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  • 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.

  • Beam focusing in reflection from flat chirped mirrors

     Cheng, Yu Chieh; Peckus, Martynas; Kicas, S.; Trull, Jose; Cojocaru, Crina Maria; Vilaseca Alavedra, Ramon; Drazdys, R.; Staliunas, Kestutis
    Physical review A
    Date of publication: 2013-04-15
    Journal article

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    We propose and show by proof-of-principle calculations and experiments that beam focusing and imaging can be obtained in reflection from a flat interface of a micromodulated dielectric structure. We show, in particular, that a one-dimensionally modulated and chirped structure can focus a beam, performing an imaging of a light pattern, i.e., can act as a transversely invariant flat focusing mirror. 2013 American Physical Society.

  • Near field focusing of beams reflected by flat mirror

     Cheng, Yu Chieh; Kicas, S.; Peckus, Martynas; Trull, Jose; Cojocaru, Crina Maria; Drazdys, R.; Vilaseca Alavedra, Ramon; Staliunas, Kestutis
    Conference on Lasers and Electro-Optics Europe and International Quantum Electronics Conference
    Presentation's date: 2013-05-13
    Presentation of work at congresses

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    We predict generally that narrow beams can focus in reflection from the flat interface photonic structures, and we demonstrate the effect experimentally in particular realization,i.e. in reflection from one-dimensional chirped mirror with flat surface.

  • Self-collimation and spatial filtering in 2D gain/loss periodic spatially modulated materials

     Botey Cumella, Muriel; Staliunas, Kestutis; Herrero Simon, Ramon; Vilaseca Alavedra, Ramon; Pradeep Kumar, Nikhil
    European Conference on Lasers and Electro-Optics - International Quantum Electronics Conference
    Presentation's date: 2012-05-24
    Presentation of work at congresses

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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.

  • Dinámica de circuitos de regulación genética en bacterias  Open access

     Espinar Calvo, Maria Lorena
    Defense's date: 2012-12-21
    Department of Applied Physics, Universitat Politècnica de Catalunya
    Theses

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    El objetivo de esta Tesis es el estudio de diferentes comportamientos celulares dinámicos en Escherichia coli y Bacillus subtilis. Es interesante comprender cómo estos organismos sencillos poseen mecanismos complejos para responder al entorno en el que se encuentran. Dicha respuesta está regulada por complicadas redes de regulación formadas por genes y proteínas, donde al igual que los instrumentistas de una orquesta, cada elemento de las redes genéticas debe tomar parte en armonía, en el momento justo y la cantidad adecuada para dar lugar a la respuesta celular apropiada. La Parte I introduce aspectos básicos de la metodología utilizada y conceptos fundamentales para la comprensión de los resultados. El Capítulo 1 es una breve introducción a los circuitos de regulación genética y el uso de proteínas fluorescentes para el estudio in vivo y en células individuales de la dinámica de dichos circuitos. El Capítulo 2 describe los materiales y técnicas utilizadas, desde el cultivo y obtención de cepas bacterianas, los métodos para filmar dichas cepas con microscopía de fluorescencia temporalizada, al análisis de las imágenes. El Capítulo 3 describe las características básicas de los procesos biológicos de estudio. El Capítulo 4 describe ciertos aspectos de la dinámica celular como el comportamiento oscilatorio o excitable de algunos sistemas biológicos, y las herramientas matemáticas usadas para contrastar los datos experimentales. La Parte II corresponde a los resultados. El Capítulo 5 describe los resultados del estudio del control del inicio de la replicación cromosómica en E. coli. Mediante una serie de perturbaciones en las proteínas que regulan este proceso, y mediante el análisis de las imágenes obtenidas por microscopía, se cuantificó el efecto ejercido sobre el inicio de replicación, comparando los resultados con una cepa control. El Capítulo 6 describe los resultados del estudio de la forma en que el circuito genético que regula la competencia en B. subtilis integra múltiples señales simultáneas. Se caracterizó experimentalmente y con un análisis de bifurcación del modelo matemático del circuito, la respuesta en células individuales e in vivo a señales químicas de diferente intensidad que controlan la expresión constitutiva de los genes que forman el circuito, y a la variación del número de copias de uno de estos genes. El Capítulo 7 describe los resultados del estudio del proceso de toma de decisión celular en B. subtilis, basado en la decisión de estas bacterias por optar entre los programas de diferenciación en competencia genética y esporulación, los cuales compiten entre sí en el tiempo. El análisis simultáneo y en células individuales de ambos programas permitió descubrir por qué las bacterias optan por uno u otro mediante un mecanismo de carrera molecular entre estos dos programas en competición. El Capítulo 8 describe los resultados del estudio de la adaptación celular al estrés mediante esporulación y la toma de decisión de una forma robusta en B. subtilis. Se analizó de forma cuantitativa la expresión de los genes implicados en la progresión hacia la formación de esporas y se desarrolló un modelo matemático poblacional para estudiar el efecto de la reversibilidad en el proceso de adaptación celular a cambios en los niveles de estrés. La Parte III corresponde a las Conclusiones y la perspectiva futura para los resultados descritos en la Parte II. Los resultados obtenidos contribuyen a la comprensión de determinados comportamientos en E. coli y B. subtilis. Estas bacterias, sencillas si se comparan con organismos superiores, ofrecen la posibilidad de estudiar mecanismos utilizados por sistemas más complejos, pero que para su estudio se requieren técnicas complicadas. El estudio en células individuales de la dinámica de redes de regulación mediante las técnicas utilizadas nos permite el análisis in vivo y en tiempo real de lo que sucede con dichas redes en el interior de las células respecto al exterior celular.

