arXiv subjects

A. Ferrando

Publications and source records attributed to A. Ferrando.

At least 19 recordsLinked to original sources

arXiv2025

Floquet states on disclinations

We show that periodic longitudinal modulation of waveguide arrays with disclination can result in the appearance of previously unexplored Floquet modes bound to the disclination core. Such modes arise due to oscillations of the waveguides in the array, periodically switching the structure between topological and trivial phases on each modulation period, so that on average it seems trivial. Localization of such modes depends on the amplitude of waveguide oscillations. Depending on the discrete rotational symmetry of the arrays with disclinations, these modes exhibit distinct spatial profiles unattainable in periodic lattices. Propagation in a medium with focusing cubic nonlinearity reveals that these Floquet states remain localized below a critical power threshold, indicating the possibility of the formation of disclination-bound Floquet solitons. Our results unveil a new regime of localization in photonic systems, bridging disclination topology, Floquet engineering, and nonlinearity.

physics.optics↗

arXiv2025

Observation of linear and nonlinear light trapping on topological dislocations

Topological dislocations in otherwise periodic lattices represent global structural defects that, nevertheless, typically leave the lattice periodicity intact far from the dislocation. Such dislocations arise in diverse physical systems ranging from crystalline solids, acoustic and photonic lattices and crystals to matter waves in optical lattices. Dislocations drastically affect the evolution of wave excitations in their vicinity, enabling novel mechanisms for trapping on topological defects and controlling the energy flow. Moreover, when combined with nonlinearity, such systems give rise to new types of self-sustained states of topological origin that have never been observed to date. Here we demonstrate experimentally, for the first time at optical frequencies, the waveguiding at various types of topological edge dislocations, resulting in the formation of localized photonic eigenstates with distinct and tunable shapes. Using femtosecond laser-writing techniques, we fabricated waveguide arrays with precisely tailored dislocation parameters, enabling full control over the degree of localization and internal structure of the associated modes. We further demonstrate both theoretically and experimentally that in the high-power regime, the families of thresholdless dislocation solitons bifurcate from such modes, which inherit shape diversity of their linear counterparts. Our results reveal a nontrivial interplay between nonlinearity and global lattice deformations and establish dislocation solitons as a new class of nonlinear topological states. They may stimulate the observation of new types of nonlinear states and interaction scenarios for excitations in nonlinear physical systems, where lattices with controllable global deformations can be created.

physics.optics↗

arXiv2025

Observation of Light Localization at the Edges of Quasicrystal Waveguide Arrays

Quasicrystals are unique systems that, unlike periodic structures, lack translational symmetry but exhibit long-range order dramatically enriching the system properties. While evolution of light in the bulk of photonic quasicrystals is well studied, experimental evidences of light localization near the edge of truncated photonic quasicrystal structures are practically absent. In this Letter, we observe both linear and nonlinear localization of light at the edges of radially cropped quasicrystal waveguide arrays, forming an aperiodic Penrose tiling. Our theoretical analysis reveals that for certain truncation radii, the system exhibits linear eigenstates localized at the edge of the truncated array, whereas for other radii, this localization does not occur, highlighting the significant influence of truncation on edge light localization. Using single-waveguide excitations, we experimentally confirm the presence of localized states in Penrose arrays inscribed by a femtosecond laser and investigate the effects of nonlinearity on these states. Our theoretical findings identify a family of edge solitons, and experimentally, we observe a transition from linear localized states to edge solitons as the power of the input pulse increases. Our results represent the first experimental demonstration of localization phenomena induced by the selective truncation of quasiperiodic photonic systems.

physics.optics↗

arXiv2022

A method for the dynamics of vortices in a Bose-Einstein condensate: analytical equations of the trajectories of phase singularities

We present a method to study the dynamics of a quasi-two dimensional Bose-Einstein condensate which contains initially many vortices at arbitrary locations. We present first the analytical solution of the dynamics in a homogeneous medium and in a parabolic trap for the ideal non-interacting case. For the homogeneous case this was introduced in the context of photonics. Here we discuss this case in the context of Bose-Einstein condensates and extend the analytical solution to the trapped case, for the first time. This linear case allows one to obtain the trajectories of the position of phase singularities present in the initial condensate along with time. Also, it allows one to predict some quantities of interest, such as the time at which a vortex and an antivortex contained in the initial condensate will merge. Secondly, the method is complemented with numerical simulations of the non-linear case. We use a numerical split-step simulation of the non-linear Gross-Pitaevskii equation to determine how these trajectories and quantities of interest are changed by the presence of interactions. We illustrate the method with several simple cases of interest both in the homogeneous and parabolically trapped systems.

