Polygons of quantized vortices in Bose-Einstein condensates with a circular trap.

We consider a disk-shaped cold atom Bose-Einstein condensate with repulsive atom-atom interactions within a circular trap, described by a two-dimensional time-dependent Gross-Pitaevskii equation with cubic nonlinearity and a circular box potential. In this setup, we discuss the existence of a type of stationary nonlinear waves with propagation-invariant density profiles, consisting of vortices located at the vertices of a regular polygon with or without an antivortex at its center. These polygons rotate around the center of the system and we provide approximate expressions for their angular velocity.

Energy- and time-controlled switching of ultrashort pulses in nonlinear directional plasmonic couplers.

We propose an ultracompact nonlinear plasmonic directional coupler for switching of ultrashort optical pulses. We show that this device can be used to control the routing of ultrashort pulses using either the energy or the duration of each individual pulse as switching parameters. The coupler is composed of two cores of a nonlinear dielectric material embedded into metallic claddings.

Vortex revivals and Fermi-Pasta-Ulam-Tsingou recurrence.

We study the self-trapped vortex-ring eigenstates of the two-dimensional Schrödinger equation with focusing Poisson and cubic nonlinearities. For each value of the topological charge l, there is a family of solutions depending on a parameter that can be understood as the relative importance of the cubic term. We analyze the perturbative stability of the solutions and simulate the fate of the unstable ones.

Remote photonic sensor to detect crude and refined oil.

This paper describes a low-cost fluorometer to detect and distinguish among different types of crude and refined oil. The device is based on the measurement of induced fluorescence using 280 and 390 nm LEDs as excitation sources and the design includes a low-cost lock-in amplifier to increase sensitivity. The sensor is able to send data remotely and is fully configurable via telecommands.

Nonlinear couplers with tapered plasmonic waveguides.

We suggest and demonstrate numerically that, by employing tapered waveguides in the geometry of a directional coupler, we can enhance dramatically the performance for optical switching of nonlinear plasmonic couplers operating at the nanoscale, overcoming the detrimental losses but preserving the subwavelength confinement. We demonstrate that, by an appropriate choice of the taper angle of the coupled metal-dielectric slot waveguides, we can compensate for the amplitude decrease and enhance the sharpness of the response for the switching operation.

Switching with vortex beams in nonlinear concentric couplers.

We demonstrate that a concentric ring coupler can be employed for nonlinear switching of the angular momentum of light carried by an optical vortex. We find different types of stationary vortex states in the nonlinear coupler and study coupling of both power and momentum of an optical vortex launched into one of the rings, demonstrating that the switching takes place well below the collapse threshold. The switching is more effective for the inner-ring excitation since it triggers more sharply and for the powers low enough to avoid the vortex instability and breakup.

Nonlinear dual-core photonic crystal fiber couplers.

We study nonlinear modes of dual-core photonic crystal fiber couplers made of a material with the focusing Kerr nonlinearity. We find numerically the profiles of symmetric, antisymmetric, and asymmetric nonlinear modes and analyze all-optical switching generated by the instability of the symmetric mode. We also describe elliptic spatial solitons controlled by the waveguide boundaries.

Stabilized vortices in layered Kerr media.

In this paper, we demonstrate the possibility of stabilizing beams with angular momentum propagating in Kerr media against filamentation and collapse. Very long propagation distances can be achieved by combining the choice of an appropriate layered medium with alternating focusing and defocusing nonlinearities with the presence of an incoherent guiding beam which is itself stabilized in this medium. The applicability of the results to the field of matter waves is also discussed.

Square vortex solitons with a large angular momentum.

We show the existence of square-shaped optical vortices with a large value of the angular momentum hosted in finite-size laser beams which propagate in nonlinear media with a cubic-quintic nonlinearity. The light profiles take the form of rings with sharp boundaries and variable sizes depending on the power carried. Our stability analysis shows that these light distributions remain stable when they propagate, probably for unlimited values of the angular momentum, provided the hosting beam is wide enough.

Single- and double-vortex vector solitons in self-focusing nonlinear media.

We study two-component spatial optical solitons carrying an angular momentum and propagating in a self-focusing saturable nonlinear medium. When one of the components is small, such vector solitons can be viewed as a self-trapped vortex beam that guides either the fundamental or first-order guided mode, and they are classified as single- and double-vortex vector solitons. For such composite vortex beams, we demonstrate that a large-amplitude guided mode can stabilize the ringlike vortex beam which usually decays due to azimuthal modulational instability.

Incoherent vector vortex-mode solitons in self-focusing nonlinear media.

We suggest a novel type of composite spatial optical soliton created by a coherent vortex beam guiding a partially incoherent light beam in a self-focusing nonlinear medium. We show that the incoherence of the guided mode may enhance, rather than suppress, the vortex azimuthal instability, and we also demonstrate strong destabilization of dipole-mode solitons by partially incoherent light.

Collisional dynamics of vortices in light condensates.

Through numerical simulation, we have studied the nucleation and annihilation of two-dimensional optical vortex solitons hosted in finite size light beams. Our study covers a wide range of angular momentum l> or =1, also referred to as its topological charge. We demonstrate that surface tension of light beams prevents beam filamentation for a certain range of total reflection angles even if the hosted hole splits and decays into several vortices with lower values of l.

Second-harmonic generation in vortex-induced waveguides.

We study the second-harmonic generation and localization of light in a reconfigurable waveguide induced by an optical vortex soliton in a defocusing Kerr medium. We show that the vortex-induced waveguide greatly improves conversion efficiency from the fundamental to the second-harmonic field.

Spatial optical solitons supported by mutual focusing.

We study composite spatial optical solitons supported by two-wave mutual focusing induced by cross-phase modulation in Kerr-like nonlinear media. We find the families of both single- and two-hump solitons and discuss their properties and stability. We also reveal remarkable similarities between recently predicted holographic solitons in photorefractive media and parametric solitons in quadratic nonlinear crystals.

Parametric vector solitons in tetragonal crystals.

We introduce novel types of spatial vector soliton that can be generated in anisotropic optical media, such as tetragonal crystals with third-order nonlinear susceptibility. We demonstrate that these vector solitons provide a nontrivial generalization to both conventional vector solitons of birefringent cubic media and parametric solitons supported by third-order cascaded nonlinearities.

Model of linewidth for laser writing on a photoresist.

We present a theoretical model to describe the feature size produced by direct laser writing upon a photoresist relative to various experimental parameters. The model allows the number of parameters required for describing the linewidth to be reduced and shows how the description can be made in terms of the ratio of laser power to writing velocity. Both of the limiting cases of the truncation of the laser beam are analyzed; i.