Browsing by Subject "Photonics."

Now showing 1 - 8 of 8

Open Access
Ald grown zno as an alternative material for plasmonic and uncooled infrared imaging applications
(2014) Kesim, Yunus Emre
Plasmonics is touted as a milestone in optoelectronics as this technology can form a bridge between electronics and photonics, enabling the integration of electronics and photonic circuits at the nanoscale. Noble metals such as gold and silver have been extensively used for plasmonic applications due to their ability to support plasmons, yet they suffer from high intrinsic optical losses. Recently, there is an increased effort in the search for alternative plasmonic materials including Si, Ge, III-Nitrides and transparent conductive oxides. The main appeal of these materials, most of them semiconductors, is their lower optical losses, especially in the infrared (IR) regime, compared to noble metals owing to their lower number of free electrons. Other advantages can be listed as low-cost and control on plasma frequency thanks to the tunable electron concentration, i.e. effective doping level. This work focuses on atomic layer deposition (ALD) grown ZnO as a candidate material for plasmonic applications. Optical constants of ZnO are investigated along with figures of merit pertaining to plasmonic waveguides. It is shown that ZnO can alleviate the trade-off between propagation length and mode confinement width owing to tunable dielectric properties. In order to demonstrate plasmonic resonances, a grating structure is simulated using finite-difference-time-domain (FDTD) method and an ultra-wide-band (4-15 µm) infrared absorber is computationally demonstrated. Finally, an all ZnO microbolometer is proposed, where ALD grown ZnO is employed as both the thermistor and the absorber of the microbolometer which is an uncooled infrared imaging unit that relies on the resistance change of the active material (thermistor) as it heats up due to the absorption of incident electromagnetic radiation. The material complexity and process steps of microbolometers could be reduced if the thermistor layer and the absorber layer were consolidated in a single layer. Computational analysis of a basic microbolometer structure using FDTD method is conducted in order to calculate the absorptivity in the long-wave infrared (LWIR) region (8-12 µm). In addition, thermal simulations of the microbolometer structure are conducted using finite element method, and time constant and noise-equivalent-temperature-difference (NETD) values are extracted.
Open Access
Bio-inpired all-polymer 2d photonic crystal fibers = Doğadan esinlenilmiş tamamen polimer 2B fotonik kristal fiberleri
(2014) Doğan, Tamer
Photonic crystals are essential part of the integrated systems which require manipulation of light in a manner that all-optical polarization and re ection properties are completely calibrated to necessary levels. However, beyond scienti c development of photonic crystals, biological systems also provided inspiration for the eld since they perfected the mechanisms in terms of coloration over millions of years. In addition, natural samples are also observed to serve and function for more than single purpose, and this further illuminates the technological designs so as to develop multifunctional structures. Anas Platyrhynchos L. (mallard) is one of the natural examples and detailed investigations yield that its neck feathers have structural coloration, iridescence and hydrophobicity. Being inspired form mallard duck, two-dimensional photonic crystal bers are produced to imitate coloration and surface architecture. The fabrication is established by iterative size reduction technique which, as a top-down method, enables design of nano-scale materials from macro-scale structures. To accurately imitate duck feathers, polycarbonate (PC) and polyvinyldi uoride (PVDF), are characterized and selected for their thermal compatibility and dielectric properties among number of polymers. Produced 2D photonic crystal bers have been demonstrated to re ect color of green like duck feathers, and also shown to have iridescence by optical means. Besides single coloration, all colors of visible spectrum are also obtained to attest potential applicability of fabrication technique and produced bers. It is also substantiated that all colors can be obtained in a single ber by tapering a thick ber. In addition, last but not least, 2D photonic crystal bers are carefully designed to have surface roughness which promoted hydrophobic feature of PVDF and provided better hydrophobicity than natural counterparts. Manufactured structures are also the rst demonstration for production of all-polymer two dimensional photonic crystal bers which may be used in textile or ltering technologies.
