Cette thèse a porté sur la réalisation et la caractérisation d'une source paramétrique guidée en GaAs/AlGaAs. Grâce à son design, basé sur la biréfringence de forme, celle-ci permet la génération paramétrique sur une gamme spectrale allant de 1.2 à 2.4 µm. Cette propriété optique et sa taille réduite font d'un tel dispositif un candidat pour la fabrication d'un oscillateur paramétrique optique intégré. Néanmoins, au cours de sa fabrication, les pertes optiques guidées augmentent de 0.1 à 0.5 cm-1 suite à l'oxydation sélective des couches riches en aluminium, les transformant en AlOx. A travers une étude par microscopie électronique en transmission, nous avons tout d'abord caractérisé les propriétés structurales et chimiques de l'AlOx et des interfaces GaAs/AlOx. Nous avons ainsi constaté une augmentation de la rugosité de ces interfaces et une modification locale des couches de GaAs induites par l'étape d'oxydation. Dans un second temps, nous avons caractérisé certaines propriétés optiques des guides d'ondes. Un calcul semi-analytique nous a permis d'établir la valeur des pertes de propagation, en bon accord avec les mesures expérimentales, induite par la rugosité des interfaces GaAs/AlOx. Nous avons ensuite établi les conditions d'oxydation optimales en mesurant systématiquement les pertes de propagation. Nous avons caractérisé les performances de notre source en effectuant la première mesure d'amplification paramétrique dans un guide d'ondes semi-conducteur. Le coefficient de gain paramétrique mesuré, compatible avec l'obtention de l'oscillation paramétrique, nous a amené à concevoir, fabriquer et caractériser différentes cavités résonnantes.

Due to the short period that some photovoltaic technologies have taken part on the solar energy market, it is crucial to evaluate the long term stability of solar cells belonging to those technologies in order to ensure a minimum lifetime of their performance. Accelerated degradation tests are thus carried out to achieve such goals. The present study analyzes the encapsulation effects on co-evaporated manufactured Copper Indium Gallium Selenide (CIGS) solar cells under damp heat conditions, consisting in 85 °C and 85 % relative humidity, during an approximated period of 1000 hours. The experimental procedure has been carried out at Solliance Solar Research facilities. Since the encapsulation packages play a critical role as a protection to achieve long term stability of the solar cells and modules, several packaging structures and materials has been taken into study. Thus, eighteen types of mini modules were manufactured including different combinations of encapsulants, front sheet foils, thin film protective barriers and CIGS cells from different manufacturers. The design of these mini modules and the manufacturing process to obtain them is also presented in this work. Various characterization techniques were carried out in order to acquire the required information about the solar cells and encapsulants performance along the damp heat degradation process. The results exposed that encapsulation packages including thin film barriers between the encapsulant and the front sheet foil allowed a longer solar cell lifetime due to their remarkable protection against moisture ingress. Moreover, the degradation of the molybdenum layer included in the CIGS cells was found as principal cause of efficiency decrement and end of performance of solar cells protected by regular encapsulant and front sheet foils. Some other findings in relation with the evaluated components are shown along the present study.

Face à la diversification des domaines d'application en optoélectronique, les émetteurs lasers, dont les VCSELs, évoluent rapidement vers une plus grande capacité d'intégration, ainsi qu'un accroissement de leurs fonctionnalités. Ceci a pour conséquence une sophistication des structures et des géométries de ces composants, impliquant la levée de certains verrous technologiques. Ce travail de thèse porte, d'une part, sur la mise en place d'une méthodologie d'optimisation de la croissance, d'analyse et de diagnostic rapide intégrée au procédé d'épitaxie par jets moléculaires (uniformité, maîtrise des propriétés optiques) démontrée sur de nouvelles structures VCSEL à multicouche complexe. D'autre part, la technologie d'oxydation d'alliages GaAlAs a été étudiée. Ce procédé, appelé AlOx, a ouvert la voie à l'obtention de composants monomodes performants grâce au confinement électro-optique latéral efficace qu'il réalise. Dans le but d'une maîtrise ultime et d'une ingénierie fine de ce confinement, nous avons approfondi la compréhension des cinétiques d'oxydation, mis en place un four avec contrôle en temps réel du front d'oxydation, et étudié une nouvelle technique d'oxydation d'une couche enterrée GaAlAs à partir de la surface. Ce travail contribue au développement des technologies de structurations verticale et latérale dans les composants à microcavité verticale, qui visent à leur ouvrir de nouvelles performances et fonctionnalités.

