Browsing by Subject "Nanophotonics."

Now showing 1 - 5 of 5

Open Access
Design and development of novel large scale applications in micro/nanophotonics and nanobiotechnology
(2014) Özgür, Erol
Developments in micro/nanophotonics and nanobiotechnology creates new opportunities regarding development of devices with unprecedented capabilities, which could improve human civilization substantially. On the other hand, a certain level of maturity in transforming these possibilities into reality still requires considerable efforts. One of the main problems of these novel technologies is that their practical know-how is so scarce that they could only be utilized within strictly determined laboratory conditions, and by highly sophisticated scientists. This thesis focuses on large scale applications at the intersection of microphotonics and nanobiotechnology, and also in nanophotonics. On microphotonics side, optical microresonators with toroidal shape were successfully fabricated and optically integrated. Having an extremely high sensitivity towards perturbations in their environments, these microcavities could be used as biological sensors; however, they are also very sensitive for nonspecific interactions. Thus, a novel surface chemistry enabling bioconjugation of molecular probes without compromising their sensitivity and enhancing their selectivity was developed, based on methylphosphonate containing silane modification of the microtoroid surface. After this functionalization, microtoroids were used in biodetection in complex media. Also, a macroscopic photodetection device composed on intrinsically aligned semiconducting selenium nanowires were demonstrated. This device could be considered as a novel and efficient demonstration of nanowire integration to the macroscopic world. Together with the research on biosensors, these are important large scale applications of emergent science of our age.
Open Access
Novel plasmonic devices for nano-photonics applications
(2013) Şahin, Levent
Plasmonics have attracted a great deal of interest because of their potential to design novel photonics devices which have unique optical properties. This dissertation focuses on novel plasmonic device designs for photonics applications. Electromagnetic properties of metamaterials are characterized and the resonance mechanism of Split Ring Resonator (SRR) structure is investigated. Furthermore, novel SRR-based metamaterial structures are studied. We demonstrated the significant plasmonic enhancement in the transmission characteristics through a sub-wavelength aperture by utilizing SRR resonances. Electrical tuning of plasmonic resonance with varying gate bias by using graphene is observed. Also, electrical properties of graphene is investigated. Fabrication of electrically gated graphene based plasmonic structures are realized. In addition, we utilized metamaterials to design novel photonic devices and we experimentally studied and numerically verified the novel propagation characteristics of graphene-based photonic devices and 3D nanostructures. The proposed structures are designed, simulated, fabricated and measured. The simulations and experimental results are in good agreement and shows significant enhancement of transmission characteristics of plasmonic devices. The dimensions of the structures that are designed in our work is less than 10 times smaller than the incident wavelength (r/λ~0.1) which is a desired property for enhanced light confinement of sensors. Also, the gate tuning of SRR's plasmonic resonance is the first demonstration in the contemporary literature according to our knowledge.
Open Access
Optical near field interaction of spherical quantum dots
(2012) Amirahmadov, Togay
Nanometer-sized materials can be used to make advanced photonic devices. However, as far as the conventional far-field light is concerned, the size of these photonic devices cannot be reduced beyond the diffraction limit of light, unless emerging optical near-fields (ONF) are utilized. ONF is the localized field on the surface of nanometric particles, manifesting itself in the form of dressed photons as a result of light-matter interaction, which are bound to the material and not massless. In this thesis, we theoretically study a system composed of differentsized quantum dots involving ONF interactions to enable optical excitation transfer. Here this is explained by resonance energy transfer via an optical nearfield interaction between the lowest state of the small quantum dot and the first dipole-forbidden excited state of the large quantum dot via the dressed photon exchange for a specific ratio of quantum dot size. By using the projection operator method, we derived the formalism for the transfered energy from one state to another for strong confinement regime for the first time. We performed numerical analyses of the optical near-field energy transfer rate for spherical colloidal quantum dots made of CdSe, CdTe, CdSe/ZnS and PbSe. We estimated that the energy transfer time to the dipole forbidden states of quantum dot is sufficiently shorter than the radiative lifetime of excitons in each quantum dot. This model of ONF is essential to understanding and designing systems of such quantum dots for use in near-field photonic devices.
Open Access
Plasmonic nanoantennas for enhanced light-matter interactions and graphene based tunable nanophotonic devices
(2015) Çakmakyapan, Semih
Focusing, manipulating and beaming of electromagnetic waves are important for many applications such as antennas, optical isolators, biological sensor, chemical sensors, and solar cells. There is an extensive research about the manipulation of light, and its interaction with di erent types of materials including subwavelength structures. However, manipulating light at the nanoscale has many di culties due to the di raction limit. In this thesis, we mainly focus on the characterization and experiments of subwavelength plasmonic structures. We investigated the spatial distribution of the electric eld through subwavelength slits by using symmetric and non-symmetric periodic metallic grating structures in order to obtain one-way transmission, o -axis beaming, collimation and diode-like beaming. We also studied various plasmonic structures such as circular rings and fractal bowtie antennas. After combining them with Raman active molecules, we showed that these plasmonic structures can be used as e cient surface enhanced Raman spectroscopy substrates. Finally, we designed, fabricated and measured nanoantennas and split ring resonators on graphene in order to tune their optical response using the electrically controllable doping property of the graphene.
Open Access
Ultraviolet-visible nanophotonic devices
(2010) Bütün, Bayram
Recently in semiconductor market, III-Nitride materials and devices are of much interest due to their mechanical strength, radiation resistance, working in the spectrum from visible down to the deep ultraviolet region and solar-blind device applications. These properties made them strongest candidates for space telecommunication, white light generation, high power lasers and laser pumping light emitting diodes. Since, like other semiconductors, there have been material quality related issues, ongoing research efforts are concentrated on growing high quality crystals and making low p-type ohmic contact. Also, in light emitting device applications, similar to the visible and infrared spectrum components, there are challenging issues like high extraction efficiency and controlled radiation. In this thesis, we worked on growth and characterizations of high quality (In,Al)GaN based semiconductors, fabricating high performance photodiodes and light emitting diodes. We studied different surface modifications and possibilities of obtaining light emitting diode pumped organic/inorganic hybrid laser sources