submicron soi waveguides - ugentphotonics.intec.ugent.be/download/ocs63.pdf · 2005. 3. 11. ·...
TRANSCRIPT
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Submicron SOI waveguides
Dries Van ThourhoutTrento ‘05
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http://photonics.intec.UGent.be 2© intec 2004
AcknowledgementsThe European Union IST-PICCO and IST-PICMOS projectThe European Space AgencyThe Belgian IAP-PHOTON networkThe Flemish Institute for the industrial advancement of Scientific and Technological Research (IWT)
The Photonic Research Group at Ghent University – IMECPieter Dumon, Wim Bogaerts, Dries Van Thourhout, Dirk Taillaert, Bert Luyssaert, Peter Bienstman, Joris Van Campenhout, Gunther Roelkens, Ilse ChristiaensThe Silicon Process division at IMECVincent Wiaux, Stephan Beckx, Johan Wouters, DizianaVangoidsenhoven, Rudi De Ruyter, Johan Mees
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OutlineSubmicron SOI-wires
Introduction: why do we need themBasic properties: design, loss, wavelength, polarizationFabricationDevices: couplers, crossings, filters …
III-V on SiliconIntroductionCoupling of lightFabricationPICMOS (Photonic Interconnect on CMOS)
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Scale differenceElectronics
Active opto-electronics
Passive photonics
1cm1mm100µm10µm1µm100nm
AWG in Silica on SiliconBend radius
linewidth in current PIC
VCSELstripe laserLED
detector
gatewidth
transistor
taperspot-sizeconvertor
2R regenerator
fibre core
flip-flop
Wavelength-scale photonics
interconnects
Wavelength-scale photonics
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PICs: today and futureToday (InP, Silica-on-Silicon...):
Size of components on a chip (both functional components and interconnect components):
103 - 106 µm2
Number of components on a chip:1 - 103
Future (10-20 years from now):Size of components on a chip (both functional components and interconnect components):
1 - 103 µm2
Number of components on a chip:103 - 106
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Silica-on-silicon
NTT (e.g. Miya e.a., IEEE STQE ’00 pp.38)
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Reduce PIC-size / increase density WE NEED:Ultra-compact waveguiding with
Sharp bends (Bend radius < 10µm)
Compact splitters and combiners
Short mode-conversion distances
Compact wavelength selective functionsHighly dispersive element
Small, high-Q resonators
Compact non-linear functionsIncrease power density by using tight confinement
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High refractive index contrast (>2:1)High refractive index contrast allows for:
Very tight bendsCompact resonators with low lossWide angle mirrorsVery compact mode size
strong field strength strong non-linear effectssmall volume to be pumped in active devices faster and/or lower power
Photonic band gap effects
air semiconductor
dielectric
High refractive index contrast is key for ultra-compact photonic circuits
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Index ContrastConventional PICs Nanophotonics
In-plane (effective) index contrast
Out
-of-p
lane
inde
x co
ntra
st
Low
Low
High
High
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Materials for nanophotonic waveguides
In-plane indexcontrast
Out-of-planeindex contrast
Si/SiO2 (SOI) 3.5 to 1 3.5 to 1.5
Si/air(membrane)
3.5 to 1 3.5 to 1
GaAs/AlOx 3.5 to 1 3.5 to 1.5
InP/SiO2 3.3 to 1 3.3 to 1.5
SiON/SiO2 2 to 1.5/1 2 to 1.5
GaAs/AlGaAs 3.5 to 1 3.5 to 3.2
InGaAsP/InP 3.3 to 1 3.3 to 3.17
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SOI nanophotonics
Start: SOI-Wafer• Thin Silicon layer• Thick SiO2 buffer
BOX thickness
Waveguide Definition
Width + Height
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SOI-wires
EBeamyes1110.0 600260Oct. 03Columbia5.0 500200
DUVyes115.0 300300Apr. '05LETI / LPM+oxidation0.8 20050G-lineyes132.0 500200Dec. '01MITEBeamno1105.0 400320Dec. '02YokohamaEBeamno36.0 300300Dec. '02NTTEBeamno35.0 470270Aug. '03CornellEBeamno23.6 445220Apr. '04IBMDUVno12.4 500220Apr. '04IMEC
Fab.top clad
BOX [um]
loss [dB/cm]
w [nm]
h [nm]
DateGroup
(Table partly from Vlasov, McNab, Opt. Expr. ’04, pp1630)
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OutlineSubmicron SOI-wires
Introduction: why do we need themBasic properties: theory, design, loss, wavelength, polarizationFabricationDevices: couplers, crossings, filters …
III-V on SiliconIntroductionCoupling of lightFabricationPICMOS (Photonic Interconnect on CMOS)
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http://photonics.intec.UGent.be 14© intec 2004
Back to basics: cavities and waveguides
How does light propagate in waveguides and cavities?
