Browsing by Author "Eyyuboglu, Halil T."

Now showing 1 - 20 of 72

Citation - WoS: 4
Citation - Scopus: 29
A 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.; 7688; Elektronik ve Haberleşme Mühendisliği
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.
Citation - WoS: 110
Citation - Scopus: 112
Active laser radar systems with stochastic electromagnetic beams in turbulent atmosphere
(Optica Publishing Group, 2008) Cai, Yangjian; Korotkova, Olga; Eyyuboglu, Halil T.; Baykal, Yahya; 7688; 7812; Elektronik ve Haberleşme Mühendisliği; Elektrik-Elektronik Mühendisliği
Propagation of stochastic electromagnetic beams through paraxial ABCD optical systems operating through turbulent atmosphere is investigated with the help of the ABCD matrices and the generalized Huygens-Fresnel integral. In particular, the analytic formula is derived for the cross-spectral density matrix of an electromagnetic Gaussian Schell-model (EGSM) beam. We applied our analysis for the ABCD system with a single lens located on the propagation path, representing, in a particular case, the unfolded double-pass propagation scenario of active laser radar. Through a number of numerical examples we investigated the effect of local turbulence strength and lens' parameters on spectral, coherence and polarization properties of the EGSM beam. (C) 2008 Optical Society of America
Citation - WoS: 25
Citation - Scopus: 27
Analysis of flat-topped Gaussian vortex beam scintillation properties in atmospheric turbulence
(Spie-soc Photo-optical instrumentation Engineers, 2019) Elmabruk, Kholoud; Eyyuboglu, Halil T.; Elektronik ve Haberleşme Mühendisliği
We analyze the scintillation properties of a flat-topped Gaussian vortex beam propagating in a weakly turbulent atmosphere. We utilize a random phase screen model to perform this analysis. We evaluate the scintillation against the changes of topological charge, beam order, operating wavelength, receiver aperture side length, and source size parameters. The results show that using a flat-topped Gaussian vortex beam with a high topological charge causes a reduction in scintillation. Increasing the receiver aperture side length reduces scintillation level. As the source size increases, scintillation decreases. Our results also indicate that a flat-topped Gaussian vortex beam with high topological charges has less scintillation than the fundamental Gaussian beam. We believe that our findings will be useful in improving the performance of next-generation optical communication links and networks. (C) 2019 Society of Photo-Optical Instrumentation Engineers (SPIE)
Citation - WoS: 0
Citation - Scopus: 0
Analysis of wave structure functions
(Ieee, 2008) Eyyuboglu, Halil T.; 7688; Elektronik ve Haberleşme Mühendisliği
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.
Citation - WoS: 12
Citation - Scopus: 12
Angle-of-arrival fluctuations for general-type beams
(Spie-soc Photo-optical instrumentation Engineers, 2007) Eyyuboglu, Halil T.; Baykal, Yahya; 7688; 7812; Elektronik ve Haberleşme Mühendisliği; Elektrik-Elektronik Mühendisliği
Starting 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.
Citation - WoS: 16
Citation - Scopus: 16
Annular, cosh and cos Gaussian beams in strong turbulence
(Springer Heidelberg, 2011) Eyyuboglu, Halil T.; 7688; Elektronik ve Haberleşme Mühendisliği
For the strong atmospheric turbulence regime, the asymptotic on-axis scintillation behavior of annular, cosh and cos Gaussian beams is theoretically derived and illustrated with numerical examples. It is observed from the plots that annular Gaussian beams exhibit more scintillations than a Gaussian beam, regardless of the amplitude coefficient and source size settings. For small source sizes, cosh Gaussian beams seem to have an advantage over Gaussian beams in terms of reduced scintillation, but for large source sizes a switchover occurs where cos Gaussian beams assume the advantage. Analysis of the effect of inner scale value shows that scintillations increases for all beams as the inner scale increases.
