The document discusses integrated silicon photonics and its components. It covers the context of electronic-photonic integration and confinement techniques. It then describes passive devices like waveguides, couplers, and wavelength division multiplexing. Finally, it discusses active devices such as detectors, modulators, light sources and lasers, and integrating photonics. It provides information on the materials, geometries, losses and metrology of silicon photonic waveguides.

1. AIM
Academy
Integrated Silicon Photonics
Jurgen Michel
MIT Microphotonics Center
© J. Michel 2016

2. AIM
Academy
Part 1:
Context
 Electronic-Photonic Integration
 Confinement
Part 2:
Passive
Devices
 Waveguides
Off-Chip Couplers
 Wavelength Division Multiplexing
Part 3:
Active
Devices
 Detectors
 Modulators
 Light Sources and Lasers
 Integrating Photonics

3. AIM
Academy
 optics: disruptive technology
 metal interconnect constraints
 materials platform
 device challenges
R. Kirchain and L.C. Kimerling, “A roadmap for nanophotonics,” Nature Photonics v.1, p.303 (2007).
Electronic-Photonic Integration:
Optical Interconnects
10
-2
10
0
10
2
10
4
10
6
10
8
1010
10
12
10
14
1880 1900 1920 1940 1960 1980 2000 2020 2040
RelativeInformationCapacity(bit/s)
Year
Telephone lines first constructed
Carrier Telephonyfirstused 12 voice
channels on one wire pair
Earlycoaxial cable links
Advanced
coaxial and
microwave systems
Communication
Satellites
Single channel
(ETDM)
Multi-channel
(WDM)
OPTICAL
FIBER
SYSTEMS

4. AIM
Academy
10
-2
10
0
10
2
10
4
10
6
10
8
1010
10
12
10
14
1880 1900 1920 1940 1960 1980 2000 2020 2040
RelativeInformationCapacity(bit/s)
Year
Telephone lines first constructed
Carrier Telephonyfirstused 12 voice
channels on one wire pair
Earlycoaxial cable links
Advanced
coaxial and
microwave systems
Communication
Satellites
Single channel
(ETDM)
Multi-channel
(WDM)
OPTICAL
FIBER
SYSTEMS
Photonics: Optical Fiber/Interconnects
Distance Bandwidth product > 10 Tb/s mm
 Historical transition from Electronic to Photonic Interconnects: 10 Mb/s•km
 RC delay + Shrinking Dimensions
 decreased chip speed
Communication Technology
R. Kirchain and L.C. Kimerling, “A roadmap for nanophotonics,” Nature Phot. v.1, p.303 (2007)

5. AIM
Academy The Future of Multicore
Parallelism replaced
clock frequency scaling
Resulting Challenges…
Programming
Power
Interconnect Performance
MIT RAW Intel 50core Knights CornerIBM Blue Gene/Q Tilera TILE64
Number of cores doubles
every 18 months

6. AIM
Academy
 Tiles can directly communicate with any other tile
 Tiles contain one or more cores
 Broadcasts require just one send
 No complicated routing on network required
 Tile resources only used when performing communication (unlike mesh
approach)
Multi-tile processor
Optical
network layer
A. Agarwal, L.C. Kimerling, J. Michel, MIT, M. Watts, Sandia NL
ATAC: All-to-All Communication
game-changing architectural paradigm

7. AIM
Academy
 Tiles can directly communicate with any other tile
 Tiles contain one or more cores
 Broadcasts require just one send
 No complicated routing on network required
 Tile resources only used when performing communication (unlike mesh
approach)
ATAC: All-to-All Communication
game-changing architectural paradigm

8. AIM
Academy
Laser
Modulator Filter
Photodetector
+
+
+
Modulator Filter
+ +
MIT
MIT
LaserPhotodetector
+ Hybrid or
Monolithic
Cornell University
Driver Electrical data Electrical data
Waveguide
Si substrate
Electronic-Photonic Integration
A Near Complete Toolkit

9. AIM
Academy
Nature 528, 534–538 (24 December 2015)
Single-chip microprocessor that communicates directly
using light

10. AIM
Academy
Confinement:
The Optics of Photonics
 total internal reflection
 resonance

11. AIM
Academy Index Confinement: The 1D Basics
 Confinement: Total Internal Reflection
 Light confinement to high refractive index core:
standing wave in x-, y-direction
 Surrounded by lower refractive index cladding:
evanescent (exponential decay) wave in x-, y-
direction
Helmholtz Equation
t
2
 n2
k0
2
   2

