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

     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.

    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.

    Missatge de l'editor: "This paper was published in Optics express and is made available as an electronic reprint with the permission of OSA. The paper can be found at the following URL on the OSA website: http://www.opticsinfobase.org/oe/fulltext.cfm?uri=oe-22-4-4705&id=279795. Systematic or multiple reproduction or distribution to multiple locations via electronic or other means is prohibited and is subject to penalties under law."

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    Unveiling the complex organization of recurrent patterns in spiking dynamical systems  Open access

     Aragoneses Aguado, Andres; Perrone, Sandro; Sorrentino Amaral, Taciano; Torrent Serra, Maria Del Carmen; Masoller Alonso, Cristina
    Scientific reports
    Date of publication: 2014-04-15
    Journal article

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    Complex systems displaying recurrent spike patterns are ubiquitous in nature. Understanding the organization of these patterns is a challenging task. Here we study experimentally the spiking output of a semiconductor laser with feedback. By using symbolic analysis we unveil a nontrivial organization of patterns, revealing serial spike correlations. The probabilities of the patterns display a well-defined, hierarchical and clustered structure that can be understood in terms of a delayed model. Most importantly, we identify a minimal model, a modified circle map, which displays the same symbolic organization. The validity of this minimal model is confirmed by analyzing the output of the forced laser. Since the circle map describes many dynamical systems, including neurons and cardiac cells, our results suggest that similar correlations and hierarchies of patterns can be found in other systems. Our findings also pave the way for optical neurons that could provide a controllable set up to mimic neuronal activity.

    Complex systems displaying recurrent spike patterns are ubiquitous in nature. Understanding the organization of these patterns is a challenging task. Here we study experimentally the spiking output of a semiconductor laser with feedback. By using symbolic analysis we unveil a nontrivial organization of patterns, revealing serial spike correlations. The probabilities of the patterns display a well-defined, hierarchical and clustered structure that can be understood in terms of a delayed model. Most importantly, we identify a minimal model, a modified circle map, which displays the same symbolic organization. The validity of this minimal model is confirmed by analyzing the output of the forced laser. Since the circle map describes many dynamical systems, including neurons and cardiac cells, our results suggest that similar correlations and hierarchies of patterns can be found in other systems. Our findings also pave the way for optical neurons that could provide a controllable set up to mimic neuronal activity.

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

     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.

    This thesis is focused on the study of stochastic and nonlinear dynamics in optical systems. First, we study experimentally the dynamics of a Brownian nanometer particle in an optical trap subjected to an external forcing. Specifically, we consider the effects of parametric noise added to a monostable or bistable optical trap and discovered a new effect which we named stochastic resonant damping (SRD). SRD concerns the minimization of the output variance position of a particle held in a harmonic trap, when an external parametric noise was added to the position trap. We compared the classical stochastic resonance (SR) with SRD and found that they are two phenomena which coexist in the same system but in different regimes. The experimentally studied monostable system showed a maximum in the signal to noise ratio, a clear signature of a resonance. We also developed a new technique to increase 10-fold the detection range of the quadrant photodiode that we used in this study, which exploits the channel crosstalk. Second, we study the stochastic dynamics of a type of semiconductor laser (SCL), known as vertical-cavity surface-emitting laser (VCSEL), that exhibits polarization bistability and hysteresis, either when the injection current or when the optically injected power are varied. We have shown how these properties can be exploited for logic operations due to the effect of the spontaneous emission noise. Two logical input signals have been encoded in three levels of optically injected power from a master laser, and the logical output response was decoded from the emitted polarization of the injected VCSEL. Correct and robust operation was obtained when the three levels of injected power were adjusted to favor one polarization at two levels and to favor the orthogonal polarization at the third level. We numerically demonstrated that the VCSEL-based logic operator allows to reproduce the truth table for the OR and NOR logic operators, while the extension to AND and NAND is straightforward. With this all-optical configuration we have been able to reduce the minimum bit time required for correct operation from 30 ns, obtained in a previous work with an optoelectronic configuration, to 5 ns. The third focus of this thesis is the study of the chaotic nonlinear dynamics of a SCL optically injected, in the regime where it can display sporadic huge intensities pulses, referred to as Rogue Waves (RWs). We found that, when adding optical noise, the region where RWs appear becomes wider. This behavior is observed for high enough noise; however, on the contrary, for very weak noise we found that noise diminishes the number of RW events in certain regions. In order to suppress or induce extreme pulses, we investigated the effects of an external periodic modulation of the laser current. We found that the modulation at specific frequencies modifies the dynamics from chaotic to periodic. Depending on the parameter region, current modulation can contribute to an increased threshold for RWs. Therefore, we concluded that the modulation can be effective for suppressing the RWs dynamics.