Citation - WoS: 20
Citation - Scopus: 21
Apertured averaged scintillation of fully and partially coherent Gaussian, annular Gaussian, flat toped and dark hollow beams
(Elsevier Science Bv, 2015) Eyyuboglu, Halil T.; 7688; Elektronik ve Haberleşme Mühendisliği
Apertured averaged scintillation requires the evaluation of rather complicated irradiance covariance function. Here we develop a much simpler numerical method based on our earlier introduced semianalytic approach. Using this method, we calculate aperture averaged scintillation of fully and partially coherent Gaussian, annular Gaussian flat topped and dark hollow beams. For comparison, the principles of equal source beam power and normalizing the aperture averaged scintillation with respect to received power are applied. Our results indicate that for fully coherent beams, upon adjusting the aperture sizes to capture 10 and 20% of the equal source power, Gaussian beam needs the largest aperture opening, yielding the lowest aperture average scintillation, whilst the opposite occurs for annular Gaussian and dark hollow beams. When assessed on the basis of received power normalized aperture averaged scintillation, fixed propagation distance and aperture size, annular Gaussian and dark hollow beams seem to have the lowest scintillation. Just like the case of point-like scintillation, partially coherent beams will offer less aperture averaged scintillation in comparison to fully coherent beams. But this performance improvement relies on larger aperture openings. Upon normalizing the aperture averaged scintillation with respect to received power, fully coherent beams become more advantageous than partially coherent ones. (C) 2014 Elsevier B.V. All rights reserved.
Citation - WoS: 53
Citation - Scopus: 58
Average intensity and spreading of an elegant Hermite-Gaussian beam in turbulent atmosphere
(Optical Soc Amer, 2009) Yuan, Yangsheng; Cai, Yangjian; Qu, Jun; Eyyuboglu, Halil T.; Baykal, Yahya; 7688; 7812; Elektronik ve Haberleşme Mühendisliği; Elektrik-Elektronik Mühendisliği
The propagation of an elegant Hermite-Gaussian beam (EHGB) in turbulent atmosphere is investigated. Analytical propagation formulae for the average intensity and effective beam size of an EHGB in turbulent atmosphere are derived based on the extended Huygens-Fresnel integral. The corresponding results of a standard Hermite-Gaussian beam (SHGB) in turbulent atmosphere are also derived for the convenience of comparison. The intensity and spreading properties of EHGBs and SHGBs in turbulent atmosphere are studied numerically and comparatively. It is found that the propagation properties of EHGBs and SHGBs are much different from their properties in free space, and the EHGB and SHGB with higher orders are less affected by the turbulence. What's more, the SHGB spreads more rapidly than the EHGB in turbulent atmosphere under the same conditions. Our results will be useful in long-distance free-space optical communications. (C) 2009 Optical Society of America
Citation - WoS: 112
Citation - Scopus: 115
Average irradiance and polarization properties of a radially or azimuthally polarized beam in a turbulent atmosphere
(Optical Soc Amer, 2008) Cai, Yangjian; Lin, Qiang; Eyyuboglu, Halil T.; Baykal, Yahya; 7688; 7812; Elektronik ve Haberleşme Mühendisliği; Elektrik-Elektronik Mühendisliği
Analytical formulas are derived for the average irradiance and the degree of polarization of a radially or azimuthally polarized doughnut beam (PDB) propagating in a turbulent atmosphere by adopting a beam coherence-polarization matrix. It is found that the radial or azimuthal polarization structure of a radially or azimuthally PDB will be destroyed (i.e., a radially or azimuthally PDB is depolarized and becomes a partially polarized beam) and the doughnut beam spot becomes a circularly Gaussian beam spot during propagation in a turbulent atmosphere. The propagation properties are closely related to the parameters of the beam and the structure constant of the atmospheric turbulence. (C) 2008 Optical Society of America.
Citation - WoS: 1
Citation - Scopus: 7
Beam Wander Characteristics of Flat-Topped, Dark Hollow, Cos and Cosh-Gaussian, J(0)- And I-0- Bessel Gaussian Beams Propagating In Turbulent Atmosphere: A Review
(Spie-int Soc Optical Engineering, 2010) Eyyuboglu, Halil T.; Baykal, Yahya; Cil, Celal Z.; Korotkova, Olga; Cai, Yangjian; 7812; 7688; Elektronik ve Haberleşme Mühendisliği; Elektrik-Elektronik Mühendisliği
In this paper we review our work done in the evaluations of the root mean square (rms) beam wander characteristics of the flat-topped, dark hollow, cos-and cosh Gaussian, J(0)-Bessel Gaussian and the I-0-Bessel Gaussian beams in atmospheric turbulence. Our formulation is based on the wave-treatment approach, where not only the beam sizes but the source beam profiles are taken into account as well. In this approach the first and the second statistical moments are obtained from the Rytov series under weak atmospheric turbulence conditions and the beam size are determined as a function of the propagation distance. It is found that after propagating in atmospheric turbulence, under certain conditions, the collimated flat-topped, dark hollow, cos-and cosh Gaussian, J(0)-Bessel Gaussian and the I-0-Bessel Gaussian beams have smaller rms beam wander compared to that of the Gaussian beam. The beam wander of these beams are analyzed against the propagation distance, source spot sizes, and against specific beam parameters related to the individual beam such as the relative amplitude factors of the constituent beams, the flatness parameters, the beam orders, the displacement parameters, the width parameters, and are compared against the corresponding Gaussian beam.