Total Internal Reflection

12. AIM
Academy
 Geometry
Strip: high confinement
 Dense integration
Ridge/rib: low confinement
 Fiber optic compatibility
 Multimode vs Single-Mode
 multimode less lossy in straight waveguides
 single-mode less lossy in turns/splits
– robust for interferometric designs
ncl < neff < nco
1/ncl
1/nco
multimode
single-mode
Helmholtz Equation
m  n2k0 cosm
Radiation Modes
Forbidden
Region
Index Confinement: The 1D Basics

13. AIM
Academy Index Confinement
2D Mode Size: influence of aspect ratio and undercladding
 Waveguide dimensions should be optimized for best confinement
 Dimensions should be restricted to single-mode cutoff
 Single mode waveguide has unique aspect ratio for optimal confinement
 Higher n waveguide requires smaller undercladding
Si strip waveguide, oxide clad (n2=3.5, n1=1.446), 250nm height
TE Polarization – E field contours

14. AIM
Academy Resonant Confinement
Standing/Traveling Wave Resonator
 Standing wave: Fabry Perot cavity, microcavity
 dmm/2neff, m=1,2,3,…
 dielectric waveguide: deff > d
 Bragg reflector: high resolution lithography
d
E(z  d,t)  Aei0 z
teid
t  (Aei0 z
teid
)reid
reid
t  (Aei0 z
teid
)reid
reid
 reid
reid
t  ... eit

Aei(0 zt)
eid
(1 r)2
1 x
, x  r2
ei2d
T 
E(z  d,t)
E(z,t)
2

eid
(1 r)2
1 r2
ei2d
2
m 
L
m
, m  1,2,3,K
(L  2d,2r)
m 
c
m
 m
c
L
FSR  m  m1 
c
L

15. AIM
Academy
 Traveling wave: (micro-) ring resonator
 2r=mm/neff, m=1,2,3,…
 horizontal coupling: >UV lithography
 vertical coupling: CMP
Q  m  m
1
vg
;
m
m
;
m
m
Finesse: F 
FSR
m
loss  ext   
1
vg
Standing: ext 
1
2d
ln
1
R




m 
L
m
, m  1,2,3,K
(L  2d,2r)
m 
c
m
 m
c
L
FSR  m  m1 
c
L
FSR  m1  m

2
L
Free Spectral Range:
Quality Factor:
Resonant Confinement
Standing/Traveling Wave Resonator

16. AIM
Academy
 Anti-resonant Confinement
 Short-range interference effect
 Different from photonic crystal low dielectric state
 ws=100 nm air slot inside Si waveguide
 Confinement influence quasi-TE mode
 Index discontinuity in E(nco/nslot)2~12
 Contains ~40% quasi-TE mode power
Hs nn 
V. R. Almeida, Q. Xu, C. A. Barrios, and M. Lipson, Guiding and confining light in void
nanostructure, Opt. Lett., vol.29, 1209-1211, 2004
Slot Waveguides
Boundary Condition Discontinuity in E-field
Q. Xu, V.R. Almeida, R.R. Panepucci and M. Lipson,“Experimental demonstration of guiding and
confiningLight in nanometer-size low-refractive-index material,” Optics Letters, v.29(14), pp. 1626-
1628 (2004).

17. AIM
Academy The Index Contrast Scale
Very Low Index
Contrast
n=0.001-0.01
VLIC HIC VHIC UHIC
High Index
Contrast
n=0.05-0.1
Very High
Index Contrast
n=0.1-0.5
Ultra High Index
Contrast
n>0.5
catt.okstate.edu/critt
www.nhkspg.co.jp
www.corning.com
www.verifiber.com
LIC
Low Index
Contrast
n=0.01-0.05
www.teemphotonics.com
Silicon
Silica
www.mit.edu
IBM, Intel, Kotura, etc.
www.infinera.com
www.wias-berlin.de/
TriPleX
www.xiophotonics.com
SOI

18. AIM
Academy
Part 1:
Context
 Electronic-Photonic Integration
 Confinement
Part 2:
Passive
Devices
 Waveguides
Off-Chip Couplers
 Wavelength Division Multiplexing
Part 3:
Active
Devices
 Detectors
 Modulators
 Light Sources and Lasers
 Integrating Photonics

