Search for: photonic-bands
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    A new low voltage precision CMOS current reference with no external components

    , Article IEEE Transactions on Circuits and Systems II: Analog and Digital Signal Processing ; Volume 50, Issue 12 , 2003 , Pages 928-932 ; 10577130 (ISSN) Dehghani, R ; Atarodi, S. M ; Sharif University of Technology
    A novel current reference with low temperature and supply sensitivity and without any external component has been developed in a 0.25 μm mixed-mode process. The circuit is based on a bandgap reference (BGR) voltage and a CMOS circuit similar to a beta multiplier. An NMOS transistor in triode region has been used in place of a resistor in conventional beta multiplier to achieve a current which has a negative temperature coefficient and only oxide thickness dependent. The BGR voltage has a positive temperature coefficient to cancel the negative temperature coefficient of the beta multiplier. The simulation results using Bsim3v3 model show max-to-min fluctuation of less than 1 % over a... 

    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  

    Construction of Dirac points using triangular supercrystals

    , Article Applied Physics A: Materials Science and Processing ; Volume 115, Issue 2 , May , 2014 , Pages 581-587 ; ISSN: 09478396 Aram, M. H ; Mohajeri, R ; Khorasani, S ; Sharif University of Technology
    We show a methodology for how to construct Dirac points that occur at the corners of Brillouin zone as the Photonic counterparts of graphene. We use a triangular lattice with circular holes on a silicon substrate to create a Coupled Photonic Crystal Resonator Array (CPCRA) which its cavity resonators play the role of carbon atoms in graphene. At first we draw the band structure of our CPCRA using the tight-binding method. For this purpose we first designed a cavity which its resonant frequency is approximately at the middle of the first H-polarization band gap of the basis triangular lattice. Then we obtained dipole modes and magnetic field distribution of this cavity using the Finite... 

    Precision photonic band structure calculation of Abrikosov periodic lattice in type-II superconductors

    , Article Physica C: Superconductivity and its Applications ; Volume 460-462 II, Issue SPEC. ISS , 2007 , Pages 1222-1223 ; 09214534 (ISSN) Kokabi, A ; Zandi, H ; Khorasani, S ; Fardmanesh, M ; Sharif University of Technology
    We have performed a numerical solution for band structure of an Abrikosov vortex lattice in type-II superconductors forming a periodic array in two dimensions for applications of incorporating the photonic crystals concept into superconducting materials with possibilities for optical electronics. The implemented numerical method is based on the extensive numerical solution of the Ginzburg-Landau equation for calculating the parameters of the two-fluid model and obtaining the band structure from the permittivity, which depends on the above parameters and the frequency. This is while the characteristics of such crystals highly vary with an externally applied static normal magnetic field,... 

    Analyzing symmetry in photonic band structure of gyro-magnetic photonic crystals

    , Article Proceedings of SPIE - The International Society for Optical Engineering ; Volume 8096 , 2011 ; 0277786X (ISSN) ; 9780819487063 (ISBN) Najafi, A ; Khorasani, S ; Gholami, F ; Sharif University of Technology
    In the band structure analysis of photonic crystals it is normally assumed that the full photonic gaps could be found by scanning high-symmetry paths along the edges of Irreducible Brillouin Zones (IBZ). We have recently shown [1] that this assumption is wrong in general for sufficiently symmetry breaking geometries, so that the IBZ is exactly half of the complete BZ. That minimal required symmetry arises from the requirement on time-reversal symmetry. In this paper we show that even that requirement might be broken by using gyro-magnetic materials in the composition of photonic structures we can observe that the IBZ extends fully to the boundaries of the complete BZ, that is IBZ must be as... 

    Transmission-line model to design matching stage for light coupling into two-dimensional photonic crystals

    , Article Optics Letters ; Volume 35, Issue 2 , 2010 , Pages 115-117 ; 01469592 (ISSN) Miri, M ; Khavasi, A ; Mehrany, K ; Rashidian, B ; Sharif University of Technology
    The transmission-line analogy of the planar electromagnetic reflection problem is exploited to obtain a transmission-line model that can be used to design effective, robust, and wideband interference-based matching stages. The proposed model based on a new definition for a scalar impedance is obtained by using the reflection coefficient of the zeroth-order diffracted plane wave outside the photonic crystal. It is shown to be accurate for in-band applications, where the normalized frequency is low enough to ensure that the zeroth-order diffracted plane wave is the most important factor in determining the overall reflection. The frequency limitation of employing the proposed approach is...