Citation - WoS: 10
Citation - Scopus: 11
Bit error rate analysis of Gaussian, annular Gaussian, cos Gaussian, and cosh Gaussian beams with the help of random phase screens
(Optical Soc Amer, 2014) Eyyuboglu, Halil T.; 7688; Elektronik ve Haberleşme Mühendisliği
Using the random phase screen approach, we carry out a simulation analysis of the probability of error performance of Gaussian, annular Gaussian, cos Gaussian, and cosh Gaussian beams. In our scenario, these beams are intensity-modulated by the randomly generated binary symbols of an electrical message signal and then launched from the transmitter plane in equal powers. They propagate through a turbulent atmosphere modeled by a series of random phase screens. Upon arriving at the receiver plane, detection is performed in a circuitry consisting of a pin photodiode and a matched filter. The symbols detected are compared with the transmitted ones, errors are counted, and from there the probability of error is evaluated numerically. Within the range of source and propagation parameters tested, the lowest probability of error is obtained for the annular Gaussian beam. Our investigation reveals that there is hardly any difference between the aperture-averaged scintillations of the beams used, and the distinctive advantage of the annular Gaussian beam lies in the fact that the receiver aperture captures the maximum amount of power when this particular beam is launched from the transmitter plane. (C) 2014 Optical Society of America
Citation - WoS: 28
Citation - Scopus: 28
Bit error rates for general beams
(Optical Soc Amer, 2008) Arpali, Serap Altay; Eyyuboglu, Halil T.; Baykal, Yahya; 51304; 7688; 7812; Elektronik ve Haberleşme Mühendisliği; Elektrik-Elektronik Mühendisliği
In order to analyze the effect of beam type on free space optical communication systems, bit error rate (BER) values versus signal-to-noise ratio (SNR) are calculated for zero order and higher order general beam types, namely for Gaussian, cos-Gaussian, cosh-Gaussian, and annular beams. BER analysis is based on optical scintillation using log-normal distribution for the intensity, which is valid in weak atmospheric turbulence. BERs for these beams are plotted under variations of propagation length, source size, wavelength of operation, and order of the beam. According to our graphical outputs, at small source sizes and long propagation distances, the smallest BER value is obtained for the annular beam. On the other hand, at large source size and small propagation distance, the smallest BER value is obtained for the cos-Gaussian beam, Moreover, our study of the order of the beam shows that higher order beams have lower BER values than the zero order beams at longer propagation distances. But this drop compared with the order seems to be incremental. (c) 2008 Optical Society of America
Citation - WoS: 4
Citation - Scopus: 4
Complex degree of coherence and power moments of cylindrical sinc Gaussian beam
(Elsevier Science Bv, 2015) Eyyuboglu, Halil T.; 7688; Elektronik ve Haberleşme Mühendisliği
Complex degree of coherence and power moment aspects of cylindrical sinc Gaussian beam are investigated. To do this, we have used the random phase screen approach. It is seen that on the source plane, cylindrical sinc Gaussian beam has zero on-axis intensity and the sidelobes resemble the sinc or the Gaussian profile depending on the relative magnitudes of width parameter and the source size. Upon propagation in turbulent atmosphere, the initially flat complex degree of coherence becomes curved as the beam propagates, it then partially follows the intensity profile, and eventually turns into a delta function. Power moments are evaluated up to the fifth degree and over two different aperture sizes. In the aperture size of pointlike scintillations, the behaviors of power moments are similar to those of intensity moments. In aperture averaging conditions however, the differences between the variations of moments with respect to the propagation distance and degree of the moments become much less. (C) 2015 Elsevier B.V. All rights reserved.
Citation - WoS: 64
Citation - Scopus: 70
Complex degree of coherence for partially coherent general beams in atmospheric turbulence
(Optical Soc Amer, 2007) Eyyuboglu, Halil T.; Baykal, Yahya; Cai, Yangjian; 7688; 7812; Elektronik ve Haberleşme Mühendisliği; Elektrik-Elektronik Mühendisliği
With 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.
