No description available.

No description available.

The influence of nano-structured overlays on the properties of fibre optic Long Period Gratings (LPGs) has been investigated. The presence of overlays of thickness of order 100 m is shown to significantly alter the response of the LPG to environmental parameters, such as the surrounding refractive index. A LPG with a nano-structured overlay was observed to exhibit enhanced sensitivity to refractive indices lower than silica, and was observed to exhibit sensitivity to refractive indices greater than that of the silica cladding, not observed in the absence of the overlay. A theoretical model predicts the observed behaviour. The observation was exploited to enhance the sensitivity of a LPG based chemical concentration sensor. The response of the transmission spectrum of concatenated long period gratings (LPGs) to ' the deposition of nano-structured overlays was also investigated. Concatenated LPGs act as a Mach-Zehnder interferometer and the phase of the interference fringes that appear within the LPGs° attenuation bands were shown to be highly sensitive to the optical thickness of the overlay, for thicknesses of order 100 mn. Several devices were fabricated with increasing path lengths to demonstrate effect of overlay thickness and refractive index on the transmission spectrum of the LPG.

In this thesis, a primary investigation into developing a compact and low-loss bandpass filter, using novel folded waveguide resonators with a footprint reduction, has been addressed. A slot coupling between adjacent resonators is introduced, which is characterized by using full-wave EM simulations and verified experimentally. Two designs of 2-pole folded waveguide resonator filters of this type have been considered, fabricated and tested. In this thesis, an even more compact FWG resonator filter using a novel slot technique is reported. The attainable size reduction is about 50%, and the filter design is based on theoretical and full-wave electromagnetic (EM) simulations. Based on FWG structure, two types of folded waveguide resonators have been studied and considered the half-wavelength resonator and the quarter-wavelength resonator. Moreover, both structures for the realization of microwave cavities with high-Q, with the result of a high spurious free range and reduced footprint, have been evaluated. Furthermore, a novel folded waveguide resonator with about a 75 % reduction of the volume from the conventional size has been described. For comparison, two types of folded waveguide resonators have been studied, i.e. the quarter-wavelength resonator of square shape and the newly proposed triangular shape. In addition, a demonstration of a filter application for miniature triangular folded waveguide resonators has been designed and simulated using an EM simulator. In addition, numbers of experiments have been conducted to develop cavity FWG and Substrate Integrated folded waveguide SIFW resonator filters using a folded structure, which is the main aim of this thesis. Furthermore, this thesis deals with the simulation and implementation for many designs and topologies of FWG and SIFW resonator filters and their frequency response. Simulation and experimental results were presented to validate the design and to show the advantages of these types of filters. In addition, a new type of filter with a compact multi-layer structure and low loss is attractive for implementation with advanced device technologies, such as micromachining, LTCC and LCP technologies.

No description available.

No description available.

There is growing demand for indoor wireless communication systems with higher bandwidth and higher data rates. However, the crowded radio frequency (RF) spectrum has caused researchers to consider optical wireless systems. In this thesis, optical signals in the visible region of the spectrum are used. White LEDs are used as transmitters as they provide higher signal-to-noise (SNR) levels and a better link budget than the infrared alternative. Typical modulation bandwidths for white LEDs are limited to tens of MHz. Thus, multiple-input multiple-output (MIMO) transmission is considered as a means to increase data rate. The development of the indoor optical wireless MIMO system begins with the geometrical and mathematical analysis of a single-input single-output (SISO) system and a single-input multiple- output (SIMO) system. The same analysis is then performed for a MIMO system. For the MIMO system, an experimental demonstration using white LEDs and non-imaging receivers are reported. Results include coverage measurements and an SNR analysis. There are limitations using non- imaging receivers, such as coverage limitations and symmetry problems, which cause problem with signal recovery. To improve these limitations, imaging receivers are considered. The design and development of an experimental demonstration of an indoor optical wireless MIMO system with an imaging receiver is presented. The experimental setup consists of a transmitter with a 2 x 2 array of white LEDs and a receiver with a 3 x 3 photo detector array. The system transmits data at a bit rate of 2Mbit/s/channel. Detailed design specifications and optical design are presented. Results show that certain positions within the system coverage area have error-free operation. The BER and SNR analysis shows that the overall BER improves with the overall SNR. In order to exploit the full potential of the system, future work should focus on improving the SNR and BER of the system.

No description available.

No description available.

No description available.