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Silicon-on-insulator (SOI) technology has become increasingly attractive because of the strong light confinement, which significantly reduces the footprint of the photonic components, and the possibility of monolithically integrating advanced photonic waveguide circuits with complex electronic circuits, which may reduce the cost of photonic integrated circuits by mass production. This thesis is dedicated to numerical simulation and experimental performance measurement of passive SOI waveguide devices. The thesis consists of two main parts. In the first part, SOI curved waveguide and corner turning mirror are studied. Propagation losses of the SOI waveguide devices are accurately measured using a Fabry-Perot interference method. Our measurements verify that the SOI corner turning mirror structures can not only significantly reduce the footprint size, but also reduce the access loss by replacing the curved sections in any SOI planar lightwave circuit systems. In the second part, an optical 90o hybrid based on 4 × 4 multimode interference (MMI) coupler is studied. Its quadrature phase behavior is verified by both numerical simulations and experimental measurements.

Silicon-on-insulator (SOI) technology has become increasingly attractive because of the strong light confinement, which significantly reduces the footprint of the photonic components, and the possibility of monolithically integrating advanced photonic waveguide circuits with complex electronic circuits, which may reduce the cost of photonic integrated circuits by mass production. This thesis is dedicated to numerical simulation and experimental performance measurement of passive SOI waveguide devices. The thesis consists of two main parts. In the first part, SOI curved waveguide and corner turning mirror are studied. Propagation losses of the SOI waveguide devices are accurately measured using a Fabry-Perot interference method. Our measurements verify that the SOI corner turning mirror structures can not only significantly reduce the footprint size, but also reduce the access loss by replacing the curved sections in any SOI planar lightwave circuit systems. In the second part, an optical 90o hybrid based on 4 × 4 multimode interference (MMI) coupler is studied. Its quadrature phase behavior is verified by both numerical simulations and experimental measurements.

Silicon-on-insulator (SOI) technology has become increasingly attractive because of the strong light confinement, which significantly reduces the footprint of the photonic components, and the possibility of monolithically integrating advanced photonic waveguide circuits with complex electronic circuits, which may reduce the cost of photonic integrated circuits by mass production. This thesis is dedicated to numerical simulation and experimental performance measurement of passive SOI waveguide devices. The thesis consists of two main parts. In the first part, SOI curved waveguide and corner turning mirror are studied. Propagation losses of the SOI waveguide devices are accurately measured using a Fabry-Perot interference method. Our measurements verify that the SOI corner turning mirror structures can not only significantly reduce the footprint size, but also reduce the access loss by replacing the curved sections in any SOI planar lightwave circuit systems. In the second part, an optical 90o hybrid based on 4 × 4 multimode interference (MMI) coupler is studied. Its quadrature phase behavior is verified by both numerical simulations and experimental measurements.

Radio propagation models provide an estimate of the power loss in a communication link caused by the surface of the ground, atmospheric refraction, foliage, and other environmental factors.  Many of the models rely on digital topographic databases to provide information about the terrain, and generally the databases are sparsely sampled relative to the electromagnetic wavelengths used for communication systems.  This work primarily develops a technique to evaluate the effects of that sparsity on the uncertainty of propagation models. That is accomplished by accurately solving the electromagnetic fields over many randomly  rough surfaces which pass through the sparse topographic data points, many possible communication links, all of which fit the underlying data, are represented.  The power variation caused by the different surface realizations is that due to the sparse sampling. Additionally, to verify that this solution technique is a good model, experimental propagation measurements were taken, and compared to the computations. / Master of Science

The electromagnetic wave absorption characteristics of composite cement-based building material have attracted much interest in recent times. Researchers have mainly focused on the 2 GHz to 12 GHz frequency range. Mobile and wireless communication systems use frequencies from 800 MHz upwards. The determination of characteristics such as reflection loss, absorption, attenuation and shielding effectiveness are crucial in the evaluation and development of these materials for the building industry. Absorption is an indication of how much of the EMW energy enters the material. Attenuation indicates how much of the absorbed energy is converted into other forms of energy by the material. Shielding effectiveness (SE) is a combination of reflection loss, attenuation and multiple internal reflections and attenuations. This research determined these characteristics by measuring the S11 and S21 parameters of the composite cement-based material in the GSM and WiFi frequency bands. The time domain gating function of a vector network analyser is applied to measure the reflection from the material. The data was then used to obtain the reflection and absorption losses in the frequency bands. The transmission loss was measured by placing the sample in the propagation path between two antennas. MnZn-ferrite and electrolytic manganese dioxide in powder form were evaluated as absorber material to increase the permeability of the cement-based material to improve absorption and attenuation capabilities to create a cost-effective practical electromagnetic wave absorber. The compound of the cement-based material was cement, sifted river sand and filler powder. The results achieved in the research showed the uniqueness of electrolytic manganese dioxide as filler in composite cement based material for electromagnetic wave shielding effectiveness improvement. The combined measurement techniques used in this research were uniquely used to determine the required electromagnetic wave absorption characteristics and shielding effectiveness of 10 dB was measured in the GSM850 and GSM900 frequency bands. / Dissertation (MEng)--University of Pretoria, 2013. / gm2014 / Electrical, Electronic and Computer Engineering / unrestricted

The field of nanophotonics is a major research topic, as it offers potential solutions to important challenges, such as the creation of low power, high bandwidth interconnects or optical sensors. Within this field, resonant structures and slow light waveguides are used to improve device performance further. Photonic crystals are of particular interest, as they allow the fabrication of a wide variety of structures, including high Q-factor cavities and slow light waveguides. The high scattering loss of photonic crystal waveguides, caused by fabrication disorder, however, has so far proven to be the limiting factor for device applications. In this thesis, I present a detailed study of propagation loss in slow light photonic crystal waveguides. I examine the dependence of propagation loss on the group index, and on disorder, in more depth than previous work by other authors. I present a detailed study of the relative importance of different components of the propagation loss, as well as a calculation method for the average device properties. A new calculation method is introduced to study different device designs and to show that photonic crystal waveguide propagation loss can be reduced by device design alone. These “loss engineered” waveguides have been used to demonstrate the lowest loss photonic crystal based delay line (35 dB/ns) with further improvements being predicted (< 20 dB/ns). Novel fabrication techniques were investigated, with the aim of reducing fabrication disorder. Initial results showed the feasibility of a silicon anneal in a nitrogen atmosphere, however poor process control led to repeatability issues. The use of a slow-fast-slow light interface allowed for the fabrication of waveguides spanning multiple writefields of the electron-beam lithography tool, overcoming the problem of stitching errors. The slow-fast-slow light interfaces were combined with loss engineering waveguide designs, to achieve an order of magnitude reduction in the propagation loss compared to a W1 waveguide, with values as low as 130 dB/cm being achieved for a group index around 60.

The Terrestrial digital radio links are used for transmitting digital information between fixed stations on a line of sight of a radio path. Each digital radio link has many characteristics and parameters for transmission. We require technical parameters in the design of digital radio link such as data rates and capacities. In this design we should take into account most effects of the electromagnetic waves propagation, if we want to meet user technical requirements of the link and if that link may correctly transmit digital signals with minimum errors. Prediction methods for the design of terrestrial line of sight systems are still in progress. Some effects of electromagnetic waves propagation and methods of the digital radio link design depend on natural variability and climate. The goal of this diploma thesis is to investigate methods for the design of terrestrial line of sight links with taking into account of ITU recommendation. Make computer program which implement this investigate methods