PubMed İndeksli Yayınlar Koleksiyonu

Permanent URI for this collectionhttps://hdl.handle.net/20.500.12416/8650

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Now showing 1 - 20 of 33

Citation - WoS: 10
Citation - Scopus: 13
Adaptive Optics Corrections of Scintillations of Hermite-Gaussian Modes in an Oceanic Medium
(Optical Soc Amer, 2020) Baykal, Yahya
Adaptive optics correction of the scintillation index is found when Hermite-Gaussian laser beams are used in oceanic turbulence. Adaptive optics filter functions are used to find how the tilt, focus, astigmatism, coma, and total correction will behave under high order mode excitation. Reduction of the oceanic scintillation under various oceanic turbulence and system parameters is examined under different high order modes. Also, the effects of the source size, wavelength, and link length on the total adaptive optics correction of Hermite-Gaussian modes in an oceanic medium are investigated for different modes. (C) 2020 Optical Society of America
Citation - WoS: 127
Citation - Scopus: 135
Average Intensity and Spreading of Cosh-Gaussian Laser Beams in the Turbulent Atmosphere
(Optical Soc Amer, 2005) Eyyuboglu, HT; Baykal, Y
The average intensity and spreading of cosh-Gaussian laser beams in the turbulent atmosphere are examined. Our research is based principally on formulating the average-intensity profile at the receiver plane for cosh-Gaussian excitation. The limiting cases of our formulation for the average intensity are found to reduce correctly to the existing Gaussian beam wave result in turbulence and the cosh-Gaussian beam result in free space (in the absence of turbulence). The average intensity and the broadening of the cosh-Gaussian beam wave after it propagates in the turbulent atmosphere are numerically evaluated versus source size, beam displacement, link length, structure constant, and two wavelengths of 0.85 and 1.55 mum, which are most widely used in currently employed free-space-optical links. Results indicate that in turbulence the beam is widened beyond its free-space diffraction values. At the receiver plane, analogous to the case of free space, this diffraction eventually leads to transformation of the cosh-Gaussian beam into an oscillatory average-intensity profile with a Gaussian envelope. (C) 2005 Optical Society of America.
Citation - WoS: 4
Citation - Scopus: 4
Beam Diffraction by a Resistive Half-Plane
(Optical Soc Amer, 2015) Umul, Yusuf Ziya
The scattering of a Gaussian beam by a resistive half-screen is investigated. Far-field approximation is used in evaluation of geometrical optics and diffracted waves. The uniform expression of the diffracted waves by the resistive half-plane, which was found with the Sommerfeld-Maliuzhinets method, is obtained. The scattered fields for the case of the beam incidence are evaluated with the technique of a complex point source. The resultant wave expressions are examined numerically. (C) 2015 Optical Society of America
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: 28
Citation - Scopus: 28
Bit Error Rates for General Beams
(Optical Soc Amer, 2008) Arpali, Serap Altay; Eyyuboglu, Halil T.; Baykal, Yahya
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: 36
Citation - Scopus: 39
Effect of Anisotropy on Bit Error Rate for an Asymmetrical Gaussian Beam in a Turbulent Ocean
(Optical Soc Amer, 2018) Ata, Yalcin; Baykal, Yahya
Effect of anisotropy on the average bit error rate (BER) is investigated when an asymmetrical Gaussian beam is propagated in an anisotropic turbulent ocean. BER is found to decrease in response to an increase in anisotropy levels in the x and y directions. Higher average signal-to-noise ratio, wavelength, and microscale length yield smaller BER values. BER starts to rise with an increase in the asymmetrical beam source size in the x and y directions, source size ratio in the x and y directions, salinity and temperature contribution factor, the dissipation of the mean squared temperature, and the propagation distance. At the fixed source size ratio in the x and y directions of the asymmetrical beam source size, larger source sizes increase BER. An anisotropic turbulent ocean seems to exhibit better BER values as compared with an isotropic turbulent ocean. (c) 2018 Optical Society of America
Citation - WoS: 9
Citation - Scopus: 11
Effect of Strong Atmospheric Non-Kolmogorov Turbulence on the M-Ary Psk Subcarrier Intensity Modulated Free Space Optical Communications System Performance
(Optical Soc Amer, 2019) Baykal, Yahya; Gokce, Muhsin C.; Ata, Yalcin
