DONLL - Dinàmica no lineal, òptica no lineal i làsers
http://hdl.handle.net/2117/3214
Sat, 29 Apr 2017 21:34:45 GMT2017-04-29T21:34:45ZConsistency of heterogeneous synchronization patterns in complex weighted networks
http://hdl.handle.net/2117/103772
Consistency of heterogeneous synchronization patterns in complex weighted networks
Malagarriga Guasch, Daniel; Villa, Alessandro; García Ojalvo, Jordi; Pons Rivero, Antonio Javier
Synchronization within the dynamical nodes of a complex network is usually considered homogeneous through all the nodes. Here we show, in contrast, that subsets of interacting oscillators may synchronize in different ways within a single network. This diversity of synchronization patterns is promoted by increasing the heterogeneous distribution of coupling weights and/or asymmetries in small networks. We also analyze consistency, defined as the persistence of coexistent synchronization patterns regardless of the initial conditions. Our results show that complex weighted networks display richer consistency than regular networks, suggesting why certain functional network topologies are often constructed when experimental data are analyzed.
Dynamical systems may synchronize in several ways, at the same time, when they are coupled in a single complex network. Examples of this diversity of synchronization patterns may be found in research fields as diverse as neuroscience, climate networks, or ecosystems. Here we report the conditions required to obtain coexisting synchronizations in arrangements of interacting chaotic oscillators, and relate these conditions to the distribution of coupling weights and asymmetries in complex networks. We also analyze the conditions required for a high statistical occurrence of the same synchronization patterns, regardless of the oscillators' initial conditions. Our results show that these persistent synchronization patterns are statistically more frequent in complex weighted networks than in regular ones, explaining why certain functional network topologies are often retrieved from experimental data. Besides, our results suggest that considering both the different coexisting synchronizations and also their statistics may result in a richer understanding of the relations between functional and structural networks of oscillators.
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Thu, 27 Apr 2017 08:54:18 GMThttp://hdl.handle.net/2117/1037722017-04-27T08:54:18ZMalagarriga Guasch, DanielVilla, AlessandroGarcía Ojalvo, JordiPons Rivero, Antonio JavierSynchronization within the dynamical nodes of a complex network is usually considered homogeneous through all the nodes. Here we show, in contrast, that subsets of interacting oscillators may synchronize in different ways within a single network. This diversity of synchronization patterns is promoted by increasing the heterogeneous distribution of coupling weights and/or asymmetries in small networks. We also analyze consistency, defined as the persistence of coexistent synchronization patterns regardless of the initial conditions. Our results show that complex weighted networks display richer consistency than regular networks, suggesting why certain functional network topologies are often constructed when experimental data are analyzed.
Dynamical systems may synchronize in several ways, at the same time, when they are coupled in a single complex network. Examples of this diversity of synchronization patterns may be found in research fields as diverse as neuroscience, climate networks, or ecosystems. Here we report the conditions required to obtain coexisting synchronizations in arrangements of interacting chaotic oscillators, and relate these conditions to the distribution of coupling weights and asymmetries in complex networks. We also analyze the conditions required for a high statistical occurrence of the same synchronization patterns, regardless of the oscillators' initial conditions. Our results show that these persistent synchronization patterns are statistically more frequent in complex weighted networks than in regular ones, explaining why certain functional network topologies are often retrieved from experimental data. Besides, our results suggest that considering both the different coexisting synchronizations and also their statistics may result in a richer understanding of the relations between functional and structural networks of oscillators.Locally parity-time-symmetric and globally parity-symmetric systems
http://hdl.handle.net/2117/103403
Locally parity-time-symmetric and globally parity-symmetric systems
Ahmed Waseem, Waqas Waseem; Herrero Simon, Ramon; Botey Cumella, Muriel; Staliunas, Kestutis
We introduce a class of systems holding parity-time (PT) symmetry locally, whereas being globally P symmetric. The potential, U = U(vertical bar r vertical bar), fulfills PT symmetry with respect to periodically distributed points r(0) : U(vertical bar r(0) + r vertical bar) = U*(vertical bar r(0) - r vertical bar) being r(0) not equal 0. We show that such systems hold unusual properties arising from the merging of the two different symmetries, leading to a strong field localization and enhancement at the double-symmetry center, r = 0, when the coupling of outward to inward propagating waves is favored. We explore such general potentials in one and two dimensions, which could have actual realizations combining gain-loss and index modulations in nanophotonic structures. In particular, we show how to render a broad aperture vertical-cavity surface-emitting laser into a bright and narrow beam source, as a direct application.
