Vitaly F. Rodriguez-Esquerre

Ge-Doped Defect-Core Microstructured Fiber Design by Genetic Algorithm for Residual Dispersion Compensation

A special microstructured optical fiber, which may be used in a wavelength-division-multiplexing (WDM) optical fiber transmission system for residual chromatic dispersion compensation, is designed and analyzed. The proposed structure is obtained by introducing a small Ge-doped core at the center of a conventional photonic crystal fiber. The behavior of the resulting geometry has been optimized by a genetic algorithm in conjunction with an efficient vectorial finite element formulation. Numerical results show that the designed photonic crystal fiber exhibits flattened negative dispersion over E + S + C + L + U wavelength bands with an average dispersion of - 212 ps ·km-1 ·nm-1.

Analysis of Straight Periodic Segmented Waveguide Using the 2-D Finite Element Method

A numerical analysis of periodic segmented waveguides (PSWs) using the 2-D finite element method (2D-FEM) in the frequency domain is presented. This method has significantly lower computational cost when compared with 3-D methods that have been used to model PSWs, and can also model back reflected signals. Unlike photonic crystal waveguides, light confinement in a PSW is due to total internal reflection as in a continuous waveguide (CWG). We show that the dispersion relation of the guided modes in PSW is strongly influenced by the dielectric periodicity along the waveguide. We calculate the mode profile of a PSW in a region far away from the bandgap and we showed that it is comparable to the mode profile of the equivalent CWG even for relatively high values of averaged refractive index contrast.

Power Coupling Optimization in 2D Waveguides by Evolutionary Algorithms

The power coupling efficiency between 2D continuous waveguides and periodic segmented subwavelength waveguides using a taper composed by a segmented waveguide section with variable segment lengths has been successfully and efficiently designed and optimized using evolutionary algorithms based on the artificial immune system and the genetic algorithm in conjunction with the frequency domain finite-element method. Coupling efficiencies higher than 90% have been achieved for both evolutionary algorithms. The impact of the mutation rates for the artificial immune system and the initial population number for the genetic algorithm has also been analyzed in detail. The coupling efficiency of the optimized structures as a function of the operating wavelength has also been analyzed considering the C-band.

Propagation characteristics analysis of subwavelength grating waveguides

The propagation characteristics of a subwavelength grating (SWG) waveguide are analyzed by an efficient frequency domain finite element approach. An equivalent continuous waveguide has been obtained for several duty cycles and for a wide bandwidth. A comparison of their electric field spatial distribution has been performed through an overlapping integral. An equivalent continuous waveguide can be considered for the analysis of SWGs.

Analysis and design of microstrip antennas by Artificial Neural Networks

The most common methods of analysis and design of microstrip antennas are the transmission line and the cavity model (analytical), that introduce some simplifications in the mechanisms of radiation from antennas, therefore, some errors are introduced in the determination of its main parameters. On the other hand, numerical methods, which are more accurate, require large computational resources, high processing time and an advanced electromagnetic knowledge. This work deals with the use of Artificial Neural Network (ANN), to represent the relationship between the antenna parameters (frequency, size and dielectric constant) for the analysis and design of several shapes of microstrip antennas.

Non-reciprocal optical devices based on linear silicon photonic crystals

Due to the promises of ultrahigh speed computation realized in the optical domain, great interest towards alloptical integrated systems has been shown. A great number of different types of optical logic gates have been proposed during the last years and the optical diode effect based on photonic crystal is of crucial importance in optical logic gates and computing integrated optical systems. The diode effect can be achieved by breaking the spatial inversion symmetry by various ways. Many different linear passive structures that exhibits optical isolation and unidirectional transmission behavior have been proposed, which exploit the properties of point defects, mode conversion and filtering, chirped structures or heterojunction slabs (two different 2D Photonic Crystals structures). Further improvements of these structures are here proposed and enhanced unidirectional behavior was achieved by optimization of the originally proposed structures where good optical isolation has been achieved. The results were obtained by efficient numerical simulations and it is shown that these devices are good candidates for building blocks of integrated optical systems.

Photonic Bandgap Inspection in 2-D Sublattices

Large photonic bandgaps (PBGs) have been obtained by sweeping linearly the parameters of complex sublattices inside the unitary cells of square- and triangular-lattice photonic crystals. An efficient frequency-domain finite-element method with periodical boundary conditions has been used for theoretical analyses. PBGs in silicon/air photonic crystals for both polarization modes have been considered for up to 21 eigenmodes and both low- and high-order PBGs have been obtained by this relatively simple systematic process.

Theoretical analysis of the minimization of thermal effects on the coupling length of directional couplers

The conditions to minimize or cancel the temperature effects on the coupling length of directional coupler have been analyzed considering the influence of the thermo-optic coefficient of their constituent materials on the coupler behavior.

Periodic segmented waveguide analysis by using the 2D finite element method

A numerical analysis of periodic segmented waveguides (PSWs) using the well known technique of two dimensional finite element method (2D-FEM) in the frequency domain is presented. Unlike photonic crystal waveguides (PCWs), light confinement in a PSW is due to total internal reflection as in a continuous waveguide (CWG). Moreover, the dispersion relation of the guided modes in PSW is strongly influenced by the dielectric periodicity along the waveguide. We calculate the mode profile of the PSW in a region far away from the band gap and compare with the mode profile of their equivalent CWG with an averaged refractive index contrast (Δneq).

Exploring photonic band gaps in sub-lattices in unitary cells in air/silicon

We have obtained large photonic band gaps by sweeping parameters of sub-lattices inside the unitary cells of square lattice photonic crystals. We have considered PBGs in silicon photonic crystals for both polarization modes.