Atmospheric turbulence is one of the significant phenomena that degrades the free space optical (FSO) communications system performance, and thus designers need to define the requirements related to turbulence and optimize the system design to ensure optimum performance. The subcarrier intensity modulation (SIM) shows superiority in terms of bandwidth usage over the other modulation techniques. Performance of FSO communication systems exercising M-ary phase-shift-keying (PSK) SIM with the PIN photodiode receiver is evaluated in non-Kolmogorov strong atmospheric turbulence when a Gaussian beam is used as the excitation. Bit-error-rate (BER) of PSK SIM FSO communication systems is examined, and the results are presented versus the non-Kolmogorov atmospheric turbulence and positive-intrinsic-negative (PIN) photodetector parameters such as PIN photodetector responsivity, equivalent load resistor, modulation order, noise factor, bandwidth, propagation distance, and beam source size. (C) 2019 Optical Society of America
Citation - WoS: 50
Citation - Scopus: 55
Expressing Oceanic Turbulence Parameters by Atmospheric Turbulence Structure Constant
(Optical Soc Amer, 2016) Baykal, Yahya
The parameters composing oceanic turbulence are the wavelength, link length, rate of dissipation of kinetic energy per unit mass of fluid, rate of dissipation of mean-squared temperature, Kolmogorov microscale, and the ratio of temperature to salinity contributions to the refractive index spectrum. The required physical entities such as the average intensity and the scintillation index in the oceanic medium are formulated by using the power spectrum of oceanic turbulence, which is described by oceanic turbulence parameters. On the other hand, there exists a rich archive of formulations and results for the above-mentioned physical entities in atmospheric turbulence, where the parameters describing the turbulence are the wavelength, the link length, and the structure constant. In this paper, by equating the spherical wave scintillation index solutions in the oceanic and atmospheric turbulences, we have expressed the oceanic turbulence parameters by an equivalent structure constant used in turbulent atmosphere. Such equivalent structure constant will help ease reaching solutions of similar entities in an oceanic turbulent medium by employing the corresponding existing solutions, which are valid in an atmospheric turbulent medium. (C) 2016 Optical Society of America
Citation - WoS: 14
Citation - Scopus: 15
Field Correlation of Spherical Wave in Underwater Turbulent Medium
(Optical Soc Amer, 2014) Ata, Yalcin; Baykal, Yahya
The absolute field correlation of the spherical wave in an underwater turbulent medium is investigated at the receiver plane by using the extended Huygens-Fresnel principle. Results denote that increase in the propagation distance, the rate of dissipation of the mean squared temperature, and microscale length cause reduction in the absolute field correlation. Field correlation increases when the wavelength and the rate of dissipation of the turbulent kinetic energy and parameters of temperature and salinity contribution to the turbulence decrease. Salinity dominated turbulence corrupts the absolute field correlation much more in comparison to the temperature dominated turbulence. Change in the receiver coordinate is found not to affect the absolute field correlation. (C) 2014 Optical Society of America
Citation - WoS: 27
Citation - Scopus: 28
Field Correlations of Laser Arrays in Atmospheric Turbulence
(Optical Soc Amer, 2014) Baykal, Yahya
Correlations of the fields at the receiver plane are evaluated after a symmetrical radial laser array beam incident field propagates in a turbulent atmosphere. The laser array configuration is composed of a number of the same size laser beamlets symmetrically located around a ring having a radius that determines the distance of the ring from the origin. The variations of the correlations of the received field originating from such laser array incidence versus the diagonal length starting from a receiver point are examined for various laser array parameters, turbulence parameters, and the locations of the reception points. Laser array parameters consist of the ring radius and the number and size of the beamlets. Structure constant, link length, and wavelength are the turbulence parameters whose effects on the field correlation of the laser arrays are also investigated. (C) 2014 Optical Society of America
Citation - WoS: 13
Citation - Scopus: 14
Fourth-Order Mutual Coherence Function in Oceanic Turbulence
(Optical Soc Amer, 2016) Baykal, Yahya
