WoS İndeksli Yayınlar Koleksiyonu

Permanent URI for this collectionhttps://hdl.handle.net/20.500.12416/8653

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Author: search.filters.author.Baykal, YahyaSubject: search.filters.subject.Optical Wave Propagation

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Now showing 1 - 10 of 19
  • Article
    Scintillation Characteristics of Annular Beam Array in Underwater Optical Links
    (IOP Publishing Ltd, 2025) Erdogdu, Ekin; Gokce, Muhsin Caner; Baykal, Yahya
    Underwater optical wireless communication systems offer a promising alternative to traditional acoustic methods for achieving high data rate transmission. However, the propagation of optical waves in underwater environments is severely impacted by oceanic turbulence, leading to intensity fluctuations and consequent performance degradation. In this work, we employ a laser beam array to model transmit spatial diversity for suppressing these fluctuations. The model uses annular-shaped lasers at the transmitter as a representation of beam shaping for turbulence mitigation, with a point detector assumed at the receiver. Through the use of the Huygens-Fresnel principle, we derive two key optical parameters: the average received intensity and the average of the intensity squared. We subsequently determine the scintillation index for this model. Our findings demonstrate reductions in scintillation under varying system parameters. For instance, increasing the number of beams in the array, the ring radius, and the secondary field amplitude of the annular beam leads to a lower scintillation index.
  • Article
    Effects of Receiver Diversity on Bit Error Rate of Underwater Optical Wireless Communication Systems in Weak Oceanic Turbulence
    (Springer, 2025) Gokce, Muhsin Caner; Baykal, Yahya; Ata, Yalcin
    The receiver spatial diversity techniques are employed in underwater optical wireless communication (OWC) systems to mitigate oceanic turbulence, improving the bit error rate performance. In this paper, we consider an OWC system employing a binary phase-shift keying (BPSK) modulated Gaussian beam at the transmitter and employing receiver spatial diversity at the receiver. The techniques for receiver spatial diversity systems considered in the study are selection combining (SC), equal gain combining (EGC), and the maximum ratio combining (MRC). The bit error rate (BER) performance of the OWC system operating in weak oceanic turbulence is investigated by calculating the Gaussian beam's turbulence-induced scintillation index and the received optical intensity. It is found that the receiver spatial diversity techniques, especially EGC and MRC, are very effective for reducing the BER of an OWC system in weak oceanic turbulence. Furthermore, the BER performance of the underwater OWC system sees an improvement with an increase in the number of photodetectors or a decrease in the level of oceanic turbulence. Moreover, an improvement in the photodetector responsivity or a reduction in the system's noise factor contributes to achieving a favorable BER performance.
  • Article
    Citation - WoS: 4
    Citation - Scopus: 4
    Transmittance of Gaussian Beams in Biological Tissues
    (Pergamon-elsevier Science Ltd, 2025) Ozcan, Murat Kaan; Gokce, Muhsin Caner; Baykal, Yahya
    The study examines the average transmittance of Gaussian beams passing through various biological tissues, taking into account the impact of turbulence, absorption, and scattering. The extended Huygens-Fresnel technique, which utilizes the power spectrum of turbulent biological tissues, is applied to determine the optical intensity at the observation point. Additionally, there are tabulated absorption and scattering coefficients available for the application of the Beer-Lambert law, facilitating the calculation of optical light attenuation in biological tissues. Examining the impact of turbulence, as well as absorption and scattering-induced attenuation on the Gaussian beam's propagation, the changes in transmittance are documented across different tissue parameters.
  • Article
    Citation - WoS: 4
    Citation - Scopus: 4
    Intensity and Degree of Coherence of Vortex Beams in Atmospheric Turbulence
    (Ieee-inst Electrical Electronics Engineers inc, 2024) Gokce, Muhsin Caner; Baykal, Yahya; Gercekcioglu, Hamza; Ata, Yalcin; Caner Gokce, Muhsin
    We utilize the Huygens-Fresnel principle to derive the mutual coherence function (MCF) for a vortex beam, which is the main focus of our investigation. Then, we examine the intensity and modulus of the complex degree of coherence (DOC) characteristics of vortex beams in atmospheric turbulence. Our results indicate that as the topological charge increases, the intensity distribution of the vortex beam becomes less affected by atmospheric turbulence. However, the modulus of the complex DOC decreases.
  • Article
    Citation - WoS: 11
    Citation - Scopus: 9
    Multimode Beam Propagation Through Atmospheric Turbulence
    (Pergamon-elsevier Science Ltd, 2024) Baykal, Yahya; Ata, Yalcin; Gercekcioglu, Hamza; Gokce, Muhsin Caner
    The 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: 3
    Citation - Scopus: 3