n1
n2
n2
n1
n2
n2
n1
n2
n2
n1
n2
n2
Propagation in waveguide
Propagation through cavity
Emission within waveguide/cavity
Propagation through waveguide discontinuity
What is the role of n2 /n1 ?
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Back to basics: cavities and waveguides
kx
kz
TotalInternalReflection
Radiation modes
n2k0 n1k0
d n1
n2
n2
k
kx
kz
• dispersion:
• continuity:
For slab waveguide: n2 /n1 0.99 0.9 0.5Fraction of (2D) k-space confined by TIR = 14% 44% 87%
For channel waveguide:Fraction of (3D) k-space confined by TIR = 2% 19% 75%
“Light line”
220 yx kkc
nnkk +=== ω
2,1, xx kk =
2
1
21 ⎟⎠
⎞⎜⎝
⎛−
nn
2
1
21 ⎟⎠
⎞⎜⎝
⎛−
nn
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Back to basics: cavities and waveguides
kx
kz
π/d
Resonance if ↓
d large → many resonancesd small → few resonances
Two types of resonances:
• guided modes confined by TIR
• resonantly enhanced radiation modes
d n1
n2
n2
k
kx
kz
Only one guided mode if
dmkz
π=
( )2121
12
nn
nd−
≤λ
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Back to basics: cavities and waveguides
Waveguide/cavity types:• conventional waveguide: n2 /n1 ≈ 0.9 - 1
single mode even for d substantially larger than λ/n1lots of radiation modes
only small fraction of k-space well controlled by TIR
hence bends, couplers need to be based onslow adiabatic transitions → longinterference with long coupling length between guided modes → long
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Back to basics: cavities and waveguides
Waveguide/cavity types:• high contrast waveguide: n2 /n1
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Back to basics: periodic stacks
n1
n1
n1
n2
n2
Λ
kx
kz
n2k0 n1k0
Strong reflection and little transmission if:(for normal incidence)
(Bragg condition)
2π/Λd1
d2
Λ=
Λ+
Λπmdkdk 2211
Λ+
Λ=
=Λ→
22
11:
2dndnnwith
nm
av
av
λ
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Back to basics: periodic stacks
Cases:• low contrast stack: n2 /n1 ≈ 1
many periods needed for strong reflection
strong reflection only for narrow angular and spectral range
• high contrast stack: n2 /n1
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Spectral accuracy and geometrical accuracy
High index contrast components:- interference based filters,
with d the waveguide width (≈λ)
- cavity resonance wavelengthwith d the cavity length (a few λ)
- photonic crystalwith d the hole diameter (≈λ)
dd∂
≈∂λλ
if tolerable wavelength error : 1 nm ⇓
tolerable length scale error : (of the order of) 1 nm
dd∂
≈∂λλ
dd∂
≈∂λλ
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Basic PropertiesEffective Index
1
1.25
1.5
1.75
2
2.25
2.5
2.75
300 400 500 600 700 800
Waveguide Width [nm]
Effe
ctiv
e In
dex
TE0
TE1
TM0TM0
TE1
Single-Mode Width
Cladding (1.44)
h=220nm – λ=1550nm – 2D calc
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1
1.25
1.5
1.75
2
2.25
2.5
2.75
300 400 500 600 700 800
Basic PropertiesEffective Index
Waveguide Width [nm]
Effe
ctiv
e In
dex TE0
TE1
TM0TM0
TE1
Single-Mode Width
Cladding (1.44)
h=220nm – λ=1550nm – 2D calc
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Basic PropertiesGroup Index
h=220nm – λ=1550nm – 2D calc