We have recently expressed the structure constant of atmospheric turbulence in terms of the oceanic turbulence parameters, which are the ratio of temperature to salinity contributions to the refractive index spectrum, rate of dissipation of kinetic energy per unit mass of fluid, rate of dissipation of the mean-squared temperature, wavelength, Kolmogorov microscale, and link length. In this paper, utilizing this recently found structure constant and the fourth-order mutual coherence function of atmospheric turbulence, we present the fourth-order mutual coherence function to be used in oceanic turbulence evaluations. Thus, the found fourth-order mutual coherence function of oceanic turbulence is evaluated for the special case of a point source located at the transmitter origin and at a single receiver point. The variations of this special case of the fourth-order mutual coherence function of oceanic turbulence against the changes in the ratio of temperature to salinity contributions to the refractive index spectrum, the rate of dissipation of kinetic energy per unit mass of fluid, the rate of dissipation of the mean-squared temperature, the wavelength, and the Kolmogorov microscale at various link lengths are presented. (C) 2016 Optical Society of America
Citation - WoS: 21
Citation - Scopus: 22
Intensity Fluctuations of Asymmetrical Optical Beams in Anisotropic Turbulence
(Optical Soc Amer, 2016) Baykal, Yahya
Intensity fluctuations of asymmetrical optical beams are examined when such beams propagate through anisotropic turbulence. Anisotropic turbulence is modeled by non-Kolmogorov von Karman spectrum. The variations of the scintillation index are observed against the changes in the asymmetry factor of the Gaussian beam, power law exponent of non- Kolmogorov spectrum, anisotropic factors in the transverse direction, and the link length. It is found that for all the conditions, asymmetry in the optical beam is a disadvantage but the anisotropy in the atmosphere is an advantage for reducing the intensity fluctuations in an optical wireless communications link operating in the atmosphere. (C) 2016 Optical Society of America
Citation - WoS: 5
Citation - Scopus: 4
Interaction of Electromagnetic Plane Waves With an Impedance Half-Plane in an Anisotropic Medium
(Optical Soc Amer, 2020) Umul, Yusuf Ziya
The diffraction process of electromagnetic plane waves by an impedance half-plane in anisotropic medium is investigated. In this case, the permittivity of the space is expressed in terms of a tensor. The incident wave is considered for magnetic polarization. The diffracted fields are obtained with the aid of the method of transition boundary. It is shown that the diffraction wave reduces to the correct field expressions for the limiting cases. The total field and its components are compared with the literature numerically. (C) 2020 Optical Society of America
Citation - WoS: 24
Citation - Scopus: 25
M-Ary Pulse Position Modulation Performance in Non-Kolmogorov Turbulent Atmosphere
(Optical Soc Amer, 2018) Baykal, Yahya; Gokce, Muhsin C.; Ata, Yalcin
The performance of atmospheric optical wireless communication systems in terms of the bit error rate (BER) is investigated when a Gaussian laser beam propagating in non-Kolmogorov turbulence is M-ary pulse-position-modulated (PPM). BER variations against the changes in different parameters such as the non-Kolmogorov power law exponent, symbol number, data bit rate, avalanche photodetector gain, equivalent load resistor, detector quantum efficiency, wavelength, turbulence structure constant, and the Gaussian beam source size are analyzed. Making the design of the PPM optical wireless communication system able to operate in a non-Kolmogorov atmosphere will give better BER performance if the parameters are taken into account in line with the trends presented in our results. (C) 2018 Optical Society of America
Citation - WoS: 6
Citation - Scopus: 7
Modeling of an Interface Between Isorefractive Media by a Resistive Surface
(Optical Soc Amer, 2018) Basdemir, Husnu Deniz
In this study, the scattering of plane waves by a half-plane with different face impedances, which lie between isorefractive media, is analyzed. A new approach for the solution of this scenario is proposed. According to this proposal, the problem of isorefractive media and an impedance half-plane is modeled by a junction of resistive and impedance sheets. Thus the diffraction coefficient of the construction is obtained with the aid of the equivalent problem. The uniform expression of the diffracted waves is derived by the method of the uniform theory of diffraction. The scattered and diffracted waves are investigated numerically. (c) 2018 Optical Society of America
Citation - WoS: 3
Citation - Scopus: 4
Performance of M-Ary Pulse Position Modulated Optical Wireless Communications Systems in the Marine Atmosphere
(Optical Soc Amer, 2021) Baykal, Yahya; Ata, Yalcin; Gokce, Muhsin C.
