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: 2Diffraction Properties of Partially Coherent Elegant High-Order Beam(Electromagnetics Acad, 2010) Eyyuboğlu, Halil Tanyer; Wang, Fei; Baykal, Yahya Kemal; Cai, Yangjian; Eyyuboglu, Halil T.; Baykal, Yahya; Elektronik ve Haberleşme Mühendisliği; Elektrik-Elektronik MühendisliğiThe diffraction properties of a partially coherent elegant higher-order beam in free space are investigated in detail. It is found that the diffraction properties of a partially coherent elegant higher-order beam upon propagation are closely related to its initial coherence. A partially coherent elegant higher-order beam spreads more slowly than a partially coherent standard higher-order beam, which has potential application in free-space optical communications.Conference Object Off-Axis Gaussian Beams With Random Displacement in Atmospheric Turbulence(int inst informatics & Systemics, 2005) Baykal, Yahya Kemal; Baykal, Yahya K.; Eyyuboğlu, Halil Tanyer; Eyyuboglu, Halil T.; Yenice, Yusuf E.; Elektronik ve Haberleşme Mühendisliği; Elektrik-Elektronik MühendisliğiOur recent work in which we study the propagation of the general Hermite-sinusoidal-Gaussian laser beams in wireless broadband access telecommunication systems is elaborated in this paper to cover the special case of an off-axis Gaussian beam. We mainly investigate the propagation characteristics in atmospheric turbulence of an off-axis Gaussian beam possessing Gaussian distributed random displacement parameters. our interest is to search for different types of laser beams that will improve the performance of a wireless broadband access system when atmospheric turbulence is considered. Our formulation is based on the basic solution of the second order mutual coherence function evaluated at the receiver plane. For fixed turbulence strength, the coherence length calculated at the receiver plane is found to decrease as the variance of the random displacement is increased. It is shown that as the turbulence becomes stronger, coherence lengths due to off-axis Gaussian beams tend to approach the same value, irrespective of the variance of the random displacement. As expected, the beam spreading is found to be pronounced for larger variance of displacement parameter. Average intensity profiles when atmospheric turbulence is present are plotted for different values of the variance of the random displacement parameter of the off-axis Gaussian beam.Conference Object Citation - WoS: 4Citation - Scopus: 33A Novel Design of Two Loosely Coupled Bandpass Filter Based on Hilbert-Zz Resonator With Higher Harmonic Suppression(Ieee, 2013) Mezaal, Yaqeen S.; Eyyuboglu, Halil T.; Ali, Jawad K.New characteristics of fractal design scheme has been introduced to generate compact two poles capacitively coupled microstrip bandpass filter by using additional coupling stubs for different wireless applications. The presented fractal scheme is based on specific type of Hilbert space-filling curve which is called Hilbert-zz fractal geometry. The performance of generated bandpass filter structure has been analyzed using Sonnet software package with a relative dielectric constant of 9 and a substrate thickness of 1.27 mm. Results show that these filters possess good transmission and return loss characteristics, besides higher harmonics suppressions; meeting the specifications of most of wireless communication systems.Article Citation - WoS: 45Citation - Scopus: 50Scintillations of Incoherent Flat-Topped Gaussian Source Field in Turbulence(Optical Soc Amer, 2007) Baykal, Yahya; Eyyuboglu, Halil T.The intensity fluctuations of incoherent flat-topped Gaussian beams are evaluated when such sources are used in weakly turbulent horizontal atmospheric links. The formulation is developed for a detector having a response time much longer than the source coherence time. The flat-topped Gaussian profile is obtained by superposing many Gaussian beams, then the incoherence is introduced through delta correlation in space. The scintillation index of the incoherent flat-topped Gaussian beams is found to be smaller than the scintillation index of the corresponding incoherent Gaussian beams at the same link length, source size, and wavelength. When compared with the coherent counterparts, the intensity fluctuations of the incoherent flat-topped Gaussian beams are much smaller, yielding the same value only at the spherical wave limit, as expected. Transmitter aperture averaging is a special case of our solution. (c) 2007 Optical Society of America.Article Citation - WoS: 91Citation - Scopus: 96Scintillation Index of Elliptical Gaussian Beam in Turbulent Atmosphere(Optical Soc Amer, 2007) Cai, Yangjian; Chen, Yuntian; Eyyuboglu, Halil T.; Baykal, YahyaA tensor method is used to formulate the on-axis scintillation index for an elliptical Gaussian beam (EGB; astigmatic Gaussian