lidar ratio). On the other hand, the multispectral lidar so far integrated is described at both hardware and control software level. Statistical validation results for the new UPC lidar (today in routine operation) in the framework of SPALI-2010 intercomparison campaign are presented as part of EARLINET quality assurance / optimisation of instruments¿ program. The methodology developed in the first part of this Ph.D. has successfully been applied to the specification case study of the IFAE/UAB lidar system, which will be installed and operated at the Cherenkov Telescope Array (CTA) observatory. Finally, specs for automated unmanned unattended lidar operation with service times close to 365/24 are presented at the end of this Ph.D. in response to the increasing demand for larger observation times and availability periods of lidar stations.

  • Premi ICREA Acadèmia

     Masoller Alonso, Cristina; Garcia Ojalvo, Jorge; Llorca Pique, Jordi
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  • NEURAL ENGINEERING TRANSFORMATIVE TECHNOLOGIES

     Pons Rivero, Antonio Javier; Torrent Serra, Maria Del Carmen; Masoller Alonso, Cristina; Garcia Ojalvo, Jorge
    Participation in a competitive project

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    Square-wave switching in vertical-cavity surface-emitting lasers with polarization-rotated optical feedback: Experiments and simulations  Open access

     Sukow, David; Gilfillan, Taylor; Pope, Brenton; Torre, Maria Susana; Gavrielides, Athanasios Tom; Masoller Alonso, Cristina
    Physical review A
    Date of publication: 2012-09-12
    Journal article

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    We study experimentally the dynamics of vertical-cavity surface-emitting lasers (VCSELs) with polarization-rotated (PR) optical feedback, such that the natural lasing polarization of a VCSEL is rotated by 90 deg and then is reinjected into the laser. We observe noisy, square-wave-like polarization switchings with periodicity slightly longer than twice the delay time, which degrade to (or alternate with) bursts of irregular oscillations. We present results of simulations that are in good agreement with the observations. The simulations demonstrate that close to threshold the regular switching is very sensitive to noise, while well above threshold is less affected by the noise strength. The frequency splitting between the two polarizations plays a key role in the switching regularity, and we identify wide parameter regions where deterministic and robust switching can be observed.

  • Dynamics of vertical-cavity surface emitting lasers under selective polarization rotated feedback and coupling

     Torre, Maria Susana; Masoller Alonso, Cristina; Gavrielides, Athanasios Tom
    "Rio de la Plata" Workshop on Laser Dynamics and Nonlinear Photonics
    Presentation's date: 2011
    Presentation of work at congresses

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    Diode laser operation under orthogonal feedback : experiments and theory  Open access

     Sorrentino, T.; Masoller Alonso, Cristina; Soares, C.; Vidal, I.; Oria, Marcos
    "Rio de la Plata" Workshop on Laser Dynamics and Nonlinear Photonics
    Presentation's date: 2011
    Presentation of work at congresses

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    We report experimental and numerical investigations concerning semiconductor lasers emission under polarization-rotated feedback. We experimentally observe that for some semiconductor lasers the weak TM mode does lase even in the absence of TM feedback and we monitor how the TE and TM emissions evolve with the increase of the TM feedback strength. The emission frequency of a semiconductor laser subject to polarization-rotated feedback experiences a shift proportional to the optical power fed back into the laser. We aim to investigate what affects the sensibility of the frequency of semiconductor lasers to polarization-rotated feedback. Experimentally, we measured the proportionality coefficient β between frequency shift and feedback power for different lasers and characterized how it varies with some parameters. Theoretically, we made numerical calculations using a rate equation model, and our results show a critical dependence of the β coefficient on the gain self- and cross-saturation of both modes and the relations between these saturation coefficients.

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    All optical implementation of a stochastic logic gate using a VCSEL with external optical injection  Open access

     Perrone, S.; Masoller Alonso, Cristina; Vilaseca Alavedra, Ramon
    "Rio de la Plata" Workshop on Laser Dynamics and Nonlinear Photonics
    Presentation's date: 2011
    Presentation of work at congresses

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    We perform numerical simulations of the dynamics of two VCSELs optically coupled in a master-slave configuration. We show that the interplay of nonlinearity and spontaneous emission noise can yield logic behavior, and the emergent outcome of such system is a reliable logic gate. Specifically in our case represents an all-optical logic gate, with the logic input encoded in the strength of the light injected in the slave laser by the master laser, and the fast and robust response decoded from the polarization state of the light emitted by the slave laser.

