Author: Çağın Ekici

Advisor: M. Salih Dinleyici

Type: Doctoral Thesis

Abstract: Quantum optics offer new possibilities, new approaches, and potentially groundbreaking new technologies whose backbone is based on creation, manipulation, and detection of special quantum states of light. The main objective of the thesis is to present a study of spontaneously arisen heralded entangled photon-pairs which play crucial role in emerging quantum enhanced technologies. We have mainly investigated discrete transverse-spatial-mode entangled photon-pairs in waveguide, because it intrinsically offers infinite dimension. Entangled states of higher dimensional systems enable realization of quantum information schemes that can offer higher information density coding and show more error resilience than can be achieved with lower dimensional systems. In this context, we have exploited a graded-index optical fiber as photon-pair-generation platform via nonlinear intermodal-four-wave mixing (FWM), since the fiber may allow different FWM processes to overlap in spectral domain, resulting in an entangled pair of spatial qubits. We have also probed joint spectral properties of the generated photons to show capability of hyperentanglement in frequency and transverse mode. We have discussed spatial Wigner function and its realization to characterize spatial properties of the quantum state. We have shown that entanglement can be verified through a violation of the Clauser – Horne – Shimony – Holt (CHSH) inequality based on spatial Wigner function and coupled-mode theory. This thesis also includes basic analysis of transverse-mode entangled photon-pair distribution in a lossy-dispersive medium. Finally, the ways to follow and the quantities to measure are touched upon. Thus, we have explained the generation and four different detection schemes, relying on a combination of photon-number statistics, joint spectral properties, and spatial entanglement measurements.

Author: Enes Ataç

Advisor: M. Salih Dinleyici

Type: Master’s Thesis

Abstract: Demand on the high-quality optical thin films has increased because of the importance in the optical sensor technologies. The thicknesses of such films are usually shorter than the wavelength of visible light. Therefore, the optical characterization of these films is not a routine procedure especially on curved surfaces such as optical fiber. Besides, the methods in the literature and commercially available systems are either expensive, destructive or non-real time. In this thesis, it is aimed to propose a simple, inexpensive and non-destructive optical characterization method of nano-scale dielectric films on curved surfaces. The methodology of that approach can be described as the near field wave-front tracing diffraction by using structured light. In this way, it has been shown that sub-wavelength film thicknesses can be estimated. The proposed diffraction method is organized in four main stages. These are the coating of optical fibers, generation of structured light, determination of wave propagation via the near field Huygens-Fresnel wave-front tracing and sensing and processing of signal from the sensor array. Layer by layer assembly technique is used in coating process to keep under control the thickness of transparent film. Selection of various source types is about to changing of point spread function of applied field and observe the effects on intensity pattern. Using near field diffraction technique, sub-wavelength thickness of thin films can be predicted by taking the higher order components of diffraction pattern by recording at very close proximity to object. In this way, determination of thickness beyond the diffraction limits can be realized. Furthermore, the resolution of sensor array in sensing part is important since pixel size of the sensor array determines your detection limits to catch all variations on diffraction pattern. The whole process has a mathematical model with numerical analysis methods. This dissertation is about the proposing a mathematical estimation model for the optical properties of nano-scale dielectric films coated on curved surfaces. The experimental results show that near field Huygens-Fresnel wave-front tracing method by using structured light is a powerful technique.tellus, luctus nec ullamcorper mattis, pulvinar dapibus leo.

