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: 1Citation - Scopus: 3Performance of a Free-Space Optical Communication System Employing Receive Diversity Techniques in Anisotropic Atmospheric Non-Kolmogorov Turbulence(Optica Publishing Group, 2022) Gokce, Muhsin Caner; Ata, Yalcin; Baykal, YahyaIn this paper, bit error rate (BER) performance of a free-space optical communication (FSOC) system operating in anisotropic non-Kolmogorov weak turbulence is investigated together with the spatial diversity techniques. The spatial diversity techniques are implemented as maximum ratio combining (MRC), equal gain combining (EGC), and selection combining (SC) and applied to the receiver. The propagating beam is the Gaussian beam wave, and the modulation scheme is binary phase-shift keying (BPSK). Results are obtained for various parameters such as the anisotropy factor, non-Kolmogorov power law exponent, photodetector responsivity, equivalent load resistor, electronic bandwidth, Gaussian beam radius, wavelength, propagation distance, and turbulence structure constant. It is found that the spatial diversity technique used at the receiver causes significant improvement in the performance of an FSOC system under the conditions of anisotropic non-Kolmogorov atmospheric turbulence. It is also observed that BER performance improves as the atmospheric turbulence becomes more anisotropic. Among the spatial diversity techniques, SC is inferior to EGC and EGC is inferior toMRC in terms of BER performance. (C) 2022 Optica Publishing GroupArticle Citation - WoS: 5Citation - Scopus: 7Analysis of Wander and Spreading of an Optical Beam by Using the Oceanic Turbulence Optical Power Spectrum(Optica Publishing Group, 2022) Baykal, Yahya; Gokce, Muhsin Caner; Ata, YalcInVariance of beam displacement and short-term and long-term spreading of a Gaussian beam propagating in the presence of underwater turbulence are examined by using the oceanic turbulence optical power spectrum (OTOPS). Analytical expressions for both beam wander displacement variance and beam spreading are presented. Results show that the underwater turbulent channel causes deflection from the on-axis mean irradiance and brings significant wander and spreading effects to the propagating Gaussian beam wave. The variations of beam wander and short- and long-term spreading are obtained depending on the underwater medium parameters such as the average temperature, average salinity concentration, temperature-salinity gradient ratio, and temperature and energy dissipation rates. In particular, the real values of the average temperature and salinity concentration of turbulent water are used to obtain the results. In addition, the effects of propagation distance, Gaussian beam source size, and wavelength are shown. The results demonstrate that the underwater turbulent channel brings displacements in the centroid and spreading of the optical beam. (C) 2022 Optica Publishing GroupArticle Citation - WoS: 3Citation - Scopus: 2Modulation Transfer Function Variation Through Anisotropic Turbulence in Biological Tissue(Optica Publishing Group, 2023) Gokce, Muhsin Caner; Baykal, Yahya; Ata, YalcinAnalysis of the long-exposure modulation transfer function (MTF) is performed for optical imaging using plane and spherical waves through anisotropic turbulence in biological tissues. To obtain the MTF, the wave structure functions of plane and spherical waves are obtained in closed-form expressions. Results are presented depending on various parameters of the turbulent medium and optical beam. The positive effect of anisotropy on optical imaging is remarkable in turbulent biological tissues. Besides scattering and absorption, taking anisotropy into account as well as turbulence will lead to a more accurate description of the performance of the medical imaging systems that use optical spectrums in biological tissues. (c) 2023 Optica Publishing GroupArticle Citation - WoS: 3Citation - Scopus: 3Laser Beam Scintillations of Lidar Operating in Weak Oceanic Turbulence(Optica Publishing Group, 2022) Baykal, Yahya; Gercekcioglu, HamzaThe formulation of light detection and ranging (LIDAR) systems is derived and examined for the scintillation index, evaluated on-axis, of laser beams in horizontal links in the ocean with weak turbulence by utilizing the Rytov method. These scintillation indices, obtained for the Gaussian beam which is collimated, the limits of plane and spherical waves, are depicted versus the source size, target size, and parameter of the normalized reflector size. It is found that the source size, target size, and normalized reflector size parameter, lessening the scintilla-tion index evaluated on-axis, are approximately 0.44 cm, 56 x 10-4 cm, and 2.2, respectively. Additionally, by using these values that minimize the scintillation index, the variation of the scintillations is shown against the propagation distance, radius of reflector, temperature and salinity fluctuation effects, mean squared temperature, and turbulent kinetic energy dissipation rate per unit mass of fluid at various selected source size and radius of reflector values. (c) 2022 Optica Publishing GroupArticle Citation - WoS: 4Citation - Scopus: 4Fiber Coupling Efficiency in Ocean With Adaptive Optics Corrections(Optica Publishing Group, 2023) Gokce, Muhsin Caner; Ata, Yalcin; Baykal, YahyaUnderwater optical wireless communication (UOWC) is a very promising technology that enables high-speed data transfer through the use of laser beams in an oceanic turbulent medium. The high-tech fiber optical devices, which are already available in the market, can be integrated with the UOWC systems. When integration is achieved, oceanic turbulence, which distorts the wavefront of the propagating laser beam, plays an important role in reducing the fiber coupling efficiency (FCE), which in turn results in reducing the light power received from the fiber optical components. In this paper, we propose the use of the adaptive optics technique in a UOWC system to mitigate the effects of oceanic turbulence and boost the FCE. For this reason, the field correlation for a Gaussian laser beam is derived by using the Huygens-Fresnel principle. This way, the light power over the coupling lens and the light power accepted by the fiber core are formulated under the effect of adaptive optics corrections, which are repre-sented by the number of Zernike modes. The results demonstrate that under the oceanic turbulence effect, the FCE of the UOWC system employing adaptive optics is always larger than that of the UOWC system employing no adaptive optics. (c) 2023 Optica Publishing Group