    The aim of this Thesis is the study of different dynamic cellular behaviors in Escherichia coli and Bacillus subtilis. It is interesting to understand how these simple organisms have not so simple mechanisms to respond to their environment. This response is regulated by complex regulatory networks consisting of genes and proteins, where as instrumentalists in an orchestra, each element of the network should operates in harmony, at the right time and the right amount to give an appropriate cellular response. Part I introduces basic aspects of the methodology and concepts for the understanding of the results presented in this Thesis. Chapter 1 provides a brief introduction to genetic regulatory circuits and the fluorescent proteins used for the study of the dynamics of such circuits in vivo and in individual cells. Chapter 2 describes the materials and techniques used, from growing and obtaining bacterial strains, to the methodology used for filming these strains by temporalized fluorescence microscopy, and to the analysis of the obtained images. Chapter 3 describes the main features of the dynamical biological processes studied in E. coli and B. subtilis. Chapter 4 refers to certain aspects of cellular dynamics such as oscillatory or excitable behavior of some biological systems, as well as the mathematical tools used to compare the data obtained experimentally. Part II corresponds to the results. Chapter 5 describes the results of the study of the control of chromosome replication initiation in E. coli. We implemented a set of perturbations in the main proteins that regulate this process, and their effect on the initiation of replication, quantified by analyzing the images obtained by fluorescence microscopy, comparing the results with a control strain. Chapter 6 describes the results obtained from the study of how a genetic circuit in B. subtilis, namely the one regulating competence, integrates multiple simultaneous inputs. We characterized experimentally the response of individual cells in vivo to different chemical signals that control the strength of the constitutive expression of genes forming the circuit, in addition to the copy number variation of one of these genes. The results were compared with a bifurcation analysis of the mathematical model of the circuit. Chapter 7 describes the results obtained in a study of the decision making process of microorganism B. subtilis. Specifically, we studied the decision of these bacteria between two differentiation programs such as genetic competence and sporulation, which compete with each other in time. The simultaneous analysis in individual cells of both programs allowed us to uncover the way in which bacteria choose between these two competing programs, showing that the competition occurs through a molecular race. Finally, Chapter 8 describes the results obtained in the study of reversible progression towards an all-or-none switch in the sporulation of B. subtilis. We quantitatively analyzed the expression of genes involved in the progression towards spore formation and a population model was developed to study the effect of reversibility in the process of cellular adaptation to changes in stress levels. Part III details the conclusions and a description of the possible future perspectives for each of the results described in Part II. The results obtained contribute to the understanding of certain dynamic behaviors in the microorganisms E. coli and B. subtilis. These bacteria, although simple when compared with higher organisms, offer the possibility of studying mechanisms that are frequently utilized by more complex systems, which require more sophisticated analysis techniques. The study at the single cell level of network dynamics of gene regulation by the techniques used in this Thesis, allows the analysis in vivo and in real time of the underlying dynamic of such networks inside cells in response to the cell environment.

