Elektrik Elektronik Mühendisliği Bölümü Yayın Koleksiyonu
Permanent URI for this collectionhttps://hdl.handle.net/20.500.12416/411
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Article Citation - WoS: 1Citation - Scopus: 3Performance of a Free-Space Optical Communication System Employing Receive Diversity Techniques in Anisotropic Atmospheric Non-Kolmogorov Turbulence(Optica Publishing Group, 2022) Gokce, Muhsin Caner; Ata, Yalcin; Baykal, YahyaIn this paper, bit error rate (BER) performance of a free-space optical communication (FSOC) system operating in anisotropic non-Kolmogorov weak turbulence is investigated together with the spatial diversity techniques. The spatial diversity techniques are implemented as maximum ratio combining (MRC), equal gain combining (EGC), and selection combining (SC) and applied to the receiver. The propagating beam is the Gaussian beam wave, and the modulation scheme is binary phase-shift keying (BPSK). Results are obtained for various parameters such as the anisotropy factor, non-Kolmogorov power law exponent, photodetector responsivity, equivalent load resistor, electronic bandwidth, Gaussian beam radius, wavelength, propagation distance, and turbulence structure constant. It is found that the spatial diversity technique used at the receiver causes significant improvement in the performance of an FSOC system under the conditions of anisotropic non-Kolmogorov atmospheric turbulence. It is also observed that BER performance improves as the atmospheric turbulence becomes more anisotropic. Among the spatial diversity techniques, SC is inferior to EGC and EGC is inferior toMRC in terms of BER performance. (C) 2022 Optica Publishing GroupArticle Citation - WoS: 3Citation - Scopus: 2Modulation Transfer Function Variation Through Anisotropic Turbulence in Biological Tissue(Optica Publishing Group, 2023) Gokce, Muhsin Caner; Baykal, Yahya; Ata, YalcinAnalysis of the long-exposure modulation transfer function (MTF) is performed for optical imaging using plane and spherical waves through anisotropic turbulence in biological tissues. To obtain the MTF, the wave structure functions of plane and spherical waves are obtained in closed-form expressions. Results are presented depending on various parameters of the turbulent medium and optical beam. The positive effect of anisotropy on optical imaging is remarkable in turbulent biological tissues. Besides scattering and absorption, taking anisotropy into account as well as turbulence will lead to a more accurate description of the performance of the medical imaging systems that use optical spectrums in biological tissues. (c) 2023 Optica Publishing GroupArticle Citation - WoS: 4Citation - Scopus: 4Fiber Coupling Efficiency in Ocean With Adaptive Optics Corrections(Optica Publishing Group, 2023) Gokce, Muhsin Caner; Ata, Yalcin; Baykal, YahyaUnderwater optical wireless communication (UOWC) is a very promising technology that enables high-speed data transfer through the use of laser beams in an oceanic turbulent medium. The high-tech fiber optical devices, which are already available in the market, can be integrated with the UOWC systems. When integration is achieved, oceanic turbulence, which distorts the wavefront of the propagating laser beam, plays an important role in reducing the fiber coupling efficiency (FCE), which in turn results in reducing the light power received from the fiber optical components. In this paper, we propose the use of the adaptive optics technique in a UOWC system to mitigate the effects of oceanic turbulence and boost the FCE. For this reason, the field correlation for a Gaussian laser beam is derived by using the Huygens-Fresnel principle. This way, the light power over the coupling lens and the light power accepted by the fiber core are formulated under the effect of adaptive optics corrections, which are repre-sented by the number of Zernike modes. The results demonstrate that under the oceanic turbulence effect, the FCE of the UOWC system employing adaptive optics is always larger than that of the UOWC system employing no adaptive optics. (c) 2023 Optica Publishing GroupArticle Citation - WoS: 6Citation - Scopus: 6Correlation of Multimode Fields in Atmospheric Turbulence(Optica Publishing Group, 2023) Gokce, Muhsin Caner; Ata, Yalcin; Gercekcioglu, Hamza; Baykal, YahyaMultimode field correlations are evaluated in atmospheric turbulence. High order field correlations are special cases of the results that we obtained in this paper. Field correlations are presented for various numbers of mul- timodes, various multimode contents of the same number of modes, and various high order modes versus the diagonal distance from various receiver points, source size, link length, structure constant, and the wavelength. Our results will be of help especially in the design of heterodyne systems operating in turbulent atmosphere and fiber coupling efficiency in systems employing multimode excitation.