WoS İndeksli Yayınlar Koleksiyonu
Permanent URI for this collectionhttps://hdl.handle.net/20.500.12416/8653
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Article Citation - WoS: 14Citation - Scopus: 12Scintillation and Bit Error Rate in Bidirectional Laser Communications Between an Aerial Vehicle and a Satellite Using Annular Optical Beams in Strong Turbulent Atmosphere(Optical Soc Amer, 2021) Gercekcioglu, Hamza; Baykal, YahyaScintillation index is examined for annular optical beams in a strong atmospheric medium of a slant path. On-axis scintillations have small- and large-scale components and are formulated for the uplink/downlink of aerial vehicle-satellite laser communications. For this purpose, the unified Rytov method and the amplitude spatial filtering of the atmospheric spectrum are utilized. Performances given by the average bit error rate (BER) are investigated by employing the corresponding scintillation index, which is found by using intensity having gamma-gamma distribution. Strong atmospheric turbulence effects on the scintillation index and BER of the collimated annular optical beam having various thicknesses are reported for the up/down vertical links, and these are compared with the scintillations of the collimated Gaussian optical beams against propagation length, source size, and the zenith angle with the selected thickness. Utilizing the scintillations found, BER changes against average signal-to-noise ratio (SNR)are plotted for up/down vertical links. The scintillation index and BER in the downlink are found to be different than the scintillation index and BER in the uplink for strong atmospheric turbulence, mainly because the structure constant is a function of the altitude. Considering the location where the aerial vehicle and satellite are deployed as the reference points, annular beams are more advantageous than the Gaussian beams at up/down slant link lengths. The effect of the thickness of the annular beam is apparent for the uplink, where thin annular beams are more advantageous at small link lengths and thick annular beams are more advantageous at large link lengths. In the downlink, thin annular beams are more advantageous at all link lengths. (C) 2021 Optical Society of AmericaArticle Citation - WoS: 5Citation - Scopus: 5Scintillation and Ber Analysis of Cosine and Cosine-Hyperbolic Beams in Turbulent Ocean(Optical Soc Amer, 2021) Keskin, Aysan; Baykal, YahyaEffects of source beam, link, and oceanic turbulence parameters on the scintillation index and bit error rate (BER) performance of cosine (cos) and cosine-hyperbolic (cosh) Gaussian light beams have been investigated in order to improve wireless optical communication link performance in oceanic turbulence. The Nikishov and Nikishov power spectrum of oceanic water and extendedHuygens Fresnel principle were used in our evaluations; the results were obtained viaMATLAB. The scintillation index andBERwere examined versus oceanic turbulence parameters, which are the rate of dissipation of mean-square temperature, the ratio of temperature and salinity contributions to the refractive index spectrum, and the dissipation rate of kinetic energy per unit fluid mass of fluid. Further, the scintillation index and BER are investigated against the source size, propagation distance, and complex displacement parameters of cos- and cosh-Gaussian beams. This study aimed to select the suitable sinusoidal beam to be employed in order to increase the performance of underwater wireless optical communication systems operating in oceanic turbulence. (C) 2021 Optical Society of AmericaArticle Citation - WoS: 3Citation - Scopus: 5Performance of M-Ary Pulse Position Modulated Optical Wireless Communications Systems in the Marine Atmosphere(Optical Soc Amer, 2021) Baykal, Yahya; Ata, Yalcin; Gokce, Muhsin C.The marine atmosphere exhibits different turbulence spectrum characteristics when compared to the turbulence spectra of the land atmosphere and underwater medium. The performance of M-ary pulse position modulated (PPM) optical wireless communications (OWC) systems operating in the marine atmosphere, as measured by the bit error rate (BER), is studied here. In our investigation, the scintillation index and the average intensity in marine atmospheric turbulence are used. The variations of BER performance are reported against the marine atmospheric turbulence parameters for various values of the average current gain of the avalanche photodetector (APD), data bit rate of theOWClink, and M value of the M-ary PPM. (C) 2021 Optical Society of AmericaArticle Citation - WoS: 5Citation - Scopus: 5Minimization of the Scintillation Index of Sinusoidal Gaussian Beams in Weak Turbulence for Aerial Vehicle-Satellite Laser Communications(Optical Soc Amer, 2021) Gercekcioglu, Hamza; Baykal, YahyaMinimization of the on-axis scintillation index of sinusoidal Gaussian beams is investigated by using the modified Rytov method in weak atmospheric turbulence for uplink/downlink of aerial vehicle-satellite laser communications. Among the focused cosh-Gaussian (cosh-G), cos-Gaussian (cos-G), annular, and Gaussian beams, a suitable displacement parameter for a cosh-G beam is determined that will minimize the scintillation index in uplink and downlink configurations. Then, for both uplink and downlink, the variations of the scintillation index against the propagation distance, source size, and zenith angle are examined and compared among themselves to show the optimum beam that possesses the minimum scintillation index. Sinusoidal Gaussian beams that are focused at the receiver and obtained by employing the appropriate displacement parameter, which we name the optimum beams, are recommended to obtain smaller intensity fluctuations in atmospheric wireless optical communication systems operating in vertical links in weak