    Performance Evaluation of Aeronautical Uplink/Downlink Free-Space Optical Communication System With Adaptive Optics Over Gamma-Gamma Turbulence Channel
    (Iop Publishing Ltd, 2022) Baykal, Yahya; Gokce, Muhsin Caner; Ata, Yalcin
    In this study, we analyze the effect of adaptive optics corrections on the performance of an aeronautical free-space optical (FSO) system with bidirectional slant path uplink and downlink communication channels. The aeronautical FSO communication (FSOC) system operates in a gamma-gamma atmospheric turbulence channel and employs adaptive optics corrections for the distorted wave front of the Gaussian beam wave. The modulation type of the aeronautical FSOC system is chosen to be M-ary phase-shift-keying-subcarrier intensity modulation and the type of the employed photodetector is positive-intrinsic-negative. In analysis, the effect of system parameters such as zenith angle, the height of transmitter/receiver on the ground, M-ary level, filter bandwidth, link distance, and the adaptive optics correction modes on bit-error-rate are demonstrated.
  • Editorial
    Citation - WoS: 1
    Citation - Scopus: 1
    Editorial: Optical Wave Propagation and Communication in Turbulent Media
    (Frontiers Media Sa, 2023) Baykal, Yahya
  • Article
    Citation - WoS: 4
    Citation - Scopus: 4
    Coupling Efficiency of Multimode Beam To Fiber in Atmospheric Turbulence
    (Pergamon-elsevier Science Ltd, 2023) Baykal, Yahya; Ata, Yalcin; Gokce, Muhsin Caner
    Atmospheric turbulence causes wavefront distortions in the propagated laser beam. By the beam shaping of the transmitted laser, wavefront distortions can be mitigated effectively. In this paper, we consider a shaped laser modeled by multimode beams at the transmitter and investigate the coupling of the light wave to a single-mode fiber under the atmospheric turbulence effect. We derive the light power on the coupling lens and light power accepted by the fiber core using the extended Huygens-Fresnel princi-ple. Then, the fiber coupling efficiency (FCE) is scrutinized for different system parameters such as the number of modes of the transmit laser, link distance, structure constant of atmosphere, focal length and radius of the coupling lens, wavelength, source size, and the number of speckles (NOS).(c) 2023 Elsevier Ltd. All rights reserved.
  • Article
    Citation - WoS: 6
    Citation - Scopus: 9
    Effects of Adaptive Optics on Bit Error Rate of M-Ary Ppm Oceanic Optical Wireless Communication Systems With Aperture Averaging in Strong Turbulence
    (Iop Publishing Ltd, 2021) Baykal, Yahya; Ata, Yalcin; Gokce, Muhsin Caner
    Scintillation is the result of oceanic turbulence reducing the bit error rate (BER) performance of oceanic optical wireless communication (OWC) systems. The scintillation, also known as intensity fluctuations, occurs due to the turbulence-induced wavefront deformations. The correction of deformations by adaptive optics (AO) reduces the scintillation effect of turbulence and results in improved BER performance. In this paper, an oceanic OWC (OOWC) system that has a Gaussian laser beam at the transmitter, finite-sized circular aperture at the receiver, employing M-ary pulse position modulation (PPM) and operating in strong oceanic turbulence, is considered. Improvement in the BER performance of the OOWC system is examined with the implementation of AO correction. Comparison of BER performances between the AO and non-adaptive optics OOWC systems is shown by calculating the metric defined. BER of M-ary PPM OOWC links is evaluated over gamma-gamma fading channels. The modified Rytov theory together with the Zernike filter functions is used to find the AO corrected aperture averaged scintillation index where extended Huygens-Fresnel technique is used to obtain the average received signal power.
  • Article
    Citation - WoS: 15
    Citation - Scopus: 19
    Adaptive Optics Effect on Performance of Bpsk-Sim Oceanic Optical Wireless Communication Systems With Aperture Averaging in Weak Turbulence
    (Pergamon-elsevier Science Ltd, 2020) Baykal, Yahya; Ata, Yalcin; Gokce, Muhsin Caner
    Turbulence-induced wavefront deformations cause the irradiance of an optical signal to fluctuate resulting a in serious degradation in the bit-error-rate (BER) performance of optical wireless communication (OWC) system. Adaptive optics is an effective technique to compensate for the wavefront aberrations to reduce the fluctuations in the received intensity. In this paper, we investigate how the adaptive optics technique affects the BER performance of an oceanic OWC (OOWC) system employing binary phase shift keying-subcarrier intensity modulation (BPSK-SIM) and aperture averaging. To evaluate BER performance in weak oceanic turbulence, the required entities such as the received optical power captured by a circular aperture and the aperture averaged scintillation index measuring the fluctuations in the received irradiance are derived. The effect of adaptive optics correction of various wavefront aberrations (i.e., tilt, defocus, astigmatism and the coma) on the BER performance is illustrated and the performance of the adaptive optics-OOWC system is compared to that of a non-adaptive optics OOWC system by the metric defined. (C) 2020 Elsevier Ltd. All rights reserved.