Author: Şeyma Arslanyürek

Advisor: M. Salih Dinleyici

Type: Master’s Thesis

Abstract: In this study, it is aimed to filter nano-sized particles using light radiation pressure explicitly scattering and gradient forces. The light wave exerts momentum when encounters to the particles inside a solution. This momentum provides pulling force towards the high-intensity point as a result of gradient force and thrust in the direction of propagation resulting from scattering force. By controlling these two forces, the particles which have dissimilar properties can be moved to distinct directions. In this way, we have experimentally shown that two different particles can be separated from one another. It has been shown mathematically that separation of two particles based on size, material properties and geometry using radiation forces. Size-based particle filtration was performed with experimental studies on particles of different sizes. A threshold dimension value was assumed between 100 nm and 200 nm so that these particles could be separated from each other, and a design has been developed such that smaller particles are attracted towards the high-intensity point of the light with gradient force effect and larger particles are thrust in the direction of light propagation with scattering force. This setup was tested for silica particles of size 87 nm, 100 nm, 120 nm, 200 nm and 340 nm. Particles smaller than this threshold value were accumulated around the high-intensity region of light, while the larger ones continued to flow in the liquid. It has been experimentally shown that the nearest 120 nm and 200 nm particles were separated from each other. This study shows that particles with a difference of 80 nm in size can be filtered using radiation forces. Finally, blood samples were used in experimental studies. It is shown that the thrombocyte, lymphocyte and erythrocyte cells contained in the blood can be separated from each other using radiation forces.

Author: Yunus Emre Karataş

Advisor: M. Salih Dinleyici

Type: Master’s Thesis

Abstract: In this thesis, the polarization and phase properties of the side-polished optical fiber (SPOF) are aimed to characterize. The Linearly Polarized (LP) modes of standard optical fibers have been affected by the side-polished geometry which breaking symmetry. At the side-polished area guided modes couple to non-symmetric modes and phase shift occurs due to the birefringent property of the SPOF. That kind of structure has an excellent usage potential as a portable optical sensor or optical fiber communication device. It was primarily concentrated on the LP modes of the standard optical fiber. LP mode field solutions extracted from Maxwell Equations were calculated with MATLAB, and mode intensity distributions were constructed accordingly. The calculated intensity distributions were utilized for figuring out the mode content of the outputs of the two-mode experiment. The recorded CCD Camera images were matched with the calculated intensity distributions, and then the best-matched LP mode combination was selected as output mode content. In the single-mode experiment at the side-polished area, quasi-degenerate fundamental modes occur. According to the state of polarization of the modes, they suffer attenuation and phase shift in different levels. Therefore, after the side-polished area, degenerate fundamental modes propagate together with a particular phase difference. This situation composes elliptical polarization at the output. Various modal polarization rotation and phase shifts were observed, and then polarization ellipses were obtained with MATLAB. The resultant ellipses demonstrate that the effect of SPOF on guided modes varies with the angle of input polarization.

Author: Çağın Ekici

Advisor: M. Salih Dinleyici

Type: Master’s Thesis

Abstract: In this thesis, we aim to characterize optical properties of thin dielectric films coated on curved surfaces. Indeed, optical thin films attract a great deal of attention especially the ones coated on silica based optical waveguides used as sensor system. Therefore, the step index optical fiber is used in the thesis as a substrate due to the fact that the sensor technology tends towards to fiber optic based platforms. In the thesis, a step index optical fiber is coated with polyvinyl alcohol (PVA), then its thickness is mathematically estimated exploiting Fresnel scalar diffraction method. Phase front of the laser light wave comes across with a phase object (fiber optic), transmits through of it and diffracts. Whole process is modeled by using numerical analysis methods and compared to experimental results to obtain desired parameters in MATLAB. The conventional least-squares method is used for comparison purpose. Although the emphasis is on optical thin film characterization, we demonstrate the application area of diffraction from fiber optic as sensor. It is used to detect adulteration of olive oil that is big concern for the food industry. The refractive index of various mixture of olive oil and sunflower oil is measured with intend to detect adulteration. This feature makes it a good candidate for fiber optic based refractive index sensor and it may bring practicability and precision to the sensing process. This dissertation gives detailed information about diffraction from fiber optic both theoretically and experimentally. The experiments were realized by using 632.8 nm continuous wave laser. Both of the experimental results demonstrate that phase diffraction method is a powerful technique to characterize optical thin films and to sense refractive index of the surrounding medium.