turbulence. (C) 2021 Optical Society of AmericaArticle Citation - WoS: 5Citation - Scopus: 4Interaction of Electromagnetic Plane Waves With an Impedance Half-Plane in an Anisotropic Medium(Optical Soc Amer, 2020) Umul, Yusuf ZiyaThe diffraction process of electromagnetic plane waves by an impedance half-plane in anisotropic medium is investigated. In this case, the permittivity of the space is expressed in terms of a tensor. The incident wave is considered for magnetic polarization. The diffracted fields are obtained with the aid of the method of transition boundary. It is shown that the diffraction wave reduces to the correct field expressions for the limiting cases. The total field and its components are compared with the literature numerically. (C) 2020 Optical Society of AmericaArticle Citation - WoS: 4Citation - Scopus: 4Diffraction of Plane Electromagnetic Waves by a Resistive Half-Screen for Skew Incidence(Optical Soc Amer, 2020) Umul, Yusuf ZiyaThe scattering process of electromagnetic plane waves by a resistive half-screen is investigated for oblique incidence. First of all, it is shown that the existing solution in the literature is not correct, because the problem was solved by considering the normal components of the electromagnetic field, in terms of which the boundary conditions cannot be expressed. Instead of these, the components of the electric field, which is parallel to the edge discontinuity, are taken into account. The diffracted fields are obtained with the aid of the method of transition boundary. The uniform field expressions are obtained by using the Fresnel function. The behaviors of the total field and its subcomponents are analyzed numerically. (C) 2019 Optical Society of AmericaArticle Citation - WoS: 10Citation - Scopus: 13Adaptive Optics Corrections of Scintillations of Hermite-Gaussian Modes in an Oceanic Medium(Optical Soc Amer, 2020) Baykal, YahyaAdaptive optics correction of the scintillation index is found when Hermite-Gaussian laser beams are used in oceanic turbulence. Adaptive optics filter functions are used to find how the tilt, focus, astigmatism, coma, and total correction will behave under high order mode excitation. Reduction of the oceanic scintillation under various oceanic turbulence and system parameters is examined under different high order modes. Also, the effects of the source size, wavelength, and link length on the total adaptive optics correction of Hermite-Gaussian modes in an oceanic medium are investigated for different modes. (C) 2020 Optical Society of AmericaArticle Citation - WoS: 3Citation - Scopus: 2Snr Advantage of Anisotropy in Oceanic Optical Wireless Communications Links(Optical Soc Amer, 2019) Baykal, YahyaSignal-to-noise ratio (SNR) of an optical wireless communication (OWC) link that operates in anisotropic oceanic turbulence is evaluated. To find the SNR advantage of the anisotropy in the oceanic turbulent medium, SNR in anisotropic oceanic turbulence is normalized by the SNR in isotropic oceanic turbulence. The dB values of this normalized SNR are examined versus the oceanic turbulence parameters of the ratio of temperature to salinity contributions to the refractive index spectrum, the rate of dissipation of mean-squared temperature, the rate of dissipation of kinetic energy per unit mass of fluid at various oceanic anisotropic factors, the avalanche multiplication factors, the radii of receiver aperture, link lengths, and detector responsivity values. It is found that as the oceanic turbulence becomes more anisotropic, at any link parameter, the SNR of the OWC link becomes advantageous over the isotropic counterpart. (c) 2019 Optical Society of AmericaArticle Citation - WoS: 183Citation - Scopus: 193Analysis of Reciprocity of Cos-Gaussian and Cosh-Gaussian Laser Beams in a Turbulent Atmosphere(Optical Soc Amer, 2004) Eyyuboglu, HT; Baykal, YIn a turbulent atmosphere, starting with a cos-Gaussian excitation at the source plane, the average intensity profile at the receiver plane is formulated. This average intensity profile is evaluated against the variations of link lengths, turbulence levels, two frequently used free-space optics wavelengths, and beam displacement parameters. We show that a cos-Gaussian beam, following a natural diffraction, is eventually transformed into a cosh-Gaussian beam. Combining our earlier results with the current findings, we conclude that cos-Gaussian and cosh-Gaussian beams act in a reciprocal manner after propagation in turbulence. The rates (paces) of conversion in the two directions are not the same. Although the conversion of cos-Gaussian beams to cosh-Gaussian beams can happen over a wide range of turbulence levels (low to moderate to high), the conversion of cosh-Gaussian beams to cos-Gaussian beams is pronounced under relatively stronger turbulence conditions. Source and propagation parameters that affect this reciprocity have been analyzed. (C) 2004 Optical Society of America.Article Citation - WoS: 88Citation - Scopus: 87Correlation and Structure Functions of Hermite-Sinusoidal Laser Beams in a Turbulent Atmosphere(Optical Soc Amer, 2004) Baykal, YTo study the performance of atmospheric optical links by using Hermite-sinusoidal-Gaussian laser beam sources, we derive the log-amplitude and the phase correlation and structure functions of such beams in a turbulent atmosphere. Our formulations correctly reduce to the known higher-order mode correlation and structure functions, which in turn reduce to the fundamental-mode (TEM00-mode) results. Several special cases of our formulation are presented, among which the case involving Hermite-cosh-Gaussian dependence is especially noted, since this case is of interest to us owing to the nature of cosh dependence exhibiting the concentration of the energy in the outer lobes of the beam. (C) 2004 Optical Society of America.