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optical-devices
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Design and construction of a fine drive system for scanning optical elements
, Article Optics and Laser Technology ; Volume 40, Issue 6 , 2008 , Pages 803-808 ; 00303992 (ISSN) ; Jafari, R ; Sharif University of Technology
2008
Abstract
The design and operation of a simple mechanical drive system, which is able to perform a fine course of angular motion, are reported. The system consists of a lead screw, a drive nut, sine bar legs, and an output shaft that can scan the optical holder mount. With a stepper motor coupled to the lead screw and interfaced to a PC, it is possible to control the scanning operation. When a 800 step/turn motor is used, it is possible to have an angular resolution of about 0.5 mdegree for a dynamic range of about 23°. The reproducibility of the results is about 0.22% for the scan angle and the hysteresis effect of the system is in the range of 1.71%. For a total scan of 51,200 steps, a scan angle of...
Photonic crystal devices analysis based on perturbation theory
, Article Photonic Crystal Materials and Devices IV, San Jose, CA, 23 January 2006 through 26 January 2006 ; Volume 6128 , 2006 ; 0277786X (ISSN); 0819461709 (ISBN); 9780819461704 (ISBN) ; Khorasani, S ; Atabaki, A ; SPIE ; Sharif University of Technology
2006
Abstract
A novel approach for photonic crystals devices analysis, based on perturbation theory is reported. In this method the photonic crystal device is considered as the superposition of a parent lattice and a perturbing one. Then the solution is investigated in terms of the eigensolutions of the parent lattice. This way, one can easily obtain analytic expressions within the first order perturbation, describing the effects of different parameters on the eigensolutions of the structure. The perturbation theory employed in this work is typical of what is conventionally used in quantum mechanics literature. The proposed method is explicit, works fast, and does not involve complicated numerical...
Investigation of Magnetic and Electromagnetic Methods in Electron Beam Shaping and their Scaling Behavior for Nanometric field Emitters
, M.Sc. Thesis Sharif University of Technology ; Rashidian, Bizhan (Supervisor)
Abstract
Nowadays electron beams have extensive applications in electon-optic devices such as microwave devices, electron microscopes and flat displays. So shaping and confinment of electron beams is of great importance. In the other hand, scaling of electron emitters to atomic limit causes new chalanges in reliability and beam shaping. Designing electron optic devices for nanoscale emitters needs great knowledge regarding materials properties and electron optic systems behavior in nano scale. In this study, beside providing basic optics of electron beam and effects Of external electronmagnetic fields, properties of electron optical devices
Considering nano scale limitations is considered. In...
Considering nano scale limitations is considered. In...
Tunable polarization converter based on one-dimensional graphene metasurfaces
, Article Journal of the Optical Society of America B: Optical Physics ; Volume 35, Issue 10 , 2018 , Pages 2574-2581 ; 07403224 (ISSN) ; Rahmani, B ; Khavasi, A ; Sharif University of Technology
OSA - The Optical Society
2018
Abstract
We introduce a new metasurface structure for controlling the polarization of light by leveraging a wellharmonized combination of graphene and dielectric. The proposed metasurface is composed of an array of rectangular pillars laterally sandwiched by ribbons of graphene. Being able to dynamically change the polarization state of the reflected wave, the proposed structure is employed to realize a switchable polarization converter, which is able to act as a reflector (co-polarizer)/right-hand circular (RHC) quarter-wave plate or RHC/cross/ left-hand circular (LHC) polarizer based on its design configuration. The reflected amplitude in all states of functionality is remarkably high. It is also...