Pour répondre aux besoins des domaines d'applications, de plus en plus ambitieux, et gagner de nouveaux domaines, les VCSELs continuent à évoluer. On note une tendance des recherches récentes à la miniaturisation des sources VCSELs et à la complexification de leurs architectures pour augmenter leur capacité d'intégration et incorporer de nouvelles fonctionnalités. Cela nécessite la maîtrise et l'adaptation des différentes étapes technologiques dont l'ingénierie du confinement électrique et optique exploitant la technologie d'oxydation sélective humide d'alliages AlGaAs, appelée AlOx. Ce travail de thèse porte, d'une part, sur l'étude des contraintes mécaniques engendrées par le procédé AlOx, qui ont un impact important sur le fonctionnement des VCSELs, leur fiabilité et leur durée de vie. D'autre part, je présente une nouvelle approche planaire de la technologie AlOx basée sur une oxydation d'une couche AlGaAs enterrée à travers des trous nanométriques gravés dans une couche GaAs fine en surface. Cette étape est suivie d'une reprise d'épitaxie par jets moléculaires (EJM) pour continuer l'empilement de la structure du composant. La nouvelle méthode offre une meilleure capacité d'intégration, une meilleure dissipation de chaleur et ouvre vers l'ingénierie libre du confinement opto-électrique.

Background Iron deficiency (ID) is the world‟s most prevalent micronutrient deficiency and predominantly affects developing countries, also South Africa. In areas with low fish consumption and high n-6 PUFA vegetable oil intake, there is a risk for having inadequate n-3 PUFA status. Both iron and n-3 PUFA play important roles in the immune response, and supplementation is a strategy to alleviate deficiencies. However, little is known about potential interactive effects between concurrent iron and n-3 PUFA supplementation on the immune system. This is also important in the context that iron supplementation may be unsafe and may increase morbidity and mortality. Aim The overall aim of this thesis was to assess the effects of iron and docosahexaenoic (DHA)/eicosapentaenoic acid (EPA) supplementation, alone and in combination, on the immune system of ID children. More specifically, these effects were investigated on the occurrence and duration of illness and school-absenteeism due to illness, peripheral blood mononuclear cell (PBMC), red blood cell (RBC) and plasma total phospholipid fatty acid composition, iron status, fatty acid-derived immune modulators and targeted PBMC gene expression. Furthermore, association of PBMC, RBC and plasma total phospholipid fatty acid composition with allergic disease, were also examined. Design In a 2-by-2 factorial, randomised, double-blind, placebo-controlled trial, South African children (n = 321, aged 6–11 y) were randomly assigned to receive oral supplements of either 1) iron (50 mg as ferrous sulphate) plus placebo; 2) DHA/EPA (420/80 mg) plus placebo; 3) iron plus DHA/EPA (420/80 mg); or 4) placebo plus placebo for 8.5 mo, four times per week. Absenteeism and illness symptoms were recorded and biochemical parameters for compliance as well as parameters fundamental to immune function were assessed at baseline and endpoint. Furthermore, in a cross-sectional design, associations of allergic disease with baseline fatty acid composition of PBMC, RBC and plasma were examined. Results The combination of iron and DHA/EPA significantly attenuated respiratory illness caused by iron supplementation. DHA/EPA supplementation alone improved respiratory symptoms at school, but increased headache-related absenteeism. DHA/EPA and iron supplementation individually tended to increase and decrease anti-inflammatory DHA and EPA-derived mediators, respectively. Furthermore the anti-inflammatory DHA-derived immune mediator, 17HDHA was higher in the DHA/EPA plus placebo and iron plus DHA/EPA groups than in the iron plus placebo group. Also, the pro-inflammatory arachidonic acid (AA)-derived modulators (5- and 15-hydroxyeicosapentaenoic acid) were significantly lower in the iron plus DHA/EPA group compared to the placebo plus placebo groups. In the study population, 27.2% of the children had allergic disease and AA in PBMC phospholipids was significantly lower in the allergic children than in the non-allergic children. In RBC phospholipids dihomo-gamma-linolenic acid (DGLA) and the ratio of DGLA: linoleic acid (LA) correlated negatively and the n-6:n-3 PUFA ratio positively with total immunoglobulin E (tIgE). Furthermore, trans-C18:1n-9, tended to be higher in the allergic group. Conclusion DHA/EPA prevented respiratory illness caused by iron supplementation and although DHA/EPA on its own reduced respiratory morbidity when the children were present at school, surprisingly it increased the likelihood of being absent with headache and fever. The biochemical findings compliment the clinical results and support previous observations about DHA/EPA supplementation to reduce inflammation, but add to the current knowledge base that a relatively high oral dose of non-haem iron modulates circulating lipid-derived immune modulators and related gene expression. Furthermore, when supplementing with iron and DHA/EPA combined, in this ID population with low fish intake, the anti-inflammatory effect of DHA/EPA is maintained concurrently with attenuation of respiratory morbidity. This finding support the notion that excess iron (probably as non-transferrin bound iron) becomes available for pathogens and is probably why we found that iron increased respiratory infectious morbidity. The improved clinical outcome with combined supplementation seems to be related to increased lipid-mediator synthesis gene expression and the availability of DHA/EPA, leading to a more pro-resolving profile and enhanced immune competence. Overall these results give better insight into immune function and infectious morbidity in relation to n-3 PUFA and iron status and treatment, as well as the possible association of fatty acid status with allergic disease in young South-African school children. / PhD (Nutrition), North-West University, Potchefstroom Campus, 2015

