Scopus İndeksli Yayınlar Koleksiyonu
Permanent URI for this collectionhttps://hdl.handle.net/20.500.12416/8651
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Article Citation - WoS: 9Citation - Scopus: 13Fiber-Coupling Efficiency of Laser Array Beam From Turbulent Atmosphere To Fiber Link(Ieee-inst Electrical Electronics Engineers inc, 2023) Baykal, Yahya; Ata, Yalcin; Gokce, Muhsin CanerFree-space optical communication (FSOC) systems are nowadays integrated with fiber optical components developed for fiber-optic communications. In such integrated systems, the collected portion of the incident beam on the receiver lens is coupled into a single-mode fiber. The process of coupling, however, is mostly affected by the atmospheric turbulence which distorts the coherency of the propagating beam i.e., it results in speckle over the coupling lens causing a reduction in the coupling efficiency. In this article, we aimed at investigating the fiber coupling efficiency of laser array beams propagating in a turbulent atmosphere. For this purpose, using the Huygens-Fresnel principle, mutual coherence function (MCF) for a laser array beam incidence is formulated. In this way, the average power coupled into the fiber and the average received power on the coupling lens are derived for a laser array beam incidence. It is found that the fiber coupling efficiency clearly increases with the increase in ring radius and the number of Gaussian beams in the array and rapidly decreases with increasing structure constant of atmosphere, link distance, and the number of speckles over the receiver aperture. We also demonstrate the effect of various FSOC system parameters on the coupling efficiency.Article Citation - WoS: 38Citation - Scopus: 45Propagation of Modified Bessel-Gaussian Beams in Turbulence(Elsevier Sci Ltd, 2008) Eyyuboglu, Halil Tanyer; Hardalac, FiratWe investigate the propagation characteristics of modified Bessel-Gaussian beams traveling in a turbulent atmosphere. The source beam formulation comprises a Gaussian exponential and the summation of modified Bessel functions. Based on an extended Huygens-Fresnel principle, the receiver plane intensity is formulated and solved down to a double integral stage. Source beam illustrations show that modified Bessel-Gaussian beams, except the lowest order case, will have well-like shapes. Modified Bessel-Gaussian beams with summations will experience lobe slicing and will display more or less the same profile regardless of order content. After propagating in turbulent atmosphere, it is observed that a modified Bessel-Gaussian beam will transform into a Bessel-Gaussian beam. Furthermore it is seen that modified Bessel-Gaussian beams with different Bessel function combinations, but possessing nearly the same profile, will differentiate during propagation. Increasing turbulence strength is found to accelerate the beam transformation toward the eventual Gaussian shape. (c) 2007 Elsevier Ltd. All rights reserved.Article Citation - WoS: 13Citation - Scopus: 12Estimation of Scintillation and Bit Error Rate Performance of Sine Hollow Beam Via Random Phase Screen(Elsevier Gmbh, 2019) Bayraktar, Mert; Mert, BayraktarWe study scintillation and bit error rate performance of sine hollow beam in turbulent atmosphere. Since source field expression involves higher order term, we model atmosphere utilizing random phase screen. We show that normal sine hollow beam (a = b) having higher order has the least scintillation index considering point like scintillation. This brings us bit error rate(BER) of this type of beam in turbulent atmosphere is less comparing with Gauss beam when we use point like receiver. BER of anomalous beam (a not equal b) having less scintillation index is lower than Gauss beam in strong turbulence region. In terms of aperture averaged scintillation, first order normal sine hollow beam and anomalous beams have less scintillation than Gauss beam.Article Citation - WoS: 1Citation - Scopus: 1Mode Coupling in Vortex Beams(Elsevier Sci Ltd, 2018) Eyyuboglu, Halil T.We examine the mode coupling in vortex beams. Mode coupling also known as the crosstalk takes place due to turbulent characteristics of the atmospheric communication medium. This way, the transmitted intrinsic mode of the vortex beam leaks power to other extrinsic modes, thus preventing the correct detection of the transmitted symbol which is usually encoded into the mode index or the orbital angular momentum state of the vortex beam. Here we investigate the normalized power mode coupling ratios of several types of vortex beams, namely, Gaussian vortex beam, Bessel Gaussian beam, hypergeometric Gaussian