Author: Gizem Soylu

Advisor: M. Salih Dinleyici, Kıvılcım Yüksel Aldoğan

Type: Master’s Thesis

Abstract: This thesis aims to develop a technique to characterize microelectronic interfaces based on Second Harmonic Generation (SHG) method. In the experiment part of this study, silicon wafers with thermal and native oxide, silicon-on-insulator (SOI), pure glass and glass with TiO2 thin film samples were used to observe Second Harmonic (SH) signal. The experiments have been performed in IMEP-LAHC laboratory in Grenoble, France. In addition, the measurements were carried out with “Harmonic F1X” which is a femtosecond laser developed by the company FemtoMetrix based in California/USA (FemtoMetrix). Three contributions to SHG were investigated experimentally: the electric dipole approximation due to symmetry breaking at the surface/interface, a dc electric field because of the charge separation at the interface, and lastly bulk contributions. Then, the phenomenological model of surface SHG (Mizrahi & Sipe, 1988) was simulated in MATLAB, and the ratios of the elements of second order nonlinear susceptibility (χzzz/χzii and χizi/χzii) for the silicon wafers were identified with comparing the model with the experimental results. In addition, it was shown that surface and bulk contributions can be separated by using specific polarization states and azimuthal orientations. To show this separation, Fourier coefficients, which describes the crystal facial orientations of the total SHG, were determined for the silicon wafers. Furthermore, it was observed that there are some critical parameters which have an effect to SHG: the polarization states of the incident light and second harmonic light, the angle of incidence of the incoming light and the oxidation types of silicon. Finally, SOI has been used to check whether the effecting factors are same for silicon wafers. The findings demonstrate that SHG is a powerful technique to characterize the surface/interface and the bulk of the sample in microelectronic industry.

Author: Özgür Önder Karakılınç

Advisor: M. Salih Dinleyici

Type: Doctoral Thesis

Abstract: It is already foreseen that future integrated photonic circuits for ultra fast all-optical signal processing will require various types of functional elements with including spectral managements. Besides, dynamical manipulations of the photonic crystals play an important role in order to switch the optical signal between the waveguide channels or may be among the layers. Hence, in this study, photonic crystal based spectral filters are proposed for all-optical communication applications. Firstly, grating structures composed with Gaussian beam interference equation and combined with nonlinearity phenomenon in photonic crystal are studied. The grating structure exhibiting special features on transmission characteristics are shown. After that, we expanded this idea applying with realistic Gaussian beam source and generated as transient grating in nonlinear photonic crystal structure. At this point, light wave interaction with nonlinear response time of matter plays a significant role on the signal manipulation. So, behavior of pulse propagation in the medium having the response of instantaneous nonlinearity (Kerr) is summarized. Then, optical resonator which is essential functional block for filtering, modulating, buffering, switching in integrated optical circuits systems is studied. Photonic crystal microcavity based dual-mode dual-band bandpass filter is designed and its transmission characteristics are investigated for various configurations. Photonic crystal resonator structure is formed by a point defect microcavity that is constituted with a large and three smaller auxiliary perturbation rods. Degenerate modes at each band may also be excited by changing the structure properties of the perturbation. Proposed photonic crystal spectral filters structure can effectively be used for optical communication applications.

Author: Can Sümer

Advisor: M. Salih Dinleyici

Type: Doctoral Thesis

Abstract: The aim of this study is to develop a node for an optical add/drop multiplexer, which is capable of packet switching at very high speeds and is controlled by light. The D-Fiber is employed as the transmission medium and the grating formation and polymerization is implemented on the fiber. The optical multiplexer is constructed by cascading two different photonic structures formed on the planar side of the D-Fiber. Multiplexing is performed by forming a temporary (transient) grating; which is the subject of another project in parallel at our laboratory. Right after this grating, will be the structure that is the subject of this thesis, which is the permanent structure fabricated via photopolymerization. The temporary grating breaks the resonance using nonlinear optical effects, coupling the fiber mode into the higher-order mode and the permanent structure extracts the mode out selectively to another fiber. Due to the very fast response of the nonlinear effects, an optical switch capable of transferring optical packets to other waveguides is formed. Photopolymerization is a method that can be used to fabricate photonic structures such as photonic crystals or permanent gratings, holographically or by direct-writing. The project involves the fabrication of the aforementioned photonic structure via photopolymerization. Even though the main aim of this project is not materials research, extensive effort has been put into optimizing the polymer recipe and characterization of the materials and processing properties.