19. AIM
Academy CMOS Fabrication
CMOS Logic Platform
− Technology node
− Silicon substrate (bulk, SOI)
− Oxide gate, SiO2
− Salicide contacts, CoSi2
− Planarization
− Interconnect levels
− Vdd – Voltage drain-drain
3 Areas of Interest
- Substrate
- FEOL to PMD
- BEOL – Metallization
Integration Priorities
- FET Performance
- Thermal cycling-proper sequencing
- Cross Contamination
- Process complexity IMD: Inter-Metal Dielectric
PMD: Pre-Metal Dielectric
FEOL: Front-End-Of-Line
BEOL: Back-End-Of-Line
*Salicide spike anneal 1050°C
• PMD – SiO2, Planarized
1.0mm
1.1mm
CMOS FET & Interconnect for 0.18 mm node
• Silicon Substrate p-type
• Gate, S/D junctions
• Metal – AlCu, Local
interconnect levels 1-4
• IMD – SiO2, Planarized
• Contacts – W studs
• Vias – W studs
900
<550
<450
750*
• Salicide, Ti, Co

20. AIM
Academy
Passive Photonics:
Waveguides
 Si-compatible
 Ultra-low loss in the IR
 Single mode design
 Losses: Measurement, Theory
 SOI, a-Si
 SiON, Si3N4
Substrate/Underlayer
SiO2 tunderclad
SiO2
200 nm
500 nm
~3.5 mm
~3 mm
Si

21. AIM
Academy Waveguide Materials
Core Si Si-rich
Si3N4
Si3N4 SiON
n 3.5 2.2 2.0 2.0-
1.445
n 2.055 0.755 0.555 0.555-0
 Dielectric waveguides
Core:
 Si: SOI, amorphous (a-Si)
 Si-rich Si3N4 / Si3N4: PECVD, LPCVD
 SiON: PECVD
Cladding:
 Undercladding: wet thermal SiO2
 Overcladding: PECVD SiO2
 Geometry
Strip
 h=0.2-1.0 mm (SOI, thin film)
 w=0.5-2.0 mm (UV-sub-UV lithography)
Ridge/rib
 h ~ 1 mm, trench=0.5-0.8 mm
 w= 1.0-5.0 mm
waveguide core refractive indices
SiO2 cladding is assumed in all cases.
Index difference: n2-0.01

22. AIM
Academy Waveguide Loss
S side roughness +  top roughness +  bulk +  substrate
Si Substrate
 Substrate Leakage – f (n, h, w, tunderclad)
 Absorption – f ( bulk, n, h,w)
 Roughness Scattering – f (n, h, w, , Lc)
 Surface loss
 Sidewall loss
 Design > isolation design rules
 Material & process method
 CMP
 Etch & Post etch treatments
Sidewall scattering often dominates: TM mode lowest loss
bulk=core+(1-)cladding
: power confinement factor
: roughness Amplitude
Lc: roughness correlation length
D. K. Sparacin, “Process and Design Techniques for Low Loss Integrated Silicon Photonics,” MIT Ph.D. Thesis (2006).

23. AIM
Academy Metrology
Fabry-Pérot Method
 work with fewer samples: spectral scan
 FSR: peak spacing; loss/length: peak/valley ratio
 a priori knowledge of insertion loss: reflectivity calc deviates for n
 need accurate measure of waveguide length
d
E(z  d,t)  Aei0 z
teid
t  (Aei0 z
teid
)reid
reid
t  (Aei0 z
teid
)reid
reid
 reid
reid
t  ... eit

Aei(0 zt)
eid
(1 r)2
1 x
, x  r2
ei2d
T 
E(z  d,t)
E(z,t)
2

eid
(1 r)2
1 r2
ei2d
2
Input
Output
~1.7 mm mode
field diameter
S.J. Spector et al., Proc. (2004).
D. K. Sparacin, “Process and Design Techniques for Low Loss Integrated Silicon Photonics,” MIT Ph.D. Thesis (2006).
S. Spector et al., Optical Amplifiers and Their Applications/Integrated Photonics Research, Technical Digest, IThE5 (OSA, 2004).
  imagimagreal i ;

24. AIM
Academy Si SOI Waveguides
 h=220 nm
 w=445 nm
Y.A. Vlasov and S.J. McNab, “Losses in single-mode silicon-on-insulator strip waveguides and
Bends,” Optics Express, v.12(8), pp. 1622-1631(2004).
TE
TE 0.3 dB/cm
H. Rong, A. Liu, R. Jones, O. Cohen, D. Hak, R. Nicolaescu, A. Fang and M. Paniccia,
“An all-silicon Raman laser,” Nature, v.433(7023),pp.292-294 (2005)
1.5 mm SOI
 w=1.5 mm
 depth=0.7 mm
Ridge SOI waveguide
— w=1 mm
— w=5 mm
 TE=3.6 ± 0.1 dB/cm
Si SOI: “photonic wire”

