arXiv subjects

Ekmel Ozbay

Publications and source records attributed to Ekmel Ozbay.

12 recordsLinked to original sources

arXiv2023

A Novel Method to Eliminate the Symmetry Dependence of Fiber Coils for Shupe Mitigation

It is a well-known fact that interferometric fiber optic gyroscopes (IFOGs) are easily distorted by thermal effects and distortion results in the degradation of the performance of these sensors. Changing the fiber coil geometry, increasing the winding symmetry, adding fiber buffer layers around the fiber coil, using different modulation methods for multifunctional integrated optic chips (MIOCs), and using special types of fibers, such as photonic crystal fibers (PCFs), are some alternative solutions for preventing this degradation. This paper, theoretically and experimentally, investigates not only how different types of fiber coil winding methods behave under different rates of temperature change but also presents a novel method, to the best of our knowledge, to eliminate the Shupe effect, without violating the simplest IFOG scheme. This method rules out the importance of the winding symmetry epochally and the need of any extra treatment for the fiber coil to increase the thermal performance of the system. Regardless of the symmetry of the fiber coil winding, the rate error due to the Shupe effect can be reduced to about $\pm$$0.05^\circ/$h for any rate of temperature change with this new method according to the experimental results.

physics.optics↗

arXiv2023

Electrically tunable radiative cooling performance of a photonic structure with thermal infrared applications

Thermal infrared (IR) radiation has attracted considerable attention due to its applications ranging from radiative cooling to thermal management. In this paper, we design a multi-band graphene-based metamaterial absorber compatible with infrared applications and radiative cooling performance. The proposed structure consists of the single-sized metal-insulator-metal (MIM) grating deposited on metal/insulator substrate and single-layer graphene. The system realizes a broadband perfect absorption ranging from 940 nm to 1498 nm and a narrowband perfect absorption at the resonance wavelength of 5800 nm. Meanwhile, the absorptivity of the structure is suppressed within the mid-wave infrared (MWIR) and long-wave infrared (LWIR) ranges. Furthermore, to demonstrate the tunability of the structure, an external voltage gate is applied to the single-layer graphene. It is shown that, by varying the chemical potential of graphene layer from 0 eV to 1 eV , the absorption resonances at the mid-infrared (MIR) range can shift toward the shorter wavelengths. It is also observed that the structure can possess an average net cooling power over 18 at the ambient temperature, when is varied from 0 eV to 1 eV. Finally, we investigate the overall performances of the structure as a function of temperature to realize thermal infrared applications.

physics.optics↗

arXiv2022

Thermally switchable polarization manipulation and diodelike transmission in scalable, resonator-free, mid-infrared metasurfaces with vanadium-dioxide grids

We conceptualized three-array scalable metasurfaces comprising only three thin strip grids and numerically demonstrated their characteristics in the mid-infrared spectral regime for switchable polarization manipulation and related asymmetric diodelike transmission (AT). A few or all of the grids were taken to be made of VO$_2$, a phase-change material. For each proposed metasurface, two effective structures and, therefore, two different functionalities exist, corresponding to the metallic and insulating phases of VO$_2$. The achieved scenarios of functionality switching that depend on the VO$_2$ phase are shown to significantly depend in the way in which VO$_2$ is incorporated to the metasurface. Switchable bands of polarization manipulation are up to 40 THz wide. The AT band can be modulated when Fabry--Perot (anti-)resonances come into play.

physics.optics↗

arXiv2019

Electromagnetic Field Tapering in the High-Roughness Substrates Coated by a Thin Film of Manganese: A Lithography-Free Approach to Ultra-Broadband, Wide-Angle, UV to FIR Perfect Absorption

