The thesis focuses on the study of asymmetric multiple quantum wells(AMQWs) grown by molecular beam epitaxy (MBE) in the Riber Compact 21T MBE system. We investigate AMQW structures in which the well width is varied but the material compositions of the wells and the barriers are kept constant. Also, we have investigated AMQWs with p-type modulation doping at the barrier region and the AMQWs of different well widths without changing the well compositions. The AMQW samples are obtained the emission spectra by using photoluminescence (PL), electroluminescence (EL), photo-current and photoreflectance (PR) in the experiments. Also, The AMQW samples (AMQ100-70-40 and AMQ-100-MD70-40) are fabricated into laser diodes to obtain the characteristics of device in this study. The threshold current density Jth of laser diode is measured about 2 kA/cm2.The internal quantum efficiency £bi and the absorption £\ of AMQ-100-70-40 are 34.7% and 9.47 cm-1 respectively. The internal quantum efficiency £bi and the absorption £\ of AMQ-100-MD70-40 are 22.2% and 10.56 cm-1 respectively. Moreover, we present the InGaAsP AMQW samples grown by MOCVD to compare with the InGaAs/InAlGaAs AMQW samples. The broad-band property is valuable for application of optical communication. It is highly desirable to have broadly tunable lasers and broad-band semiconductor optical amplifiers (SOAs) in the 1.3 or 1.55£gm to handle more number of channels increasing the volume of information traffic for future optical communication networks. The band-band light source is also desirable in medical science for the optical coherence tomography (OCT).

In this thesis, strong optical feedback is utilized to realize broad-band wavelength tuning and to stabilize the frequency of a semiconductor diode laser in a grating-external-cavity (GEC) configuration. To reach the regime of strong optical feedback, the laser facet through which the feedback occurs has to be antireflection (AR) coated. Multi-layer AR coatings were designed using SiO2, Si3N4, SiOxNy, and a:Si for specific laser waveguide structures, and were fabricated by an electron cyclotron resonance, plasma enhanced, chemical vapor deposition (ECR-PECVD) system. The film thickness and refractive index were monitored by in situ ellipsometry during the deposition. This scheme permitted very low reflectivities, in the order of 5 x 10-4, to be readily and reproducibly obtained. The diode laser thus obtained was used in a strong feedback configuration. Light emitted from the coated facet was collimated and fed back onto the laser cavity after being reflected off a diffraction grating. The diffraction grating provides frequency selectivity, which is a desirable feature for obtaining a stable single longitudinal mode laser. The laser in this configuration oscillated in a single mode with a greater than 30 dB side mode suppression ratio and a wide tuning range. / Thesis / Master of Applied Science (MASc)