  • Experimental study of feedback-induced dynamics in semiconductor lasers:from symbolic analysis to subwavelength position sensing

     Aragoneses Aguado, Andres
    Defense's date: 2014-06-18
    Department of Physics and Nuclear Engineering, Universitat Politècnica de Catalunya
    Theses

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    El objetivo de esta tesis es el estudio de la dinámica inducida por realimentación óptica en láseres de semiconductor. Dicho estudio persigue, por un lado, profundizar en el conocimiento de aspectos generales de los sistemas complejos, y por otro lado, utilizar dicha dinámica para crear un protocolo para medir desplazamientos en dos dimensiones con una resolución mucho menor que la longitud de onda del láser utilizado. La intensidad de la luz emitida por un láser de semiconductor es estable salvo fluctuaciones debidas al ruido de emisión espontánea. Sin embargo, cuando la luz del láser se refleja en una superficie y parte de esta luz vuelve a entrar en el láser, la intensidad de la luz emitida se puede desestabilizar y mostrar una amplia gama de comportamientos dinámicos. Uno de los regímenes dinámicos presentes en láseres con realimentación óptica es el de fluctuaciones de baja frecuencia (LFF de sus siglas en inglés). Está dinámica se caracteriza por caídas abruptas de la intensidad del láser (hasta casi apagarse), seguidas de recuperaciones graduales, siendo la separación temporal entre dos caídas consecutivas irregular. La primera parte de esta tesis está entrada en este régimen dinámico, habiéndose realizado un detallado estudio experimental para caracterizarlo. Se ha utilizado un análisis simbólico de series de datos basado en patrones ordinales, definidos mediante la comparación de tiempos consecutivos entre caídas. En la dinámica del láser de semiconductor con realimentación intervienen varios factores: la interacción no lineal entre luz y materia en el medio activo del láser, el ruido cuántico debido a la emisión espontánea y la señal retardada de la realimentación. Por ello las caídas en el régimen de LFFs pueden ser inducidas tanto por ruido como por procesos deterministas. En esta tesis, mediante el análisis simbólico se ha conseguido distinguir estadísticamente, qué caídas pueden ser inducidas por ruido y cuales presentan una estadística que muestra señales de determinismo. En esta tesis también se ha estudiado la dinámica simbólica del régimen de LFF y se han encontrado correlaciones entre varias caídas consecutivas. También se ha encontrado una estructura jerárquica en la dinámica simbólica que incluye emparejamientosde las probabilidades de los patrones simbólicos. Además se ha encontrado un modelo simple a tiempo discreto (mapa) que describe adecuadamente la dinámica simbólica del régimes de LFF. Debido a la importancia de forzamientos externos en sistemas dinámicos, se han realizado experimentos incorporando modulación en la corriente de inyección del láser. Estos experimentos han permitido caracterizar el efecto de la amplitud de la modulación en la dinámica simbólica, encontrando cambios claros en la estructura simbólica, inducidos por la modulación, pero que se conservan los emparejamientos observados sin modulación. El modelo simple ha sido verificado ya que reproduce satisfactoriamente la dinámica simbólica encontrada en los datos experimentales. Asimismo, en esta tesis se ha demostrado experimentalmente un protocolo que permite detectar desplazamientos de doegimens objetos independientes en una escala muy inferior a la longitud de onda de la luz empleada (lambda/160). Para ello se ha diseñado un experimento donde el láser esta sometido a realimentación de dos espejos que se mueven de manera independiente. Además de la alta resolución, otra ventaja de este protocolo reside en que únicamente es preciso medir una variable para calcular los dos desplazamientos.

