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Porous silicon offers many potential advantages for the realisation of optoelectronic circuits and systems. Foremost is the demonstration of photoluminescence [1] and solid state electroluminescent devices [2,3] which, when married with silicon based photodetectors and the well established electronic fabrication processes, has opened up the possibility for the realisation of monolithic all-silicon optoelectronic integrated circuits (OEIC’s). Another important feature is the ability to selectively produce insulating regions in CMOS circuitry by converting the porous silicon to silicon dioxide by oxidation. Oxidation of porous silicon also provides a new route to the realisation of the basic building block for all optoelectronic circuits - the optical waveguide.

Porous silicon is a widely studied material which has significant potential for the realisation of monolithic, all-silicon optoelectronic integrated circuits. To maintain monolithicity, irrespective of the light source technology used, silicon-based optical waveguides will be required, these enabling light from the source to be routed and split to different points, on-chip or otherwise. Although a number of silicon-based waveguide technologies are available, the aim of the present study is to highlight the use of, and flexibility afforded by, porous silicon as a waveguide medium.

EMC measurements are typically performed on an open area test site (OATS), in a screened room or in a special test cell designed to generate well defined electromagnetic waves. A screened room is a metal structure that provides high electromagnetic isolation up to high frequencies. The minimum size of enclosure that is acceptable must allow for the equipment under test (EUT), a minimum separation between the EUT and an antenna used as source or detector, and the thickness of any damping material. Small rooms might be employed to test table top equipment whereas larger rooms, with associated higher costs, may examine complete vehicles. The paper reviews, at a basic level, some electromagnetic issues underpinning test chamber measurement and principles.

Previous work on the validation of the transmission-line modelling (TLM) numerical modelling technique is further developed to investigate cavity backed apertures with inhomogeneous dielectric loading. To ensure general use, any method adopted for modelling such systems needs to be simple and generally applicable-TLM is such a method. This paper uses TLM to predict the performance of a cavity with a small amount of dielectric 'tuning' and compares the results to those obtained from experimental studies. Good agreement is obtained.

We report on the fabrication and optical assessment of an all-solid tellurite-glass photonic bandgap fiber. The manufacturing process via a preform drawing approach and the fiber characterization procedures are described and discussed. The fiber exhibits some minor morphological deformations that do not prevent the observation of optical confinement within the fiber by bandgap effects. The experimental fiber attenuation spectrum displays clear bandgap confinement regions whose positions are confirmed by modeling the guiding properties of the ideal geometry using a plane-wave expansion method. The model identifies the bound modes of the structure and provides confirmation of experimentally observed mode field profiles.

In this work the optoelectronic properties of InAs/GaSb superlattices are investigated. The k∙p method and four-band Kane model were used to calculate the electronic states in the structure at 0K. Superlattices with different period thickness and two types of interfaces were considered. In the calculations strain and nonparabolicity effects were taken into account. Transition energies and the corresponding cut-off wavelengths were determined.

Wires are the fundamental means of coupling electromagnetic energy to and from electrical equipment. It is therefore of great importance to the modelling of practical EMC phenomena that any modelling method used should efficiently model wires and wire-like structures. Transmission-line modelling (TLM) is a method used extensively for studying the behaviour of structures in order to derive their EMC performance. There has recently been an upsurge in the interest in efficient methods for wire modelling. This paper extends a general method for the accurate modelling of wires to the modelling of thin wires (wires with diameters smaller than the local node size) placed centrally within a node. A mechanism for modelling wires displaced from the centre of a node is also discussed. Results obtained from the TLM models are validated against those obtained from experimental studies.

It is shown that a finite difference method for numerically determining the propagation characteristics of optical waveguide devices can be extended to deal with structures containing complex refractive indices in a straightforward manner. The resulting complex finite difference method has been validated and its potential as a design tool demonstrated with studies of a silicon based p-i-n optical rib waveguide modulator and a semiconductor laser.

A rigorous implementation of Fourier operators is applied to the analysis of open dielectric waveguide devices. The method is exact and easily implemented using readily available numerical techniques. The method is applied to two problems of practical interest in integrated optics: (1) the analysis of reflection and transmission at a general slab waveguide discontinuity or as a special case, a laser facet; and (2) the scalar analysis of a rib waveguide. The solution is exact and a polarisation correction may be applied to yield polarised mode propagation constants.

Semiconductor waveguides are widely used in the field of integrated optics as the basis of active and passive devices. Since no analytical solution to the wave equation is available for rib, ridge or strip loaded structures many modelling techniques have been developed to analyze the guiding properties of these structures. These methods vary considerably in accuracy and ease of application. This paper considers two of these analysis methods, the Finite Difference (FD) Method and the Spectral Index (SI) Method, and notes that both approaches can be extended for use in the complex case ie when the local refractive index of the waveguide cross-section may become complex due to the presence of loss or gain. This gives rise to a complex propagation constant. Complex propagation constants obtained from the FD and SI methods are compared for the first time.

