Browsing by Author "Caglayan H."

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Open Access
Experimental observation of cavity formation in composite metamaterials
(Optical Society of American (OSA), 2008) Caglayan H.; Bulu I.; Loncar, M.; Özbay, Ekmel
In this paper, we investigated one of the promising applications of left-handed metamaterials: composite metamaterial based cavities. Four different cavity structures operating in the microwave regime were constructed, and we observed cavity modes on the transmission spectrum with different quality factors. The effective permittivity and permeability of the CMM structure and cavity structure were calculated by use of a retrieval procedure. Subsequently, in taking full advantage of the effective medium theory, we modeled CMM based cavities as one dimensional Fabry-Perot resonators with a subwavelength cavity at the center. We calculated the transmission from the Fabry-Perot resonator model using the one-dimensional transfer matrix method, which is in good agreement with the measured result. Finally, we investigated the Fabry-Perot resonance phase condition for a CMM based cavity, in which the condition was satisfied at the cavity frequency. Therefore, our results show that it is possible to treat metamaterial based cavities as one-dimensional Fabry-Perot resonators with a subwavelength cavity. © 2008 Optical Society of America.
Open Access
Highly directive radiation and negative refraction using photonic crystals
(Institute of Physics Publishing, 2005) Özbay, Ekmel; Bulu, I.; Aydin, K.; Caglayan H.; Alici, K. B.; Guven, K.
In this article, we present an experimental and numerical study of certain optical properties of two-dimensional dielectric photonic crystals (PCs). By modifying the band structure of a two-dimensional photonic crystal through its crystal parameters, we show how it is possible to confine the angular distribution of radiation from an embedded omnidirectional source. We then demonstrate that the anomalous band dispersions of PCs give rise to completely novel optical phenomena, in particular, the negative refraction of electromagnetic waves at the interface of a PC. We investigate the spectral negative refraction, which utilizes a transverse magnetic (TM)-polarized upper band of a PC, in detail and show that a high degree of isotropy can be achieved for the corresponding effective index of refraction. The presence of nearly a isotropic negative refractive index leads to focusing of omnidirectional sources by a PC slab lens, which can surpass certain limitations of conventional (positive refractive) lenses. These examples indicate the potential of PCs for photonics applications utilizing the band structure.
Open Access
Physics and applications of photonic crystals
(Nanotechnology Research Center NANOTAM, 2004) Özbay, Ekmel; Bulu I.; Aydin, K.; Caglayan H.; Guven, K.
In this article, we investigate how the photonic band gaps and the variety of band dispersions of photonic crystals can be utilized for various applications and how they further give rise to completely novel optical phenomena. The enhancement of spontaneous emission through coupled cavity waveguides in a one-dimensional silicon nitride photonic microcrystal is investigated. We then present the highly directive radiation from sources embedded in two-dimensional photonic crystals. The manifestation of novel and intriguing optical properties of photonic crystals are exemplified experimentally by the negative refraction and the focusing of electromagnetic waves through a photonic crystal slab with subwavelength resolution. © 2004 Elsevier B.V. All rights reserved.
Open Access
Rapid and sensitive colorimetric ELISA using silver nanoparticles, microwaves and split ring resonator structures
(2010) Addae, S.A.; Pinard, M.A.; Caglayan H.; Cakmakyapan, S.; Caliskan, D.; Özbay, Ekmel; Aslan, K.
We report a new approach to colorimetric Enzyme-Linked Immunosorbent Assay (ELISA) that reduces the total assay time to < 2 min and the lower-detection-limit by 100-fold based on absorbance readout. The new approach combines the use of silver nanoparticles, microwaves and split ring resonators (SRR). The SRR structure is comprised of a square frame of copper thin film (30 μm thick, 1 mm wide, overall length of ~9.4 mm on each side) with a single split on one side, which was deposited onto a circuit board (2×2 cm 2). A single micro-cuvette (10 μl volume capacity) was placed in the split of the SRR structures. Theoretical simulations predict that electric fields are focused in and above the micro-cuvette without the accumulation of electrical charge that breaks down the copper film. Subsequently, the walls and the bottom of the micro-cuvette were coated with silver nanoparticles using a modified Tollen's reaction scheme. The silver nanoparticles served as a mediator for the creation of thermal gradient between the bioassay medium and the silver surface, where the bioassay is constructed. Upon exposure to low power microwave heating, the bioassay medium in the micro-cuvette was rapidly and uniformly heated by the focused electric fields. In addition, the creation of thermal gradient resulted in the rapid assembly of the proteins on the surface of silver nanoparticles without denaturing the proteins. The proof-of-principle of the new approach to ELISA was demonstrated for the detection of a model protein (biotinylated-bovine serum albumin, b-BSA). In this regard, the detection of b-BSA with bulk concentrations (1 μM to 1 pM) was carried out on commercially available 96-well high throughput screening (HTS) plates and silver nanoparticle-deposited SRR structures at room temperature and with microwave heating, respectively. While the room temperature bioassay (without microwave heating) took 70 min to complete, the identical bioassay took < 2 min to complete using the SRR structures (with microwave heating). A lower detection limit of 0.01 nM for b-BSA (100-fold lower than room temperature ELISA) was observed using the SRR structures. © 2010 S.A. Addae et al.
Open Access
Spoof-plasmon relevant one-way collimation and multiplexing at beaming from a slit in metallic grating
(Optical Society of America, 2012) Çakmakyapan, Semih; Serebryannikov, A.E.; Caglayan H.; Özbay, Ekmel
Diode and collimator/multiplexer functions are suggested to be combined in one device that is based on a thin metallic grating with a single subwavelength slit. A proper choice of the structural (a)symmetry of the grating can result in obtaining one-way collimation and multiplexing with a single on-axis or off-axis, or two off-axis narrow outgoing beams. It is possible due to freedom in utilizing different combinations of the excitation conditions of the spoof surface plasmons at the four grating parts - right and left front-side and right and left back-side ones. Such a combining provides one with an efficient tool to engineer one-way collimators and multiplexers with the desired characteristics. Strong asymmetry in transmission with respect to the incidence direction (forward vs backward case) can be obtained within a wide range of variation of the incident beam parameters, i.e., angle of incidence and frequency, while the outgoing radiation is concentrated within a narrow range of the observation angle variation. Most of the observed asymmetric transmission features can be qualitatively explained using the concept of the equivalent source placed inside the slit. © 2012 Optical Society of America.
Open Access
Surface wave splitter based on metallic gratings with sub-wavelength aperture
(Optical Society of American (OSA), 2008) Caglayan H.; Özbay, Ekmel
We investigated the splitting of surface electromagnetic waves trapped at the output surface of a one-dimensional metallic grating structure. The output gratings of the structure asymmetrically such that the output surfaces at the different sides of the subwavelength aperture can support surface waves at different frequencies. The transmission amplitude as measured at the left side is 1,000 times of that at the right side at 16 GHz. At 24 GHz, the transmission measured at the right side is 20 times that of the left side of the structure. Therefore, surface waves are guided into the different sides of the aperture at different frequencies via metallic gratings. The experimental results are in agreement with the theoretical results. © 2008 Optical Society of America.