beam) propagating in a weak turbulent atmosphere. Variations of the on-axis scintillation of an EGB are studied. It is interesting to find that the scintillation index of an EGB can be smaller than that of a circular Gaussian beam in a weakly turbulent atmosphere under certain conditions and is closely related to the ratio of the beam waist size along the long axis to that along the short axis of the EGB, the wavelength, and the structure constant of the turbulent atmosphere. (C) 2007 Optical Society of America.Article Citation - WoS: 64Citation - Scopus: 70Complex Degree of Coherence for Partially Coherent General Beams in Atmospheric Turbulence(Optical Soc Amer, 2007) Eyyuboglu, Halil T.; Baykal, Yahya; Cai, YangjianWith the use of the general beam formulation, the modulus of the complex degree of coherence for partially coherent cosh-Gaussian, cos-Gaussian, Gaussian, annular and higher-order Gaussian optical beams is evaluated in atmospheric turbulence. For different propagation lengths in horizontal atmospheric links, the moduli of the complex degree of coherence at the source and receiver planes are examined when reference points are taken on the receiver axis and off-axis. In the on-axis case, it is observed that in propagation, the moduli of the complex degree of coherence are symmetrical and look like the intensity profile of the related coherent beam propagating in a turbulent atmosphere. For all the beams considered, the moduli of the complex degree of coherence profiles turn into Gaussian shapes beyond certain propagation lengths. In the off-axis case, the moduli of complex degree of coherence patterns become drifted at the earlier propagation lengths. Among the beams investigated, the cos-Gaussian beam is found to be almost independent of the changes in the source partial coherence parameter, and the annular beam seems to be affected the most against the variations of the source partial coherence parameter. (c) 2007 Optical Society of America.Conference Object Analysis of Wave Structure Functions(Ieee, 2008) Eyyuboglu, Halil T.Wave structure function (WSF) of spherical wave is used in extended Huygens-Fresnel integral to induce the effect of turbulent atmosphere on the propagating laser beam. Depending on the approximation made and the choice of the spatial power spectral density of refractive index fluctuation function, different forms of WSFs become available. In this study, five different WSFs are numerically evaluated for pure Gaussian, cosh-Gaussian, sinh-Gaussian, cos-Gaussian and sine-Gaussian types of source plane beams. In the range of adapted source and propagation parameters, namely under weak fluctuation conditions, no substantial deviations are found to occur with respect to the WSF selection. Our results are offered in terms of graphical illustrations showing the differences in the receiver intensity profiles against the varying propagation distance.Conference Object Citation - WoS: 5Citation - Scopus: 9Incoherent Sinusoidal-Gaussian and Annular Beam Scintillations(Spie-int Soc Optical Engineering, 2008) Baykal, Yahya; Eyyuboglu, Halil T.; Cai, YangjianThe scintillation index is evaluated in horizontal turbulent atmospheric optical links for incidences of incoherent cosh-Gaussian (IChG), cos-Gaussian (ICG) and annular (IA) beams. Weak turbulence solution is obtained for a slow detector. Dependence of the intensity fluctuations of the IChG, ICG and IA beams on the link length, source size, wavelength and the structure constant are examined. At all the link lengths, fixed size IChG and ICG beams exhibit lower scintillations for larger absolute displacement parameters. At a fixed link length, IChG beam yields lower fluctuations than the ICG beam having the same absolute displacement parameter. For the same size primary beams, IA beam with narrower ring scintillates less than the IA beam with wider ring, and this holds to be valid for each link length. Investigation of the scintillation versus the source size reveals that increase in the source size lowers the scintillations for all types of the incoherent beams. At the same source size and the same absolute displacement parameter, IChG beams have lower fluctuations than the ICG beams, larger absolute displacement parameters exhibiting lower scintillations at the same source size for both beams. For IA beams, as the size of the primary beam is increased, the scintillations are reduced for all ring sizes, the reduction being pronounced for narrower rings. As the wavelength increases, the scintillations of IChG and ICG beams first increase, then at around the wavelength forming the Fresnel zone, the scintillations start to decrease and eventually for all types of IChG and ICG beams, the scintillation indices merge towards a certain value. Similar behaviour of the scintillations versus the wavelength is observed for IA beams as well. As long