  • CONTROL DE LA DIFRACCON DE LA LUZ EN MEDIOS MODULADOS

     Font Garcia, Josep Lluís; Vilaseca Alavedra, Ramon; Cojocaru, Crina Maria; Trull, Jose; Staliunas, Kestutis
    Participation in a competitive project

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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.

    Postprint (author’s final draft)

  • Efficient generation of the second harmonic inhomogeneous component in opaque cavities

     Cojocaru, Crina Maria; Roppo, Vito; Raineri, F.; Trull, Jose; Chouteau, David; Sagnes, I.; Raj, R; Vilaseca Alavedra, Ramon; Scalora, M.
    International Conference on Transparent Optical Networks
    Presentation's date: 2011-06
    Presentation of work at congresses

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  • Nonlinear frequency conversion under general phase mismatched condition: the role of phase locking and random nonlinear domains  Open access  awarded activity

     Roppo, Vito
    Defense's date: 2011-06-15
    Department of Applied Physics, Universitat Politècnica de Catalunya
    Theses

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    In the field of second harmonic (SH) generation most studies have been concerned with maximizing conversion efficiencies, generally achievable at the phase matching (PM) condition. Outside of the PM the conversion efficiency drastically decreases. This has caused that the possible working conditions out of PM to remain largely unexplored. In this thesis work we initiated a systematic study of the SH behavior in under conditions of large phase mismatch. When a pump pulse crosses an interface between a linear and a nonlinear medium there are always two generated SH components. These components may be understood on the basis of the mathematical solution of the inhomogeneous wave equations at the SH frequency. The homogeneous (HOM) solution is a component with wave-vector k(2¿) as expected from the dispersion relation and exchanges energy with the pump until the inevitable walk-off. The inhomogeneous (INH) solution is a component with a wave-vector 2k(¿), twice the pump wave-vector, and travels locked to the pump pulse. We divide our work in two parts, one for each generated component. Inhomogeneous component. We start a systematic study of the behavior of the generated INH component, phase locked to the pump. The consequences of phase locking (PL) can guide us towards new scenarios by allowing working conditions hitherto assumed inaccessible for absorbing materials. We show that while the HOM component travels with the group velocity given by material dispersion, the IHN component is captured by the pump pulse and experiences the same effective dispersion of the pump. It does not follow the PM condition. It naturally follows that the suppression of absorption at the SH wavelengths will occur if the pump is tuned to a region of transparency. We extended the same theory for the generated third harmonic (TH). We then studied the surprising behavior of SH and TH INH components with frequencies above the absorption edge when the material is placed inside a cavity resonant only at the fundamental frequency. We have shown that the PL mechanism not only inhibits absorption but also fosters the enhancement of harmonic generation by several orders of magnitude compared to the no-cavity case. Finally, we tested the INH SH and TH behaviors in metallic frequency regime of material. Homogeneous component. The techniques used to PM the nonlinear interaction enable efficient nonlinear interactions but drastically limit the spectral bandwidth of the nonlinear optical process, making the designed frequency converter only suitable for a fixed input wavelength and single interaction only. It has been shown that the use of disordered nonlinear media relaxes the PM condition thus allowing one to achieve relatively efficient broad bandwidth regime of the frequency conversion. An example of a quadratic nonlinear medium with a disordered domain structure is an un-poled Strontium Barium Niobate (SBN) crystal. It is composed of a system of random size anti parallel ferroelectric domains that allow to phase-match any second-order parametric process over a broad range of wavelengths without any poling. We have initiated an experimental and theoretical investigation of the properties of the SH waves generated in SBN crystals, with an extension to the generated TH. This study covers the coherence and polarization properties of the generated signal, as well as its spatial distribution. In addition, we have made an experimental study of the noncollinear interaction of short optical pulses in a SBN crystal by using two fundamental waves intersecting inside the crystal. We have shown that this effect may be employed as a simple tool for monitoring both the pulse duration and initial chirp. This method offers a simple and economic alternative to the existing methods for pulse characterization.

