Solar power is a clean, renewable source of energy. There is a growing demand for cheap, high efficiency photovoltaic cells. Of the many emerging solar harvesting technologies, a concept that has not been widely explored is that of optical antennas. In 1972 Bailey et al.[1] explored scaling down of antenna technology to match the solar spectrum. A recent review was given by Lukas Novotny et al.[2], in which they outline the major hurdles as being the lack of reliable nano-fabrication and an inability to rectify into the Tera-hertz frequencies band. Presently we aim to fabricate photovoltaic cells that incorporate an array of vertically aligned metallic nano-rods (MNR). Porous aluminum oxide (PAO) is used as a nano-structured template for growth of the MNR. PAO exhibit vertically aligned pores (D = 20 - 200nm) in a densely packed hexagonal arrangement. MNR fabrication is achieved through templated electrochemical deposition, and investigated with SEM and VIS-IR spectroscopy. MNR samples have been specifically designed to be incorporated as a photoactive material for a novel photovoltaic cell. Through fine control of their length, the MNR excitation energy can be tuned to the visible spectrum. Excitation of the MNR leads to energy transfer with localized acceptor molecules, creating a rectification of the field. The fabrication of MNR helps progress the development of the proposed antenna photovoltaic device. [1] R. L. Bailey, “A Proposed New Concept for a Solar-Energy Converter," Journal of Engineering for Power, pp. 73-77, Apr. 1972. [2] P. Bharadwaj, B. Deutsch, and L. Novotny, “Optical Antennas," Advances in Optics and Photonics, vol. 1, pp. 438-483, May 2009. / Thesis (Master, Chemistry) -- Queen's University, 2013-01-07 12:36:57.17

Optical nanoantennas have raised much interest during the past decade for their vast potential in photonics applications. This thesis investigates the response of periodic arrays of nanomonopoles and nanodipoles on a silicon substrate, covered by water, to variations of antenna dimensions. These arrays are illuminated by a plane wave source located inside the silicon substrate. Modal analysis was performed and the mode in the nanoantennas was identified. By characterizing the properties of this mode certain response behaviours of the system were explained. Expressions are offered to predict approximately the resonant length of nanomonopoles and nanodipoles, by accounting for the fringing fields at the antenna ends and the effects of the gap in dipoles. These expressions enable one to predict the resonant length of nanomonopoles within 20% and nanodipoles within 10% error, which significantly facilitates the design of such antennas for specific applications.

Optical nanoantennas have raised much interest during the past decade for their vast potential in photonics applications. This thesis investigates the response of periodic arrays of nanomonopoles and nanodipoles on a silicon substrate, covered by water, to variations of antenna dimensions. These arrays are illuminated by a plane wave source located inside the silicon substrate. Modal analysis was performed and the mode in the nanoantennas was identified. By characterizing the properties of this mode certain response behaviours of the system were explained. Expressions are offered to predict approximately the resonant length of nanomonopoles and nanodipoles, by accounting for the fringing fields at the antenna ends and the effects of the gap in dipoles. These expressions enable one to predict the resonant length of nanomonopoles within 20% and nanodipoles within 10% error, which significantly facilitates the design of such antennas for specific applications.

Optical nanoantennas have raised much interest during the past decade for their vast potential in photonics applications. This thesis investigates the response of periodic arrays of nanomonopoles and nanodipoles on a silicon substrate, covered by water, to variations of antenna dimensions. These arrays are illuminated by a plane wave source located inside the silicon substrate. Modal analysis was performed and the mode in the nanoantennas was identified. By characterizing the properties of this mode certain response behaviours of the system were explained. Expressions are offered to predict approximately the resonant length of nanomonopoles and nanodipoles, by accounting for the fringing fields at the antenna ends and the effects of the gap in dipoles. These expressions enable one to predict the resonant length of nanomonopoles within 20% and nanodipoles within 10% error, which significantly facilitates the design of such antennas for specific applications.

Influence optical response on underetching of plasmonic antennas is observed in this thesis. When light falls with resonant wavelength on the optical antennas, the electromagnetic field is amplified near this antennas. The resonant wavelength depends on the length of the antenna and on effective refractive index given by the ambient properties around the antenna. The contact surface with substrate (dielectric) is reduced by underetching the antenna and the effective refractive index is changed and thus the optical response of the antenna is changed.

No description available.