Performance analysis of optically bistable thresholders in optical code division multiple access networks
, Article ICONO 2007: Coherent and Nonlinear Optical Phenomena, Minsk, 28 May 2007 through 1 June 2007 ; Volume 6729 , 2007 ; 0277786X (ISSN) ; 081946886X (ISBN); 9780819468864 (ISBN) ; Mehrany, K ; Salehi, J. A ; Rashidian, B ; Sharif University of Technology
2007
Abstract
Optical code division multiple access (OCDMA) is a promising multiple-access technique for future all optical networks. In this manuscript, the usefulness of exploiting bistable optical elements as threshold devices in coherent OCDMA systems is analytically investigated, in which the bistability effect is modeled by a simple square loop
Implementation of optical tracker system for marker-based human motion tracking
, Article 15th IASTED International Conference on Applied Simulation and Modelling, Rhodes, 26 June 2006 through 28 June 2006 ; Volume 2006 , 2006 , Pages 252-257 ; 0889865612 (ISBN); 9780889865617 (ISBN) ; Hoviatalab, M ; Rezaeian, T ; Alizadeh, M ; Bostan, M ; Sharif University of Technology
2006
Abstract
In this paper a complete design of a high speed optical human motion tracking system has been described for biomechanical human motion analysis and animation craft applications. The main core of the image processing unit that is implemented by the differential algorithm procedure and some intelligent and conservative procedures that facilitate the search algorithm have also been proposed and implemented for the processing of human motions tracking images. In the next step an optimized modified direct linear transformation (MDLT) method has been used to reconstruct 3D locations of markers as an input data for animation unit. The low computational cost and the high precision in detecting and...
Two-dimensional edge detection by guided mode resonant metasurface
, Article IEEE Photonics Technology Letters ; Volume 30, Issue 9 , 1 May , 2018 , Pages 853-856 ; 10411135 (ISSN) ; Tavakol, M. R ; Karimi Khoozani, P ; Khavasi, A ; Sharif University of Technology
Institute of Electrical and Electronics Engineers Inc
2018
Abstract
In this letter, a new approach to perform edge detection is presented using an all-dielectric complimentary metal-oxide-semiconductor-compatible metasurface. Our design is based on the guided-mode resonance, which provides a high quality factor resonance to make the edge detection experimentally realizable. The proposed structure is easy to fabricate, and it can be exploited for detection of edges in two dimensions due to its symmetry. In addition, a tradeoff between gain and the resolution of edge detection is discussed, which can be adjusted using appropriate design parameters. The proposed edge detector potentially can be used in ultrafast analog computing and image processing. ©...
Terahertz quarter wave-plate metasurface polarizer based on arrays of graphene ribbons
, Article IEEE Photonics Technology Letters ; Volume 31, Issue 12 , 2019 , Pages 931-934 ; 10411135 (ISSN) ; Rahmani, B ; Khavasi, A ; Sharif University of Technology
Institute of Electrical and Electronics Engineers Inc
2019
Abstract
We propose a novel graphene-dielectric-based metasurface for manipulating the polarization of the incident light in the terahertz regime. The proposed structure comprised two orthogonally oriented periodic array of graphene ribbons (PAGRs) which are separated by a dielectric spacer and deposited on an Au-backed dielectric substrate. Based on the transmission line theory, an equivalent model with excellent accuracy is suggested for the proposed structure. By leveraging the simplicity of the model, we design a three-state quarter wave plate that is able to dynamically switch the polarization of the reflected wave to linear, right-, and left-hand polarizations while keeping the reflected...
Analysis and simulation of ring resonator silicon electro-optic modulators based on PN junction in reverse bias
, Article Optical Engineering ; Vol. 53, issue. 12 , 2014 ; ISSN: 00913286 ; Akbari, M ; Sharif University of Technology
Abstract
The theory of silicon optical modulators of ring resonators based on PN diode in reverse bias is primarily discussed. It secondarily provides a full-featured simulator to investigate the behavior of such modulators. Wave equation for ring structure will be solved by using the conformal transformation method and the matrix method as it was used to analyze bent planar optical waveguides. Power coupling between ring and straight waveguides will be calculated by coupled theory of nonparallel waveguides based on experimental results. The time response demonstrates the capability of this device to operate correctly at up to 10 Gbs-1 bitrate, and the frequency spectrum analysis of device shows a >...
Two building blocks of microwave photonics filters in the presence of group delay ripple: A comparative survey
, Article Optical and Quantum Electronics ; Volume 44, Issue 8-9 , 2012 , Pages 403-414 ; 03068919 (ISSN) ; Akbari, M ; Sharif University of Technology
Springer
2012
Abstract
We have developed an analytic approach to investigate the effect of group delay ripple of the dispersive devices on the performance of two major building blocks of microwave- photonic filters. Firstly, performance of PM-based block in the presence of an arbitrary group delay ripple (GDR) is analyzed and compared with the ripple-free case to reveal the destructive effects of added group delay ripple. In the next step, we repeat the proposed approach for the AM-based one; again, the performance is compared with the ripple-free case. Two distortion metrics are also introduced to quantify this distortion. Comparison of the performance of two building blocks in the presence of group delay ripple...