  • 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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  • Second harmonic generation in sub-diffractive two-dimensional photonic crystals

     Nistor, Ioan Cristian
    Defense's date: 2011-01-26
    Department of Applied Physics, Universitat Politècnica de Catalunya
    Theses

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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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    Enhanced efficiency of the second harmonic inhomogeneous component in an opaque cavity  Open access

     Roppo, Vito; Raineri, F.; Raj, R; Sagnes, I.; Trull, Jose; Vilaseca Alavedra, Ramon; Scalora, M.; Cojocaru, Crina Maria
    Optics letters
    Date of publication: 2011-05-15
    Journal article

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    In this Letter, we experimentally demonstrate the enhancement of the inhomogeneous second harmonic conversion in the opaque region of a GaAs cavity with efficiencies of the order of 0.1% at 612nm, using 3 ps pump pulses having peak intensities of the order of 10MW=cm2. We show that the conversion efficiency of the inhomogeneous, phase-locked second harmonic component is a quadratic function of the cavity factor Q.

  • Broadband third harmonic generation in quadratic media with disordered ferroelectric domains

     Kalinowski, K.; Roppo, Vito; Wang, W.; Neshev, Dragomir N.; Kong, Y.; Cojocaru, Crina Maria; Trull, Jose; Vilaseca Alavedra, Ramon; Staliunas, Kestutis; Krolikowski, W.; Kivshar, Yu.
    Nonlinear Photonics
    Presentation's date: 2010-06-21
    Presentation of work at congresses

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  • Second and third harmonic generation in disordered quadratic nonlinear media: application to short-pulse characterization

     Roppo, Vito; Wang, W.; Kalinowski, K.; Vilaseca Alavedra, Ramon; Trull, Jose; Cojocaru, Crina Maria; Staliunas, Kestutis; Krolikowski, W.; Kivshar, Yu.
    International Conference on Transparent Optical Networks
    Presentation's date: 2010-06-27
    Presentation of work at congresses

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  • Generation efficiency of the second harmonic inhomogeneous component

     Roppo, Vito; Cojocaru, Crina Maria; Trull, Jose; Raineri, F.; Chouteau, David; Sagnes, I.; Raj, R; Vilaseca Alavedra, Ramon; Scalora, M.
    European Optical Society Annual Meeting
    Presentation's date: 2010-10-26
    Presentation of work at congresses

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  • Second-harmonic generation in disordered quadratic media: role of a ferroelectric domain structure

     Roppo, Vito; Kalinowski, K.; Wang, W.; Cojocaru, Crina Maria; Trull, Jose; Vilaseca Alavedra, Ramon; Scalora, M.; Krolikowski, W.; Kivshar, Yu.
    International Conference on Transparent Optical Networks
    Presentation's date: 2010-06-27
    Presentation of work at congresses

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  • Second-harmonic generation in disordered quadratic media: role of a ferroelectric domain structure

     Roppo, Vito; Kalinowski, K.; Wang, W.; Cojocaru, Crina Maria; Trull, Jose; Vilaseca Alavedra, Ramon; Scalora, M.; Krolikowski, W.; Kivshar, Yu.
    Nonlinear Photonics
    Presentation's date: 2010-06-21
    Presentation of work at congresses

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  • The role of ferroelectric domain structure in second harmonic generation in random quadratic media

     Roppo, Vito; Wang, W.; Kalinowski, K.; Kong, Y.; Cojocaru, Crina Maria; Trull, Jose; Vilaseca Alavedra, Ramon; Scalora, M.; Krolikowski, W.; Kivshar, Yu.
    Optics express
    Date of publication: 2010
    Journal article

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  • Cavity behavior of second and third harmonic inhomogeneous solutions of Maxwell¿s equations

     Roppo, Vito; Cojocaru, Crina Maria; Trull, Jose; Vilaseca Alavedra, Ramon; Scalora, M.
    Waves in random and complex media
    Date of publication: 2010
    Journal article

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    We study second and third harmonic generation of ultrashort pulses in a cavity environment and focus on the role of a phase locking phenomenon that causes the pump to trap and drag the generated harmonic fields. The results reveal strong field localisation and resonance conditions for the phase locked components, which are tuned in a spectral region of huge nominal material absorption. This unique behavior suggests the possibility of new optical phenomena and new applications for opaque materials (i.e. semiconductors) in the visible and UV ranges, such as new laser sources with relatively high conversion efficiencies.