Wed, 05 Apr 2017 15:54:50 GMThttp://hdl.handle.net/2117/1034032017-04-05T15:54:50ZAhmed Waseem, Waqas WaseemHerrero Simon, RamonBotey Cumella, MurielStaliunas, KestutisWe introduce a class of systems holding parity-time (PT) symmetry locally, whereas being globally P symmetric. The potential, U = U(vertical bar r vertical bar), fulfills PT symmetry with respect to periodically distributed points r(0) : U(vertical bar r(0) + r vertical bar) = U*(vertical bar r(0) - r vertical bar) being r(0) not equal 0. We show that such systems hold unusual properties arising from the merging of the two different symmetries, leading to a strong field localization and enhancement at the double-symmetry center, r = 0, when the coupling of outward to inward propagating waves is favored. We explore such general potentials in one and two dimensions, which could have actual realizations combining gain-loss and index modulations in nanophotonic structures. In particular, we show how to render a broad aperture vertical-cavity surface-emitting laser into a bright and narrow beam source, as a direct application.Linear and Nonlinear Bullets of the Bogoliubov-de Gennes Excitations
http://hdl.handle.net/2117/103389
Linear and Nonlinear Bullets of the Bogoliubov-de Gennes Excitations
Kumar, Shubham; Perego, A.M.; Staliunas, Kestutis
We report on the focalization of Bogoliubov–de Gennes excitations of the nonlinear Schrödinger equation in the defocusing regime (Gross-Pitaevskii equation for repulsive Bose-Einstein condensates) with a spatially modulated periodic potential. Exploiting the modification of the dispersion relation induced by the modulation, we demonstrate the existence of localized structures of the Bogoliubov–de Gennes excitations, in both the linear and nonlinear regimes (linear and nonlinear “bullets”). These traveling Bogoliubov–de Gennes bullets, localized both spatially and temporally in the comoving reference frame, are robust and propagate remaining stable, without spreading or filamentation. The phenomena reported in this Letter could be observed in atomic Bose-Einstein condensates in the presence of a spatially periodic potential induced by an optical lattice.
Wed, 05 Apr 2017 14:01:12 GMThttp://hdl.handle.net/2117/1033892017-04-05T14:01:12ZKumar, ShubhamPerego, A.M.Staliunas, KestutisWe report on the focalization of Bogoliubov–de Gennes excitations of the nonlinear Schrödinger equation in the defocusing regime (Gross-Pitaevskii equation for repulsive Bose-Einstein condensates) with a spatially modulated periodic potential. Exploiting the modification of the dispersion relation induced by the modulation, we demonstrate the existence of localized structures of the Bogoliubov–de Gennes excitations, in both the linear and nonlinear regimes (linear and nonlinear “bullets”). These traveling Bogoliubov–de Gennes bullets, localized both spatially and temporally in the comoving reference frame, are robust and propagate remaining stable, without spreading or filamentation. The phenomena reported in this Letter could be observed in atomic Bose-Einstein condensates in the presence of a spatially periodic potential induced by an optical lattice.Two-dimensional domain structures in Lithium Niobate via domain inversion with ultrafast light
http://hdl.handle.net/2117/103122
Two-dimensional domain structures in Lithium Niobate via domain inversion with ultrafast light
Chen, Xin; Karpinski, Pawel; Shvedov, Vladlen; Wang, Bingxia; Trull Silvestre, José Francisco; Cojocaru, Crina; Boes, A.; Mitchell, A.; Krolikowski, Wieslaw; Sheng, Yan
Periodic inversion of ferroelectric domains is realized in a lithium niobate crystal by focused femtosecond near-infrared laser beam. One and two-dimensional domain patterns are fabricated. Quasi-phase matched frequency doubling of 815nm light is demonstrated in a channel waveguide with an inscribed periodic domain pattern with conversion efficiency as high as 17.45%.