Open Access
Design and fabrication of resonant nanoantennas on chalcogenide glasses for nonlinear photonic applications
(2013) Duman, Hüseyin
Optical nanoantennas are the metallic nanostructures which confine electromagnetic waves into sub-wavelength volumes at resonant conditions. They are used for various applications including biological and chemical sensing, single molecule spectroscopy, manipulation and generation of light. Combining extremely large electromagnetic field enhancement in plasmonic resonant nanoantenna with high optical nonlinearity of chalcogenide glass leads to a low-threshold broadband light generation scheme in sub-wavelength chip-scale structures. New frequency generation with ultra-low pumping power in plasmonic nanostructures allows compact on-chip light sources which can find applications in single molecule spectroscopy, optical signal processing and broadband lasers. We propose plasmonic nanoantenna chalcogenide glass systems for initiating nonlinear phenomena at low threshold. Size and shape of antennas are optimized according to linear refractive index of substrate and surrounding media for this purpose by finite difference time domain (FDTD) simulations. Resonant behaviour of antennas at their near-field and nonlinear response of optically highly nonlinear chalcogenide glasses are investigated. On resonance, strong field accumulation at the interface of the gold stripe and highly nonlinear As2Se3 glass triggers a start of the spectral broadening of incident beam accompanied by third harmonic generation at an ultra-low threshold power level of 3 W/µm2 . Moreover, we fabricate the designed structures by electron beam lithography, wet chemical techniques and optimize each fabrication step of processes by several experiments. Fabrication steps are explained and SEM images of related steps are presented.
Open Access
EBL fabricated plasmonic nanostructures for sensing applications
(2013) Cinel, Neval A
Plasmonics is a major branch of photonics dealing with light-matter interactions in metallic nanostructures. Plasmonic devices provide extreme confinement of electromagnetic oscillations to very small volumes beyond diffraction limit at optical frequencies. Our aim in this thesis study is to demonstrate the utilization of plasmonics for several applications such as optical localized surface plasmon resonance (LSPR) biosensor design, enhancement of signal intensity in surface enhanced Raman spectroscopy (SERS) and absorption enhancement in photodetectors. Firstly, a sensor structure that detects the changes in the refractive index of the surrounding medium by optical transmission measurements was designed. Periodic silver nano-disk arrays on sapphire substrate written by Electron-Beam Lithography (EBL) were used for this aim. Optical characterization was done through transmission/reflection measurements and supported by finite difference time domain (FDTD) simulations. The sensor was first verified by a biotinavidin bioassay. Real time binding studies showed that the sensor response was saturated within the first 30 minutes of application. Concentration dependency of the sensor structure showed an adequate response at the 1 nM-100 nM range. The refractive index sensitivity of the sensor was determined as 354 nm/RIU. The idea was finally applied to the detection of heat killed E.Coli bacteria. Promising results that indicate the possibility of using the sensor for bacteria detection was obtained. Secondly, tandem truncated nano-cones composed of Au-SiO2-Au layers that exhibit highly tunable double resonance behavior were shown to increase SERS signal intensity, for the first time. Enhancement factor (EF) calculations indicated an enhancement factor of 3.86 x107 . The double resonance design showed a 10 fold better enhancement when compared to its single resonance counterpart. This enhancement is believed to be even more prominent for applications such as NIR-SERS and Surface Enhanced Hyper Raman Scattering (SEHRS). Another SERS substrate containing dual layer, periodic, “coupled” concentric rings, separated by a dielectric spacer provided Raman signal intensity 630 times larger than plain gold film and 8 times larger than an “etched” concentric ring structure. The design provided an enhancement factor of 1.67x107 . Finally, Al nanoparticles with plasmonic resonance at UV wavelengths fabricated in between the Schottky contacts of an MSM detector on semi-insulating GaN was shown to yield 1.5 fold enhancement in absorption and photocurrent collection. Plasmonic enhancement in UV was studied for the first time with this study. Another UV-MSM photodetector on GaN that includes subwavelength apertures surrounded by nano-structured metal gratings was compared to a conventional design without gratings. Results indicated an 8 fold enhancement in the photocurrent at the resonant wavelength.
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
Rational design of two photon absorbing Bodipy dyes
(2010) Kılıç, Bilal
Two photon absorption is a nonlinear process which is of particular interest in various applications such as optical data storage, fluorescence imaging, O2 sensing and photodynamic therapy. These applications have created a strong demand for new dyes which have high two photon absorption cross section. In the two- photon absorption process there is an interaction of the two photons which are simultaneously absorbed by materials. For this purpose, we have designed and synthesized a novel class of distyryl-substituted boradiazaindacene (BODIPY) dyes which absorb two one photon in the green or two photons in the near IR regions of the (electromagnetic) spectrum and have D-A-D structure. As expected, as the strength of the donor groups which were introduced to the 3,5 position of the BODIPY core increase, absorption and emission maxima of the BODIPY dyes are shifted in the near IR regions of the spectrum. Furthermore, GM values increase due to the enhancement donor strength of the terminal groups. In summary, we have successfully synthesized a novel class of BODIPY derivatives which have large TPA cross section values.
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