Browsing by Subject "photonic crystal"

Now showing 1 - 4 of 4

Open Access
Fabrication of novel core-shell nanostructures for photonics applications
(2013) Khudiyev, Tural
Developments in nanoscale fabrication and characterization techniques have led to fundamental changes in the scientific understanding of many fields, and novel nanostructures have been utilized to investigate the conceptual underpinnings behind a diverse array of natural phenomena. However, nanofabrication methods are frequently hindered by issues such as misalignment, small batch sizes, high production costs and constraints in material choice or nanostructure diversity, which decrease their potential utility and prevent their widespread application in nanoscale optics and photonics. In this work, a new top-down nanofabrication method is described, which is called Iterative Size Reduction (ISR), where step-by-step reduction is utilized to decrease structure dimensions from macro- to nanosizes and produce indefinitely long one-dimensional core-shell nanostructures with properties highly suitable for use in optical applications. Plateau-Rayleigh instabilities are then utilized to thermally degrade ISR-produced nanowire arrays into complex core-shell schemes, which are produced successively in a hitherto-undescribed transitory region between core-shell nanowires and core-shell nanospheres. A diverse array of optical phenomena have been observed on fabricated novel core-shell nano-platforms, which are utilized in the design of novel nanostructures for emerging photonics applications. Briefly, (a) the resonant Mie scattering behavior is characterized on glass-polymer nanostructures and these nanostructures are designed for large-area structural coloration, (b) a novel non-resonant Mie scattering regime responsible for the scattering characteristics exhibited by all-polymer core-shell nanowires is described, (c) a nanoscale analogue to the thin film interference phenomenon is demonstrated that occurs on the core-shell boundary of ISR-produced micro- and nanostructures, (d) an unusual photonic crystal structure observed in the neck feathers of mallard drakes is investigated and imitated, (e) a series of all-polymer core-shell nanowires to function as novel light-trapping platforms and sensors are engineered and (f) the generation of supercontinuum light in well-ordered arrays of As2Se3 nanowires is reported.
Open Access
Novel approaches to control the propagation of electromagnetic waves : metamaterials and photonic crystals
(2007) Bulu, İrfan
Applications in areas such as photonics, antennas, imaging and optics require the control of propagation of electromagnetic waves and the control of emission of electromagnetic radiation. Achievements in three key research fields may provide the answer to these problems. These emerging research fields are metamaterials, photonic crystals and surface plasmons. This thesis will be about our work on metamaterials and photonic crystals. Metamaterials are a new class of artificial structures whose electromagnetic response can be described by effective permeability and permittivity functions that may attain negative values. I will present our results on the properties of a metamaterial structure that we proposed recently, the labyrinth structure. I will demonstrate that the labyrinth structure can be used to design a medium that exhibits negative permeability values within a certain frequency range. Moreover, I will explore the possibility of negative refraction and sub-wavelength focusing of electromagnetic waves by two and threedimensional labyrinth structure based left-handed mediums. Novel applications such as metamaterial based compact size antennas, ultra-small high-Q cavities will be also discussed. Another type of artificial electromagnetic structures are the photonic crystals. Photonic crystals can be described by a periodic modulation of the permittivity and/or the permeability of a medium. I will discuss two phenomena arising from the dispersion properties of photonic crystals and their possible applications. One of these phenomena is the existence of surfacebound electromagnetic modes and the other is the negative refraction effect. I will further show that the surface-bound modes can be used for applications such as beaming of electromagnetic waves and enhancement of transmission through sub-wavelength apertures. In addition, I will demonstrate that the negative refraction effect can be utilized to focus electromagnetic waves emitted from a finite size source.
Open Access
Quantum entanglement and light propagation through Bose-Einstein condensate (BEC)
(2009) Taşgın, Mehmet Emre
We investigate the optical response of coherent media, a Bose-Einstein condensate (BEC), to intense laser pump stimulations and weak probe pulse propagation. First, we adopt the coherence in sequential superradiance (SR) as a tool for continuous-variable (CV) quantum entanglement of two counter-propagating pulses from the two end-fire modes. In the first-sequence the end-fire and side mode are CV entangled. In the second sequence of SR, this entanglement is swapped in between the two opposite end-fire modes. Second, we investigate the photonic bands of an atomic BEC with a triangular vortex lattice. Index contrast between the vortex cores and the bulk of the condensate is achieved through the enhancement of the index via atomic coherence. Frequency dependent dielectric function is used in the calculations of the bands. We adopt a Poynting vector method to distinguish the photonic band gaps from absorption/gain regimes.
Open Access
Radiation properties of sources inside photonic crystals
(2003) Bulu, İrfan
The control of spontaneous emission is an important problem both in basic and applied physics. Two main problems arise in the control of emission: enhancement or suppression and angular confinement of radiation. In this work we studied the properties of emission of radiation from a localized microwave source embedded inside a photonic crystal. We showed that by using a photonic crystal it is possible to enhance the emitted power. We achieved up to 22 times enhancement of power at the band edge of the photonic crystal. We also studied the properties of emission of radiation from a source embedded inside a single defect structure and embedded inside a coupled defect structure. Enhanced emission for single defect and coupled defect structures was also observed. Moreover, angular distribution of power from a localized microwave source embedded inside a photonic crystal was studied. Angular confinement was achieved near the band edge of the photonic crystal. Half power beam widths as small as 6 degrees were obtained. This is the smallest half power beam width in the literature obtained by using photonic crystals. We also investigated frequency and size dependence of the angular distribution. We observed that the angular confinement strongly depends on frequency and on the size of the photonic crystal. In fact, we showed that angular confinement could be obtained just at the band edge frequency. In conclusion, our work showed that the problem of controlling the spontaneous emission could be solved at once by using photonic crystals.