José R. Salgueiro

Making optical vortices with computer-generated holograms

An optical vortex is a screw dislocation in a light field that carries quantized orbital angular momentum and, due to cancellations of the twisting along the propagation axis, experiences zero intensity at its center. When viewed in a perpendicular plane along the propagation axis, the vortex appears as a dark region in the center surrounded by a bright concentric ring of light. We give detailed instructions for generating optical vortices and optical vortex structures by computer-generated holograms and describe various methods for manipulating the resulting structures.

Nonlinear plasmonic directional couplers

A study on the nonlinear modes of plasmonic directional couplers created by two nonlinear dielectric slot waveguides with metallic claddings is presented. The calculated power diagram shows substantial differences from the case of nonlinear dielectric couplers. The power-dependent switching and the effect of losses on the coupler performance are studied using finite-difference time-domain numerical simulations.

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.

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.

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.

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.

Controllable scattering of vector Bose-Einstein solitons

We show the possibility of producing matter-wave switching devices by using Manakov interactions between vector matter-wave solitons using two-species Bose-Einstein condensates (BECs). Our results establish the experimental parameters for three interaction regimes in two-species BECs: symmetric and asymmetric splitting, down-switching, and up-switching. We have studied the dependence upon the initial conditions and the kind of interaction between the two matter-wave solitons.

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.

3D printing of Al2O3 photonic crystals for terahertz frequencies

Reported here is the fabrication and characterization of a three-dimensional photonic crystal for terahertz frequencies based on 3D printing of Al2O3. Specific inks containing Al2O3, the material required for the structure, are synthesized with the viscosity and rheological properties necessary to be extruded through nozzles of micrometric section. The process is completed by a thermal sintering to obtain compact structures. SEM measurements are performed to evaluate the quality of the structures and measure the geometrical parameters. Finally, the presence of the band gap is demonstrated by THz time-domain spectroscopy.

Complex modes in plasmonic nonlinear slot waveguides

We analyze linear and nonlinear modes of metal–dielectric–metal slot waveguides taking into account the effect of losses at the metallic cladding. First, we study a linear core and then assume it to be nonlinear with a Kerr-type nonlinear response. In the linear case, we summarize the earlier results of the frequency dispersion analysis showing the mode transformation when losses are increasing. For the nonlinear case, after a brief review of the earlier results on the lossless plasmonic slot waveguides, we demonstrate that losses lead to the existence of complex nonlinear modes which we describe through the dependence of mode power on the propagation constant. We show that losses bring many novel features into this nonlinear system resulting in novel bifurcations and novel types of nonlinear guided modes, as well as the existence of limiting values for the propagation constant and the modes with an unlimited power. We also study the mode stability by means of numerical simulation using the finite difference time domain method.