Elektronik ve Haberleşme Mühendisliği Bölümü Yayın Koleksiyonu
Permanent URI for this collectionhttps://hdl.handle.net/20.500.12416/260
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Article Citation - WoS: 27Citation - Scopus: 28Analysis of Flat-Topped Gaussian Vortex Beam Scintillation Properties in Atmospheric Turbulence(Spie-soc Photo-optical instrumentation Engineers, 2019) Elmabruk, Kholoud; Eyyuboglu, Halil T.We analyze the scintillation properties of a flat-topped Gaussian vortex beam propagating in a weakly turbulent atmosphere. We utilize a random phase screen model to perform this analysis. We evaluate the scintillation against the changes of topological charge, beam order, operating wavelength, receiver aperture side length, and source size parameters. The results show that using a flat-topped Gaussian vortex beam with a high topological charge causes a reduction in scintillation. Increasing the receiver aperture side length reduces scintillation level. As the source size increases, scintillation decreases. Our results also indicate that a flat-topped Gaussian vortex beam with high topological charges has less scintillation than the fundamental Gaussian beam. We believe that our findings will be useful in improving the performance of next-generation optical communication links and networks. (C) 2019 Society of Photo-Optical Instrumentation Engineers (SPIE)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: 13Citation - Scopus: 13Per Unit Received Power Apertured Averaged Scintillation of Partially Coherent Sinusoidal and Hyperbolic Gaussian Beams(Elsevier Sci Ltd, 2015) Eyyuboglu, Halil T.; Eyyuboʇlu, Halil T.We evaluate the per unit power received power aperture averaged scintillation performance of fully and partially coherent sinusoidal and hyperbolic Gaussian beams. Our analysis includes fundamental Gaussian, cosh Gaussian, cos Gaussian and annular Gaussian beams. The method is based on our earlier introduced semi-analytic approach. Scintillation performance is measured upon dividing the aperture averaged scintillation by the received power. Assessment is made both for aperture sizes that are adjusted separately for full and partially coherent beams to capture 10% and 20% of the equal source power and also for fixed aperture sizes. This way, the scintillation performance of the different beams in question is compared. From this comparison, we find that partially coherent beams have lower scintillation than the fully coherent ones, when adjustable aperture size is used. But upon switching to fixed aperture size, the reverse happens and coherent beams become more advantageous. In all cases of comparison, small source sized annular Gaussian beam and large source sized Gaussian beam seem to offer the lowest scintillation when aperture size is adjusted to capture 20% of the equal source power. (C) 2015 Elsevier Ltd. All rights reserved.Article Citation - WoS: 20Snr Bounds of Fso Links and Its Evaluation for Selected Beams(Taylor & Francis Ltd, 2015) Bayraktar, Mert; Eyyuboglu, Halil T.We formulate the signal-to-noise ratio (SNR) for free-space optical links. Upon inserting typical operating parameters, it is seen that SNR well approximates to the inverse of aperture averaged scintillation parameter. By adopting a common source beam power of 10 mW, we select three different source sizes of Gaussian, annular Gaussian (AG), and cosh-Gaussian beams. We then evaluate the SNR of these beams. Our results indicate that when fixed aperture opening is used, fully and partially coherent beams yield almost the same SNR performance. On the other hand, however, focusing and lowering wavelength of operation appear to be quite instrumental in improving the SNR performance. In this context, medium-sized AGB seems to exhibit the best performance.Article Citation - WoS: 11Citation - Scopus: 11Non-Kolmogorov Spectrum Scintillation Aspects of Dark Hollow and Flat Topped Beams(Elsevier Science Bv, 2012) Eyyuboglu, Halil T.; Cai, YangjianThe scintillation aspects of dark hollow (DH) and fiat topped (FT) beams propagating in the turbulent atmosphere containing the non-Kolmogorov power spectrum are investigated. It is found that low scintillations will occur when the exponent of the power spectrum is just above the numeric value of 3. Initially, the rises in scintillations will take place as the exponent becomes larger, but later the scintillation reductions will be experienced as the exponent grows further, eventually