Search for: photonic-crystals
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    Design and modeling of a high single mode power long wavelength InGaAsP photonic crystal VCSEL

    , Article Australian Journal of Basic and Applied Sciences ; Volume 5, Issue 7 , 2011 , Pages 1064-1069 ; 19918178 (ISSN) Marjani, S ; Faez, R ; Marjani, A ; Sharif University of Technology
    In the present work, a new vertical cavity surface emitting laser (VCSEL) structure employing combined oxide layer and single defect photonic crystal index guiding layer has been investigated for L-band optical fiber application. The basic design goal was to obtain photonic crystal VCSEL (PhC VCSEL) with the high power, high slop efficiency and low threshold that operate at 1.55-1.6μm wavelength single mode region. By using the combination of photonic crystal and oxide layer, we have achieved high power VCSEL that operated fundamental mode. The influence of the hole etching depth of photonic crystal looking for the highest power and the lowest threshold current is also investigated  

    Novel variational approach for analysis of photonic crystal slabs

    , Article Materials Research Express ; Volume 2, Issue 5 , April , 2015 ; 20531591 (ISSN) Aram, M. H ; Khorasani, S ; Sharif University of Technology
    Institute of Physics Publishing  2015
    We propose a new method, based on variational principle, for the analysis of photonic crystal (PC) slabs. Most of the methods used today treat PC slabs as three-dimensional (3D) crystal, and this makes these methods very time and/or memory consuming. In our proposed method, we use the Bloch theorem to exp and the field on infinite plane waves, whose amplitudes depend on the component perpendicular to the slab surface. By approximating these amplitudes with appropriate functions, we can find modes of PC slabs almost as fast as we can find modes of two-dimensional crystals. In addition to this advantage, we can also calculate radiation modes with this method, which is not feasible with the 3D... 

    Design and Analysis of Delay Lines Based on Photonic Crystal Coupled Cavities

    , M.Sc. Thesis Sharif University of Technology Bayat, Mina (Author) ; Khorasani, Sina (Supervisor)
    In the recent years, photonic crystal (PhC) devices vastly have been paid attention due to their ignorable loss, very low group velocity, flexibility in shape and dimension.In this thesis a PhC coupled cavity ring known as superresonator is introduced and its properties and applications is studied. Also modes of the structure are extracted through both coupled-resonator model and FDTD method, and two of its application is described and studied. Add-drop filter is one of the essential devices in WDM systems. First, an application of superresonator in designing add-drop filters is explained and a novel filter based on the superresonator is introduced and analyzed by FDTD and coupled mode... 

    Numerical study of index guiding quasi-crystal fibers by employing FEM method

    , Article Optoelectronics and Advanced Materials, Rapid Communications ; Volume 11, Issue 3-4 , 2017 , Pages 134-138 ; 18426573 (ISSN) Bahrampour, A ; Dehghanisanij, M ; Rooholamininejad, H ; Bahrampour, A ; Sharif University of Technology
    National Institute of Optoelectronics  2017
    In this paper quasi photonic crystal fibers (QPCFs) based on 8-fold and Penrose symmetries are analyzed. The confinement loss of both proposed QPCFs with employing perfect matching layer by finite element method has been calculated. It is shown for both presented structures, the confinement loss is negligible relative to Rayleigh scattering loss. The birefringence of Penrose tile QPCF, is 80 times greater than that of Amnan Beenker quasicrystal fiber. We present numerically the existence of endlessly single mode fiber and zero birefringence QPCFs as advantage of employing novel rotational symmetry. © 2017, National Institute of Optoelectronics. All rights reserved  

