Thesis (M.S.) -- Middle East Technical University, 2004. / Keywords: Traffic Engineering, Rerouting, Sequence Planning, MPLS, Label Switched Paths.

Thesis (PH.D.) -- Syracuse University, 2004. / Advisers: Elsherbeni, Atef Z. ; Arvas, Ercument. "Publication number AAT 3135873."

Thesis (M.S. in Electronic Warfare Systems Engineering and M.S. in Electrical Engineering)--Naval Postgraduate School, September 2009. / Thesis Advisor(s): Tummala, Murali ; Jenn, David. "September 2009." Description based on title screen as viewed on November 6, 2009. Author(s) subject terms: Cooperative Spectrum Sensing, Source Localization, Multi-Resolution Spectrum Sensing, Three-Bit Hard Combination, RSS-Based Localization, Cognitive Radio, Wireless Sensor Networks, Electronic Warfare. Includes bibliographical references (p. 87-90). Also available in print.

In this thesis, approaches for increasing the output power in monolithically integrated semiconductor mode locked (ML) lasers were investigated. The wavelength range considered is the range of operation of low temperature grown GaAs photomixers, devices commonly used for THz generation. In particular, two GaAs/AlGaAs quantum well laser epistructures (operating at 830 nm and 795 nm) were considered, both with reduced optical confinement and elongated vertical optical mode size. In this work, such laser epistructures, commonly used by high power semiconductor laser manufacturers, were successfully employed, for the first time, for producing passively ML devices. Improved average powers (up to 48 mW) under ML operation were demonstrated, around ten times higher than values previously reported in monolithic GaAs/AlGaAs ML lasers. In continuous wave operation, the output power was limited by the catastrophic damage of the laser facets at around 50 mW. For this reason, facet passivation techniques were investigated, allowing for powers up to 124 mW to be achieved. In ML regime, the output power was instead limited by the catastrophic damage of the reverse biased section of the laser. This failure mechanism was investigated and explained considering thermal effects on the reverse biased section. Such effects limited the output power to around 27 mW in 830 nm devices, which was then improved by 70% in 795 nm devices with a 70% larger optical mode area. The larger mode size, combined to a small duty-cycle laser geometry, enabled a record peak power of 9.8 W to be achieved at 6.83 GHz. This particular repetition rate was specifically designed for coherent population trapping experiments in 87Rb vapors. Sub-picosecond transform limited pulses were achieved in both the laser materials considered, with a minimum duration of 0.43 ps at 126 GHz. With the values of peak power achieved, the developed devices may also be directly used for two-photon microscopy applications.

Electricity is vital for our daily life in modern cites. In order to ensure its reliability and supply, an electric power monitoring system is indispensable in an electric power system. Currently, most electric power monitoring systems are designed for steady-state monitoring only. They may not be able to monitor instantaneous power disturbances, such as voltage surge, happened in electric power systems. In fact, instantaneous power disturbances are frequently found in electric power systems, which result in equipment failures and cause financial losses. Therefore, a novel electric power monitoring system is proposed in this thesis. Besides traditional functions, the proposed system is capable of monitoring and analyzing instantaneous power disturbances in electric power systems. Novelties of the proposed monitoring system are in the following three major aspects. Firstly, the proposed system is capable of monitoring instantaneous power disturbances. Unlike traditional monitoring systems, the proposed system captures not only statistical power quantities (e.g. kW, kWh), but also voltage and current waveforms. Since a considerable communication network bandwidth is required to transmit electric waveforms in a remote monitoring system, a novel waveform compression algorithm is proposed to realize real-time electric power waveform monitoring on low-speed communication networks (e.g. Zigbee). Secondly, the proposed system is capable of identifying various kinds of power disturbances automatically. It relieves electrical engineers from manned disturbance identification on preserved waveforms. Unlike traditional disturbance identification algorithms, the proposed system can identify not only voltage disturbances, but also current disturbances. Hence, it can provide a better chance in identifying more problems and disturbances in electric power systems. Thirdly, a novel time-frequency analysis method is proposed to analyze preserved waveforms. The proposed method is an improvement to the well-known Discrete Wavelet Packet Transform (DWPT). DWPT has been used by researchers and engineers to analyze disturbances and harmonics in electric power systems. However, DWPT is subjected to a non-uniform leakage problem, which has been discussed intensively in many studies. In order to tackle this issue, a frequency shifting scheme is introduced in the proposed method. A prototype has been implemented to demonstrate the feasibility of the proposed electric power monitoring system. There are two major components – a prototype meter and a central monitoring system. The performance of the prototype has been evaluated by conducting experiments and field tests. The capability of the proposed system for realtime remote monitoring has been verified on Zigbee network, which is a low-power, low speed wireless communication network.