Citation - WoS: 79
Citation - Scopus: 83
Convergence of general beams into Gaussian intensity profiles after propagation in turbulent atmosphere
(Elsevier Science Bv, 2006) Eyyuboglu, Halil T.; Baykal, Yahya; Sermutlu, Emre; 7688; 7812; 17647; Matematik; Elektronik ve Haberleşme Mühendisliği; Elektrik-Elektronik Mühendisliği
It is shown that a general shaped laser beam will eventually approach a Gaussian average intensity profile after propagation in turbulent atmosphere. In our formulation, source field at the exit plane of the laser is taken as the product of arbitrary functions of source transverse coordinates with Gaussian exponential modulations. Following the expansion of the arbitrary functions in terms of Hermite polynomials, the average receiver intensity expression is derived using the extended Huygens-Fresnel principle and the conditions for the intensity profile to assume a Gaussian shape are stated. The results are illustrated by simulating various source field distributions. (c) 2006 Elsevier B.V. All rights reserved.
Citation - WoS: 2
Citation - Scopus: 2
Correction of amplitude distortions for truncated Bessel beam and SER estimation for 4ASK
(Taylor & Francis Ltd, 2016) Eyyuboglu, Halil T.; 7688; Elektronik ve Haberleşme Mühendisliği
We apply amplitude corrections to a truncated Bessel beam that has propagated through turbulent atmosphere modelled by random phase screens. These corrections are realized via transmitting an unmodulated beam in parallel to the one carrying the 4 amplitude shift keying (ASK) modulated message signal. On the receiver side, the amplitude corrections are obtained by dividing the intensity of the unmodulated beam by its free space equivalence. The corrections are then used to restore the amplitude distortions of the beam carrying the 4ASK modulated message signal and in the determination of decision boundaries for the received 4ASK symbols. The success of the system is visually inspected by comparing the received intensity profiles before and after the application of corrections. Furthermore, simulation analysis of symbol error rate (SER) is made, where the proposed set-up is found to be quite insensitive to wavelength difference between the unmodulated and modulated beams. On the other hand, the difference in the structure constant values of these two beams seems to have profound effect on system performance.
Citation - WoS: 2
Citation - Scopus: 0
Diffraction properties of partially coherent elegant high-order beam
(Electromagnetics Acad, 2010) Wang, Fei; Cai, Yangjian; Eyyuboglu, Halil T.; Baykal, Yahya; 7688; 7812; Elektronik ve Haberleşme Mühendisliği; Elektrik-Elektronik Mühendisliği
The 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.
Citation - WoS: 20
Citation - Scopus: 33
Effect of beam types on the scintillations: A review
(Spie-int Soc Optical Engineering, 2009) Baykal, Yahya; Eyyuboglu, Halil T.; Cai, Yangjian; 7812; 7688; Elektronik ve Haberleşme Mühendisliği; Elektrik-Elektronik Mühendisliği
When 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.
Citation - WoS: 28
Citation - Scopus: 30
Estimation of aperture averaged scintillations in weak turbulence regime for annular, sinusoidal and hyperbolic Gaussian beams using random phase screen
(Elsevier Sci Ltd, 2013) Eyyuboglu, Halil T.; 7688; Elektronik ve Haberleşme Mühendisliği
Using the random phase screen method, aperture averaged scintillations for annular, sinusoidal and hyperbolic Gaussian beams are estimated. Prior to this estimation, the designed random phase screen setup is tested against the known results of the existing literature from the aspects of receiver intensity distribution, point-like scintillation index and aperture averaged scintillation of spherical and Gaussian beam waves. Having obtained satisfactory results, we then proceed to estimate aperture averaged scintillations for annular, sinusoidal and hyperbolic Gaussian beams. Our findings indicate that at a fixed aperture radius of 5 cm, sine Gaussian beam exhibits the highest scintillation, annular Gaussian beam has on the other hand has the lowest scintillations. When examined against varying aperture sizes, the scintillation ordering of beams does not change. Furthermore, although larger aperture sizes achieve substantial scintillation reductions, the rate of reductions gradually become smaller. (C) 2013 Elsevier Ltd. All rights reserved.
Citation - WoS: 61
Citation - Scopus: 66
Evolution of the degree of polarization of an electromagnetic Gaussian Schell-model. beam in a Gaussian cavity
(Optical Soc Amer, 2008) Yao, Min; Cai, Yangjian; Eyyuboglu, Halil T.; Baykal, Yahya; Korotkova, Olga; 7688; 7812; Elektronik ve Haberleşme Mühendisliği; Elektrik-Elektronik Mühendisliği
The interaction of an electromagnetic Gaussian Schell-model (EGSM) beam with a Gaussian cavity is analyzed. In particular, the evolution of the degree of polarization of the EGSM beam is investigated. The results show that the behavior of the degree of polarization depends on both the statistical properties of the source that generates the EGSM beam and the parameter of the cavity. (C) 2008 Optical Society of America