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The contributions of this thesis include designing and analyzing novel medium access control (MAC) protocols for two types of wireless networks: (1) duty-cycling cooperative multi-hop wireless sensor networks (MHWSNs), and (2) single-hop Terahertz networks (TeraNets). For MHWSNs, the specific contributions are two new scalable MAC protocols for alleviating the “energy-hole” problem with cooperative transmission (CT). The energy-hole is known to limit the life of battery-powered MHWSNs. The hole occurs when nodes near the Sink exhaust their energy first because their load is heavier: they must transmit packets they originate and relay packets from and to other nodes farther from the Sink. Effective techniques for extending lifetime in MHWSNs include duty cycling (DC) and, more recently introduced, cooperative transmission (CT) range extension. However, a scalable MAC protocol has not been presented that combines both. From the MAC perspective, conducting CT in an asynchronous duty-cycling network is extremely challenging. On the one hand, the source, the cooperators and the destination need to reach consensus about a wake-up period, during which CT can be performed. This dissertation develops novel MAC protocols that solve the challenge and enable CT in an asynchronous duty-cycling network. On the other hand, the question arises, “Does the energy cost of the MAC cancel out the lifetime benefits of CT range extension?” We show that CT still gives as much as 200% increase in lifetime, in spite of the MAC overhead. The second contribution of this dissertation is a comprehensive analytical framework for MHWSNs. The network performance of a MHWSN is a complex function of the traffic volume, routing protocol, MAC technique, and sensors' harvested energy if sensors are energy-harvesting (EH) enabled. The optimum performance provides a benchmark for heuristic routing and MAC protocols. However, there does not exist such an optimization framework that is able to capture all of these protocol aspects. The problems and performance metrics of non-EH networks and EH networks are different. Because the non-EH nodes depend on a battery, a suitable performance metric is the lifetime, defined as the number of packets delivered upon the first or a portion of nodes' death. Thus, the lifetime is governed by the absorbing states in a controlled dynamic system with finite decision horizon. On the other hand, the lifetime of an EH network is theoretically infinite unless the sensors are broken or destroyed. Therefore, an infinite horizon problem is formulated towards the performance of EH networks. The proposed model departs significantly from past analyses for single-hop networks that do not capture routing and past analyses for multi-hop networks that miss MAC aspects. To our knowledge, this is the first work to model the optimal performance of MHWSNs, by jointly considering MAC layer link admission, routing queuing, energy evolution, and cooperative transmission. The third contribution of this dissertation is a novel MAC protocol for Terahertz (THz) Band wireless networks, which captures the peculiarities of the THz channel and takes advantage of large antenna arrays with fast beam steering capabilities. Communication in THz Band (0.1-10THz) is envisioned as a key wireless technology in the next decade to provide Terabits-per-second links, however, the enabling technology is still in its infancy. Existing MAC protocols designed for classical wireless networks that provide Megabits-per-second to Gigabits-per-second do not scale to THz networks, because they do not capture the peculiarities of the THz Band, e.g., the very high molecular absorption loss or the very high reflection loss at THz Band frequencies. In addition, to overcome the high path loss and extend communication range, the proposed MAC design takes advantage of fast beam steering capabilities provided by the large antenna arrays, in particular, beam-switching at the pulse level.

External modulators will become key components in fiberoptical communica- tion systems operating at 40Gbit/s andhigher bitrates. Semiconductor electro- absorption (EA)modulators are promising candidates because of their high-speed potential, and their process compatibility with thecorresponding semi- conductor laser light sources. Thetraveling-wave (TW) electrode concept for electro-opticmodulators has been used for a long time in order to resolvethe con°ict between high modulation depth and highmodulation bandwidth. Re- cently, it has been adopted for EAmodulators as well. This thesis presents the work carried out on design,fabrication and analysis of traveling-wave EA modulators(TWEAM) based on InP-InGaAsP. The lengths of TWEAM arecomparable to the lengths of their lumped counterparts. Theexperimental data of this work were analyzed in order show thatthe traveling- wave concept results in better performance evenfor short EA modulators. One key issue is the impedancematching. The low intrinsic characteristic modulator impedancehas to be matched with a corresponding load. In this case, theTW con figuration leads to a much higher bandwidth than for alumped EA modulator with the same length and the same connectedload. An InP process was developed allowing the fabrication ofTWEAM with integrated termination resistors. Experimentalmicrowave properties were ob- tained for different TWEAMgeometries. It is reported on long TWEAM that showstate-of-the-art bandwidth. A 450&#956m long TWEAM reached43GHz, and 67GHz (beyond characterization limit) were indicatedfor a 250&#956m device. The experimental results onmicrowave properties were compared to full-wave, and circuitmodel simulations. The analysis reveals an impedance bandwidthtrade- off for the cross sectional electrode configuration. Results of a new high-impedance design in form of asegmented TWEAM are presented. The devices were processedwithin the frame of this work and record bandwidth performanceis reported. At 50&#937­ impedance a bandwidth in the90GHz region was indicated.

