36339437 Photonic Crystal

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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!

36339437 Photonic Crystal

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