beam and Laguerre Gaussian beam. It is found that smaller mode numbers lead to less mode coupling. The same is partially observed for increasing source sizes. Comparing the vortex beams amongst themselves, it is seen that hypergeometric Gaussian beam is the one retaining the most power in intrinsic mode during propagation, but only at lowest mode index of unity. At higher mode indices this advantage passes over to the Gaussian vortex beam. (C) 2017 Elsevier Ltd. All rights reserved.Article Citation - WoS: 22Citation - Scopus: 21Multimode Laser Beam Scintillations in Non-Kolmogorov Turbulence(Ieee-inst Electrical Electronics Engineers inc, 2015) Baykal, YahyaEmploying the Rytov solution, the scintillation index at the origin of the receiver plane is evaluated in non-Kolmogorov weak atmospheric turbulence when multimode laser incidence is used. The solution presented can be used when the multimode is composed of even modes. The novelty of this work lies in the theoretical combination of multimode laser beam excitation and non-Kolmogorov turbulence in the scintillation evaluations, which is not known both theoretically and experimentally. The study involves mathematical rigor but no experimental results. Being valid for any power law exponent of the non-Kolmogorov turbulence, the scintillations of the multimode beams are found to be smaller than the scintillation index of a single Gaussian beam. For the multimode laser beam excitation, the scintillation index is smaller at smaller power law exponent values. If the multimode content is formed by beams with larger mode numbers, the scintillations decrease for any non-Kolmogorov realization. When large sized beams are used in the multimode, the scintillations increase as compared to small sized content, and the scintillations become almost the same as the Gaussian beam scintillations. Comparing the multimode structures that have the same number of beams, the ones with higher order modes yield smaller scintillations, and for such multimode structures, very similar scintillation index behaviour versus the power law exponent can be obtained by varying the amplitudes of the modes composing the multimode. The main contribution of this paper is the formulation and evaluation of the scintillation noise in order to understand whether the use of multimode laser excitation will improve the link performance of optical wireless communication systems operating in a non-Kolmogorov atmosphere.Article Citation - WoS: 13Citation - Scopus: 13Averaging of Receiver Aperture for Flat-Topped Incidence(Elsevier Sci Ltd, 2013) Kamacioglu, Canan; Baykal, Yahya; Yazgan, ErdemUsing a flat-topped profile for the incident beam, the power scintillation index for weak atmospheric turbulence is formulated and analytically evaluated. Through the use of the aperture averaging factor, the averaging effect of the finite receiver aperture on the intensity fluctuations for a flat-topped incident beam is examined. The influence of the order of flatness on the averaging is investigated. At large propagation lengths, increasing the flatness parameter decreases the power scintillations and it is possible to further reduce the scintillation by increasing the receiver aperture. Increasing the structure constant increases this effect. (C) 2013 Elsevier Ltd. All rights reserved.Article Citation - WoS: 18Citation - Scopus: 19Field Correlations of Flat-Topped Gaussian and Annular Beams in Turbulence(Elsevier Sci Ltd, 2011) Baykal, YahyaStarting from the second order moment formulation for multi-beam incidence, field correlations at the receiver plane of flat-topped Gaussian and annular beams are found in turbulence. Reflecting the information on both the randomness due to turbulence and the field profile of the incident field, field correlations of the fiat-topped Gaussian beams are found to become larger at larger source size, smaller flatness parameters and smaller turbulence strengths. For the annular beam structures, field correlations are larger for thicker beams. Field correlations of larger primary beam sized annular incidences are smaller at smaller diagonal distances and larger at larger diagonal distances. As expected, annular beam field correlations are found to be larger at smaller structure constants and at smaller wavelengths. However, at large link lengths, field correlations could be larger than at smaller link lengths due to fact that for annular beams, the field at the centre of the receiver attains very small value at smaller link lengths, however, on propagation in turbulence, receiver field distribution changes to a Gaussian profile. (C) 2011 Elsevier Ltd. All rights reserved.