as the structure constant is kept within the range of interest to remain in the weak turbulence, raising the structure constant first increases the intensity fluctuations of beams for all the mentioned beam types where further rises in the structure constant result in the same level of scintillation index. Comparison of the scintillations of IChG, ICG and IA beams with their coherent counterparts and the coherent Gaussian beam shows that the IChG, ICG and IA beams are favorable for large sized sources.Conference Object Citation - WoS: 20Citation - Scopus: 33Effect of Beam Types on the Scintillations: a Review(Spie-int Soc Optical Engineering, 2009) Eyyuboglu, Halil T.; Cai, Yangjian; Baykal, YahyaWhen different incidences are launched in atmospheric turbulence, it is known that the intensity fluctuations exhibit different characteristics. In this paper we review our work done in the evaluations of the scintillation index of general beam types when such optical beams propagate in horizontal atmospheric links in the weak fluctuations regime. Variation of scintillation indices versus the source and medium parameters are examined for flat-topped-Gaussian, cosh-Gaussian, cos-Gaussian, annular, elliptical Gaussian, circular (i.e., stigmatic) and elliptical (i.e., astigmatic) dark hollow, lowest order Bessel-Gaussian and laser array beams. For flat-topped-Gaussian beam, scintillation is larger than the single Gaussian beam scintillation, when the source sizes are much less than the Fresnel zone but becomes smaller for source sizes much larger than the Fresnel zone. Cosh-Gaussian beam has lower on-axis scintillations at smaller source sizes and longer propagation distances as compared to Gaussian beams where focusing imposes more reduction on the cosh-Gaussian beam scintillations than that of the Gaussian beam. Intensity fluctuations of a cos-Gaussian beam show favorable behaviour against a Gaussian beam at lower propagation lengths. At longer propagation lengths, annular beam becomes advantageous. In focused cases, the scintillation index of annular beam is lower than the scintillation index of Gaussian and cos-Gaussian beams starting at earlier propagation distances. Cos-Gaussian beams are advantages at relatively large source sizes while the reverse is valid for annular beams. Scintillations of a stigmatic or astigmatic dark hollow beam can be smaller when compared to stigmatic or astigmatic Gaussian, annular and flat-topped beams under conditions that are closely related to the beam parameters. Intensity fluctuation of an elliptical Gaussian beam can also be smaller than a circular Gaussian beam depending on the propagation length and the ratio of the beam waist size along the long axis to that along the short axis (i.e., astigmatism). Comparing against the fundamental Gaussian beam on equal source size and equal power basis, it is observed that the scintillation index of the lowest order Bessel-Gaussian beam is lower at large source sizes and large width parameters. However, for excessively large width parameters and beyond certain propagation lengths, the advantage of the lowest order Bessel-Gaussian beam seems to be lost. Compared to Gaussian beam, laser array beam exhibits less scintillations at long propagation ranges and at some midrange radial displacement parameters. When compared among themselves, laser array beams tend to have reduced scintillations for larger number of beamlets, longer wavelengths, midrange radial displacement parameters, intermediate Gaussian source sizes, larger inner scales and smaller outer scales of turbulence. The number of beamlets used does not seem to be so effective in this improvement of the scintillations.Article Citation - WoS: 4Citation - Scopus: 4The Performance Bounds of an Optical Communication System Using Irradiance Profile Modulation(Taylor & Francis Ltd, 2017) Eyyuboglu, Halil T.We assess the performance bounds of an optical communication system that uses irradiance profile modulation. This modulation is based on the four different orders of vortex beams. To this end, we find the turbulence induced average irradiance profiles of Gaussian, Bessel-Gaussian and modified Bessel-Gaussian vortex beams on the receiver plane. Each one is then cross correlated against the free space equivalents. Plotting the cross-correlation coefficients, it becomes possible to identify the borders of correct decision and error regions, thus, deduce the performance bounds of such a system. When measured in terms of structure constant, i.e. the turbulence strength and the propagation length being fixed to 3km, it is seen that the error region extends beyond the structure constant values of 10(-13) m(-2/3) and higher. There seem to be some variations with the beam type and the order of the vortex beam. The performance of Bessel-Gaussian vortex beam comes out to be slightly better than the rest.