cond-mat.quant-gas↗

arXiv2020

Nonlinear higher-order polariton topological insulator

We address the resonant response and bistability of the exciton-polariton corner states in a higher-order nonlinear topological insulator realized with kagome arrangement of microcavity pillars. Such states are resonantly excited and exist due to the balance between pump and losses, on the one hand, and between nonlinearity and dispersion in inhomogeneous potential landscape, on the other hand, for pump energy around eigen-energies of corresponding linear localized modes. Localization of the nonlinear corner states in a higher-order topological insulator can be efficiently controlled by tuning pump energy. We link the mechanism of corner state formation with symmetry of the truncated kagome array. Corner states coexist with densely packed edge states, but are well-isolated from them in energy. Nonlinear corner states persist even in the presence of perturbations in corner microcavity pillar.

physics.optics↗

arXiv2019

Graded-index optical fiber emulator of an interacting three-atom system: illumination control of particle statistics and classical non-separability

We show that a system of three trapped ultracold and strongly interacting atoms in one-dimension can be emulated using an optical fiber with a graded-index profile and thin metallic slabs. While the wave-nature of single quantum particles leads to direct and well known analogies with classical optics, for interacting many-particle systems with unrestricted statistics such analoga are not straightforward. Here we study the symmetries present in the fiber eigenstates by using discrete group theory and show that, by spatially modulating the incident field, one can select the atomic statistics, i.e., emulate a system of three bosons, fermions or two bosons or fermions plus an additional distinguishable particle. We also show that the optical system is able to produce classical non-separability resembling that found in the analogous atomic system.

physics.optics↗

arXiv2017

Nonequilibrium quantum dynamics of partial symmetry breaking for ultracold bosons in an optical lattice ring trap

A vortex in a Bose-Einstein condensate on a ring undergoes quantum dynamics in response to a quantum quench in terms of partial symmetry breaking from a uniform lattice to a biperiodic one. Neither the current, a macroscopic measure, nor fidelity, a microscopic measure, exhibit critical behavior. Instead, the symmetry memory succeeds in identifying the point at which the system begins to forget its initial symmetry state. We further identify a symmetry energy difference in the low lying excited states which trends with the symmetry memory.

cond-mat.quant-gas↗

arXiv2016

Analytical solution for multisingular vortex Gaussian beams: The mathematical theory of scattering modes

We present a novel procedure to solve the Schr\"odinger equation, which in optics is the paraxial wave equation, with an initial multisingular vortex Gaussian beam. This initial condition has a number of singularities in a plane transversal to propagation embedded in a Gaussian beam. We use the scattering modes, which are solutions of the paraxial wave equation that can be combined straightforwardly to express the initial condition and therefore permit to solve the problem. To construct the scattering modes one needs to obtain a particular set of polynomials, which play an analogous role than Laguerre polynomials for Laguerre-Gaussian modes. We demonstrate here the recurrence relations needed to determine these polynomials. To stress the utility and strength of the method we solve first the problem of an initial Gaussian beam with two positive singularities and a negative one embedded in. We show that the solution permits one to obtain analytical expressions. These can used to obtain closed expressions for meaningful quantities, like the distance at which the positive and negative singularities merge, closing the loop of a vortex line. Furthermore, we present an example of calculation of an specific discrete-Gauss state, which is the solution of the diffraction of a Laguerre-Gauss state showing definite angular momentum (that is, a highly charged vortex) by a thin diffractive element showing certain discrete symmetry. We show that thereby this problem is solved in a much simpler way than using the previous procedure based in the integral Fresnel diffraction method.

physics.optics↗

arXiv2014

Supercontinuum optimization for dual-soliton based light sources using genetic algorithms in a Grid platform

We present a numerical strategy to design fiber based dual pulse light sources exhibiting two predefined spectral peaks in the anomalous group velocity dispersion regime. The frequency conversion is based on the soliton fission and soliton self-frequency shift occurring during supercontinuum generation. The optimization process is carried out by a genetic algorithm that provides the optimum input pulse parameters: wavelength, temporal width and peak power. This algorithm is implemented in a Grid platform in order to take advantage of distributed computing. These results are useful for optical coherence tomography applications where bell-shaped pulses located in the second near-infrared window are needed.

physics.optics↗

arXiv2013

Variational theory of soliplasmon resonances

We present a first-principles derivation of the variational equations describing the dynamics of the interaction of a spatial soliton and a surface plasmon polariton (SPP) propagating along a metal/dielectric interface. The variational ansatz is based on the existence of solutions exhibiting differentiated and spatially resolvable localized soliton and SPP components. These states, referred to as soliplasmons, can be physically understood as bound states of a soliton and a SPP. Their respective dispersion relations permit the existence of a resonant interaction between them, as pointed out in Ref.[1]. The existence of soliplasmon states and their interesting nonlinear resonant behavior has been validated already by full-vector simulations of the nonlinear Maxwell's equations, as reported in Ref.[2]. Here, we provide the theoretical demonstration of the nonlinear resonator model previously introduced in our previous work and analyze all the approximations needed to obtain it. We also provide some extensions of the model to improve its applicability.

