No description available.

Nowadays Optical fiber communication is one of the important way to convey information, and there is strong competition in optical long-haul transmission to achieve high channel bit rates and large transmission capacity. Therefore, it is important to study a technology to improve the performance of such system. As we have already known, the dispersion flattened fiber (DFF) and Return-to-zero differential phase shift keying (RZ-DPSK) modulation are attractive, because it can improve the transmission performance of the long-haul system, therefore, it is possible to improve the transmission performance by a combination of the RZ-DPSK and the DFF, and the performance improvement investigation is required, because it will contribute to improve the system design of the long-haul optical fiber communication systems in near future. In this master thesis, a theoretical study focused on the RZ-DPSK transmission system using DFF is conducted. One important technology of current long-haul optical fiber communication system is a dispersion map. In this master thesis, difference of the transmission performance is characterized with regard to number of dispersion blocks within the dispersion map, different repeater output power and different compensation scheme within dispersion map, etc., all of them calculated by a numerical simulator .The goal is to clarify the optimum dispersion map design of the long-haul DPSK based transmission and find the effective method to improve the transmission performance.

In an attempt to mitigate the effects of the atmosphere on the coherence of an optical (laser) beam, interest has recently been shown in changing the beam shape to determine if a different power distribution at the transmitter will reduce the effects of the random fluctuations in the refractive index. Here, a model is developed for the field of a flattened Gaussian beam as it propagates through atmospheric turbulence, and the resulting effects upon the scintillation of the beam and upon beam wander are determined. A comparison of these results is made with the like effects on a standard TEM00 Gaussian beam. The theoretical results are verified by comparison with a computer simulation model for the flattened Gaussian beam. Further, a determination of the probability of fade and of mean fade time under weak fluctuation conditions is determined using the widely accepted lognormal model. Although this model has been shown to be somewhat optimistic when compared to results obtained in field tests, it has value here in allowing us to compare the effects of atmospheric conditions on the fade statistics of the FGB with those of the lowest order Gaussian beam. The effective spot size of the beam, as it compares to the spot size of the lowest order Gaussian beam, is also analyzed using Carter's definition of spot size for higher order Gaussian beams.

