Browsing by Author "Gökçe, Muhsin C."

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Laser array beam scintillation in oceanic turbulence
(2020) Baykal, Yahya; Ata, Yalçın; Gökçe, Muhsin C.; 7812
In this study, on-axis scintillation of laser array beam in oceanic turbulent medium is investigated. By using Rytov method, scintillation index variations are reported in connection with the propagation distance, rate of dissipation of turbulent kinetic energy, microscale length, rate of dissipation of the mean squared temperature, salinity ratio, radius of the ring of beamlets which compose the beam array, source size and number of beamlets. Results show that turbulence effect on the laser beam increases with the propagation distance, microscale length, rate of dissipation of the mean squared temperature, salinity ratio, array radius, source size and number of beamlets but decreases when rate of dissipation of turbulent kinetic energy increases. © 2020 IEEE.
Performance of M-ary pulse position modulated optical wireless communications systems in the marine atmosphere
(2021) Baykal, Yahya; Ata, Yalçın; Gökçe, Muhsin C.; 7812
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 the OWC link, and M value of the M-ary PPM.
Underwater turbulence, its effects on optical wireless communication and imaging: A review
(2022) Baykal, Yahya; Ata, Yalçın; Gökçe, Muhsin C.
Theory of optical turbulence in underwater medium and the effects of underwater turbulence on various applications done in underwater or under ocean are reviewed. A detailed survey of underwater turbulence studies in literature is reported. Underwater physics covering salinity, temperature and dissipation rates, various power spectra such as Hill, Nikishov and Nikishov, Li, new form and the oceanic turbulence optical power spectrum (OTOPS) spectra are explained. Wave and phase structure functions, related coherence length, anisotropy, intensity, field correlations in underwater turbulence are elaborated. Scintillation indices of spherical, plane, Gaussian, and other types of optical beams are mentioned. Bit-error-rate (BER), signal-to-noise-ratio (SNR) performances of optical wireless communication systems operating in underwater, and the effects of modulation types of these systems on the performances are reported. Channel capacity of underwater optical wireless communication systems when the channel experiences log-normal, gamma-gamma, Weibull, and negative exponential statistics are reflected. Underwater imaging and the related modulation transfer function, underwater turbulence mitigation techniques in the form of aperture averaging, adaptive optics, receiver, transmitter and multiple-input, multiple-output (MIMO) spatial diversity techniques are revised.