Surface plasmon waveguides - Hanyangoptics.hanyang.ac.kr/~shsong/10-SPP...
Transcript of Surface plasmon waveguides - Hanyangoptics.hanyang.ac.kr/~shsong/10-SPP...
Surface plasmon waveguides
dielectric waveguide
~ 10 λ
CMOS transistor:
Photonic integrated system with subwavelength scale components
Medium-sized molecule
Size Mismatch between Scaled CMOS Electronics and Planar Photonics
Introduction
Silicon Photonics?
A World of Nanophotonic Devices
Could such an Architecture be Realized with Metal rather than Dielectric Waveguide Technology?
Harry Atwater, California Institute of Technology
On-chip light source
Short-range(~ nm) waveguides
Nano-photonics
~ cm
Long-range(~ cm) waveguides
Nano-electronics
Photonic integrated circuit
Could such an Architecture be Realized with Metal rather than Dielectric Waveguide Technology?
Metal Optics: An introduction
Photonic functionality based on metals?!
Surface-plasmon-polariton waveguides
Dispersion relation of surface plasmon polaritons excited on very-thin metal strips
Modes of very-thin(~ 10 nm) metal strips
Experimental results on SPP waveguide devices
50nm
A World of Nanophotonic Devices
Could such an Architecture be Realized with Metal rather than Dielectric Waveguide Technology?
Harry Atwater, California Institute of Technology
On-chip light sourceShort-range(~ nm)
waveguides
Nano-photonics
~ cm
Long-range(~ cm) waveguides
Nano-electronics
Photonic integrated circuit
0 20 40 60 80 1000
2
4
6
8ω=c kx
λ=337 nm; ε1= -1
ω (1
015 s
-1)
kx (μm-1)
Plasmons at Planar Metal-Dielectric Interfaces
surface plasmons are longitudinal charge density fluctuations on the surface of a conductor Surface Plasmon dispersion relation for Ag in air
surface plasmon dispersion relation:
Plasmons are highly localized at metal-dielectric interfaces, so potential for: • Ultrasmall Optical Devices
• “2D-Optics” on metal surfaces
(Light line)
Plasmon Dispersion Relation
λ = 337 nm
λ << 337 nm
Harry Atwater, California Institute of Technology
ε1 : metal
ε2 : dielectric
x
1 2
1 2xk
cε εω
ε ε=
+
'1 2
1At large ( ), z .ixx
kk
ε ε→ − ≈
Strong confinement at the interface
Nano focusing
'1At low ( 1),xk ε >>
'1 in air :z
x
Ei
Eε= −
( : , : - )z xE iE air i metal i= ± +
'1
1 in metal :z
x
Ei
E ε=
0 20 40 60 80 1000
2
4
6
8ω=c kx
λ=337 nm; ε1= -1
ω (1
015 s
-1)
kx (μm-1)
Broad dispersion
Low loss at the interface
Wave guiding
Nano Focusing & Wave Guiding
Surface Plasmons excited on thin metal films
Dielectric – ε3
Dielectric – ε1
Metal – ε2
Several 1 cm long, 15 nm thin and 8 micron wide gold stripes guiding LRSPPs3-6 mm long control electrodes low driving powers (approx. 100 mW) and high extinction ratios (approx. 30 dB) response times (approx. 0.5 ms)total (fiber-to-fiber) insertion loss of approx. 8 dB when using single-mode fibers
When the film thickness becomes finite.
modeoverlap
Possibility of Propagation Range Extensionfr
eque
ncy
in-plane wavevector
Long-Range SP: weak surface confinement, low loss
Short-Range SP:strong surface confinement, high loss
Symmetric mode(long-range SPP)
Anti-symmetric mode(short-range SPP)
E
H
SPP modes at a very thin metal film
Introduction: Dependence of dispersion on film thickness
practically forbidden
200 400 600 800
-1
-0.75
-0.5
-0.25
0.25
0.5
0.75
1
200 400 600 800
-1
-0.75
-0.5
-0.25
0.25
0.5
0.75
1
60h nm=
250 500 750 1000 1250 1500
-1
-0.75
-0.5
-0.25
0.25
0.5
0.75
1
250 500 750 1000 1250 1500
-1
-0.75
-0.5
-0.25
0.25
0.5
0.75
1
10h nm=
0 20 40 60 80 1000
5
10
15
20
25
30
35
40
Ws/W
a
thickness of metal film [nm]
Field solution and dispersion relation of coupled SPP’s
Symmetric Asymmetric
Propagation loss and field confinement of SPP’syz
z
0z =
h
1ε
2ε
3ε
[ ]0( , ) ( )expyx z L f z i xβ=L e
Magnetic field : L=H/Zo
2 2 20j js kβ ε= −
.