    Band structures of coupled electromagnetic slow waves

    , Article Journal of Optics A: Pure and Applied Optics ; Volume 6, Issue 10 , 2004 , Pages 937-942 ; 14644258 (ISSN) Mehrany, K ; Rashidian, B ; Sharif University of Technology
    In this paper, a modified transfer matrix method is applied for the analysis of electromagnetic slow wave propagation in Kronig-Penny photonic crystals. Analytic expressions for Bloch wavenumbers in terms of normalized frequency are derived and the asymptotic behaviour of electromagnetic slow wave propagation in these structures is investigated at different regimes. The tight binding method is also used for the analysis of electromagnetic slow wave propagation in Kronig-Penny photonic crystals and analytic expressions are given. It has been shown that forbidden wavenumbers rather than forbidden frequencies can be observed under specific circumstances  

    Interface electromagnetic waves between Kronig-Penney photonic crystals

    , Article Aplications of Photonic Technology, Quebec City, 1 June 2002 through 6 June 2002 ; Volume 4833 , 2002 , Pages 535-541 ; 0277786X (ISSN) Mehrany, K ; Momeni, B ; Khorasani, S ; Rashidian, B ; Sharif University of Technology
    The electromagnetic interface states formed in a heterostructure composed of two semi-infinite Kronig-Penny photonic crystals were studied. Modified transfer matrices were used for the study to show strong similarity between solid-state physics and electromagnetics. The calculations were limited to TE polarization and the numerical examples for both surface and interface states were given  

    Quantum optics of a quantum dot embedded in a photonic crystal cavity

    , Article Photonic Crystal Materials and Devices VII, San Jose, CA, 21 January 2008 through 23 January 2008 ; Volume 6901 , 2008 ; 0277786X (ISSN); 9780819470768 (ISBN) Sodagar, M ; Khorasani, S ; Atabaki, A. H ; Adibi, A ; Sharif University of Technology
    In this paper we analyze a disk-like quantum dot embedded in an engineered two-dimensional (2D) photonic crystal cavity as an artificial atom. In this quantum dot electron and hole form an exciton where photon and electron-hole bound state can interact. Within the engineered electromagnetic vacuum of the PBG material, the exciton can emit and reabsorb a photon. If the exciton energy lies near the photonic band gap edge the exciton level splits into two levels. This is similar to the interaction of field and an atom in a high Q cavity. Here excitonic states are evaluated taking in to account the band mixing for holes. Also energy associated with dressed exction is evaluated  

    Determination of complex modes in photonic crystal waveguides using the phase variation in characteristic coefficients

    , Article Optics Letters ; Volume 37, Issue 15 , 2012 , Pages 3078-3080 ; 01469592 (ISSN) Hosseinnia, A. H ; Khavasi, A ; Sarrafi, P ; Mehrany, K ; Sharif University of Technology
    OSA Pub  2012
    An efficient frequency-domain method, the phase variation monitoring (PVM) method, is proposed to determine the electromagnetic eigenmodes in two-dimensional photonic crystal waveguides. The proposed method is based on monitoring the reflection and transmission coefficients of incident plane waves. It is successfully applied to an illustrative line-defect photonic crystal waveguide and proved to be capable of calculating the in-plane leakage through the finite-size photonic crystal surrounding the line-defect. Calculation of the leakage loss is not only important for proper understanding of wave propagation within the defect but also for its significant role in applications of photonic... 

    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) Habibi, N ; Khavasi, A ; Miri, M ; Mehrany, K ; Sharif University of Technology
    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... 

    Superprism properties in 2D polymer photonic crystals at high normal frequencies

    , Article Optics Communications ; Volume 282, Issue 17 , 2009 , Pages 3620-3625 ; 00304018 (ISSN) Asadi, R ; Tavassoly, M. T ; Khorasani, S ; Sharif University of Technology
    The superprism effects of higher bands, i.e., for normal frequencies of higher than one, in two-dimensional (2D) polymer photonic crystals (PCs) are investigated. It is shown that in a polymer PC of triangular symmetry with filling factor of about 31%, the gradual transition of the hexagonal into triangular equi-frequency dispersion contours leads to a strong superprism in the 6th band at a normal frequency of 1.2. This dispersion is more prominent than those observed in the lower bands in 2D PCs. Also, this requires a lattice constant longer than the concerned wavelength. Furthermore, in a 2D polymer PC with a filling factor of about 83% a strong discontinuous superprism effect occurs at... 