In this work present the broad-band noise structure in the 2-60 keV data of Cataclysmic Variables (CVs) with Anomalous X-Ray Pulsars (AXPs) and Soft Gamma Repeaters (SGRs). We analyzed Rossi X-ray Timing Explorer (RXTE) PCA data and derived time series from 27 CVs, 4 AXPs and 1 SGR using the RXTE archive. In general, CVs of different types all show broad band noise which can be fitted with power laws, using exponentional cut-offs, and Lorentzians in a similar way to power spectral (noise) characteristics of X-ray Binaries (XRBs). In general terms the power spectra show a power law index of (-)1.2-2. A rather large scale flattening of the power spectra exits in nonmagnetic systems in the low to very low frequency range. We observe that in low and high states/outbursts the noise in the high frequency range and low frequency range is changed. CVs show considerably low frequency noise. In addition, we recovered several possible QPOs in the X-ray wavelengths from CVs mainly from Intermediate Polar systems. AXP and SGR sources which are thought to be powered by either magnetic decay or accretion show band limited noise in their low frequencies. We also correlated their equal time interval noise characteristic with their burst states and discovered that in the two AXPs (1E 2259+586, 1E 1048.1-5937) noise correlates with their bursts.

<p>External modulators will become key components in fiberoptical communica- tion systems operating at 40Gbit/s andhigher bitrates. Semiconductor electro- absorption (EA)modulators are promising candidates because of their high-speed potential, and their process compatibility with thecorresponding semi- conductor laser light sources. Thetraveling-wave (TW) electrode concept for electro-opticmodulators has been used for a long time in order to resolvethe con°ict between high modulation depth and highmodulation bandwidth. Re- cently, it has been adopted for EAmodulators as well.</p><p>This thesis presents the work carried out on design,fabrication and analysis of traveling-wave EA modulators(TWEAM) based on InP-InGaAsP. The lengths of TWEAM arecomparable to the lengths of their lumped counterparts. Theexperimental data of this work were analyzed in order show thatthe traveling- wave concept results in better performance evenfor short EA modulators. One key issue is the impedancematching. The low intrinsic characteristic modulator impedancehas to be matched with a corresponding load. In this case, theTW con figuration leads to a much higher bandwidth than for alumped EA modulator with the same length and the same connectedload.</p><p>An InP process was developed allowing the fabrication ofTWEAM with integrated termination resistors. Experimentalmicrowave properties were ob- tained for different TWEAMgeometries. It is reported on long TWEAM that showstate-of-the-art bandwidth. A 450&#956m long TWEAM reached43GHz, and 67GHz (beyond characterization limit) were indicatedfor a 250&#956m device. The experimental results onmicrowave properties were compared to full-wave, and circuitmodel simulations. The analysis reveals an impedance bandwidthtrade- off for the cross sectional electrode configuration.</p><p>Results of a new high-impedance design in form of asegmented TWEAM are presented. The devices were processedwithin the frame of this work and record bandwidth performanceis reported. At 50&#937­ impedance a bandwidth in the90GHz region was indicated.</p>

The purpose of this thesis is to make a broadband antireflection coating configuration known as a quarter-wave stack consisting of one layer of titania and of one layer of silica nanoparticles. We utilize much that is already known about silica nanoparticle deposition. The first objective of this thesis is deposition and characterization of titania nanoparticle films deposited on glass microscope slides by a technique known as Ionic Self-Assembled Multilayers or ISAM deposition. This technique takes advantage of the electrostatic attraction between oppositely charged materials and ideally results in a uniform nanoparticle film whose thickness and optical properties can be tightly controlled. Deposition of a quarter-wave stack based on ISAM deposition of silica and titania nanoparticles is significantly simpler and less expensive than alternative deposition methods. Initial attempts to deposit titania films were unsuccessful because of excess diffuse scattering due to inhomogeneities in the film. In order to reduce diffuse scattering, two approaches were considered. The first approach was to improve the deposition process itself by experimenting with different values of deposition parameters such as solution pH and solution molarity. The other approach focused on removing the large nanoparticle aggregates from the colloidal solutions of titania nanoparticles that were suspected to be responsible for rough film surfaces resulting in diffuse scattering. This approach was successful. In addition, evidence suggested that surface roughness contributed more to diffuse scattering than the bulk of the films. After minimizing diffuse scattering from titania nanoparticle films, we used known results from research on silica nanoparticle films to deposit quarter-wave stacks consisting of one layer of titania nanoparticles with high refractive index and one layer of silica nanoparticles with low refractive index. This contrast in refractive indices is a desirable characteristic of quarter-wave stacks. The thicknesses and refractive indices of the two layers in the quarter-wave stacks were measured by ellipsometry and compared to the nominal thicknesses of these layers. Finally, the reflectance was derived from a model of the quarter-wave stack and was compared to the measured reflectance. It was found that construction of a quarter-wave stack by ISAM is possible but that it will be necessary to acquire data from more experiments. / Ph. D.

