Browsing by Subject "Gaussian beams"

Now showing 1 - 5 of 5

Open Access
Asymmetric transmission in prisms using structures and materials with isotropic-type dispersion
(Optical Society of America, 2015) Gundogdu, F. T.; Serebryannikov, A. E.; Cakmak, A. O.; Özbay, Ekmel
It is demonstrated that strong asymmetry in transmission can be obtained at the Gaussian beam illumination for a single prism based on a photonic crystal (PhC) with isotropic-type dispersion, as well as for its analog made of a homogeneous material. Asymmetric transmission can be realized with the aid of refraction at a proper orientation of the interfaces and wedges of the prism, whereas neither contribution of higher diffraction orders nor anisotropic-type dispersion is required. Furthermore, incidence toward a prism wedge can be used for one of two opposite directions in order to obtain asymmetry. Thus, asymmetric transmission is a general property of the prism configurations, which can be obtained by using simple geometries and quite conventional materials. The obtained results show that strong asymmetry can be achieved in PhC prisms with (nearly) circular shape of equifrequency dispersion contours, in both cases associated with the index of refraction 0 < n < 1 and n > 1. For the comparison purposes, results are also presented for solid uniform nonmagnetic prisms made of a material with the same value of n. It is shown in zero-loss approximation that the PhC prism and the ultralow-index material prism ( 0 < n < 1) can replace each other in some cases without affecting the scenario of asymmetric transmission. Moreover, the PhC prism and the solid dielectric prism can show the same scenario at n > 1. Possible contributions of scattering on the individual rods and diffraction on the wedge to the resulting mechanism are discussed. Analogs of unidirectional splitting and unidirectional deflection regimes, which are known from the studies of PhC gratings, are obtained in PhC prisms and solid uniform prisms, i.e. without higher diffraction orders. ©2015 Optical Society of America.
Open Access
Calculation of the scalar diffraction field from curved surfaces by decomposing the three-dimensional field into a sum of Gaussian beams
(Optical Society of America, 2013) Şahin, E.; Onural, L.
We present a local Gaussian beam decomposition method for calculating the scalar diffraction field due to a twodimensional field specified on a curved surface. We write the three-dimensional field as a sum of Gaussian beams that propagate toward different directions and whose waist positions are taken at discrete points on the curved surface. The discrete positions of the beam waists are obtained by sampling the curved surface such that transversal components of the positions form a regular grid. The modulated Gaussian window functions corresponding to Gaussian beams are placed on the transversal planes that pass through the discrete beam-waist position. The coefficients of the Gaussian beams are found by solving the linear system of equations where the columns of the system matrix represent the field patterns that the Gaussian beams produce on the given curved surface. As a result of using local beams in the expansion, we end up with sparse system matrices. The sparsity of the system matrices provides important advantages in terms of computational complexity and memory allocation while solving the system of linear equations.
Open Access
Scalar diffraction field calculation from curved surfaces via Gaussian beam decomposition
(Optical Society of America, 2012-06-29) Şahin, E.; Onural, L.
We introduce a local signal decomposition method for the analysis of three-dimensional (3D) diffraction fields involving curved surfaces. We decompose a given field on a two-dimensional curved surface into a sum of properly shifted and modulated Gaussian-shaped elementary signals. Then we write the 3D diffraction field as a sum of Gaussian beams, each of which corresponds to a modulated Gaussian window function on the curved surface. The Gaussian beams are propagated according to a derived approximate expression that is based on the Rayleigh-Sommerfeld diffraction model. We assume that the given curved surface is smooth enough that the Gaussian window functions on it can be treated as written on planar patches. For the surfaces that satisfy this assumption, the simulation results show that the proposed method produces quite accurate 3D field solutions.
Open Access
Spatial beam self-cleaning accompanied by self-similar propagation in few-mode graded-index fiber
(Optica Publishing Group (formerly OSA), 2023-07-20) Graini, Leila; Ortaç, Bülend
We numerically investigated a nonlinear Kerr beam self-cleaning (KBSC) dynamics accompanied by self-similar propagation regimes, which leads to single-mode parabolic pulse reshaping and simultaneously high beam quality based on KBSC, for special distributions of initially excited modes in graded-index multimode fiber (GRIN-MMF). We coupled a Gaussian pulse at 1060 nm, with 100 fs duration, into GRIN-MMF supporting 10 modes that fall into four discrete mode groups. As a result, by using initial powers below the KBSC threshold reported in the literature, the output spatial beam evolves from a speckled pattern into a bell-shaped beam; hence, the generated parabolic pulse is mainly carried by the fundamental mode, which is boosted by the KBSC process. We also provide promising indications for KBSC on different higher-order modes.
Open Access
Unidirectional transmission in photonic-crystal gratings at beam-type illumination
(Optical Society of American (OSA), 2010) Cakmak, A.O.; Colak, E.; Serebryannikov, A.E.; Özbay, Ekmel
Unidirectional transmission is studied theoretically and experimentally for the gratings with one-side corrugations (non-symmetric gratings), which are based on two-dimensional photonic crystals composed of alumina rods. The unidirectional transmission appears at a fixed angle of incidence as a combined effect of the peculiar dispersion features of the photonic crystal and the properly designed corrugations. It is shown that the basic unidirectional transmission characteristics, which are observed at a plane-wave illumination, are preserved at Gaussian-beam and horn antenna illuminations. The main attention is paid to the single-beam unidirectional regime, which is associated with the strong directional selectivity arising due to the first negative diffraction order. An additional degree of freedom for controlling the transmission of the electromagnetic waves is obtained by making use of the asymmetric corrugations at the photonic crystal interface. © 2010 Optical Society of America.