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Photonic Crystal Textiles
(Izmir Institute of Technology, 2022) Çetin, Zebih; Sözüer, Hüseyin Sami
Photonic crystals are man-made structures that can be used to manipulate the flow of light. They are classified as one-, two- and three-dimensional photonic crystals according to the periodic variation of the dielectric profile in space. Apart from artificial photonic crystals there are numerous examples of naturally occurring photonic crystals which have evolved mostly for structural coloration, such as wings of butterflies, natural opal gem stone, peacock feathers to name a few. Using photonic crystal structures the propagation of electromagnetic waves can entirely be prohibited by means of photonic band gap. Considering the fact that approximately two thirds of the heat loss of the human body occurs through electromagnetic radiation with a wavelength around 10 microns, it becomes important to consider photonic crystals for the purpose of reducing heat loss in textiles. We observe that the textile, by virtue of the fact that it has been produced by weaving, already has a periodic structure, and thus is a potential candidate for a photonic crystal. With the right fiber that the textile is woven and the right weave pattern, the textile itself would be a photonic crystal. The most common weave patterns used in the textile industry are plain weave, basket weave, dutch weave and twill weave. In this thesis, we used the finite-difference time-domain method to search for the optimum weave pattern to minimize heat loss by the human body.
The Fabrication of Plasmonic/Photonic Nanostructures in Polymers: Mechanical Sensor Applications
(Izmir Institute of Technology, 2019) Topçu, Gökhan; Demir, Mustafa Muammer; Eanes, Mehtap
Functional polymer nanocomposites offer futuristic properties by the association of inorganic additive micro-/nanostructures into the polymers. With the growing knowledge of the physical fundamentals, stimuli-responsive polymeric composites enable detection of chemical, thermal, and mechanical changes by optical sensors and probes. Since the accurate real-time detection of the change in mechanical loading is vital for construction and industrial fields, the use of colorimetric pressure elements in a static body is important for the prediction of catastrophic failures. In this thesis, strain/pressure responsive colorimetric films were produced. A number of polymer nanocomposite-based mechanical sensors are presented. By transferring the optical activity (coherent reflection and plasmonic coupling) of the additives into various polymeric matrices having different mechanical features, the strain and pressure sensors are developed for practical applications. There are two approaches used for the fabrication of polymeric mechanical sensors: i) PDMS/SiO2 composites, ii) PAAm/Au NP composites. The coherent reflectivity of SiO2 colloidal particle arrays was used to develop strain sensors while controllable localized surface plasmon resonance of Au NPs was employed for pressure sensors. These optical systems were separately associated with viscoelastic and elastic polymeric systems, and sensor properties were discussed.
Mathematical Modelling of Light Propagation in Pohotonic Crystal Waveguides
(Izmir Institute of Technology, 2014) Eti, Neslihan; Sözüer, Hüseyin Sami
Photonic crystals are artificially engineered materials where the dielectric constant varies periodically. A photonic band gap can be created by scattering at the dielectric interfaces, which forbids propagation of light in a certain frequency range of light. This property enables us to control light, which is normally impossible with conventional optics. Moreover, by placing a linear defect into the photonic crystal, one can construct a waveguide, which keeps light inside the waveguide in the desired direction. Thus, by using photonic crystal waveguides one can control light propagation in integrated circuit devices. The goal of this work is to provide a comprehensive understanding of how to bend light using photonic crystal waveguides. The purpose is to create a 90◦ bend for line defect photonic crystal assisted waveguides and present fully three-dimensional calculations with optimized geometrical parameters that minimize the bending loss. The scheme uses one-dimensional photonic crystal slab waveguides for straight sections, and a corner element that employs a square photonic crystal with a band gap at the operating frequency.. The two different structures, with either silicon-silica or with silicon-air are used in the guiding photonic crystal layer. Furthermore, the guiding layer is sandwiched between either air on both top and bottom, or between air on top and silica substrate at the bottom, to serve as the ”cladding” medium. Calculations are presented for the transmission values of TE-like modes where the electric field is strongly transverse to the direction of propagation, with and without the photonic crystal corner element for comparison. We find that the bending loss can be reduced to under 2%.

Phd Degree / Doktora

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