1
1.5
2
2.5
3
3.5
4
4.5
5
1500 1525 1550 1575 1600Wavelength [nm]
n eff
-ngr
oup
w=400-600
w=400-600
1.52
2.53
3.54
4.55
400 450 500 550 600Waveguide Width [nm]
νν+=
λλ−=
ddnn
ddnnng Determines filter properties
ngroup
neff
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Substate Leakage
BOX Buffer Thickness [um]
Subs
trat
e Le
akag
e Lo
ss [d
B/c
m]
w=300nmw=500nm
1dB/cm
h=220nm – λ=1550nm
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Losses
EBeamyes1110.0 600260Oct. 03Columbia5.0 500200
DUVyes115.0 300300Apr. '05LETI/ LPM
+oxidation0.8 20050
G-lineyes132.0 500200Dec. '01MIT11EBeamno1105.0 400320Dec. '02Yokohama
EBeamno36.0 300300Dec. '02NTTEBeamno35.0 470270Aug. '03Cornell
2.5EBeamno23.6 445220Apr. '04IBM< 5DUVno12.4 500220Apr. '04IMEC
σroughness [nm]
Fab.top clad
BOX [um]
loss [dB/cm]
w [nm]
h [nm]
DateGroup
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0
5
10
15
20
25
30
35
40
300 350 400 450 500 550
Wire width (nm)
Loss
es (d
B/c
m)
w400nm440nm450nm500nm
33.89.47.42.4
Propagation losses± 1.7 dB/cm± 1.8 dB/cm± 0.9 dB/cm± 1.6 dB/cm
Loss (IMEC)
22
2s
2s n
dxEE
∆σ
∝α∫ Refractive index contrast
Field at interfaceSurface Roughness
Width [nm]
Loss
[dB
/cm
]
IBM
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Loss (IBM)2
2
2s
2s n
dxEE
∆σ
∝α∫
Wavelength [nm]
Loss
[dB
/cm
]
3.5dB/cm
(Vlasov, McNab, Optics Express, ’04)
w=450nmh=220nm
TETM
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Loss - otherOxidationDifference TE/TM
TM higher substrate leakage
TM higher scattering at vertical roughness
TE higher field intensityRoughness Correlation lengthGrillot e.a., PTL ’04, pp. 1661
(MIT)(Grillot)
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Polarisation
EBeamyes1110.0 600260Oct. 03Columbia5.0 500200
DUVyes115.0 300300Apr. '05LETI/LPM
+oxidation0.8 20050
G-lineyes132.0 500200Dec. '01MIT11EBeamno1105.0 400320Dec. '02Yokohama
EBeamno36.0 300300Dec. '02NTTEBeamno35.0 470270Aug. '03Cornell
2.5EBeamno23.6 445220Apr. '04IBM< 5DUVno12.4 500220Apr. '04IMEC
σroughness [nm]
Fab.top clad
BOX [um]
loss [dB/cm]
w [nm]
h [nm]
DateGroup
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PolarisationIssues:
Rectangular cross-section: very different neffSquare cross-section:
neff,TE = neff,TMBut: polarisation conversion + higher losses
Polarisation conversion in bends studied by SakaiFDTD: Conversion < 25dB (R>1um)Experiment: -13dB to -10dBReason: side wall angle (85o)
Polarisation insensitivity: hopeless ??Use polarisation diversity
(Sakai, Fukazawa, Baba, JLT ’04, pp. 520)
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Temperature dependence
K/pm140dTdK1079.1
dTdn c14Si =λ⇒×= −−
Classical Filters: dTdn
dd c =
λλ
(λc : central wavelength)
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Temperature DependenceUse Temperature Dependence for TO-switch
Espinola e.a. (PTL ’03, pp. 1366)
Lh=650um
Switching time = 3.5us
Switching power = 50mW
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Waveguide Density
Photonic Crystal Guides have smaller mode diameter but require several rows of holes !!!
Further scaling: increase height, increase index (?)
Surface Plasmon waveguides ?
