Browsing by Author "Baykal, Y."

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Citation - WoS: 0
Citation - Scopus: 0
Analysis of Field Correlations in Atmospheric Optical MIMO Systems
(Institute of Electrical and Electronics Engineers Inc., 2014) Baykal, Y.; Uysal, M.
In this paper, we evaluate the absolute field correlations for a free space optical (FSO) multiple-input multiple-output (MIMO) link operating in a turbulent atmosphere. Such knowledge is needed in heterodyne reception to keep all the optical detectors within the region in which a predefined correlation value is fulfilled. The variations of the absolute field correlations versus the longest distance between the detectors are found for different array, medium and receiver parameters such as the number of beamlets, the radius of the radial array, beamlet size, link length, wavelength, structure constant and the position of the detectors. © 2014 IEEE.
Citation - WoS: 22
Citation - Scopus: 23
Annular beam scintillations in non-Kolmogorov weak turbulence
(Springer, 2012) Gercekcioglu, H.; Baykal, Y.; 7812
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.
Citation - WoS: 72
Citation - Scopus: 78
Average intensity and spreading of partially coherent standard and elegant Laguerre-Gaussian beams in turbulent atmosphere
(Emw Publishing, 2010) Wang, F.; Cai, Y.; Eyyuboglu, H. T.; Baykal, Y.; 7688; 7812
Analytical expressions for the average intensity, mean-squared beam width and angular spread of partially coherent standard and elegant Laguerre-Gaussian (LG) beams propagating in turbulent atmosphere are derived. The properties of the average intensity, spreading and directionality of partially coherent standard and elegant LG beams in turbulent atmosphere are studied numerically and comparatively. It is found that the beam parameters and structure constant of turbulence together determine the properties of the beams in turbulent atmosphere. Partially coherent standard and elegant LG beams with smaller coherence length, larger beam orders and longer wavelength are less affected by the turbulence. A partially coherent elegant LG beam is less affected by turbulence than a partially coherent standard LG beam under the same condition. Furthermore, it is found that there exist equivalent partially coherent standard and elegant LG beams, equivalent fully coherent standard and elegant LG beams, equivalent Gaussian Schell-model beams that may have the same directionality as a fully coherent Gaussian beam both in free space and in turbulent atmosphere. Our results will be useful in long distance free-space optical communications.
Citation - WoS: 26
Citation - Scopus: 26
Beam wander characteristics of cos and cosh-Gaussian beams
(Springer, 2009) Cil, C. Z.; Eyyuboglu, H. T.; Baykal, Y.; Cai, Y.; 7688; 7812; Elektronik ve Haberleşme Mühendisliği
Within the context of a general beam formulation, beam wander characteristics of cos and cosh-Gaussian beams are derived and numerically evaluated. In our graphs, the fundamental Gaussian beam is used as a benchmark for comparisons. The associated plots reveal that at small source sizes, a cos-Gaussian beam has the lowest beam wander, while this property is enhanced with increasing values of the displacement parameter. At large source sizes however, this advantage is taken over by cosh-Gaussian beam. Joint examination against the changing source sizes and propagation lengths shows that the range of source sizes, where the beam wander of cos-Gaussian beam remains lower, is enlarged as we go toward higher propagation lengths. Asymmetric beams tend to exhibit higher beam wanders both at small and large source sizes, but for the intermediate source size ranges, the beam wanders of asymmetric beams will fall below those of the symmetric beams. Explanations concerning these behaviors are offered. A historical account of beam wander formulation is also included.
Citation - WoS: 26
Citation - Scopus: 27
Beam Wander of J (0)- and I (0)-Bessel Gaussian Beams Propagating In Turbulent Atmosphere
(Springer, 2010) Cil, C. Z.; Eyyuboglu, H. T.; Baykal, Y.; Korotkova, O.; Cai, Y.; 7812; 7688; Elektronik ve Haberleşme Mühendisliği
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.
Beam wander of J 0- and i 0-Bessel Gaussian beams propagating in turbulent atmosphere
(2010) Çil, C.Z.; Eyyuboğlu, H.T.; Baykal, Y.; Korotkova, O.; Cai, Y.; 7812
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.
Citation - Scopus: 0
Ber of Annular Beams in Strong Turbulence
(Optical Society of America (OSA), 2010) Gerçekcioglu, H.; Baykal, Y.; Eyyuboglu, H.T.; 7688; 7812
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.
