Articles de revista
http://hdl.handle.net/2117/3215
2015-09-04T18:59:08ZTwo-dimensional complex parity-time-symmetric photonic structures
http://hdl.handle.net/2117/76568
Two-dimensional complex parity-time-symmetric photonic structures
Turduev, M.; Botey Cumella, Muriel; Giden, I.; Herrero Simon, Ramon; Kurt, H.; Ozbay, E; Staliunas, Kestutis
We propose a simple realistic two-dimensional complex parity-time-symmetric photonic structure that is described by a non-Hermitian potential but possesses real-valued eigenvalues. The concept is developed from basic physical considerations to provide asymmetric coupling between harmonic wave components of the electromagnetic field. The structure results in a nonreciprocal chirality and asymmetric transmission between in- and out-coupling channels into the structure. The analytical results are supported by a numerical study of the Bloch-like mode formations and calculations of a realistic planar semiconductor structure.
2015-02-20T00:00:00ZQuantifying 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.
2015-06-01T00:00:00ZAcoustically 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.
2015-01-21T00:00:00ZExact 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.
2014-09-01T00:00:00ZFlat focusing mirror
http://hdl.handle.net/2117/27287
Flat focusing mirror
Cheng, Yu Chieh; Kicas, Simonas; Trull Silvestre, José Francisco; Peckus, Martynas; Cojocaru, Crina; Vilaseca Alavedra, Ramon; Drazdys, Ramutis; Staliunas, Kestutis
The control of spatial propagation properties of narrow light beams such as divergence, focusing or imaging are main objectives in optics and photonics. In this letter, we propose and demonstrate experimentally a flat focusing mirror, based on an especially designed dielectric structure without any optical axis. More generally, it also enables imaging any light pattern in reflection. The flat focusing mirror with a transversal invariance can largely increase the applicability of structured photonic materials for light beam propagation control in small-dimension photonic circuits.
2014-09-17T00:00:00ZPolarization switching and hysteresis in vertical-cavity surface-emitting lasers subject to orthogonal optical injection
http://hdl.handle.net/2117/27173
Polarization switching and hysteresis in vertical-cavity surface-emitting lasers subject to orthogonal optical injection
Salvide, Matias Fernando; Masoller Alonso, Cristina; Torre, Maria Susana
We study polarization switching and hysteresis in a vertical-cavity surface-emitting laser (VCSEL) subject to an orthogonal optical injection, such that the polarization of the injected light is perpendicular to that of the free-running VCSEL. We use the framework of the spin-flip model to characterize the polarization state of the VCSEL as a function of the frequency detuning. With appropriated injection conditions, the orthogonal polarization turns on and locks to the injected field. Increasing and decreasing the detuning across the two locking boundaries results either in narrow or wide hysteresis cycles, or even in irreversible switching. These results are in a good agreement with recent experimental observations.
2014-10-01T00:00:00ZSuppression of modulation instability in broad area semiconductor amplifiers
http://hdl.handle.net/2117/27140
Suppression of modulation instability in broad area semiconductor amplifiers
Kumar, Shubham; Herrero Simon, Ramon; Botey Cumella, Muriel; Staliunas, Kestutis
We show that a two-dimensional periodic modulation of the pump profile (modulation both along and perpendicular to the optical axis) can suppress the modulation instability in broad emission area semiconductor amplifiers. In the case of a realistic finite-width amplifier the modulation instability can be completely eliminated.
2014-10-01T00:00:00ZCollective stochastic coherence and synchronizability in weighted scale-free networks
http://hdl.handle.net/2117/26958
Collective stochastic coherence and synchronizability in weighted scale-free networks
Balenzuela, Pablo; Rue Queralt, Pau; Boccaletti, Stefano; García Ojalvo, Jordi
Coupling frequently enhances noise-induced coherence and synchronization in interacting nonlinear systems, but it does so separately. In principle collective stochastic coherence and synchronizability are incompatible phenomena, since strongly synchronized elements behave identically and thus their response to noise is indistinguishable to that of a single element. Therefore one can expect systems that synchronize well to have a poor collective response to noise. Here we show that, in spite of this apparent conflict, a certain coupling architecture is able to reconcile the two properties. Specifically, our results reveal that weighted scale-free networks of diffusively coupled excitable elements exhibit both high synchronizability of their subthreshold dynamics and a good collective response to noise of their pulsed dynamics. This is established by comparing the behavior of this system to that of random, regular, and unweighted scale-free networks. We attribute the optimal response of weighted scale-free networks to a balance between degree heterogeneity, which ensures a good collective response to noise, and the coupling-strength weighting procedure, which overcomes the paradox of heterogeneity that would otherwise impair synchronization.
2014-01-21T00:00:00ZGap soliton in a waveguide array with a saturating defocusing nonlinearity
http://hdl.handle.net/2117/26937
Gap soliton in a waveguide array with a saturating defocusing nonlinearity
Gaizzuskas, E; Savickas, A.; Staliunas, Kestutis
We investigate radiation of the solitary waves in the first band gap of the waveguide array with a defocusing nonlinearities of different types (Kerr nonlinearity and saturating nonlinearity). We confirm recent findings that gap solitons (GSs) are unstable for their eigenfrequencies around the middle of the band gap for Kerr nonlinearity. The instability is mediated by four-wave mixing process and appears in the form of radiation of solitons into mode continua of the upper and lower bands. We find that this soliton radiation is reduced (and even suppressed completely) in case of a saturating nonlinearity, resulting in substantial stabilization of the GSs.
2014-03-01T00:00:00Z