Articles de revista
http://hdl.handle.net/2117/3924
2016-12-10T18:38:24ZSolitary-wave vortices in type II second-harmonic generation
http://hdl.handle.net/2117/97968
Solitary-wave vortices in type II second-harmonic generation
Pérez Torres, Juan; Soto-Crespo, J M; Torner Sabata, Lluís; Petrov, Dimitri
We find families of optical bright, vortex solitary waves in bulk quadratic nonlinear media under conditions for type II second-harmonic generation. We study the main properties of the families of solitary waves, including their stability. The vortex solitary waves are found to be azimuthally unstable and their decay into sets of stable spatial solitons is shown. We calculate the growth rates of the possible azimuthal perturbations with different azimuthal index and show how those affect the pattern of output light. Numerical simulations to check the predictions of the stability analysis are also reported.
2016-12-09T19:58:27ZPérez Torres, JuanSoto-Crespo, J MTorner Sabata, LluísPetrov, DimitriWe find families of optical bright, vortex solitary waves in bulk quadratic nonlinear media under conditions for type II second-harmonic generation. We study the main properties of the families of solitary waves, including their stability. The vortex solitary waves are found to be azimuthally unstable and their decay into sets of stable spatial solitons is shown. We calculate the growth rates of the possible azimuthal perturbations with different azimuthal index and show how those affect the pattern of output light. Numerical simulations to check the predictions of the stability analysis are also reported.Anderson cross-localization
http://hdl.handle.net/2117/97965
Anderson cross-localization
Stützer, Simon; Kartashov, Yaroslav V.; Vysloukh, Victor A.; Tünnermann, A.; Nolte, Stefan; Lewenstein, Maciej; Torner Sabata, Lluís; Szameit, Alexander
We report Anderson localization in two-dimensional optical waveguide arrays with disorder in waveguide separation introduced along one axis of the array, in an uncorrelated fashion for each waveguide row. We show that the anisotropic nature of such disorder induces a strong localization along both array axes. The degree of localization in the cross-axis remains weaker than that in the direction in which disorder is introduced. This effect is illustrated both theoretically and experimentally.
2016-12-09T18:27:47ZStützer, SimonKartashov, Yaroslav V.Vysloukh, Victor A.Tünnermann, A.Nolte, StefanLewenstein, MaciejTorner Sabata, LluísSzameit, AlexanderWe report Anderson localization in two-dimensional optical waveguide arrays with disorder in waveguide separation introduced along one axis of the array, in an uncorrelated fashion for each waveguide row. We show that the anisotropic nature of such disorder induces a strong localization along both array axes. The degree of localization in the cross-axis remains weaker than that in the direction in which disorder is introduced. This effect is illustrated both theoretically and experimentally.Spatial solitons in optofluidic waveguide arrays with focusing ultrafast Kerr nonlinearity
http://hdl.handle.net/2117/97964
Spatial solitons in optofluidic waveguide arrays with focusing ultrafast Kerr nonlinearity
Vieweg, M.; Gissibl, T.; Kartashov, Yaroslav V.; Torner Sabata, Lluís; Giessen, H.
We present an optofluidic nonlinear waveguide array that is fabricated by selectively filling several strands of a photonic crystal fiber with the liquid CCl4, which exhibits a large focusing ultrafast Kerr nonlinearity. We demonstrate a power dependent formation of a spatial soliton in this novel optofluidic device. The large thermo-optical effect of liquids enables us to control the characteristics of the spatial soliton formation in these nonlinear structures. This opens the road toward flexible designs and the realization of a new class of optofluidic devices with complex nonlinear landscapes and novel effects.
2016-12-09T18:25:23ZVieweg, M.Gissibl, T.Kartashov, Yaroslav V.Torner Sabata, LluísGiessen, H.We present an optofluidic nonlinear waveguide array that is fabricated by selectively filling several strands of a photonic crystal fiber with the liquid CCl4, which exhibits a large focusing ultrafast Kerr nonlinearity. We demonstrate a power dependent formation of a spatial soliton in this novel optofluidic device. The large thermo-optical effect of liquids enables us to control the characteristics of the spatial soliton formation in these nonlinear structures. This opens the road toward flexible designs and the realization of a new class of optofluidic devices with complex nonlinear landscapes and novel effects.Coupling plasmons and dyakonons
http://hdl.handle.net/2117/97963
Coupling plasmons and dyakonons
Takayama, Osamu; Artigas García, David; Torner Sabata, Lluís
We study the coupling of plasmons and Dyakonov surface waves propagating at the interfaces between isotropic-birefringent-metal layered structures. Efficient coupling is shown to occur with a proper choice of the crystal birefringence, the refractive index of the isotropic medium, and the light propagation direction relative to the crystal optical axis. In the case of low-loss metals, coupling efficiencies as high as 90% are predicted to be possible.
