Sharif Digital Repository

In this article, the feasibility of a programmable diffraction grating based on the interaction of light and controlled interface charges is explored. The diffraction grating is obtained by stacking the plasma wave modulator/switch1-4, and programming is realized by controlling the densities of interface charges via independent DC transverse voltages as discussed throughout. It is shown that the diffraction efficiency, polarization, and even the direction of reflection and transmission modes can be controlled  

Li's Fourier factorization rule [J. Opt. Soc. Am. A 13, 1870 (1996)] was recently shown to be problematic to apply to highly conducting metallic gratings. We provide further information about the applicability of different differential methods and are concerned with the relation of observed numerical artifacts, the total number of retained space harmonics, the presence of both positive and negative permittivity inside the groove region, and the validity of Li's inverse rule. Two different cases corresponding to lossless and low-loss binary metallic gratings are considered, and it is shown that an increase in the number of retained space harmonics can relieve the presence of numerical... 

We describe a semi-analytical approach for the three-dimensional analysis of photonic crystal fibre devices. The approach relies on modal transmission-line theory. We offer two examples illustrating the utilization of this approach in photonic crystal fibres: the verification of the coupling action in a photonic crystal fibre coupler and the modal reflectivity in a photonic crystal fibre distributed Bragg reflector. © 2005 IOP Publishing Ltd  

The idea of pure coupled mode approach is extended to the analysis of volume grating structures. In this approach, diffraction orders inside the grating are expanded over TE and TM components and unperturbed wavevectors are used instead of Floquet wavevectors of conventional coupled wave approach. Coupling between these orders are considered to model the diffraction. Three-dimensional grating structures are analyzed, and comparisons with rigorous coupled wave analysis are made to verify the accuracy and determine the range of applicability of the proposed method. © 2004 IEEE  

We present an analytical method for solution of one-dimensional optical systems, based on the differential transfer matrices. This approach can be used for exact calculation of various functions including reflection and transmission coefficients, band structures, and bound states. We show the consistency of the WKB method with our approach and discuss improvements for even symmetry and infinite periodic structures. Moreover, a general variational representation of bound states is introduced. As application examples, we consider the reflection from a sinusoidal grating and the band structure of an infinite exponential grating. An excellent agreement between the results from our differential... 

An improved coupled mode approach is presented for the analysis of plane-wave interaction with a spatially periodic permittivity dielectric layer. The method consists of two parts, in the first part the eigenvalues and eigenvectors of coupled mode system of equations are corrected to reduce the inherent errors, which arise by neglecting second-order derivatives. In the second part, a scattering matrix representation of cascaded systems is used to model the effect of boundaries. The problem under consideration is a 2-D planar grating structure illuminated by a TE polarized incident wave, but the method can be applied to other grating structures such as couplers, or any other structure for... 

The performance of the adaptive spatial resolution technique is improved by making the resolution function of the coordinate transformation as smooth as possible. To this end, the smoothness of the resolution function is probed and a quantitative criterion is proposed to make the jump points; which were conventionally equidistant from each other, regularized. The here-proposed regularization is applied to two different recent formulations and its effects on the overall convergence rate and on the presence of numerical artifacts in analysis of highly conducting gratings are studied. Dielectric and metallic gratings at optical and microwave frequencies are considered and the helpfulness of the... 

Three-dimensional vectorial diffraction analysis of phase and amplitude gratings in conical mounting is presented based on Legendre expansion of electromagnetic fields. In the so-called conical mounting, different fields components are coupled and the solution is not separable in terms of independent TE and TM cases. In contrast to conventional RCWA in which the solution is obtained using state variables representation of the coupled wave amplitudes by expanding space harmonic amplitudes of the fields in terms of the eigenfunctions and eigenvectors of the coefficient matrix defined by rigorous coupled wave equations, here the solution of first order coupled Maxwell's equations is expanded in... 

We have previously reported the results of plasmonic behavior of an Au nanodisk array in the far-field coupling regime under oblique illumination with transverse electric polarization. In this paper, those results are studied in more detail. Here, results for transverse magnetic polarization are also presented and discussed. In addition to the far-field coupling regime, the results for the near-field coupling regime are also reported. Effects of different parameters, such as substrate thickness and array periodicity on the shape of plasmon spectra are discussed. It will be shown that in the far-field coupling regime, the diffractive grating orders can have a major role in the behavior of the... 

A circuit model is proposed for periodic 1-D array of metallic strips in the sub-wavelength regime. The parameters of the proposed circuit and their dependence on frequency are all explicitly given by closed form expressions. The necessity of using numerical simulation to extract model parameters is thus sidestepped. It is demonstrated that the proposed model is valid at different incident angles and for arbitrary surrounding mediums given that there is only one propagating diffracted order outside the grating and only one guided mode supported by the slits. Both major polarizations are studied in this paper  

A new scheme for investigating electromagnetically induced grating in four-level cascade-Type of 87Rb cold atoms is presented. The novel result indicates that the diffraction efficiency of phase grating is dramatically enhanced due to the presence of an RF-driven field and a diffraction efficiency up to 34% can be obtained. Furthermore, it is found that the frequency detuning of the applied laser fields with the corresponding atomic transition and the interaction length can improve the efficiency of the phase grating in the present atomic model. This work has potential applications in all-optical communication processes  

The equivalent circuit approach (ECA) is used in this work to analyze and design a previously proposed one-dimensional planar blazed grating of the resonant type. The analysis covers both the classical Littrow configuration, when the direction of the relevant diffracted order coincides with that of the incident wave (Bragg blazing), and when these directions are different (off-Bragg blazing). Once the scattering problem of the grating structure is posed as a discontinuity problem inside an equivalent generalized waveguide (corresponding to the unit cell of the original structure) and studied in terms of its equivalent circuit network, the possibility of transferring all the power of the... 

Metagrating is a new concept for wavefront manipulation that, unlike phase gradient metasurfaces, does not suffer from low efficiency and also has a less complicated fabrication process. In this paper, a compound metallic grating (a periodic metallic structure with more than one slit in each period) is proposed for anomalous reflection. We propose an analytical method for analyzing the electromagnetic response of this grating. Closed-form and analytical expressions are presented for the reflection coefficients of zeroth diffracted order and also higher diffracted orders. The proposed method is verified against full-wave simulations and the results are in excellent agreement. Thanks to the... 

Three-dimensional vectorial diffraction analysis of gratings is presented based on Legendre polynomial expansion of electromagnetic fields. In contrast to conventional rigorous coupled wave analysis (RCWA) in which the solution is obtained using state variables representation of the coupled wave amplitudes, here the solution of first-order coupled Maxwell's equations is expanded in terms of Legendre polynomials, where Maxwell's equations are analytically projected in the Hilbert space spanned by Legendre polynomials. This approach yields well-behaved algebraic equations for deriving diffraction efficiencies and electromagnetic field profiles without facing the problem of numerical... 

A new formulation for the solution of wave propagation in inhomogeneous optical systems, based on the extension of conventional differential-transfer matrices into modified differential-transfer matrices, is given. In justification of our proposed method, several examples are presented, and the greater accuracy of our modified differential transfer matrices compared with that of conventional differential-transfer matrices is observed in several cases. It is also shown that the modified differential-transfer-matrix method is accurate enough even in those cases that the conventional differential-transfer-matrix method fails to yield acceptable results. © 2005 Optical Society of America  

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...