Browsing by Subject "Photonic Crystal"

Now showing 1 - 7 of 7

Open Access
Beaming and localization of electromagnetic waves in periodic structures
(2010) Çağlayan, Hümeyra
We want to manipulate light for several applications: microscopy, data storage, leds, lasers, modulators, sensor and solarcells to make our life healthier, easier or more comfortable. However, especially in small scales manipulating light have many difficulties. We could not focus or localize light into subwavelength dimensions easily, which is the key solution to beat today’s devices both in performance and cost. Achievements in three key research fields may provide the answer to these problems. These emerging research fields are metamaterials, photonic crystals and surface plasmons. In this thesis, we investigated beaming and localization of electromagnetic waves in periodic structures such as: subwavelength metallic gratings, photonic crystals and metamaterials. We studied off-axis beaming from both a metallic subwavelength aperture and photonic crystal waveguide at microwave regime. The output surfaces are designed asymmetrically to change the beaming angle. Furthermore, we studied frequency dependent beam steering with a photonic crystal with a surface defect layer made of dimmers. The dispersion diagram reveals that the dimer-layer supports a surface mode with negative slope. Thus, a photonic crystal based surface wave structure that acts as a frequency dependent leaky wave antenna was presented. Additionally, we investigated metamaterial based cavity systems. Since the unit cells of metamaterials are much smaller than the operation wavelength, we observed subwavelength localization within these metamaterial cavity structures. Moreover, we introduced coupled-cavity structures and presented the transmission spectrum of metamaterial based coupled-cavity structures. Finally, we demonstrated an ultrafast bioassay preparation method that overcomes the today’s bioassay limitations using a combination of low power microwave heating and split ring resonator structures.
Open Access
Ferroelectric Based Photonic Crystal Cavity by Liquid Crystal Infiltration
(Taylor & Francis, 2014) Karaomerlioglu, F.; Simsek S.; Mamedov, A. M.; Özbay, Ekmel
A novel type of two-dimensional photonic crystal is investigated for it optical properties as a core-shell-type ferroelectric nanorod infiltrated with nematic liquid crystals. Using the plane wave expansion method and finite-difference time-domain method, the photonic crystal structure, which is composed of a photonic crystal in a core-shell-type ferroelectric nanorod, is designed for the square lattice and the hexagonal lattice. It has been used 5CB as a photonic crystal core, and LiNbO3 as a ferroelectric material. The photonic crystal with a core-shell-type LiNbO3 nanorod infiltrated with nematic liquid crystals is compared with the photonic crystal with solid LiNbO3 rods and the photonic crystal with hollow LiNbO3 rods.
Open Access
Hollow core photonic bandgap fibers for medical applications
(2009) Vural, Mert
The design, fabrication and characterization of photonic band gap (PBG) based optical polymer fibers is discussed. Unlike conventional total internal reflection (TIR) fibers, used primarily in telecommunications, PBG fibers can be made hollow core and can be used to guide infrared radiation of any wavelength, a property known as wavelength scalability. Since the electromagnetic radiation is transmitted in the hollow core of the fiber, the intrinsic absorption of the fiber core as well as the insertion Fresnel losses at front and end faces are avoided, giving rise to extraordinarily high power densities to be delivered. The fiber production line includes material characterization, and the design of nanoscale quarter wavestacks using common thermoplastic polymers (poly ether sulphone and poly ether imide) and chalcogenide glasses (As2S3, As2Se3, Ge15As25Se15Te45). The fiber preform is fabricated using rolling mechanism of thermally evaporated chalcogenide glasses on large area polymers. Subsequently, the fiber preforms are thermally drawn to obtain nano-structured PBG fibers.Two different fibers are designed and produced, signifying wavelength scalability of the overall process, for the widely used holmium (Ho:YAG) and carbon dioxide (CO2) medical lasers. The transmission characteristics of the fibers proved that they can be used to safely deliver 15Wlaser power, along a 3 meter fiber with external diameter of 1.5 mm and hollow core diameter of 0.5 mm, corresponding to a laser power density of 1kW/cm2 with a loss of -10dB/m. The PBG fibers are expected to be widely used in high precision surgical laser for incision, photoablation and coagulation where infrared radiation is the radiation of choice for its superior laser-tissue interaction properties.