Background Iron deficiency (ID) is the world‟s most prevalent micronutrient deficiency and predominantly affects developing countries, also South Africa. In areas with low fish consumption and high n-6 PUFA vegetable oil intake, there is a risk for having inadequate n-3 PUFA status. Both iron and n-3 PUFA play important roles in the immune response, and supplementation is a strategy to alleviate deficiencies. However, little is known about potential interactive effects between concurrent iron and n-3 PUFA supplementation on the immune system. This is also important in the context that iron supplementation may be unsafe and may increase morbidity and mortality. Aim The overall aim of this thesis was to assess the effects of iron and docosahexaenoic (DHA)/eicosapentaenoic acid (EPA) supplementation, alone and in combination, on the immune system of ID children. More specifically, these effects were investigated on the occurrence and duration of illness and school-absenteeism due to illness, peripheral blood mononuclear cell (PBMC), red blood cell (RBC) and plasma total phospholipid fatty acid composition, iron status, fatty acid-derived immune modulators and targeted PBMC gene expression. Furthermore, association of PBMC, RBC and plasma total phospholipid fatty acid composition with allergic disease, were also examined. Design In a 2-by-2 factorial, randomised, double-blind, placebo-controlled trial, South African children (n = 321, aged 6–11 y) were randomly assigned to receive oral supplements of either 1) iron (50 mg as ferrous sulphate) plus placebo; 2) DHA/EPA (420/80 mg) plus placebo; 3) iron plus DHA/EPA (420/80 mg); or 4) placebo plus placebo for 8.5 mo, four times per week. Absenteeism and illness symptoms were recorded and biochemical parameters for compliance as well as parameters fundamental to immune function were assessed at baseline and endpoint. Furthermore, in a cross-sectional design, associations of allergic disease with baseline fatty acid composition of PBMC, RBC and plasma were examined. Results The combination of iron and DHA/EPA significantly attenuated respiratory illness caused by iron supplementation. DHA/EPA supplementation alone improved respiratory symptoms at school, but increased headache-related absenteeism. DHA/EPA and iron supplementation individually tended to increase and decrease anti-inflammatory DHA and EPA-derived mediators, respectively. Furthermore the anti-inflammatory DHA-derived immune mediator, 17HDHA was higher in the DHA/EPA plus placebo and iron plus DHA/EPA groups than in the iron plus placebo group. Also, the pro-inflammatory arachidonic acid (AA)-derived modulators (5- and 15-hydroxyeicosapentaenoic acid) were significantly lower in the iron plus DHA/EPA group compared to the placebo plus placebo groups. In the study population, 27.2% of the children had allergic disease and AA in PBMC phospholipids was significantly lower in the allergic children than in the non-allergic children. In RBC phospholipids dihomo-gamma-linolenic acid (DGLA) and the ratio of DGLA: linoleic acid (LA) correlated negatively and the n-6:n-3 PUFA ratio positively with total immunoglobulin E (tIgE). Furthermore, trans-C18:1n-9, tended to be higher in the allergic group. Conclusion DHA/EPA prevented respiratory illness caused by iron supplementation and although DHA/EPA on its own reduced respiratory morbidity when the children were present at school, surprisingly it increased the likelihood of being absent with headache and fever. The biochemical findings compliment the clinical results and support previous observations about DHA/EPA supplementation to reduce inflammation, but add to the current knowledge base that a relatively high oral dose of non-haem iron modulates circulating lipid-derived immune modulators and related gene expression. Furthermore, when supplementing with iron and DHA/EPA combined, in this ID population with low fish intake, the anti-inflammatory effect of DHA/EPA is maintained concurrently with attenuation of respiratory morbidity. This finding support the notion that excess iron (probably as non-transferrin bound iron) becomes available for pathogens and is probably why we found that iron increased respiratory infectious morbidity. The improved clinical outcome with combined supplementation seems to be related to increased lipid-mediator synthesis gene expression and the availability of DHA/EPA, leading to a more pro-resolving profile and enhanced immune competence. Overall these results give better insight into immune function and infectious morbidity in relation to n-3 PUFA and iron status and treatment, as well as the possible association of fatty acid status with allergic disease in young South-African school children. / PhD (Nutrition), North-West University, Potchefstroom Campus, 2015