Min
. Cen
ter-
to-c
ente
r [µ
m]
Waveguide Width [µm]
Single mode
Crosstalk < 20dB/cm
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Bends
4040
0.150.05
2.05.0
500220LETI/LPM
2 bends1.3resonant 400340Columbia
poly-Si0.3resonant 12 bends0.51.0 500200MIT
31.0 400320Yokohama0.173.0
24 bends0.462.0 300300NTT05.0 ?2.0 ?1.0 500220IMEC05.0
0.0132.0 20 bends0.0861.0 445220IBMNote
Loss [dB/90]
Radius [um]
w [nm]
h [nm]Group
(Table partly from Vlasov, McNab, Opt. Expr. ’04, pp1630)
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Bends
Wide λ-range
No need for resonant bends ?
(Vlasov, Mc Nab)
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Submicron SOI-wiresIntroduction: why do we need themBasic properties: design, loss, wavelength, polarizationFabricationDevices: couplers, crossings, filters …
III-V on SiliconIntroductionCoupling of lightFabricationPICMOS (Photonic Interconnect on CMOS)
Outline
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http://photonics.intec.UGent.be 38© intec 2004
Fabrication: Review
RIE (CF4:Ar)AluminiumEBeamyes1110.0 Columbiamixed5.0
HBr etchingSiO2DUVyes115.0 LETIoxidation0.8
RIE (SF6)SiO2G-lineyes32.0 MITICP (CF4 + Xe)metalEBeamno1105.0 Yokohama
SF6/CF4 etch, ECR-etchEBeamno36.0 NTTICPEBeamno35.0 Cornell
CF4/CHF3/Ar (Oxide) + HBr (Silicon)SiO2EBeamno23.6 IBM
Cl2/He/Hbr/O2ResistDUVno12.4 IMEC
Etch MethodMaskFab.top clad
BOX [um]
loss [dB/c
m]
Group
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FabricationEBeam
Best suited for research, Features < 50nmSlow, not compatible with mass-fabrication (?)
Standard Litho (G-line, I-Line)OK for 500nm linesProblem for smaller features (gaps in direction coupler, PhC, taper tips
DUV (248nm, 193nm)Resolution OK (but characterisation needed !)Compatible with Mass-FabricationExpensive mask
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Original fabrication process
Si-substrate
SiO2Si
Photoresist Photoresist
AR-coating
wafer Photoresist(UV3)
Bare Soft bake AR coating Illumination(248nm deep UV)
bakePost Development Silicon etch Oxide etch Resist strip
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Line width with exposure dose
200
300
400
500
600
700
800
900
10 15 20 25 30 35 40
200
300
400
500
600
700
DesignedLine Width
Line width (nm)
Exposure dose (mJ)
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Hole size with exposure dose
150
200
250
300
350
400
450
500
550
10 15 20 25 30 35 40
400/240400/320450/270450/360500/300500/400550/220550/330550/440600/240600/360600/480
DesignedPitch/diameter
Hole size (nm)
Exposure dose (mJ)
Sufficient ProcesswindowMarginally
sufficient
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-5%-10%-15% +5% +10% +15%
-0.4
-0.2
Bestfocus
+0.2
+0.4
Exposure Energy [∆E/E0 ]
Bestenergy
Focu
s [µ
m]
λ = 248nmNA = 0.63resist = UV3
λ = 248nmNA = 0.7resist = UV3
λ = 248nmNA = 0.7resist = TIS
Process WindowDesign Pitch/Size: 500nm /300nmTarget size: 300nm
5% deviation ellipse
λ = 193nmNA = 0.63resist = TIS
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-5%-10%-15% +5% +10% +15%
-0.2
-0.1
Bestfocus
+0.1
+0.2
Exposure Energy [∆E/E0 ]
Bestenergy
Focu
s [µ
m]
λ = 248nmNA = 0.63resist = UV3
λ = 248nmNA = 0.7resist = UV3
λ = 248nmNA = 0.7resist = TIS
Process WindowDesign Pitch/Size: 400nm /240nmTarget size: 200nm
5% deviation ellipse
λ = 193nmNA = 0.63resist = TIS
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Optical proximity effectsexample:
triangular lattice
pitch = 530nm
Diameter = 420nm
r/a = 0.4
1um
resist
Bulk hole = 420nm
Border hole = 380nm
Corner hole = 350nm
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Optical proximity effectsW1 waveguide
pitch = 500nmhole Ø in bulk lattice = 300nm
0.400.42 0.44 0.46 0.48 0.50k
0.26
0.27
0.28
0.29
0.30
0.31
0.32a/λ
Light cone
Oddlattice
modes
Even lattice modes
0.42 0.44 0.46 0.48 0.50k
0.40
MSB MSB
Øborder=310nm Øborder=320nm λ(nm)
1925
1850
1785
1725
1665
1610
1560
0.42 0.44 0.46 0.48k
0.40
MSB
Øborder=300nm
0.50
Light cone
Oddlattice
modes
Even lattice modes
Light cone
Oddlattice
modes
Even lattice modes
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Optical Proximity CorrectionProblem: Optical Proximity EffectsHoles at lattice boundary are different than holes in bulk due to interference effects
Correction on mask required (also on PICCO_03)
Original Mask layout Resist on wafer Mask layout with OPC
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Optical proximity correctionsDetermine empirically from PICCO_01
Example: 500nm pitch, 300→320nm holes
Border hole
bias (nm)
Corner hole bias (nm)
Hol
e si
ze d
evia
tion
(nm
)
Bulk
Border hole
Corner hole
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Deep Etch RoughnessExample: Ring resonator
Straight wire=400nmRing wire = 500nm
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OxidationThermal oxidation of top Silicon layer.
