Elektronik ve Haberleşme Mühendisliği Bölümü Yayın Koleksiyonu
Permanent URI for this collectionhttps://hdl.handle.net/20.500.12416/260
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Correction Uniform Theory for the Diffraction of Evanescent Plane Waves: Publisher's Note (Vol 24, Pg 2426, 2007)(Optical Soc Amer, 2007) Umul, Yusuf Z.Article Citation - WoS: 5Citation - Scopus: 4Interaction of Electromagnetic Plane Waves With an Impedance Half-Plane in an Anisotropic Medium(Optical Soc Amer, 2020) Umul, Yusuf ZiyaThe diffraction process of electromagnetic plane waves by an impedance half-plane in anisotropic medium is investigated. In this case, the permittivity of the space is expressed in terms of a tensor. The incident wave is considered for magnetic polarization. The diffracted fields are obtained with the aid of the method of transition boundary. It is shown that the diffraction wave reduces to the correct field expressions for the limiting cases. The total field and its components are compared with the literature numerically. (C) 2020 Optical Society of AmericaArticle Citation - WoS: 4Citation - Scopus: 4Diffraction of Plane Electromagnetic Waves by a Resistive Half-Screen for Skew Incidence(Optical Soc Amer, 2020) Umul, Yusuf ZiyaThe scattering process of electromagnetic plane waves by a resistive half-screen is investigated for oblique incidence. First of all, it is shown that the existing solution in the literature is not correct, because the problem was solved by considering the normal components of the electromagnetic field, in terms of which the boundary conditions cannot be expressed. Instead of these, the components of the electric field, which is parallel to the edge discontinuity, are taken into account. The diffracted fields are obtained with the aid of the method of transition boundary. The uniform field expressions are obtained by using the Fresnel function. The behaviors of the total field and its subcomponents are analyzed numerically. (C) 2019 Optical Society of AmericaArticle Citation - WoS: 183Citation - Scopus: 193Analysis of Reciprocity of Cos-Gaussian and Cosh-Gaussian Laser Beams in a Turbulent Atmosphere(Optical Soc Amer, 2004) Eyyuboglu, HT; Baykal, YIn a turbulent atmosphere, starting with a cos-Gaussian excitation at the source plane, the average intensity profile at the receiver plane is formulated. This average intensity profile is evaluated against the variations of link lengths, turbulence levels, two frequently used free-space optics wavelengths, and beam displacement parameters. We show that a cos-Gaussian beam, following a natural diffraction, is eventually transformed into a cosh-Gaussian beam. Combining our earlier results with the current findings, we conclude that cos-Gaussian and cosh-Gaussian beams act in a reciprocal manner after propagation in turbulence. The rates (paces) of conversion in the two directions are not the same. Although the conversion of cos-Gaussian beams to cosh-Gaussian beams can happen over a wide range of turbulence levels (low to moderate to high), the conversion of cosh-Gaussian beams to cos-Gaussian beams is pronounced under relatively stronger turbulence conditions. Source and propagation parameters that affect this reciprocity have been analyzed. (C) 2004 Optical Society of America.Article Citation - WoS: 127Citation - Scopus: 135Average Intensity and Spreading of Cosh-Gaussian Laser Beams in the Turbulent Atmosphere(Optical Soc Amer, 2005) Eyyuboglu, HT; Baykal, YThe average intensity and spreading of cosh-Gaussian laser beams in the turbulent atmosphere are examined. Our research is based principally on formulating the average-intensity profile at the receiver plane for cosh-Gaussian excitation. The limiting cases of our formulation for the average intensity are found to reduce correctly to the existing Gaussian beam wave result in turbulence and the cosh-Gaussian beam result in free space (in the absence of turbulence). The average intensity and the broadening of the cosh-Gaussian beam wave after it propagates in the turbulent atmosphere are numerically evaluated versus source size, beam displacement, link length, structure constant, and two wavelengths of 0.85 and 1.55 mum, which are most widely used in currently employed free-space-optical links. Results indicate that in turbulence the beam is widened beyond its free-space diffraction values. At the receiver plane, analogous to the case of free space, this diffraction eventually leads to transformation of the cosh-Gaussian beam into an oscillatory average-intensity profile with a Gaussian envelope. (C) 2005 Optical Society of America.Article Citation - WoS: 48Citation - Scopus: 55Log-Amplitude and Phase Fluctuations of Higher-Order Annular Laser Beams in a Turbulent Medium(Optical Soc Amer, 