Christos Themistos

Characterization of Silver/Polystyrene (PS)-Coated Hollow Glass Waveguides at THz Frequency

Finite-element analysis based on the full-vectorial H-field formulation has been established as one of the most powerful and accurate modal solution approaches for optical guided-wave devices. Among the available optical waveguides, those incorporating thin metal layers supporting the surface plasmon modes (SPMs) and coupling of these modes to dielectric modes have recently been proven to be attractive for many applications. In this paper, the H-field approach incorporating the perturbation technique is used in calculating the complex propagation characteristics of silver/polystyrene (PS)-coated hollow glass waveguides for terahertz frequency radiation. The propagation and attenuation characteristics of the SPMs at the metal/dielectric interfaces are presented. The formation of the coupled supermodes and the effect of the PS coating thickness on the attenuation characteristics of these waveguides are also investigated and shown to be critical to their design optimization.

Characterization of metal-clad TE/TM mode splitters using the finite element method

A metal-clad directional coupler-based polarizer with two-dimensional (2-D) modal confinement has been designed and its performance has been rigorously computed by using the accurate vector H-field finite element method after taking into consideration the polarization-dependent coupling lengths, phase mismatchings and losses due to metal-cladding of the system involved.

Design considerations for an electrooptic directional coupler modulator

A rigorous numerical model is presented for an electrooptic directional coupler (DC) modulator. It was observed that it is possible for such a device to be optimized by the variation of a number of fabrication parameters. The applied field, the induced refractive index changes, and hence the change in the waveguide optical field due to the antisymmetric refractive index change are calculated for an elected structure. Finally, the product of switching voltage and coupling length, the power transfer efficiency, obtained using the least squares boundary residual (LSBR) method, and the optical loss due to the metal electrodes are also given.

Optimization of the optical properties of a deeply etched semiconductor electrooptic modulator

A rigorous numerical study of a deeply etched semiconductor electrooptic modulator is presented. A Laplace equation solver followed by a full-vectorial modal solution technique for general anisotropic optical waveguides, all based on the versatile finite-element method, is used to find the potential distribution, the modulating electric fields, the changes in the permittivity tensor associated with the electrooptic effect, and the different modes of propagation. In particular, the optimization of the optical properties of the modulator structure such as the half-wave voltage length product V/sub /spl pi//L and the optical losses due to the imperfectly conducting electrodes has been carefully carried out and results reported. In addition, the effect of the waveguide parameters on the microwave properties such as the microwave index n/sub m/ and characteristic impedance Z/sub c/ is explained.

Finite element analysis for lossy optical waveguides by using perturbation techniques

A finite element analysis, based on the variational procedure, is used to find the modal loss or gain for both the TE and TM modes with the application of the perturbation technique. Results for the modal gain for the buried heterostructure diode laser are presented, as well as the loss estimation for both the TE and TM modes for the asymmetrical multilayer metal-clad planar optical waveguides. The results obtained agree very well, for a wide range of loss/gain values, with the previously published work using alternative approaches.<<ETX>>

Characterization of Silica Nanowires for Optical Sensing

In this paper, the optical properties of silica nanowires in a Mach-Zehnder-based optical sensor for detecting biomaterial specimens have been studied using the full vectorial H-field formulation of the finite element method. The variation of the propagation constant, the power fraction in the composite nanowires with the variation of the nanowire size and the specimen refractive index, temperature, and wavelength are also presented.

Design issues of a multimode interference-based 3-dB splitter

We have investigated important issues such as the power loss, the loss imbalance the fabrication tolerances, and the wavelength dependence for the design of a multimode interference-based 3-dB splitter on deeply etched InP waveguides under general, restricted, and symmetric interference mechanisms. For this investigation, we used the finite-element-based beam propagation approach. Results are presented.

Finite Element Solutions of Surface-Plasmon Modes in Metal-Clad Dielectric Waveguides at THz Frequency

Finite element analysis, based on the vector H-field formulation and incorporating the perturbation technique, is used to calculate the complex propagation characteristics of metal-coated dielectric waveguides at terahertz frequencies. The propagation and attenuation characteristics of surface-plasmon modes (SPMs) at the metal/dielectric interfaces are presented. The effects on the modal properties of metal-clad dielectric guides with the cladding thickness and the formation of the supermodes due to coupling between the SPMs in the presence of different surrounding materials are also investigated

Finite-element analysis of surface-plasmon modes for lossy optical waveguides by the use of perturbation techniques

A finite-element analysis, with the aid of perturbation techniques, is used to determine the complex propagation characteristics of surface-plasmon modes that are supported by metal-dielectric interfaces. Symmetrical and nonsymmetrical three-layer optical waveguides incorporating a thin metal layer are studied, and the variations of the effective index and the attenuation constant with metal thicknesses are presented for both the short-range and long-range modes. Results are compared with previously published research, which was based on alternative approaches. Furthermore, for the first time to our knowledge, the complex propagation characteristics are presented for a coupled structure incorporating a surface-plasmon region with two-dimensional confinement.

Characterization of surface-plasmon modes in metal-clad optical waveguides

Finite-element analysis, based on the vector H-field formulation and incorporating the perturbation technique, is used to calculate the complex propagation characteristics of metal-coated dielectric waveguides. The propagation and attenuation characteristics of the surface-plasmon modes at the metal/dielectric interfaces are presented. The effects on the optical properties of metal-clad optical fibers with infinite and finite cladding thickness and the formation of the supermodes due to the coupling between the surface-plasmon modes in the presence of different surrounding materials are also investigated.