  • Phase locked second and third harmonic localization in semiconductor cavities

     Roppo, Vito; Cojocaru, Crina Maria; D'Aguanno, G.; Raineri, F.; Trull, Jose; Halioua, Y.; Vilaseca Alavedra, Ramon; Raj, R; Scalora, M.
    Journal of optoelectronics and advanced materials
    Date of publication: 2010-01
    Journal article

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  • El láser, fuente de fenómenos y dinámicas no lineales

     Vilaseca Alavedra, Ramon
    Revista española de física
    Date of publication: 2010-10-01
    Journal article

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  • Second- and third-harmonic parametric scattering in disordered quadratic media

     Wang, W.; Kalinowski, K.; Roppo, Vito; Sheng, Yan; Koynov, Kaloian; Kong, Y.; Cojocaru, Crina Maria; Trull, Jose; Vilaseca Alavedra, Ramon; Krolikowski, W.
    Journal of physics B. Atomic molecular and optical physics
    Date of publication: 2010
    Journal article

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  • Subdiffraction and spatial filtering due to periodic spatial modulation of the gain-loss profile

     Staliunas, Kestutis; Herrero Simon, Ramon; Vilaseca Alavedra, Ramon
    Physical review A
    Date of publication: 2009-07
    Journal article

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  • Doppler-free adiabatic self-induced transparency

     Loiko, Yury; Serrat, C; Vilaseca Alavedra, Ramon; Ahufinger, V; Mompart, J; Corbalan, R
    Physical review A
    Date of publication: 2009-05
    Journal article

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  • Characterization of femtosecond pulses via transverse second-harmonic generation in random nonlinear media

     Trull, Jose; Saltiel, S; Roppo, Vito; Cojocaru, Crina Maria; Dumay, D; Krolikowski, W; Neshev, Dn; Vilaseca Alavedra, Ramon; Staliunas, Kestutis; Kivshar, Ys
    Applied physics B. Lasers and optics
    Date of publication: 2009-06
    Journal article

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  • Modeling a semiconductor laser with an intracavity atomic absorber

     Masoller Alonso, Cristina; Oria, M; Vilaseca Alavedra, Ramon
    Physical review A
    Date of publication: 2009-07
    Journal article

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  • Processos multifotònics en feixos atòmics de 39K

     Fernandez Soler, Juanjo
    Defense's date: 2009-06-11
    Department of Physics and Nuclear Engineering, Universitat Politècnica de Catalunya
    Theses

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  • Femtosecond pulse duration measurement by transverse second harmonic generation in random nonlinear media

     Vilaseca Alavedra, Ramon; Roppo, Vito; Trull, Jose; Cojocaru, Crina Maria; Staliunas, Kestutis; Dumay, David; Krolikowski, W.; Saltiel, Salomon M.; Neshev, Dragomir N.; Kivshar, Yu.
    Nonlinear Optics: Materials, Fundamentals and Applications
    Presentation's date: 2009-07-12
    Presentation of work at congresses

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  • The role of the phase locking phenomenon in the second and third harmonics cavity localization

     Roppo, Vito; Cojocaru, Crina Maria; D'Agunaro, G.; Ranieri, F.; Raj, R.; Trull, Jose; Vilaseca Alavedra, Ramon; Scalora, M.
    OSA Annual Meeting
    Presentation's date: 2009-10-11
    Presentation of work at congresses

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  • Phase locked second harmonic etalon localization

     Roppo, Vito; D'Aguanno, G.; Cojocaru, Crina Maria; Raineri, F.; Trull, Jose; Vilaseca Alavedra, Ramon; Raj, R; Scalora, M.
    European Conference on Lasers and Electro-Optics / European Quantum Electronics Conference
    Presentation's date: 2009-06-14
    Presentation of work at congresses

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  • The effect of domain distribution on second harmonic generation in disordered nonlinear media

     Roppo, Vito; Saltiel, Salomon M.; Wang, W.; Kalinowski, K.; Trull, Jose; Cojocaru, Crina Maria; Neshev, Dragomir N.; Krolikowski, W.; Vilaseca Alavedra, Ramon; Staliunas, Kestutis; Kivshar, Yu.
    OSA Annual Meeting
    Presentation's date: 2009-10-11
    Presentation of work at congresses

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  • Third-harmonic generation via broadband cascading in disordered quadratic nonlinear media

