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: 11Citation - Scopus: 9Multimode Beam Propagation Through Atmospheric Turbulence(Pergamon-elsevier Science Ltd, 2024) Baykal, Yahya; Ata, Yalcin; Gercekcioglu, Hamza; Gokce, Muhsin CanerThe investigation focuses on studying the propagation characteristics of multimode lasers in the turbulent amosphere. By employing the Huygens-Fresnel integral, we develop analytical formulations for various propagation parameters. These include the average intensity distribution, kurtosis parameter, beam spread, and the average transmittance of multimode beams in turbulent atmosphere. Our findings reveal that as the propagation distance or the structure constant of the atmosphere increases, i.e., turbulence becomes stronger, the kurtosis parameter and the beam spread increase. The multimode beam exhibits a Gaussian like intensity profile when the propagation distance is significantly increased or when the structure constant becomes sufficiently large. For the case of the Gaussian beam, the kurtosis parameter is found to be 3. The multimode beam's kurtosis parameter rises as the turbulence becomes stronger and eventually approaches 3. Raising the mode content leads to a rise in the average transmittance; however, it leads to a decline in the Kurtosis parameter and the beam spread.Article Citation - WoS: 6Citation - Scopus: 6Mitigation of Atmospheric Turbulence on Up and Downlink Optical Communication Systems Using Receiver Diversity and Adaptive Optics(Springer, 2022) Gokce, Muhsin Caner; Baykal, Yahya; Ata, YalcinImprovement in the performance of uplink and downlink optical communication systems by means of receive diversity and adaptive optics correction is investigated. We develop a communication system model using adaptive optics correction in the transmitter and maximum ratio combining diversity technique in the receiver. The effect of adaptive optics correction modes, receive diversity, zenith angle, link length, wind speed and the height of transmitter/receiver on the ground are evaluated. Performance improvement is observed with both adaptive optics correction and the receive diversity. It is aimed to provide researchers an option to determine the method they will use to reduce the effect of turbulence. As the numerical values of the main results, we report that adaptive optics correction with 5 mode Zernike removal reduces BER from 10(-8) to 10(-10) for one receiver. When the number of receivers is 6, BER is found to reduce from 10(-6) to 10(-12). The results obtained in this study can be beneficial to optimize the design of the slant path uplink and downlink optical communication links between the ground and low-orbit satellites that are exposed to atmospheric turbulence.Article Citation - WoS: 9Citation - Scopus: 8Effect of Partial Coherence on Signal-To Ratio Performance of Free Space Optical Communication System in Weak Turbulence(Elsevier, 2022) Aymelek, Goerkem; Yolcu, Beguem; Kayam, Orkun; Unal, Onur; Caner Gokce, Muhsin; Baykal, Yahya; Akbucak, Volkan; Gökçe, Muhsin CanerThe effect of source coherence on the average signal-to-noise ratio ((SNR)) performance of free space optical communication (FSOC) systems operating in weak atmospheric turbulence is investigated with the help of the extended Huygens-Fresnel principle. For an FSOC system that uses a partially coherent laser source, first, the received power at the finite-sized receiver aperture is derived. Then, the power scintillation index is evaluated that reflects the aperture averaging. Using these derived optical entities, the variations of (SNR) are examined versus parameters such as the degree of source coherence, wavelength, link distance, source size, structure constant of atmosphere and the receiver aperture radius. Obtained results show that a decrease in the degree of source coherence has a positive effect on (SNR).Article 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.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.Article Citation - WoS: 9Citation - Scopus: 13Fiber-Coupling Efficiency of Laser Array Beam From Turbulent Atmosphere To Fiber Link(Ieee-inst Electrical Electronics Engineers inc, 2023) Baykal, Yahya; Ata, Yalcin; Gokce, Muhsin CanerFree-space optical communication (FSOC) systems are nowadays integrated with fiber optical components developed for fiber-optic communications. In such integrated systems, the collected portion of the incident beam on the receiver lens is coupled into a single-mode fiber. The process of coupling, however, is mostly affected by the atmospheric turbulence which distorts the coherency of the propagating beam i.e., it results in speckle over the coupling lens causing a reduction in the coupling efficiency. In this article, we aimed at investigating the fiber coupling efficiency of laser array beams propagating in a turbulent atmosphere. For this purpose, using the Huygens-Fresnel principle, mutual coherence function (MCF) for a laser array beam incidence is formulated. In this way, the average power coupled into the fiber and the average received power on the coupling lens are derived for a laser array beam incidence. It is found that the fiber coupling efficiency clearly increases with the increase in ring radius and the number of Gaussian beams in the array and rapidly decreases with increasing structure constant of atmosphere, link distance, and the number of speckles over the receiver aperture. We also demonstrate the effect of various FSOC system parameters on the coupling efficiency.Article Citation - WoS: 2Citation - Scopus: 1Signal-To Ratio With Adaptive Optics Compensation in Non-Kolmogorov Weak Turbulent Atmosphere(Taylor & Francis Ltd, 2021) Baykal, Yahya; Gokce, Muhsin Caner; Ata, YalcinThis study investigates the average signal-to-noise ratio < SNR > at the shot-noise limited receiver of an optical wireless communication system (OWC) that uses collimated Gaussian beam with adaptive optics correction in non-Kolmogorov weak turbulent atmosphere. < SNR > and the variation in the percentage < SNR > are calculated and the results are presented against various adaptive optics correction modes, non-Kolmogorov power-law exponent, receiver aperture size, Gaussian beam source size, photodetector quantum efficiency, electronic bandwidth, link length, and turbulence strength. Adaptive optics correction is analyzed for tilt, defocus, astigmatism, coma and trefoil modes and their variations. The effects of adaptive optics compensation are examined that cause an increase in SNR, hence improve the performance of an OWC system using collimated Gaussian beam and operating in the non-Kolmogorov weak turbulent atmosphere.Article Citation - WoS: 8Citation - Scopus: 9Multimode Laser Beam Scintillations in Weak Atmospheric Turbulence for Vertical Link Laser Communications(Taylor & Francis Ltd, 2022) Sayan, Omer F.; Gercekcioglu, Hamza; Baykal, YahyaScintillation index of multimode laser beams used for communication systems in vertical paths of weak atmospheric turbulent medium are examined by employing the Rytov method. On-axis scintillation index is examined versus the source size, propagation distance and zenith angle for vertical link including uplink and downlink. At the selected values of source sizes and propagation distances, scintillation responses of multimode laser beams are evaluated. In general, it is found for both uplink and downlink that the laser beam with multimode content has larger scintillation noise as compared to a Gaussian laser beam. However, for the downlink at L=700 km, at the chosen parameters, the multimode beam possessing larger mode content, is found to attain slightly smaller scintillations.Article Citation - WoS: 8Citation - Scopus: 8M-Ary Pulse Position Modulation Performance With Adaptive Optics Corrections in Atmospheric Turbulence(Taylor & Francis Ltd, 2020) Gokce, Muhsin C.; Baykal, Yahya; Ata, YalcinThe performance of M-ary pulse position modulated (PPM) optical wireless communication (OWC) systems in atmospheric weak turbulence medium is evaluated by using adaptive optics corrections. Piston, tilt, defocus and coma components of adaptive optics corrections are applied to the avalanche photodetector (APD) type of receiver and the results are obtained depending on various turbulence and receiver parameters. The lognormal channel distribution is used to model the weak atmospheric turbulence conditions. Adaptive optics correction increases the bit-error-rate (BER) performance of an OWC system operating in atmospheric turbulence conditions. Piston component yields the highest BER performance, followed by the tilt, defocus and coma adaptive optics correction components respectively.Article Citation - WoS: 34Citation - Scopus: 36Hermite Gaussian Beam Scintillations in Weak Atmospheric Turbulence for Aerial Vehicle Laser Communications(Elsevier, 2020) Sayan, Omer F.; Gercekcioglu, Hamza; Baykal, YahyaScintillation index of Hermite Gaussian beams used for air vehicle communication systems in vertical paths of weak atmospheric turbulent medium are investigated by employing the modified Rytov method. By evaluating the on-axis scintillation index, variations of the scintillation indices of these beams are examined against the changes in the Gaussian beam size of the Hermite Gaussian beam mode, propagation distances and the zenith angles at the realistic propagation distances involved in uplink and downlink configurations. In the atmospheric environment, for uplink, the Hermite Gaussian beam modes have no advantage over the Gaussian beams at short propagation distances like L = 20 km,as well as at long propagation distances like L = 700 km. However, for downlink, although Hermite Gaussian beam modes are disadvantageous over the Gaussian beams at short propagation distances like L = 20 km, they are found advantageous over the Gaussian beams at long propagation distances like L = 700 km. The results of this study may encourage to use Hermite Gaussian beams, especially in the air vehicle laser communication links, and can be used in the design of an optical wireless communication link utilizing the vertical atmospheric medium.Conference Object Citation - Scopus: 1Intensity Fluctuations of Incoherently Superposed Gaussian Beams in Atmospheric Turbulence(Spie-int Soc Optical Engineering, 2010) Baykal, YahyaIntensity fluctuations of incoherently superposed Gaussian beams are formulated in weak turbulence by employing the extended Huygens-Fresnel principle. Each individual beam superposed is taken to be fully incoherent. The scintillation index evaluated for different number of beams indicates that as the number of beams increase, scintillations decrease. Incoherent superposition of smaller sized Gaussian sources exhibits smaller fluctuations. Comparing the scintillation index arising from incoherently superposed Gaussian beams to the scintillation index of coherently superposed Gaussian beams of the same structure shows that incoherent superposition yields lower intensity fluctuations, thus can be advantageous in atmospheric optical communication links.