Elektronik ve Haberleşme Mühendisliği Bölümü Yayın Koleksiyonu

Permanent URI for this collectionhttps://hdl.handle.net/20.500.12416/260

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Now showing 1 - 14 of 14

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.
Citation - WoS: 16
Citation - Scopus: 16
Annular, Cosh and Cos Gaussian Beams in Strong Turbulence
(Springer Heidelberg, 2011) Eyyuboglu, Halil T.
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.
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: 11
Citation - Scopus: 12
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.
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: 4
Citation - Scopus: 4
Complex Degree of Coherence and Power Moments of Cylindrical Sinc Gaussian Beam
(Elsevier Science Bv, 2015) Eyyuboglu, Halil T.
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: 2
Citation - Scopus: 2
Correction of Amplitude Distortions for Truncated Bessel Beam and Ser Estimation for 4ask
(Taylor & Francis Ltd, 2016) Eyyuboglu, Halil T.
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: 30
Citation - Scopus: 31
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.
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: 1
Citation - Scopus: 1
Mode Coupling in Vortex Beams
(Elsevier Sci Ltd, 2018) Eyyuboglu, Halil T.
We examine the mode coupling in vortex beams. Mode coupling also known as the crosstalk takes place due to turbulent characteristics of the atmospheric communication medium. This way, the transmitted intrinsic mode of the vortex beam leaks power to other extrinsic modes, thus preventing the correct detection of the transmitted symbol which is usually encoded into the mode index or the orbital angular momentum state of the vortex beam. Here we investigate the normalized power mode coupling ratios of several types of vortex beams, namely, Gaussian vortex beam, Bessel Gaussian beam, hypergeometric Gaussian beam and Laguerre Gaussian beam. It is found that smaller mode numbers lead to less mode coupling. The same is partially observed for increasing source sizes. Comparing the vortex beams amongst themselves, it is seen that hypergeometric Gaussian beam is the one retaining the most power in intrinsic mode during propagation, but only at lowest mode index of unity. At higher mode indices this advantage passes over to the Gaussian vortex beam. (C) 2017 Elsevier Ltd. All rights reserved.
Citation - WoS: 13
Citation - Scopus: 13
Per Unit Received Power Apertured Averaged Scintillation of Partially Coherent Sinusoidal and Hyperbolic Gaussian Beams
(Elsevier Sci Ltd, 2015) Eyyuboglu, Halil T.
We evaluate the per unit power received power aperture averaged scintillation performance of fully and partially coherent sinusoidal and hyperbolic Gaussian beams. Our analysis includes fundamental Gaussian, cosh Gaussian, cos Gaussian and annular Gaussian beams. The method is based on our earlier introduced semi-analytic approach. Scintillation performance is measured upon dividing the aperture averaged scintillation by the received power. Assessment is made both for aperture sizes that are adjusted separately for full and partially coherent beams to capture 10% and 20% of the equal source power and also for fixed aperture sizes. This way, the scintillation performance of the different beams in question is compared. From this comparison, we find that partially coherent beams have lower scintillation than the fully coherent ones, when adjustable aperture size is used. But upon switching to fixed aperture size, the reverse happens and coherent beams become more advantageous. In all cases of comparison, small source sized annular Gaussian beam and large source sized Gaussian beam seem to offer the lowest scintillation when aperture size is adjusted to capture 20% of the equal source power. (C) 2015 Elsevier Ltd. All rights reserved.
Citation - WoS: 4
Citation - Scopus: 4
The 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.
Citation - WoS: 33
Citation - Scopus: 38
Propagation Analysis of Ince-Gaussian Beams in Turbulent Atmosphere
(Optical Soc Amer, 2014) Eyyuboglu, Halil T.
We analyze the properties of Ince-Gaussian beams propagating in turbulent atmosphere. Due to analytic difficulties, this analysis is done with the aid of a random phase screen setup. Intensity profile, beam size, and the kurtosis parameter are evaluated against the changes in beam orders, propagation distance, and turbulence levels. It is found that when propagating in turbulence, Ince-Gaussian beams will no longer keep their beam profile invariant like in free space but will experience beam profile changes. These changes will cause additional beam spreading, as well as an increase in beam size and the kurtosis parameter. (C) 2014 Optical Society of America
Citation - WoS: 15
Citation - Scopus: 17
Scintillation Analysis of Hypergeometric Gaussian Beam Via Phase Screen Method
(Elsevier, 2013) Eyyuboglu, Halil T.
We give a scintillation treatment of hypergeometric Gaussian beams via the use of random phase screens. In particular, we analyse the on-axis, point-like and aperture averaged power scintillation characteristics of this beam that cannot be undertaken easily by analytic means. Within the range of examined source and propagation parameters, our evaluations show that there will be less scintillation, with increasing hollowness at small source sizes and zero topological charge. At larger source sizes or topological charges, this is reversed and decreasing hollowness will reduce scintillation. More or less the same trend is observed for aperture averaging such that at small source sizes and zero topological charge, increased hollowness will result in lower scintillation. At larger source size and topological charges, there will be a transition from the case of smaller values of hollowness giving rise to less scintillation at smaller aperture openings to the case of larger values of hollowness giving rise to less scintillation at larger aperture openings. In general nonzero topological charges will produces more scintillations, both in on-axis and aperture averaged cases. (C) 2013 Elsevier B.V. All rights reserved.
Citation - WoS: 40
Citation - Scopus: 45
Scintillation Behavior of Airy Beam
(Elsevier Sci Ltd, 2013) Eyyuboglu, Halil T.
We make an analysis on scintillation behavior of Airy beam using the Rytov method. To this end, scintillation index is formulated for a single receiver coordinate location. Area scintillation expressions are also derived. At peaks of receiver intensity, Airy beam is found to offer quite less scintillation at width values of around 1.6 cm. Furthermore, smaller values of the exponential truncation factor are also seen to cause less scintillation. When compared to Gaussian beam, on equal source and received power basis, it is observed that Airy beam will generally have less area scintillation. (C) 2012 Elsevier Ltd. All rights reserved.
Citation - WoS: 5
Citation - Scopus: 6
Scintillations of Multiwavelength Gaussian, Cos, Cosh and Annular Gaussian Beams
(Springer Heidelberg, 2012) Eyyuboglu, Halil T.
We provide the scintillation formulation for a multiwavelength source. Within this context, the scintillation aspects of Gaussian, cos, cosh and annular Gaussian beams are investigated. For all situations examined, it is found that for a source comprising many wavelengths, there will be less scintillations as compared to a single wavelength source of the lowest wavelength and but the reverse will be true if the comparison is with respect to the single wavelength source of the highest wavelength. The same is observed at all propagation distances, source sizes, on-axis and off-axis positions considered. Additionally, it is seen that the scintillation characteristics of multiwavelength sources will follow similar trends of single wavelength sources. The analysis is based on the Rytov approximation, therefore our results are valid for conditions of weak atmospheric turbulence.

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