Ben-Hur V. Borges

Split-field PML implementations for the unconditionally stable LOD-FDTD method

We introduce and compare two split-field implementations of the perfectly matched layer (PML) for the unconditionally stable locally one-dimensional (LOD) finite-difference time-domain (FDTD) method. The LOD-FDTD formalism is expanded in terms of a symmetric source implementation. It is verified that the relative performance of both PML implementations is superior to the split PML performance in the alternating direction implicit (ADI) FDTD method

Analysis of High-Speed Optical Wavelength/Time CDMA Networks Using Pulse-Position Modulation and Forward Error Correction Techniques

This paper presents a comprehensive analysis of an optical code-division multiple access (OCDMA) network based on two distinct modulation formats, namely ON-OFF keying (OOK) and pulse-position modulation (PPM). We also investigate how each of these modulation formats performs under two distinct 2-D coding schemes, i.e., single-pulse per row (SPR) and multiple-pulse per row (MPR). For both cases, we have accounted for the simultaneous effect of many different dispersion and noise mechanisms (including multiple access interference (MAI) that impair the overall system performance. We have included the laser relative intensity noise at the transmitter side, the fiber dispersive effects (group velocity dispersion (GVD), and first-order polarization-mode dispersion (PMD), and beat, avalanche photodiode (APD), and thermal noises at the receiver side. The effect of GVD and PMD, as well as the influence of noises, on the performance of SPR and MPR codes is also investigated. Another effect studied in this paper is the influence of the APD photodetector on the beat noise of an incoherent OCDMA network. To mitigate systems noises and bit error rate (BER), we have adopted a forward error correction (FEC) RS(255, 239) algorithm in both networks investigated here. New expressions for the BER with all noises and dispersion mechanisms were also derived for the SPR and MPR code schemes. Results indicated that OOK and PPM modulation schemes without additional mechanisms to mitigate MAI and other noise effects are not sufficient to accommodate 32 simultaneous users in an error-free environment (BER < 10-12). This occurs due to the already high BER at the FEC input, which severely affects FECs at the receiver side.

An Extended FDTD Method for the Analysis of Electromagnetic Field Rotators and Cloaking Devices

This paper presents a dispersive finite difference time domain (FDTD) method suitable for the analysis of electromagnetic field rotator (and cloaking) devices. The method employs a coordinate transformation which accurately accounts for the radial dependence of the permittivity and permeability tensors, with Drude material models applied to the respective diagonal elements. The key aspect of the present formulation is the inclusion of the radial dependence of the plasma frequency, which makes this formalism quite attractive for the modeling of a general class of cloaking and field rotator geometries. Firstly, the method is validated by comparing its results with a previously published simulation of a cloaking device. Then, it is applied for the first time to the analysis of dispersive effects on the performance of field rotators.

Theoretical analysis of supercontinuum generation in a highly birefringent D-shaped microstructured optical fiber

This paper carries out a rigorous analysis of supercontinuum generation in an improved highly asymmetric microstructured fiber (MF) design. This geometry, defined simply as D-MF, has the advantage of being produced with a regular stacking and drawing technology. We have obtained birefringence values on the order of 4.87x10(-3) at the adopted pump wavelength and a significantly smaller effective area when compared to a whole MF, which makes this fiber quite attractive for SCG. Therefore, this D-MF design is a promising alternative for SCG since it provides new degrees of freedom to control field confinement, birefringence, and dispersion characteristics of MFs.

Influence of film thickness on the optical transmission through subwavelength single slits in metallic thin films

Silver and gold films with thicknesses in the range of 120-450 nm were evaporated onto glass substrates. A sequence of slits with widths varying between 70 and 270 nm was milled in the films using a focused gallium ion beam. We have undertaken high-resolution measurements of the optical transmission through the single slits with 488.0 nm (for Ag) and 632.8 nm (for Au) laser sources aligned to the optical axis of a microscope. Based on the present experimental results, it was possible to observe that (1) the slit transmission is notably affected by the film thickness, which presents a damped oscillatory behavior as the thickness is augmented, and (2) the transmission increases linearly with increasing slit width for a fixed film thickness.