25. AIM
Academy
TE=0.32  0.05 dB/cm
S. Spector, M. W. Geis, D. Lennon, R. C. Williamson, and T. M. Lyszczarz, " Hybrid multi-mode/single-mode waveguides for low loss," in
Optical Amplifiers and Their Applications/Integrated Photonics Research, Technical Digest (CD) (Optical Society of America, 2004), paper IThE5.
Mode-Engineered SOI Waveguides
 Couple light to first-order mode
 Multimode straight waveguide segments
 power remains confined to first-order mode
 minimal (TE) overlap with sidewalls
 Turns: adiabatic taper to single-mode waveguide

26. AIM
Academy
Conduction
Band
Valence
Band
Conduction
Band
Valence
Band
Conduction
Band
Valence
Band
Conduction
Band
Valence
Band
Conduction
Band
Valence
Band
Amorphous Silicon (a-Si) Waveguides
Dangling Bond States Absorb Light
 Extremely attractive as upper-level waveguide material
 Previous Reports of ~ 300 dB/cm Waveguide Loss
 H-passivation of a-Si reduces dangling bond states
 H-concentration in PECVD deposited a-Si materials is
high, should have low loss
D. K. Sparacin, “Process and Design Techniques for Low Loss Integrated Silicon Photonics,” MIT Ph.D. Thesis (2006).

27. AIM
Academy
Sample Resonance
wavelength (nm)
Extinction ratio
(dB)
-3 dB bandwidth
(pm)
Q factor Loss
(dB/cm)
1 1558.146 12.3 69.4 22452 12.0 ± 1.8
2 1559.587 5.4 25.8 60449 6.5 ± 0.9
3 1560.319 6.9 11.0 141847 2.7 ± 0.4
a-Si Waveguide, SiN clad
R. Sun, K. McComber, J. Cheng, D. K. Sparacin, M. Beals, J. Michel and L. C. Kimerling, “Transparent amorphous silicon channel waveguides
with silicon nitride intercladding layer,” Appl. Phys. Lett. v.94(14), p.141108 (2009)
TE-polarization, ring resonator measurements

28. AIM
Academy Slot Waveguides
 Low index slot regions: potential host matrix for optically active dopants (Er,
nanocrystals)
 Access to effective index/group index values intermediate to Si3N4  Si waveguides
R. Sun, P. Dong, N. Feng, C.Y. Hong, J. Michel, M. Lipson, L.C. Kimerling, “Horizontal single and multiple slot waveguides: optical transmission at =1550 nm,” Opt. Exp. v.15(26), p.17967 (2007).
Expt Theory
74.6 pm/K 76.8 pm/K
65.4 pm/K 64.6 pm/K
Single Slot
Triple Slot
Si: 102.7 pm/K
dTd /

29. AIM
Academy
Passive Photonics:
Off-Chip Coupler
 Size mismatch of optical modes
 Index mismatch of materials
Optical Fiber Core
(8 mm )
SiO2
Cladding
Silicon Waveguide
(0.2 x 0.5 mm2)

30. AIM
Academy Adiabatic Taper
 Waveguide taper length >> wavelength
 In-plane taper: linear, parabolic, exponential,
Gaussian, hyperbolic
 Good Design: 80% power (TE) remains in
source mode
 Novel studies: rectangular taper
 TM mode more stable than TE
E.Marcatili, “Dielectric tapers with curved axes and no loss,” IEEE J.Quantum Electron., QE 21, 307-314 (1985).
G. Jin, S. Shi, A. Sharkawy and D.W. Prather, “Polarization effects in tapered dielectric
waveguides,” Opt. Express, v.11(16), pp.1931-1941 (2003).

31. AIM
Academy Inverted Taper Coupler
 CMOS process flow and fabrication
 100 modal area reduction
 10 coupling efficiency
V.R. Almeida, R.R. Panepucci and M. Lipson, “Nanotaper for compact mode conversion,”
Optics Lett., v.28(15), pp.1302-1304 (2003).
K.K. Lee, L.C. Kimerling, et al., “Mode transformer for miniaturized optical circuits,” Opt.
Lett. v.8(5), pp.498-500 (2005).
T. Tsuchizawa, H. Morita et al., “Microphotonics Devices Based on
Silicon Microfabrication Technology,” IEEE J. Select. Topics Quant. Elect., v.11(1),
pp.232-240 (2005).

