We present a tool for the simulation of active and passive photonic integrated circuits (PIC) based on EME (eigenmode
expansion) for modelling the details of circuit elements plus the travelling wave time domain (TWTD) technique for
connecting the circuit together and modelling non-linear elements such as SOAs. We show how the two algorithms can
be linked together using FIR filters to create a highly efficient PIC simulator. We discuss the strengths and weaknesses
of the approach and illustrate it with the simulation of a variety of active and passive examples.
A numerical optimization technique coupled with a finite element frequency domain solver was applied to a variety of
Si nanowire photonic devices in an attempt to improve transmissions or matching to predefined criteria. The
optimisation procedures are iterative in nature, in that they approach the optimal solution by exploring a sequence of
carefully selected points in the parameter space. For any optimisation procedure to be effective, a good optimiser needs
to be coupled with an efficient solver capable of modeling correctly all device configurations allowed by the parameter
space. In the case of electromagnetic problems, it is particularly important that the divergence free condition is obeyed.
The solver used here satisfies this condition and therefore greatly reduces the chances of the optimiser finding artificial
optimal solutions with incorrect field distributions. This FEFD is used by a deterministic global optimisation method,
which systematically subdivides the parameter space to split more quickly in regions most likely to contain an optimum.
Since the entire parameter space is eventually explored, this optimisation technique is not only guaranteed to
(eventually) find the globally optimal solution, but can also show other interesting local optima. As no gradient
information is required, the method works well even in the presence of the random errors typically occurring when
using Finite Element solvers where a unique optimised mesh is generated for each calculation.
We present structures obtained with numerical optimization techniques capable of efficiently channeling light at a fraction of the length of a conventional taper. These results could open the way to novel designs in ultra-short light injection devices. We also consider the rather different problem of how to optimise the transmission through a photonic crystal bend. We show how, using a deterministic global optimisation algorithm, novel optimal geometries can be obtained leading to considerable performance improvements.
With the rapid growth of the telecommunications industry over the last 5 to 10 years has come the need to solve ever more complex electromagnetic problems and to solve them more precisely than ever before. The basic EME (EigenMode Expansion) technique is a powerful method for calculation of electromagnetic propagation which has been well known amongst academic environments and also in microwave fields, representing the electromagnetic fields everywhere in terms of a basis set of local modes. It is at the same time a rigorous solution of Maxwell's Equations and is able to deal with very long structures. We discuss here progress that the authors and others have made recently in applying and extending it to integrated, fibre, and diffractive optics - including development of efficient ways of modelling tapers and other smoothly varying structures, new more efficient boundary conditions and improved mode finders. We outline the advantages it has over other techniques and also its limitations. We illustrate its application with a variety of real life examples, including diffractive elements, directional couplers, tapers, MMI's, bend modelling, periodic structures and others.
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