Elektronik ve Haberleşme Mühendisliği Bölümü Yayın Koleksiyonu
Permanent URI for this collectionhttps://hdl.handle.net/20.500.12416/260
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Article Citation - WoS: 13Citation - Scopus: 13Angle-Of Fluctuations for General-Type Beams(Spie-soc Photo-optical instrumentation Engineers, 2007) Eyyuboglu, Halil T.; Baykal, YahyaStarting with the recently introduced phase correlation function of a general-type beam, the angle-of-arrival fluctuations are derived and evaluated in atmospheric turbulence for lowest-order Gaussian, cos-Gaussian, cosh-Gaussian, annular, and flat-topped beams. Our motivation is to examine the improvement in the performance of optical atmospheric links when such beams are employed. For these beams, the dependence of the angle-of-arrival fluctuations on the propagation length, displacement and focusing parameters, source size, inner and outer scales of turbulence, and receiver radius is investigated. It is found that in the majority of the cases examined, the angle- of- arrival fluctuations remain small and hence are not expected to adversely affect the operation of free-space atmospheric links. It is observed that amongst the beams considered, the cos-Gaussian beam offers the least amount of angle-of-arrival fluctuations, while the worst behavior is exhibited by the cosh-Gaussian beam. This situation is reversed, however, if focused beams are used. (C) 2007 Society of Photo-Optical Instrumentation Engineers.Article Citation - WoS: 9Citation - Scopus: 10Aperture 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.; Kamacoʇlu, CananMultiple-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)Article Citation - WoS: 16Citation - Scopus: 17Performance 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 CanerMultiple-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)Article Citation - WoS: 11Citation - Scopus: 10Receiver-Aperture Averaging of Annular Beams Propagating Through Turbulent Atmosphere(Spie-soc Photo-optical instrumentation Engineers, 2013) Kamacioglu, Canan; Baykal, Yahya; Yazgan, ErdemFor an annular beam incidence, the power scintillation index in a weakly turbulent atmosphere is derived at the receiver plane, which has a Gaussian aperture. Employing this derivation, the receiver-aperture averaging factor is evaluated. Annular beams are found more advantageous than the Gaussian beams when compared on receiver-aperture averaging basis. The analyses indicate that the effect of the aperture averaging increases as the propagation length increases. Increase in the structure constant and the secondary beam source size is observed to strengthen the effect of the aperture averaging when the primary beam source size is fixed. (C) 2013 Society of Photo-Optical Instrumentation Engineers (SPIE)Article Citation - WoS: 8Citation - Scopus: 8Crossbeam Intensity Fluctuations in Turbulence(Spie-soc Photo-optical instrumentation Engineers, 2014) Baykal, YahyaIntensity fluctuations of a crossbeam are evaluated in weak atmospheric turbulence. A crossbeam is defined as two asymmetrical Gaussian beams oriented perpendicular to each other, and one of these beams is wider along the x-axis whereas the other beam is wider along the y-axis. Our results indicate that in terms of the intensity fluctuations in weak turbulence, focused crossbeams offer favorable results when compared to the corresponding focused Gaussian beam intensity fluctuations. However, for collimated crossbeams, such a comparison is in favor of the collimated Gaussian beam. (C) 2014 Society of Photo-Optical Instrumentation Engineers (SPIE)Article Citation - WoS: 7Citation - Scopus: 10Effect of Source Spatial Partial Coherence on the Angle-Of Fluctuations for Free-Space Optics Links(Spie-soc Photo-optical instrumentation Engineers, 2006) Baykal, Yahya; Eyyuboglu, Halil TanyerThe dependence of angle-of-arrival fluctuations on source coherence for free-space optics links in a turbulent atmosphere is examined. A monochromatic beam is taken, and the variation of the angle-of-arrival fluctuations for a spatially partially coherent source is investigated. Results are obtained for the currently used free-space optics links, which use infrared wavelengths of 0.85 and 1.55 mu m with link lengths of 3 and 5 km. The angle-of-arrival fluctuations are calculated and plotted against normalized source size and inner and outer scales of turbulence. It is observed that the angle-of-arrival fluctuations show behavior that is essentially independent of the degree of source partial coherence. In fact, as the source size increases, this dependence seems to almost disappear. It is further observed that mean square angle-of-arrival fluctuations become larger at greater propagation distances, at smaller inner scales of turbulence, and at larger outer scales of turbulence. However, the numerical values of the angle-of-arrival fluctuations found for all cases are not expected to degrade substantially the performance of a practical optical receiver having a field of view in the order of several milliradians. Our results presented here are compared with the existing theoretical and experimental work, and the range of applicability of our formulation is discussed. (C) 2006 Society of Photo-Optical Instrumentation Engineers.