Roughness reduction
Lithography Si+SiO2 Etch 20-60nm thermal oxide
Oxide removalwith HF dip
optiona
l
10nmoxide
30nmoxide 50nm
oxide
Roughness onair-oxide interface
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Shallow etchingShallow etching → less roughnessBut: Scattering at bottom of hole
Roughness reduction
Lithography Si Etch 10nm oxide Oxide deposition
Re-fill hole with oxide to reduce asymmetry
200nm hole
optiona
l
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Silicon-only etch
Deep etching Si-only etching
Less roughness
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Etch bias with Silicon-only etchThick resist layer: 800nm UV3
needed for deep etching200-300nm hole Ø: high aspect ratiocauses litho-etch bias
800n
m
300nmhole Ø
Litho Etch Result
shadowof thickresist
230-250nmhole Ø
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Etch bias with Silicon-only etchOptimal Solution:
new litho + etch development: no time.Short-term Solution:
Resist-hardening/Resist Trimming plasma treatment
800n
m
300nmhole Ø
Litho Etch ResultRH
300nmhole Ø
smallershadow
Still slightly sloped sidewalls
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Updated Fabrication Process
Si-substrate
SiO2Si
Photoresist Photoresist
AR-coating
wafer Photoresist(UV3)
Bare Soft bake AR coating Illumination(248nm deep UV)
bakePost Development Resist Hardening
Silicon etch Resist strip
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http://photonics.intec.UGent.be 56© intec 2004
2-step processingTwo types of structures
Waveguides: requires deep etch (al least through Silicon)
Fibre couplers: require 50nm etch
Two-step processingFibre couplers first: 50nm etch gives little topography
Wafer-scale alignment: Alignment markers on the wafer and reticle periphery, not between the structures
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2-step processing
deep trench
shallow fibre coupler
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CMOS-compatible ?Well, it is SiliconIt is processed in a CMOS line
ButCMOS = layered
We: lines, holes, gaps, tips all in same layerCMOS = vias but rather low density
Phot Crystals = superdense latticesLine-edge roughness: no issue in CMOS (till now)
Roughness kills everything
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Submicron SOI-wiresIntroduction: why do we need themBasic properties: design, loss, wavelength, polarizationFabricationDevices
III-V on SiliconIntroductionCoupling of lightFabricationPICMOS (Photonic Interconnect on CMOS)
Outline
• Couplers• Crossings• Ring Resonators• AWG• Cascaded MachZehnder• Fibre-chip couplers
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Couplers - SplittersDirectional Couplers
Used in ring resonators, cascaded MZI …“Easy” to choose splitting ratioSensitive to fabrication issues (optical proximity, deviations in widths)
Multi-mode interference couplers (MMI)Fabrication tolerant
Standard Y-juncionSymmetric, narrow gap
Advanced CouplersSakai, Fukazawa, Baba, IEICE Trans ’02, 1033
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CouplersYokohama Nat. Univ
Simulation:
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CrossingsCrosstalk free crossings in optics ?
Standard crossingLarge diffractionLarge crosstalk (-9dB)Large loss (1.4dB)
Enhanced versionsBetter performanceLarger
NOT acceptable for large density circuitsUse multiple waveguide layers ??