nlin.PS↗

arXiv2012

Symmetry breaking and singularity structure in Bose-Einstein condensates

We determine the trajectories of vortex singularities that arise after a single vortex is broken by a discretely symmetric impulse in the context of Bose-Einstein condensates in a harmonic trap. The dynamics of these singularities are analyzed to determine the form of the imprinted motion. We find that the symmetry-breaking process introduces two effective forces: a repulsive harmonic force that causes the daughter trajectories to be ejected from the parent singularity, and a Magnus force that introduces a torque about the axis of symmetry. For the analytical non-interacting case we find that the parent singularity is reconstructed from the daughter singularities after one period of the trapping frequency. The interactions between singularities in the weakly interacting system do not allow the parent vortex to be reconstructed. Analytic trajectories were compared to the actual minima of the wavefunction, showing less 0.5% error for impulse strength of (v=0.00005). We show that these solutions are valid within the impulse regime for various impulse strengths using numerical integration of the Gross-Pitaevskii equation. We also show that the actual duration of the symmetry breaking potential does not significantly change the dynamics of the system as long as the strength is below (v=0.0005).

cond-mat.quant-gas↗

arXiv2009

Continuum generation by dark solitons

We demonstrate that the dark soliton trains in optical fibers with a zero of the group velocity dispersion can generate broad spectral distribution (continuum) associated with the resonant dispersive radiation emitted by solitons. This radiation is either enhanced or suppressed by the Raman scattering depending on the sign of the third order dispersion.

physics.optics↗

arXiv2008

A topological charge selection rule for phase singularities

We present an study of the dynamics and decay pattern of phase singularities due to the action of a system with a discrete rotational symmetry of finite order. A topological charge conservation rule is identified. The role played by the underlying symmetry is emphasized. An effective model describing the short range dynamics of the vortex clusters has been designed. A method to engineer any desired configuration of clusters of phase singularities is proposed. Its flexibility to create and control clusters of vortices is discussed.

nlin.PS↗

arXiv2008

Resonant Plasmon-Soliton Interaction

We describe an effective resonant interaction between two localized wave modes of different nature: a plasmon-polariton at a metal surface and a self-focusing beam (spatial soliton) in a non-linear dielectric medium. Propagating in the same direction, they represent an exotic coupled-waveguide system, where the resonant interaction is controlled by the soliton amplitude. This non-linear system manifests hybridized plasmon-soliton eigenmodes, mutual conversion, and non-adiabatic switching, which offer exciting opportunities for manipulation of plasmons via spatial solitons.

physics.optics↗

arXiv2008

Angular Pseudomomentum Theory for the Generalized Nonlinear Schr\"{o}dinger Equation in Discrete Rotational Symmetry Media

We develop a complete mathematical theory for the symmetrical solutions of the generalized nonlinear Schr\"odinger equation based on the new concept of angular pseudomomentum. We consider the symmetric solitons of a generalized nonlinear Schr\"odinger equation with a nonlinearity depending on the modulus of the field. We provide a rigorous proof of a set of mathematical results justifying that these solitons can be classified according to the irreducible representations of a discrete group. Then we extend this theory to non-stationary solutions and study the relationship between angular momentum and pseudomomentum. We illustrate these theoretical results with numerical examples. Finally, we explore the possibilities of the generalization of the previous framework to the quantum limit.

nlin.PS↗

arXiv2008

Noncommutative space and the low-energy physics of quasicrystals

We prove that the effective low-energy, nonlinear Schroedinger equation for a particle in the presence of a quasiperiodic potential is the potential-free, nonlinear Schroedinger equation on noncommutative space. Thus quasiperiodicity of the potential can be traded for space noncommutativity when describing the envelope wave of the initial quasiperiodic wave.

math-ph↗

arXiv2004

Nodal solitons and the nonlinear breaking of discrete symmetry

We present a new type of soliton solutions in nonlinear photonic systems with discrete point-symmetry. These solitons have their origin in a novel mechanism of breaking of discrete symmetry by the presence of nonlinearities. These so-called nodal solitons are characterized by nodal lines determined by the discrete symmetry of the system. Our physical realization of such a system is a 2D nonlinear photonic crystal fiber owning C6v symmetry.

nlin.PS↗

arXiv1998

Full-vector analysis of a realistic photonic crystal fiber

We analyze the guiding problem in a realistic photonic crystal fiber using a novel full-vector modal technique, a biorthogonal modal method based on the nonselfadjoint character of the electromagnetic propagation in a fiber. Dispersion curves of guided modes for different fiber structural parameters are calculated along with the 2D transverse intensity distribution of the fundamental mode. Our results match those achieved in recent experiments, where the feasibility of this type of fiber was shown.

physics.optics↗