The progress, and current challenges, in fabricating rare-earth-doped chalcogenide-glass fibers for developing mid-infrared (IR) fiber lasers are reviewed. For the first time a coherent explanation is forwarded for the failure to date to develop a gallium-lanthanum-sulfide glass mid-IR fiber laser. For the more covalent chalcogenide glasses, the importance of optimizing the glass host and glass processing routes in order to minimize non-radiative decay and to avoid rare earth ion clustering and glass devitrification is discussed. For the first time a new idea is explored to explain an additional method of non-radiative depopulation of the excited state in the mid-IR that has not been properly recognized before: that of impurity multiphonon relaxation. Practical characterization of candidate selenide glasses is presented. Potential applications of mid-infrared fiber lasers are suggested.

This paper reports on two important issues that arise in the context of the global optimization of photonic components where large problem spaces must be investigated. The first is the implementation of a fast simulation method and associated matrix solver for assessing particular designs and the second, the strategies that a designer can adopt to control the size of the problem design space to reduce runtimes without compromising the convergence of the global optimization tool. For this study an analytical simulation method based on Mie scattering and a fast matrix solver exploiting the fast multipole method are combined with genetic algorithms (GAs). The impact of the approximations of the simulation method on the accuracy and runtime of individual design assessments and the consequent effects on the GA are also examined. An investigation of optimization strategies for controlling the design space size is conducted on two illustrative examples, namely, 60° and 90° waveguide bends based on photonic microstructures, and their effectiveness is analyzed in terms of a GA's ability to converge to the best solution within an acceptable timeframe. Finally, the paper describes some particular optimized solutions found in the course of this work.

We demonstrate the usefulness of the recently introduced modified Pade approximant operators for the solution of time-domain beam propagation problems. We show this both for a wideband method, which can take reflections into account, and for a split-step method for the modeling of ultrashort unidirectional pulses. The resulting approaches achieve high-order accuracy not only in space but also in time.

An elegant and accurate technique of interfacing segments of a uniform computational mesh with different spatial resolution is described. The technique is illustrated in the time-domain for a TLM mesh. Results show that a seamless interface is achieved between different mesh areas, thus allowing multi-scale problems to be accurately mapped onto the mesh.

A simple and intuitive TLM algorithm has been developed to model nonlinear optical phenomena in photonic bandgap structures such as fibre Bragg gratings. The method is used to simulate periodic nonlinear media having a Kerr nonlinearity. Many phenomena occuring in these devices, such as bistable switching, soliton propagation and limiting, are modelled and discussed. The numerical time-domain approach gives valuable insight into the behaviour of these devices.

The simulation of beam-wave interaction devices usually requires calculation of macroscopic source terms to allow for the contribution of electrons to the electromagnetic wave. In certain circumstances this approach may be problematic. This can be overcome if the beam-wave interaction is modelled using a TLM technique.

An exact Fourier operator transform method (F-OPT) is presented for finding the polarised mode propagation constants of a rib waveguide with any number of supporting layers and an arbitrary cladding. The implementation is of the order of one hundred times faster than the finite difference method for the same accuracy of the normalised propagation constant.

An all-link line symmetrical condensed node capable of modelling inhomogeneous materials is described. It is shown that it has significant advantages in storage and run time over the conventional stub-loaded symmetrical condensed node.

A method of interfacing field problems described by TLM to lumped parameter circuits is presented. The technique permits the study of the interaction of complex circuits with components described by a full field model. The procedure is illustrated by results obtained for a capacitive circuit where the capacitor is described by a two-dimensional TLM model.

Recent years have seen the rapid evolution of silicon-based optoelectronics. The absorption properties of Si1−xGex alloys make them excellent materials for the realisation of photodetectors operating at the near-infrared wavelengths of 1.3 and 1.55 μm which are important for fibre optic communication systems. An important design consideration for such systems is the efficient coupling of optical fibres to optoelectronic integrated circuits. A Si1−xGex rib waveguide spot-size transformer is presented that performs two essential roles: the transformation of the large spot fibre to a small spot waveguide mode, and subsequently the transfer of the mode from a passive Si waveguiding region to an active Si1−xGex region where optical absorption may occur. This transformation is accomplished by the use of a tapered waveguide structure. An analysis technique based on the spectral index method is used to investigate the local modal behaviour of the structure and experimental results confirm its successful operation.

New results are presented for the reflectivity of a buried waveguide at a realistic depth incident on a coated facet. Diffractive effects are shown to be significant enough to prevent previously reported two-layer coatings meeting the practical specifications for high performance semiconductor optical amplifiers.

