WoS İndeksli Yayınlar Koleksiyonu
Permanent URI for this collectionhttps://hdl.handle.net/20.500.12416/8653
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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: 18Citation - Scopus: 16Ber of Annular and Flat-Topped Beams in Strong Turbulence(Elsevier, 2013) Gercekcioglu, Hamza; Baykal, YahyaThe average bit error rate (< BER >) of annular and flat-topped beams are evaluated in strong turbulence. In this respect, our earlier results on the scintillation indices obtained by the unified Rytov method are employed and the intensity is taken to be gamma-gamma distributed. For comparison purposes, < BER > for the log-normal intensity distribution is also evaluated. It is found that for the annular beams, the ones that are thinner, possessing smaller ratio of primary to secondary beam size, and smaller focal lengths will have smaller average BER in strong turbulence. For the flat-topped beams, the ones that are flatter and possessing large source sizes have smaller average BER in strong turbulence. Large average SNR substantially reduces the average BER in weak and moderate turbulence, whereas in strong turbulence, the average BER stays at the same value no matter what the average SNR is. Comparison of the log-normal and the gamma-gamma statistics for the intensity shows that the average BER will be higher for the log-normal case when the average SNR is small and the reverse relationship holds at large average SNR. For both the gamma-gamma and the log-normal intensity distributions, < BER > obtained for the annular and the, flat-topped beams in strong turbulence is advantageous over the Gaussian beam < BER > values. (C) 2013 Elsevier B.V. All rights reserved.Article Citation - WoS: 15Citation - Scopus: 17Scintillation Analysis of Hypergeometric Gaussian Beam Via Phase Screen Method(Elsevier, 2013) Eyyuboglu, Halil T.We give a scintillation treatment of hypergeometric Gaussian beams via the use of random phase screens. In particular, we analyse the on-axis, point-like and aperture averaged power scintillation characteristics of this beam that cannot be undertaken easily by analytic means. Within the range of examined source and propagation parameters, our evaluations show that there will be less scintillation, with increasing hollowness at small source sizes and zero topological charge. At larger source sizes or topological charges, this is reversed and decreasing hollowness will reduce scintillation. More or less the same trend is observed for aperture averaging such that at small source sizes and zero topological charge, increased hollowness will result in lower scintillation. At larger source size and topological charges, there will be a transition from the case of smaller values of hollowness giving rise to less scintillation at smaller aperture openings to the case of larger values of hollowness giving rise to less scintillation at larger aperture openings. In general nonzero topological charges will produces more scintillations, both in on-axis and aperture averaged cases. (C) 2013 Elsevier B.V. All rights reserved.Article Citation - WoS: 87Citation - Scopus: 94Scintillation Index of a Multi-Gaussian Schell-Model Beam in Turbulent Atmosphere(Elsevier, 2013) Yuan, Yangsheng; Liu, Xianlong; Wang, Fei; Chen, Yahong; Cai, Yangjian; Qu, Jun; Eyyuboglu, Halil T.Multi-Gaussian Schell-model (MGSM) beam was introduced recently [Sahin and Korotkova, Opt. Lett. 37 (2012) 2970; Korotkova et al., J. Opt. Soc. Am. A 29 (2012) 2159]. In this paper, an explicit expression for the scintillation index of a multi-Gaussian Schell-model (MGSM) beam in weakly or extremely strong turbulent atmosphere is derived with the help of a tensor method. Applying the derived formulae, the scintillation properties of a MGSM beam and a GSM beam in weakly or extremely strong turbulent atmosphere are studied numerically and comparatively. Our results show that a MGSM beam has advantage over a GSM beam for reducing turbulence-induced scintillation, which will be useful for long-distance free-space optical communications. (C) 2013 Elsevier B.V. All rights reserved.Article Citation - WoS: 32Citation - Scopus: 32Ber of Annular and Flat-Topped Beams in Non-Kolmogorov Weak Turbulence(Elsevier, 2013) Gercekcioglu, Hamza; Baykal, YahyaThe average bit error rate (BER) of multi-Gaussian beams in non-Kolmogorov weak turbulence is examined. For each specific incidence of annular and flat-topped optical beam, a power law of non-Kolmogorov spectrum is found which is defined as the worst power law at which the average BER attains the maximum value. Using these values of the worst power laws, it is observed that thinner collimated annular, larger focal length annular and flatter small sized collimated flat-topped structures have a slight advantage in obtaining smaller average BER. (C) 2012 Elsevier B.V. All rights reserved.