Este trabalho tem como objetivo fornecer contribuições metodológicas à implementação da tecnologia PLC/BPL em seus diversos ambientes reais de instalação. São apresentados os aspectos básicos envolvidos, princípio de operação, as topologias das redes PLC, vantagens e desvantagens e exemplos de aplicação. Além disso, são apresentadas as contribuições deste trabalho, as quais visam estabelecer procedimentos no desenvolvimento dos projetos de redes de comunicação que utilizam a tecnologia PLC, assim como procedimentos de instalação nos diversos ambientes reais e os procedimentos para o comissionamento das redes implantadas. São destacados os aspectos relacionados às redes comerciais, as quais possuem inúmeros requisitos de desempenho, manutenção preventiva e/ou corretiva, além dos aspectos financeiros dos projetos e os pontos importantes para atendimento da legislação atualmente em vigor. Finalmente, para cada procedimento apresentado, o mesmo é contextualizado através da apresentação de um caso prático associado. / This work aims to provide methodological contributions to PLC/BPL implementations in their several real installation environments. It is presented the basic aspects of the technology as well as the operation principle, the networks topologies, the advantages and the disadvantages and application examples. Furthermore, it is presented the contributions of this work, which goal is to establish procedures related to projects developments of PLC communication networks, some procedures related to the installation process in their real environments and the procedures for commissioning a deployed network. It is emphasized the commercial networks aspects, which demand several performance requirements, the preventive and/or corrective maintenance, as well as the financial aspects and the main topics to comply with the current regulation. Finally, every presented procedure is exemplified with a real case in order to demonstrate its practical functionality.

Este trabalho tem como objetivo fornecer contribuições metodológicas à implementação da tecnologia PLC/BPL em seus diversos ambientes reais de instalação. São apresentados os aspectos básicos envolvidos, princípio de operação, as topologias das redes PLC, vantagens e desvantagens e exemplos de aplicação. Além disso, são apresentadas as contribuições deste trabalho, as quais visam estabelecer procedimentos no desenvolvimento dos projetos de redes de comunicação que utilizam a tecnologia PLC, assim como procedimentos de instalação nos diversos ambientes reais e os procedimentos para o comissionamento das redes implantadas. São destacados os aspectos relacionados às redes comerciais, as quais possuem inúmeros requisitos de desempenho, manutenção preventiva e/ou corretiva, além dos aspectos financeiros dos projetos e os pontos importantes para atendimento da legislação atualmente em vigor. Finalmente, para cada procedimento apresentado, o mesmo é contextualizado através da apresentação de um caso prático associado. / This work aims to provide methodological contributions to PLC/BPL implementations in their several real installation environments. It is presented the basic aspects of the technology as well as the operation principle, the networks topologies, the advantages and the disadvantages and application examples. Furthermore, it is presented the contributions of this work, which goal is to establish procedures related to projects developments of PLC communication networks, some procedures related to the installation process in their real environments and the procedures for commissioning a deployed network. It is emphasized the commercial networks aspects, which demand several performance requirements, the preventive and/or corrective maintenance, as well as the financial aspects and the main topics to comply with the current regulation. Finally, every presented procedure is exemplified with a real case in order to demonstrate its practical functionality.