Browsing by Subject "Optical instruments"

Now showing 1 - 7 of 7

Open Access
Camera tamper detection using wavelet analysis for video surveillance
(IEEE, 2007-09) Aksay, A.; Temizel, A.; Çetin, A. Enis
It is generally accepted that video surveillance system operators lose their concentration after a short period of time and may miss important events taking place. In addition, many surveillance systems are frequently left unattended. Because of these reasons, automated analysis of the live video feed and automatic detection of suspicious activity have recently gained importance. To prevent capture of their images, criminals resort to several techniques such as deliberately obscuring the camera view, covering the lens with a foreign object, spraying or defocusing the camera lens. In this paper, we propose some computationally efficient wavelet domain methods for rapid camera tamper detection and identify some real-life problems and propose solutions to these. © 2007 IEEE.
Open Access
Carrier-induced refractive index change in InN
(Wiley, 2008) Bulutay, Ceyhun; Zakhleniuk, N. A.
Rapid development of InN technology demands comprehensive assessment of the electronic and optoelectronic potential of this material. In this theoretical work the effect of free electrons on the optical properties of the wurtzite phase of InN is investigated. The blue shift of the optical absorption edge by the free-carrier band filling is known as the Burstein-Moss effect for which InN offers to be a very suitable candidate as has been recently demonstrated experimentally. Due to well known Kramers-Kronig relations, a change in absorption is accompanied by a change in the index of refraction. Considering n-type InN samples with free electron concentrations ranging from 5x10 17 to 5x1020 cm-3, and employing a nonlocal empirical pseudopotential band structure, it is shown that this leads to a few percent change of the index of refraction. These carrier-induced refractive index changes can be utilized in optical switches, futhermore it needs to be taken into account in the design of InN-based optical devices such as lasers and optical modulators.
Open Access
Highly asymmetric transmission of linearly polarized waves realized with a multilayered structure including chiral metamaterials
(IOP Publishing, 2014) Li, Z.; Mutlu, M.; Özbay, Ekmel
We numerically and experimentally demonstrate highly asymmetric transmission of linearly polarized waves with a multilayered metallic structure. The whole structure has a subwavelength thickness and consists of a thin slab of chiral metamaterial sandwiched between two 90° twisted linear polarizers. The chiral metamaterial is made of two sets of twisting cross wires that can rotate the polarization by 90° at resonance, and the two linear polarizers are simple metallic grating polarizers. The operation principle of the whole structure can be well interpreted by using the Jones matrix method. Our experimental results also verify that chiral metamaterials can be safely integrated into complex structures and treated as an effective medium as long as their resonant modes are not affected by the environment.
Open Access
Mesoscopic Fano effect in an Aharonov-Bohm interferometer Coulomb-coupled to a nearby quantum dot
(Wiley, 2007) Tolea, M.; Moldoveanu, V.; Tanatar, Bilal
Motivated by the pionieering experiments of Buks et al. [Nature 391, 871 (1998)] we investigate the visibility of the Fano effect in a single-dot Aharonov-Bohm interferometer which is Coulomb-coupled to a nearby quantum dot. The latter acts as a 'Which Path Detector' and is coupled to two leads on which a finite bias is applied. Using the non-equilibrium Keldysh-Green function formalism we compute the currents through the detector and the interferometer. We take into account the first two contributions to the interaction selfenergy and emphasize the correction to the Landauer formula which appears beyond the single-particle approximation. Particular attention is given to the coherence properties of the interferometer in the presence of the electron-electron interaction between the embedded dot and the detector. We show that when the detector is subjected to a finite bias the amplitude of Aharonov-Bohm oscillations of the current through the interferometer decreases. The Fano line is in turn rather stable under interaction. Our results generalize an earlier work of Silva and Levit [Phys. Rev. B 63, 201309 (2001)] and complement the existing description of the controlled dephasing.
Open Access
Novel optical antenna designs of comb shaped split ring architecture for NIR and MIR enhanced field localization
(IEEE, 2014) Kılıç, Veli Tayfun; Ertürk, Vakur B.; Demir, Hilmi Volkan
We demonstrated NIR/MIR resonance behavior in optical antennas of comb-shaped split-ring resonators enabling substantially larger field enhancements than single/array of dipoles with the same side length, despite their simple architecture.
Open Access
Physical optics modeling of 2D dielectric lenses
(Optical Society of America, 2009-01-27) Yurchenko, V. B.; Altintas, A.
We propose an advanced physical optics formulation for the accurate modeling of dielectric lenses used in quasi-optical systems of millimeter, submillimeter, and infrared wave applications. For comparison, we obtain an exact full-wave solution of a two-dimensional lens problem and use it as a benchmark for testing and validation of asymptotic models being considered.
Open Access
Video gözetleme uygulamalarında kamera sabotaj sezimi
(IEEE, 2007-06) Aksay, A.; Temizel, A.; Çetin, A. Enis
Son yıllarda video gözetim uygulamaları için kullanılan kamera sayılarında kayda değer artış olmuştur. Bu kameraların amaçlandığı gibi çalışıyor olması anlamlı bilgi yakalaması önemlidir. Suç işleyecek kişiler kamera önünü kapatarak, boya püskürterek ya da kamera odağını bozarak görüntülerinin ve eylemlerinin kaydedilmesini engellemek yoluna başvurmaktadır. Kameraları gözleyen birisinin olmaması ya da dikkatinin dağınık olması sabotajın fark edilememesine neden olur ve sistem normal olarak çalışıyor ve kaydediyor olsa bile kayıtların kullanılamaz olmasına yolaçar. Bu bildiride, dalgacık alanında arkaplan çıkarımı yöntemi kullanılarak kamerada görüş azalması ve kamera önünün kapatılması durumlarının gerçek zamanlı kestirimi önerilmektedir. Ayrıca, sistemin gerçek hayat koşullarında daha güvenilir çalışması için bazı yöntemler de önerilmiştir.