ABSTRACT:
With the advent of semiconductor lasers and low-loss optical fibres in mid 60s, the progress of optical technology has been significant in the field of optical communications. Recently, the novel photonic crystal fibre (PCF), showing great promise any may revolutionize the way we would transmits optical signals in the future. Spot-size converters, may alleviate the problem of coupling active devices with fibres, and accelerate the introduction of wide-band fibre-to-the-home. High-speed modulators have increased the data rate beyond 40 Gb/s, WDM technology allows dense multiplexing of many signal channels and optical amplifier to increase the span lengths.
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) [1] has been established as one of the most powerful and versatile methods. Over the last two decades this technique has been used to characterise 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, power splitters, etc 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 [2] 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 [3] 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, 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, would be presented, such as photonic crystal fibres, photonic crystals, THz waveguides, high-speed modulators, spot-size converters, optical polarizers and polarization rotators.
[1] B M A Rahman and J B Davies, J. Lightwave Tech., 2, pp.682-688, Oct. 1984.
[2] B M A Rahman and J B Davies, J. Lightwave Tech., 6, pp.52-57, 1988.
[3] S S A Obayya, B M A Rahman and H A El-Mikati, J. Lightwave Technol., pp.409-415, March 2000.
Brief Biography of Prof. B M A Rahman
Prof. B. M. Azizur Rahman received his PhD degree from University College London in 1982 and now a full Professor at City University London. At City University, he leads a large research group of 12 post-docs and PhD students, working on Photonics Modelling, specialised in the development and use of rigorous and full-vectorial numerical approaches to design, analyse and optimise 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 1400 times. He is a senior member of IEEE (USA), member of the Optical Society of America and IEE (UK).
School of Engineering and mathematical Sciences, City University, London EC1V 0HB, UK, Tel: +44-20-7040-8123 Telefax: +44-20-7040-8568 , Email: B.M.A.Rahman@city.ac.uk