Date: August 3, 2010
Time: 10 am to 11 am
Location: Bahen Centre for Information Technology, Room 1180
Speaker: Professor B. M. Azizur Rahman, City University London
Abstract: As optical technology has reached maturity, the associated devices have themselves become more complex. The optimization of such advanced devices requires an accurate knowledge of their lightwave propagation characteristics and their dependence on the system fabrication parameters. The optimization of existing realistic designs or the evaluation of new designs for optoelectronic devices and sub-systems has created significant interest in the development and use of effective numerical methods, as simple analytical approaches are often inadequate. Of the different numerical approaches for modal solutions reported so far, the finite element method (FEM) has been established as one of the most powerful and versatile methods.
Over the last two decades this technique has been used to characterize a wide range of waveguides. In the finite element approach, the problem domain is suitably divided into a patchwork of a finite number of subregions called elements. Each element can have a different shape and size and using many elements, a complex problem can be accurately represented. A wide range of photonic devices with more complex shapes can be modelled as each element can be considered to have different optical parameters such as refractive index, anisotropic tensors, nonlinearity, and loss or gain factors. Many important photonic devices, such as optical modulators, filters, polarization splitters, polarization rotators, and power splitters, may be fabricated by combining several butt-coupled uniform waveguide sections.
To design and analyse such photonic devices, it is important to use a junction analysis program in association with a modal analysis program. One of the most rigorous approaches, the least squares boundary residual (LSBR) method, has been developed by the speaker. On the other hand, to simulate the propagation of optical waves through a z-dependent linear or nonlinear structure, the finite element-based beam propagation method (BPM) has been developed using a fully vectorial approach with a difference scheme along the axial directions. Such an approach is particularly useful in the characterization of tapered sections, such as up-tapered SOA or down-tapered SSC, and Y and X junctions and nonlinear optical devices.
More recently, the FE-based time domain approach is being developed to study devices with strong reflections. Numerically simulated results for many important guided-wave photonic devices, using the full vectorial finite element-based approaches, will be presented, such as photonic crystal fibres, silicon nanowires, plasmonic metal structures, photonic crystals, THz waveguides, high-speed modulators, spot-size converters, optical polarizers, and polarization rotators.
Professor B. M. Azizur Rahman received his PhD from University College London in 1982 and is now a full Professor at City University London. At City University, he leads a research group of 12 post-docs and PhD students, working on Photonics Modelling, specialising in the development and use of rigorous and full-vectorial numerical approaches for the design, analysis and optimization of a wide range of photonic devices. He has published more than 350 journal and conference papers, and his journal papers have been cited more than 1600 times. He is a senior member of IEEE (USA), a member of the Optical Society of America, SPIE, and IET (UK). He can be reached at B.M.A.Rahman@city.ac.uk.
The talk is hosted by IOS, IEEE, and ECTI.