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Photonic crystal: Semiconductorsof light
Dr. P. Nath, Sr. Lecturer
Dept. of Electronics andCommunication Technology
Gauhati University
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Plan of talk
Introduction
Basic theory behind photonic band gap
Types of photonic crystal
Some applications of photonic crystal
Photonic crystal directional coupler
Future outlook
References
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Introduction
Over the past 50 years semiconductor technologyhas played a major role in our daily lives.Miniaturization of high speed performanceelectronic ICs has stimulated considerableresearch interest around the world.
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However
Miniaturization results in circuits with increased resistanceand higher level of power dissipation, and higher speed
leads to a greater sensitivity to signal synchronization.
In an effort to further the progress of high density integrationscientist are now turning to light instead of electron as theinformation carrier.
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Light has several
advantages over electron
It can travel at much greater speed
Large information carrying capacity (THz) Light particles are not as strongly interacting as
electrons which helps reduce energy loss.
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To exploit these advantages, scientistsaround the world are now trying to fabricate anew class of optical material, termed as
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PhotonicCrystal (PhC)!
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The early ideas stem from
E. Yablonovitch, PRL, 58, 2059 062(1987)
S. John, PRL, 58, 2486 2489, (1987)
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Both Yablonovitch and John suggested that
structures with periodic variations in dielectricconstant could influence the nature ofphotonic modes in the material
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In PhC, the periodicity is dueto lattice of macroscopic
dielectric. If the d.e.c. of theconstituent media are differentenough then, Bragg scatteringoff the dielectric interface canproduce many of the same
phenomena for photon as theatomic potential does forelectrons.
In a semiconductor, theatomic lattice presents a
periodic potential to anelectron propagating throughthe lattices.
The geometry of the latticeand the strength of the
potential are such that , owingto Bragg like diffraction fromthe atoms, electron isforbidden to propagate in anydirection
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Thus, a PhC could be designed to possess a
complete photonic band gap a range offrequencies for which light is forbidden toexist within the interior of the crystal.Forbidden , that is unless there is a defect
state in the otherwise perfect crystal.
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A defect or mistake in the periodicity could
lead to localize photonic states in the bandgap, whose shapes and properties would bedictated by the nature of the defect. A pointdefect could act like a microcavity a line
defect like a waveguide and a planar defectlike a perfect mirror
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Defect mode in PhC!
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Helmholtz equation
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H(r ) is the magnetic field, w is its frequency
c is the speed of light and (r) is the macrscopic
dielectric functionThe solution H( r) and are determind completely by
the strength and symmetry properties of (r) .
If (r) is perfectly periodic the solution is characterisedby wavevector k and band index n
The region of all allowed wavevectors is called aBrillouin zone and the collection of all solution istermed as band structure.
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Types of photonic crystal
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Percentage of splitting
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Future outlook:
Highly efficient photonic crystal lasers and extremelybright LED will be available very soon
In 5 10 years time scale we will have photonic crystaldiode and transistor
Within 10 15 years photonic crystal logic circuit willbe materialized
Within 25 years first photonic crystal based opticalcomputer will be available
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References:
E. Yablonovitch , inhibited spontaneous emission in solidstate physics & Electronics Phy. Rev. Lett. 58, 2059 2061
(1987) J. Joannopoulos, R. Meade, J . Winn, Photonic crystals:
Molding the flow of light( Princeton university, Princeton,N.J., 1995)
Chuang Shun Lien, Physics of Optoelectronic Devices,( Wiley series in pure and applied optics, 1995)
E. Yablonovitch Photonic crystal, J. Mod. Opt. 41,173 194 (1994)
A. Mekis, J.C. chen , I. Kurland , S. Fan, P.R. Villeneuve andJ.D. Joannopoulos, High transmission through sharp bendsin photonic crystal waveguide, Phy Rev. Lett.77, pp3787 3790, 1996
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T.D.Happ, M. Kamp and A. Forchel., photonic crystal tapersfor ultra compact mode conversion, Opt. Lett. 26, 1102 1104
(2001) P. Bienstman and R. Baetd, Optical modeling of photoniccrystal and VCSELs using eigenmode expansionand perfectlymatched layers, Opt. Quantum Electron. 33,327 341(2001)
C.Grillet, C. Smith, D.Freeman, S.Madden, B.L.Davis,E.C.Magi, D.J.Moss, B.J Eggleton, Efficient coupling to
chalcogenide glass photonic crystal waveguides vie silicaoptical fiber nanowire, Opt. Express. 14, 3 1070 1079(2006)
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Thank you for your attention!
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