Search for: photonic-devices
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    Formation of terahertz superconducting photonic devices based on patterned irradiation

    , Article IEEE Transactions on Applied Superconductivity ; Volume 23, Issue 5 , Oct , 2013 ; 10518223 (ISSN) Kamrani, H ; Azadeh, M. S. S ; Kokabi, A ; Fardmanesh, M ; Sharif University of Technology
    A high-temperature superconductor slab irradiated by a desired pattern of light is proposed to behave as a completely controllable 2-D photonic media that could be applied in a wide range of photonic devices. In this case, the permittivity spatial variation, which is fundamentally required in many photonic devices, can be achieved by means of the selective variation of cooper-pair density under patterned irradiation. The process of photo-effect in superconductors is the proposed mechanism for the deformation of the spatial distribution of cooper-pair density and for the creation of nonuniform permittivity. In this perspective, the effects of nonuniform photon irradiation on the density of... 

    Electromagnetically induced phase grating via population trapping condition in a microwave-driven four-level atomic system

    , Article Journal of the Optical Society of America B: Optical Physics ; Vol. 31, issue. 11 , November , 2014 , p. 2879-2884 ; ISSN: 07403224 Naseri, T ; Sadighi-Bonabi, R ; Sharif University of Technology
    An electromagnetically induced phase grating (EIG) controlled by coherent population trapping (CPT) in a fourlevel Y-type atomic system is studied. The CPT condition promotes significantly the dispersion of light into the first-order diffraction in constructing a phase modulation grating by transferring energy from zero-order to firstorder diffraction. The diffraction efficiency of the phase grating is enhanced by up to 30% of the total probe intensity at the first-order diffraction. The present atomic scheme takes full advantage of the microwave-driven field for generating the EIG, which induces the quantum coherence and controls linear and nonlinear behaviors of the present system.... 

    Significant crosstalk reduction using all-dielectric CMOS-compatible metamaterials

    , Article IEEE Photonics Technology Letters ; Volume 28, Issue 24 , 2016 , Pages 2787-2790 ; 10411135 (ISSN) Khavasi, A ; Chrostowski, L ; Lu, Z ; Bojko, R ; Sharif University of Technology
    Institute of Electrical and Electronics Engineers Inc  2016
    A recent computational result suggests that highly confined modes can be realized by all-dielectric metamaterials. This substantially decreases crosstalk between dielectric waveguides, paving the way for high-density photonic circuits. Here, we experimentally demonstrate, on a standard silicon-on-insulator platform, that using a simple metamaterial between two silicon strip waveguides results in about a tenfold increase in coupling length. The proposed structure may lead to significant reduction in the size of devices in silicon photonics  

    Efficient analysis of confined guided modes in phoxonic crystal slabs

    , Article Journal of Lightwave Technology ; Volume 35, Issue 17 , 2017 , Pages 3734-3742 ; 07338724 (ISSN) Aram, M. H ; Khorasani, S ; Sharif University of Technology
    Today's standard fabrication processes are just capable of manufacturing slab of photonic and phononic crystals, so an efficient method for analysis of these crystals is indispensable. Plane wave expansion (PWE) as a widely used method in studying photonic and phononic (phoxonic) crystals in full three dimensions is not suitable for slab analysis in its standard form, because of convergence and stability issues. Here, we propose a modification to this method which overcomes these limitations. This improved method can be utilized for calculation of both photonic and phononic modes in phoxonic slabs. While in the standard three-dimensional PWE, Fourier series are used to estimate the field... 

    A new method for solving nonhermitian perturbation theory for the microdisc resonators with phi-periodic refractive index

    , Article Proceedings of SPIE- Silicon Photonics and Photonic Integrated Circuits, Strasbourg, 7 April 2008 through 10 April 2008 ; Volume 6996 , 2008 ; 0277786X (ISSN) ; 9780819471949 (ISBN) Keyvaninia, S ; Karvar, M ; Bahrampour, A ; Sharif University of Technology
    The radiation loss in the whispering gallery resonators causes the eigenvalues of the Maxwell equations with the corresponding boundary conditions complex. The corresponding operators are nonhermitian and for these operators the standard perturbation techniques have some difficulties. In this paper by employing the Floquet theorem a new technique for the φ periodic perturbations is developed. The method is applied to obtain the change of resonance frequencies and losses of φ -perturbed microresonators with cylindrical symmetry. The results are compatible with that are obtained by the Volume Current Method  

    High intensity enhancement of unidirectional propagation of a surface plasmon polariton beam in a metallic slit-groove nanostructure

    , Article Scientia Iranica ; Vol. 21, issue. 6 , 2014 , p. 2508-2512 ; 10263098 Eftekharinia, B ; Nabavi, S. H ; Moshaii, A ; Dabirian, A ; SharifUniversity of Technology
    We propose an innovative design for metallic slit-groove nanostructure to increase the propagation intensity of a unidirectional Surface Plasmon Polariton (SPP) light beam. Our idea is based on the combination of the concept of unidirectional plasmonic wave propagation in a metallic slit-groove nanostructure and the well-known hybrid modes of a hybrid metal-dielectric waveguide. Our results demonstrate that the hybrid structure results in up to 5 times enhancement in the SPP beam intensity relative to the conventional design of slit-groove nanostructure. This new design of SPP based nano source can be applied in many applications including nano photonic devices  