     Wang, W.; Roppo, Vito; Kalinowski, K.; Kong, Y.; Neshev, Dn; Cojocaru, Crina Maria; Trull, Jose; Vilaseca Alavedra, Ramon; Staliunas, Kestutis; Krolikowski, W; Saltiel, S M; Kivshar, Y
    Optics express
    Date of publication: 2009
    Journal article

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  • Field localization and enhancement of phase-locked second- and third-order harmonic generation in absorbing semiconductor cavities

     Roppo, Vito; Cojocaru, Crina Maria; Raineri, F; D'Aguanno, G.; Trull, Jose; Halioua, Y.; Sagnes, I.; Vilaseca Alavedra, Ramon; Scalora, M.
    Physical review. A, general physics
    Date of publication: 2009-10
    Journal article

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  • Propagació i generació de llum en nanoestructures fotòniques  Open access

     Botey Cumella, Muriel
    Defense's date: 2009-07-24
    Department of Physics and Nuclear Engineering, Universitat Politècnica de Catalunya
    Theses

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    Els materials nanoestructats periòdics han ofert, en les dues darreres dècades, un nou marc per a l'estudi de la interacció entre la radiació electromagnètica i la matèria. Aquestes estructures permeten modelar les propietats electromagnètiques dels materials i han esdevingut una eina idònia per confinar, guiar, suprimir, localitzar, dividir, dispersar, i filtrar la llum. L'abast del control de radiació electromagnètica va des de la propagació fins a la generació de la llum. Els cristalls fotònics han demostrat ser eficients per suprimir o afavorir mecanismes de generació de llum com l'emissió espontània o els processos no lineals.L'eix central d'aquesta tesi se centra en investigar els efectes fintis i fins a quin punt les propietats d'estructures ideals infinites o infinitament periòdiques es mantenen per a estructures que tenen un caràcter finit. Fins fa poc, els desenvolupaments tant experimentals com teòrics en el camp de cristalls fotònics es basaven, principalment, en càlculs que consideraven estructures ideals amb condicions de contorn perfectament periòdiques. Des dels inicis del camp, però, es van observar desajustos a les prediccions fetes amb aquestes condicions. Tanmateix, alguns d'ells resten, en gran part, inexplicats. En aquest el treball, tractem alguns d'aquests aspectes relacionats amb la propagació i generació del llum en cristalls fotònics finits reals, és a dir, com els que es fabriquen. Amb aquest propòsit, en realitzem un estudi tant teòric com experimental. Estudiem els efectes fintis tant en la regió de la primera banda de reflexió de Bragg com en el rang d'energies altes, on la longitud d'ona de la llum és de l'ordre o més petita que el paràmetre de xarxa.En concret, part del treball es dedica a l'estudi dels cristalls col·loïdals en el rang d'energies baixes. Desenvolupem un model vectorial 3D en l'aproximació de Rayleigh-Gans per simular estructures amb contrasts d'índexs baixos. Aquest model contempla aspectes rellevants dels cristalls reals com són ara les condicions de contorn, inclou una lleugera dispersió en el diàmetre de les esferes com també una absorció eficaç que descriu la difusió de Rayleigh i la dispersió inelàstica causada per la presència d'imperfeccions. Aquest model s'utilitza per estudiar la propagació dins de nanoestructures fotòniques reals, i per determinar-ne les propietats dispersives. Les prediccions del model es contrasten amb mesures experimentals dependents de la polarització de l'estructura de bandes parcial d'un cristall col·loïdal real. També determinem el temps de confinament del fotons, a l'extrem de la primera banda fotònica prohibida, per mitjà de la deformació d'un pols provocada per canvis en la velocitat de grup que acompanya l'atrapament dels fotons.Per explicar la propagació de llum en el rang d'energies altes, utilitzem el model vectorial KKR que ens permet determinar la velocitat de grup d'òpals artificials prims. Trobem que, per determinades freqüències, la velocitat de grup pot ser superlumínica, positiva, negativa o tendir a zero depenent del guix del cristall i la seva absorció. Aquest comportament es pot atribuir al carácter finit de l'estructura i explica observacions experimentals presents a la literatura. La mateixa propagació amb velocitats de grup anòmales pot explicar l'observació experimental de l'augment de la generació de segon harmònic en un òpal prim no lineal. Confirmant així que la disminució de velocitat de grup proporciona un mecanisme que afavoreix els processos no lineals.En darrer lloc, considerem una altra configuració en què la interacció no lineal quadràtica té lloc en una capa de menys d'una longitud d'ona de gruix. Demostrem que, en presència d'una superfície reflectora, la contribució de termes que no conserven el moment lineal de la llum, i que no tindrien cap contribució en un medi infinitament llarg, són els més determinants.