32. AIM
Academy Grating Couplers
 Diffract incident light into waveguide
 1D Photonic Crystal (on SOI)
 Couple out-of-plane incident light
into modes propagating away from
in-plane stopband reflector
 Stopband location controlled by etch
depth
 Performance
 TE: 1 dB insertion loss
 35 nm 3dB-bandwidth
Source: http://silicon-photonics.ief.u-psud.fr
C. Li, H. Zhang, M. Yu, G. Q. Lo, Opt. Express 21, 7868-7874 (2013)

33. AIM
Academy 2D Grating Coupler
 2D Photonic Crystal in SOI
 Fiber TE/TM mode couple into different ridge
waveguides
 TM fiber mode transformed into TE
waveguide mode
 Built-in Polarization Diversity
D. Taillaert, H. Chong, P.I. Borel, L.H. Frandsen, R.M. De La Rue and R. Baets, “A Compact Two-Dimensional
Grating Coupler Used as a Polarization Splitter,” IEEE Phot. Tech. Lett., v.15(9), pp.1249-1251 (2003).

34. AIM
Academy Coupler Comparison
Coupler
Type
Coupler
Length/
Area
Coupling
Efficiency
Wavelength
Range
Polarization
Dependent
Adiabatic
Taper
40 μm 80% (TE) ultra-broadband yes
Inverted Taper 100 μm 90 % ultra-broadband yes
1D Grading
2D Grading
~10 μm
~100 μm2
80%
20%
broadband
broadband
yes
no

35. AIM
Academy
Passive Photonics:
Wavelength Division Multiplexing
 Dense WDM function
 Si-compatible, compact footprint
 Microrings, racetracks, slot rings
 Higher-order filters, embedded rings
T. Barwicz et al., Optics Express v.12(7), (2004).

36. AIM
Academy
 Lithography: 248nm
 Q ~ 2000, FSR~16 nm
1st-Order Ring & Racetrack Microring Filters
1x4 WDM (silicon nitride Rings)
1515 1520 1525 1530 1535 1540 1545
Wavelength (nm)
Power--samescale(au)
Port1
Port2
Port3
Port4
Thru
Q~500
6 mm
6 mmIn
Drop
Silicon
Thru-port 1 2 3 4
Thru-port
D. R. Lim, B. E. Little , K. K. Lee, M. Morse, H. H. Fujimoto, H. A. Haus, and L. C. Kimerling, “Micron-sized channel dropping filters
using silicon waveguide devices,” Proc. SPIE, 3847, pp.65-71 (1999).
Si3N4Si
,...2,1
20


m
r
n
m
eff


1520 1540 1560
2mm Ring
FSR=48.6nm; Q=1050
DropPortPower(ArbUnits)
Wavelength (nm)
3 mm Ring
FSR=21nm; Q=3000
5 mm ring
FSR=18nm Q=3875

37. AIM
Academy
M.A. Popović, H.I. Smith et al., “Multistage high-order microring-resonator add-drop filters,” Opt. Lett., vol. 31,
no. 17, pp. 2571-2573, September 2006.
M.A. Popović, H.I. Smith et al., “High-index-contrast, wide-FSR microring-resonator filter design and realization
with frequency-shift compensation,” in Optical Fiber Communication Conference (OFC/NFOEC) Technical
Digest (Optical Society of America, Washington, DC, March 6-11, 2005), paper OFK1, vol. 5, pp. 213-215.
>2nd Order Rings: Resonance Frequency
 Central ring: different
coupling coefficient 
different resonant frequency
 Compensated ring design
(wider waveguide) ensures
common resonance
frequency
 flatband response
 e-beam lithography
B.E. Little et al., IEEE Photon. Technol. Lett. 16, 2263 (Oct 2004)

38. AIM
Academy WDM Resonator Comparison
Resonator
Type
Quality
Factor
Bandwidth FSR
(L=50 –
100 μm)
Insertion Loss
1st Order Ring 104 - 105
(easy to achieve
high Q)
~103 – 102
GHz
(WDM)
6000 – 3000
GHz
<0.5 dB for gap
< 100 nm
Higher Order
Ring
102 - 103
(high Q
challenging)
~103 – 10
GHz flatband
(DWDM)
6000 – 3000
GHz
>1 dB for gap
< 100 nm
Racetrack 102 - 104 ~103 – 102
GHz
(WDM)
6000 – 3000
GHz
<1 dB for gap
< 100 nm

