Scopus İndeksli Yayınlar Koleksiyonu
Permanent URI for this collectionhttps://hdl.handle.net/20.500.12416/8651
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Article Citation - WoS: 5Citation - Scopus: 6Bit Error Rate of M-Pulse Position Modulated Laser Beams for Vertical Links Operating in Weak Oceanic Turbulence(Iop Publishing Ltd, 2024) Gercekcioglu, Hamza; Baykal, YahyaThe on-axis scintillation index of laser beams is investigated by employing the Rytov method in a weakly turbulent oceanic medium for up/downlink coupling of laser communication between any underwater vehicles or divers. For vertical links, the formulation of the on-axis scintillation index of laser beams is derived analytically and evaluated for plane, collimated Gaussian and spherical beams in specific mediums, including the Atlantic Ocean at mid and low latitudes associating temperature and salinity changes at low latitudes, at mid latitude-summer and at mid latitude-winter. Using the scintillation index, bit error rate (BER) performance of M-pulse position modulation is investigated for these types of laser beams. The variations of the scintillation index against the uplink/downlink propagation distances, source size and zenith angle are examined, and BER variations versus the Kolmogorov microscale and the symbol orders, and results are compared. It is noted that the behavior of the scintillation index that depends on the relative strength of temperature and salinity fluctuations which changes in depth, is different for uplink/downlink and for each latitude due to its distinct characteristics. The source size that minimizes the scintillation index values is in the range of about 0.1 cm-0.2 cm for all latitudes.Article Citation - WoS: 4Citation - Scopus: 6Scintillation of Laser Beams in Weak Atmospheric Turbulence for Aerial Vehicle in the Use of Lidar(Ieee-inst Electrical Electronics Engineers inc, 2022) Baykal, Yahya; Gercekcioglu, HamzaFormulation of on-axis scintillation of laser beams is found in weak atmospheric turbulence for aerial vehicle in the use of light detection and ranging (LIDAR) systems by employing the Rytov method. The formulation derived for collimated Gaussian, plane and spherical beams is evaluated in vertical link involving up/down link. In this medium, the behavior of these beams in terms of deterioration is examined. In this context, the on-axis scintillation index values are plotted versus normalized target size parameter, target size, source size, propagation distance and zenith angle, and the results are obtained for LIDAR systems operating for aerial vehicle in vertical atmospheric link by using ground/space transceiver. The degradation is greater in operating with ground transceiver than in operating with space transceiver. Additionally, while the on-axis scintillation index is minimized in the smaller target size in use of ground transceiver than in use of space transceiver, that is, it can also be minimized in the larger target size in use of space transceiver. The values of source size and the normalized target size parameter minimizing the obtained scintillation index, are 1.2 cm, 10, and 6 cm and 5 for ground transceiver and space transceiver, respectively.Article Citation - WoS: 7Citation - Scopus: 5Tissue Turbulence and Its Effects on Optical Waves: a Review(Elsevier, 2023) Ata, Yalcin; Baykal, Yahya; Gokce, Muhsin CanerTissue turbulence and the effects of tissue turbulence on the propagation of optical waves are reviewed. After the introduction of a survey on the reported research in this area, various topics are elaborated. These topics include the spectrum of tissue turbulence, propagation of light in the tissue, average intensity, beam spread that occur at the receiver plane in the tissue. Other entities examined are the signal to noise ratio (SNR), intensity correlation, beam wander, mutual coherence function and the spectral degree of coherence. Furthermore, spectral change, cross spectral density, spectral correlation function, scintillation, bit error rate (BER), coupling efficiency in tissue turbulence are investigated. The refractive index structure of tissues, imaging in the presence of turbulence in the tissue, scattering, absorption and polarization aspects in tissues are reported. Finally, optical coherence tomography applications in turbulent tissues are reviewed.Article Citation - WoS: 8Citation - Scopus: 8M-Ary Pulse Position Modulation Performance With Adaptive Optics Corrections in Atmospheric Turbulence(Taylor & Francis Ltd, 2020) Gokce, Muhsin C.; Baykal, Yahya; Ata, YalcinThe performance of M-ary pulse position modulated (PPM) optical wireless communication (OWC) systems in atmospheric weak turbulence medium is evaluated by using adaptive optics corrections. Piston, tilt, defocus and coma components of adaptive optics corrections are applied to the avalanche photodetector (APD) type