S.S.A. Obayya

New full-vectorial numerically efficient propagation algorithm based on the finite element method

A new full-vectorial beam propagation algorithm based on the versatile finite element method, in order to accurately characterize three-dimensional (3-D) optical guided-wave devices, is presented. The computationally efficient formulation is based on the two transverse components of the magnetic field without destroying the sparsity of the matrix equation. The robust perfectly matched layer (PML) boundary condition is incorporated into the formulation so as to effectively absorb the unwanted radiation out of the computational domain. The efficiency and precision of the proposed full-vectorial propagation approach is demonstrated through the analysis of single optical waveguide, directional couplers, and electrooptic modulator.

Design and characterization of compact single-section passive polarization rotator

In this paper an improved design for a short and low-loss polarization rotator is proposed, consisting of a single-section asymmetrical waveguide butt-coupled between two standard rib waveguides. At a wavelength of 1.55 /spl mu/m, nearly 100% polarization conversion ratio is obtained, with a relatively short (320 /spl mu/m) device length and an extremely low 0.5 dB total insertion loss. The simulation results are obtained using the full vectorial finite-element-based beam propagation, the junction analysis, and the modal solution approaches.

Fabrication tolerance study of a compact passive polarization rotator

In this paper, the expected performance of a compact low-loss passive polarization rotator is reported by using rigorous numerical approaches. The effects of waveguide width, slant angle, etch depth, and refractive index variations during its fabrication on the overall polarization conversion and polarization crosstalk are reported. It is also expected that over the 1.53to 1.61-/spl mu/m wavelength range, polarization conversion would be more than 99% and polarization crosstalk would be better than -20 dB.

Polarization conversion in passive deep-etched GaAs/AlGaAs waveguides

Experimental results are presented to demonstrate polarization conversion in passive deep-etched gallium arsenide waveguides. The effect due to process-dependent features of waveguide cross-section geometry, in particular the asymmetry resulting from nonvertical etching, is investigated. A qualitative agreement with vector finite element method (VFEM) simulations is shown. A coupled-mode formulation is used to describe the behavior. The results are compared with an elliptical-polarization analysis, obtained from measurements of the polarization angles of the fundamental waveguide modes and the difference between their effective indices. A novel technique used to carry out effective-index-difference measurements is reported

Full-vectorial finite-element beam propagation method for nonlinear directional coupler devices

A new full-vectorial beam propagation algorithm based on the computationally-efficient finite element method is presented which can accurately model nonlinear directional couplers. The robust perfectly matched layer boundary condition is incorporated into the formulation so as to effectively absorb the unwanted radiation out of the computational domain. The accuracy of the proposed vectorial propagation approach is demonstrated through comparison with other semivectorial approaches and the weaknesses of the commonly-used scalar approaches are highlighted. The proposed full-vectorial approach considers only two transverse components of the magnetic field without destroying the sparsity of the matrix equation, so it is numerically very efficient.

Novel polarization-independent optical bends for compact photonic integrated circuits

In this paper a novel polarization-independent optical waveguide bend has been designed, by using the full vectorial finite element-based beam propagation method. The influence of the guide thickness and the index contrasts on the radiation loss are also studied in some detail.

Modal Solutions for Square and Circular Rod Photonic Crystals by the Finite Element Method

Modal solutions for Photonic Crystal with circular and square shaped rods have been obtained using the Finite Element method. We compare the field distributions and effective indices with rod shape in the Photonic Crystal.

Rigorous numerical analysis of mode beating in tapered semiconductor amplifiers

The evolution of the optical beam profile along a high-power tapered semiconductor amplifier has been demonstrated by using rigorous and full-vectorial numerical approaches, based on the finite-element method. Numerically simulated results indicate the generation of many higher order modes, and their interference with the fundamental mode causes a variation of the optical beam, both along the transverse and the axial directions, which could significantly modify the output beam quality.

Designs of compact monolithically integrated semiconductor spot-size converters for efficient laser-fiber coupling

A rigorous numerical approach, based on the full vectorial finite element method, is used to design various types of monolithically integrated spot-size converters to achieve efficient coupling to standard single-moded optical fibers. Results are presented for tapered spot-size converters, spot-size converters employing two uniform non-identical phased matched guides and a compact MMI-based uniform structure.

Rigorous full vectorial finite element analysis of sharp optical waveguide corners

A novel and rigorous analysis of an abrput bend in a dielectric waveguide is presented, obtained by using a combination of the vector finite element method (FEM) formulation and the least squares boundary residual boundary (LSBR) method. The transmission efficiency of an optical wave through a guided-wave structure incorporating a sharp corner is investigated. After validating the newly developed numerical approach for a planar structure, results for a more realistic structure with a three-dimensional structure are also presented.