Elektrik Elektronik Mühendisliği Bölümü Yayın Koleksiyonu

Permanent URI for this collectionhttps://hdl.handle.net/20.500.12416/411

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  • Article
    Citation - WoS: 11
    Citation - Scopus: 9
    Multimode Beam Propagation Through Atmospheric Turbulence
    (Pergamon-elsevier Science Ltd, 2024) Baykal, Yahya; Ata, Yalcin; Gercekcioglu, Hamza; Gokce, Muhsin Caner
    The investigation focuses on studying the propagation characteristics of multimode lasers in the turbulent amosphere. By employing the Huygens-Fresnel integral, we develop analytical formulations for various propagation parameters. These include the average intensity distribution, kurtosis parameter, beam spread, and the average transmittance of multimode beams in turbulent atmosphere. Our findings reveal that as the propagation distance or the structure constant of the atmosphere increases, i.e., turbulence becomes stronger, the kurtosis parameter and the beam spread increase. The multimode beam exhibits a Gaussian like intensity profile when the propagation distance is significantly increased or when the structure constant becomes sufficiently large. For the case of the Gaussian beam, the kurtosis parameter is found to be 3. The multimode beam's kurtosis parameter rises as the turbulence becomes stronger and eventually approaches 3. Raising the mode content leads to a rise in the average transmittance; however, it leads to a decline in the Kurtosis parameter and the beam spread.
  • Article
    Citation - WoS: 3
    Citation - Scopus: 5
    Depth Dependence of Oceanic Turbulence Optical Power Spectrum Under Any Temperature and Salinity Concentration
    (Iop Publishing Ltd, 2024) Gercekcioglu, Hamza; Baykal, Yahya
    The Oceanic Turbulence Optical Power Spectrum (OTOPS) with depth variations is acquired under any temperature and salinity concentration. It is supposed that specific medium is the Atlantic Ocean at high latitude and the Pacific Ocean at high, mid and low latitudes. For the OTOPS model, a depth-varying functions that include low-latitude, high- and mid-latitude-summer and mid-latitude-winter salinity and temperature changes are found. With the help of the equations for the temperature and salinity changes, figures are obtained for the eddy diffusivity ratio depth of seawater and OTOPS model against the depth and kappa at these media. In the ocean, downlink (uplink) is defined as the optical wireless communication link where the receiver (transmitter) is located at a deeper point than the transmitter (receiver), i.e., in the downlink, optical signal proceeds from a point close to ocean surface to deeper ocean and in the uplink, optical signal proceeds from deeper ocean to a point close to ocean surface. In this paper, the OTOPS model is investigated on how its properties change in the underwater environment in downlink and uplink. Different behavior of the OTOPS model is exhibited.
  • Article
    Citation - WoS: 5
    Citation - Scopus: 6
    Underwater Turbulence Effect on Optical Imaging
    (Iop Publishing Ltd, 2022) Gokce, Muhsin Caner; Baykal, Yahya; Ata, Yalcin
    Modulation transfer function (MTF) of oceanic turbulence plays an essential role in the design and quality of underwater image sensing systems capturing optical signals. MTF gives clues about the characteristics of turbulence which can help image reconstruction where the image resolution can be increased in this way. In the paper, under the conditions of weak turbulence and Gaussian beam propagation, we derive the modulation transfer function for short-exposure and long-exposure images based on the recently developed turbulence spectrum model: Oceanic turbulence optical power spectrum (OTOPS). With the aid of the OTOPS model, the effect of measurable turbulence parameters, namely average temperature, average salinity concentration, and temperature-salinity gradient ratios, as well as imaging system parameters, namely receiver aperture radius and wavelength of the laser source on the MTF are reported. Obtained results indicate that MTF rapidly decreases with increasing relative spatial frequency and turbulence strength. Turbulence becomes stronger with the increase in the average temperature, average salinity concentration, energy dissipation rate, temperature-salinity gradient ratio and with the decrease in the temperature dissipation rate, wavelength.
  • Article
    Citation - WoS: 3
    Citation - Scopus: 3
    Performance Evaluation of Aeronautical Uplink/Downlink Free-Space Optical Communication System With Adaptive Optics Over Gamma-Gamma Turbulence Channel
    (Iop Publishing Ltd, 2022) Baykal, Yahya; Gokce, Muhsin Caner; Ata, Yalcin
    In this study, we analyze the effect of adaptive optics corrections on the performance of an aeronautical free-space optical (FSO) system with bidirectional slant path uplink and downlink communication channels. The aeronautical FSO communication (FSOC) system operates in a gamma-gamma atmospheric turbulence channel and employs adaptive optics corrections for the distorted wave front of the Gaussian beam wave. The modulation type of the aeronautical FSOC system is chosen to be M-ary phase-shift-keying-subcarrier intensity modulation and the type of the employed photodetector is positive-intrinsic-negative. In analysis, the effect of system parameters such as zenith angle, the height of transmitter/receiver on the ground, M-ary level, filter bandwidth, link distance, and the adaptive optics correction modes on bit-error-rate are demonstrated.