Au cours des dernières années, la communauté scientifique s'est intéressée de plus en plus à l'acquisition de sources d'énergie renouvelables vertes et propres par rapport aux combustibles fossiles traditionnels. Le rayonnement solaire est une source particulièrement abondante d'énergie renouvelable qui a été largement utilisée dans les véhicules, les machines et les bâtiments, entre autres. Il y a généralement deux manières différentes d'utiliser l'énergie solaire: la chaleur et l'électricité. La principale motivation de ce travail de thèse est d'utiliser cette abondante source d'énergie pour produire une petite fraction de la tension et du courant continu de sortie. Puisque le spectre solaire se situe dans les longueurs d'onde à l'échelle nanométrique ou dans la bande térahertz, les antennes optiques seront utilisées comme une nouvelle technologie de nanotechnologie pour capter et récolter l'énergie solaire. Les antennes optiques ont des propriétés similaires à celles de leurs homologues micro-ondes, mais leur avantage réside dans des moyens sans précédent pour adapter les champs électromagnétiques dans tous leurs aspects et applications. Par conséquent, avec les détails mentionnés ci-dessus, l'idée principale de cette thèse est de capturer le rayonnement infrarouge solaire et l'utiliser pour produire une tension continue de sortie. La première partie de cette thèse est consacrée à la compréhension du fonctionnement de la collecte d'énergie par radiofréquence (RF) et à la présentation d'un concept de rectenna. La deuxième partie traite de l'introduction et de la simulation d'antennes optiques à base de résonateurs diélectriques (DR) car elles offrent moins de pertes à la bande THz. Deux conceptions de DR différentes sont proposées fonctionnant à la fréquence centrale de 193,5 THz (longueur d'onde 1550 nm). La troisième partie traite de la contribution principale à ce travail en termes de conception, simulation et fabrication d'une antenne optique Yagi-uda à haut gain et large bande. La technique de lithographie par faisceau d'électrons est utilisée pour réaliser la structure proposée. En dehors de la conception de l'élément unique Yagi-uda, diverses configurations de réseau ont été simulées avec la réalisation d'un réseau d'éléments 100 x 100 fabriqué sur un substrat de silicium. Pour produire une certaine quantité de tension de sortie, deux techniques ont été utilisées pour tester le réseau d'antennes optiques Yagi-uda. La première technique impliquait l'intégration du réseau Yagi-uda avec une diode fermionique du commerce qui produisait une tension de sortie de 0,15 V par excitation à partir d'une lumière visible et de 0,52 V par excitation directe à partir d'un laser à 1550 nm. La deuxième technique est basée sur la dissipation thermique entre des métaux dissemblables produisant une tension de sortie. Quatre lasers à longueurs d'onde différents (532 nm, 650 nm, 940 nm et 1550 nm) ont excité trois conceptions de nantenna réalisées. Parmi ces conceptions, la tension de sortie maximale de 0,82 V a été produite par le réseau Yagi-uda lorsqu'il est excité via un laser de 1550 nm. / Recent years have witnessed an increased interest by the scientific community to acquire green and clean renewable sources of energy compared to traditional fossil fuels. Solar radiation is one particular abundant source of renewable energy that has been widely applied in vehicles, machines, and buildings, among others. There are generally two different ways in which solar energy is used – heat and electricity. The main motivation of this thesis work is to utilize that abundant source of energy in producing a small fraction of output DC voltage and current. Since the solar spectrum lies in the nano scale wavelengths or terahertz band, optical antennas as a novel nano fabrication technology will be used to capture and harvest the solar energy. Optical antennas have properties similar to their microwave counterparts, but the advantage they have is in terms of unprecedented means to tailor electromagnetic fields in all its aspects and applications. Therefore, with the aforementioned details, the main idea of this thesis is to capture the solar infrared radiation and utilize it for producing output DC voltage. The first part of this thesis is dedicated to understanding the working of radio frequency (RF) energy harvesting and presenting a rectenna design. The second part deals with the introduction and simulation of optical antennas based of dielectric resonators (DR) as they offer fewer losses at the THz band. Two different DR designs are proposed working at the center frequency of 193.5 THz (1550 nm wavelength). The third part discusses the main contribution to this work in terms of design, simulation and fabrication of a high gain and wideband Yagi-uda optical antenna. E-beam lithography technique is used to realize the proposed structure. Apart for the single element Yagi-uda design, various array configurations have been simulated with realization of a 100 x 100 elements array fabricated on a silicon substrate. To produce a certain amount of output voltage, two techniques were deployed in testing the realized Yagi-uda optical antenna array. The first technique involved integration of the Yagi-uda array with a commercial fermionic diode that produced output voltage of 0.15 V via excitation from a visible light and 0.52 V with direct excitation from a 1550 nm laser. The second technique is based on thermal dissipation among dissimilar metals producing an output voltage. Four different wavelength (532 nm, 650 nm, 940 nm and 1550 nm) lasers excited three realized nantenna designs. Among these designs, the maximum output voltage of 0.82 V was produced by the Yagi-uda array when excited via 1550 nm laser.