This thesis aims to explore and demonstrate the potential of using optical fibres both as a waveguide material and a transducer for wide sensing applications, based on a comprehensive review of the localised surface plasmon resonance (LSPR) phenomenon, which occurs at a nanoscale level when light interacts with metallic nanoparticles at a resonance wavelength. The LSPR effect of metallic nanomaterials has shown a strong dependence on the local surrounding environment. A small change for example in the refractive index or in the solution concentration can result in a variation in the LSPR spectrum. Based on this underpinning sensing mechanism, a portable system using an optical fibre coated with gold nanoparticles (AuNPs) as a sensing probe has been developed and tested for the refractive index measurement. Coupled with this, a systematic approach has been developed and applied in this work to optimize the performance of the developed system by considering several key factors, such as the size of nanoparticles produced, pH, coating time and coating temperature. The above optimised probes coated with gold-nanoparticles are further cross-compared with those optimized but coated with gold nanorods with a high aspect ratio. Both types of probes are also prepared for a specific biosensing application based on the antibody-antigen interaction to create wavelength-based sensors for the detection of anti-human IgG. Both probes have exhibited excellent refractive index (RI) sensitivity, showing ~914 nm/RIU (refractive index unit) for the probe coated with gold nanoparticles and ~601 nm/RIU for the one coated with gold nanorods. When using the modified probes for the detection of anti-human IgG, both probes are able to achieve a good LOD (limit of detection) at 1.6 nM. Based on the above cross-comparison, further research has been undertaken to explore the potential of nanoparticles of the alloy of gold and silver, with an aim to combine the robustness of gold and the excellent LSPR effect of silver. To do so, various alloy particles with varied gold/silver ratio and sizes have been prepared and tested for their respective refractive index sensitivities. The probe coated with alloy particles with bigger size and higher silver content has shown better performance in RI sensing. The work has shown a clear relationship between the size of alloys, the content ratio of alloys and RI sensitivity. Research has also been undertaken in this thesis to explore the excellent LSPR effect of hollow nanoparticles resulting from the enhanced coupling between the interior and exterior of the hollow particles. Gold hollow nanocages have been successfully synthesised and tested with different hollowness and a LSPR sensor coated with gold nanocages has shown an excellent sensitivity as high as ~1933 nm/RIU, which is more than 3 times higher than that coated with AuNPs. This result has confirmed that a significant improvement in sensitivity can be made possible for further biosensing as well as chemical sensing applications.