2005) Baykal, YLog-amplitude and phase-correlation and structure functions of higher-order annular laser beams in a turbulent atmosphere are derived. A higher-order annular beam source is defined as the superposition of two different higher-order Hermite-Gaussian beams. A special case of such an excitation is the annular Gaussian beam in which two beams operate at fundamental modes of different Gaussian beam sizes, yielding a doughnut-shaped (annular) beam when the second beam is subtracted from the first beam. Our formulation utilizes Rytov approximation, which makes it applicable in the weak-turbulence regime, especially for log-amplitude fluctuations. Limiting cases of our formulations correctly match with known higher-order-mode solutions that in turn reduce to the Gaussian-beam-wave (TEM00-mode) results. Our results can be applied to determine the scintillation index and the phase fluctuations in free-space optics links under higher-order annular laser beam excitation. Except for the numerical evaluation of a specific example covering an annular Gaussian beam, the results in general are left in integral form and need to be numerically evaluated in detail to obtain quantitative results. (c) 2005 Optical Society of America.Article Citation - WoS: 83Citation - Scopus: 86Hermite-Cosine Laser Beam and Its Propagation Characteristics in Turbulent Atmosphere(Optical Soc Amer, 2005) Eyyuboglu, HTHermite-cosine-Gaussian (HcosG) laser beams are studied. The source plane intensity of the HcosG beam is introduced and its dependence on the source parameters is examined. By application of the Fresnel diffraction integral, the average receiver intensity of HcosG beam is formulated for the case of propagation in turbulent atmosphere. The average receiver intensity is seen to reduce appropriately to various special cases. When traveling in turbulence, the HcosG beam initially experiences the merging of neighboring beam lobes, and then a TEM-type cosh-Gaussian beam is formed, temporarily leading to a plain cosh-Gaussian beam. Eventually a pure Gaussian beam results. The numerical evaluation of the normalized beam size along the propagation axis at selected mode indices indicates that relative spreading of higher-order HcosG beam modes is less than that of the lower-order counterparts. Consequently, it is possible at some propagation distances to capture more power by using higher-mode-indexed HcosG beams. (C) 2005 Optical Society of America.Article Citation - WoS: 37Citation - Scopus: 38Diffraction by a Black Half Plane: Modified Theory of Physical Optics Approach(Optical Soc Amer, 2005) Umul, YZThe scattered fields from a black half plane which absorbs all the incoming electromagnetic energy are evaluated by defining a new modified theory of physical optics surface current. This current eliminates the reflected fields, coming from the first stationary point of the reflection integral and only creates a reflected diffracted field. The incident scattered fields are found from the same integral, written for the perfectly conducting half plane. The scattered fields are evaluated by using the stationary phase method and edge point technique. The evaluated fields are plotted numerically. (c) 2005 Optical Society of America.Article Citation - WoS: 67Citation - Scopus: 67Equivalent Functions for the Fresnel Integral(Optical Soc Amer, 2005) Umul, YZFresnel integral is modeled with three equivalent functions. The first function is derived by considering the sum of the first term of the Fresnel integral's asymptotic expansion {(F) over cap (x)} and an exponential function which approaches to infinity at the zero of the Fresnel function's argument and has the properties of a unit step function. The second one is the sum of a unit step function and the transition function defined for the simplified uniform theory of diffraction. The third function considers directly eliminating the infinity coming from (F) over cap (x). The amplitude and the phase of Fresnel integral and its equivalent functions are compared numerically. The result is applied to the modified theory of physical optics solution of the diffraction of edge waves from a half plane problem. (c) 2005 Optical Society of America.Article Citation - WoS: 11Citation - Scopus: 10Modified Theory of the Physical-Optics Approach To the Impedance Wedge Problem(Optical Soc Amer, 2006) Umul, YZThe problem of a wedge with equal face impedances is examined with a modified theory of physical optics. The surface integral is constructed by use of the impedance boundary condition. The aperture equivalent current is estimated from the behavior of the reflected diffracted field. The integrals obtained are evaluated asymptotically and compared with the exact solution numerically. (c) 2006 Optical Society of America.