Browsing by Author "Gerçekçioğlu, Hamza"

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Annular beam scintillations in strong turbulence
(Optical Soc Amer, 2010) Gerçekçioğlu, Hamza; Baykal, Yahya; Nakiboğlu, Cem; 7812
A scintillation index formulation for annular beams in strong turbulence is developed that is also valid in moderate and weak turbulence. In our derivation, a modified Rytov solution is employed to obtain the small-scale and large-scale scintillation indices of annular beams by utilizing the amplitude spatial filtering of the atmospheric spectrum. Our solution yields only the on-axis scintillation index for the annular beam and correctly reduces to the existing strong turbulence results for the Gaussian beam-thus plane and spherical wave scintillation indices-and also correctly yields the existing weak turbulence annular beam scintillations. Compared to collimated Gaussian beam, plane, and spherical wave scintillations, collimated annular beams seem to be advantageous in the weak regime but lose this advantage in strongly turbulent atmosphere. It is observed that the contribution of annular beam scintillations comes mainly from the small-scale effects. At a fixed primary beam size, the scintillations of thinner collimated annular beams compared to thicker collimated annular beams are smaller in moderate turbulence but larger in strong turbulence; however, thinner annular beams of finite focal length have a smaller scintillation index than the thicker annular beams in strong turbulence. Decrease in the focal length decreases the annular beam scintillations in strong turbulence. Examining constant area annular beams, smaller primary sized annular structures have larger scintillations in moderate but smaller scintillations in strong turbulence. (C) 2010 Optical Society of America
Ber of Annular Beams in Strong Turbulence
(2010) Gerçekçioğlu, Hamza; Baykal, Yahya; Eyyuboğlu, Halil T.; 7688; 7812
Bit error rate (BER) of annular beams is found in strong turbulence. Examining effects of beam and medium parameters on BER reveals that annular beams become favorable in stronger turbulence and at smaller focal lengths.
Hermite Gaussian beam scintillations in weak atmospheric turbulence for aerial vehicle laser communications
(2020) Sayan, Ömer F.; Gerçekçioğlu, Hamza; Baykal, Yahya; 7812
Scintillation index of Hermite Gaussian beams used for air vehicle communication systems in vertical paths of weak atmospheric turbulent medium are investigated by employing the modified Rytov method. By evaluating the on-axis scintillation index, variations of the scintillation indices of these beams are examined against the changes in the Gaussian beam size of the Hermite Gaussian beam mode, propagation distances and the zenith angles at the realistic propagation distances involved in uplink and downlink configurations. In the atmospheric environment, for uplink, the Hermite Gaussian beam modes have no advantage over the Gaussian beams at short propagation distances like L = 20 km,as well as at long propagation distances like L = 700 km. However, for downlink, although Hermite Gaussian beam modes are disadvantageous over the Gaussian beams at short propagation distances like L = 20 km, they are found advantageous over the Gaussian beams at long propagation distances like L = 700 km. The results of this study may encourage to use Hermite Gaussian beams, especially in the air vehicle laser communication links, and can be used in the design of an optical wireless communication link utilizing the vertical atmospheric medium.
Laser beam scintillations of LIDAR operating in weak oceanic turbulence
(2023) Gerçekçioğlu, Hamza; Baykal, Yahya; 7812
The formulation of light detection and ranging (LIDAR) systems is derived and examined for the scintillation index, evaluated on-axis, of laser beams in horizontal links in the ocean with weak turbulence by utilizing the Rytov method. These scintillation indices, obtained for the Gaussian beam which is collimated, the limits of plane and spherical waves, are depicted versus the source size, target size, and parameter of the normalized reflector size. It is found that the source size, target size, and normalized reflector size parameter, lessening the scintillation index evaluated on-axis, are approximately 0.44 cm, 56×10-4 cm, and 2.2, respectively. Additionally, by using these values that minimize the scintillation index, the variation of the scintillations is shown against the propagation distance, radius of reflector, temperature and salinity fluctuation effects, mean squared temperature, and turbulent kinetic energy dissipation rate per unit mass of fluid at various selected source size and radius of reflector values.
Minimization of scintillation index against displacement parameters
(Elsevier Science, 2008) Eyyuboğlu, Halil T.; Gerçekçioğlu, Hamza; Baykal, Yahya; 7688; 7812
For sinusoidal beams, minimization of scintillation index is carried out against the displacements parameters. It is found-that x-y asymmetric cosh-Gaussian beam fulfills the requirements of such optimum beam. Our minimization procedure reveals that the optimum beam is achieved by continually focusing it at the chosen propagation length and by further adjusting displacements parameters to be propagation distance dependent. Scintillation index of thus constructed optimum beam is formulated and numerically evaluated., Our graphical comparisons entailing collimated and focused versions of cos-, cosh-Gaussian, annular-Gaussian and Gaussian beams show that the optimum beam yields the lowest scintillations provided that Propagation range is less than or equal to the focusing distance. (C) 2008 Elsevier B.V. All rights reserved
Minimization of the scintillation index of sinusoidal Gaussian beams in weak turbulence for aerial vehicle-satellite laser communications
(2021) Gerçekçioğlu, Hamza; Baykal, Yahya; 7812
Minimization 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 inweak turbulence. © 2021 Optical Society of America.
Transmittance for Dense Wavelength Division Multiplexing system in non-Kolmogorov turbulence
(2012) Ata, Yalçın; Baykal, Yahya; Gerçekçioğlu, Hamza; 7812
Transmittance for a Dense Wavelength Division Multiplexing (DWDM) system operating in non-Kolmogorov medium is evaluated. MODTRAN (MODerate resolution atmospheric TRANsmission) is also used to include the absorption and scattering effects due to atmospheric gases, aerosols and molecules. Increase in the power law of the non-Kolmogorov spectrum is found to decrease the transmittance at all the wavelengths employed in DWDM. Being valid for all the DWDM wavelengths and for all the power law exponent values of non-Kolmogorov spectra, as the turbulence falls into stronger regimes, the transmittance levels decrease.