DONLL - Dinàmica no lineal, òptica no lineal i làsers
http://hdl.handle.net/2117/3214
2015-09-01T06:08:15ZAsymmetric light transmission by using 2D PT-symmetric photonic nanostructure
http://hdl.handle.net/2117/76340
Asymmetric light transmission by using 2D PT-symmetric photonic nanostructure
Turduev, M.; Botey Cumella, Muriel; Herrero Simon, Ramon; Kurt, H.; Staliunas, Kestutis; Giden, I.
We propose for the first time a simple realization of a two-dimensional Parity-Time symmetric hexagonal shaped photonic structure composed of honeycomb lattice. The structure has a symmetric periodic modulation of the refractive index on the wavelength scale, which is combined with an anti-symmetric gain/loss distribution on the same scale. That leads to non-reciprocal light coupling at resonant frequencies. The design of the realistic structure is based on a simple physical concept: alternating low index cylinders with gain and loss in a honeycomb configuration, embedded in a higher index dielectric background.
2015-01-01T00:00:00ZQuantifying sudden changes in dynamical systems using symbolic networks
http://hdl.handle.net/2117/76333
Quantifying sudden changes in dynamical systems using symbolic networks
Masoller Alonso, Cristina; Hong, Yanhua; Ayad, Sarah; Gustave, Francois; Barland, Stéphane; Pons Rivero, Antonio Javier; Gómez, Sergio; Arenas, Alex
We characterize the evolution of a dynamical system by combining two well-known complex systems' tools, namely, symbolic ordinal analysis and networks. From the ordinal representation of a time series we construct a network in which every node weight represents the probability of an ordinal pattern (OP) to appear in the symbolic sequence and each edge's weight represents the probability of transitions between two consecutive OPs. Several network-based diagnostics are then proposed to characterize the dynamics of different systems: logistic, tent, and circle maps. We show that these diagnostics are able to capture changes produced in the dynamics as a control parameter is varied. We also apply our new measures to empirical data from semiconductor lasers and show that they are able to anticipate the polarization switchings, thus providing early warning signals of abrupt transitions.
2015-02-24T00:00:00ZUltrashort pulse chirp measurement via transverse second-harmonic generation in strontium barium niobate crystal
http://hdl.handle.net/2117/28568
Ultrashort pulse chirp measurement via transverse second-harmonic generation in strontium barium niobate crystal
Trull Silvestre, José Francisco; Sola, Ïñigo; Wang, Bingxia; Parra, Albert; Krolikowski, W.; Sheng, Y.; Vilaseca Alavedra, Ramon; Cojocaru, Crina
Pulse compression in dispersive strontium barium niobate crystal with a random size and distribution of the anti-parallel orientated nonlinear domains is observed via transverse second harmonic generation. The dependence of the transverse width of the second harmonic trace along the propagation direction allows for the determination of the initial chirp and duration of pulses in the femtosecond regime. This technique permits a real-time analysis of the pulse evolution and facilitates fast in-situ correction of pulse chirp acquired in the propagation through an optical system.
2015-06-01T00:00:00ZSuppression of modulation instability by spatio-temporal modulation
http://hdl.handle.net/2117/28105
Suppression of modulation instability by spatio-temporal modulation
Staliunas, Kestutis
Modulation Instability (MI) is at the basis of spontaneous pattern formation in many nonlinear spatially extended systems in Nature, technologies, and in everyday live. In spite of variety of spatial patterns in different systems, the very onset of a spatio-temporal dynamics, the breaking of initial spatial and temporal symmetry, is initiated by MI. The said is valid for dissipative nonlinear systems, where dissipative patterns set in, but also for conservative systems. The examples in latter case ranges from the filamentation of light in Kerr-nonlinear media, instabilities of Bose condensates with attractive interactions, to perhaps, the recently much discussed formation of the “rogue waves”.
