Elektronik ve Haberleşme Mühendisliği Bölümü Yayın Koleksiyonu
Permanent URI for this collectionhttps://hdl.handle.net/20.500.12416/260
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Conference Object Citation - WoS: 1Citation - Scopus: 1Scintillations in Weak Turbulence of Annular Beams Whose Individual Components Are Incoherent(Electromagnetics Acad, 2010) Eyyuboğlu, Halil Tanyer; Baykal, Y.; Eyyuboglu, H. T.; Baykal, Yahya Kemal; Cai, Y.; Elektronik ve Haberleşme Mühendisliği; Elektrik-Elektronik MühendisliğiThe scintillation index, arising from the intensity fluctuations in weak atmospheric turbulence of annular beams whose individual components are incoherent, is formulated. For such beams whose annularities are obtained by varying the source sizes and magnitudes of the individual beams, evaluations show that at very small sized beam structures, thinner beams possess smaller scintillations. As the sizes increase, the scintillation index values of thick and thin beams approach each other, eventually exhibiting the same scintillation behavior at large sized beam structures. Examination of the intensity fluctuations of the annular beams, whose individual incoherent components are at the same size but at different magnitudes, yield reverse behavior such that at very small sized beam structures, thicker beams possess smaller scintillations, however the scintillation values are very close to each other. Again, for large sized beams, the scintillation index values of thick and thin beams approach each other, eventually exhibiting the same scintillation behavior at large sized beam structures. Comparing the scintillation indices of annular beams whose individual components are incoherent to those of traditional annular beams of coherent components, it seems that for large sized beams, incoherently subtracted beams are advantageous, however the reverse is valid for very small sized beam structures.Conference Object Citation - WoS: 1Formulation of Scintillations for Optical Incidence of Arbitrary Field Profile(Electromagnetics Acad, 2008) Eyyuboğlu, Halil Tanyer; Baykal, Y.; Eyyuboglu, H. T.; Baykal, Yahya Kemal; Cai, Y.; Elektronik ve Haberleşme Mühendisliği; Elektrik-Elektronik MühendisliğiScintillation index on the receiver axis is formulated in random medium when an optical source with an arbitrary field profile is employed. To represent the arbitrary source field profile, source is decomposed into pixels and the incident field to form the scintillations is expressed as the superposition of the fields from each pixel area. Thus obtained arbitrary field distribution is then introduced into the weak atmospheric turbulence formulation by using Rytov method. Our result, which is in summa ion and integral forms, reduces correctly to the known scintillation index of a Gaussian beam wave in atmospheric turbulence.Article Citation - Scopus: 70Influence of Turbulence on the Effective Radius of Curvature of Radial Gaussian Array Beams(Optical Society of American (OSA), 2010) Ji, X.; Eyyuboglu, H.T.; Baykal, Y.The analytical formula for the effective radius of curvature of radial Gaussian array beams propagating through atmospheric turbulence is derived, where coherent and incoherent beam combinations are considered. The influence of turbulence on the effective radius of curvature of radial Gaussian array beams is studied by using numerical calculation examples. © 2010 Optical Society of America.Conference Object Citation - Scopus: 1Transmittance for Dense Wavelength Division Multiplexing System in Non-Kolmogorov Turbulence(2012) Ata, Y.; Baykal, Y.; Gercekcioglu, H.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. © 2012 IEEE.Conference Object Ber of Annular Beams in Strong Turbulence(Optical Society of America (OSA), 2010) Gerçekcioglu, H.; Baykal, Y.; Eyyuboglu, H.T.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. ©2010 Optical Society of America.Article Citation - WoS: 27Citation - Scopus: 28Beam Wander of J 0- and I 0-Bessel Gaussian Beams Propagating in Turbulent Atmosphere(Springer, 2010) Eyyuboglu, H. T.; Baykal, Y.; Korotkova, O.; Cai, Y.; Cil, C. Z.Root mean square (rms) beam wander of J (0)-Bessel Gaussian and I (0)-Bessel Gaussian beams, normalized by the rms beam wander of the fundamental Gaussian beam, is evaluated in atmospheric turbulence. Our formulation is based on the first and the second statistical moments obtained from the Rytov series. It is found that after propagating in atmospheric turbulence, the collimated J (0)-Bessel Gaussian and the I (0)-Bessel Gaussian beams have smaller rms