Open Access
Organic semiconductor-based photonic crystals for solar cell arrays: band gap and optical properties
(Taylor & Francis, 2014) Karaomerlioglu, F.; Mamedov, A. M.; Özbay, Ekmel
Photonic crystals (PCs) hold great potential for designing new optical devices because of the possibility of the manipulation of light with PCs. There has been an increase in research on tuning the optical properties of PCs to design devices. We design organic semiconductor-based PC structures and calculate optical properties using the plane wave expansion method and finite-difference time-domain method in an air background for a hexagonal lattice. We showed the possibility of the solar cell arrays for a 2D PC cavity on an organic semiconductor base infiltrated with a nematic liquid crystal. E7 type has been used as a nematic liquid crystal and 4,4-Bis[4-(diphenylamino) styryl]biphenyl as an organic semiconductor material.
Open Access
Photonic crystal based multi-mode high-qcavity
(IEEE, 2011) Akosman, Ahmet Emin; Mutlu, Mehmet; Kurt H.; Özbay, Ekmel
An optical race-track has been investigated in order to obtain a multi resonant structure with high-Q factors. Photonic crystal based structure provides strong field confinement and scalability in the dimensions of the structure. The average value of the quality factors at the resonances have been calculated to be on the order of ∼105. © 2011 IEEE.
Open Access
Physics and applications of coupled-cavity structures in photonic crystals
(2002) Bayındır, Mehmet
We proposed and demonstrated a new type of propagation mechanism for the electromagnetic waves in photonic band gap materials. Photons propagate through coupled cavities due to interaction between the highly localized neighboring cavity modes. We reported a novel waveguide, which we called coupled-cavity waveguide (CCW), in two- and three-dimensional photonic structures. By using CCWs, we demonstrated lossless and reflectionless waveguide bends, efficient power splitters, and photonic switches. We also experimentally observed the splitting of eigenmodes in coupled-cavities and formation of defect band due to interaction between the cavity modes. We reported the modification of spontaneous emission from hydrogenated amorphous silicon-nitride and silicon-oxide multilayers with coupled Fabry-Perot microcavities. We observed that the spontaneous emission rate is drastically enhanced at the coupledmicrocavity band edges due to very long photon lifetime. We also simulated our photonic structures by using the Transfer-Matrix-Method (TMM) and the Finite-Difference-Time-Domain (FDTD) method. The tight-binding (TB) approach, which was originally developped for the electronic structure calculations, is applied to the photonic structures, and compared to our experimental results. The measured results agree well with the simulations and the prediction of TB approximation. The excellent agreement between the measured, simulated, and the TB results is an indication of potential usage of TB approximation in photonic structures. Our achievements open up a new research area, namely physics and applications of coupled-cavities, in photonic structures. These results are very promising to construct for the future all-optical components on a single chip.
Open Access
Physics and applications of photonic crystals
(2000) Temelkuran, Burak
We first fabricated a dielectric based layer-by-layer photonic crystal, with a three-dimensional photonic band gap at microwave frequencies. We investigated the transmission, reflection and defect characteristics of the crystal. A Fabry-Perot cavity analogy was used to understand the localization of the electromagnetic (EM) fields around defects. We then showed the enhancement of the EM held within the defect volumes, and suggested a possible application: resonant cavity enhanced detectors built around photonic crystals. We demonstrated that a detector inserted inside the defect volume benefits from the frequency selectivity and the highly enhanced field of the cavity. Next, we investigated the radiation of the EM fields from a source inserted in the defect volume, and observed that the radiated field has a very high directivity and efficiency. The experimental results agreed well with the theoretical expectations. We demonstrated waveguiding structures built around photonic crystals. We showed that EM waves could be guided through a planar air gap between two photonic crystals, in which the wave is coupled inside the defect volume, and having no where else to go, propagates through this opening. The dispersion diagrams for these planar waveguide structures also agreed well with the theoretical expectations of our waveguide model. We also showed that, the wave could be guided along a single missing rod, and demonstrated the bending of the EM waves for these waveguide structures with “L” shaped openings. We tested metallic photonic crystals built in different dimensions and diflferent filling ratios. We observed many superiorities of these structures when compared to dielectric-based photonic crystals. A full characterisation of various metallic photonic crystals was performed. We also showed that metallic photonic crystals are suitable for some of the applications we have demonstrated for dielectric structures. We also fabricated a new layer-by-layer photonic crystal using highly doped silicon wafers processed by semiconductor micromachining techniques, with a band gap at millimeter wave frequencies. We showed that the transmission and defect characteristics of these structures are analogous to metallic photonic crystals, as we have predicted. The experimental results agree well with the predictions of the transfer matrix method (TMM) simulations. The method can be extended to fabricate these crystals at THz. frequencies.