Author: Osman Akın

Advisor: M. Salih Dinleyici

Type: Doctoral Thesis

Abstract: In this thesis, we developed an in-fiber all optical switching device exploiting a transient grating as a control mechanism that was formed by interference of laser light beams via the Kerr effect. The switching device is designed by partial removal of thefiber cladding and replacing the polished cladding with a nonlinear polymer film (slab waveguide) that exhibits higher third order (Kerr) optical nonlinearity. The proposed device structure is analyzed considering Four Wave Mixing (FWM) of Gaussian beams of the grating and propagating modes of the optical fiber in the evanescent region where the nonlinear material is placed. The fields of modes and the grating forming beams interact in the nonlinear medium according to the matching conditions and evoke power transfer among the fiber modes. Thus, the coupling between the modes is directed by means of the transient grating. In the experimental part, polymeric thin films are prepared and linear refractive indices are measured using Fresnel diffraction method (developed in the laboratory) by matching the model with the experimental output. Then, z-scan method is employed to characterize the third order nonlinear optical properties of the thin films and pump-probe experiments are exploited to ensure existence of the transient grating and its diffraction capability. Finally, the side polished fiber is coated with the Methyl Red doped PVA composite polymer and by generating transient gratings on the polymer film, the switching capability of the device is introduced. The switching can be achieved either by a bulk refractive index change (no grating) or a transient grating between the modes of the optical fiber.

Author: Taner Şen

Advisor: M. Salih Dinleyici

Type: Master’s Thesis

Abstract: A laser microphone is a surveillance device that uses a laser beam to detect sound vibrations in a distant object. The object is typically inside a room where a conversation is taking place, and can be anything that can vibrate (for example, picture or window) in response to the sound waves of the conversation. The object preferably has a smooth surface. The laser beam is directed into the room through a window, reflected off the object and returned to a receiver that converts the beam to audio signal. The beam is mostly bounced off the window itself. Usually these kinds of devices are used by surveillance intelligence in some parts of governments and these kinds of weapons analyze the laser beam which reflects from window.In this thesis a countermeasure to the detection of laser beam is analyzed. In order to make this possible, the reflection from dielectric stratified surfaces of a Gaussian laser beam needs to be described.The reflected beam profile of electromagnetic radiation exposes to various effects different from reflected plane waves. Gaussian beams which reflect from a dielectric slab experience in a shifting maximum point in one direction; lateral shift, focal shift and angular divergence are the shift and distortion of the beam profile.The Gaussian beam propagates in z direction and broadens in transverse plane, in two dimensions and is decomposed into plane wave components. Upon analyzing the reflection coefficient and beam profile, reduction of beam power after reflection from stratified films is described.

Author: Nasrettin Yunus

Advisor: M. Salih Dinleyici

Type: Master’s Thesis

Abstract: Polarization enhancement in liquid crystal display (LCD) backlighting systems comprises important part of works on improvement of the brightness. Optical films containing scatterer particles are used in these systems. Therefore, dielectric scatterer particles are greatly needed to be analyzed for their optical scattering properties, and especially for polarizing effects. Depending on the sizes relative to the wavelength and the shape of the particles various computation approaches have been developed based on electromagnetic scattering theories such as Mie scattering, T-matrix methods etc… Simulation programs of these approaches have been examined and applied for spherical and nonspherical particles. In general, for the particles those a few times large in size compared to the incident wavelength, the polarization differentiation is insignificant for a spherical particle compared to a spheroid one. And, the prolate spheroids with higher aspect ratio have been able to produce most significant differentiating figures. Polarization measurements have been carried on commercially available dielectric optical films of two different set and also on the films with/without nonspherical zeolite particles prepared in the laboratory. Since the commercial films consist of spherical scatters, they show no polarization discrimination at all. On the other hand existence of zeolite particles in the film resulted in significant polarization discrimination at forward scattering angle. The results for polarization discrimination properties of the prolate spheroid particles have been compared with the spherical ones. Consequently, the discrepancy induced on the polarization that way has a good potential to be used in improvement of the brightness.