This thesis discusses two important designs, analysis and optimization of polarization-based devices such as polarization rotator and splitter. Many optical sub-systems integrate with guided wave photonic devices with two-dimensional confinement and high contrast between the core and cladding. The modes present in such waveguides are not purely of the TE or TM type. They are hybrid in nature, where all six components of the magnetic and electric fields are present. This causes the system fully to be polarization dependent. Currently, the polarization issue is a major topic to be dealt with during the design of high efficiency optoelectronic subsystems for further enhancement of their performances. To characterize the device polarization properties a vectrorial approach is needed. In this work, the numerical analysis has been carried out by using the powerful and versatile full vectorial H-field based finite element method (FEM). This method has been proved to be one of the most accurate numerical methods to date for calculating the modal hybridness, birefringence and consequently to calculate the device length, which is an important parameter when designing devices concerning the polarization issues. Polarization devices may be fabricated by combining several butt-coupled uniform waveguide sections. The Least Squares Boundary Residual (LSBR) method is used to obtain transmission and reflection coefficients of all the polarized modes by considering both the guided and the radiated modes. On the other hand, finite element method cannot calculate the power transfer efficiency directly, hence the LSBR method is used along with the FEM for this purpose. The LSBR method is rigorously convergent, satisfying the boundary conditions in the least square sense over the discontinuity interface. Using this method, the power transfer from the input to the coupler section and at the output ports can be evaluated. When designing polarization rotators, it is necessary to calculate the modal hybridness of a mode. In this research, it is identified that when the symmetric waveguides are broken, the modal hybridity is enhanced, and thereby a high polarization conversion is expected. This work is devoted to the study of design optimization of a compact silicon nanowire polarization device. An interesting and useful comparison is made on their operating properties such as the crosstalk, device length, polarization dependence, and fabrication tolerances of the polarization in directional coupler based devices. In this study initially the H-field modal field profile for a high index contrast silicon nanowire waveguide is shown. The effects of waveguide’s width on the effective indices, hybridness, power confinement in the core, and the cladding have been investigated. The modal birefringence of such silicon nanowire waveguides also is shown. It is presented here that for a silicon nanowire waveguide with height of 220 nm, fundamental and second modes exist in the region of the width being 150 – 300 nm, and 500 – 600 nm, respectively. A compact 52.8 μm long passive polarization rotator (PR) using simple silicon nanowire waveguides is designed with a power transfer of 99 % from input TE to output TM power mode, with cross-talk better than – 20 dB and loss value lower than 0.1 dB. Furthermore, an extensive study of fabrication tolerances of a compact (PR) is undertaken. The design of an ultra-compact polarization splitter (PS) based on silicon-on-insulator (SOI) platform is presented. It is shown here that a low loss, 17.90 μm long compact PS, and wide bandwidth over the entire C-band can be achieved.

Therapeutic ultrasound is a promising treatment method for many common cancers, including prostate cancer. Magnetic resonance image (MRI) guidance of therapeutic ultrasound permits targeting and monitoring of therapy. In this thesis a prototype MRI compatible positioning device for the treatment of prostate cancer using therapeutic ultrasound is presented. The accuracy, MRI compatibility and functionality of the positioning device was evaluated in in vitro experiments (using gel phantoms and in vitro). The MRI was used as the imaging guidance technique. The proposed device incorporates a portable electronic system and operates in two PC controlled stages, linear and angular (X - Θ) and one manual driven stage Z (height of the probe). The device is small and portable and can be placed on the patient’s table to any commercial MRI scanner. The proposed device was tested on two clinical MRI scanners of different manufacturers. Additionally, in this thesis a software that controls an MRI guided focus ultrasound system is presented. The software was written in C sharp and consists of the following options: a) connection with DAQ device, b) tab that controls 2D device, c) tab that controls 3D device, d) tab that controls ultrasound protocol and e) operation command history list, g) MRI compatible camera, h) open and control the DICOM images captured from the MRI scanner during the therapy, i) temperature reading of the HIFU focal point. The proposed positioning device offers approximately 20μm accuracy on linear and angular stages. It incorporates MRI compatible optical encoders as mechanical motion feedback. The accuracy measurements were taken using a digital calibre. The positioning device has range of 111mm in linear stage, ±90o on angular stage and 50mm on Z stage. The design was based on measurements that were taken by a 100 patients. The MRI compatibility and motion accuracy images were taken by scanning gel phantoms using T2W FSE on 1.5T and 3T MRI scanner.