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    Inferring long memory processes in the climate network via ordinal pattern analysis  Open access

     Barreiro, Marcelo; Marti, Arturo; Masoller Alonso, Cristina
    Chaos
    Date of publication: 2011-03
    Journal article

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    We analyze climatological data from a complex networks perspective, using techniques of nonlinear time series symbolic analysis. Specifically, we employ ordinal patterns and binary representations to analyze monthly averaged surface air temperature (SAT) anomalies. By computing the mutual information of the time series in regular grid points covering the Earth’s surface and then performing global thresholding, we construct climate networks that uncover short-term memory processes, as well as long ones (5–6 yr). Our results suggest that the time variability of the SAT anomalies is determined by patterns of oscillatory behavior that repeat from time to time with a periodicity related to intraseasonal variations and to El Niño on seasonal to interannual time scales. The present work is located at the triple intersection of three highly active interdisciplinary research fields in nonlinear science: symbolic methods for nonlinear time series analysis, network theory, and non linear processes in the earth climate. While a lot of effort is being done in order to improve our understanding of natural complex systems, with many different methods for mapping time series to network representations being investigated and employed in complex systems such as the human brain, our work is the first one aimed at characterizing the global climate network in terms of oscillatory patterns that tend to repeat from time to time, with various time scales. By mapping these processes into a global network, using ordinal patterns and binary representations, we find that the structure of the network changes drastically at different time scales.

  • Numerical characterization of transient polarization square-wave switching in two orthogonally coupled VCSELs

     Torre, Maria Susana; Gavrielides, Athanasios Tom; Masoller Alonso, Cristina
    Optics express
    Date of publication: 2011-10-10
    Journal article

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    Deterministic optical rogue waves  Open access

     Bonatto, Cristian; Feyereisen, Michael; Barland, Stéphane; Giudici, Massimo; Masoller Alonso, Cristina; Rios Leite, José R.; Tredicce, Jorge R.
    Physical review letters
    Date of publication: 2011-07-29
    Journal article

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    Experimental observations of rare giant pulses or rogue waves were done in the output intensity of an optically injected semiconductor laser. The long-tailed probability distribution function of the pulse amplitude displays clear non-Gaussian features that confirm the rogue wave character of the intensity pulsations. Simulations of a simple rate equation model show good qualitative agreement with the experiments and provide a framework for understanding the observed extreme amplitude events as the result of a deterministic nonlinear process.

  • STOCHASTICITY,COMPLEXITY AND SYNCHRONIZATION IN SEMICONDUCTOR LASERS  Open access

     Tiana Alsina, Jordi
    Defense's date: 2011-11-10
    Department of Applied Physics, Universitat Politècnica de Catalunya
    Theses

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    The purpose of this Thesis is study the dynamical behavior of semiconductor lasers with optical feedback, as well as analyze the synchronization of this kind of systems under different coupling arquitectures. This study has been done from an experimental point of view, but in some cases we have used numerical models in order to verify and/or extend the experimental results. A semiconductor laser in absence of any optical feedback emits light at constant power. If one wants to induce dynamics in the laser, a good strategy is to introduce an external cavity able to reflect the emitted light back into the laser. Due to this feedback, the laser can show a large variety of dynamical behaviors. In this Thesis we will focus mainly in a dynamical regime known as low frequency fluctuations regime (LFF). The LFF regime takes place when the pump current of the laser is close to its threshold current and the feedback strength is sufficiently large, and it consists in sudden intensity dropouts arising at irregular times, followed by a gradual and stepwise recovery. During this Thesis, we have characterized in detail the dynamical behavior of the time between intensity dropouts for a semiconductor laser with feedback, by using different statistical techniques based on information theory concepts. We have quantified the probability of appearance of certain patterns within the temporal series, as well as its degree of complexity. As a result of these studies, we can conclude that the dynamics of a semiconductor laser with optical feedback is stochastic for pump current values close to the laser threshold. On the other hand, for larger pump currents the dynamics is basically deterministic (chaotic). Numerical simulations have shown a good qualitative and quantitive agreement with the experimental results. During this Thesis we have also studied the ability of semiconductor lasers to synchronize under different coupling architectures. First, we have characterized the leader-laggard dynamics showed by two semiconductor lasers bidirectionally coupled operating at the LFF regime, with a method that takes into account the number of forbidden patterns that appears in the temporal series. We have quantified the degree of stochasticity of the system as a function of the pump current of both lasers. A second coupling architecture studied here, consists in two lasers unidirectionally coupled via two paths. In this case, we have analyzed how the synchronization is affected under different values of the coupling strength of both paths, as well as the potential of this system (or rather, the lack thereof) to be used in chaotic communications. Finally we have characterized the synchronization at zero lag for two lasers coupled bidirectionally via a passive relay. In particular, we have studied the desynchronization events and their statistics for different pump currents. The experimental results obtained in this Thesis give a global perspective of the dynamical statistical properties of semiconductor laser dynamics, both isolated or coupled to other lasers, which contributes to a better understanding of this kind of dynamical systems.