Author: Osman Akın

Advisor: M. Salih Dinleyici

Type: Master’s Thesis

Abstract: In this study we investigate an all-optical switching node which can be controlled via transient grating formed by interference of two Gaussian beams. This design considers 3-D architecture of switching fabrics, real profile of Gaussian beams and nonlinearity for fast switching time requirements. Four Wave Mixing (FWM) is applied in the evanescent field region of waveguide to estimate the reflection angle and the efficiency of switching node. The effect of the formed grating on the propagation of mode is analysed by coupled mode theory and co-directional mode coupling coefficient is found by using Distributed Feedback Laser approach. A method for overall diffraction efficiency is proposed and optimization parameters for better efficiency are described.

Advisor: Okan Karatay

Danışman: M. Salih Dinleyici, Mustafa A. Altınkaya

Type: Master’s Thesis

Abstract: In recent years commercial and military interest in free-space optical (FSO) communication has been growing due to advantages of high bandwidths, portability and high security. Despite of the numerous advantages, atmospheric events such as attenuation and scintillation severely affects the link quality. Novel methods of mitigating atmospheric events have been applied. Usage of large aperture lenses and high transmitted power decreases the degradation effects, but increases the overall system cost. Fresnel lenses, as an alternative to the classical optic system for mitigating scintillation effects would be a low-cost solution. As a result of the technological improvements on output power and divergence angles of VCSEL (Vertical Cavity Surface Emitting Laser) high-speed cost effective FSO communication system design became possible. In this thesis commercially available FSO systems are reviewed and an alternative low-cost system relying on Fresnel lens optical unit is theoretically and experimentally investigated. The system has been tested and compared for two-day periods with various configurations under atmospheric effects. The results indicated that the Fresnel lenses perform comparably well in contrast to bulk optic lenses. Thus, the large aperture Fresnel optic unit can be deployed for better performance at the scintillation dominating situation without a penalty at the cost. IV

Author: Bora Mocan

Advisor: M. Salih Dinleyici

Type: Master’s Thesis

Abstract: Increasing bandwidth demand, driven by Internet Protocol (IP), let the communication industry change to IP-centric networks. To satisfy the needs, optical fiber communication links provides a usable transmission bandwidth of 25,000,000 MHz. Despite the huge potential of the optical links, electronic-based networking devices (Router, switch, repeater, etc.) act as bottlenecks of the system because of the material limitations of the electronics. Optical networks appear to be the solution of choice for providing faster networking infrastructure that can meet the explosive growth of the Internet. This thesis discusses architectures and technology issues for the design of a high performance all-optical router. In particular, it focuses on the concept of an optical router for packet switched computer networks as an edge network device, functioning as an interface between autonomous systems. A novel architecture is proposed and simulated by means of special software. Implementation problems and the limitations of the architecture are discussed in detail component by component. 

Author: Mehmet Erdal Özbek

Advisor: M. Salih Dinleyici

Type: Master’s Thesis

Abstract: Ever-increasing demand for high capacities brought by Internet usage forces designing faster transport networks for carrying information packets. In the last ten years much attention has been focused on transporting packets directly over the optical transport networks. Researches in this area range from simple electronic and optical switching/routing methods to hybrid and more complicated all-optical packet switching systems. However, major bottleneck in all these methods is designing fast, reliable and inexpensive optical routing/switching devices. In this thesis, a method for optical routing using fiber Bragg gratings is proposed. In this method, electronic interface is used only for routing information (routing table) update cycle while packet header extraction and switching is done in optical domain. Routing is performed optically by controlling the refractive index change in fiber gratings. Four bits of header (label) information is used for routing packets to three different output routes. The network is simulated and its performance is evaluated by special software of Virtual Photonics.