    Photonic periodic nanostructures have offered, in the last two decades, a new framework for the study of the interaction between electromagnetic radiation and matter. Such structures can engineer the electromagnetic properties of materials and have become a powerful tool used to confine, route, suppress, localize, split, disperse, and filter light. The scope of the electromagnetic radiation control can be extended to light propagation and generation. Photonic crystals have successfully been used as host materials to suppress or enhance light generation mechanisms such as spontaneous emission or nonlinear processes.The aim of this thesis is to investigate finite-size effects and to what extent the properties of ideal infinite or infinitely periodic structures hold for structures that are finite in size. Until recently, experimental as well as theoretical developments in the field of photonic crystals have been based, mostly, on calculations that consider ideal structures with perfectly periodic boundary conditions.Deviations from the behavior predicted form such assumptions were already observed when the field was born. However, some of them remained, for the most part, unexplained. In the present work, we tackle some of these aspects related to light propagation and generation in the real finite photonic crystals that can be fabricated. With this purpose, we perform such study from, both, an experimental as well as a theoretical perspective. We study finite-size effects in the region of the first order Bragg reflection band as well as in the high energy range where the wavelength of light is on the order or smaller than the lattice parameter.To be more specific, part of the work is devoted to the study of colloidal crystals at the range of low energy. We develop 3D full wave vector calculation in the Rayleigh-Gans approximation to simulate low index contrast structures. This model accounts for relevant real crystal's aspects such as boundary conditions, a slight dispersion in the spheres diameter and includes an effective absorption accounting for Rayleigh scattering and inelastic diffusion due to imperfections. This model is used to study light propagation within real photonic nanostructures, and to determine their dispersive properties. The predictions of the model are contrasted with experimental polarization dependent measurements of the partial band structure of an actual colloidal crystal. We also determine the experimental photon's lifetime, at the edge of the first order pseudogap, by means of the pulse reshaping induced by changes in the group velocity accompanied by the photon trapping.To explain light propagation in the high energy range, we use a vector KKR calculation that we apply to understand the group velocity of light propagating in artificial opals slabs. We show that for certain frequencies, the group velocity can either be superluminal, positive or negative or approach zero depending on the crystal size and absorption. Such behavior can be attributed to the finite character of the structure and accounts for previously reported experimental observations. The same propagation at anomalous group velocity may explain the experimental observation of second harmonic generation enhancement of light from a nonlinear opal film. Indeed, the group velocity slowing-down provides an enhancement mechanism for nonlinear processes.We finally consider another configuration such that the quadratic nonlinear interaction occurs within a sub-wavelength layer. In the presence of a nearby reflecting surface we demonstrate that the contribution of terms that do not conserve light momentum, and that would vanish in an infinitely long medium, is the most relevant one.

  • Remote ion traps for quantum networking: two-photon interference and correlations

     Rohde, Felix
    Defense's date: 2009-10-02
    Department of Physics and Nuclear Engineering, Universitat Politècnica de Catalunya
    Theses

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  • ONDAS DE LUZ EN MEDIOS LINIALES Y NOLIANIALES MODULADOS EN EL ESPACIO

     Vilaseca Alavedra, Ramon; Font Garcia, Josep Lluís; Cojocaru, Crina Maria; Trull, Jose; Staliunas, Kestutis
    Participation in a competitive project

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  • PROPIETATS DINÀMIQUES I NO LINIALS DE MATERIALS I SITEMES FOTÒNICS, ELÈCTRICS I BIOLÒGICS