[ ] [ ] [ ] ( )
[ ] [ ] ( )
[ ] ( )
2 12 2 3
1 2
2 12 2
1 2
1
cosh sinh exp ( )
( ) cosh sinh 0
exp 0
ss h s h s z h z hs
sf z s z s z z hs
s z z
εε
εε
⎧⎛ ⎞+ − − ≥⎪⎜ ⎟
⎝ ⎠⎪⎪⎪= + ≤ ≤⎨⎪⎪ ≤⎪⎪⎩ Confinement
Propagation Loss
Asymmetric mode
Symmetric mode
18nm 20nm14nm 16nm
T
Fundamental symmetric mode of a metal stripe : thickness (T)
W=10um
LR-SP WG
P. Berini, PhotonicWest 2005.
(Spectalis Co.)
Fundamental asymmetric mode of a metal stripe : Δn
1.68
1.68+ Δn
Δn = 0.001 Δn = 0.002 Δn = 0.003
T=16 nm, W=10um
Symmetric mode guided by a metallic channel waveguide
silicon 9μm
20nmfiberAu (-96+i11)Polymer (n=1.47) @ 1.55μm
15mm
Propagation loss : 21dB/ cm
~10μm
Y-branch
Channel-1 Channel-2
1 2
Wavelength shifts by direct heating a metal wire
1 5 4 0 1 5 4 5 1 5 5 0 1 5 5 5 1 5 6 0
-7 0
-6 5
-6 0
-5 5
-5 0
-4 5
-4 0
Tran
smitt
ance
(dB
)
W a v e le n g th (n m )
1544.1 1558.3
INPUT OUTPUT
Polymer 1Substrate
+ -
Polymer 2
Tunable Wavelength Filter
Vertical directional couplers
H. Won, APL vol.88, 011110 (2006)
Vertical directional couplers
0 2 4 6 8 10 12 14 16
1.470
1.471
1.472
1.473
1.474
1.475
1.476
1.477εmetal=-116+11.58i (gold)εdielectric=2.16λ0=1550nmt=20nm
symmetric even mode symmetric odd mode
R/k0
distance(d : distance between two slabs)
εd = 2.16
εm = −116 +11.58id
t= 20nm
d=4um 254 umd=6um 558 um
Even mode and odd mode : directional couplers based on LRSPP
4μm, even mode 4μm, odd mode
7μm, even mode 7μm, odd mode
21μm, even mode 21μm, odd mode
0.08μm, even mode 0.08μm, odd mode
3μm, even mode 3μm, odd mode
23μm, even mode 23μm, odd mode
Vertical Lateral D
D
Vertical directional couplers
even mode odd mode
oddodd
Lateral DC
Extinction ration at 400um : 27dB
Channel 1 Channel 2
Vertical directional couplers
Variable optical attenuator based on LR-SPPSubmitted to EL, S. Park & S. Song
Extremely long-range SPP ?
in-plane wavevector
freq
uenc
y
Symmetrically coupled LRSP
Anti-symmetrically coupled LRSP
D. Sarid (PRL, 1981) J. J. Burke (APL, 1986)
Extension of SPP propagation length
Thin metal film
P. Berini (PRB, 2000)
Finite-width metal strip
metal
n4
n3n2
n0
n1 > n0~n4
n1
F. Y. Kou et al (OL, 1987)
LR SPP
G. I. Stegman et al (APL, 1983)
Metal
n1
n1
n2
n2 > n1
Double metal films Metal-dielectric films
0 1000 2000 3000 4000
0.1
1
10
1001 1.4 1.45 1.46
1.47
1.48
1.49
1.5
1.6
prop
agat
ion
leng
th(m
m)
separation distance(D : μm)
Extended Long-Range SPPs
Metal
n1
n1
n2 D
metal
n5
n4n3
n2
n0
n5 ~n1> n0~n2~n4
n1
Range extension with finite-width metal stripes
D < Dcutoff
n2 < n1
No good
Two fundamental modes Even mode only
n1
n2 Dt
w
0 1 2 3 4
1
10
100
1.46
1.451.40
1.48
1.50
1.47
prop
agat
ion
leng
th (m
m)
separation distance (D: μm)0 1 2 3 4
1.470
1.472
1.474
1.476
1.478
1.480
1.482
1.4 1.45 1.46
1.47
1.48
1.50
β r/k
0
separation distance (D: μm)
Propagation length and effective index
1 1.47 5 20n w m t nmμ= = =
n2 1.40 1.45 1.46Cutoff (D: μm ) 0.23 0.78 1.78P-length (mm) 240 230 60
Propagation length of a single stripe is only about 11mm.
Propagation length of double stripes can be extended more than 10 times!
