Elektrik Elektronik Mühendisliği Bölümü

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Citation - WoS: 8
Citation - Scopus: 9
Aperture Averaging in Multiple-Input Single-Output Free-Space Optical Systems
(Spie-soc Photo-optical instrumentation Engineers, 2015) Baykal, Yahya; Kamacioglu, Canan; Uysal, Murat; Gokce, Muhsin C.
Multiple-input single-output systems are employed in free-space optical links to mitigate the degrading effects of atmospheric turbulence. We formulate the power scintillation as a function of transmitter and receiver coordinates in the presence of weak atmospheric turbulence by using the extended Huygens Fresnel principle. Then the effect of the receiver aperture averaging is quantified. To get consistent results, parameters are chosen within the range of validity of the wave structure functions. Radial array beams and a Gaussian weighting aperture function are used at the transmitter and the receiver, respectively. It is observed that the power scintillation decreases when the source size, the ring radius, the receiver aperture radius, and the number of array beamlet increase. However, increasing the number of array beamlets to more than three seems to have negligible effect on the power scintillation. It is further observed that the aperture averaging effect is stronger when radial array beams are employed instead of a single Gaussian beam. (C) 2015 Society of Photo-Optical Instrumentation Engineers (SPIE)
Citation - WoS: 2
Citation - Scopus: 2
Bit-Error Performance of Optical Wireless System Using Higher Order Mode Laser in Anisotropic Non-Kolmogorov Turbulence
(Spie-soc Photo-optical instrumentation Engineers, 2018) Ata, Yalcin; Baykal, Yahya
The average bit-error-rate, (BER), of optical wireless system using higher order mode laser beam is investigated when atmospheric turbulence shows anisotropic and non-Kolmogorov characteristics. Results reveal that increase in anisotropy in both x- and y-directions positively affects the optical wireless systems performance. Increase in the beam order results in an increase in (BER) for any anisotropy level, and thus, higher order beams adversely affect the optical wireless systems performance. Larger structure constant, beam source size, and propagation distance result in larger (BER), but larger wavelength, inner scale length, and signal-tonoise ratio tend to reduce (BER). Increase in the power-law exponent of non-Kolmogorov turbulent spectrum first increases the (BER) until a certain value, and then (BER) starts to decrease when the power-law exponent is further increased. Adverse effect of higher order laser beam holds to be valid for any power-law exponent of non-Kolimogorov turbulence. (C) 2018 Society of Photo-Optical Instrumentation Engineers (SPIE)
Citation - WoS: 10
Citation - Scopus: 10
Cross-Beam Scintillations in Underwater Medium
(Spie-soc Photo-optical instrumentation Engineers, 2016) Baykal, Yahya
The fluctuation in the intensity, which is quantified by the scintillation index, is evaluated for cross beams when such beams propagate in an underwater medium experiencing turbulence. The variations in the scintillation index are investigated against the changes in the size of the cross beams, 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. (C) 2016 Society of Photo-Optical Instrumentation Engineers (SPIE)
Citation - WoS: 7
Citation - Scopus: 7
Flat-Topped Beam Transmittance in Anisotropic Non-Kolmogorov Turbulent Marine Atmosphere
(Spie-soc Photo-optical instrumentation Engineers, 2017) Ata, Yalcin; Baykal, Yahya
Turbulence affects optical propagation, and, as a result, the intensity is attenuated along the path of propagation. The attenuation becomes significant when the turbulence becomes stronger. Transmittance is a measure indicating how much power is collected at the receiver after the optical wave propagates in the turbulent medium. The on-axis transmittance is formulated when a flat-topped optical beam propagates in a marine atmosphere experiencing anisotropic non-Kolmogorov turbulence. Variations in the transmittance are evaluated versus the beam source size, beam number, link distance, power law exponent, anisotropy factor, and structure constant. It is found that larger beam source sizes and beam numbers yield higher transmittance values; however, as the link distance, power law exponent, anisotropy factor, or structure constant increase, transmittance values are lowered. Our results will help in the performance evaluations of optical wireless communication and optical imaging systems operating in a marine atmosphere. (C) 2017 Society of Photo-Optical Instrumentation Engineers (SPIE)
Citation - WoS: 12
Citation - Scopus: 15
M-Ary Phase Shift Keying-Subcarrier Intensity Modulation Performance in Strong Oceanic Turbulence
(Spie-soc Photo-optical instrumentation Engineers, 2019) Baykal, Yahya; Ata, Yalcin; Gokce, Muhsin Caner
In strong oceanic turbulence, we investigate the bit error rate (BER) performance of underwater wireless optical communication links by employing phase shift keying subcarrier intensity modulated Gaussian laser beam at the transmitter and positive-intrinsic-negative photodetector having finite sized aperture at the receiver. Using the extended Huygens-Fresnel principle, which is conventionally used to analyze the optical beam propagation through turbulence, we evaluate the optical intensity and corresponding signal power over the receiver aperture. Gamma-gamma statistical model for the received intensity is adopted due to strong oceanic turbulence and the required aperture averaged scintillation for this model is obtained by the use of asymptotic Rytov theory. In our performance investigation, we consider the effects of various oceanic turbulences, modulation, receiver noise type, and the photodetector parameters on the BER performance. (C) 2019 Society of Photo-Optical Instrumentation Engineers (SPIE).
Citation - WoS: 14
Citation - Scopus: 15
Performance Analysis of Multiple-Input Multiple-Output Free-Space Optical Systems With Partially Coherent Gaussian Beams and Finite-Sized Detectors
(Spie-soc Photo-optical instrumentation Engineers, 2016) Baykal, Yahya; Uysal, Murat; Gokce, Muhsin Caner
Multiple-input multiple-output (MIMO) techniques are employed in free-space optical (FSO) links to mitigate the degrading effects of atmospheric turbulence. We consider a MIMO FSO system, which consists of a radial laser array with partially coherent Gaussian beams at the transmitter and a detector array with Gaussian apertures at the receiver. The average power and the power correlation function at the finite-sized receiver apertures are formulated by using the extended Huygens-Fresnel principle in weak atmospheric turbulence. This let us further quantify the performance metrics such as the power scintillation index, the aperture averaging factor, and the average bit error rate (BER) as functions of system parameters. The derived power scintillation equation correctly reduces to the existing coherent and partially coherent Gaussian beam scintillation indices in the limiting cases. Using the performance metrics, we analyze the effect of various practical system parameters on the performance of a MIMO FSO system. Practical system parameters include the transmitter and receiver ring radius, number of beamlets, number of finite-aperture receivers, source size, degree of source coherence, receiver aperture radius, link distance, and the structure constant of atmosphere. (C) 2016 Society of Photo-Optical Instrumentation Engineers (SPIE)

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