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dispersion--waves
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Effect of dispersion fluctuations on longitudinal gain evolution in phase-sensitive parametric amplifiers
, Article Optics InfoBase Conference Papers ; 2014 ; ISSN: 21622701 ; ISBN: 9781557529992 ; Vedadi, A ; Shoaie, M. A ; Soto, M. A ; Denisov, A ; Mehrany, K ; Thevenaz, L ; Bres, C. S ; Sharif University of Technology
Abstract
A Brillouin probing method is proposed to extract the distribution of signal power along phase-sensitive parametric amplifiers. Operation near the zero-dispersion-wavelength shows enhanced sensitivity to dispersion fluctuations, allowing effective extraction of the dispersion map
The nonlinear diffusion bandwidth: A simple tool for optimizing dispersion maps
, Article Optical Transmission, Switching, and Subsystems IV, Gwangju, 5 September 2006 through 7 September 2006 ; Volume 6353 I , 2006 ; 0277786X (ISSN) ; 0819464481 (ISBN); 9780819464484 (ISBN) ; Fischer, J. K ; Louchet, H ; Jamshidi, K ; Petermann, K ; Sharif University of Technology
2006
Abstract
The concept of a nonlinear transfer function of a fibre-optic communication link is reviewed. Also an approximation of the nonlinear transfer function is introduced, which allows to define an equivalent single-span model of a dispersion-managed multi-span system. In this paper we will show its limits of validity and try to extent these limits by enhancing the theoretical model. In this respect we will discuss the impact of dispersion precompensation and show the influence of residual dispersion per span, number of spans and local dispersion on transmission systems with on-off keying and differential phase-shift keying modulation formats. This approach allows fast assessment of the...
Dispersion and gain investigation of free electron laser based on legendre polynomial expansion
, Article Photonic Applications in Nonlinear Optics, Nanophotonics, and Microwave Photonics, Toronto, ON, 12 September 2005 through 14 September 2005 ; Volume 5971 , 2005 ; 0277786X (ISSN) ; Chamanzar, M ; Mehrany, K ; Rashidian, B ; Ranjbaran, M ; Morandotti R. A ; Ruda H. E ; Yao J ; Sharif University of Technology
2005
Abstract
Free electron lasers have been the subject of intensive interest during the recent decades. In this paper, free electron laser having sheet electron beam with arbitrary inhomogeneous profile of transverse distribution of the beam current density is studied in the linear regime, whereas a novel approach based on the Legendre polynomial expansion of eigenfunctions, already used in analyzing optical structures including stratified structures and diffraction gratings, is adapted to find the eigenfunctions and eigenvalues of the structure. As for this method is unconditionally stable, it works pretty well even in those cases in which the conventional transfer matrix method suffers from numerical...
Nondestructive Test in Geopolymer Concrete with Aid of Ultrasonic Waves
, M.Sc. Thesis Sharif University of Technology ; Toufigh, Vahab (Supervisor)
Abstract
In recent decades, particle composite materials have a wide range of applications in engineering. Particle composites are a group of heterogeneous materials with different length scales and are characterized by particles that are randomly distributed in a matrix phase. Geopolymer concrete is a special type of concrete that its binder is made by reacting alumina and silicate carriers with an activating agent and in recent years with the expansion of its use has reduced the amount of cement consumption. In addition to the many advantages of geopolymer concrete, it has disadvantages in terms of setting time. That is why the use of cement has been proposed as a solution to the problem. This...
Circuit model for mode extraction in lossy/lossless photonic crystal waveguides
, Article Journal of the Optical Society of America B: Optical Physics ; Volume 29, Issue 1 , 2012 , Pages 170-177 ; 07403224 (ISSN) ; Khavasi, A ; Miri, M ; Mehrany, K ; Sharif University of Technology
Abstract
An approximate circuit model is proposed for mode extraction in two-dimensional photonic crystal waveguides. The dispersion equation governing the complex propagation constant of the photonic crystal waveguide is then related to the resonance condition in the proposed circuit model. In this fashion, a scalar complex transcendental equation is given for mode extraction. To avoid searching for the complex roots of the derived scalar dispersion equation, however, the real and imaginary parts of the sought-after propagation constant are extracted by using the physical resonance condition and its corresponding quality factor in the here-proposed circuit model, respectively. All the necessary...