A new full-vectorial FD-BPM scheme: application to the analysis of magnetooptic and nonlinear saturable media

A new three-dimensional (3-D) full-vectorial finite-difference (FD)-based beam-propagation method (BPM) is introduced for the analysis of magnetooptic and nonlinear materials. The refractive-index growth in the nonlinear material is allowed to saturate at high optical power densities (cubic-quintic media). The new formalism is capable of handling any combination of linear, nonlinear, and magnetooptic media, and combines, for the first time, the alternating-direction implicit technique (to improve computational performance) with the leapfrog longitudinal scheme (to simplify the solution of the coupled equations for transverse field components). The result is a numerical method that is both computationally efficient and numerically robust. The proposed BPM formalism is applied to investigate a (nonreciprocal) magnetooptic rib waveguide, as well as the new striking phenomena of light condensates propagation in cubic-quintic (saturable) media, the dynamics of which resemble those of liquid droplets.

A Study on Unconditionally Stable FDTD Methods for the Modeling of Metamaterials

We assess the performance of three unconditionally stable finite-difference time-domain (FDTD) methods for the modeling of doubly dispersive metamaterials: 1) locally one-dimensional FDTD; 2) locally one-dimensional FDTD with Strang splitting; and (3) alternating direction implicit FDTD. We use both double-negative media and zero-index media as benchmarks.

Coupled-mode analysis of highly asymmetric directional couplers with periodic perturbation

This paper presents an in-depth analysis of highly asymmetric grating assisted directional couplers. The directional coupler consists of a polymer waveguide with dimensions and refractive indices closely matching a single-mode fiber fabricated atop a Ga/sub 0.6/Al/sub 0.4/As/GaAs/Ga/sub 0.4/Al/sub 0.6/As waveguide. The structure is investigated analytically by means of a new orthogonal coupled-mode theory formulated in terms of the Lorentz reciprocity theorem. For the first time, the analysis includes three distinct loss mechanisms, namely, the leakage of power toward the semiconductor substrate, the power lost to radiation modes (mode mismatching), and the grating radiation loss.

An improved wide-angle FD-BPM for nonlinear and nonreciprocal waveguides

An improved wide-angle finite-difference beam-propagation method for the simulation of multifunction optical waveguides employing simultaneously nonlinear and nonreciprocal materials is introduced in this paper. This formalism can be applied to nonlinear Kerr-type materials exhibiting any kind of nonlinearity mechanisms. The nonreciprocal behavior is based on the difference between forward and backward propagation constants for TM modes. The z derivatives of the inverse permittivity are also taken into account so that longitudinal varying structures can be more accurately simulated.

Throughput Performance Evaluation of Multiservice Multirate OCDMA in Flexible Networks

In this paper, new analytical formalisms to evaluate the packet throughput of multiservice multirate slotted ALOHA optical code-division multiple-access (OCDMA) networks are proposed. The proposed formalisms can be successfully applied to 1-D and 2-D OCDMA networks with any number of user classes in the system. The bit error rate (BER) and packet correct probability expressions are derived, considering the multiple-access interference as binomially distributed. Packet throughput expressions, on the other hand, are derived considering Poisson, binomial, and Markov chain approaches for the composite packet arrivals distributions, with the latter defined as benchmark. A throughput performance evaluation is carried out for two distinct user code sequences separately, namely, 1-D and 2-D multiweight multilength optical orthogonal code (MWML-OOC). Numerical results show that the Poisson approach underestimates the throughput performance in unacceptable levels and incorrectly predicts the number of successfully received packets for most offered load values even in favorable conditions, such as for the 2-D MWML-OOC OCDMA network with a considerably large number of simultaneous users. On the other hand, the binomial approach proved to be more straightforward, computationally more efficient, and just as accurate as the Markov chain approach.