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: 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: 13Citation - Scopus: 13Per Unit Received Power Apertured Averaged Scintillation of Partially Coherent Sinusoidal and Hyperbolic Gaussian Beams(Elsevier Sci Ltd, 2015) Eyyuboglu, Halil T.; Eyyuboʇlu, Halil T.We evaluate the per unit power received power aperture averaged scintillation performance of fully and partially coherent sinusoidal and hyperbolic Gaussian beams. Our analysis includes fundamental Gaussian, cosh Gaussian, cos Gaussian and annular Gaussian beams. The method is based on our earlier introduced semi-analytic approach. Scintillation performance is measured upon dividing the aperture averaged scintillation by the received power. Assessment is made both for aperture sizes that are adjusted separately for full and partially coherent beams to capture 10% and 20% of the equal source power and also for fixed aperture sizes. This way, the scintillation performance of the different beams in question is compared. From this comparison, we find that partially coherent beams have lower scintillation than the fully coherent ones, when adjustable aperture size is used. But upon switching to fixed aperture size, the reverse happens and coherent beams become more advantageous. In all cases of comparison, small source sized annular Gaussian beam and large source sized Gaussian beam seem to offer the lowest scintillation when aperture size is adjusted to capture 20% of the equal source power. (C) 2015 Elsevier Ltd. All rights reserved.Article Citation - WoS: 20Snr Bounds of Fso Links and Its Evaluation for Selected Beams(Taylor & Francis Ltd, 2015) Bayraktar, Mert; Eyyuboglu, Halil T.We formulate the signal-to-noise ratio (SNR) for free-space optical links. Upon inserting typical operating parameters, it is seen that SNR well approximates to the inverse of aperture averaged scintillation parameter. By adopting a common source beam power of 10 mW, we select three different source sizes of Gaussian, annular Gaussian (AG), and cosh-Gaussian beams. We then evaluate the SNR of these beams. Our results indicate that when fixed aperture opening is used, fully and partially coherent beams yield almost the same SNR performance. On the other hand, however, focusing and lowering wavelength of operation appear to be quite instrumental in improving the SNR performance. In this context, medium-sized AGB seems to exhibit the best performance.