With ever increasing safety and operating restrictions being imposed on high-performance military aircraft, space vehicles, missile technology and satellites, for example, it is of increasing importance to measure and quantify the performance of experimental procedures. All experiments are subject to some inherent inaccuracy or loading and a detailed knowledge of experimental repeatability can assist in determining the levels of acceptable experimental error. Validation of the results of one experimental technique against another using the method detailed, allows the potential benefit of assessing and, more importantly, locating common errors in both methods, thus providing a rigorous framework for confidence building. The validation technique can also be used to identify best practice in a situation where there are ill defined test plans. The authors illustrate how sets of experimental results can be compared and their differences quantified. Furthermore, the interpretation of these results allows rational decisions to be made regarding the quality of measurement techniques or facilities, allowing them to be used with a measured level of confidence.

The authors report a new self-aligned method for the fabrication of porous silicon optical waveguides which is simple and avoids the typical processing problems associated with the chemically-reactive nature of the porous silicon internal surface. The method is compatible with high temperature oxidation, enabling waveguides operating between visible (633 nm) and infra-red (1.3 /spl mu/m) to be fabricated.

A new spectral method is proposed and applied to the analysis and design of integrated optical spotsize transformers. Results presented are of the same accuracy as those from a finite difference method. The new method is simple, efficient and gives propagation constants and fields over a wide range of structures in seconds, making it well suited to the class of optical waveguide problems involving interacting rib and buried waveguides.

A novel beam propagation algorithm is presented that eliminates errors caused by modelling tapered optical structures with staircase approximations. In consequence, highly accurate results are obtained with a substantial improvement in computational efficiency. The algorithm is developed from a nonorthogonal co-ordinate system that intrinsically describes the taper geometry and can be implemented using conventional beam propagation techniques.

Scattering in the transmission-line modelling (TLM) method is determined for a variety of nodes using a simple, rigorous and physically satisfying process. The suggested method is simpler to apply, and more advantageous from the methodological and computational points of view compared to the conventional method.

A vector correction is derived to the propagation constants obtained from a polarised analysis of graded-index optical waveguides. This general formula is reduced to a form suitable for use with semiconductor rib and strip-loaded waveguides. Corrected propagation constants calculated for a range of semiconductor rib waveguide structures coincide with available results from a full vector approach. Moreover, the vector correction term is always small, underpinning the accuracy of this simple and fast polarised approach for the first time.

A radiation mode technique, first used in optical fibre theory, is used to study the propagation of waves in practical optoelectronic devices. The method is validated against other techniques for step discontinuities, tapers, air-gaps and Y junctions. The solution deals successfully with reflected waves and is found to be accurate enough to be used for design purposes.

A simple exact implementation of Fourier operators is introduced and used for analysing reflection and transmission at open dielectric waveguide discontinuities, including the laser facet. The method is stable, and readily implemented using standard numerical techniques.

A simple formula is derived which is applied as a quasi-TE- or quasi-TM-mode corrector to the propagation constant values obtained from a scalar treatment of semiconductor rib waveguides. The resulting polarised propagation constants agree favourably with well established benchmark values for both types of mode. The present approach offers advantages in the speed and simplicity of solution.

The use of transmission-line modelling (TLM) as a general tool for designing cavity applications for microwave heating purposes is discussed. This method is used to validate a recent procedure for designing rectangular cavities loaded with an inhomogeneous dielectric layer. The influence of dielectric losses on the cavity resonances is studied.

A saddle point variational principle, for estimating the propagation constant of an optical rib waveguide mode from a discontinuous trial function, is generalised to provide a theoretical underpinning for the familiar effective index method. It is shown that better accuracy can be achieved in a rigorous manner, while maintaining much of the simplicity that makes the original effective index approach so attractive.

A simple vector correction is applied to the polarised solution obtained from a single component wave equation. The resulting propagation constants are shown to be indistinguishable from six-component vector finite element results used as a benchmark. This considerably strengthens the validity of the polarised solution for the accurate modelling of rib and stripe waveguides, and shows that emphasis should be placed on finding quick and reliably accurate methods for the polarised approximation. Only then does the vector correction itself become accurate.

Pulse sharpening using ferrite material was first noticed in the mid-fifties during the development of storage devices for telecommunication and computer systems. Since that time various workers have explained how a switched ferrite can change the propagation characteristics of a transmission line to improve the rise time of an input pulse. In the paper the advantages achievable by imposing electron spin resonance and subsequent frequency enhancement, which has greatly improved the performance of these lines, are described for the first time. Experimental evidence of the benefits of spin conditions is provided and a simple transmission line model introduced to simulate the pulse sharpening effects.

