P. Sewell

The application of porous silicon to optical waveguiding technology

The porosification of silicon can be achieved by the partial electrochemical dissolution (anodization) of the surface of a silicon wafer. The degree of porosity is dependent on the anodization parameters and can generally be controlled within the constraints imposed by substrate dopant type and concentration. Control of porosity leads to control of refractive index, and therein lies the concept of using porous silicon as an optical waveguide. We discuss porous silicon wavegides, for the visible to the infrared, produced by a number of approaches: 1) epitaxial growth onto porous silicon (where the porous layer acts as a substrate for a higher refractive index waveguide epilayer); 2) ion implantation (where either selective areas of high electrical resistivity can be produced, which act as a barrier against porosification, or where the surface of a porosified layer is amorphised to form a waveguide; 3) porous silicon multilayers (where the anodization parameters are periodically varied to produce alternate layers of different porosity and thus refractive index); and 4) oxidation of porous silicon (where a porosified layer is oxidized to form a graded-index, dense or porous, oxide waveguide).

The use of Unscented Transforms for statistical analysis in EMC

The use of unscented transforms UT for the statistical analysis of nonlinear linear problems is described. The UT methodology is then applied to the analysis of wire coupling within an enclosure which is a typical problem encountered in EMC studies. The UT results are compared with the more traditional Monte Carlo approach. It is demonstrated that UT is a powerful technique that can greatly improve the computation of the uncertainty encountered in many EMC studies.

Fast and accurate reflectivity calculations for shaped core optical fibres

A novel scalar (i.e. paraxial) free space radiation mode method is presented for calculating the normal incidence facet reflectivity of the main guided mode of a step-index optical fibre with generally shaped smooth core. Numerical results are presented and discussed for several cases of the Nth order super-elliptical core shape, including the circular, elliptical, rectangular-type and slab limiting cases.

The dispersion characteristics of oblique coordinate beam propagation algorithms

The use of an oblique coordinate system with the finite difference beam propagation method has previously been demonstrated to offer significant computational advantages over using rectangular coordinates for a wide range of practical optical structures. The effects of finite mesh resolution, step size, and order of the algorithm in terms of numerical dispersion and dissipation are here investigated and quantified for the first time.

Nonstandard beam propagation

A nonorthogonal coordinate system that extends the present range of angled configurations for which the beam propagation method (BPM) is accurate is introduced. This offers an extra degree of freedom within configuration and method when the BPM is applied in the design of general photonic integrated circuits incorporating angled waveguide sections.

The optical properties of chalcogenide glasses: From measurement to electromagnetic simulation tools

Chalcogenide glasses are promising candidate materials for a wide range of photonics applications. The design and realisation of optical components based on these materials requires detailed information on their optical properties, frequently over a range of wavelengths. In this paper we review experimental refractive index data for three chalcogenide glass compositions, and discuss how various numerical fits to the data prove useful within electromagnetic simulation tools.

Novel glass compositions and fabrication technologies for photonic integrated circuits

Heavy metal fluoride, chalcogenide, and fluoro-tellurite glasses proffer photonic integrated circuit functionality over a wide wavelength range, and combine high optical non-linearity with the ability to incorporate active dopants. The ability to access a range of glass compositions offers great flexibility in both design and processing. In this paper, we present fabrication methodologies for producing such novel glass-based waveguide components.

Wide angle beam propagation using oblique coordinates transformation

We propose a new wide-angle beam propagation algorithm based on an oblique coordinate transformation which extends the range of angled configurations for which beam propagation methods are accurate. This offers an extra degree of freedom within configuration and method when applying BPMs in the design of general photonic integrated circuits incorporating angled waveguide sections. The present oblique wide angle propagation technique is compared with the conventional wide angle BPM through numerical examples which are a tilted propagation in a dielectric waveguide and the diffraction of a focused Gaussian beam in a homogeneous medium.

Embedding Multiple Wires Within a Single TLM Node

Transmission Line Modelling, TLM, is an established technique for simulating electromagnetic fields in a wide variety of application areas. As with any numerical algorithm, the complexity of the problem that can be practically dealt with is determined by the availability of computational resources.

Simulation of Nonlinear Integrated Photonics Devices: A Comparison of TLM and Numerical Time Domain Integral Equation Approaches

The Time Domain Volterra Integral Equation method, TDVIE, and Transmission Line Modelling, TLM, are two approaches for simulating electromagnetic fields in a wide variety of application areas. While TLM is a well-established time-domain numerical technique, TDVIE is still in the early stages of testing. In this paper the main features of each approach are analysed and a direct comparison of the two methods presented, focusing on resonators, switches and non-linear materials in photonics. The objective is to illustrate the capability of the TDVIE approach and to establish guidelines for its selection in preference to TLM.