A novel method for band structure analysis of photonic crystal slabs
, Article IEEE Photonics Journal ; Volume 3, Issue 6 , 2011 , Pages 1111-1122 ; 19430655 (ISSN) ; Akbari, M ; Mehrany, K ; Sharif University of Technology
2011
Abstract
We propose a new method to extract the modes of photonic crystal slabs and, thus, obtain their band structures. These slabs, which are 2-D periodic structures with finite thickness, can completely confine light and have the important advantage of simple construction for applications in integrated optic devices. In this paper, reflection pole method (RPM) is utilized to analyze photonic crystal slabs. Modes are poles of reflection and transmission coefficients of multilayered structures. According to this principle, modes can be detected by only pursuing phase variations of transmission coefficients that are equal to π rad. Therefore, extraction of modes becomes fast and simple through...
Inverse design of 2-D subsonic ducts using flexible string algorithm
, Article Inverse Problems in Science and Engineering ; Volume 17, Issue 8 , 2009 , Pages 1037-1057 ; 17415977 (ISSN) ; Dural, M ; Hajilouy Benisi, A ; Ghadak, F ; Sharif University of Technology
Abstract
The duct inverse design in fluid flow problems usually involves finding the wall shape associated with a prescribed distribution of wall pressure or velocity. In this investigation, an iterative inverse design method for 2-D subsonic ducts is presented. In the proposed method, the duct walls shape is changed under a novel algorithm based on the deformation of a virtual flexible string in flow. The deformation of the string due to the local flow conditions resulting from changes in wall geometry is observed until the target shape satisfying the prescribed wall's pressure distribution is reached. The flow field at each step is analysed using Euler equations and the advection upstream splitting...
Optimization and simulation of micrometre-scale ring resonator modulators based on p-i-n diodes using firefly algorithm
, Article Optik ; Volume 128 , 2017 , Pages 101-112 ; 00304026 (ISSN) ; Akbari, M ; Sharif University of Technology
Elsevier GmbH
2017
Abstract
Field analysis of ring resonator modulators based on p-i-n diodes has been dissected in this paper. This analysis is performed in time and frequency domains. The conformal transformation method has been used for solving 3-D wave equation. Coupling coefficient between the ring and straight waveguides are obtained by developing the coupled-mode assumption. In the resonant wavelength of 1573.91 nm, a drop of more than 15 dB in frequency spectrum of the device has been observed. Time domain simulation shows that this modulator could support up to 0.4 Gb/s and up to 1.5 Gb/s for NRZ and RZ signals, respectively. Obtained simulation results in both domains have been properly complied with...
OptCAM: An ultra-fast all-optical architecture for DNA variant discovery
, Article Journal of Biophotonics ; Volume 13, Issue 1 , August , 2020 ; Koohi, S ; Kavehvash, Z ; Mashaghi, A ; Sharif University of Technology
Wiley-VCH Verlag
2020
Abstract
Nowadays, the accelerated expansion of genetic data challenges speed of current DNA sequence alignment algorithms due to their electrical implementations. Essential needs of an efficient and accurate method for DNA variant discovery demand new approaches for parallel processing in real time. Fortunately, photonics, as an emerging technology in data computing, proposes optical correlation as a fast similarity measurement algorithm; while complexity of existing local alignment algorithms severely limits their applicability. Hence, in this paper, employing optical correlation for global alignment, we present an optical processing approach for local DNA sequence alignment to benefit both...
Free-Space optical neural network based on optical nonlinearity and pooling operations
, Article IEEE Access ; Volume 9 , 2021 , Pages 146533-146549 ; 21693536 (ISSN) ; Koohi, S ; Paranj, A. F ; Sharif University of Technology
Institute of Electrical and Electronics Engineers Inc
2021
Abstract
Despite various optical realizations of convolutional neural networks (CNNs), optical implementation of nonlinear activation functions and pooling operations are still challenging problems. In this regard, this paper proposes an optical saturable absorption nonlinearity and its atomic-level model, as well as two various optical pooling operations, namely optical average pooling and optical motion pooling, by means of 4f optical correlators. Proposing these optical building blocks not only speed up the neural networks due to negligible optical processing latency, but also facilitate the concatenation of optical convolutional layers with no optoelectrical conversions in-between, as the...