39. AIM
Academy
Part 1:
Context
 Electronic-Photonic Integration
 Confinement
Part 2:
Passive
Devices
 Waveguides
Off-Chip Couplers
 Wavelength Division Multiplexing
Part 3:
Active
Devices
 Photodetectors
 Modulators
 Light Sources and Lasers
 Integrating Photonics

40. AIM
Academy
Active Photonics:
Photodetectors
 Broadband, highly efficiency IR detector
 Bandwidth considerations
 Adaption to size of optical mode
 Low voltage operation
 Si processing, integrated into CMOS process flow
 Integration with ICs
G. Dehlinger et al., IEEE Phot. Tech. Lett.,v.16(11), (2004).
Active Photonics: Photodetectors

41. AIM
Academy
Photodetector Basics - Absorption
1.55 1.242.07 0.62
λ (μm)
Physics of Semiconductor Devices, by S.M. Sze and K.K. Ng (Wiley-Interscience, 3rd edition, 2006)
Photodetector Basics - Absorption

42. AIM
Academy
Ge Epitaxy on Si
Si
Ge Ge epitaxial growth
on Si at 550C
Si
Ge
Ge Epitaxy on Si

43. AIM
Academy
H.C. Luan, D.R. Lim, K.K. Lee, K.M. Chen, J.G. Sandland, K. Wada and L.C.
Kimerling,
APL, v.75(19), pp.2909-2911 (1999).
L. Colace, G. Masini, G. Assanto, H.C. Luan, K. Wada and L.C. Kimerling,
APL, v.76(10), pp.1231-1233 (2000).
J. Liu, J. Michel, W. Giziewicz, D. Pan, K. Wada, D. D. Cannon, S.
Jongthammanurak, D. T. Danielson, L. C. Kimerling, J. Chen, F. O. Ilday, F. X.
Kartner, and J. Yasaitis, Appl. Phys. Lett. 87, 103501 (2005).
Ge-on-Si Photodetector
 2-step UHV-CVD + cyclic thermal annealing
 780-900C anneal
 10 TDD: 2.3107 cm-2 2.3106 cm-2
 increases hole mobility
Ge-on-Si Photodetector

44. AIM
Academy
Waveguide-integrated
Photodetector
Waveguide - Photodetector Integration
Performance Gain
10
2
10
3
10
4
0
10
20
30
40
50
60
70
80
(Bandwidth)x(Quantumefficiency)(GHz)
Detector Size (mm2
)
d=0.5μm
5mm20mm
Q.E: 90%
Discrete, free-space
Photodetectors
RC time limitTransit time
limit
RC time limit
d=2.0μm
J. Michel, J. F. Liu, L.C. Kimerling, , Nat. Photonics 4, 527 (2010)
Waveguide - Photodetector Integration

45. AIM
Academy
44
Ge-directly-on-Si Photodetector
Waveguide Integration
IMEC EPIXFAB Platform IME Singapore Platform
A. Novak, Optics Express 21, 28387 (2013)

46. AIM
Academy
Monolithic germanium/silicon avalanche photodiodes
Y. Kang, H.-D. Liu, M. Morse, M. J. Paniccia, M. Zadka, S. Litski, G. Sarid,
A. Pauchard, Y.-H. Kuo, H.-W. Chen, W. S. Zaoui, J. E. Bowers,
A. Beling, D. C. McIntosh, X. Zheng, J. C. Campbell, Nat. Photonics 3, 59 (2009)
Measured 3-dB bandwidth versus gain of 30-mm-diameter germanium/silicon APDs at a
wavelength of 1,300 nm. The coloured symbols are measured bandwidths from four
devices. The blue line is the calculated bandwidth assuming carrier transit time and RC
time constant are the limiting factors for the device bandwidth. The black line is a
calculated result considering the avalanche build-up effect13 with keff ¼ 0.08. The
corresponding gain–bandwidth product is 340 GHz, which fits the measured values. BW,
bandwidth.