(c) 2023 Optica Publishing GroupArticle Citation - WoS: 3Citation - Scopus: 5Performance 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 AmericaArticle Citation - WoS: 5Effect of Anisotropy on Performance of M-Ary Phase Shift Keying Subcarrier Intensity-Modulated Optical Wireless Communication Links Operating in Strong Oceanic Turbulence(Iop Publishing Ltd, 2020) Baykal, Yahya; Ata, Yalcin; Gokce, Muhsin CanerIn strong oceanic turbulence, the performance of M-ary phase shift keying subcarrier intensity-modulated optical wireless communication (OWC) links is investigated in terms of the bit-error-rate (BER) by considering the effect of anisotropy of the oceanic channel. To calculate the BER of the OWC link, a gamma-gamma statistical channel model is adopted. The extended Huygens-Fresnel principle and the asymptotic Rytov theory are used to obtain the received optical power and the large-scale and small-scale log-intensity variances, respectively. Our graphical illustrations include the BER versus anisotropic factor for various system parameters such as the modulation order, filter bandwidth, link distance, peak amplitude of each subcarrier and the oceanic turbulence parameters.Article Citation - WoS: 22Citation - Scopus: 19Laser Array Beam Propagation Through Liver Tissue(Springer, 2020) Baykal, Yahya; Ata, Yalcin; Gokce, Muhsin CanerLaser array beam propagating through mouse liver tissue is investigated. The turbulence power spectrum of the liver tissue is employed in the extended Huygens-Fresnel method to obtain an optical intensity profile and beam broadening at the observation point in biological liver tissue. Variations of the beam profile and the beam broadening are simulated based on the number of beamlets, source size, wavelength and the ring radius of the array. A biological tissue, illuminated by the laser array beam, exhibits different beam profiles and beam spot radius variations when the number of beamlets, source size, wavelength and the ring radius of the laser array beam are varied. Examining these variations observed in the propagated optical beam and comparing them with the test cases, abnormalities such as cancer and tumor in a biological liver tissue can be diagnosed.Article Citation - WoS: 12Citation - Scopus: 14M-Ary Pulse Position Modulation Performance in Strong Atmospheric Turbulence(Optical Soc Amer, 2018) Baykal, Yahya; Ata, Yalcin; Gokce, Muhsin CanerThe performance of an M-ary pulse position modulated (PPM) optical wireless communication system operating in strong atmospheric turbulence is investigated. Bit error rate (BER) is employed as the measure for the performance. In our overall performance formulation, average received power as measured by a finite-sized avalanche photodiode (APD) detector is used by the help of the extended Huygens-Fresnel principle. For the aperture averaged scintillation evaluations, the asymptotic Rytov theory with the gamma-gamma intensity statistics is utilized. Gamma-gamma statistics together with the large-scale and the small-scale log-intensity variances yield the scintillation index valid both in weak and strong atmospheric turbulence regimes. BER variations versus the plane wave scintillation index are examined at different values of receiver aperture diameters, data bit rates, M values of M-ary PPM, quantum efficiency, and average APD gain. (C) 2018 Optical Society of AmericaArticle Citation - WoS: 8Citation - Scopus: 8Structure Parameter of Anisotropic Atmospheric Turbulence Expressed in Terms of Anisotropic Factors and Oceanic Turbulence Parameters(Optical Soc Amer, 2019) Ata, Yalcin; Gokce, Muhsin C.; Baykal, YahyaThe structure parameter of the anisotropic atmospheric turbulence is expressed in terms of atmospheric, oceanic anisotropic factors in x and y directions, and the oceanic turbulence parameters, which are the wavelength, the link length, the ratio of temperature to salinity contributions to the refractive index spectrum, the rate of dissipation of mean-squared temperature, and the rate of dissipation of kinetic energy per unit mass of fluid. For the purpose of expressing the structure parameter of the anisotropic atmospheric turbulence in terms of atmospheric, oceanic anisotropic factors and the oceanic turbulence parameters, the spherical wave scintillation indices that are found in weak anisotropic atmospheric turbulence and in weak oceanic turbulence are equated to each other. We aim to utilize the structure parameter expressed in this paper in the evaluations of various physical entities such as the average intensity, scintillation index, and beam spread in anisotropic oceanic turbulence by exploiting the existing solutions for the same physical entities in anisotropic atmospheric turbulence. Use of this structure parameter will help us to obtain the anisotropic oceanic turbulence results easily because such results will be found by just inserting the structure parameter expressed in this paper to the already reported corresponding results of anisotropic atmospheric turbulence. (C) 2019 Optical Society of AmericaArticle Citation - WoS: 9Citation - Scopus: 11Effect 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, YalcinAtmospheric 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