The finite difference time domain (FDTD) method is a popular technique, being used successfully to analyse the electromagnetic properties of many structures, including a range of optical or photonic devices. This method offers several major advantages such as, a minimum level of calculation is required for each of the cells into which the structure is divided, as well as data parallelism and explicit and easy implementation. However, due to the use of the Finite Difference grid, this method suffers from higher numerical dispersion and inaccurate discretisation due to staircasing at slanted and curve edges. The rectangular computational domain in 2D and cuboid computational domain in 3D sometimes makes the method very resource intensive especially for large simulations. Although the finite element (FE) approach is superior for the discretisation of both 2D and 3D structures, most of the FE-based time domain approaches reported so far suffer from limitations due to the implicit or iterative form or the mass matrix formulation, for example. Therefore, the speed of the simulation is much slower than the FDTD method. Time domain analysis of electromagnetic is a very resource intensive numerical technique. Due to the slow performance the FE based techniques are not as popular as the FDTD method. In this research work a new FE based time domain technique has been proposed for both 2D and 3D problems which is similar to the FDTD method explicit and data parallel in nature. The method proposed does not requires any matrix formulation or iteration. It uses minimum possible CPU cycles among any FE-based techniques. The method also utilises a unique meshing scheme to reduce the number of calculation to at least half for 2D and one fifth for 3D compared to any full mesh FE based technique. The method also shows very low numerical dispersion when used with equilateral elements in both 2D and 3D. Thus the proposed method effectively produces results with less numerical dispersion error with lower density mesh compared to the FDTD method. When the advantage in resolution is taken into consideration, calculation of each time-step using the proposed method is significantly faster than the FDTD method.

The aim of this work was to design, fabricate and characterize InP high electron mobility transistor (HEMT) based monolithic millimetre wave integrated circuits (MMIC) which operate at 770Hz. To achieve this active and passive circuit elements were designed, fabricated and characterized and accurate equivalent circuit models extracted. All circuits were designed with coplanar waveguide (CPW) as the transmission medium. Electron beam lithography was used for most fabrication processes in this work. A range of passive elements such as CPW discontinuities, series and parallel MIM and interdigital capacitors of different sizes and NiCr resistors were designed fabricated and measured. Equivalent circuit models of these elements were extracted which were shown to be valid to 110 OHz. Passive circuits such as branch-line coupler, rat-race coupler, Lange coupler and Wilkinson divider were successfully demonstrated at W-band frequencies. In all cases the circuits have equal power splitting characteristics with low insertion losses and very good input and output match over large bandwidth. Equivalent circuits of these circuits were extracted and were used in design of MMICs. Active devices were fabricated on a lattice matched InAIAs/InOaAs InP HEMT material structure. Two different 0.12 f..UD T -gate processes were used to make these devices with a UVIIIIPMMA based process giving superior high frequency performance when compared to a conventional CopolymerlPMMA based T -gate structure. The end to end gate resistance of UVIIIIPMMA T -gate was comparable to the lowest 0.1 J..lm gate resistance ever reported. The HEMTs fabricated in this work have shown fT as high as 1930Hz and MAO of 13 dB at 940Hz. Equivalent circuit models of these HEMTs were extracted and were valid up to 1100Hz. These passive and active circuit models were used to design MMICs, in particular reactively matched single ended, balanced and balanced switching amplifiers at 77 OHz. Direct carrier modulators including BPSK, bi-phase amplitude modulation, QPSK and QAM were designed, fabricated and measured at 770Hz. These modulators are designed with reflection type topology to perform the different modulation schemes. The Balanced BPSK modulator circuit was used to ' .. ~ . demonstrate switching operation· with ON-OFF isolation better than 25 dB. The Pagel Abstract two ON states showed 180±5° phase difference which is almost ideal for BPSK modulation. For all states, the input and output reflections were measured to be better than -17 dB at the design frequency. In the case of QAM and QPSK modulation, the circuits showed non-ideal performance with high insertion loss and phase errors but the input and out put reflections were better than -10 dB.