Ma thèse est consacrée aux nouveaux phénomènes nano-optiques et aux dispositifs basés sur l'interaction spin-orbite de la lumière (SOI). Tout d'abord, il a été démontré un SOI uniquement piloté par le champ magnétique de la lumière permettant de diriger avec précision les ondes de surface de Bloch, offrant ainsi une nouvelle manifestation du champ magnétique optique. Ensuite, nous avons proposé et démontré le concept de nano-antenne plasmonique hélicoïdale à ondes progressives (TW-HPA), c’est-à-dire un fil hélicoïdal en or étroit alimenté optiquement par une nano-antenne dipolaire dans une configuration « end-firing ». Une telle nano-antenne a été démontrée comme la première optique de polarisation sublongueur d’onde. L’agencement de TW-HPAs à l’échelle de quelques microns a permis de convertir « à la carte » un faisceau polarisé linéairement en une distribution de faisceaux directifs présentant des polarisations différentes définies de façon déterministe par la géométrie et les dimensions des nano-antennes. Par le biais d’un couplage en champ proche de quatre nano-antennes à hélicités opposées, nous avons obtenus une optique sublongueur d’onde permettant un degré de liberté dans le contrôle de la polarisation qui est interdit avec les composants et méthodes classiques basées sur l’exploitation de matériaux biréfringents ou dichroïques, ou de métamatériaux imitant ces propriétés. / My thesis is devoted to novel nano-optical phenomena and devices based on spin-orbit interaction (SOI) of light. First, magnetic spin-locking, i.e., an SOI solely driven by the magnetic field of light, is demonstrated with Bloch surface waves. It provides a new manifestation of the magnetic light field. Then, we propose and demonstrate the concept of traveling-wave plasmonic helical antenna (TW-HPA), consisting of a narrow helical gold-coated wire non-radiatively fed with a dipolar nano-antenna. By swirling surface plasmons, the TW-HPA combines subwavelength illumination and polarization transformation. The TW-HPA is demonstrated to radiate on the subwavelength scale almost perfectly circularly polarized optical waves upon illumination with linearly polarized light. With this subwavelength plasmonic antenna, we developed strongly integrated arrays of point-light emissions of opposite handedness and tunable intensities. Finally, by coupling two couples of TW-HPAs of opposite handedness, we obtained new polarization properties so far unattainable.

Decades of efforts have pushed the replacement of electrical interconnects by optical links to the interconnects between computers, racks and circuit boards. It may be expected that optical solutions will further be used for inter-chip and intra-chip interconnects with potential benefits in bandwidth, capacity, delay, power consumption and crosstalk. Silicon integration is emerging to be the best candidate nowadays due to not only the dominant status of silicon in microelectronics but also the great advantages brought to the photonic integrated circuits (PICs). Regarding the recent breakthroughs concerning active devices on silicon substrate, the question left is no longer the feasibility of the optical interconnects based on silicon but the competitiveness of the silicon device compared with other alternatives. This thesis focuses on the study of two key components for the optical interconnects, both especially designed and fabricated for silicon platform. One is a high speed electroabsorption modulator (EAM), realized by transferring an InP-based segmented design to the hybrid silicon evanescent platform. The purpose here is to increase the speed of the silicon PICs to over 50  Gb/s or more. The other one is a high performance grating coupler, with the purpose to improve the optical interface between the silicon PICs and the outside fiber-based communication system. An general approach based on the transmission line analysis has been developed to evaluate the modulation response of an EAM with a lumped, traveling-wave, segmented or capacitively-loaded configuration. A genetic algorithm is used to optimize its configuration. This method has been applied to the design of the EAMs on hybrid silicon evanescent platform. Based on the comparison of various electrode design, segmented configuration is adopted for the target of a bandwidth over 40 GHz with as low as possible voltage and high extinction ratio. In addition to the common periodic analysis, the grating coupler is analyzed by the antenna theory assisted with an improved volume-current method, where the directionality of a grating coupler can be obtained analytically. In order to improve the performance of the grating coupler, a direct way is to address its shortcoming by e.g. increasing the coupling efficiency. For this reason, a nonuniform grating coupler with apodized grooves has been developed with a coupling efficiency of 64%, nearly a double of a standard one. Another way is to add more functionalities to the grating coupler. To do this, a polarization beam splitter (PBS) based on a bidirectional grating coupler has been proposed and experimentally demonstrated. An extinction ratio of around -20 dB, as well as a maximum coupling efficiency of over 50% for both polarizations, is achieved by such a PBS with a Bragg reflector underneath. / QC 20100906