  • Article
    Citation - WoS: 7
    Citation - Scopus: 7
    Intensity Fluctuations in Biological Tissues at Any Turbulence Strength
    (Iop Publishing Ltd, 2022) Baykal, Yahya; Ata, Yalcin; Gokce, Muhsin Caner
    This study investigates the intensity fluctuations of the optical plane and spherical waves in biological tissue that experience any strength of turbulence. Biological tissue is a random and complex medium for optical wave propagation, having a power spectrum reflecting the turbulent characteristics that depend on the structural parameters. It is important to accurately determine the strength of turbulence and classify turbulence regimes for the correct modeling of the behavior of the optical wave propagation. To classify weak, moderate and strong turbulent regimes, closed-form expressions of modified Rytov variances are obtained. Based on the modified Rytov variance that involves the large-scale and small-scale variations, the intensity fluctuations specified by the metric of scintillation index, are calculated versus various parameters such as the propagation distance, refractive index, characteristic length of heterogeneity, small length-scale factor, wavelength, fractal dimension and strength of the refractive index fluctuations. Behavior of optical plane and spherical waves in different turbulent regimes and the comparison of intensity fluctuations in different specimens of human and animal tissues are shown.
  • Article
    Citation - WoS: 9
    Citation - Scopus: 8
    Effect of Partial Coherence on Signal-To Ratio Performance of Free Space Optical Communication System in Weak Turbulence
    (Elsevier, 2022) Aymelek, Goerkem; Yolcu, Beguem; Kayam, Orkun; Unal, Onur; Caner Gokce, Muhsin; Baykal, Yahya; Akbucak, Volkan; Gökçe, Muhsin Caner
    The effect of source coherence on the average signal-to-noise ratio ((SNR)) performance of free space optical communication (FSOC) systems operating in weak atmospheric turbulence is investigated with the help of the extended Huygens-Fresnel principle. For an FSOC system that uses a partially coherent laser source, first, the received power at the finite-sized receiver aperture is derived. Then, the power scintillation index is evaluated that reflects the aperture averaging. Using these derived optical entities, the variations of (SNR) are examined versus parameters such as the degree of source coherence, wavelength, link distance, source size, structure constant of atmosphere and the receiver aperture radius. Obtained results show that a decrease in the degree of source coherence has a positive effect on (SNR).
  • Article
    Citation - WoS: 7
    Citation - Scopus: 6
    Adaptive Optics Correction of Beam Spread in Biological Tissues
    (Pergamon-elsevier Science Ltd, 2022) Baykal, Yahya
    Beam spread in turbulent biological tissues is examined when the tissue is excited with a collimated Gaussian laser beam. Adaptive optics correction is applied to the beam spread in the form of piston only (P Only), tilt only (T Only), piston + tilt (P + T), and the reduction in the beam spread is evaluated as com-pared to the no adaptive optics (No AO) corrected beam spread. No AO and adaptive optics corrected beam spread are expressed for various biological tissue types, against the variations in the strength co-efficient of the refractive-index fluctuations, source size, small length-scale factor of turbulence, tissue length, fractal dimension, characteristic lengths of heterogeneity and the wavelength. For the examined tissue types of liver parenchyma (mouse), intestinal epithelium (mouse), upper dermis (human) and deep dermis (mouse), No AO beam spread and the adaptive optics corrected beam spread are found to increase as the strength coefficient of the refractive-index fluctuations, tissue length, fractal dimension, the char-acteristic lengths of heterogeneity increase, and to decrease as the source size, small length-scale factor, wavelength increase. Reduction ratio of P + T correction is almost the same for all the evaluated cases which is 74%.(C) 2022 Elsevier Ltd. All rights reserved.
  • Editorial
    Citation - WoS: 1
    Citation - Scopus: 1
    Editorial: Optical Wave Propagation and Communication in Turbulent Media
    (Frontiers Media Sa, 2023) Baykal, Yahya
  • Article
    Citation - WoS: 6
    Citation - Scopus: 8
    Squeezed State Generation Using Cryogenic Inp Hemt Nonlinearity
    (Iop Publishing Ltd, 2023) Salmanogli, Ahmad
    This study focuses on generating and manipulating squeezed states with two external oscillators coupled by an InP HEMT operating at cryogenic temperatures. First, the small-signal nonlinear model of the transistor at high frequency at 5 K is analyzed using quantum theory, and the related Lagrangian is theoretically derived. Subsequently, the total quantum Hamiltonian of the system is derived using Legendre transformation. The Hamiltonian of the system includes linear and nonlinear terms by which the effects on the time evolution of the states are studied. The main result shows that the squeezed state can be generated owing to the transistor's nonlinearity; more importantly, it can be manipulated by some specific terms introduced in the nonlinear Hamiltonian. In fact, the nonlinearity of the transistors induces some effects, such as capacitance, inductance, and second-order transconductance, by which the properties of the external oscillators are changed. These changes may lead to squeezing or manipulating the parameters related to squeezing in the oscillators. In addition, it is theoretically derived that the circuit can generate two-mode squeezing. Finally, second-order correlation (photon counting statistics) is studied, and the results demonstrate that the designed circuit exhibits antibunching, where the quadrature operator shows squeezing behavior.
  • Article
    Citation - WoS: 7
    Citation - Scopus: 5
    Tissue Turbulence and Its Effects on Optical Waves: a Review
    (Elsevier, 2023) Ata, Yalcin; Baykal, Yahya; Gokce, Muhsin Caner
    Tissue turbulence and the effects of tissue turbulence on the propagation of optical waves are reviewed. After the introduction of a survey on the reported research in this area, various topics are elaborated. These topics include the spectrum of tissue turbulence, propagation of light in the tissue, average intensity, beam spread that occur at the receiver plane in the tissue. Other entities examined are the signal to noise ratio (SNR), intensity correlation, beam wander, mutual coherence function and the spectral degree of coherence. Furthermore, spectral change, cross spectral density, spectral correlation function, scintillation, bit error rate (BER), coupling efficiency in tissue turbulence are investigated. The refractive index structure of tissues, imaging in the presence of turbulence in the tissue, scattering, absorption and polarization aspects in tissues are reported. Finally, optical coherence tomography applications in turbulent tissues are reviewed.