Optical ray theory is used to design a phase-corrected microwave horn antenna of short-length which produces a tapered aperture amplitude distribution in the E-plane. The basis of the design is the creation of a region where the effective refractive index varies with hyperbolic secant (HYSEC) form in a direction normal to the horn axis. In a practical realisation this effective refractive index distribution is achieved in both smooth and stepped form by varying the plate separation of the planar waveguide supporting a TE/sub 01/ mode. Good agreement is found between predicted and experimentally determined aperture and far-field distributions. Finally, the study is extended to the design of a novel antenna incorporating dielectric loading which, in theory, allows for operation at even shorter horn lengths.

A finite-difference method is used to design a sectoral horn antenna that uses corner channel inserts to produce a tapered aperture amplitude distribution in the E-plane. The channel inserts effectively suppress sidelobe levels in the radiation pattern. Good agreement is found between predicted and experimental far-field distributions.

Bent-guide structures will undoubtedly play an important role in increasing packing density in future integrated optical circuits. A method for forming bends in waveguides in III-V semiconductors by reflection off an etched vertical wall is proposed for providing wave-guiding through 90° with negligible loss.

The background to and methods for an experiment on the design, fabrication and test of microstrip circuits are presented. The experiment is intended to complement final year of undergraduate or M.Sc. level electromagnetics sections of Electrical and Electronic Engineering courses. The circuits are fabricated using p.c.b. techniques thus keeping costs to a minimum.

We report low-loss, single-mode rib optical waveguides on-chip, fabricated using hot-embossing for the first time of radio-frequency sputtered $$\hbox {As}_{2}\hbox {Se}_{3}$$ chalcogenide-glass thin films on a chalcogenide-glass substrate. Waveguides 4–6 $$\upmu \hbox {m}$$ wide and $$1.9 \pm 0.1~\upmu \hbox {m}$$ high are fabricated. Waveguide optical loss, using the Fabry–Perot technique, which is known to over-estimate loss, is found to be $$

A simple Dy3+-doped chalcogenide glass fibre laser design for mid-infrared light generation is studied using a one dimensional rate equation model. The fibre laser design employs the concept of cascade lasing. The results obtained demonstrate that efficient cascade lasing may be achieved in practice without the need for fibre grating fabrication, as a sufficient level of feedback for laser action is provided by Fresnel light reflection at chalcogenide glass fibre–air interfaces. Further enhancement of the laser efficiency can be achieved by terminating one of the fibre ends with a mirror. A numerical analysis of the effect of the Dy3+ doping concentration and fibre loss on the laser operation shows that with 5 W of pump power, at 1.71 μm wavelength, output powers above 100 mW at ∼ 4.5 μm wavelength can be achieved with Dy3+ ion concentrations as low as 3 × 1019 cm−3, when fibre loss is of the order 1dB/m.

We demonstrate how the coupling of a full-wave time-domain boundary element method (BEM) solver with a circuit solver can be used to model 1) the generation of high frequency oscillations in resonant tunneling diode (RTD) oscillators, and 2) the mutual coupling and synchronization of non-identical RTDs with significant differences in frequencies to achieve coherent power combination. Numerical simulations show a combined output power of up to 3.7 times a single oscillator in synchronized devices. The non-differential conductance of the RTD is modeled as a lumped component with a non-linear current-voltage relationship. The lumped element is coupled to the radiating structure using a finite-gap model in a consistent and discretisation independent manner. The resulting circuit equations are solved simultaneously and consistently with time-domain electric field integral equations that model the transient scattering of electromagnetic (EM) fields from conducting surfaces that make up the device. This paper introduces three novel elements: (i) the application of a mesh independent feed line to the modelling of feed lines of RTD devices, (ii) the coupling of the radiating system to a strongly non-linear component with negative differential resistance, and (iii) the verification of this model with circuit models where applicable and against the experimental observation of synchronisation when two RTDs are placed in close proximity. These three elements provide a methodology that create the capacity to model RTD sources and related technology.

Global and local multitrace formulations (MTFs) provide a flexible and efficient method for the modeling of scattering and transmission of time harmonic electromagnetic (EM) waves by composite structures. This contribution extends the domain of applicability of global MTFs to cases where penetrable domains, perfectly conducting domain, and perfectly conducting thin sheets are all part of the design. A novel and easy to implement resonance-free equation to model scattering by perfect conductors is introduced. A Calderon preconditioner designed to limit the number of iterations required for the solution of the discrete system is designed and studied. The accuracy, flexibility, and efficiency of the method are demonstrated on a representative range of examples.

A boundary integral equation method is combined with a genetic algorithm to simulate and optimise dielectric and semiconductor microcavities. Waveguide filters and microlaser resonators are tuned by modifying the microcavity shape, coupling mechanism, gain/loss.