    L’objectiu d’aquesta Tesi ´es l’estudi de la din`amica de l`asers de semiconductor amb retroalimentaci´o `optica, aix´ý com l’an`alisis de la sincronitzaci´o d’aquest tipus de sistemes sota diferents arquitectures d’acoblament. Aquest estudi s’ha fet sempre des d’un punt de vista b`asicament experimental, tot i que en alguns casos hem utilitzat models num`erics per tal de verificar i/o ampliar els resultats experimentals. Un l`aser de semiconductor en abs`encia de retroalimentaci´o `optica o altres perturbacions externes, emet llum a una intensitat pr`acticament constant. Aix´ý doncs, si el que es vol ´es indu¨ýr din`amica en el l`aser, una bona estrat`egia ´es introdu¨ýr una cavitat externa capa¸c de reflexar la llum cap al l`aser. Un cop la llum ´es reinjectada, els l`asers de semiconductor poden mostrar una gran varietat de comportaments din`amics. En aquesta tesis ens centrarem principalment en un r`egim din`amic anomenat r`egim de fluctuacions de baixa frequ`encia (LFF en les seves sigles en angl`es). El r`egim d’LFF es d´ona quan el corrent d’injecci´o del l`aser es troba a prop del seu corrent llindar i la intensitat de la retroalimentaci´o ´es suficientment gran, i est`a caracteritzat per sobtades caigudes de la intensitat a temps irregulars, seguides per una recuperaci´o gradual i escalonada. Durant aquesta Tesi, hem caracteritzat de forma detallada el comportament din`amic de la distribuci´o dels temps entre les caigudes d’intensitat d’un l`aser de semiconductor amb retroalimentaci´o `optica, utilitzant diferents m`etodes estad´ýstics basats en conceptes de teoria de la informaci´o. En particular, hem quantificat la probabilitat d’aparici´o de certs patrons dins les s`eries temporals, aix´ý com el grau de complexitat d’aquestes. Durant aquest estudi hem observat que la din`amica d’un l`aser de semiconductor amb retroalimentaci´o es estoc`astica per valors del corrent d’injecci´o propers al corrent llindar del l`aser. D’altra banda, per a valors m´es grans del corrent d’injecci´o la din`amica ´es m´es determinista (ca`otica). Les simulacions num`eriques realitzades han mostrat un acord qualitatiu i quantitatiu amb els resultats experimentals. Durant aquesta Tesi tamb´e hem estudiat la sincronitzaci´o entre l`asers de semiconductor. Hem analitzat diferents arquitectures d’acoblament. Primer hem caracteritzat la din`amica leader-laggard que presenten dos l`asers de semiconductor acoblats bidireccionalment operant en r`egim de LFFs, amb un m`etode que t´e en compte el nombre de patrons prohibits que apareixen en la s`erie temporal. Hem quantificat el grau d’estocasticitat del sistema en funci´o del nivell de bombeig al qual est`an sotmesos els dos l`asers. La seg¨uent arquitectura d’acoblament que hem estudiat consisteix en dos l`asers acoblats unidireccionalment a trav´es de dos camins. En aquest cas hem analitzat com es veu afectada la sincronitzaci´o sota diferents valors de l’acoblament dels dos camins, aix´ý com el potencial d’aquest esquema experimental per realitzar comunicacions ca`otiques. Per ´ultim hem caracteritzat la sincronitzaci´o a retard zero per dos l`asers acoblats bidireccionalment, a on els dos l`asers tenen la seva pr`opia realimentaci´o `optica. En particular, hem estudiat els events de desincronitzaci´o i la seva estad´ýstica per a diferents corrents d’injecci´o. Els resultats experimentals obtinguts en aquesta Tesi, ofereixen una prespectiva global de les propietats estad´ýstiques de la din`amica de l`asers de semiconductor, tant a¨ýllats com acoblats a altres l`asers, que contribueixen a entendre millor aquests sistemes din`amics.

