Scopus İndeksli Yayınlar Koleksiyonu

Permanent URI for this collectionhttps://hdl.handle.net/20.500.12416/8651

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Now showing 1 - 10 of 27
  • Article
    Citation - WoS: 1
    Citation - Scopus: 1
    Structure Functions for Optical Waves in a Complex Medium of Turbulent Biological Tissues
    (Optica Publishing Group, 2022) Ata, Yalcin; Baykal, Yahya; Gokce, Muhsin caner
    Although optical wave propagation is investigated based on the absorption and scattering in biological tissues, the turbulence effect can also not be overlooked. Here, the closed-form expressions of the wave structure func-tion (WSF) and phase structure function (PSF) of plane and spherical waves propagating in biological tissue are obtained to help with future research on imaging, intensity, and coherency in turbulent biological tissues. This paper presents the effect of turbulent biological tissue on optical wave propagation to give a perception of the per-formance of biomedical systems that use optical technologies. The behavior of optical waves in different types of turbulent biological tissues such as a liver parenchyma (mouse), an intestinal epithelium (mouse), a deep dermis (mouse), and an upper dermis (human) are investigated and compared. It is observed that turbulence becomes more effective with an increase in the characteristic length of heterogeneity, propagation distance, and the strength of the refractive index fluctuations. However, an increase in the fractal dimension, wavelength, and small length scale factor has a smaller turbulence effect on the propagating optical wave. We envision that our results may be used to interpret the performance of optical medical systems operating in turbulent biological tissues.(c) 2022 Optica Publishing Group
  • Article
    Citation - WoS: 3
    Citation - Scopus: 3
    Field Correlations of Multimode Optical Beams in Underwater Turbulence
    (Optica Publishing Group, 2024) Baykal, Yahya; Gokce, Muhsin C.; Ata, Yalcin; Gercekcioglu, Hamza
    For multimode optical beams, field correlations at the receiver plane are found in underwater turbulence. Field correlations of single high order beams in underwater turbulence are special cases of our formulation. Variations of field correlations against the underwater turbulence parameters and the diagonal length from various receiver points are examined for different multimode and single high order beams. Stronger underwater turbulence is found to reduce the field correlations of multimode and single high order optical beams. The results will be of help in heterodyne detection analysis and fiber coupling efficiency in an underwater medium experiencing turbulence. (c) 2024 Optica Publishing Group
  • Article
    Citation - WoS: 5
    Citation - Scopus: 6
    Underwater Turbulence Effect on Optical Imaging
    (Iop Publishing Ltd, 2022) Gokce, Muhsin Caner; Baykal, Yahya; Ata, Yalcin
    Modulation transfer function (MTF) of oceanic turbulence plays an essential role in the design and quality of underwater image sensing systems capturing optical signals. MTF gives clues about the characteristics of turbulence which can help image reconstruction where the image resolution can be increased in this way. In the paper, under the conditions of weak turbulence and Gaussian beam propagation, we derive the modulation transfer function for short-exposure and long-exposure images based on the recently developed turbulence spectrum model: Oceanic turbulence optical power spectrum (OTOPS). With the aid of the OTOPS model, the effect of measurable turbulence parameters, namely average temperature, average salinity concentration, and temperature-salinity gradient ratios, as well as imaging system parameters, namely receiver aperture radius and wavelength of the laser source on the MTF are reported. Obtained results indicate that MTF rapidly decreases with increasing relative spatial frequency and turbulence strength. Turbulence becomes stronger with the increase in the average temperature, average salinity concentration, energy dissipation rate, temperature-salinity gradient ratio and with the decrease in the temperature dissipation rate, wavelength.
  • Article
    Citation - WoS: 5
    Citation - Scopus: 4
    Laser Array Field Correlations in Underwater Turbulence
    (Taylor & Francis Ltd, 2022) Gokce, Muhsin C.; Baykal, Yahya; Ata, Yalcin
    In underwater turbulent medium, field correlations are found when the incidence is a laser beam array. Variations of the field correlations against the variations in the ring radius of laser array beam, number of beamlets composing the laser array, source size, underwater turbulence parameters, i.e. the ratio of temperature to salinity contributions to the refractive index spectrum, rate of dissipation of mean-squared temperature and rate of dissipation of kinetic energy per unit mass of fluid, are investigated. Field correlations of laser arrays are found to be larger than the field correlations of the single beams. The effect of underwater turbulence is to reduce the field correlation of laser arrays.
  • Article
    Citation - WoS: 7
    Citation - Scopus: 7
    Intensity Fluctuations in Biological Tissues at Any Turbulence Strength
    (Iop Publishing Ltd, 2022) Baykal, Yahya; Ata, Yalcin; Gokce, Muhsin Caner
    This study investigates the intensity fluctuations of the optical plane and spherical waves in biological tissue that experience any strength of turbulence. Biological tissue is a random and complex medium for optical wave propagation, having a power spectrum reflecting the turbulent characteristics that depend on the structural parameters. It is important to accurately determine the strength of turbulence and classify turbulence regimes for the correct modeling of the behavior of the optical wave propagation. To classify weak, moderate and strong turbulent regimes, closed-form expressions of modified Rytov variances are obtained. Based on the modified Rytov variance that involves the large-scale and small-scale variations, the intensity fluctuations specified by the metric of scintillation index, are calculated versus various parameters such as the propagation distance, refractive index, characteristic length of heterogeneity, small length-scale factor, wavelength, fractal dimension and strength of the refractive index fluctuations. Behavior of optical plane and spherical waves in different turbulent regimes and the comparison of intensity fluctuations in different specimens of human and animal tissues are shown.
  • Article
    Citation - WoS: 6
    Citation - Scopus: 6
    Correlation of Multimode Fields in Atmospheric Turbulence
    (Optica Publishing Group, 2023) Gokce, Muhsin Caner; Ata, Yalcin; Gercekcioglu, Hamza; Baykal, Yahya
    Multimode 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 Group
  • Article
    Citation - WoS: 3
    Citation - Scopus: 5
    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
  • 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: 8
    Citation - Scopus: 8
    M-Ary Pulse Position Modulation Performance With Adaptive Optics Corrections in Atmospheric Turbulence
    (Taylor & Francis Ltd, 2020) Gokce, Muhsin C.; Baykal, Yahya; Ata, Yalcin
    The 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: 6
    Citation - Scopus: 10
    Application of Adaptive Optics on Bit Error Rate of M-Ary Pulse-Position Oceanic Optical Wireless Communication Systems
    (Iop Publishing Ltd, 2020) Gokce, Muhsin C.; Ata, Yalcin; Baykal, Yahya
    An adaptive optics correction arising from the sum of tilt, focus, astigmatism and coma components is applied to the bit error rate (BER) of M-ary pulse-position-modulated (PPM) oceanic optical wireless communication systems. The percentage reduction in BER is evaluated versus the oceanic turbulence parameters of the ratio of temperature to salinity contributions to the refractive index spectrum, the rate of dissipation of mean-squared temperature and that of kinetic energy per unit mass of fluid under different data bit rates, avalanche photodiode (APD) average current gains and the M values of the M-ary PPM. Our findings indicate that the percentage reduction in BER becomes larger when the ratio of temperature to salinity contributions to the refractive index spectrum or the rate of dissipation of mean-squared temperature or the data bit rate or the M value of the M-ary PPM is smaller, and when the rate of dissipation of kinetic energy per unit mass of fluid or the APD average current gain is larger.