Scattering of an anti-plane shear wave by an embedded cylindrical micro-/nano-fiber within couple stress theory with micro inertia
, Article International Journal of Solids and Structures ; Volume 58 , April , 2015 , Pages 73-90 ; 00207683 (ISSN) ; Goodarzi, A ; Delfani, M. R ; Haftbaradaran, H ; Sharif University of Technology
Elsevier Ltd
2015
Abstract
The inadequacy of traditional theory of elasticity in describing such a phenomenon as dispersion associated to a propagating wave with wavelength comparable to the intrinsic length of the medium of interest is well-known. Moreover, under certain circumstances it is incapable of capturing all the propagating waves. A remedy to such dilemmas is the employment of the more accurate higher order continuum theories which give rise to the appearance of at least one new characteristic length in the formulation. The experimental evidences as well as lattice dynamic analysis suggest that, although higher order continuum theories result in some improvements, but cannot fully overcome the...
Inverse scattering problem of reconstruction of an embedded micro-/nano-size scatterer within couple stress theory with micro inertia
, Article Mechanics of Materials ; Volume 103 , 2016 , Pages 123-134 ; 01676636 (ISSN) ; Fotouhi, M ; Shodja, H. M ; Sharif University of Technology
Elsevier
2016
Abstract
As long as the size of the embedded scatterer in comparison to the internal length scale of its surrounding elastic matrix is large, then the linear sampling method (LSM) and singular sources method (SSM) can be used in conjunction with classical theory of elasticity to reconstruct the size of the scatterer with reasonable accuracy. On the other hand, for the micro-/nano-size scatterer this treatment ceases to hold due to the shortcomings of classical theory of elasticity. Moreover, in the realm of this theory, wave propagation through a homogeneous medium is nondispersive on the macro-scale even for high frequency waves. This outcome is incompatible with the practical observations. A remedy...
Sensitive and accurate dispersion map extraction of HNLFs by frequency tuning of a degenerate FWM
, Article Journal of Lightwave Technology ; Volume 34, Issue 18 , 2016 , Pages 4197-4204 ; 07338724 (ISSN) ; Vedadi, A ; Shoaie, M. A ; Bres, C. S ; Mehrany, K ; Sharif University of Technology
Institute of Electrical and Electronics Engineers Inc
Abstract
A sensitive and accurate method for dispersion map extraction along an arbitrarily profiled highly nonlinear fiber (HNLF) is proposed. High sensitivity is achieved by positioning the wavelength of a signal at the band edge of the modulation instability (MI) spectrum generated by an intense degenerate four wave mixing (FWM) pump. In doing so, the to-be-extracted dispersion fluctuations leave a more drastic effect on the FWM-generated power since they either inflate or deflate the MI spectrum. The accuracy of the method is increased by monitoring the distribution of power along the fiber. Once the power distribution is measured along the fiber, dispersion map of the HNLF is extracted using an...
Acoustical gas-leak detection in the presence of multiple reflections, dispersion, and uncorrelated noise using optimized residual complexity
, Article Journal of the Acoustical Society of America ; Volume 140, Issue 3 , 2016 , Pages 1817-1827 ; 00014966 (ISSN) ; Amjadi, A ; Bahrampour, A. R ; Ravanbod, H ; Tofighi, S ; Sharif University of Technology
Acoustical Society of America
2016
Abstract
Precise acoustical leak detection calls for robust time-delay estimates, which minimize the probability of false alarms in the face of dispersive propagation, multiple reflections, and uncorrelated background noise. Providing evidence that higher order modes and multi-reflected signals behave like sets of correlated noise, this work uses a regression model to optimize residual complexity in the presence of both correlated and uncorrelated noise. This optimized residual complexity (ORC) is highly robust since it takes into account both the level and complexity of noise. The lower complexity of the dispersive modes and multiple reflections, compared to the complexity of the plane mode, points...
Develop of a fully nonlinear and highly dispersive water wave equation set; analysis of wave interacting with varying bathymetry
, Article Prediction and Simulation Methods for Geohazard Mitigation - Proceedings of the International Symposium on Prediction and Simulation Methods for Geohazard Mitigation, IS-KYOTO 2009, 25 May 2009 through 27 May 2009, Kyoto ; 2009 , Pages 213-218 ; 9780415804820 (ISBN) ; Ataie Ashtiani, B ; Sharif University of Technology
Abstract
Extended Boussinesq-type water wave equations are derived in two horizontal dimensions to capture the nonlinearity effects and frequency dispersion of wave in a high accuracy order. A multi-parameter perturbation analysis is applied in several steps to extend the previous second order Boussinesq-type equations in to 6th order for frequency dispersion and consequential order for nonlinearity terms. The presented high-order Boussinesq-type equation is applied in a numerical model to simulate the wave field transformation due to physical processes such as shoaling, refraction and diffraction. The models results are compared with available experimental data which obtained in a laboratory wave...
