Browsing by Author "Ozbay, Ekmel"

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94.8 Km-Range Direct Detection Fiber Optic Distributed Acoustic Sensor
(IEEE, 345 E 47TH ST, NEW YORK, NY 10017 USA, 01.01.2019) Uyar, Faruk; Onat, Talha; Unal, Canberk; Unal, Canberk; Ozdur, Ibrahim; Ozbay, Ekmel; 0000-0003-3552-1650; AGÜ, Mühendislik Fakültesi, Elektrik - Elektronik Mühendisliği Bölümü
This work demonstrates an ultra-long range direct detection fiber optic distributed acoustic sensor which can detect vibrations at a distance of 94.8 km with 10 m resolution along the sensing fiber. (C) 2019 The Author(s)
Coupling enhancement of split ring resonators on graphene
(PERGAMON-ELSEVIER SCIENCE LTD, THE BOULEVARD, LANGFORD LANE, KIDLINGTON, OXFORD OX5 1GB, ENGLAND, 2014) Cakmakyapan, Semih; Caglayan, Humeyra; Ozbay, Ekmel; AGÜ, Mühendislik Fakültesi, Elektrik & Elektronik Mühendisliği Bölümü;
Metallic 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.
A Direct Detection Fiber Optic Distributed Acoustic Sensor With a Mean SNR of 7.3 dB at 102.7 km
(IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 445 HOES LANE, PISCATAWAY, NJ 08855-4141 USA, 2019) Uyar, Faruk; Onat, Talha; Unal, Canberk; Kertelog, Tolga; Ozbay, Ekmel; Ozdur, Ibrahim; AGÜ, Mühendislik Fakültesi, Elektrik & Elektronik Mühendisliği Bölümü;
In this work, we present the experimental results of a direct detection phi-OTDR based distributed acoustic sensor system. The system uses two cascaded acousto-optic modulators in order to generate optical pulses with very high extinction ratio and dual photodetector scheme for high dynamic range. The proposed schemes are investigated in detail and their performance enhancement is experimentally verified. Four piezoelectric based fiber stretchers are placed on a similar to 104 km single-mode test fiber at the distances of 1 km, 10 km, 87 km and 102.7 km and used for perturbation tests. The stretchers generated vibration signals which are analyzed to quantify the system performance. The signal-to-noise ratio (SNR) of vibration signals at the monitored distances is measured over the 12-hour recorded data within 34-second time windows considering the multi-point random interference of scattered light and fading phenomena. Using the 12-hour data, SNR histograms at four different locations are generated and mean SNR values are obtained. The signals received from 102.7 km has a maximum SNR of 24.7 dB and a mean SNR of 7.3 dB with a spatial resolution of 15 m. To the best of our knowledge, this is the highest-range reported direct detection phi-OTDR based distributed acoustic sensor system.
Enhanced transmission and beaming via a zero-index photonic crystal
(AMER INST PHYSICS, 1305 WALT WHITMAN RD, STE 300, MELVILLE, NY 11747-4501 USA, 2016) Hajian, Hodjat; Ozbay, Ekmel; Caglayan, Humeyra; AGÜ, Mühendislik Fakültesi, Elektrik & Elektronik Mühendisliği Bölümü;
Certain 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.
Enhanced tunability of V-shaped plasmonic structures using ionic liquid gating and graphene
(PERGAMON-ELSEVIER SCIENCE LTD, THE BOULEVARD, LANGFORD LANE, KIDLINGTON, OXFORD OX5 1GB, ENGLAND, 2016) Ozdemir, Onur; Aygar, A. Melis; Balci, Osman; Kocabas, Coskun; Caglayan, Humeyra; Ozbay, Ekmel; AGÜ, Mühendislik Fakültesi, Elektrik & Elektronik Mühendisliği Bölümü;
Graphene 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.
Experimental Analysis of Non-linear Phenomena due to Perturbation Amplitude in φ-OTDR Based Fiber Optic Distributed Vibration Sensor
(Optica Publishing Group (formerly OSA), 2020) Uyar, Faruk; Kartaloǧlu, Tolga; Ozbay, Ekmel; Ozdur, Ibrahim Tuna; AGÜ, Mühendislik Fakültesi, Elektrik - Elektronik Mühendisliği Bölümü; Ozdur, Ibrahim Tuna
We experimentally analyze the non-linearity effect due to the perturbation amplitude in the φ-OTDR based fiber optic distributed vibration sensor by investigating the effects of large disturbance signal.
