Elektrik Elektronik Mühendisliği Bölümü Yayın Koleksiyonu
Permanent URI for this collectionhttps://hdl.handle.net/20.500.12416/411
Browse
9 results
Search Results
Article 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: 30Citation - Scopus: 32Bit Error Rate of Pulse Position Modulated Optical Wireless Communication Links in Oceanic Turbulence(Optical Soc Amer, 2018) Baykal, YahyaThe upper bound of the average bit error rate (BER) of a pulse position modulated (PPM) optical wireless communication (OWC) link operating in oceanic turbulence is formulated. BER variations against the changes in the ratio of temperature to salinity contributions to the refractive index spectrum, the rate of dissipation of mean-squared temperature, and the rate of dissipation of kinetic energy per unit mass of fluid are found at various data bit rates, average current gains of the avalanche photodiode (APD), and M values of the M-ary PPM. It is found that under any oceanic turbulence parameters, BER performance of the PPM OWC system becomes favorable at smaller data bit rates, M values, and at larger average current gains of APD. (c) 2018 Optical Society of AmericaArticle Citation - WoS: 65Citation - Scopus: 70Intensity Fluctuations of Multimode Laser Beams in Underwater Medium(Optical Soc Amer, 2015) Baykal, YahyaIn an oceanic optical communications link, the received intensity fluctuations, quantified by the scintillation index, are formulated and evaluated when a multimode laser is used. The variations of the scintillation index versus the oceanic turbulence parameters are examined for different multimode laser structures. Oceanic turbulence parameters used are the rate of dissipation of kinetic energy per unit mass of fluid, the rate of dissipation of mean-squared temperature, the Kolmogorov inner scale, and the parameter w that defines the ratio of temperature to salinity contributions to the refractive index spectrum. The results in this paper can be used to improve performance in the design of oceanic optical communications links. (C) 2015 Optical Society of AmericaArticle Citation - WoS: 50Citation - Scopus: 55Expressing Oceanic Turbulence Parameters by Atmospheric Turbulence Structure Constant(Optical Soc Amer, 2016) Baykal, YahyaThe parameters composing oceanic turbulence are the wavelength, link length, rate of dissipation of kinetic energy per unit mass of fluid, rate of dissipation of mean-squared temperature, Kolmogorov microscale, and the ratio of temperature to salinity contributions to the refractive index spectrum. The required physical entities such as the average intensity and the scintillation index in the oceanic medium are formulated by using the power spectrum of oceanic turbulence, which is described by oceanic turbulence parameters. On the other hand, there exists a rich archive of formulations and results for the above-mentioned physical entities in atmospheric turbulence, where the parameters describing the turbulence are the wavelength, the link length, and the structure constant. In this paper, by equating the spherical wave scintillation index solutions in the oceanic and atmospheric turbulences, we have expressed the oceanic turbulence parameters by an equivalent structure constant used in turbulent atmosphere. Such equivalent structure constant will help ease reaching solutions of similar entities in an oceanic turbulent medium by employing the corresponding existing solutions, which are valid in an atmospheric turbulent medium. (C) 2016 Optical Society of AmericaArticle Citation - WoS: 23Citation - Scopus: 24Higher-Order Laser Beam Scintillation in Weakly Turbulent Marine Atmospheric Medium(Optical Soc Amer, 2016) Baykal, YahyaThe atmosphere above the sea or ocean, known as the marine atmosphere, affects optical waves propagating through it in a different manner than the atmosphere above land. Like other system design parameters, intensity fluctuations of laser light propagating in marine atmosphere, quantified by the scintillation index, also show different variations. The on-axis scintillations of higher-order laser beams are formulated and evaluated when such excitations are employed in a weakly turbulent marine atmospheric medium. Variations of the scintillation index with respect to the changes in the Gaussian beam size of the higher-order mode, link length, wavelength, and structure constant are reported. Our results can be used in the design of an optical wireless communication link design operating in marine atmospheres. (C) 2016 Optical Society of AmericaArticle Citation - WoS: 13Citation - Scopus: 14Fourth-Order Mutual Coherence Function in Oceanic Turbulence(Optical Soc Amer, 2016) Baykal, YahyaWe have recently expressed the structure constant of atmospheric turbulence in terms of the oceanic turbulence parameters, which are the ratio of temperature to salinity contributions to the refractive index spectrum, rate of dissipation of kinetic energy per unit mass of fluid, rate of dissipation of the mean-squared temperature, wavelength, Kolmogorov microscale, and link length. In this paper, utilizing this recently found structure constant and the fourth-order mutual coherence function of atmospheric turbulence, we present the fourth-order mutual coherence function to be used in oceanic turbulence evaluations. Thus, the found fourth-order mutual coherence function of oceanic turbulence is evaluated for the special case of a point source located at the transmitter origin and at a single receiver point. The variations of this special case of the fourth-order mutual coherence function of oceanic turbulence against the changes in the ratio of temperature to salinity contributions to the refractive index spectrum, the rate of dissipation of kinetic energy per unit mass of fluid, the rate of dissipation of the mean-squared temperature, the wavelength, and the Kolmogorov microscale at various link lengths are presented. (C) 2016 Optical Society of AmericaArticle Citation - WoS: 21Citation - Scopus: 22Intensity Fluctuations of Asymmetrical Optical Beams in Anisotropic Turbulence(Optical Soc Amer, 2016) Baykal, YahyaIntensity fluctuations of asymmetrical optical beams are examined when such beams propagate through anisotropic turbulence. Anisotropic turbulence is modeled by non-Kolmogorov von Karman spectrum. The variations of the scintillation index are observed against the changes in the asymmetry factor of the Gaussian beam, power law exponent of non- Kolmogorov spectrum, anisotropic factors in the transverse direction, and the link length. It is found that for all the conditions, asymmetry in the optical beam is a disadvantage but the anisotropy in the atmosphere is an advantage for reducing the intensity fluctuations in an optical wireless communications link operating in the atmosphere. (C) 2016 Optical Society of AmericaArticle Citation - WoS: 21Citation - Scopus: 27Scintillations of Led Sources in Oceanic Turbulence(Optical Soc Amer, 2016) Baykal, YahyaThe scintillation index of light emitting diode (LED) sources is evaluated when such sources are employed in oceanic wireless optical communication (UWOC) links. In the formulation, LED source radiation is taken to be perfectly incoherent with a Gaussian field distribution. We have utilized the scintillation index solution of an incoherent source in atmospheric turbulence, together with our recently obtained expression that expresses the structure constant of atmospheric turbulence in terms of the oceanic turbulence and UWOC link parameters. Oceanic turbulence parameters of interest are the ratio of temperature to salinity contributions to the refractive index spectrum, rate of dissipation of kinetic energy per unit mass of fluid, rate of dissipation of mean-squared temperature, and viscosity. UWOC link parameters are the LED source size, link length, and the wavelength. Scintillation index results are presented for various variations of the oceanic turbulence and UWOC link parameters. (C) 2016 Optical Society of America