WoS İndeksli Yayınlar Koleksiyonu
Permanent URI for this collectionhttps://hdl.handle.net/20.500.12416/8653
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Article Citation - WoS: 1Citation - Scopus: 1Optical Wireless Sensor Networks in Underwater Turbulence Using Multimode Beams(Elsevier Sci Ltd, 2025) Baykal, YahyaOptical wireless sensor networks (OWSN) that employ multimode optical beams operating in underwater turbulence are investigated. For this purpose, off-axis average intensity at the destination point (receiver) is formulated in underwater turbulence when the incidences at the sensors are multimode optical beams. Based on the trends of the appropriately determined off-axis received average intensities of various multimode beams, identification of the sensor can be made. The proposed procedure is also applied as special cases, to optical wireless sensor networks that employ single higher mode beams.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: 1Citation - Scopus: 1Speckle Contrast for Flat-Topped Field Profiles(Elsevier Sci Ltd, 2013) Baykal, YahyaSpeckle contrast is evaluated for flat-topped field profiles where the characterization and evaluation of speckle contrast are based on mathematical formulation and theoretical parameter variation. The speckle field which is represented by the random phase shift and the random phase tilt is multiplied by the flat-topped shaped field. The increase in the source size of the flat-topped field first causes the speckle contrast to increase, then reaches saturation. Increase in the variance of the phase shift of a flat-topped field causes an appreciable increase in the speckle contrast. Depending on the diffraction characteristics of the finite sized flat-topped field distribution, upon changing the variance of the phase shift, the speckle contrast exhibits different behavior at short and long propagation distances. However, especially for small variances of phase tilts, the speckle contrast seems to monotonically increase as the propagation distance becomes larger. The effect of the order of flatness on the speckle contrast is small at short propagation distances which can be appreciable at long propagation distances. (C) 2012 Elsevier Ltd. All rights reserved.Article Citation - WoS: 14Citation - Scopus: 15Intensity Correlations of General Type Beam in Weakly Turbulent Atmosphere(Elsevier Sci Ltd, 2011) Baykal, YahyaIn weakly turbulent atmosphere, intensity correlations at the receiver plane are formulated for a general type optical beam. Evaluating our formula at the appropriate source parameters versus the diagonal distance, intensity correlations for cos Gaussian, cosh Gaussian, annular and flat-topped Gaussian beams are obtained. As compared to Gaussian beam, intensity correlations are found smaller for cos Gaussian and larger for cosh Gaussian beams. Intensity correlations of cos Gaussian, cosh Gaussian and flat-topped Gaussian beams become larger at large source sizes. Thicker annular beams and flatter flat-topped Gaussian beams show larger intensity correlations. Without generalizing, intensity correlations tend to increase when the link length and the structure constant decrease and the wavelength increases. Our results show that the intensity correlations are not only built up using random medium effects, but also using the diffraction pattern formed at the receiver plane for the specific incidence investigated. As a check point, for all source types and medium parameters, our evaluations indicate that intensity correlations approach zero at sufficiently large diagonal distances. (C) 2011 Elsevier Ltd. All rights reserved.