Citation - WoS: 13
Citation - Scopus: 17
Correlation properties of random electromagnetic beams in laser resonators
(Springer Heidelberg, 2009) Tong, Z.; Korotkova, O.; Cai, Y.; Eyyuboglu, H. T.; Baykal, Y.; 7688; 7812
With the help of the generalized Huygens-Fresnel principle and the tensor approach for electromagnetic stochastic beams we investigate the behavior of their two-point spatial correlation properties on interaction with a laser resonator. In particular, the evolution of the degree of coherence, of the degree of cross-polarization and of the intensity correlations (at one and two points in space) is analyzed for typical beams and cavities. The theory is illustrated by numerical curves pertaining to various correlation properties of typical electromagnetic Gaussian Schell-model beams.
Citation - WoS: 59
Citation - Scopus: 64
Degree of polarization for partially coherent general beams in turbulent atmosphere
(Springer, 2007) Eyyuboglu, H. T.; Baykal, Y.; Cai, Y.; 7688; 7812
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.
Citation - Scopus: 0
Effects of type of incidence on the second and fourth order moment parameters evaluated in turbulent atmosphere
(2010) Baykal, Y.; 7812; Elektrik-Elektronik Mühendisliği
Using a general type incidence, the second and fourth order moments are formulated in atmospheric turbulence. Received field and intensity correlations are evaluated and the behaviour of these correlations are compared for different beam types. © 2010 OSA/FiO/LS.
Citation - Scopus: 0
Expert systems in access telecommunication networks
(2009) Şahin, S.; Tolun, M.R.; Baykal, Y.
Access telecommunication systems are categorized as digital subscriber line (xDSL), fiber-to-the-home (FTTH), hybrid fiber-coaxial (HFC), power line systems, local multipoint distribution system (LMDS), free space optics (FSO), satellite and worldwide interoperability for microwave access (WIMAX) systems. Basic specifications, such as the rate of information for upstream and downstream, access link length, frequency licence requirement for these access telecommunication networks are defined. Expert system analysis is applied to find out the possible systems that can be employed among the abovementioned choices of access telecommunication within the user defined inputs describing the requirements of the end user. The rule-based structure of the expert system is formed by using the Exsys expert system development tool. © 2008 IEEE.
Citation - WoS: 1
Citation - Scopus: 0
Formulation of scintillations for optical incidence of arbitrary field profile
(Electromagnetics Acad, 2008) Baykal, Y.; Eyyuboglu, H. T.; Cai, Y.; 7812; 7688
Scintillation 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.
Citation - WoS: 12
Citation - Scopus: 13
Generalized tensor ABCD law for an elliptical Gaussian beam passing through an astigmatic optical system in turbulent atmosphere
(Springer, 2009) Cai, Yangjian; Lin, Q.; Eyyuboglu, H. T.; Baykal, Y.; 7688; 7812
The propagation of an elliptical Gaussian beam (EGB) through an astigmatic ABCD optical system in a turbulent atmosphere is investigated. An analytical formula for the average intensity of an EGB and a generalized tensor ABCD law for the generalized complex curvature tensor are derived. As an application example, we derived an analytical formula for the average intensity of an elliptical flat-topped beam propagating through an astigmatic ABCD optical system in a turbulent atmosphere. As a numerical example, the focusing properties of an EGB focused by a thin lens in a turbulent atmosphere are studied. It is found that the focused beam at the focal plane becomes a circular Gaussian beam when the atmospheric turbulence is strong enough, and the beam width of the circular Gaussian beam is determined by atmospheric turbulence strength, focal length of the thin lens, and wavelength of the initial beam but is independent of the initial beam widths (i.e., initial intensity distribution).
Citation - Scopus: 68
Influence 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.
Citation - WoS: 57
Citation - Scopus: 62
Intensity fluctuations in J-Bessel-Gaussian beams of all orders propagating in turbulent atmosphere
(Springer, 2008) Eyyuboglu, H. T.; Sermutlu, E.; Baykal, Y.; Cai, Y.; Korotkova, O.; 7688; 17647; 7812; Matematik
The scintillation index of a J (n) -Bessel-Gaussian beam of any order propagating in turbulent atmosphere is derived and numerically evaluated at transverse cross-sections with the aid of a specially designed triple integral routine. The graphical outputs indicate that, just like the previously investigated J (0)-Bessel-Gaussian beam, higher-order members of the family also offer favorable scintillation characteristics at large source sizes. This advantage is maintained against rising beam orders. Viewed along the propagation axis, beams with lower orders and smaller widths exhibit smaller values of the scintillation index at shorter propagation distances and large values at longer propagation distances. Further, it is shown that the scintillation index of the J (n) -Bessel-Gaussian beams (n > 0) is larger than that of the fundamental Gaussian and the J (0)-Bessel-Gaussian beams only near the on-axis points, while remaining smaller towards the edges of the beam.