The marine atmosphere exhibits different turbulence spectrum characteristics when compared to the turbulence spectra of the land atmosphere and underwater medium. The performance of M-ary pulse position modulated (PPM) optical wireless communications (OWC) systems operating in the marine atmosphere, as measured by the bit error rate (BER), is studied here. In our investigation, the scintillation index and the average intensity in marine atmospheric turbulence are used. The variations of BER performance are reported against the marine atmospheric turbulence parameters for various values of the average current gain of the avalanche photodetector (APD), data bit rate of theOWClink, and M value of the M-ary PPM. (C) 2021 Optical Society of America
Citation - WoS: 5
Citation - Scopus: 5
Performance of M-Ary Pulse Position Modulation for Aeronautical Uplink Communications in an Atmospheric Turbulent Medium
(Optical Soc Amer, 2019) Baykal, Yahya; Gokce, Muhsin Caner; Ata, Yalcin
This paper discusses the bit-error-rate (BER) performance of an aeronautical uplink optical wireless communication system (OWCS) when a Gaussian beam is employed and the M-ary pulse position modulation technique is used in an atmospheric turbulent medium. Weak turbulence conditions and log-normal distribution are utilized. The Gaussian beam is assumed to propagate on a slant path, the transmitter being ground-based, and the airborne receiver is on-axis positioned. Variations of BER are obtained against the variations in the link length, Gaussian beam source size, zenith angle, wind speed, wavelength, modulation order, data bit rate, equivalent load resistor, avalanche photodetector gain, and detector quantum efficiency. It is observed that the performance of the aeronautical uplink OWCS is affected from atmospheric turbulence significantly. (C) 2019 Optical Society of America
Citation - WoS: 3
Citation - Scopus: 4
Physical Optics-Based Diffraction Coefficient for a Wedge With Different Face Impedances
(Optical Soc Amer, 2018) Umul, Yusuf Ziya
A new diffraction field expression is introduced with the aid of the modified theory of physical optics for a wedge with different face impedances. First, the scattered geometrical optics fields are determined when both faces of the wedge are illuminated by the incident wave. The geometrical optics waves are then expressed in terms of the sum of two different fields that occur for different impedance wedges. The diffracted fields are determined for the two cases separately, and the total diffracted field is obtained as a sum of these waves. Lastly, the uniform field expressions are obtained, and the resultant fields are numerically compared with the solution of Maliuzhinets. (C) 2018 Optical Society of America
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: 11
Citation - Scopus: 11
Scattered Fields of Conducting Half-Plane Between Two Dielectric Media
(Optical Soc Amer, 2010) Yalcin, Ugur; Umul, Yusuf Z.
We investigate the scattering process of plane waves by a conducting half-plane between two dielectric media by introducing novel boundary conditions, in terms of soft and hard surfaces. The cases of soft and hard half-planes are studied independently. The scattered waves are examined numerically. The numerical results show that the behavior of the fields is in harmony with the theory. The transition between the two dielectric media is continuous, and the structure of the method enables one also to examine more complex geometries, such as wedges having soft and hard boundary conditions. (C) 2010 Optical Society of America

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