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Novel electro-magnetic phenomena:
one-way-waveguidesone way waveguides
and
i l t fwireless power transfer
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Unidirectional backscattering-immunebackscattering immune
topological electromagnetic states
Dr. Zheng Wang Dr. Yidong ChongProf. John JoannopoulosProf. Marin Soljačić
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Metamaterial:
optical properties determined from it t tits nano-structure
(rather than its composition)
High index Allowed
Forbidden
eque
ncy
High indexof refraction
Low indexof refraction
AllowedFre
3D photonic crystal:a “semiconductor for photons”
of refraction
a semiconductor for photons
Yablonovitch (1987)John (1987)
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Electronic and Photonic Crystals
atoms in diamond structureatoms in diamond structure
ediu
m dielectric spheres, diamond lattice
~300nm
iodi
c M
eP
eri
~0.1nm
gygram
uenc
y
ctro
n en
erg
and
Dia
g
oton
freq
u
wavevector
elecBa
wavevector
pho
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Optical waveguides
conventional waveguides
photonic crystalphotonic crystal waveguides
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In both conventional and PhC waveguides…
?T-symmetry ⇒
REFLECTIONS: IMMUNE TO DISORDER!
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Topologically-nontrivial Electromagnetic States
Integer Quantum Hall Effect : unusual phenomena in a 2D system of electrons in crystals, subjected to a perpendicular strong magnetic field
Chiral Edge States (CESs)Chiral Edge States (CESs)• Unidirectional transport• Dissipationless transport in presence of impurities
Thouless et al. (1982)Simon (1983)Kohmoto (1985) Enabled by:Kohmoto (1985)Haldane (1988)Hatsugai (1993)
• nontrivial topology of band structure• T-reversal symmetry breaking
Can one extend these ideas to E&M States in photonic crystals?
Haldane & Raghu PRL 100 013904 (2008)Haldane & Raghu, PRL 100, 013904 (2008)Raghu & Haldane, PRA 78, 033834 (2008)Wang, Chong, Joannopoulos & Soljačić, PRL 100, 013905 (2008)
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How does this work?
Intro to Chern numbers
Chern number of n-th band:Chern number of n th band:
cn: integer ⇒ always changes abruptly
Σ c =0Σncn=0
T-symmetric systems ⇒ cn=0
p ?p + Δ
p + Δ
q ? q - Δq - Δ
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Hatsugai's Relation
Δ
T-symmetric T-brokenone-way edge modes
−Δ
|Δ| one way edge modes|Δ|
The # of CESs in a gap = Σ Cn over lower bands
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Break T-symmetry
00
0← one-way edge states
0
YIGYIGB ~ 0.2T
increase H → cn changes discontinuously at degenerate-k points
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Create one-way edge-states at the PhC boundary
eque
ncy
Fre
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Truly reflectionless!
CES waveguide source metal scatterer
Absorbing Absorbing gregion
gregion
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Truly reflectionless!
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Contrast with conventional waveguides
“conventional” PhC waveguide CES waveguide
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Observation: CESDC magnetic field
CES Waveguide
Antenna B
DC magnetic field0.2 Tesla
Metal Wall
Antenna A
CopperPlate
Magneto-opticalPhotonic Crystal
(ferrites)MicrowaveMicrowaveAbsorber
Waveguide
Wang, Chong, Joannopoulos & Soljačić, Nature 461, 772 (2009)
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Observation: backscattering-immunity
Scatterer of variable length (l )
Waveguide
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Summary: one-way states• Chiral Edge States:g
• Unidirectional transport• backscattering-immunity
• enabled by:• enabled by:• nontrivial topology of band structure• T-reversal symmetry breaking
• previously known in quantum Hall effect (electronic system)
• observed for the first time as electromagnetic (photonic) states
Dr. Yidong Chong Dr. Zheng Wang
Prof. Marin Soljačić Prof. John Joannopoulos
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WiTricity:WiTricity:
non-radiative i l t fwireless power transfer
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Motivation
Tesla tower: cca. 1904
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Wi-Fi (wireless internet) concept: radiationradiation
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Resonant coupling as energyResonant coupling as energy transfer
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Resonances in quantum mechanics –nonradiative transfernonradiative transfer
2 V(r) V(r)ψψ E
m=∇−
2
2h
Schrödinger equation
V(r) V(r)
Schrödinger equation
EE 222 ω=∇− c
e-quantum tunneling e-
Maxwell equation Hydrogen atom proton
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Magnetic resonances
B
EE
Outside: U « UOutside: UE « UBMost materials: μ~μAIR
⇒ weak interaction with B-field!⇒ weak interaction with B field!
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Examples of “magnetic technology”
Maglev
Magnetically levitating bed
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Coupled mode theory
resonant object (Source) resonant object (Device)
( )S iiida
Γ ( )D iiidaΓ( ) DS
S aiaiidt
κω +Γ−−= ( ) SDD aiaii
dtκω +Γ−−=
Γ=
2ωQΓ2
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“Strong Coupling”:Strong Coupling :
/Γ 1κ/Γ » 1
⇒ efficient energy transfer
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“Strong Coupling” ⇒ efficient transfer
Karalis, Joannopoulos & Soljačić, Annals of Physics 323, 34 (2008)
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E i t l ltExperimental results
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source devicesource device
200 cm 30 cm
60W bulb
Kurs, Karalis, Moffatt, Joannopoulos, Fisher & Soljačić, Science 317, 83 (2007)
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same thing, different viewing angle
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Experimental proof of strongly-coupled regimest o g y coup ed eg e
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source devicesource device
200 cm 30 cm
60W bulb
ffi i 50% (Q 1000)efficiency ~50% (Q~1000)
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Efficiency vs. distance
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Comparison with inductive coupling
D » L
L
D Efficiency ≈ ηR/Q2
/1 000 000L
D~ ηR/1,000,000
L » D L
Efficiency ≡ ηRy ηR
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Andre Kurs Prof. J.D.JoannopoulosProf. Marin Soljačić
bulb
Dr Aristeidis KaralisProf Peter Fisher Robert Moffatt Dr. Aristeidis KaralisProf. Peter Fisher Robert Moffatt
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Experiments with 1 source, 2 devices -different sizes
Kurs, Moffatt & Soljačić, Appl. Phys. Lett. 96, 101110 (2010)
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Some potential applications
Industrial, military, and household robots
Portable personal electronics Electric vehicles
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Summary: wireless power transfer
• mid-range non-radiative
energy transfer scheme
based on strongly-coupled
resonances
• as a powerful concept, it could
enable a wide range of applicationsenable a wide range of applications
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WiTricity TED talk – summer 2009
Eric Giler; CEO, WiTricity Corporation