Thu, 30 Mar 2017 16:32:04 GMThttp://hdl.handle.net/2117/1031222017-03-30T16:32:04ZChen, XinKarpinski, PawelShvedov, VladlenWang, BingxiaTrull Silvestre, José FranciscoCojocaru, CrinaBoes, A.Mitchell, A.Krolikowski, WieslawSheng, YanPeriodic inversion of ferroelectric domains is realized in a lithium niobate crystal by focused femtosecond near-infrared laser beam. One and two-dimensional domain patterns are fabricated. Quasi-phase matched frequency doubling of 815nm light is demonstrated in a channel waveguide with an inscribed periodic domain pattern with conversion efficiency as high as 17.45%.Axisymmetric photonic structures with PT-symmetry
http://hdl.handle.net/2117/102467
Axisymmetric photonic structures with PT-symmetry
Ahmed Waseem, Waqas Waseem; Herrero Simon, Ramon; Botey Cumella, Muriel; Staliunas, Kestutis
PT-symmetric structures in photonic crystals, combining refractive index and gain-loss modulations is becoming a research field with increasing interest due to the light directionality induced by these particular potentials. Here, we consider PT-symmetric potentials with axial symmetry to direct light to the crystal central point obtaining a localization effect. The axial and PT-symmetric potential intrinsically generates an exceptional central point in the photonic crystal by the merge of both symmetries. This particular point in the crystal lattice causes field amplitude gradients with exponential slopes around the crystal center. The field localization strongly depends on the phase of the central point and on the complex amplitude of the PT-potential.
The presented work analyzes in a first stage 1D linear PT-axisymmetric crystals and the role of the central point phase that determines the defect character, i.e. refractive index defect, gain-loss defect or a combination of both. The interplay of the directional light effect induced by the PT-symmetry and the light localization around the central point through the axial symmetry enhances localization and allows higher field concentration for certain phases. The linearity of the studied crystals introduces an exponential growth of the field that mainly depends on the complex amplitude of the potential. The work is completed by the analysis of 2D PT-axisymmetric potentials showing different spatial slopes and growth rates caused by symmetry reasons.
Copyright 2016 Society of Photo-Optical Instrumentation Engineers. One print or electronic copy may be made for personal use only. Systematic reproduction and distribution, duplication of any material in this paper for a fee or for commercial purposes, or modification of the content of the paper are prohibited.
Tue, 14 Mar 2017 17:19:20 GMThttp://hdl.handle.net/2117/1024672017-03-14T17:19:20ZAhmed Waseem, Waqas WaseemHerrero Simon, RamonBotey Cumella, MurielStaliunas, KestutisPT-symmetric structures in photonic crystals, combining refractive index and gain-loss modulations is becoming a research field with increasing interest due to the light directionality induced by these particular potentials. Here, we consider PT-symmetric potentials with axial symmetry to direct light to the crystal central point obtaining a localization effect. The axial and PT-symmetric potential intrinsically generates an exceptional central point in the photonic crystal by the merge of both symmetries. This particular point in the crystal lattice causes field amplitude gradients with exponential slopes around the crystal center. The field localization strongly depends on the phase of the central point and on the complex amplitude of the PT-potential.
The presented work analyzes in a first stage 1D linear PT-axisymmetric crystals and the role of the central point phase that determines the defect character, i.e. refractive index defect, gain-loss defect or a combination of both. The interplay of the directional light effect induced by the PT-symmetry and the light localization around the central point through the axial symmetry enhances localization and allows higher field concentration for certain phases. The linearity of the studied crystals introduces an exponential growth of the field that mainly depends on the complex amplitude of the potential. The work is completed by the analysis of 2D PT-axisymmetric potentials showing different spatial slopes and growth rates caused by symmetry reasons.Mode-locking via dissipative Faraday instability
http://hdl.handle.net/2117/102229
Mode-locking via dissipative Faraday instability
Tarasov, N.; Perego, A.M.; Churkin, D.V.; Staliunas, Kestutis; Turitsyn, S.K.