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

     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.

    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.

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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  Open access

     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.

    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.

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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.

  • On the effects of lag-times in networks constructed from similarities of monthly fluctuations of climate fields

     Tirabassi, Giulio; Masoller Alonso, Cristina
    Europhysics letters
    Date of publication: 2013-06
    Journal article

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    he complex network framework has been successfully applied to the analysis of climatological data, providing, for example, a better understanding of the mechanisms underlying reduced predictability during El Niño or La Niña years. Despite the large interest that climate networks have attracted, several issues remain to be investigated. Here we focus on the influence of the periodic solar forcing in climate networks constructed via similarities of monthly averaged Surface Air Temperature (SAT) anomalies. We shift the time series in each pair of nodes such as to superpose their seasonal cycles. In this way, when two nodes are located in different hemispheres we are able to quantify the similarity of SAT anomalies during the winters and during the summers. We find that data time-shifting does not significantly modify the network Area Weighted Connectivity (AWC), which is the fraction of the total area of the Earth to which each node is connected. This unexpected network property can be understood in terms of how data time-shifting modifies the strength of the links connecting geographical regions in different hemispheres, and how these modifications are washed out by averaging the AWC

  • 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.

  • Inferring interdependencies in climate networks constructed at inter-annual, intra-season and longer time scales

     Deza, Juan Ignacio; Masoller Alonso, Cristina; Barreiro, Marcelo
    European physical journal. Special topics
    Date of publication: 2013-06
    Journal article

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    We study global climate networks constructed by means of ordinal time series analysis. Climate interdependencies among the nodes are quantified by the mutual information, computed from time series of monthly-averaged surface air temperature anomalies, and from their symbolic ordinal representation (OP). This analysis allows identifying topological changes in the network when varying the time-interval of the ordinal pattern. We consider intra-season time-intervals (e.g., the patterns are formed by anomalies in consecutive months) and inter-annual time-intervals (e.g., the patterns are formed by anomalies in consecutive years). We discuss how the network density and topology change with these time scales, and provide evidence of correlations between geographically distant regions that occur at specific time scales. In particular, we find that an increase in the ordinal pattern spacing (i.e., an increase in the timescale of the ordinal analysis), results in climate networks with increased connectivity on the equatorial Pacific area. On the contrary, the number of significant links decreases when the ordinal analysis is done with a shorter timescale (by comparing consecutive months), and interpret this effect as due to more stochasticity in the time-series in the short timescale. As the equatorial Pacific is known to be dominated by El Niño-Southern Oscillation (ENSO) on scales longer than several months, our methodology allows constructing climate networks where the effect of ENSO goes from mild (monthly OP) to intense (yearly OP), independently of the length of the ordinal pattern and of the thresholding method employed.

  • 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.

  • 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
    Participation in a competitive project

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  • Distinguishing signatures of determinism and stochasticity in spiking complex systems

     Masoller Alonso, Cristina
    Dynamics Days Europe
    Presentation's date: 2013-06
    Presentation of work at congresses

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  • 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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  • 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.

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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.

  • NEURAL ENGINEERING TRANSFORMATIVE TECHNOLOGIES

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

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  • Nonlinear time-series analysis of low-frequency fluctuations in semiconductor lasers with optical feedback

     Aragoneses Aguado, Andres; Rubido, Nicolás; Sorrentino, T.; Tiana Alsina, Jordi; Torrent Serra, Maria Del Carmen; Masoller Alonso, Cristina
    European Optical Society Annual Meeting
    Presentation's date: 2012-09-25
    Presentation of work at congresses

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  • Detecting long-range teleconnections in the climate network via ordinal pattern time-series analysis

