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Elektrik Elektronik Mühendisliği Bölümü Yayın Koleksiyonu

Permanent URI for this collectionhttps://hdl.handle.net/20.500.12416/411

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End date: 2019Publisher: search.filters.publisher.Optical Soc Amer

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Now showing 1 - 10 of 23
  • Article
    Citation - WoS: 3
    Citation - Scopus: 2
    Snr Advantage of Anisotropy in Oceanic Optical Wireless Communications Links
    (Optical Soc Amer, 2019) Baykal, Yahya
    Signal-to-noise ratio (SNR) of an optical wireless communication (OWC) link that operates in anisotropic oceanic turbulence is evaluated. To find the SNR advantage of the anisotropy in the oceanic turbulent medium, SNR in anisotropic oceanic turbulence is normalized by the SNR in isotropic oceanic turbulence. The dB values of this normalized SNR are examined 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, the rate of dissipation of kinetic energy per unit mass of fluid at various oceanic anisotropic factors, the avalanche multiplication factors, the radii of receiver aperture, link lengths, and detector responsivity values. It is found that as the oceanic turbulence becomes more anisotropic, at any link parameter, the SNR of the OWC link becomes advantageous over the isotropic counterpart. (c) 2019 Optical Society of America
  • Article
    Citation - WoS: 88
    Citation - Scopus: 87
    Correlation and Structure Functions of Hermite-Sinusoidal Laser Beams in a Turbulent Atmosphere
    (Optical Soc Amer, 2004) Baykal, Y
    To study the performance of atmospheric optical links by using Hermite-sinusoidal-Gaussian laser beam sources, we derive the log-amplitude and the phase correlation and structure functions of such beams in a turbulent atmosphere. Our formulations correctly reduce to the known higher-order mode correlation and structure functions, which in turn reduce to the fundamental-mode (TEM00-mode) results. Several special cases of our formulation are presented, among which the case involving Hermite-cosh-Gaussian dependence is especially noted, since this case is of interest to us owing to the nature of cosh dependence exhibiting the concentration of the energy in the outer lobes of the beam. (C) 2004 Optical Society of America.
  • Article
    Citation - WoS: 5
    Citation - Scopus: 5
    Raman Mode Non-Classicality Through Entangled Photon Coupling To Plasmonic Modes
    (Optical Soc Amer, 2018) Salmanogli, Ahmad
    In this article, non-classical properties of Raman modes are investigated. The original goal, actually, is to identify how and by which method we can induce non-classicality in Raman modes. We introduce a plasmonic system in which Raman dye molecules are buried between two shells of the plasmonic materials, similar to an onionlike core/shell nanoparticle. This system is excited by the entangled two-photon wave, followed by analysis of its dynamics of motion using the Heisenberg-Langevin equations by which the time evolution of the signalidler mode and Raman modes are derived. Interestingly, the entangled two-photon wave is coupled to the plasmonic modes, which are used to improve the non-classicality. It is shown that the exciting system with the entangled photons leads to inducing the non-classicality in Raman modes and entanglement between them. Moreover, it is seen that the plasmon-plasmon interaction in the gap region has a strong effect on the non-classicality of the input modes and also affects entangling of the Raman modes, which means that plasmonic modes generated by the core/shell nanoparticles manipulate the Raman modes' quantum properties. It is shown that the quantum properties in the designed system are dramatically influenced by the environmental temperature and the location of the Raman molecules in the gap region. The modeling results demonstrate that by changing the location of the Raman molecules, the non-classicality of the Raman modes and their entanglement are altered. Finally, as an important result, it is revealed that the Raman modes, such as the Stokes and anti-Stokes modes, show a revival behavior, which is a quantum phenomenon. (c) 2018 Optical Society of America.
  • Article
    Citation - WoS: 12
    Citation - Scopus: 14
    M-Ary Pulse Position Modulation Performance in Strong Atmospheric Turbulence
    (Optical Soc Amer, 2018) Baykal, Yahya; Ata, Yalcin; Gokce, Muhsin Caner
    The 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 America
  • Article
    Citation - WoS: 106
    Citation - Scopus: 115
    Effect of Eddy Diffusivity Ratio on Underwater Optical Scintillation Index
    (Optical Soc Amer, 2017) Elamassie, Mohammed; Uysal, Murat; Baykal, Yahya; Abdallah, Mohamed; Qaraqe, Khalid
    The performance of underwater optical wireless communication systems is severely affected by the turbulence that occurs due to the fluctuations in the index of refraction. Most previous studies assume a simplifying, yet inaccurate, assumption in the turbulence spectrum model that the eddy diffusivity ratio is equal to unity. It is, however, well known that the eddy diffusivities of temperature and salt are different from each other in most underwater environments. In this paper, we obtain a simplified spatial power spectrum model of turbulent fluctuations of the seawater refraction index as an explicit function of eddy diffusivity ratio. Using the derived model, we obtain the scintillation index of optical plane and spherical waves and investigate the effect of the eddy diffusivity ratio. (C) 2017 Optical Society of America
  • Article
    Citation - WoS: 8
    Citation - Scopus: 8
    Structure 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, Yahya
    The 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 America
  • Article
    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
  • Article
    Citation - WoS: 12
    Citation - Scopus: 16
    Off-Axis Average Transmittance and Beam Spread of a Partially Coherent Flat-Topped Beam in a Turbulent Underwater Medium
    (Optical Soc Amer, 2019) Keskin, Aysan; Baykal, Yahya
    The effects of oceanic turbulence on the off-axis optical transmittance and beam spread are examined when a partially coherent flat-topped beam wave propagates in an underwater medium. To observe the oceanic turbulence effect, the power spectrum of homogeneous and isotropic oceanic water combining the effects of salinity and temperature is used. Employing the extended Huygens-Fresnel integral and Carter's definition for the general beam formulation that is applied to a partially coherent flat-topped beam, the effects of the parameters of power spectrum, the link on the off-axis average transmittance, and beam spread are analyzed. The results obtained with the help of the MATLAB program indicate that if the flatness of the optical beam increases, the average transmittance increases, and the beam spread decreases. Partial coherence is found to be inversely proportional to the average transmittance and directly proportional to beam spread. Increase in the source size is found to increase the average transmittance and to reduce the beam spread. Loss of the kinetic energy of fluid causes less turbulence. The rate of dissipation of kinetic energy per unit mass of fluid is directly proportional to the average transmittance, while it is inversely proportional to the beam spread. The rate of dissipation of the mean square temperature is inversely proportional to the average transmittance and directly proportional to the beam spread. When the temperature-induced optical turbulence is dominant, the average transmittance almost never decreases. However, the salinity-induced optical turbulence sharply reduces the average transmittance and increases the beam spread of the partially coherent flat-topped beam in underwater turbulence. When the off-axis parameter becomes larger, average transmittance decreases. (C) 2019 Optical Society of America
  • Article
    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
  • Article
    Citation - WoS: 30
    Citation - Scopus: 32
    Bit Error Rate of Pulse Position Modulated Optical Wireless Communication Links in Oceanic Turbulence
    (Optical Soc Amer, 2018) Baykal, Yahya
    The upper bound of the average bit error rate (BER) of a pulse position modulated (PPM) optical wireless communication (OWC) link operating in oceanic turbulence is formulated. BER variations against the changes in 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 are found at various data bit rates, average current gains of the avalanche photodiode (APD), and M values of the M-ary PPM. It is found that under any oceanic turbulence parameters, BER performance of the PPM OWC system becomes favorable at smaller data bit rates, M values, and at larger average current gains of APD. (c) 2018 Optical Society of America