    Optimization of ASR and Combination with FMM for the Analysis of Metamaterials and Photonic Crystals in Three Dimensional Structures

    , M.Sc. Thesis Sharif University of Technology Nekuee, Amir Hossein (Author) ; Akbari, Mahmood (Supervisor) ; Mehrani, Khashayar (Supervisor)
    To design and identify specific properties of Metamaterials we need methods that accurately and quickly provide precise information about these composite materials for engineers. In this thesis we use FMM method with ASR technique for the analysis of Metamaterials and photonic crystals in three dimensional structures. In the second chapter FMM method is described briefly and then ASR technique for applying in the FMM method is introduced. ASR approach has large convergence rates in all types of gratings particularly metallic ones and with optimization that we have done for two dimensional periodic gratings convergence speed is increased more. In the third chapter using ASR reflection and... 

    Rigorous Calculation of Guided Modes in Photonic Crystal Waveguides and Contriving Homogenized Models

    , M.Sc. Thesis Sharif University of Technology Habibi, Nasim (Author) ; Mehrany, Khashayar (Supervisor)
    In this thesis an approximate method is proposed for analysis of two dimensional photonic crystal waveguides. In this method an equivalent impedance is assigned to photonic crystal regions and the waveguide region is modeled with a transmission line. Waveguide’s loss is also analysed and computed by this method. In other words the proposed method is able to determine the complex propagation constant of guided modes without computing any complex roots for dispersion equation. Although like any other approximate method, the accuracy of this method is dependent to some special conditions but it’s advantage over other numerical methods is its simplicity and its capability for waveguide designs.... 

    Wideband tunable photonic crystal cavity with electrostatic actuation

    , Article 2012 IEEE Photonics Conference, IPC 2012, 23 September 2012 through 27 September 2012 ; September , 2012 , Pages 266-267 ; 9781457707315 (ISBN) Miri, M ; Sodagar, M ; Eftekhar, A. A ; Mehrany, K ; Rashidian, B ; Adibi, A ; Sharif University of Technology
    We present a wideband tunable optical cavity based on electrostatic actuation. Over 60nm shift in wavelength is achieved by applying less than 1 Volt corresponds to a mechanical displacement of 30nm  

    A transmission line resonator model for fast extraction of electromagnetic properties of cavities in two-dimensional photonic crystals

    , Article IEEE Photonics Journal ; Volume 2, Issue 4 , August , 2010 , Pages 677-685 ; 19430655 (ISSN) Miri, M. A ; Khavasi, A ; Miri, M ; Mehrany, K ; Sharif University of Technology
    In this paper, photonic cavities made of point defects in 2-D photonic crystals are modeled by finite-size transmission lines terminated at both ends by appropriate scalar impedances. The proposed model forms a simple transmission line resonator and is demonstrated to be quite beneficial in fast extraction of resonant frequency, quality factor, and mode profile of such photonic cavities. In this manner, an approximate yet quite accurate approach is introduced to characterize the electromagnetic properties of photonic crystal cavities. This method is successfully applied to different structures for both major polarizations and is shown to be as accurate as rigorous numerical methods, viz. the... 

    Calculation of density of states in a 2D photonic crystal with separable profile of permittivity

    , Article Photonic Crystal Materials and Devices VII, San Jose, CA, 21 January 2008 through 23 January 2008 ; Volume 6901 , 2008 ; 0277786X (ISSN); 9780819470768 (ISBN) Baradaran Ghasemi, A. H ; Khorasani, S ; Latifi, H ; Atabaki, A. H ; The International Society for Optical Engineering (SPIE) ; Sharif University of Technology
    When the periodic permittivity of two-dimensional (2D) photonic crystal (PC) can be separated in x- and y- coordinates, one can consider the structure as two separate 1D photonic crystals, one of them being periodic in x coordinate and the other in y coordinate. If it is possible to find a proper separable permittivity function, we can approximate a 2D PC with two distinct 1D structures. One of the advantages is rapid calculation the density of state of a 2D PC. In this article an analytical calculation of the density of states for such a 2D PC has been done with the aim of taking this advantage. For calculating the density of states we use the effective resonance approach to analyze the 1D... 