2016-12-09T18:17:28ZTakayama, OsamuArtigas García, DavidTorner Sabata, LluísWe study the coupling of plasmons and Dyakonov surface waves propagating at the interfaces between isotropic-birefringent-metal layered structures. Efficient coupling is shown to occur with a proper choice of the crystal birefringence, the refractive index of the isotropic medium, and the light propagation direction relative to the crystal optical axis. In the case of low-loss metals, coupling efficiencies as high as 90% are predicted to be possible.Stable bright and vortex solitons in photonic crystal fibers with inhomogeneous defocusing nonlinearity
http://hdl.handle.net/2117/97962
Stable bright and vortex solitons in photonic crystal fibers with inhomogeneous defocusing nonlinearity
Lobanov, Valery E.; Borovkova, Olga V.; Kartashov, Yaroslav V.; Malomed, Boris A.; Torner Sabata, Lluís
We predict that a photonic crystal fiber whose strands are filled with a defocusing nonlinear medium can support stable bright solitons and also vortex solitons if the strength of the defocusing nonlinearity grows toward the periphery of the fiber. The domains of soliton existence depend on the transverse growth rate of the filling nonlinearity and nonlinearity of the core. Remarkably, solitons exist even when the core material is linear.
2016-12-09T18:14:54ZLobanov, Valery E.Borovkova, Olga V.Kartashov, Yaroslav V.Malomed, Boris A.Torner Sabata, LluísWe predict that a photonic crystal fiber whose strands are filled with a defocusing nonlinear medium can support stable bright solitons and also vortex solitons if the strength of the defocusing nonlinearity grows toward the periphery of the fiber. The domains of soliton existence depend on the transverse growth rate of the filling nonlinearity and nonlinearity of the core. Remarkably, solitons exist even when the core material is linear.Tunable ultrafast nonlinear optofluidic coupler
http://hdl.handle.net/2117/97961
Tunable ultrafast nonlinear optofluidic coupler
Vieweg, M.; Pricking, S.; Gissibl, T.; Kartashov, Yaroslav V.; Torner Sabata, Lluís; Giessen, H.
We present an optofluidic nonlinear coupler fabricated by selective filling of two strands of a photonic crystal fiber with the liquid CCl 4 which exhibits a large ultrafast Kerr nonlinearity. We demonstrate power dependent switching in this novel optofluidic device. The large thermo-optical effect of liquids enables us to tune the behavior of the nonlinear coupler by changing the coupling strength with temperature. This opens the road towards flexible designs and realization of a new class of tunable ultrafast nonlinear couplers with switching times below 1 ps.
2016-12-09T18:11:39ZVieweg, M.Pricking, S.Gissibl, T.Kartashov, Yaroslav V.Torner Sabata, LluísGiessen, H.We present an optofluidic nonlinear coupler fabricated by selective filling of two strands of a photonic crystal fiber with the liquid CCl 4 which exhibits a large ultrafast Kerr nonlinearity. We demonstrate power dependent switching in this novel optofluidic device. The large thermo-optical effect of liquids enables us to tune the behavior of the nonlinear coupler by changing the coupling strength with temperature. This opens the road towards flexible designs and realization of a new class of tunable ultrafast nonlinear couplers with switching times below 1 ps.Object-based image coding
http://hdl.handle.net/2117/97957
Object-based image coding
Pardàs Feliu, Montse
Object-based compression methods describe images in terms of a set of regions (a partition), and of some information for each region to be used by the receiver to reconstruct the image (its texture). Different techniques can be used to define the partition as well as for coding it and its texture. In this paper we propose a general multi-resolution segmentation algorithm which can deal with many different types of images selecting the appropriated criteria. We also review most outstanding techniques for coding in this context.