Emergence of coherent structures and patterns at the nonlinear stage of modulation
instability of a uniform state is an inherent feature of many biological, physical and engineering
systems. There are several well-studied classical modulation instabilities, such as
Benjamin–Feir, Turing and Faraday instability, which play a critical role in the self-organization
of energy and matter in non-equilibrium physical, chemical and biological systems. Here
we experimentally demonstrate the dissipative Faraday instability induced by spatially
periodic zig-zag modulation of a dissipative parameter of the system—spectrally dependent
losses—achieving generation of temporal patterns and high-harmonic mode-locking in a fibre
laser. We demonstrate features of this instability that distinguish it from both the Benjamin–
Feir and the purely dispersive Faraday instability. Our results open the possibilities for new
designs of mode-locked lasers and can be extended to other fields of physics and engineering.
Thu, 09 Mar 2017 15:22:54 GMThttp://hdl.handle.net/2117/1022292017-03-09T15:22:54ZTarasov, N.Perego, A.M.Churkin, D.V.Staliunas, KestutisTuritsyn, S.K.Emergence of coherent structures and patterns at the nonlinear stage of modulation
instability of a uniform state is an inherent feature of many biological, physical and engineering
systems. There are several well-studied classical modulation instabilities, such as
Benjamin–Feir, Turing and Faraday instability, which play a critical role in the self-organization
of energy and matter in non-equilibrium physical, chemical and biological systems. Here
we experimentally demonstrate the dissipative Faraday instability induced by spatially
periodic zig-zag modulation of a dissipative parameter of the system—spectrally dependent
losses—achieving generation of temporal patterns and high-harmonic mode-locking in a fibre
laser. We demonstrate features of this instability that distinguish it from both the Benjamin–
Feir and the purely dispersive Faraday instability. Our results open the possibilities for new
designs of mode-locked lasers and can be extended to other fields of physics and engineering.Study of the charge profile of thermally poled electrets
http://hdl.handle.net/2117/101794
Study of the charge profile of thermally poled electrets
Parsa, Seyedeh Elaheh; Trull Silvestre, José Francisco; Colom Fajula, Xavier; Sellarès González, Jordi
The charge profile of thermally poled electrets has been studied using two different methods, laser induced pressure pulse (LIPP) and pulsed electroacoustic (PEA), to gain insight into the mechanisms that are activated and assess which is the most appropriate method to study the charge profile. Disc–shaped PET samples have been conventionally poled to activate both the a and the ¿ relaxation and, right after, partially discharged up to a temperature Tpd . In this way, samples with a different combination of dipolar and space charge polarization have been obtained. Both LIPP and PEA reveal asymmetric profiles for Tpd below the glass transition temperature, that progressively become antisymmetric for higher temperatures. The shape and evolution of the charge profiles can be explained assuming injection of negative carriers from the anode that enhances the trapping of positive carriers near this electrode. It can be observed that PEA is able to detect a wider variety of polarization mechanisms in the system while LIPP gives a simpler picture of the charge profile.