47. AIM
Academy
Active Photonics:
Modulators
 Compact, integrated, Si-compatible
 Low power consumption
J. Liu, S. Jongthammanurak, D. Pan, J. Michel and L.C. Kimerling
Silicon Microphotonics
Sandia Si ring
Active Photonics: Modulators

48. AIM
Academy
Modulator Principles
 Physical Principles
 Thermo-optical Effect
Change the refractive index of Si by heating.
 Plasma Dispersion Effect
Change the refractive index of Si by carrier injection in a diode structure or carrier accumulation in a MOS structure.
 Electric Field Effect
- Franz-Keldysh Effect in Bulk GeSi
Change the absorption or refractive index of GeSi by electric field.
- Quantum Confined Stark Effect in Ge/GeSi Quantum Wells
Change the absorption or refractive index of Ge Q-wells by electric field.
 Basic Device Structures
 Mach-Zehnder Interferometers
Interferes two beams of light with different phases. Phase shift achieved by changing the refractive index.
 Ring Modulators
Change the resonance frequency of a ring by varying its refractive index, thereby controlling the coupling of light
from an adjacent waveguide.
 Electro-absorption Modulators
Light passes through an active material whose absorption can be changed by varying the applied electric field
 Plasmonic Modulators
Modulator Principles

49. AIM
Academy
Mach Zehnder Modulator
 Phase delay in lower arm
causes interference
 Large device size due to
small effect
 Length 0.5-3mm
Mach Zehnder Modulator

50. AIM
Academy
MOS-Enhanced Mach Zehnder Modulator
 FET design: rapid injection and extraction of
free carriers
 Phase delay due to n from plasma
dispersion
 Large device size due to small effect: MZ-arm
length 1-3mm
 > 15 dB Mod. Depth @ 3 V
 Up to 30Gbps
A. Liu, L. Liao, D. Rubin, H. Nguyen, B. Ciftcioglu, Y. Chetrit, N.
Izhaky, and M. Paniccia, Optics Express 16, 660 (2007)
MOS-Enhanced Mach Zehnder Modulator

51. AIM
Academy
Microring Modulators
1.5 Gbit/s using RZ pattern
 Power consumption of >50fJ/bit
 Less than 0.3V and µA current needed for
complete modulation in DC
 In AC, 3.3Vpp and 1mA current were used
 Expected theoretical bandwidth limit
>10Gb/s
Diameter = 12μm
Width = 450nm
Gap = 200nm
M. Lipson, “Switching light on a silicon chip,” Opt. Mat., v.27, pp.731-739 (2005).
Q. Xu, B. Schmidt, S. Pradhan and M. Lipson, “Micrometre-scale silicon electro-
optic modulator,” Nature, v.435, pp.325-327 (2005).
P. Dong et al., “Low Vpp, ultralow-energy, compact, high-speed silicon electro-
optic modulator”, Optics Express, Vol 17 No 25 (2009)
Microring Modulators

52. AIM
Academy
Low Power Si Ring Modulators
W.A. Zortman, M. R. Watts, D. C. Trotter, R. W. Young and A. L. Lentine, “Low-Power High-Speed Silicon Microdisk Modulators,“ OSA / CLEO/QELS 2010 CThJ4
Low Power Si Ring Modulators

53. AIM
Academy
Plasmonic Modulators
 Plasmonic mode concentrates optical field within
nm thin film
 Optical absorption of thin film can be tuned by
carrier injection
 Length of 3
 Power consumption of <50fJ/bit expected
 Expected theoretical bandwidth limit >300Gb/s
V.J. Sorger, N.D. Lanzillotti-Kimura,R.-M. Ma, X. Zhang” Ultra-compact silicon nanophotonic modulator with
broadband response.” Nanophotonics 1, 17-22 (2012).
Plasmonic Modulators

54. AIM
Academy
Electro Absorption Modulator
Quantum Confined Stark Effect
 Weak EO effect in Si
 mm-scale MZ modulator, Q ring resonator
 Stark Effect: l100-400 mm, V1 V, Q=0
 Observe QCSE: Ge/SiGe type I confinement and strong direct
gap absorption
 comparable to III-Vs (t<ps, mod. rate >50GHz)
 Exciton peak 80 meV above Ge Ec

- 36 meV strain shift
- 56 meV quantum confinement
 Clear shift of exciton peak with 5 V: /6 @ =1.46 mm
Y.-H. Kuo, Y.K. Lee, Y. Ge, S. Ren, J.E. Roth, T.I. Kamins, D.A.B. Miller and J.S. Harris, "Strong quantum-confined Stark effect in germanium quantum-well structures on silicon,"
Nature, v.437, pp.1334-1336 (2005).
Electro Absorption Modulator

