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: 34Citation - Scopus: 36Hermite Gaussian Beam Scintillations in Weak Atmospheric Turbulence for Aerial Vehicle Laser Communications(Elsevier, 2020) Sayan, Omer F.; Gercekcioglu, Hamza; Baykal, YahyaScintillation index of Hermite Gaussian beams used for air vehicle communication systems in vertical paths of weak atmospheric turbulent medium are investigated by employing the modified Rytov method. By evaluating the on-axis scintillation index, variations of the scintillation indices of these beams are examined against the changes in the Gaussian beam size of the Hermite Gaussian beam mode, propagation distances and the zenith angles at the realistic propagation distances involved in uplink and downlink configurations. In the atmospheric environment, for uplink, the Hermite Gaussian beam modes have no advantage over the Gaussian beams at short propagation distances like L = 20 km,as well as at long propagation distances like L = 700 km. However, for downlink, although Hermite Gaussian beam modes are disadvantageous over the Gaussian beams at short propagation distances like L = 20 km, they are found advantageous over the Gaussian beams at long propagation distances like L = 700 km. The results of this study may encourage to use Hermite Gaussian beams, especially in the air vehicle laser communication links, and can be used in the design of an optical wireless communication link utilizing the vertical atmospheric medium.Article Citation - WoS: 12Citation - Scopus: 12Scintillation Index of Higher Order Mode Laser Beams in Strong Turbulence(Elsevier Science Bv, 2017) Baykal, YahyaThe scintillation index of higher order laser modes is examined in strong atmospheric turbulence. In our formulation, modified Rytov theory is employed with the inclusion of existing modified turbulence spectrum which presents the atmospheric turbulence spectrum as a linear filter having refractive and diffractive spatial frequency cutoffs. Variations of the scintillation index in strong atmospheric turbulence are shown against the weak turbulence plane wave scintillation index for various higher order laser modes of different sizes. Use of higher order modes in optical wireless communication links operating in strongly turbulent atmosphere is found to be advantageous in reducing the scintillation noise.Article Citation - WoS: 71Citation - Scopus: 82Aperture Averaging and Ber for Gaussian Beam in Underwater Oceanic Turbulence(Elsevier Science Bv, 2018) Baykal, Yahya; Gokce, Muhsin CanerIn an underwater wireless optical communication (UWOC) link, power fluctuations over finite-sized collecting lens are investigated for a horizontally propagating Gaussian beam wave. The power scintillation index, also known as the irradiance flux variance, for the received irradiance is evaluated in weak oceanic turbulence by using the Rytov method. This lets us further quantify the associated performance indicators, namely, the aperture averaging factor and the average bit-error rate (<BER>). The effects on the UWOC link performance of the oceanic turbulence parameters, i.e., the rate of dissipation of kinetic energy per unit mass of fluid, the rate of dissipation of mean-squared temperature, Kolmogorov microscale, the ratio of temperature to salinity contributions to the refractive index spectrum as well as system parameters, i.e., the receiver aperture diameter, Gaussian source size, laser wavelength and the link distance are investigated. (c) 2017 Elsevier B.V. All rights reserved.Article Citation - WoS: 7Citation - Scopus: 9Scintillations of Partially Coherent Annular and Flat-Topped Array Beams in Extremely Strong Turbulent Medium(Elsevier Science Bv, 2015) Oztan, Mehmet A.; Baykal, YahyaScintillation index of partially coherent multi-Gaussian array beams is analytically derived and numerically evaluated in extremely strong atmospheric turbulence. In the evaluations, partially coherent annular array and Bat-topped array beams are considered. When compared to the non-array partially coherent multi-Gaussian beam, it is shown that such array beams have smaller scintillations. The scintillation index is found to decrease with an increase in the number of beamlets. Laser at beams exhibit less scintillations when the beams become less coherent. Scintillations decrease when the radial distance of beamlets from the origin increases. At a fixed degree of partial coherence, thin ring sized annular array beams possess smaller scintillations than the thick ones. Flat-topped Gaussian array beams with higher flatness parameter. N have smaller scintillations in extremely strong turbulence. (C) 2015 Elsevier B.V. All rights reservedArticle Citation - WoS: 71Citation - Scopus: 82Scintillation Index in Strong Oceanic Turbulence(Elsevier Science Bv, 2016) Baykal, YahyaScintillation index of spherical wave in strongly turbulent oceanic medium is evaluated. In the evaluation, modified Rytov solution and our recent formulation that expresses the oceanic turbulence parameters by the atmospheric turbulence structure constant, are employed. Variations of the scintillation index in strong oceanic turbulence are examined versus the oceanic turbulence parameters such as the rate of dissipation of kinetic energy per unit mass of fluid, the rate of dissipation of mean-squared temperature, viscosity, wavelength, the link length, and the ratio of temperature to salinity contributions to the refractive index spectrum. (C) 2016 Elsevier B.V. All rights reserved.