arXiv subjects

Lluis Torner

Publications and source records attributed to Lluis Torner.

At least 127 records · Page 7Linked to original sources

arXiv2008

Nonlinear photonic crystals near the supercollimation point

We uncover a strong coupling between nonlinearity and diffraction in a photonic crystal at the supercollimation point. We show this is modeled by a nonlinear diffraction term in a nonlinear schroedinger type equation, in which the properties of solitons are investigated. Linear stability analysis shows solitons are stable in an existence domain that obeys the Vakhitov-Kolokolov criterium. In addition, we investigate the influence of the nonlinear diffraction on soliton collision scenarios.

physics.optics↗

arXiv2008

Soliton modes, stability, and drift in optical lattices with spatially modulated nonlinearity

We put forward new properties of lattice solitons in materials and geometries where both, the linear refractive index and the nonlinearity are spatially modulated. We show that the interplay between linear and out-of-phase nonlinear refractive index modulations results in new soliton properties, including modifications of the soliton stability and transverse mobility, as well as shape transformations that may be controlled, e.g., by varying the light intensity.

physics.optics↗

arXiv2008

Propagation of solitons in thermal media with periodic nonlinearity

We address the existence and properties of solitons in layered thermal media made of alternating focusing and defocusing layers. Such structures support robust bright solitons even if the averaged nonlinearity is defocusing. We show that non-oscillating solitons may form in any of the focusing domains, even in those located close to the sample edge, in contrast to uniform thermal media where light beams always oscillate when not launched exactly on the sample center. Stable multipole solitons may include more than four spots in layered media.

physics.optics↗

arXiv2008

Nonlinear switching of low-index defect modes in photonic lattices

We address nonlinear signal switching between two low-index defect channels induced in periodic optical lattices. In contrast to conventional directional couplers, where the guiding mechanism is total internal reflection or refraction, in such Bragg-type coupler, the guidance is of a photonic-bandgap origin. The coupling length in the low-index coupler is controlled by the lattice parameters and by the channel spacing. In the nonlinear regime the Bragg-type coupler behaves as an all-optical switch, exhibiting a remarkable difference of switching power for focusing versus defocusing nonlinearity.

physics.optics↗

arXiv2008

Bragg guiding of domain-like nonlinear modes and kink arrays in lower-index core structures

We introduce a novel class of stable nonlinear modes trapped in a lower-index film core sandwiched between two optical lattices, or in the cylindrical core of a radial lattice, imprinted in defocusing media. Such family of nonlinear modes transforms into defect lattice solitons when the core width is sufficiently small or into an array of kinks when the width is large enough. We find that higher-order modes with multiple zeros inside the guiding core can be stable in one-dimensional settings.

physics.optics↗

arXiv2008

Brownian soliton motion

We reveal fundamental analogies between soliton dynamics in light-induced random photonic lattices and Brownian motion of particles. In particular, we discover that the average squared soliton displacement increases linearly with distance after an initial ballistic regime of propagation. We also find that in shallow lattices the average soliton displacement grows linearly with increasing lattice depth.

physics.optics↗

arXiv2008

Stabilization of dipole solitons in nonlocal nonlinear media

We address the stabilization of dipole solitons in nonlocal nonlinear materials by two different approaches. First, we study the properties of such solitons in thermal nonlinear media, where the refractive index landscapes induced by laser beams strongly depend on the boundary conditions and on the sample geometry. We show how the sample geometry impacts the stability of higher-order solitons in thermal nonlinear media and reveal that dipole solitons can be made dynami-cally stable in rectangular geometries in contrast to their counterparts in thermal samples with square cross-section. Second, we discuss the impact of the saturation of the nonlocal nonlinear response on the properties of multipole solitons. We find that the saturable response also stabi-lizes dipole solitons even in symmetric geometries, provided that the input power exceeds a criti-cal value.

nlin.PS↗

arXiv2008

Surface lattice solitons in diffusive nonlinear media

We address the properties of surface solitons supported by optical lattices imprinted in photorefractive media with asymmetric diffusion nonlinearity. Such solitons exist only in finite gaps of lattice spectrum. In contrast to latticeless geometries, where surface waves exist only when nonlinearity deflects light towards the material surface, the surface lattice solitons exist in settings where diffusion would cause beam bending against the surface.

physics.optics↗

arXiv2008

Nonlocal surface dipoles and vortices

We predict the existence and address the stability of two-dimensional surface solitons featuring topologically complex shapes, including dipoles, vortices, and bound states of vortex solitons, at the interface of nonlocal thermal media. Unlike their counterparts in bulk media, surface dipoles are found to be stable in the entire existence domain. Surface vortices are found to exhibit strongly asymmetric intensity and phase distributions, and are shown to be stable, too. Bound states of surface vortex solitons belong to a novel class of surface solitons having no counterparts in bulk media. Such states are found to be stable provided that their energy flow does not exceed an upper threshold. Our findings constitute the first known example of topologically complex solitons located at nonlocal two-dimensional interfaces.