minimum scintillations will be seen when the exponent has reached the value of 4. This will be the case, for scintillation variations against propagation distance, source size, wavelength, inner and outer scales of turbulence. Furthermore, it is found that at the small source sizes, DH beams will offer less scintillation than FT beams, while at the large source sizes, the reverse will be applicable. (C) 2011 Elsevier B.V. All rights reserved.Article Citation - WoS: 8Citation - Scopus: 9Scintillation Properties of a Truncated Flat-Topped Beam in a Weakly Turbulent Atmosphere(Elsevier Sci Ltd, 2013) Liu, Xianlong; Liang, Chunhao; Yuan, Yangsheng; Cai, Yangjian; Eyyuboglu, Halil T.We derive derive an explicit expression for the scintillation index of a truncated flat-topped (FT) beam in a weakly turbulent atmosphere. Under suitable conditions, the derived formula reduces to the expression for the scintillation index of a FT beam or Gaussian beam without truncation. The scintillation properties of a truncated FT beam in a weakly turbulent atmosphere are illustrated numerically. It is found that the truncation parameter has strong influence on the scintillation properties, and the advantage of a FT beam over a Gaussian beam for reducing the negative influence of turbulence disappears gradually as the truncation parameter decreases. (C) 2012 Elsevier Ltd. All rights reserved.Article Citation - WoS: 40Citation - Scopus: 45Scintillation Behavior of Airy Beam(Elsevier Sci Ltd, 2013) Eyyuboglu, Halil T.We make an analysis on scintillation behavior of Airy beam using the Rytov method. To this end, scintillation index is formulated for a single receiver coordinate location. Area scintillation expressions are also derived. At peaks of receiver intensity, Airy beam is found to offer quite less scintillation at width values of around 1.6 cm. Furthermore, smaller values of the exponential truncation factor are also seen to cause less scintillation. When compared to Gaussian beam, on equal source and received power basis, it is observed that Airy beam will generally have less area scintillation. (C) 2012 Elsevier Ltd. All rights reserved.Article Citation - WoS: 30Citation - Scopus: 31Estimation of Aperture Averaged Scintillations in Weak Turbulence Regime for Annular, Sinusoidal and Hyperbolic Gaussian Beams Using Random Phase Screen(Elsevier Sci Ltd, 2013) Eyyuboglu, Halil T.Using the random phase screen method, aperture averaged scintillations for annular, sinusoidal and hyperbolic Gaussian beams are estimated. Prior to this estimation, the designed random phase screen setup is tested against the known results of the existing literature from the aspects of receiver intensity distribution, point-like scintillation index and aperture averaged scintillation of spherical and Gaussian beam waves. Having obtained satisfactory results, we then proceed to estimate aperture averaged scintillations for annular, sinusoidal and hyperbolic Gaussian beams. Our findings indicate that at a fixed aperture radius of 5 cm, sine Gaussian beam exhibits the highest scintillation, annular Gaussian beam has on the other hand has the lowest scintillations. When examined against varying aperture sizes, the scintillation ordering of beams does not change. Furthermore, although larger aperture sizes achieve substantial scintillation reductions, the rate of reductions gradually become smaller. (C) 2013 Elsevier Ltd. All rights reserved.Article Citation - WoS: 18Citation - Scopus: 18Minimization of Scintillation Index Against Displacement Parameters(Elsevier Science Bv, 2008) Eyyuboglu, Halil T.; Gercekcioglu, Hamza; Baykal, YahyaFor sinusoidal beams, minimization of scintillation index is carried out against the displacements parameters. It is found-that x-y asymmetric cosh-Gaussian beam fulfills the requirements of such optimum beam. Our minimization procedure reveals that the optimum beam is achieved by continually focusing it at the chosen propagation length and by further adjusting displacements parameters to be propagation distance dependent. Scintillation index of thus constructed optimum beam is formulated and numerically evaluated., Our graphical comparisons entailing collimated and focused versions of cos-, cosh-Gaussian, annular-Gaussian and Gaussian beams show that the optimum beam yields the lowest scintillations provided that Propagation range is less than or equal to the focusing distance. (C) 2008 Elsevier B.V. All rights reserved.