0118 11.58 , 1550m i nmε λ= − + =
10μm
D=100nm, t= 20nm D=300nm, t= 20nm
D=500nm, t= 20nm D=780nm, t= 20nm
t= 20nm
t= 16 nm
Mode profile & Mode size
1 21.47 , 1.45, 5n n w mμ= = =
Propagation length = 230 mm Propagation length = 46 mm
Both of two modes have mode size of ~ 10 μm
Double metal stripe Single metal stripe
0 100 200 300 400 500 600 700 800
2.0x10-4
3.0x10-4
4.0x10-4
fra
ctio
n of
the
field
con
fined
met
al a
rea
(%)
separation distance ( D : nm )0 100 200 300 400 500 600 700 800
2
3
4
5
6
7
8
9
10
fract
ion
of th
e fie
ld c
onfin
ed n
2 are
a (%
)
separation distance ( D : nm )
Fraction of field energy in metal and area
-2 0 20.0
0.2
0.4
0.6
0.8
1.0
metal stripe
D = 780nm
Abs
(Ey)
vertical distance(μm)
2n
In metal stripes In n2 dielectric
Butt-coupling efficiency with a SM fiber
-10 -8 -6 -4 -2 0 2 4 6 8 100.0
0.2
0.4
0.6
0.8
1.0
Abs(
E y)
vertical distance ( μm )
double stripe single stripe
-10 -8 -6 -4 -2 0 2 4 6 8 100.0
0.2
0.4
0.6
0.8
1.0
Abs
(Ey)
lateral distance ( μm )
single stripe double stripe 1 double stripe 2
Vertical profile
Lateral profile
20 18 16 14 12 100.40
0.45
0.50
0.55
0.60
0.65
0.70
coup
ling
loss
wtih
fibe
r ( d
B )
thickness of metal ( t : nm)
100 200 300 400 500 600 700 800
0.50
0.55
0.60
0.65
coup
ling
loss
wtih
fibe
r ( d
B )
separation distance ( D : nm )
Mode profile Coupling loss with fiber
Single metal strip
Double metal strips
Jung (ETRI), 40 Gbit/s light signal transmission on a long-range SPP waveguide, APL, PTL, 2007.
14 nm-thick, 2.5 μm-wide gold stripes
0.6 dB/cm : World best record in propagation loss. (Previous world record : 3.2 dB/cm by Berini, 2006)
0.5 1.0 1.5 2.0 2.50
1
2
3
4
5
6
Loss
(dB
)
Waveguide length (cm)
λ= 1310 nm
Plasmonic Flexible-wires for 40 GHz interconnections
LR-SPP waveguide
VCSEL array
Drive IC
TIA & Pre amp IC
SMA SMA
PD array
Rx
Tx
40 Gb/s World best
εd3
εd3
ε2D
D
wSPP mode
metal strip
metal slab
core
cladding
εd1
Y-branchS-band
metal stripmetal slab
Double-electrode metal waveguides : Lines, S-band, Y-branchJoo, Long-range surface -plasmon--polaritons on asymmetric double-electrode structures, APL, 2008.
Localized Surface Plasmons : Nanofocusing and Nanolithography
'1 2
1At large ( ), z .ixx
kk
ε ε→ − ≈
Strong confinement at the interface
Nano focusing
( : , : - )z xE iE air i metal i= ± +
0 20 40 60 80 1000
2
4
6
8ω=c kx
λ=337 nm; ε1= -1
ω (1
015 s
-1)
kx (μm-1)
Broad dispersion
Beam radius -> zero!
Propagation Loss(asymmetric mode)
High
Propose metal nanowires.
Asymmetric mode : field enhancement at a metallic tip
Er EzEr
Ez
* See MOVIES : SPP propagation through a metallic tip
M. I. Stockman, “Nanofocusing of Optical Energy in Tapered Plasmonic Waveguides,” Phys. Rev. Lett. 93, 137404 (2004)]
50nm
2007/5/1 ~
an optical range resonator based on single mode metal-insulator-metal plasmonic gap waveguides. A small bridge between the resonator and the input waveguide can be used to tune the resonance frequency.
FDTD with the perfectly matched layer boundary conditions
Plasmonic Crystal Demultiplexer and Multiports
the realization of two-dimensional optical wavelength demultiplexers and multiports for surface plasmons polaritons (SPPs) based on plasmonic crystals, i.e., photonic crystals for SPPs.
Slow Propagation, Anomalous Absorption, and Total External Reflection of Surface Plasmon Polaritons in Nanolayer Systems
n=0
n=1n=2
we show how the dispersion relation of surface plasmon polaritons (SPPs) propagating along a perfectly conducting wire can be tailored by corrugating its surface with a periodic array of radial grooves. Importantly, the propagation characteristics of these spoof SPPs can be controlled by the surface geometry, opening the way to important applications such as energy concentration on cylindrical wires and superfocusing using conical structures.
Summary : Plasmonic Waveguides for Photonics
* Long-range (symmetric modes) : Low loss is achievable!
-> Trade-off between Localization and Loss
* Short-range (asymmetric modes) : Nano localization is achievable!
Plasmonics: the next chip-scale technology
Plasmonics is an exciting new device technology that has recently emerged. A tremendous synergy can be attained by integrating plasmonic, electronic, and conventional dielectric photonic devices on the same chip and taking advantage of the strengths of each technology.
Plasmonic devices,therefore, might interface naturally with similar speed photonic devicesand similar size electronic components. For these reasons, plasmonicsmay well serve as the missing link between the two devicetechnologies that currently have a difficult time communicating. Byincreasing the synergy between these technologies, plasmonics may beable to unleash the full potential of nanoscale functionality andbecome the next wave of chip-scale technology.
Summary : Plasmonic Photonics