Les nano-antennes optiques sont de nouveaux éléments, généralement métalliques, permettant d’améliorer les interactions électromagnétiques entre le rayonnement lumineux et un objet sub-longueur d’onde. Ces dispositifs innovants, fonctionnant dans une gamme de longueur d’onde correspondant au spectre visible et proche infrarouge, répondent à certaines contraintes inhérentes à l’optique lorsque les échelles d’interactions relèvent du nanomètre. En particulier, les propriétés des antennes optiques métalliques sont régies par l’apparition de résonances plasmons qui permettent, d’une part de confiner le champ électromagnétique dans des volumes très inférieurs aux limites imposées par la diffraction, et d’autre part d’exalter fortement les processus optiques à faibles sections efficaces. L’objectif de cette thèse est de comprendre par l’expérience quels sont les paramètres clés qui caractérisent une nano-antenne optique afin d’en contrôler son fonctionnement. Ces paramètres ont été accessibles expérimentalement grâce au développement d’une microscopie adaptée basée sur une illumination diascopique à faible ouverture numérique avec soit une détection coronographique confocale ou conoscopique. Cet appareillage nous a permis de mesurer la capacité d’une antenne optique unique à diffuser un rayonnement lumineux. Les études ont débutées avec des systèmes modèles simples (nanoparticules) pour évoluer vers des antennes couplées (dimères). Par analogie avec le domaine radiofréquences, les paramètres importants d’une antenne optique que sont la plage fréquentielle, le désaccord, le gain et le diagramme de rayonnement ont été définis et mesurés. L’influence des caractéristiques morphologiques de l’antenne sur ces paramètres a complété l’étude. Toujours par comparaison avec les antennes radiofréquences, nous avons introduit le concept de tuner optique. Le principe est de modifier la réponse optique de la charge de l’antenne, c’est-à-dire le milieu dans lequel elle émet son rayonnement. Dans ce but, nous avons utilisé un milieu anisotrope composé des molécules de cristal liquide dont l’orientation de l’ellipsoïde des indices peut être commandée par un champ électrostatique. Le fonctionnement du tuner, c’est-à-dire l’accord de l’antenne à une fréquence de travail, a été démontré pour des antennes optiques couplées. / Optical nanoantennas are a new class of optical devices, generally constituted of metal nanoparticles, used for enhancing the interaction between an electromagnetic wave and a nano-scale object. These components are operating in the visible to near infra-red part of the spectrum and are offering solutions for the inherent limitations of optics at the nanometer scale. In particular, the properties of optical antennas are governed by the surface plasmon resonances of the underlying structure. These resonances are associated with a large field confinement, beyond the diffraction limit, and an enhancement of the local electromagnetic response that is used to amplify weak optical processes. The objective of this doctoral thesis is to understand by an experimental approach what are the key parameters characterizing an optical antenna with the aim to control its operation. Through the development of an original microscopy based on a low numerical aperture diascopic illumination and a subsequent spatial filtering, the scattering characteristics of a single optical nano-antenna were successfully measured. Our approach was first tested with simple model antennas (nanoparticles) before investigating multi-element coupled antennas (dimers). In analogy to radiofrequency theory, we have defined and measured important antenna characteristics: operating frequency, detuning factor, gain and emission diagram. We have studied the influence of the morphology of the antenna on these characteristics. Continuing the comparison with microwave antennas, we have introduced the concept of an optical tuner. The operating principle is to modify the medium in which the antenna is emitting its radiation i.e. the load of the device. To this aim, we have employed anisotropic liquid crystal molecules. With this load medium, the orientation of the anisotropy can be controlled by a static electric field. The operation of the optical tuner, i.e. tuning of the antenna to a broadcasting frequency, is demonstrated for electromagnetically coupled antennas.