nlin.PS↗

arXiv2008

Optical surface waves supported and controlled by thermal waves

We address the formation of optical surface waves at the very edge of semiconductor materials illuminated by modulated light beams that generate thermal waves rapidly fading in the bulk material. We find families of thresholdless surface waves which existing due to the combined action of thermally-induced refractive index modulations and instantaneous Kerr-type nonlinearity.

physics.optics↗

arXiv2007

Surface solitons in two-dimensional chirped photonic lattices

We study surface modes in semi-infinite chirped two-dimensional photonic lattices in the frame- work of an effective discrete nonlinear model. We demonstrate that the lattice chirp can change dramatically the conditions for the mode localization near the surface, and we find numerically the families of surface modes, in linear lattices, and discrete surface solitons, in nonlinear lattices. We demonstrate that, in a sharp contrast to one-dimensional discrete surface solitons, in two-dimensional lattices the mode threshold power is lowered by the action of both the surface and lattice chirp. By manipulating with the lattice chirp, we can control the mode position and its localization.

nlin.PS↗

arXiv2007

Highly-asymmetric soliton complexes in parabolic optical lattices

We introduce multipole soliton complexes in optical lattices induced by nondiffracting parabolic beams. Despite the symmetry-breaking dictated by the curvature of the lattice channels, we find that complex, asymmetric higher-order states can be stable. The unique topology of parabolic lattices affords new types of soliton motion: single solitons launched into the lattice with nonzero transverse momentum perform periodic oscillations along parabolic paths.

physics.optics↗

arXiv2007

Ring surface waves in thermal nonlinear media

We address ring-shaped surface waves supported by defocusing thermal media with circular cross-section. Such waves exist because of the balance between repulsion from the interface and deflection of light from the bulk medium due to defocusing nonlocal nonlinearity. The properties of such surface waves are determined by the geometry of the sample. Nodeless ring surface waves are stable for all values of their winding number, while surface waves with a small number of azimuthal nodes can be metastable.

physics.optics↗

arXiv2007

Resonant mode flopping in modulated waveguiding structures

We put forward the concept of resonant, Rabi-like flopping and adiabatic transitions between confined light modes in properly modulated multimode waveguides. The phenomenon is shown to take place in both, the linear and the nonlinear regimes. In addition, we find that the mode transitions occur not only in simple geometries, but also in complex confining multimode structures. The phenomenon is analogous to the familiar stimulated state transitions that occur in multilevel quantum systems.

physics.optics↗

arXiv2007

Soliton percolation in random optical lattices

We introduce soliton percolation phenomena in the nonlinear transport of light packets in suitable optical lattices with random properties. Specifically, we address lattices with a gradient of the refractive index in the transverse plane, featuring stochastic phase or amplitude fluctuations, and we discover the existence of a disorder-induced transition between soliton-insu-lator and soliton-conductor regimes. The soliton current is found to reach its maximal value at intermediate disorder levels and to drastically decrease in both, almost regular and strongly disordered lattices.

physics.optics↗

arXiv2007

Dynamics of surface solitons at the edge of chirped optical lattices

We address soliton formation at the edge of chirped optical lattices imprinted in Kerr-type nonlinear media. We find families of power thresholdless surface waves that do not exist at other types of lattice interfaces. Such solitons form due to combined action of internal reflection at the interface, distributed Bragg-type reflection, and focusing nonlinearity. Remarkably, we discover that surfaces of chirped lattices are soliton attractors: Below an energy threshold, solitons launched well within the lattice self-bend toward the interface, and then stick to it.

physics.optics↗

arXiv2007

Enhanced soliton interactions by inhomogeneous nonlocality and nonlinearity

We address the interactions between optical solitons in the system with longitudinally varying nonlocality degree and nonlinearity strength. We consider a physical model describing light propagation in nematic liquid crystals featuring a strongly nonlocal nonlinear response. We reveal that the variation of the nonlocality and nonlinearity along the propagation direction can substantially enhance or weaken the interaction between out-of-phase solitons. This phenomenon manifests itself as a slowdown or acceleration of the soliton collision dynamics in one-dimensional geometries or of the soliton spiraling rate in bulk media. Therefore, one finds that by engineering the nonlocality and nonlinearity variation rate one can control the output soliton location.

nlin.PS↗

arXiv2007

Rotating surface solitons

We introduce a novel type of surface waves that form at the edge of guiding structures consisting of several concentric rings. Such surface waves rotate steadily upon propagation and, in contrast to nonrotating waves, for high rotation frequencies they do not exhibit power thresholds for their existence. There exists an upper limit for the surface wave ro-tation frequency, which depends on the radius of the outer guiding ring and on its depth.

physics.optics↗