Metallic layers are known to be used for the suppression of wave transmission when their thickness is sufficiently higher than the skin depth of metal. If in addition to blocking the transmission, metallic layers have the feature of blocking the reflection, too, they would make perfect absorbers. In this work, we propose an experimental approach of using a single thin layer of Manganese (Mn) as both the transmission suppresser and the reflection suppresser. This approach leads to obtaining lithography-free ultra-broadband perfect absorption in an ultra-wide spectrum ranging from Ultraviolet (UV) to Far Infrared (FIR). The measured average absorption is approximately 99%. Such a promising result can be achieved by only coating a single Mn layer on high-roughness substrates that include random nano-pyramids on it. In other words, we do not need a stack of different materials and combinations of geometrical features. The high roughness is realized on a commercial Silicon wafer substrate by inductively coupled plasma (ICP) etching. The key to this ultra-wideband absorption is electromagnetic field tapering which exists due to the graded-index feature of the structure (known as moth-eye effect), along with the ideal optical properties of Mn which makes it an excellent metal for broadband absorption applications. A full experimental characterization of the fabricated samples is presented along with the physical analysis of the phenomena. The findings of this paper can be used for the realization of lithography-free, cost-effective and high-throughput mass production of broadband absorbers.

physics.optics↗

arXiv2019

Electrically Switchable Metadevices via Graphene

Metamaterials bring sub-wavelength resonating structures together to overcome the limitations of conventional materials. The realization of active metadevices has been an outstanding challenge that requires electrically reconfigurable components operating over a broad spectrum with a wide dynamic range. The existing capability of metamaterials, however, is not sufficient to realize this goal. Here, by integrating passive metamaterials with active graphene devices, we demonstrate a new class of electrically controlled active metadevices working in microwave frequencies. The fabricated active metadevices enable efficient control of both amplitude (> 50 dB) and phase (> 90°) of electromagnetic waves. In this hybrid system, graphene operates as a tunable Drude metal that controls the radiation of the passive metamaterials. Furthermore, by integrating individually addressable arrays of metadevices, we demonstrate a new class of spatially varying digital metasurfaces where the local dielectric constant can be reconfigured with applied bias voltages. Additionally, we reconfigure resonance frequency of split ring resonators without changing its amplitude by damping one of the two coupled metasurfaces via graphene. Our approach is general enough to implement various metamaterial systems that could yield new applications ranging from electrically switchable cloaking devices to adaptive camouflage systems.

physics.optics↗

arXiv2018

Lithography-Free, Manganese-Based Ultra-Broadband Absorption Through Annealing-Based Deformation of Thin Layers into metal-air composites

Fabrication, characterization, and analysis of an ultra-broadband lithography-free absorber is presented. An over 94% average absorption is experimentally achieved in the wavelength range of 450-1400 nm. This ultra-broadband absorption is obtained by a simple annealed tri-layer metal-insulator-metal (MIM) configuration. The metal used in the structure is Manganese (Mn), which also makes the structure cost-effective. It is shown that the structure retains its high absorption for TM polarization, up to 70 degrees, and, for TE polarization, up to 50 degrees. Moreover, the physical mechanism behind this broadband absorption is explained. Being both lithography-free and cost-effective, the structure is a perfect candidate for large-area and mass production purposes.

physics.optics↗

arXiv2018

A Route to Unusually Broadband Absorption Spanning from Visible to Mid-Infrared

In this paper, a route to ultra-broadband absorption is suggested and demonstrated by a feasible design. The high absorption regime (absorption above 90%) for the suggested structure ranges from visible to mid-infrared (MIR), i.e. for the wavelength from 478 to 3,278 nm that yields an ultra-wide bandwidth of 2,800 nm. The structure consists of a top-layer-patterned metal-insulator-metal (MIM) configuration, into the insulator layer of which, an ultra-thin 5 nm layer of Manganese (Mn) is embedded. The MIM configuration represents a Ti-Al2O3-Ti tri-layer. It is shown that, without the ultra-thin layer of Mn, the absorption bandwidth is reduced to 274 nm. Therefore, adding only a 5 nm layer of Mn leads to a more than tenfold increase in the width of the absorption band. It is explained in detail that the physical mechanism contributing to this ultra-broadband result is a combination of plasmonic and non-plasmonic resonance modes, along with the appropriate optical properties of Mn. This structure has the relative bandwidth (RBW) of 149%, while only one step of lithography is required for its fabrication, so it is relatively simple to fabricate. This makes it rather promising for practical applications.

physics.optics↗

arXiv2018

Broadband mixing of ${\cal PT}$-symmetric and ${\cal PT}$-broken phases in photonic heterostructures with a one-dimensional loss/gain bilayer