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Fibre coupling
InP ridge wg
SM-fibre core
SOI PhC wg
µmMode mismatch between waveguide and fibre
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Coupling to fiberImportant:
Large bandwidth
Low loss
FabricationLimited extra processingTolerant to fabrication deviations
Coupling tolerance If coupling to SMF: same for all types of taperCoupling to high-NA fiber: lower
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Fiber-chip couplingRegular taper
Difficult to fabricate
Multi-mode
Facet coating required
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Coupling to fiberInverse taper
Broad wavelength range
Single mode
Easy to fabricate (if you can do the tips)
Low facet reflections
0.4µm
80nm
0.2µm
500 µm
polished facet
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Coupling to fiber
3x32x002x2
Cladding Size
0.8Polymer60.0200.0 300300NTT< 4dBSiO2100.040.0 470270Cornell< 1dBPolymer75.0150.0 445220IBM
tbdPolymer500220IMEC
LossCladding Material
tip width [nm]
L [um]
w [nm]
h [nm]
Group
0.4µm
80nm
0.2µm
500 µm
polished facet
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http://photonics.intec.UGent.be 68© intec 2004
Coupling to fibreTip fabrication
EBeam
Modified DUV (resist trimming)
220nm
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http://photonics.intec.UGent.be 69© intec 2004
spot size convertor
Single modefiber core
Coupling to fiberThe vertical fiber coupler
use a grating to couple light from/to a fiber perpendicular to the PIC
use a spot-sizeconvertor in plane
wafer scale, no need to cleave/polish the devices
good alignment tolerances
relatively broadband
works for TE only
(artist’s impression)
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http://photonics.intec.UGent.be 70© intec 2004
Out-of-plane coupler
What is new ?Other grating couplers
long (>100µm)
very narrow bandwidth
couple in and out
high efficiency (>50%)
Our grating couplershort (10µm)
bandwidth > 50nm possible
couple in and out
high efficiency ?
Grating couplers :‘Second’ order grating (Λ=λ /neff)
First order diffraction couples light out of the waveguide producing a surface normal propagating field
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http://photonics.intec.UGent.be 71© intec 2004
Fabricated DevicesAlternative: Grating couplers
Waferscale testing
Waferscale packaging
High alignment tolerance
deep trench
shallow fibre coupler
Towards optical circuit
Single modefiber core
From Fibre
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Tran
smis
sion
[dB
]
Wavelength [nm]
∆λ1dB = 35nm
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wavelength [nm]
T [d
B] passdrop
bcb cladding, ring resonator with bend coupling, R=8µm
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http://photonics.intec.UGent.be 73© intec 2004
Fiber CouplersCoupling light from waveguide to optical fiber on top
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http://photonics.intec.UGent.be 74© intec 2004
Experimental results
33% efficiency (4.8dB coupling loss)35-40nm 1dB bandwidth
0.00
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1520 1560 1600 1640
wavelength (nm)
fiber
cou
plin
g ef
ficie
ncy
620nm period630nm period620nm theory630nm theory
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http://photonics.intec.UGent.be 75© intec 2004
2D grating fiber couplerFiber to waveguide interface for polarisationindependent photonic integrated circuit
2D grating
couples each fiber polarisationin its own waveguide
in the waveguides the polarisation is the same (TE)
Allows for polarisationdiversity approach
patent
Single modefiber core
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http://photonics.intec.UGent.be 76© intec 2004
Experimental resultsFabrication
SOI: 220nm Si / 1000nm SiO2Etch depth: 90nm
Square lattice of holes: 580nm period
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http://photonics.intec.UGent.be 77© intec 2004
Optical Ring ResonatorsOptical Ring Resonators
For a given loss: trade-offHigh Q Low coupling
ButLow coupling Low drop efficiency !!!
Relevant Characteristics:• Free Spectral Range (Period)• Quality Factor
Determined by:• Coupling ratio• Round-trip loss• Length (=radius)
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http://photonics.intec.UGent.be 78© intec 2004
Optical Ring Resonator
1um
5um
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http://photonics.intec.UGent.be 79© intec 2004
Optical Ring Resonators
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Ring resonator demux4 rings in series
Linearly increasing radius
λc does not increase linearly as expected !!
