Browsing by Subject "Waves"

Now showing 1 - 6 of 6

Open Access
Composite chiral metamaterials with negative refractive index and high values of the figure of merit
(Optical Society of America, 2012) Li, Z.; Caglayan, H.; Alici, K. B.; Kafesaki, M.; Soukoulis, C. M.; Özbay, Ekmel
A composite chiral metamaterial (CCMM) is designed and studied both numerically and experimentally. The CCMM is constructed by the combination of a continuous metallic wires structure and a purely chiral metamaterial (CMM) that consists of conjugated Rosettes. For the CMM, only very small, useful bands of negative index can be obtained for circularly polarized waves. These bands are all above the chiral resonance frequencies because of the high value of the effective parameter of relative permittivity epsilon. After the addition of the continuous metallic wires, which provide negative permittivity, the high value of epsilon can be partially compensated. Thus, a negative index band for the left circularly polarized wave that is below the chiral resonance frequency is obtained for the CCMM. At the same time, a negative index band for the right circularly polarized wave that is above the chiral resonance frequency is also obtained. Furthermore, both negative index bands correspond to the transmission peaks and have high values of the figure of merit. Therefore, the CCMM design that is proposed here is more suitable than the CMM for the construction of chiral metamaterials with a negative index. (C) 2012 Optical Society of America
Open Access
Dimensioning shared-per-node recirculating fiber delay line buffers in an optical packet switch
(Elsevier, 2013) Akar, N.; Gunalay, Y.
Optical buffering based on fiber delay lines (FDLs) has been proposed as a means for contention resolution in an optical packet switch. In this article, we propose a queuing model for feedback-type shared-per-node recirculating FDL optical buffers in asynchronous optical switching nodes. In this model, optical packets are allowed to recirculate over FDLs as long as the total number of recirculations is less than a pre-determined limit to meet signal loss requirements. Markov Modulated Poisson Process (MMPP)-based overflow traffic models and fixed-point iterations are employed to provide an approximate analysis procedure to obtain blocking probabilities as a function of various buffer parameters in the system when the packet arrival process at the optical switch is Poisson. The proposed algorithm is numerically efficient and accurate especially in a certain regime identified with relatively long and variably-sized FDLs, making it possible to dimension optical buffers in next-generation optical packet switching systems.
Open Access
Exact analysis of single-wavelength optical buffers with feedback markov fluid queues
(Optical Society of America, 2009-10-15) Kankaya H. E.; Akar, N.
Optical buffering via fiber delay lines is used for contention resolution in optical packet and optical burst switching nodes. This article addresses the problem of exactly finding the blocking probabilities in an asynchronous single-wavelength optical buffer. Packet lengths are assumed to be variable and modeled by phase-type distributions, whereas the packet arrival process is modeled by a Markovian arrival process that can capture autocorrelations in interarrival times. The exact solution is based on the theory of feedback fluid queues for which we propose numerically efficient and stable algorithms. We not only find the packet blocking probabilities but also the entire distribution of the unfinished work in this system from which all performance measures of interest can be derived.
Open Access
High-refractive-index measurement with an elastromeric grating coupler
(Optical Society of America, 2005) Kocabas, A.; Ay, F.; Dana, A.; Kiyat, A.; Aydınlı, Atilla
An elastomeric grating coupler fabricated by the replica molding technique is used to measure the modal indices of a silicon-on-insulator (SOI) planar waveguide structure. Because of the van der Waals interaction between the grating mold and the waveguide, the elastomeric stamp makes conformal contact with the waveguide surface, inducing a periodic index perturbation at the contact region. The phase of the incident light is changed to match the guided modes of the waveguide. The modal and bulk indices are obtained by measuring the coupling angles. This technique serves to measure the high refractive index with a precision better than 10(-3) and allows the elastomeric stamp to be removed without damaging the surface of the waveguide.
Restricted
The relationship between world war I and the Spanish flu in the late Ottoman Empire
(Bilkent University, 2023) Saad, Amal; Atajanov, Davut; Karimov, Islomjon; Tulkibayeva, Mariya; Ghayoumi, Narges; Umar, Ushna
Nearing the end of the year 1918, humanity thought it had finally overcome one of its worst catastrophes — World War I. Just as the world escaped the death and destruction of the war, however, an even bigger calamity took hold of the globe: that is, a pandemic. In the summer of 1918, Spain reported the existence of influenza — with the symptoms of the common flu, which deteriorated into pneumonia, bronchitis, etc. — which was later given the misnomer of the infamous “Spanish flu.” The tragedy of the war often overshadows the crippling effect the Spanish flu had on the world and the Ottoman Empire — a warzone, in more than one way — in particular. The fact of the matter remains that Spanish flu had a just as catastrophic effect as World War I — if not worse. This paper aims to explore the ramifications of World War I and the Spanish flu taking place in the same time period through the use of first-hand accounts of both the war and influenza. It will do so in the form of letters, pictures dating back to Ottoman times, memoirs of soldiers, newspaper articles — both from inside and outside the Ottoman Empire — and the Turkish Red Crescent archive. In addition to those primary sources, research papers and books that offer varying perspectives on the subject will also be used. This begs the question — did the war exacerbate the effects of influenza and its aftermath? Simply put, yes; this paper realizes that the fallout of World War I, joined with that of the Spanish flu, resulted in devastating repercussions for the Ottoman Empire in terms of health, the quality of life of its population, and even its economy.
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.