    Plasmonic propagation modes of a structured two-dimensional conducting interface

    , Article Journal of Optics A: Pure and Applied Optics ; Volume 10, Issue 2 , 2008 ; 14644258 (ISSN) Zandi, H ; Khorasani, S ; Hosseini, A ; Mehrany, K ; Rashidian, B ; Adibi, A ; Sharif University of Technology
    In this paper, we present a detailed analysis of a two-dimensional lossless and non-dispersive structured conducting interface, which is approximated by a two-dimensional ideal one-component plasma-like conducting sheet enclosed by two isotropic dielectrics. We present a Green's function formalism to analyze the propagation of surface plasmons and find new expressions. We also present analytical extensions of the approach to include loss, and discuss the results and applications of the theory. We study the symmetry properties of eigenmodes and show that the symmetries of the eigenmodes at high-symmetry points of the Brillouin zone are similar to those of the E-polarization eigenmodes of a... 

    Propagation of light in photonic crystal fibre devices

    , Article Journal of Optics A: Pure and Applied Optics ; Volume 7, Issue 11 , 2005 , Pages 663-668 ; 14644258 (ISSN) Dabirian, A ; Akbari, M ; Mortensen, N. A ; Sharif University of Technology
    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  

    Analysis of Kronig-Penny photonic crystals by modified transfer matrices

    , Article Photonic Bandgap Materials and Devices 2002, 19 January 2002 through 25 January 2002 ; Volume 4655 , 2002 , Pages 260-266 ; 0277786X (ISSN) Khorasani, S ; Rashidian, B ; Sharif University of Technology
    SPIE  2002
    In this article, the transfer matrix method (TMM) is modified for study of optical wave propagation in layered media with conducting interfaces. Both the TE and TM mode transfer matrices are presented and their properties are discussed. The application of the modified TMM to study of propagation in a Kronig-Penny photonic crystal is explained. The practical realization of a Kronig-Penny photonic crystal through heterostructures with conducting interfaces is also demonstrated. © 2002 SPIE  

    Surface wave excitation control by using interface conductivity on one-dimensional photonic crystals

    , Article Novel Optical Systems Design and Optimization V, Seatle, MA, 9 July 2002 through 9 July 2002 ; Volume 4768 , 2002 , Pages 170-175 ; 0277786X (ISSN) Mehrany, K ; Khorasani, S ; Rashidian, B ; Sharif University of Technology
    In several recent papers, layered waveguide structures with conductive interfaces have been discussed, whose propagation properties are controlled by a transverse voltage. These structures have wide range of applications. In this paper, surface wave excitation on one-dimensional photonic crystals at the presence of interface conductivity is discussed. It is shown that excitation of electromagnetic surface waves can be controlled by the interface conductivity. This property can be used in constructing miscellaneous optical devices such as optical modulators, switches and tunable optical filters. Devices based on these waves can be superior to surface plasmon waves since they are not lossy.... 

    A heuristic approach to the realization of the wide-band optical diode effect in photonic crystal waveguides

    , Article Journal of Optics (United Kingdom) ; Volume 15, Issue 7 , June , 2013 ; 20408978 (ISSN) Khavasi, A ; Rezaei, M ; Fard, A. P ; Mehrany, K ; Sharif University of Technology
    In this paper a highly efficient optical diode is demonstrated in photonic crystal waveguides with broken spatial symmetry. The structure is made of isotropic linear materials and does not need high power optical beams or strong magnetic fields. While the proposed structure shows almost complete light transmission (>99%) in one direction, it blocks light transmission in the opposite direction. This unidirectional transmission is retained within a wide range of frequencies (>4% of central frequency). In order to achieve an optical diode effect, the optical mode of the waveguide is manipulated by designing an ultra-compact mode converter and an efficient mode filter. The dimensions of the...