     Belana Punseti, Juan; Nistor, Ioan Cristian; Masoller Alonso, Cristina; Domedel Puig, Nuria; Diego Vives, Jose Antonio; Cañadas Lorenzo, Juan Carlos; Mudarra Lopez, Miguel; Òrrit Prat, Jordi; Aragoneses Aguado, Andres; Trull, Jose; Staliunas, Kestutis; Herrero Simon, Ramon; Torrent Serra, Maria Del Carmen; Vilaseca Alavedra, Ramon; Font Garcia, Josep Lluís; Cojocaru, Crina Maria; Espinar Calvo, Maria Lorena; De Sancristobal Alonso, Belen; Pons Rivero, Antonio Javier; Sellarès González, Jordi; Tiana Alsina, Jordi; Zamora Munt, Jordi; Roppo, Vito; Garcia Ojalvo, Jorge
    Participation in a competitive project

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  • Access to the full text
    Gain/loss periodic spatial modulated materials on a wavelength scale  Open access

     Staliunas, Kestutis; Herrero Simon, Ramon; Vilaseca Alavedra, Ramon
    International Conference on Transparent Optical Networks
    Presentation's date: 2009-01-01
    Presentation of work at congresses

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    We predict self-collimation and superdiffusion of light propagating in materials with periodically modulated gain/loss profile. The modulation is parallel and transverse to the light propagation direction and its periodicity is on the wavelength scale. The self-collimation (or diffraction-free propagation) of the beams is found, which is similar to that observed in photonic crystals. The superdiffusion is also predicted, which means a dependence of the beam amplification on the propagation direction, which results in the spatial frequency filtering of the beams. We justify the predictions by the numerical simulations of the paraxial wave propagation equations.

  • Phase Locked Harmonics Etalon Localization in Opaque Materials

     Cojocaru, Crina Maria; Roppo, Vito; D'Aguanno, G.; Raineri, F.; Trull, Jose; Raj, R; Vilaseca Alavedra, Ramon; Scalora, M.
    International Conference on Transparent Optical Networks
    Presentation's date: 2009
    Presentation of work at congresses

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  • Phase locked harmonic localization and enhancement in an absorbing semiconductor cavity

     Roppo, Vito; Cojocaru, Crina Maria; D'Aguanno, G.; Raineri, F.; Trull, Jose; Halioua, Y.; Vilaseca Alavedra, Ramon; Raj, R; Scalora, M.
    Proceedings of SPIE, the International Society for Optical Engineering
    Date of publication: 2009
    Journal article

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  • Transverse effects in a thin slab of material with local-field induced intrinsic optical bistability

     Font Garcia, Josep Lluís; Vilaseca Alavedra, Ramon; Staliunas, Kestutis; Roldán, E; Valcárcel, G J De
    Journal of the Optical Society of America B. Optical physics
    Date of publication: 2008-12
    Journal article

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  • Planar second-harmonic generation with noncollinear pumps in disordered media

     Roppo, Vito; Dumay, D; Trull, Jose; Cojocaru, Crina Maria; Saltiel, S M; Staliunas, Kestutis; Vilaseca Alavedra, Ramon; Neshev, D N; Krolikowski, W; Kivshar, Yu S
    Optics express
    Date of publication: 2008-08
    Journal article

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  • Room-temperature spectral hole burning in an engineered inhomogeneously broadened resonance

     Adrian, A Juarez; Vilaseca Alavedra, Ramon; Zhaoming, Zhu; Gauthier, And Daniel J
    Optics letters
    Date of publication: 2008-08
    Journal article

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  • Ultra-fast optical reconfiguration via nonlinear effects in semiconductor photonic crystals

     Cojocaru, Crina Maria; Trull, Jose; Vilaseca Alavedra, Ramon; Fabrice, Raineri; Levenson, Ariel; Rama, Raj
    Date of publication: 2008-06
    Book chapter

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  • Room-temperature spectral hole burning via SBS

     Gauthier, Daniel J; Adrian, A Juarez; Vilaseca Alavedra, Ramon; Zhaoming, Zhu
    FRONTIERS IN OPTICS 2008 / LASER SCIENCE XXIV
    Presentation of work at congresses

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  • Broadband second harmonic parametric scattering in ferroelectric crystals with random domain structures

     Cojocaru, Crina Maria; Trull, Jose; Fischer, R; Saltiel, S; Krolikowski, W; Staliunas, Kestutis; Herrero Simon, Ramon; Vilaseca Alavedra, Ramon; Kivshar, Y
    10th International Conference on Transparent Networks/7th European Symposium on Photonic Crystals
    Presentation of work at congresses

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