Thesis (MSc)--Stellenbosch University, 2011. / ENGLISH ABSTRACT: Lasers are commonly used in the industry for various applications such as laser cutting, laser drilling, lithography, medical applications, surface cleaning and a myriad of other applications. In any application of a laser the beam properties are significant. In the paint removal application discussed in this thesis, the beam properties of the laser beam can have a large impact on the efficiency of the paint removal process. The pulse energy or the average output power of the laser is normally an important parameter in laser materials processing applications. The spatial profile or intensity distribution of the beam also has an influence on the process. The propagation of the laser beam from the laser to the working point is also significant in applying the laser beam to the material. In the ideal scenario one would like to control all the parameters of the laser in terms of the output, in energy or output power, the propagation of the laser beam and the intensity distribution of the beam. The process of laser-based paint removal is no different to this. In this process a TEA CO2 laser is used for the ablation of paint from a substrate. In this application high pulse energy is required from the laser together with good beam propagation properties for delivery of the beam over a long distance. For this application the multimode beam of the TEA CO2 laser can be applied for the paint removal. The multimode beam has sufficiently high pulse energy for the paint removal process, but is not suitable for propagating over long distances through a beam path with a finite aperture. Furthermore the multimode beam does not have a uniform energy intensity distribution. It would therefore be ideal if the TEA CO2 laser could be designed with a custom beam that has a uniform intensity distribution, high pulse energy and good beam propagation. These requirements lead to the study of flattened irradiance profile laser beams. In this thesis flattened irradiance profile beams in the form of Flattened Gaussian beams are investigated. The theory of the Flattened Gaussian profile as well as the propagation of the beam is investigated. Furthermore the generation of such a beam internally to the laser resonator is studied. In succession to this a custom laser resonator was designed and implemented on the TEA CO2 laser. The resulting Flattened Gaussian Beam was characterised and applied to the application of laser paint removal. It was finally shown that the Flattened Gaussian Beam could be successfully generated and applied with equal success in the application of laser paint removal. / AFRIKAANSE OPSOMMING: Lasers word algemeen in die industrie gebruik vir toepassings soos laser snywerk, laser boorwerk, litografie, mediese toepassings, oppervlakreiniging en verskeie ander. In enige toepassing van 'n laser is die eienskappe van die laserbundel van groot belang vir die proses. In die verf verwydering toepassing wat bespreek word in hierdie tesis het die bundel eienskappe 'n groot invloed op die effektiwiteit van die verf stropings proses. Die pulsenergie of uitset drywing van die laser is gewoonlik 'n belangrike parameter in 'n materiaalverwerkings toepassing. Die ruimtelike profiel of energie intensiteitprofiel van die bundel het ook 'n invloed op die proses. Die voortplanting van die bundel vanaf die laser na die werkspunt het ook 'n beduidende invloed op die toepassing van die laserbundel op die materiaal. In die ideale geval sal mens graag al die parameters van die laserbundel soos pulsenergie of drywing, die bundel voortplanting en energie intensiteitprofiel wil beheer. Die toepassing van die laser vir verfverwydering vereis ook die beheer van hierdie unieke parameters wat reeds genoem is. In hierdie proses is 'n TEA CO2 laser gebruik vir die verwydering van verf van 'n substraat. Die toepassing vereis hoë pulsenergie saam met goeie bundel voortplantingseienskappe vir lewering van die bundel oor lang afstande. Die multimode bundel van die laser kan gebruik word vir hierdie toepassing. Die multimode bundel bevat genoegsame energie vir die verfstropings proses maar is nie geskik vir voortplanting oor lang afstande deur 'n bundelpad wat 'n beperking op die bundel grootte het nie. Verder het die multimode bundel ook nie 'n uniforme energie intensiteitprofiel nie. Dit sou ideal wees as die TEA CO2 laser toegerus kon word met 'n toepassingsgerigte bundel wat hoë puls energie, goeie bundel voortplanting en 'n uniforme intensiteitprofiel het. Hierdie vereiste het gelei tot die studie van laserbundels met 'n uniforme plat energie intensiteitprofiel. In hierdie tesis word plat intensiteit bundels in die vorm van plat Gaussiese bundels ondersoek. Die teorie van plat Gaussiese bundels sowel as die voortplanting van hierdie bundels word hier ondersoek. Verder word die opwekking van hierdie bundels intern tot die laserresonator ook ondersoek. Na die ondersoek is daar oorgegaan in die ontwerp en implementering van 'n doelgemaakte resonator op 'n TEA CO2 laser. Die resonator het 'n plat Gaussiese bundel as uitset gelewer. Die bundel was gevolglik gekarakteriseer en aangewend in 'n verfstropings toepassing. Ten einde is daar getoon dat 'n plat Gaussiese bundel suksesvol opgewek en toegepas kon word.

With the increasing demand on wireless and portable devices, the radio frequency front end blocks are required to feature properties such as wideband, high frequency, multiple operating frequencies, low cost and compact size. However, the current radio frequency system blocks are designed by combining several individual frequency band blocks into one functional block, which increase the cost and size of devices. To address these issues, it is important to develop novel approaches to further advance the current design methodologies in both space and spectrum domains. In recent years, the concept of artificial materials has been proposed and studied intensively in RF/Microwave, Terahertz, and optical frequency range. It is a combination of conventional materials such as air, wood, metal and plastic. It can achieve the material properties that have not been found in nature. Therefore, the artificial material (i.e. meta-materials) provides design freedoms to control both the spectrum performance and geometrical structures of radio frequency front end blocks and other high frequency systems. In this dissertation, several artificial materials are proposed and designed by different methods, and their applications to different high frequency components and circuits are studied. First, quasi-conformal mapping (QCM) method is applied to design plasmonic wave-adapters and couplers working at the optical frequency range. Second, inverse QCM method is proposed to implement flattened Luneburg lens antennas and parabolic antennas in the microwave range. Third, a dual-band compact directional coupler is realized by applying artificial transmission lines. In addition, a fully symmetrical coupler with artificial lumped element structure is also implemented. Finally, a tunable on-chip inductor, compact CMOS transmission lines, and metamaterial-based interconnects are proposed using artificial metal structures. All the proposed designs are simulated in full-wave 3D electromagnetic solvers, and the measurement results agree well with the simulation results. These artificial material-based novel design methodologies pave the way toward next generation high frequency circuit, component, and system design.