2013-01-01T00:00:00ZStochastic competition between two populations in space
http://hdl.handle.net/2117/28093
Stochastic competition between two populations in space
Pigolotti, Simone; Benzi, Roberto; Jensen, Mogens H.; Perlekar, Prasad; Toschi, Federico
2014-06-10T00:00:00ZAcoustically penetrable sonic crystals based on fluid-like scatterers
http://hdl.handle.net/2117/28088
Acoustically penetrable sonic crystals based on fluid-like scatterers
Cebrecos, A.; Romero García, Vicenç; Pico Vila, Rubén; Sánchez Morcillo, Victor José; Botey Cumella, Muriel; Herrero Simon, Ramon; Cheng, Yu Chieh; Staliunas, Kestutis
We propose a periodic structure that behaves as a fluid-fluid composite for sound waves, where the building blocks are clusters of rigid scatterers. Such building-blocks are penetrable for acoustic waves, and their properties can be tuned by selecting the filling fraction. The equivalence with a fluid-fluid system of such a doubly periodic composite is tested analytical and experimentally. Because of the fluid-like character of the scatterers, sound structure interaction is negligible, and the propagation can be described by scalar models, analogous to those used in electromagnetics. As an example, the case of focusing of evanescent waves and the guided propagation of acoustic waves along an array of penetrable elements is discussed in detail. The proposed structure may be a real alternative to design a low contrast and acoustically penetrable medium where new properties as those shown in this work could be experimentally realized.
2015-01-21T00:00:00ZBeam focusing in chirped mirror with a defect
http://hdl.handle.net/2117/27767
Beam focusing in chirped mirror with a defect
Cheng, Yu Chieh; Staliunas, Kestutis
Recently the beam focusing in reflection from chirped dielectric mirror has been proposed and demonstrated, where the negative (anomalous) diffraction is responsible for this flat mirror focusing. For a strong focusing performance (large focal distance), a wide angular range of strong (negative) angular dispersion is required. We show that a defect layer in the dielectric mirror (one layer is of a double size), can increase the angular dispersion, and thus improve the focusing performance. By introducing a defect layer in the chirped mirror, the focal distances can be increase from 12 µm up to 22 µm in a specific, calculated, structure, as our numerical integration show.
2004-01-01T00:00:00ZExcitation/inhibition patterns in a system of coupled cortical columns
http://hdl.handle.net/2117/27684
Excitation/inhibition patterns in a system of coupled cortical columns
Malagarriga Guasch, Daniel; Villa, Alessandro; García Ojalvo, Jordi; Pons Rivero, Antonio Javier
We study how excitation and inhibition are distributed mesoscopically in small brain regions, by means of a computational model of coupled cortical columns described by neural mass models. Two cortical columns coupled bidirectionally through both excitatory and inhibitory connections can spontaneously organize in a regime in which one of the columns is purely excitatory and the other is purely inhibitory, provided the excitatory and inhibitory coupling strengths are adequately tuned. We also study the case of three columns in different coupling configurations (linear array and all-to-all coupling), finding abrupt transitions between heterogeneous and homogeneous excitatory/inhibitory patterns and strong multistability in their distribution.
2014-01-01T00:00:00ZExact detection of direct links in networks of interacting dynamical units
http://hdl.handle.net/2117/27390
Exact detection of direct links in networks of interacting dynamical units
Rubido, Nicolas; Marti, Arturo; Bianco-Martinez, Ezequiel; Grebogi, Celso; Baptista, Murilo; Masoller Alonso, Cristina
The inference of an underlying network topology from local observations of a complex system composed of interacting units is usually attempted by using statistical similarity measures, such as cross-correlation (CC) and mutual information (MI). The possible existence of a direct link between different units is, however, hindered within the time-series measurements. Here we show that, for the class of systems studied, when an abrupt change in the ordered set of CC or MI values exists, it is possible to infer, without errors, the underlying network topology from the time-series measurements, even in the presence of observational noise, non-identical units, and coupling heterogeneity. We find that a necessary condition for the discontinuity to occur is that the dynamics of the coupled units is partially coherent, i.e., neither complete disorder nor globally synchronous patterns are present. We critically compare the inference methods based on CC and MI, in terms of how effective, robust, and reliable they are, and conclude that, in general, MI outperforms CC in robustness and reliability. Our findings could be relevant for the construction and interpretation of functional networks, such as those constructed from brain or climate data.
2014-09-01T00:00:00ZBeam focalization by chirped mirrors
http://hdl.handle.net/2117/27289
Beam focalization by chirped mirrors
Cheng, Yu Chieh; Peckus, Martynas; Kicas, Simonas; Trull Silvestre, José Francisco; Cojocaru, Crina; Vilaseca Alavedra, Ramon; Drazdys, Ramutis; Staliunas, Kestutis
A novel application of chirped dielectric mirrors for narrow beam focalization is proposed and demonstrated numerically and experimentally. Analogy to temporal dispersion compensation by chirped dielectric mirrors is discussed.
2014-01-01T00:00:00Z