2016-12-09T16:07:53ZPardàs Feliu, MontseObject-based compression methods describe images in terms of a set of regions (a partition), and of some information for each region to be used by the receiver to reconstruct the image (its texture). Different techniques can be used to define the partition as well as for coding it and its texture. In this paper we propose a general multi-resolution segmentation algorithm which can deal with many different types of images selecting the appropriated criteria. We also review most outstanding techniques for coding in this context.A novel ekf-based recovery in ds scheme for ds/cdma systems tracking code delay
http://hdl.handle.net/2117/97956
A novel ekf-based recovery in ds scheme for ds/cdma systems tracking code delay
Díaz Romero, M. del Pilar; Agustí Comes, Ramon
Classical delay-lock loops (DLL) have beenwidely considered for code synchronization purposes inDS/CDMA systems, although they have not been devised foroperation when channel fading is present. This paper describes a new code synchronizationscheme based on a previously proposed extended Kalmanfilter (EKF) approach. The scheme proposed in this paperis able to operate under low signal-to-interference ratios (SIR), usual at the receiver input incellular CDMA mobile environments, and it outperformsthe behavior of previously proposed EKF-based schemes,which failed in such environments. Performance results under realistic mobile environment conditionsare shown in terms of the mean time to lose lock (MTLL)and the tracking error variancest2 for a wide range ofSIR values and under Rayleigh fading. Moreover, the Cramer-Rao lower boundonst2 is also computed inorder to validate the results obtained viasimulations
2016-12-09T16:03:26ZDíaz Romero, M. del PilarAgustí Comes, RamonClassical delay-lock loops (DLL) have beenwidely considered for code synchronization purposes inDS/CDMA systems, although they have not been devised foroperation when channel fading is present. This paper describes a new code synchronizationscheme based on a previously proposed extended Kalmanfilter (EKF) approach. The scheme proposed in this paperis able to operate under low signal-to-interference ratios (SIR), usual at the receiver input incellular CDMA mobile environments, and it outperformsthe behavior of previously proposed EKF-based schemes,which failed in such environments. Performance results under realistic mobile environment conditionsare shown in terms of the mean time to lose lock (MTLL)and the tracking error variancest2 for a wide range ofSIR values and under Rayleigh fading. Moreover, the Cramer-Rao lower boundonst2 is also computed inorder to validate the results obtained viasimulationsAnalysis and synthesis of textures through the inference of Boolean functions
http://hdl.handle.net/2117/97955
Analysis and synthesis of textures through the inference of Boolean functions
Domínguez Pumar, Manuel; Torres Urgell, Lluís
This work deals with Boolean functions of non-linear and linear basis. The Boolean random functions of non-linear basis were proposed by Serra (1988,1989). These functions are generated through a Poisson point process upon which a family of independent functions, called germ functions, are installed. This process of installation consists in taking the Sup (supremum), point to point, of the result of placing the germ functions upon the points of the Poisson process. Boolean functions of linear basis, which are defined and proposed in this paper, are generated in the same manner as the non-linear functions but with a modified installation process. Instead of taking the Sup point to point, the sum point to point is defined. So the process is then equivalent to the convolution of a Poisson train of deltas with a random pulse. The aim of this paper is to analyse textures through these two models, in order to infere their genetics through a given realisation of the process, i.e., to analyse the complete statistics of the germ functions and the density of the associated Poisson process in order to characterise a given texture. Experiments and results are provided which prove that the real textures can be understood as realisations of Boolean random functions (of linear and non-linear basis), and that it has been possible to infere the genetics of unidimensional Boolean random functions of linear basis with the algorithm proposed here. It has also been possible to do it with non-linear Boolean functions but only by imposing two restrictive conditions on the genetics of the realisation.
2016-12-09T15:57:51ZDomínguez Pumar, ManuelTorres Urgell, LluísThis work deals with Boolean functions of non-linear and linear basis. The Boolean random functions of non-linear basis were proposed by Serra (1988,1989). These functions are generated through a Poisson point process upon which a family of independent functions, called germ functions, are installed. This process of installation consists in taking the Sup (supremum), point to point, of the result of placing the germ functions upon the points of the Poisson process. Boolean functions of linear basis, which are defined and proposed in this paper, are generated in the same manner as the non-linear functions but with a modified installation process. Instead of taking the Sup point to point, the sum point to point is defined. So the process is then equivalent to the convolution of a Poisson train of deltas with a random pulse. The aim of this paper is to analyse textures through these two models, in order to infere their genetics through a given realisation of the process, i.e., to analyse the complete statistics of the germ functions and the density of the associated Poisson process in order to characterise a given texture. Experiments and results are provided which prove that the real textures can be understood as realisations of Boolean random functions (of linear and non-linear basis), and that it has been possible to infere the genetics of unidimensional Boolean random functions of linear basis with the algorithm proposed here. It has also been possible to do it with non-linear Boolean functions but only by imposing two restrictive conditions on the genetics of the realisation.Esquemas de acceso para sistemas móviles de tercera generación: cdma
http://hdl.handle.net/2117/97954
Esquemas de acceso para sistemas móviles de tercera generación: cdma
Díaz Romero, M. del Pilar
2016-12-09T15:53:26ZDíaz Romero, M. del Pilar