WoS İndeksli Yayınlar Koleksiyonu
Permanent URI for this collectionhttps://hdl.handle.net/20.500.12416/8653
Browse
5 results
Search Results
Article Citation - WoS: 10Citation - Scopus: 7Analysis of Laser Multimode Content on the Angle-Of Fluctuations in Free-Space Optics Access Systems(Spie-soc Photo-optical instrumentation Engineers, 2005) Eyyuboglu, HT; Baykal, YThe effects of laser beam multimode content on the angle-of-arrival fluctuations are examined for free-space optics (FSO) access systems. Multimode excitation is represented by coherent addition of Hermite-Gaussian modes. Mean square angle-of-arrival fluctuations are formulated using our previously reported multimode phase structure function. Numerical evaluations are obtained for practical FSO links operating at 1.55- and 0.85-mu m wavelengths with link spans of up to 5 km. Mode content is arranged by sequentially grouping all possible mode combinations starting from the single fundamental mode (TEM00) up to a certain higher order (n,m). Angle-of-arrival fluctuations are found to be of the order of several tens of microradians, except for the cases when the mode group terminates with an odd mode or when the extremely higher order modes are present. In these instances, the fluctuations will rise to the radian level. From these results, it is concluded that the performance of a practical FSO receiver, having a field of view of several milliradians, will not be substantially affected by the angle-of-arrival fluctuations due to multimode excitation, provided that the mode content of source excitation is confined to mode indices below 20. (c) 2005 Society of Photo-Optical Instrumentation Engineers.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: 2Citation - Scopus: 2Bit-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, YahyaThe 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)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)