Polymer/nanodiamond composites - a comprehensive review from synthesis and fabrication to properties and applications
, Article Advances in Colloid and Interface Science ; Volume 269 , 2019 , Pages 122-151 ; 00018686 (ISSN) ; Salkhi Khasraghi, S ; Hashemi, M ; Rabiei, S ; Shojaei, A ; Sharif University of Technology
Elsevier B.V
2019
Abstract
Nanodiamond (ND)is an allotrope of carbon nanomaterials which exhibits many outstanding physical, mechanical, thermal, optical and biocompatibility characteristics. Meanwhile, ND particles possess unique spherical shape containing diamond-like structure at the core with graphitic carbon outer shell which intuitively contains many oxygen-containing functional groups at the outer surface. Such superior properties and unique structural morphology of NDs are essentially attractive to develop polymer composites with multifunctional properties. However, despite a long history from the discovery of NDs, which is dated back to the1960s, this nanoparticle has been less explored in the field of...
Torsional surface wave propagation in a transversely isotropic FG substrate with piezoelectric over-layer within surface/interface theory
, Article Acta Mechanica ; Volume 231, Issue 6 , 2020 , Pages 2203-2216 ; Mohamadi Shodja, H ; Sharif University of Technology
Springer
2020
Abstract
Propagation of the torsional surface waves in a medium consisting of a functionally graded (FG) substrate bonded to a thin piezoelectric over-layer has been analytically formulated in the mathematical framework of surface/interface elasticity theory. In the cases where the wavelength and/or the thickness of the over-layer are comparable to the surface/interface characteristic length, then the surface/interface effects are not negligible. It is assumed that the over-layer is made of hexagonal 622 crystals with a single axis of rotational symmetry coinciding with the axis of polarization. The half-space is made of an FG transversely isotropic material in which the elasticity tensor and the...
Improved depth resolution and depth-of-field in temporal integral imaging systems through non-uniform and curved time-lens array
, Article Optics Express ; Volume 28, Issue 5 , 2020 , Pages 6261-6276 ; Behzadfar, S ; Kavehvash, Z ; Sharif University of Technology
OSA - The Optical Society
2020
Abstract
Observing and studying the evolution of rare non-repetitive natural phenomena such as optical rogue waves or dynamic chemical processes in living cells is a crucial necessity for developing science and technologies relating to them. One indispensable technique for investigating these fast evolutions is temporal imaging systems. However, just as conventional spatial imaging systems are incapable of capturing depth information of a three-dimensional scene, typical temporal imaging systems also lack this ability to retrieve depth information—different dispersions in a complex pulse. Therefore, enabling temporal imaging systems to provide these information with great detail would add a new facet...
Spectral analysis using a new opto-mechanical instrument
, Article Journal of Applied Sciences ; Volume 8, Issue 20 , 2008 , Pages 3669-3675 ; 18125654 (ISSN) ; Golnabi, H ; Sharif University of Technology
2008
Abstract
Design and operation of an opto-mechanical system for spectral analysis using a double fiber design for light delivery are reported in this study. A simple mechanical drive system is used, which is able to perform a fine course of angular motion for the scanning of the dispersive optical element. The presented system consists of a mechanical drive system, a dispersive element, a double fiber assembly and a photodetector. A source light, a digital multimeter and a PC are used to test the presented design. The first-order diffraction of the white light source is obtained by using a reflection diffraction grating in Littrow arrangement. By comparing the output reflection signals of the plane...
A higher-order Boussinesq-type model with moving bottom boundary: Applications to submarine landslide tsunami waves
, Article International Journal for Numerical Methods in Fluids ; Volume 53, Issue 6 , 2007 , Pages 1019-1048 ; 02712091 (ISSN) ; Najafi Jilani, A ; Sharif University of Technology
2007
Abstract
A two-dimensional depth-integrated numerical model is developed using a fourth-order Boussinesq approximation for an arbitrary time-variable bottom boundary and is applied for submarine-landslide-generated waves. The mathematical formulation of model is an extension of (4,4) Padé approximant for moving bottom boundary. The mathematical formulations are derived based on a higher-order perturbation analysis using the expanded form of velocity components. A sixth-order multi-step finite difference method is applied for spatial discretization and a sixth-order Runge-Kutta method is applied for temporal discretization of the higher-order depth-integrated governing equations and boundary...