The performance of fused fiber couplers is wavelength dependent. Wavelength spectral compensation is a technique to decrease the effect of the wavelength dependence, which is an essential task for many applications in fiber optic communication systems. Fiber devices such as wavelength-flattened couplers (WFCs) can be fabricated using wavelength spectral compensation methods. In this dissertation, wavelength spectral compensation techniques in fused biconical taper (FBT) couplers including both multimode and single-mode fiber couplers are studied in detail. In multimode fiber coupler operation, a novel theoretical model based on frustrated total internal reflection (FTIR) has been developed to effectively describe the power coupling and loss mechanism. Experimental results support the theoretical predictions. In single-mode fiber couplers, the conventional technique of fabricating WFCs is discussed. An alternative analytical model has been developed based upon coupled mode theory, which provides a relatively simple and mathematically sound explanation to the wavelength spectral compensation. Aiming to simplify WFC fabrication, a new way of constructing WFCs is proposed and demonstrated by connecting regular single-mode fiber couplers, some of which serve as wavelength spectral compensators. WFCs of various structures including 2x2, 1x3, 1x2ᴺ, and 4x4 have been developed, and the experimental data agree with theoretical predictions of performance. Potential applications and future research directions in wavelength spectral compensation are also presented. / Ph. D.

I learned to authentically connect by observing the pedagogues who mentored me. My lived experience with them inspired me to base my pedagogical approach on the constructs of community and engagement that youth dismantled by displaying increasing disengagement, which transferred into disaffected relationships. This reflexive/narrative autoethnography investigates the problematic phenomenon affecting youth: the loss of authentic connectivity. I critically examine my professional journey with pre-digital, digital, and post-digital university students by analysing our common, cultural context, thereby interpreting my behaviour, thoughts, and experiences in relation to them. Hermeneutic phenomenology’s framework deepens the inquiry, as it involves a broader cultural, political, and social understanding to uncover deeper meaning in changing behaviours by reflecting on what is the lived experience of authentic connectivity for youth. My comprehensive research evidences that youth’s technological addiction has influenced rapid brain evolution, and exploded their visual and multimodal skills. Neuroscience has broadly concluded that the new forms of learning technology offers are changing the way the brain processes information. I suggest that youth are experiencing a biological conflict, the brain’s rapid evolution overwhelming more slowly evolving physical responses, effectively interfering with the flow of affective information that requires hemispheric transfer. Neither moving beyond the premise of intelligence as being predominantly brain-based, nor acknowledging the cooperative role our bodily intelligence plays, as the latter is embedded in our lived experience, the greater understanding of the whole of learning, and its ally, authentic connectivity, cannot be achieved. I submit that moving beyond the absoluteness of a purely scientific approach to the brain, and integrating both human and cognitive sciences are key in moving toward a more holistic, autonomous learning pedagogy, so to layer our understanding of the ‘person process’, that which includes whole thinking and whole being. To counter the affective devolution, which is detrimental not only to learning, but to being a well-adjusted person, this paper proposes a foundational shift in teacher training curriculum design by suggesting tools that foster an observational pedagogy, which seeks to teach those navigational skills that support higher-level analytical processes that can counteract the excessive reactions that impede learning, and teaching.

The thesis is concerned with a prominent phenomenon of the mountain areas - the anemo- orographic systems which occur as a consequence of the collaboration of prevailing winds and of the large windward valleys, the summit flattened surfaces and the leeward slopes. Their presence has a vast influence of numerous physical-geographical realms, mainly due to the highly uneven spatial snow cover distribution within these systems. The focus of the thesis lies on the highest elevations of the Hrubý Jeseník Mts. which reach or exceed the alpine treeline. In this area, the anemo-orographic systems were already defined earlier but a thorough description and of their presence and activity has not been carried out so far, which is the main aim of the thesis. A detailed and spatially compact mapping and measurement of the flag or banner trees has been performed, as these, thanks to their deformed asymmetric shape, attest to the prevailing or mean wind direction as well as its velocity with a high accuracy. As a secondary and comparative data source the meteorological measurements from the summits of Praděd and Šerák Mounts and a modern and detailed wind model has been used. A verification measurement of snow cover depth at selected locations under presumed strong wind action was executed as well. The acquired...