     Deza, Juan Ignacio; Barreiro, Marcelo; Masoller Alonso, Cristina
    Annual meeting of the German physics association
    Presentation's date: 2012-03-28
    Presentation of work at congresses

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  • Inferring Interdependencies in Climate Networks Constructed at Inter-Annual, Intra-Season and Longer Time Scales

     Deza, Juan Ignacio; Barreiro, Marcelo; Masoller Alonso, Cristina
    International Symposium on Nonlinear Theory and its Applications
    Presentation's date: 2012-10-23
    Presentation of work at congresses

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  • Ordinal time-series analysis of low-frequency fluctuations in semiconductor lasers with optical feedback

     Aragoneses Aguado, Andres; Rubido, Nicolás; Sorrentino, T.; Tiana Alsina, Jordi; Torrent Serra, Maria Del Carmen; Masoller Alonso, Cristina
    Congreso de Física Estadística
    Presentation's date: 2012-10-18
    Presentation of work at congresses

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  • Experimental study of the spiking activity of semiconductor lasers with time-delayed optical feedback

     Aragoneses Aguado, Andres; Rubido, Nicolás; Sorrentino, T.; Tiana Alsina, Jordi; Torrent Serra, Maria Del Carmen; Masoller Alonso, Cristina
    International Symposium on Nonlinear Theory and its Applications
    Presentation's date: 2012-10-25
    Presentation of work at congresses

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

     Masoller Alonso, Cristina
    International Workshop Nonlinear Dynamics in Semiconductor Lasers
    Presentation's date: 2012-09-14
    Presentation of work at congresses

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  • Exploiting the interplay of bistability, time delay and noise to obtain robust all-optical switching

     Masoller Alonso, Cristina
    International Conference on Delayed Complex Systems
    Presentation's date: 2012-06-12
    Presentation of work at congresses

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  • Climate network analysis based on statistics of ordinal patterns and symbolic dynamics

     Masoller Alonso, Cristina; Barreiro, Marcelo; Marti, Arturo C.
    Experimental Chaos and Complexity Conference
    Presentation's date: 2012-05-12
    Presentation of work at congresses

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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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    Postprint (author’s final draft)

  • Detecting long-range tele-connections in the climate network via ordinal pattern analysis

     Deza, Juan Ignacio; Barreiro, Marcelo; Masoller Alonso, Cristina
    European Geosciences Union General Assembly
    Presentation's date: 2012-04-25
    Presentation of work at congresses

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  • Climate networks at inter-annual and intra-season time scales constructed via ordinal time-series analysis

     Deza, Juan Ignacio; Barreiro, Marcelo; Masoller Alonso, Cristina
    Congreso No Lineal
    Presentation's date: 2012-06-04
    Presentation of work at congresses

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  • Premi ICREA Acadèmia

     Masoller Alonso, Cristina; Garcia Ojalvo, Jorge; Llorca Pique, Jordi
    Award or recognition

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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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  • 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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  • 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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  • 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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    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.

  • 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.

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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.

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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.

  • 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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  • 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
    Participation in a competitive project

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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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  • Crowd synchrony and quorum sensing transition in star-coupled non-identical semiconductor lasers with time delay

     Masoller Alonso, Cristina; Zamora Munt, Jordi; Garcia Ojalvo, Jorge; Roy, Rajarshi
    Congreso de Física Estadística
    Presentation's date: 2011-06-03
    Presentation of work at congresses

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  • Experimental study of different LFF regimes in semiconductor lasers with an external cavity

     Aragoneses Aguado, Andres; Zamora Munt, Jordi; Tiana Alsina, Jordi; Torrent Serra, Maria Del Carmen; Masoller Alonso, Cristina
    Congreso de Física Estadística
    Presentation's date: 2011-06-03
    Presentation of work at congresses

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  • Polarization square-wave switching in orthogonally delay-coupled semiconductor lasers

     Masoller Alonso, Cristina; Sciamanna, Marc; Gavrielides, Athanasios Tom
    European Nonlinear Dynamics Conference
    Presentation's date: 2011-07-24
    Presentation of work at congresses

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