  • Nonlinear and Stochastic Dynamics of Semiconductor Lasers: Modulation, Transient Dynamics and Synchronization

     Zamora Munt, Jordi
    Defense's date: 2011-06-21
    Department of Physics and Nuclear Engineering, Universitat Politècnica de Catalunya
    Theses

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  • LEARNING ABOUT INTERACTING NETWORKS IN CLIMATE

     Kurths, Jürgen; Havlin, Shlomo; Dijkstra, Hendrik; Barreiro, Marcelo; Hernandez García, Emilio; Mudelsee, Manfreed; Abel, Markus; Roest, Mark; Masoller Alonso, Cristina
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  • Laboratorio de dinámica de láseres

     Masoller Alonso, Cristina; Torrent, M.C.; Garcia Ojalvo, Jorge; Bonatto, Cristian; Tiana Alsina, Jordi; Zamora Munt, Jordi; Aragoneses Aguado, Andres; Rubido, Nicolás
    Date: 2011-03-17
    Report

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  • Research activities of the group on nonlinear dynamics, nonlinear optics and lasers (DONLL) at the universitat politècnica de catalunya (Campus de Terrassa)

     Tiana Alsina, Jordi; Zamora Munt, Jordi; Nistor, Ioan Cristian; Roppo, Vito; Maigyte, Lina; Aragoneses Aguado, Andres; Khumar, N.P.; Martinez Gonzalez, Maria Cristina; Fernandez Soler, Juanjo; Serrat Jurado, Carles; Font Garcia, Josep Lluís; Herrero Simon, Ramon; Cojocaru, Crina Maria; Trull, Jose; Masoller Alonso, Cristina; Staliunas, Kestutis; Torrent Serra, Maria Del Carmen; Garcia Ojalvo, Jorge; Vilaseca Alavedra, Ramon
    Óptica pura y aplicada
    Date of publication: 2011-06
    Journal article

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  • Quantifying the complexity of the delayed logistic map

     Masoller Alonso, Cristina; Rosso, Osvaldo A.
    Philosophical transactions of the Royal Society A. Mathematical physical and engineering sciences
    Date of publication: 2011-01-28
    Journal article

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  • Complex transitions to synchronization in delay-coupled networks of logistic maps

     Masoller Alonso, Cristina; Atay, F. M.
    European physical journal D
    Date of publication: 2011-03
    Journal article

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    A network of delay-coupled logistic maps exhibits two different synchronization regimes, depending on the distribution of the coupling delay times. When the delays are homogeneous throughout the network, the network synchronizes to a time-dependent state, which may be periodic or chaotic depending on the delay; when the delays are sufficiently heterogeneous, the synchronization proceeds to a steady-state, which is unstable for the uncoupled map. Here we characterize the transition from time-dependent to steady-state synchronization as the width of the delay distribution increases. We also compare the two transitions to synchronization as the coupling strength increases. We use transition probabilities calculated via symbolic analysis and ordinal patterns. We find that, as the coupling strength increases, before the onset of steady-state synchronization the network splits into two clusters which are in anti-phase relation with each other. On the other hand, with increasing delay heterogeneity, no cluster formation is seen at the onset of steady-state synchronization; however, a rather complex unsynchronized state is detected, revealed by a diversity of transition probabilities in the network nodes.

  • Language organization and temporal correlations in the spiking activity of an excitable laser: experiments and model comparison

     Rubido, Nicolás; Tiana Alsina, Jordi; Torrent Serra, Maria Del Carmen; Garcia Ojalvo, Jorge; Masoller Alonso, Cristina
    Physical review E: statistical, nonlinear, and soft matter physics
    Date of publication: 2011-08-09
    Journal article

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    Bifurcation to square-wave switching in orthogonally delay-coupled semiconductor lasers: Theory and experiment  Open access

     Masoller Alonso, Cristina; Sukow, D.; Gavrielides, Athanasios Tom; Sciamanna, Marc
    Physical review A
    Date of publication: 2011-08-22
    Journal article

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    We analyze the dynamics of two semiconductor lasers with so-called orthogonal time-delayed mutual coupling: the dominant TE (x) modes of each laser are rotated by 90∘ (therefore, TM polarization or y) before being coupled to the other laser. Although this laser system allows for steady-state emission in either one or in both polarization modes, it may also exhibit stable time-periodic dynamics including square waveforms. A theoretical mapping of the switching dynamics unveils the region in parameter space where one expects to observe long-term time-periodic mode switching. Detailed numerical simulations illustrate the role played by the coupling strength, the mode frequency detuning, or the mode gain to loss difference. We complement our theoretical study with several experiments and measurements. We present time series and intensity spectra associated with the characteristics of the square waves and other waveforms observed as a function of the strength of the delay coupling. The experimental observations are in very good agreement with the analysis and the numerical results.