Preprint
Wed, 01 Mar 2017 12:55:42 GMThttp://hdl.handle.net/2117/1017942017-03-01T12:55:42ZParsa, Seyedeh ElahehTrull Silvestre, José FranciscoColom Fajula, XavierSellarès González, JordiThe charge profile of thermally poled electrets has been studied using two different methods, laser induced pressure pulse (LIPP) and pulsed electroacoustic (PEA), to gain insight into the mechanisms that are activated and assess which is the most appropriate method to study the charge profile. Disc–shaped PET samples have been conventionally poled to activate both the a and the ¿ relaxation and, right after, partially discharged up to a temperature Tpd . In this way, samples with a different combination of dipolar and space charge polarization have been obtained. Both LIPP and PEA reveal asymmetric profiles for Tpd below the glass transition temperature, that progressively become antisymmetric for higher temperatures. The shape and evolution of the charge profiles can be explained assuming injection of negative carriers from the anode that enhances the trapping of positive carriers near this electrode. It can be observed that PEA is able to detect a wider variety of polarization mechanisms in the system while LIPP gives a simpler picture of the charge profile.Emergence of spike correlations in periodically forced excitable systems
http://hdl.handle.net/2117/101786
Emergence of spike correlations in periodically forced excitable systems
Reinoso, Jose A.; Torrent Serra, Maria del Carmen; Masoller Alonso, Cristina
Wed, 01 Mar 2017 12:11:41 GMThttp://hdl.handle.net/2117/1017862017-03-01T12:11:41ZReinoso, Jose A.Torrent Serra, Maria del CarmenMasoller Alonso, CristinaPredictability of optical rogue waves in optically injected semiconductor lasers
http://hdl.handle.net/2117/101604
Predictability of optical rogue waves in optically injected semiconductor lasers
Martinez Alvarez, Nuria; Reinoso, Jose A.; Masoller Alonso, Cristina
The predictability of ultra-high pulses emitted by optically injected semiconductor lasers is studied by using symbolic time-series analysis. Pulse patterns that are likely to occur before the rogue wave are identified.
Mon, 27 Feb 2017 10:14:31 GMThttp://hdl.handle.net/2117/1016042017-02-27T10:14:31ZMartinez Alvarez, NuriaReinoso, Jose A.Masoller Alonso, CristinaThe predictability of ultra-high pulses emitted by optically injected semiconductor lasers is studied by using symbolic time-series analysis. Pulse patterns that are likely to occur before the rogue wave are identified.Global atmospheric dynamics investigated by using Hilbert frequency analysis
http://hdl.handle.net/2117/101413
Global atmospheric dynamics investigated by using Hilbert frequency analysis
Zappala, Dario; Barreiro, Marcelo; Masoller Alonso, Cristina
The Hilbert transform is a well-known tool of time series analysis that has been widely used to investigate oscillatory signals that resemble a noisy periodic oscillation, because it allows instantaneous phase and frequency to be estimated, which in turn uncovers interesting properties of the underlying process that generates the signal. Here we use this tool to analyze atmospheric data: we consider daily-averaged Surface Air Temperature (SAT) time series recorded over a regular grid of locations covering the Earth’s surface. From each SAT time series, we calculate the instantaneous frequency time series by considering the Hilbert analytic signal. The properties of the obtained frequency data set are investigated by plotting the map of the average frequency and the map of the standard deviation of the frequency fluctuations. The average frequency map reveals well-defined large-scale structures: in the extra-tropics, the average frequency in general corresponds to the expected one-year period of solar forcing, while in the tropics, a different behaviour is found, with particular regions having a faster average frequency. In the standard deviation map, large-scale structures are also found, which tend to be located over regions of strong annual precipitation. Our results demonstrate that Hilbert analysis of SAT time-series uncovers meaningful information, and is therefore a promising tool for the study of other climatological variables.
Wed, 22 Feb 2017 19:10:46 GMThttp://hdl.handle.net/2117/1014132017-02-22T19:10:46ZZappala, DarioBarreiro, MarceloMasoller Alonso, CristinaThe Hilbert transform is a well-known tool of time series analysis that has been widely used to investigate oscillatory signals that resemble a noisy periodic oscillation, because it allows instantaneous phase and frequency to be estimated, which in turn uncovers interesting properties of the underlying process that generates the signal. Here we use this tool to analyze atmospheric data: we consider daily-averaged Surface Air Temperature (SAT) time series recorded over a regular grid of locations covering the Earth’s surface. From each SAT time series, we calculate the instantaneous frequency time series by considering the Hilbert analytic signal. The properties of the obtained frequency data set are investigated by plotting the map of the average frequency and the map of the standard deviation of the frequency fluctuations. The average frequency map reveals well-defined large-scale structures: in the extra-tropics, the average frequency in general corresponds to the expected one-year period of solar forcing, while in the tropics, a different behaviour is found, with particular regions having a faster average frequency. In the standard deviation map, large-scale structures are also found, which tend to be located over regions of strong annual precipitation. Our results demonstrate that Hilbert analysis of SAT time-series uncovers meaningful information, and is therefore a promising tool for the study of other climatological variables.