Master Degree / Yüksek Lisans Tezleri

Permanent URI for this collectionhttps://hdl.handle.net/11147/3008

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Now showing 1 - 7 of 7
  • Master Thesis
    Optical Spectroscopy of Single Defects in Hexagonal Boron Nitride
    (01. Izmir Institute of Technology, 2021) Birinci, Ayşenur; Ateş, Serkan
    Single photon sources are main component for several applications in quantum information technologies. Hexagonal boron nitride (hBN) is a suitable material to create heterostructures with two dimensional materials. It is a popular two dimensional material and single photon source due to having stable and bright emission in visible range. In this thesis, optical properties of single defects in bulk hBN were investigated. Defects have been selected using the micro-Photoluminescence setup, and it was observed that the defects have high degree of polarization and show typical optical saturation behavior. Time-resolved photoluminescence measurements were done by time-correlated single photon counting. Single photon nature of generated light from individual defects were demonstrated using Hanbury-Brown and Twiss interferometer.
  • Master Thesis
    Quantum Walks: Entanglement Between Spatial Degrees of Freedom and Interference in Multi-Photon Walks
    (Izmir Institute of Technology, 2020) Karlı, Yusuf; Çakır, Özgür
    Quantum walks can be described as quantum analogues of classical random walks. In quantum walks, the direction of the walker is dictated by the quantum state of a coin in a coherent fashion. Unlike classical random walk with a fair coin, quantum walk has non-Markovian property. First, we studied 2-D quantum walk analytically and numerically with one-walker and two entangled coins to investigate the transfer of the entanglement in initial coins state to spatial degrees of freedom. The coins are Hadamard Coin, Fourier Coin, among which the Fourier coin generates entanglement, thus increase entanglement between spatial degrees of freedom. Here we calculated the amount of entanglement using negativity. In the second part we studied average photon number correlations for 1-D quantum walk with many body bosonic walkers, like different light sources, to investigate quantum interference effects and we showed the second-order intensity correlations function in terms of the probability amplitudes of the 1-D quantum walk with Hadamard coin. We compared the resulting correlations for various initial many photon states.
  • Master Thesis
    Temperature Dependence of Zero Phonon Line Emission From Defects in Hexagonal Boron Nitride and Design of Photon-Pair Source
    (Izmir Institute of Technology, 2017) Polat, Nahit; Ateş, Serkan
    This thesis presents studies of the defect centers in hBN and design of nonlinear waveguide. The multilayer hBN flakes and Si3N4 waveguide are available materials in modern nanophotonics applications. The color centers in hBN are consisted of quantized states because each defect center has different saturation power and dipole polarization. The line shape of emission from defect centers is directly depended photon vibrations and temperature of sample. Moreover, phonon bands in the color centers affect the wavelength of emission and we statistically worked on the phonon effects on ZPL. The Si3N4 waveguide can be more efficient chip scale photon pair sources to create entangled photons in visible band. The zero dispersion wavelength calculations give an efficient waveguide geometry as 650×600 nm2 for 780 nm pump wavelength.
  • Master Thesis
    Effects of Dark Photons on Pulsar Kicks
    (Izmir Institute of Technology, 2012) Tosun, Onur; Demir, Durmuş Ali
    Several studies that have been carried out on supernova explosions and their remnants (pulsars) so far ended up with two fundamental problems: How are the left-handed neutrinos released out of the star and how do the supernova explosions happen even the inner core region of the star is extremely dense for propagation of the left-handed neutrinos? How can the pulsars attain very high kick velocities after the burst? The main goal of this thesis is to contribute to resolutions of the aforementioned problems by using new particles. The particles under concern are dark-photon which is immune to all the forces in the SM but gravity and interacts with the SM spectrum through only its kinetic mixing with the photon (actually the hypercharge gauge boson) and the right-handed neutrino which posseses dark electric charge (couples to dark photon). By proposing new particles, we find an interval for the photon-dark photon mixing parameter consistent with the values proposed by the string theory and the experiments. We calculate some pulsar kick velocities consistent with the observations for some magnetic field values and mixing parameter values. We show that the right-handed neutrinos may have electric charges which are not quantized and on the order of 10−6e.
  • Master Thesis
    One dimensional photonic crystal waveguide
    (Izmir Institute of Technology, 2004) Sevim, Koray; Sözüer, Hüseyin Sami
    This thesis deals with the implementation of a numerical method to describe how electromagnetic waves propagate through a one-dimensional photonic crystal waveguide. The one-dimensional photonic crystal waveguide is a periodic arrangement of dielectric slabs of alternating dielectric constant with an impurity slab introduced as the guiding layer. This impurity guides, and connes light within a given range of frequencies by producing waveguide modes within the photonic band gap. These modes are different from those of conventional waveguides that use total internal reflection as the basic guiding mechanism. Photonic crystal waveguides are expected to lead to compact photonic integrated circuits.
  • Master Thesis
    Photonic Crystal Assisted L-Shaped Waveguide Bend
    (Izmir Institute of Technology, 2009) Şengün, Hediye Duygu; Sözüer, Hüseyin Sami
    Photonic crystals are periodic dielectric structures. This periodicity allow us to manipulate light in ways that have not been possible before. As a result, photonic crystal waveguide components play a significant role in integrated optical circuit design because waveguides allow only certain electromagnetic wave modes to propagate inside the structure. There are many corresponding applications that rely on total internal reflection. However, with total internal reflection, there is a problem in guiding light through sharp corners, large optical losses occur around tight curves with a small bending radius. A simple explanation for these losses is that the angle of the incident light too low for total internal reflection when wave turns through a sharp corner. Thus, an unacceptable fraction of the electromagnetic energy is radiated out of the waveguide. To overcome this difficulty, in this thesis, we demonstrate a novel method for guiding light through sharp corners, using a 1 photonic crystal slab waveguide for the straight sections, and assisted by 2D Line Defect Waveguide at the corners.Plane Wave Method and Supercell Method are used to Figure out parameters and obtain the guided mode for our proposed structure. Then, numerical simulations (FDTD) reveal nearly perfect transmission at certain frequency ranges. Also, in this thesis different corner elements are used to show highly efficient transmission of light through sharp corners. Thus, light can be guided through a 90. corner, almost without loss, by using different corner elements. "Crystals are like people, it is the defect in them which tend do make them interesting". Colin Humphreys.
  • Master Thesis
    Frequency Splitting With Two Dimensional Triangular Photonic Crystal
    (Izmir Institute of Technology, 2009) Erol, Adem Enes; Sözüer, Hüseyin Sami
    Photonic crystals are periodically arranged dielectric materials. If the periodicity is broken along a line, i.e. a line defect is formed, then the line defect can behave like a waveguide. In this thesis, a frequency splitting device for electromagnetic waves is designed and tested theoretically using line defect waveguides. The theoretical design of the waveguides is accomplished using the plane wave expansion and the supercell method. The testing is done by the finite difference time domain method. Frequency mixing and splitting, or multiplexers and demultiplexers as they are known in industry, for electromagnetic waves are important since they lead to a multiplication in capacity for optical communications. Multiplexers and demultiplexers have been in use for a long time. However, designing photonic crystal multiplexers has a history of about ten years. In this thesis, a new photonic crystal demultiplexer design is suggested using photonic crystal line defect waveguides.