Waves in linear time-varying dielectric media
, Article 16th European Conference on Antennas and Propagation, EuCAP 2022, 27 March 2022 through 1 April 2022 ; 2022 ; 9788831299046 (ISBN) ; Mirmoosa, M. S ; Tretyakov, S. A ; Sharif University of Technology
Institute of Electrical and Electronics Engineers Inc
2022
Abstract
In this paper, focusing on the frequency domain, we write the constitutive relation and the Helmholtz equation for linear, dispersive, and inhomogeneous time-varying media. Next, by assuming spatial homogeneity, we simplify the equations and explain how to calculate dispersion curves (the angular frequency with respect to the wave vector) for propagating waves. Furthermore, we show that under the simplifying assumption of instantaneous response, the developed general approach provides the same dispersion curves as reported earlier for the dispersion-less model of time-varying dielectric media. We believe that this study is important for investigations of wave phenomena in time-varying media,...
Dispersion around a circular cylinder in surface wave motion
, Article Scientia Iranica ; Vol. 21, issue. 3 , 2014 , p. 548-556 ; 10263098 ; Jamali, M ; Sharif University of Technology
Abstract
In this paper, we examine fluid flow and associated dispersion around a circular cylinder under progressive surface wave motion. The flow field and vortex shedding patterns were studied using flow visualization and Particle Image Velocimetry (PIV). Several patterns of vortex shedding were identified around a single cylinder. The vortex shedding patterns under progressive wave motion are similar to those observed in planar oscillatory flow, except in the way the vortices form and in the orientation they take. The observed vortex patterns in progressive wave motion are more unstable than those in planar oscillatory flow. Using particle tracking and the Lagrangian dispersion method, the...
Wave dispersion under finite deformation
, Article Wave Motion ; Volume 50, Issue 3 , April , 2013 , Pages 374-388 ; 01652125 (ISSN) ; Hussein, M. I ; Sharif University of Technology
2013
Abstract
We derive exact dispersion relations for axial and flexural elastic wave motion in a rod and a beam under finite deformation. For axial motion we consider a simple rod model, and for flexural motion we employ the Euler-Bernoulli kinematic hypothesis and consider both a conventional transverse motion model and an inextensional planar motion model. The underlying formulation uses the Cauchy stress and the Green-Lagrange strain without omission of higher order terms. For all models, we consider linear constitutive relations in order to isolate the effect of finite motion. The proposed theory, however, is applicable to problems that also exhibit material nonlinearity. For the rod model, we...
The effect of fractures' geometrical properties on the recovery mechanism of the top-down in situ combustion process
, Article Petroleum Science and Technology ; Volume 30, Issue 2 , Feb , 2011 , Pages 147-158 ; 10916466 (ISSN) ; Kharrat, R ; Sharif University of Technology
2011
Abstract
The top-down in situ combustion (ISC) involves the stable propagation of the combustion front from the top vertical injector to the bottom horizontal producer. Apart from laboratory studies in conventional sandstones, no application of the process in fractured carbonates has been addressed yet. The authors modified a successful combustion tube history matched model of an Iranian low-permeable heavy oil reservoir called Kuh-E-Mond to investigate the feasibility of ISC in fractured carbonate reservoirs mimicking block-scale combustion cells. Effects of fractured geometrical properties such as orientation, location, extension, density, spacing, and dispersion were considered. Results confirmed...
Square-hexagonal nanostructured photonic crystal fiber at 1550 nm wavelength
, Article 10th International Symposium on Communication Systems, Networks and Digital Signal Processing, CSNDSP 2016, 20 July 2016 through 23 July 2016 ; 2016 ; 9781509025268 (ISBN) ; Nikoosohbat, A ; Mohebzadeh Bahabady, A ; Chizari, A ; Sharif University of Technology
Institute of Electrical and Electronics Engineers Inc
2016
Abstract
Photonic crystal fibers (PCFs) are widely used in optical communications systems, nonlinear devices, gas sensors, high power transmission, and so on. Photonic crystal fiber with minimum values of confinement loss, nonlinear effects, and chromatic dispersion is used in optical communication. But in some applications, high nonlinear coefficient is required. This paper presents new design of index-guiding photonic crystal fiber (IGPCF) with characteristics appropriate for nonlinear applications. In the present design with a square-hexagonal nano-structure having air holes with unequal diameters, nearly zero dispersion at the wavelength range of 1540 to 1550 nm is achieved. The simulation...