Field Test and Fading Measurement of a Distributed Acoustic Sensor System over a 50 km-long Fiber
(SPIE-INT SOC OPTICAL ENGINEERING, 1000 20TH ST, PO BOX 10, BELLINGHAM, WA 98227-0010 USA, 2018) Uyar, Faruk; Kartaloglu, Tolga; Ozdur, Ibrahim; Ozbay, Ekmel; AGÜ, Mühendislik Fakültesi, Elektrik & Elektronik Mühendisliği Bölümü;
In 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.
Guided Plasmon Modes of a Graphene-Coated Kerr Slab
(SPRINGER, 233 SPRING ST, NEW YORK, NY 10013 USA, 2016) Hajian, Hodjat; Rukhlenko, Ivan D.; Leung, Pui Tak; Caglayan, Humeyra; Ozbay, Ekmel; AGÜ, Mühendislik Fakültesi, Elektrik & Elektronik Mühendisliği Bölümü;
We 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.
The Investigation of Rayleigh Backscattered Signal Statistics in a phi-OTDR System Incorporating Optical Pre-Amplifier
(IEEE, 345 E 47TH ST, NEW YORK, NY 10017 USA, 2020) Uyar, Faruk; Kartaloglu, Tolga; Ozbay, Ekmel; Ozdur, Ibrahim; AGÜ, Mühendislik Fakültesi, Elektrik - Elektronik Mühendisliği Bölümü
We theoretically model and experimentally demonstrate the photon statistics of Rayleigh backscattered signal in a phi-OTDR based distributed fiber optical sensor in the presence of amplified spontaneous emission noise caused by optical pre-amplifier.
Multiple slow waves and relevant transverse transmission and confinement in chirped photonic crystals
(OPTICAL SOC AMER, 2010 MASSACHUSETTS AVE NW, WASHINGTON, DC 20036 USA, 2014) Serebryannikov, Andriy E.; Cakmak, A. Ozgur; Colak, Evrim; Caglayan, Humeyra; Kurt, Hamza; Ozbay, Ekmel; AGÜ, Mühendislik Fakültesi, Elektrik & Elektronik Mühendisliği Bölümü;
The dispersion properties of rod-type chirped photonic crystals (PhCs) and non-channeled transmission in the direction of the variation of structural parameters from one cell of such a PhC to another are studied. Two types of configurations that enable multiple slow waves but differ in the utilized chirping scheme are compared. It is demonstrated that the multiple, nearly flat bands with a group index of refraction exceeding 180 can be obtained. For these bands, transmission is characterized by multiple narrow peaks of perfect transmission, strong field enhancement inside the slab, and large values of the Q-factor. Among the bands, there are some that show negative phase velocity. Symmetry with respect to the slab mid-plane must be kept in order to obtain constructive interferences that are necessary for reflection-free transmission. It is shown that 15 and more slow wave bands can be obtained in one configuration. The corresponding transmission peaks are well separated from each other, being the only significant feature of the transmission spectrum, while the Q-factor can exceed 10(5). The observed features are preserved in a wide range of the incidence angle variation. They can be used for tuning the locations and spectral widths of the transmission peaks. Some comparisons with the chirped multilayer structures have been carried out. (C) 2014 Optical Society of America
A Simple Method for Enhancing the SNR in Direct Detection (p-OTDR based Distributed Acoustic Sensors
(IEEE, 345 E 47TH ST, NEW YORK, NY 10017 USA, 2020) Uyar, Faruk; Kartaloglu, Tolga; Unal, Canberk; Ozbay, Ekmel; Ozdur, Ibrahim; AGÜ, Mühendislik Fakültesi, Elektrik - Elektronik Mühendisliği Bölümü
A simple and effective method for increasing the SNR and range in fp-OTDR based direct -detection distributed acoustic sensors is proposed and experimentally verified. The proposed method results in 11 dB SNR improvement at 66 km. (fD 2020 The Author(s)