Fabrication problem: mask discretisation
Solution: vary parameter which is less sensitive to fabrication
Other:Peak splitting due to reflections
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http://photonics.intec.UGent.be 80© intec 2004
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http://photonics.intec.UGent.be 81© intec 2004
Increasing Index ContrastLow Contrast - Fiber Matched
(silica or polymer based)Bend Radius ~ 5 mmSize ~ several cm^2
Medium Contrast (InP-InGaAsP)
Bend Radius ~ 500µm
5 mm
Ulra-high Contrast (SOI based)
Bend Radius < 50µm
200
µm
5 cm
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http://photonics.intec.UGent.be 82© intec 2004
AWG DesignVarious devices were designed :
∆ν = 400GHzFSR = 8 x 400GHzw = 0.5µm# arms = 18 or 24R = 75µm ~ 150µmwi = 0.6µm ~ 1.0µmwg = 0.6µm ~ 1.0µmg = 0.2µm
200µm To gratingcouplers
R
wg
wiw
All designs fabricated with different exposure doses (during litho)
different actual waveguide widths
wg
wi
g
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http://photonics.intec.UGent.be 83© intec 2004
200µmAWG ResultsAWG, 400GHz spacing, 8 channels
∆ν = 340GHz 360GHz (different exposure times)8dB on-chip loss
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Tran
smis
sion
[dB
]
Wavelength [nm]
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http://photonics.intec.UGent.be 84© intec 2004
O2
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200µmAWG Results5 x 8 AWG, 400GHz spacing, 8 Channels
300µm x 300µm area8dB on-chip loss6-10 dB crosstalk
Tran
smis
sion
[dB
]
Wavelength [nm]
7dB
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http://photonics.intec.UGent.be 85© intec 2004
AWGYokohama Nat. University
(Fukazawa, Ohno, Baba, Jap. J of Appl. Physics, ’04)
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http://photonics.intec.UGent.be 86© intec 2004
AWG Crosstalk OriginPossible reasons for crosstalk
“Overspill” in star-coupler
Reflections in star-coupler
Phase errors in grating arms
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http://photonics.intec.UGent.be 87© intec 2004
AWG Crosstalk OriginPhase errors in Waveguide arms ?
Assume standard deviation for phase-error given by :
ic
Lfi
πσφ1
=
Cro
ssta
lk L
evel
[dB
]
fc
Calculated Crosstalk vs. fc
Correlation length [µm]0.01 0.1 1 10 100 103 104
Rou
ghne
ss[n
m]
5
10
fc=100
fc
fc=100
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http://photonics.intec.UGent.be 88© intec 2004
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Cascaded MZ FilterExample: 5 stage CMZ
3.2nm bandwidth
17nm FSR
coupling efficiency ~80%
-10 dB crosstalk
wavelength [nm]no
rmal
ized
out
put [
dB]
pass
drop
20µm 14µm 20µm 20µm 14µm 20µm
∆L = 32.8µm
gap width = 220nm
waveguide width= 535nm
waveguide width= 565nm
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http://photonics.intec.UGent.be 89© intec 2004
PICCO04: Cascaded MZ FilterExample: 5 stage CMZ
2.6nm bandwidth
17nm FSR
coupling efficiency ~100%
-10 dB crosstalk-25.00
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wavelength [nm]no
rmal
ized
out
put [
dB]
pass
drop
26µm 14µm 20µm 20µm 14µm 26µm
∆L = 32.8µm
gap width = 220nm
waveguide width= 535nm
waveguide width= 565nm
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http://photonics.intec.UGent.be 90© intec 2004
Optical ProximityEffectsOptical Lithography
Images of neighbouringstructures interfere
Effect can be additiveof subtractive
= optical proximity effects
Example:isolated line width: 565
gap width: 220nm
line width in coupling section: 535nm
wg
wi
wc
W. Bogaerts et al. to be published in JLT (Oct 2004)
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http://photonics.intec.UGent.be 91© intec 2004
ConclusionsSub-micron SOI-waveguides:
Powerful platform for high-density Photonic circuitsWe have all basic building blocs (and no need for these complicated Photonic Crystals)
Fabrication issues to be solvedOptical proximity (narrow lines, fine gaps)Phase-Errors, control central wavelength of devicesFurther reduction losses needed ?
Next step: active functionality ?