of receiver and the results are obtained depending on various turbulence and receiver parameters. The lognormal channel distribution is used to model the weak atmospheric turbulence conditions. Adaptive optics correction increases the bit-error-rate (BER) performance of an OWC system operating in atmospheric turbulence conditions. Piston component yields the highest BER performance, followed by the tilt, defocus and coma adaptive optics correction components respectively.Article Citation - WoS: 49Citation - Scopus: 47Scintillation Index of Higher-Order Cos-Gaussian, Cosh-Gaussian and Annular Beams(Taylor & Francis Ltd, 2008) Arpali, Serap Altay; Eyyuboglu, Halil T.; Baykal, YahyaIn this paper, via the generalized beam formulation, we evaluate the scintillation index for higher-order general beams propagating through the weak atmospheric turbulence. The investigated higher-order beam types are cos-Gaussian, cosh-Gaussian and annular beams. The scintillation indices of these beams are plotted with respect to propagation length, source size and order of the beam. According to our graphical outputs, higher-order beams have less on-axis scintillation index than zero-order beams at longer propagation distances. The on-axis scintillation exhibits a slight increase when the order of even-ordered beams is made higher. Moreover, our study on the source size variation shows that, for most of the source size range, cos-Gaussian beams have a lower scintillation index than the other beams.Article Citation - WoS: 29Citation - Scopus: 35Ber Evaluations for Multimode Beams in Underwater Turbulence(Taylor & Francis Ltd, 2016) Arpali, Serap Altay; Baykal, Yahya; Arpali, CaglarIn underwater optical communication links, bit error rate (BER) is an important performance criterion. For this purpose, the effects of oceanic turbulence on multimode laser beam incidences are studied and compared in terms of average BER (< BER >), which is related to the scintillation index. Based on the log-normal distribution, < BER > is analysed for underwater turbulence parameters, including the rate of dissipation of the mean squared temperature, the rate of dissipation of the turbulent kinetic energy, the parameter that determines the relative strength of temperature and salinity in driving index fluctuations, the Kolmogorov microscale length and other link parameters such as link length, wavelength and laser source size. It is shown that use of multimode improves the system performance of optical wireless communication systems operating in an underwater medium. For all the investigated multimode beams, decreasing link length, source size, the relative strength of temperature and salinity in driving the index fluctuations, the rate of dissipation of the mean squared temperature and Kolmogorov microscale length improve the < BER >. Moreover, lower < BER > values are obtained for the increasing wavelength of operation and the rate of dissipation of the turbulent kinetic energy in underwater turbulence.Article Citation - WoS: 38Citation - Scopus: 42Propagation Factor of Partially Coherent Flat-Topped Beam Array in Free Space and Turbulent Atmosphere(Elsevier Sci Ltd, 2012) Yuan, Yangsheng; Cai, Yangjian; Eyyuboglu, Halil T.; Baykal, Yahya; Chen, JunAnalytical expressions for the propagation factor of partially coherent radial flat-topped (FT) beam array in free-space and turbulent atmosphere are derived. Our formulae can be applied to study the beam propagation factors of partially coherent Gaussian beam, partially coherent FT beam and partially coherent radial Gaussian beam array. The evolution properties of the propagation factors of those beams in turbulent atmosphere are studied numerically and comparatively. From the aspect of the propagation factor, our results show that partially coherent radial FT beam array is less affected by turbulence than partially coherent Gaussian beam, partially coherent FT beam and partially coherent radial Gaussian beam array. (C) 2011 Elsevier Ltd. All rights reserved.Article Citation - WoS: 16Citation - Scopus: 17Turbulence Effect on Transmittance of Atmospheric Optics Telecommunication System Using Dense Wavelength Division Multiplexing(Taylor & Francis Ltd, 2011) Ata, Yalcin; Baykal, YahyaThe effect of atmospheric turbulence on atmospheric optics telecommunication links employing dense wavelength division multiplexing (DWDM) systems is examined. For this purpose, transmittance obtained by using the MODTRAN (MODerate resolution atmospheric TRANsmission) code is modified by the transmittance due to turbulence when the incidence is a partially coherent optical beam. The spanned wavelengths cover the range employed in a practical DWDM system operating in the range of 1550 nm. The effect of turbulence is manifest as a decrease in the transmittance calculated by MODTRAN, being more effective when the incidence becomes less coherent.