  • Transient low-frequency fluctuations in semiconductor lasers with optical feedback

     Zamora Munt, Jordi; Masoller Alonso, Cristina; Garcia Ojalvo, Jorge
    Physical review A
    Date of publication: 2010-03-11
    Journal article

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  • Quantifying the statistical complexity of low-frequency fluctuations in semiconductor lasers with optical feedback

     Tiana Alsina, Jordi; Torrent Serra, Maria Del Carmen; Rosso, Osvaldo A.; Masoller Alonso, Cristina; Garcia Ojalvo, Jorge
    Physical review A
    Date of publication: 2010
    Journal article

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  • Introduction to the Topical Issue on Laser Dynamics and Nonlinear Photonics

     Masoller Alonso, Cristina; Brener, Igal
    European physical journal D
    Date of publication: 2010-06
    Journal article

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  • Thermal effects and dynamical hysteresis in the turn-on and turn-off of vertical-cavity surface-emitting lasers

     Hong, Yanhua; Masoller Alonso, Cristina; Torre, Maria Susana; Priyadarshi, Sanjay; Qader, Abdulqader A; Spencer, Paul S.; Shore, K. Alan
    Optics letters
    Date of publication: 2010-11-01
    Journal article

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  • Frequency dynamics of semiconductor lasers with atomic absorbers: theory and experiments

     Masoller Alonso, Cristina; Oria, M.
    European physical journal D
    Date of publication: 2010-06
    Journal article

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  • Multi-stability and transient chaotic dynamics in semiconductor lasers with time-delayed optical feedback

     Zamora Munt, Jordi; Masoller Alonso, Cristina; Garcia Ojalvo, Jorge
    Date of publication: 2010
    Book chapter

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    We investigate numerically the chaotic transient dynamics of a semiconductor laser with time-delayed optical feedback. This transient behavior is seen in the low-frequency fluctuations (LFF) regime ocurring when the laser is pumped close to thereshold and is subjected to moderate feedback strengths. We characterize the transient dynamics in terms of its duration, the time intervals between consecutive dropouts, and the total in each transient event. We statistically analyze these quantities as a function of the noise strength and other system parameters related to different nonlinear mechanisms of light-matter interaction inside the laser active medium.

  • Learning about Interating Networks in Climate

     Masoller Alonso, Cristina
    Participation in a competitive project

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  • DINAMICA NOLINEAL Y ESTOCASTICA EN SISTEMAS FISICOS Y BIOFISICOS

     Zamora Munt, Jordi; Masoller Alonso, Cristina; Domedel Puig, Nuria; Torrent Serra, Maria Del Carmen; Espinar Calvo, Maria Lorena; De Sancristobal Alonso, Belen; Pons Rivero, Antonio Javier; Tiana Alsina, Jordi; Rue Queralt, Pau; Dies Miracle, Marta; Garcia Ojalvo, Jorge
    Participation in a competitive project

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  • AJUT ICREA ACADEMIA 2010

     Masoller Alonso, Cristina
    Participation in a competitive project

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  • Dynamical Hysteresis and Thermal Effects in Vertical-Cavity Surface-Emitting Lasers

     Torre, Maria Susana; Masoller Alonso, Cristina
    IEEE journal of quantum electronics
    Date of publication: 2010-11-15
    Journal article

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  • Numerical implementation of a VCSEL-based stochastic logic gate via polarization bistability

     Zamora Munt, Jordi; Masoller Alonso, Cristina
    Optics express
    Date of publication: 2010-08-02
    Journal article

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  • Crowd Synchrony and Quorum Sensing in Delay-Coupled Lasers

     Zamora Munt, Jordi; Masoller Alonso, Cristina; Garcia Ojalvo, Jorge; Roy, Rajarshi
    Physical review letters
    Date of publication: 2010-12-22
    Journal article

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