Combining loss and gain components in one photonic heterostructure opens a new route to efficient manipulation by radiation, transmission, absorption, and scattering of electromagnetic waves. Therefore, loss/gain structures enabling ${\cal PT}$-symmetric and ${\cal PT}$-broken phases for eigenvalues have extensively been studied in the last decade. In particular, translation from one phase to another, which occurs at the critical point in the two-channel structures with one-dimensional loss/gain components, is often associated with one-way transmission. In this report, broadband mixing of the ${\cal PT}$-symmetric and ${\cal PT}$-broken phases for eigenvalues is theoretically demonstrated in heterostructures with four channels obtained by combining a one-dimensional loss/gain bilayer and one or two thin polarization-converting components (PCCs). The broadband phase mixing in the four-channel case is expected to yield advanced transmission and absorption regimes. Various configurations are analyzed, which are distinguished in symmetry properties and polarization conversion regime of PCCs. The conditions necessary for phase mixing are discussed. The simplest two-component configurations with broadband mixing are found, as well as the more complex three-component configurations wherein symmetric and broken sets are not yet mixed and appear in the neighbouring frequency ranges. Peculiarities of eigenvalue behaviour are considered for different permittivity ranges of loss/gain medium, i.e., from epsilon-near-zero to high-epsilon regime.

physics.optics↗

arXiv2013

Two-Dimensional Ferroelectric Photonic Crystals: Optics and Band Structure

In this report we present an investigation of the optical properties and band structure calculations for the photonic structures based on the functional materials- ferroelectrics. A theoretical approach to the optical properties of the 2D and 3D photonic crystals which yields further insight in the phenomenon of the reflection from different families of lattice planes in relation to the presence of photonic gaps or photonic bands. We calculate the photonic bands and optical properties of LiNbO3 based photonic crystals. Calculations of reflection and transmission spectra show the features correspond to the onset of diffraction, as well as to additional reflectance structures at large values of the angle of incidence.

physics.optics↗

arXiv2012

Electron Energy-Loss Spectroscopy and the Electronic Structure of ABO3 Ferroelectrics: First Principle Calculations

The electronic structures of ABO3 ferroelectrics are calculated within the density functional theory, and their evolution is analyzed as the crystal-field symmetry changes from cubic to rhombohedral via tetragonal phases. Electronic structure fingerprints that characterize each phase from their electronic spectra are identified. We carried out electron-energy loss spectroscopy experiments by using synchrotron radiation and compared these results to the theoretical spectra calculated within DFT-LDA. The dominant role of the BO6 octahedra in the formation of the energy spectra of ABO3 compounds was demonstrated. Anomalous behavior of plasmons in ferroelectrics was exhibited by the function representing the characteristic energy loss in the region of phase transition.

cond-mat.mtrl-sci↗

arXiv2011

Mechanism of the electro-optic effect and nonlinear optical susceptibilities of some ferroelectrics: ab initio calculation

The nonlinear optical properties and electro-optic effects of some oxygen-octahedric ferroelectrics are studied by the density functional theory (DFT) in the local density approximation (LDA) expressions based on first principle calculations without the scissor approximation. We present calculations of the frequency- dependent complex dielectric function and the second harmonic generation response coefficient \c{hi}(2)(-2ω,ω,ω) over a large frequency range in tetragonal and rhombohedral phases. The electronic linear electrooptic susceptibility \c{hi}(2) (-ω,ω,0) is also evaluated below the band gap. These results are based on a series of the LDA calculation using DFT. Results for \c{hi}(2) (-ω,ω,0) are in agreement with the experiment below the band gap and those for \c{hi}(2)(-2ω,ω,ω) are compared with the experimental data where available.

cond-mat.mtrl-sci↗

arXiv2008

Split ring resonator-coupled enhanced transmission through a single subwavelength aperture

We report the enhanced transmission of electromagnetic waves through a single subwavelength aperture by making use of the resonance behavior of a split ring resonator (SRR) at microwave frequencies. By placing a single SRR at the near-field of the aperture, strongly localized electromagnetic fields are effectively coupled to the aperture with a radius that is twenty times smaller than the resonance wavelength. We obtained 740-fold transmission enhancement by exciting the electric resonance of SRR. A different coupling mechanism, through the magnetic resonance of SRR, is also verified to yield enhanced transmission. Good agreement is obtained between the microwave measurements and numerical simulations.

physics.optics↗