Scopus İndeksli Yayınlar Koleksiyonu
Permanent URI for this collectionhttps://hdl.handle.net/20.500.12573/395
Browse
5 results
Search Results
Article Citation - WoS: 27Citation - Scopus: 27Guided Plasmon Modes of a Graphene-Coated Kerr Slab(Springer, 2015-10-14) Hajian, Hodjat; Rukhlenko, Ivan D.; Leung, P. T.; Caglayan, Humeyra; Ozbay, EkmelWe study analytically propagating surface plasmon modes of a Kerr slab sandwiched between two graphene layers. We show that some of the modes that propagate forward at low field intensities start propagating with negative slope of dispersion and positive flux of energy (fast-light surface plasmons) when the field intensity becomes high. We also discover that our structure supports an additional branch of low-intensity fast-light guided modes. The possibility of dynamically switching between the forward and the fast-light plasmon modes by changing the intensity of the excitation light or the chemical potential of the graphene layers opens up wide opportunities for controlling light with light and electrical signals on the nanoscale.Conference Object Citation - WoS: 3Citation - Scopus: 5Field Test and Fading Measurement of a Distributed Acoustic Sensor System Over a 50 Km-Long Fiber(Spie-Int Soc Optical Engineering, 2018-05-14) Uyar, Faruk; Kartaloglu, Tolga; Ozdur, Ibrahim; Ozbay, EkmelIn this study, we present a direct detection distributed acoustic sensor based on phase-sensitive optical time domain reflectometer (phi-OTDR) with long sensing range and high signal-to-noise ratio (SNR), which is field-tested over a 50 km-long fiber. Due to the random nature of Rayleigh backscattered light and fading phenomena, it is hard to characterize the performance of the system. For this reason, the performance of our sensor is specified in a statistical manner in which the mean SNR is determined using the histograms of the SNR. The SNR values are measured for identical acoustic signals in five different days, total of 48 hours and the SNR histograms are obtained for fiber distances of 100 m, 12 km, 21 km, 30 km, 40 km and 50 km. The system is field-tested using external disturbances that are generated from a 50-Hz vibrator. The SNR values are extracted from the power spectral density (psd) of the collected data over the monitored fiber span. Our results show that the phi-OTDR system exhibits a mean SNR of 22.5 dB at 50 km distance.Article Citation - WoS: 29Citation - Scopus: 30Enhanced Transmission and Beaming via a Zero-Index Photonic Crystal(Amer Inst Physics, 2016-07-18) Hajian, Hodjat; Ozbay, Ekmel; Caglayan, HumeyraCertain types of photonic crystals with Dirac cones at the Gamma point of their band structure have a zero effective index of refraction at Dirac cone frequency. Here, by an appropriate design of the photonic structure, we obtain a strong coupling between modes around the Dirac cone frequency of an all-dielectric zero-index photonic crystal and the guided ones supported by a photonic crystal waveguide. Consequently, we experimentally demonstrate that the presence of the zero-index photonic crystal at the inner side of the photonic crystal waveguide leads to an enhancement in the transmission of some of the guided waves passing through this hybrid system. Moreover, those electromagnetic waves extracted from the structure with enhanced transmission exhibit high directional beaming due to the presence of the zero-index photonic crystal at the outer side of the photonic crystal waveguide. Published by AIP Publishing.Article Citation - WoS: 11Citation - Scopus: 13Enhanced Tunability of V-Shaped Plasmonic Structures Using Ionic Liquid Gating and Graphene(Pergamon-Elsevier Science Ltd, 2016-11) Ozdemir, Onur; Aygar, A. Melis; Balci, Osman; Kocabas, Coskun; Caglayan, Humeyra; Ozbay, EkmelGraphene is a strong candidate for active optoelectronic devices because of its electrostatically tunable optical response. Current substrate back-gating methods are unable to sustain high fields through graphene unless a high gate voltage is applied. In order to solve this problem, ionic liquid gating is used which allows substrate front side gating, thus eliminating the major loss factors such as a dielectric layer and a thick substrate layer. On the other hand, due to its two dimensional nature, graphene interacts weakly with light and this interaction limits its efficiency in optoelectronic devices. However, V-shaped plasmonic antennas can be used to enhance the incident electric field intensity and confine the electric field near graphene thus allowing further interaction with graphene. Combining V-shaped nanoantennas with the tunable response of graphene, the operation wavelength of the devices that utilize V-shaped antennas can be tuned in situ. In the present paper, we demonstrate a graphene-based device with ionic liquid gating and V-shaped plasmonic antennas to both enhance and more effectively tune the total optical response. We are able to tune the transmission response of the device for up to 389 nm by changing the gate voltage by 3.8 V in the mid-infrared regime. (C) 2016 Elsevier Ltd. All rights reserved.Article Citation - WoS: 16Citation - Scopus: 19Coupling Enhancement of Split Ring Resonators on Graphene(Pergamon-Elsevier Science Ltd, 2014-12) Cakmakyapan, Semih; Caglayan, Humeyra; Ozbay, EkmelMetallic split ring resonator (SRR) structures are used in nanophotonics applications in order to localize and enhance incident electromagnetic field. Electrically controllable sheet carrier concentration of graphene provides a platform where the resonance of the SRRs fabricated on graphene can be tuned. The reflectivity spectra of SRR arrays shift by applying gate voltage, which modulates the sheet carrier concentration, and thereby the optical conductivity of monolayer graphene. We experimentally and numerically demonstrated that the tuning range can be increased by tailoring the effective mode area of the SRR and enhancing the interaction with graphene. The tuning capability is one of the important features of graphene based tunable sensors, optical switches, and modulator applications. (C) 2014 Elsevier Ltd. All rights reserved.