    Influence of asymmetry on the band structure of photonic crystals

    , Article Proceedings of SPIE - The International Society for Optical Engineering, 26 January 2010 through 28 January 2010 ; Volume 7609 , January , 2010 ; 0277786X (ISSN) ; 9780819480057 (ISBN) Moosavi Mehr, S. H ; Khorasani, S ; Sharif University of Technology
    Computer calculation of photonic band structure for unit cells of various symmetry in the two-dimensional square lattice suggests that the bandgap calculated by traversing the ΓXM triangle in k-space is only reliable when the unit cell is C4v symmetric. For structures of lower symmetry, examining a two-dimensional subset of the first Brillouin zone will give smaller bandgaps  

    An analytical approach for evaluating the optical spectrum emitted from a strongly-coupled single quantum-dot photonic-crystal cavity system

    , Article Proceedings of SPIE - The International Society for Optical Engineering, 26 January 2010 through 28 January 2010 ; January , 2010 , Volume 7609 ; 0277786X (ISSN) ; 9780819480057 (ISBN) Ahmadi, E ; Chalabi, H. R ; Miri, M ; Bayat, M ; Khorasani, S ; Sharif University of Technology
    A theory is presented for the quantum radiation emitted from a single exciton in a quantum dot. We assume that the quantum dot is in strong coupling to a slab photonic crystal cavity. A dielectric function of spatial coordinates is used to explain the effects of the macroscopic medium. It has been proved that the electric field in such a medium can be described using the so-called K-function. We derive a formula for obtaining the frequency spectrum, and present an analytical result for the optical spectrum, which is dependent on the K-function. We also have considered a slab photonic crystal configuration with hexagonal structure containing a cavity to evaluate the frequency spectrum in such... 

    Stable semi-analytical method for analysis of plasmonic propagation on periodically patterned metal plates

    , Article Proceedings of SPIE - The International Society for Optical Engineering, 26 January 2010 through 28 January 2010 ; January , 2010 ; 0277786X (ISSN) ; 9780819480057 (ISBN) Yasrebi, N ; Khorasani, S ; Karami Taheri, H ; Rashidian, B ; Hosseini, A ; Sharif University of Technology
    The need for antennas with improved characteristics for communication and radar applications has resulted in an ever-increasing demand for research in the field of high impedance surfaces, which can work as an artificial magnetic conductor. One method in fabrication of these surfaces is formation of a metamaterial by patterning a metallic surface in the shape of space filling curves (e.g. Hilbert or Peanu Curves). In this paper, we present a novel semi-analytical solution to the problem of plasmonic propagation on these surfaces. The method is based on a previously presented Green's function formalism, which has been reported in an earlier paper of ours. We have modified and improved the... 

    OptCAM: An ultra-fast all-optical architecture for DNA variant discovery

    , Article Journal of Biophotonics ; Volume 13, Issue 1 , August , 2020 Maleki, E ; Koohi, S ; Kavehvash, Z ; Mashaghi, A ; Sharif University of Technology
    Wiley-VCH Verlag  2020
    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... 

    Optical bistable switching with Kerr nonlinear materials exhibiting a finite response time in two-dimensional photonic crystals

    , Article Volume 7713 ; Proceedings of SPIE - The International Society for Optical Engineering, 12 April 2010 through 15 April 2010 , 2010 ; 0277786X (ISSN) ; 9780819481863 (ISBN) Naqavi, A ; Monem Haghdoost, Z ; Abediasl, H ; Khorasani, S ; Mehrany, K ; Sharif University of Technology
    Effect of relaxation time on the performance of photonic crystal optical bistable switches based on Kerr nolinearity is discussed. This paper deals with optical pulses with the duration of about 50 ps. In such cases the steady state response of the optical device can be used to approximate the pulse evolution if the nonlinearity is assumed instantaneous, hence analytical solutions such as the coupled mode theory can be used to obtain the time evolution of the electromagnetic fields. However if the relaxation time of the material nonlinear response is also considered, changes in the power levels and in the shape of the hystersis loop is observed. In this case, we use the nonlinear finite... 

    Dynamic behavior of electric field in the microrings in the presence of Kerr and two-photon absorption

    , Article Proceedings of SPIE - The International Society for Optical Engineering, 7 April 2008 through 10 April 2008, Strasbourg ; Volume 6996 , 2008 ; 0277786X (ISSN) ; 9780819471949 (ISBN) Keyvaninia, S ; Karvar, M ; Bahrampour, A ; Sharif University of Technology
    This paper a simple semi-analytical model for calculation of the time evolution and spatial variation of the electric field in microring resonators in the presence of The Kerr effect and two-photon absorption (TPA) is presented. The theoretical analysis is based on the delayed feedback model, which is well known in microring theory. The model is applied to the Chalcogenide glass and AlGaAs microrings to study the Kerr and TPA effects on the spatial and temporal variation of electric field respectively across the microring. The effects of microring parameters and input signal shapes on the transient behavior are taken into consideration. It is shown that, the results are in good agreement...