Citation - WoS: 28
Citation - Scopus: 31
Intensity fluctuations of partially coherent laser beam arrays in weak atmospheric turbulence
(Springer, 2011) Arpali, C.; Arpali, S. A.; Baykal, Y.; Eyyuboglu, H. T.; 7812; 7688
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.
Citation - Scopus: 0
Multimode Laser Beam Field Correlations for Vertical Links Operating in Oceanic Turbulence
(Institute of Electrical and Electronics Engineers Inc., 2025) Gercekcioglu, H.; Baykal, Y.; Gokce, M.C.
In underwater optical vertical link medium, based on the extended Huygens-Fresnel principle, multimode laser beam field correlation is derived and evaluated analytically in the Atlantic Ocean at high latitude and high latitude- low latitudes. With the depth of seawater, the coherence length of a spherical wave operating in the underwater turbulent medium is demonstrated for the range of 0-4000 m. By utilizing the coherence length varying with parameters such as the rate of dissipation of turbulent kinetic energy per unit mass of fluid ε, the rate of dissipation of the mean squared temperature χT and nondimensional representing the relative strength of temperature and salinity fluctuations ω, which depend on depth, the field correlation is examined in detail for single modes and multimode. Their variations are exhibited. Our results indicate clearly that as the mode increases, field correlation gets better. © 1965-2012 IEEE.
Citation - WoS: 13
Citation - Scopus: 17
Partially coherent elegant Hermite-Gaussian beam in turbulent atmosphere
(Springer, 2011) Wang, F.; Cai, Y.; Eyyuboglu, H. T.; Baykal, Y.; 7688; 7812
Based on the extended Huygens-Fresnel integral, analytical formulas for the cross-spectral density, mean-squared beam width and angular spread of a partially coherent elegant Hermite-Gaussian (HG) beam in turbulent atmosphere are derived. The evolution properties of the average intensity, spreading and directionality of a partially coherent elegant HG beam in turbulent atmosphere are studied numerically. It is found that the partially coherent elegant HG beam with smaller initial coherence width, larger beam order and longer wavelength is less affected by the atmospheric turbulence. Compared to the partially coherent standard HG beam, the partially coherent elegant HG beam is less affected by turbulence under the same condition. Furthermore, it is found that there exist equivalent partially coherent standard and elegant HG beams, equivalent fully coherent standard and elegant HG beams, and an equivalent Gaussian-Schell-model beam may have the same directionality as a fully coherent Gaussian beam whether in free space or in turbulent atmosphere. Our results can be utilized in short and long atmospheric optical communication systems.
Citation - WoS: 12
Citation - Scopus: 14
Partially coherent elegant Hermite-Gaussian beams
(Springer Heidelberg, 2010) Wang, F.; Cai, Y.; Eyyuboglu, H. T.; Baykal, Y.; Cil, C. Z.; 7688; 7812; Elektronik ve Haberleşme Mühendisliği
Elegant Hermite-Gaussian beams (EHGBs) are extended to the partially coherent case. An explicit and analytical formula is derived for the cross-spectral density of a partially coherent EHGB propagating through an aligned or misaligned paraxial ABCD optical system. The propagation properties of a partially coherent EHGB in free space and its focusing properties through a thin lens are studied numerically, and are compared to those of a partially coherent standard Hermite-Gaussian beam (SHGB). It is found that the propagation and focusing properties of a partially coherent EHGB are closely related to its initial coherence. A partially coherent EHGB spreads slower than a partially coherent SHGB in free-space propagation. A partially coherent EHGB can be focused more tightly than a partially coherent SHGB.
Citation - WoS: 130
Citation - Scopus: 151
Propagation of laser array beams in a turbulent atmosphere
(Springer Heidelberg, 2007) Cai, Y.; Chen, Y.; Eyyuboglu, H. T.; Baykal, Y.; 7688; 7812
The propagation of phase-locked and non-phase-locked laser array beams of radial and rectangular symmetries in a turbulent atmosphere are investigated based on the extended Huygens-Fresnel integral. The beamlet used in our paper for constructing the laser array beams is of elliptical Gaussian mode. Analytical formulae for the average irradiance of phase-locked and non-phase-locked radial and rectangular laser array beams are derived through vector integration and tensor operation. The irradiance properties of these laser array beams in a turbulent atmosphere are studied numerically. It is found that both phase-locked and non-phase-locked radial and rectangular laser array beams eventually become circular Gaussian beams in a turbulent atmosphere, which is much different from their propagation properties in free space. The propagation properties are closely related to the parameters of laser array beams and the structure constant of the turbulent atmosphere.