beam wander than that of the Gaussian beam, regardless of the choice of Bessel width parameter. However, the extent of such an advantage depends on the chosen width parameter, Gaussian source size, propagation distance and the wavelength. Focusing at finite distances of the considered beams causes the rms beam wander to decrease sharply at the propagation distances equal to the focusing parameter.Article Citation - WoS: 60Citation - Scopus: 65Degree of Polarization for Partially Coherent General Beams in Turbulent Atmosphere(Springer, 2007) Eyyuboglu, H. T.; Baykal, Y.; Cai, Y.The degree of polarization is found for optical excitations of cosh-Gaussian, cos-Gaussian and annular-Gaussian beams in a turbulent atmosphere. The related formulation is based on the beam coherence polarization matrix. The self and mutual coherence functions appearing in the beam coherence polarization matrix are evaluated, when the above mentioned excitations exhibit partial source coherence for self and cross fields. Plots showing the variation of the degree of polarization are provided versus the propagation length when the source size, displacement parameter, structure constant and the degree of source coherence for self and cross fields change.Article Citation - WoS: 23Citation - Scopus: 24Annular Beam Scintillations in Non-Kolmogorov Weak Turbulence(Springer, 2012) Gercekcioglu, H.; Baykal, Y.In a weakly turbulent atmosphere governed by the non-Kolmogorov spectrum, the on-axis scintillation index is formulated and evaluated when the incidence is an annular Gaussian type. When the power law of the non-Kolmogorov spectrum is varied, the scintillation index first increases, and reaches a peak value, then starts to decrease, and eventually approaches zero. The general trend is that when turbulence has a non-Kolmogorov spectrum with power law larger than the Kolmogorov power law, the scintillation index values become smaller. For all power laws, collimated annular Gaussian beams exhibit smaller scintillations when compared to pure Gaussian beams of the same size. Intensity fluctuations at a fixed propagation distance diminish for the non-Kolmogorov spectrum with a very large power law, irrespective of the focal length and the thickness of optical annular Gaussian sources.Article Citation - WoS: 20Citation - Scopus: 21Scintillation Behavior of Laguerre Gaussian Beams in Strong Turbulence(Springer, 2011) Eyyuboglu, H. T.; Baykal, Y.; Falits, A.In strong atmospheric turbulence, the asymptotic on-axis scintillation behaviors of Laguerre Gaussian (LG) beams are examined. To arrive at the strong-turbulence solution, we utilize the existing filtering approach for weak-turbulence solutions and our recently reported weak-turbulence scintillation index formula for LG beams. In the limiting case, our solution correctly predicts the asymptotic strong-turbulence behavior of Gaussian beam wave scintillation. Investigation of the scintillations versus the propagation distance, source size, wavelength and refractive index structure parameter lead to the conclusion that the LG beams with higher order radial modes can provide less scintillation. The results are applicable to long-haul atmospheric optical communication links.Article Citation - WoS: 29Citation - Scopus: 32Intensity Fluctuations of Partially Coherent Laser Beam Arrays in Weak Atmospheric Turbulence(Springer, 2011) Arpali, C.; Arpali, S. A.; Baykal, Y.; Eyyuboglu, H. T.The intensity fluctuation of a partially coherent laser beam array is examined. For this purpose, the on-axis scintillation index at the receiver plane is analytically formulated via the extended Huygens-Fresnel diffraction integral in conditions of weak atmospheric turbulence. The effects of the propagation length, number of beamlets, radial distance, source size, wavelength of operation and coherence level on the scintillation index are investigated for a horizontal propagation path. It is found that, regardless of the number of beamlets, the scintillation index always rises with an increasing propagation length. If laser beam arrays become less coherent, the scintillation index begins to fall with growing source sizes. Given the same level of partial coherence, slightly less scintillations will occur when the radial distance of the beamlets from the origin is increased. At partial coherence levels, lower scintillations are observed for larger numbers of beamlets. Both for fully and partially coherent laser beam arrays, scintillations will drop on increasing wavelengths.
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