55. AIM
Academy
Electro Absorption Modulator
Franz-Keldysh Effect in GeSi
 Linear electro-optic effect
 n(E), (E)
 Ge-on-Si: comparable to InP
 Strong F-K effect
 strain reduces separation between Eg
 and Eg
L
 F-K regime in low absorption background
 Expected mod. depth: 10dB @ >30GHz
 Experimental mod. depth: 10dB
 Experimental bandwidth: 1.2 GHz
 Ultra low power consumption: 25 pJ/bit
J.F. Liu, M. Beals, A. Pomerene, S. Bernardis, R. Sun, J. Cheng, L. C. Kimerling, and J. Michel, ”Waveguide-
integrated, ultra-low energy GeSi electro-absorption modulators,” Nature Photonics 2, 433 (June 2008)
Electro Absorption Modulator

56. AIM
Academy
 Si ridge waveguide – low loss
 strain reduces separation
between Eg
 and Eg
L
 F-K regime in low
absorption background
 Mod. depth: 4-7.5dB @ >30GHz
 Max. experimental mod.
depth: 7.5dB
 Low power consumption: 100
fJ/bit
N.-N. Feng et al., ” 30GHz Ge electro-absorption modulator integrated with 3μm silicon-on-insulator
waveguide,” Optics Express 72, 7062 (April 2011)
Electro Absorption Modulator
Franz-Keldysh Effect in GeSi
Electro Absorption Modulator

57. AIM
Academy
Modulator Comparison
Modulator
Type
Footprint
Power
Consumption
Wavelengths
Range
Applications
Si Mach
Zehnder
> 500 mm2 > 10pJ/bit large, tunable
Active Optical
Cable, Telecom
Si Ring
modulator
< 10 mm2 > 5fJ/bit (w/o
heating)
single
wavelength
Telecom, On-
chip Integration
Ge EA
modulator
< 10 mm2 25fJ/bit ~ 15nm range
On-chip
Integration
Plasmonic
modulator
2.5 mm2 < 50fJ/bit large, ~ 1mm
On-chip
Integration
Modulator Comparison

58. AIM
Academy
Active Photonics:
Light Sources and Lasers
 IR light source: SOI waveguides
 Laser: DWDM, sub-mm structures interferometric structures
 III-V monolithic integration
 Si hybrid laser
 Ge laser
 Frequency comb based light sources
K. Vahala et al., APL, v.84(7), (2004).
J. Bowers et al., IEEE Phot. Tech. Lett., v.18(10), (2006).
57
Active Photonics:
Light Sources and Lasers

59. AIM
Academy
Monolithic Integration of III-V laser on SiGe/Si
 Long RT CW-lifetime GaAs laser: 4 hrs
 pre-growth CMP of SiGe graded layer
 TDD=2x106 cm-2
 λ=858 nm, d=0.4, Jth=269 A/cm2
 InGaAs laser
 λ=890 nm, d=0.26, Jth=700 A/cm2
M.E. Groenert, E.A. Fitzgerald et al., “Monolithic integration of room-temperature cw GaAs/AlGaAs
lasers on Si substrates via relaxed graded GeSi buffer layers,” J. Appl. Phys., v.93(1), pp.362-367
(2003).
M.E. Groenert, E.A. Fitzgerald et al., “Improved room-temperature
continuous wave GaAs/AlGaAs and InGaAs/GaAs/AlGaAs lasers fabricated on Si substrates
via relaxed graded GexSi1-x buffer layers,” J. Vac. Sci. Tech. B, v.21(3), pp.1064-1069 (2003).
misfit
dislocation
Monolithic Integration

60. AIM
Academy
 Si waveguide bonded to AlGaInAs QWs
 SOI ridge waveguide, SiO2/Ta2O5 facet mirror
 Overlap: Si=0.6-9, QWs=0.01-0.06
 Hybrid integration: zero alignment tolerance
 Bonding: low T oxygen plasma-assisted wafer bonding
 T=250 °C tolerate Thermal Expansion Mismatch
 <5 nm reactive oxide layer
 Endures dicing, facet polishing
CW lasing (=1568 nm)
 Optical Pumping
 Pth=23 mW, Pmax=4.5 mW
 Electrical Injection
 Ithres=65 mA, Pmax=1.8 mW, eff=0.13
H. Park, J.E. Bowers et al, Opt. Exp., v.13(23),pp.9460-9464 (2005).
A.W. Fang, J.E. Bowers et all., IEEE Phot. Tech. Lett., v. 18(10), pp.1143-1145 (2006).
A.W. Fang, J.E. Bowers et al., Opt. Exp., v.14(20), pp.9203-9210 (2006).
A.W. Fang, J.E. Bowers et al., Matls. Today, v.10(7-8), pp.28-35 (2007).
Hybrid Integration of III-V laser on SiGe/Si
Hybrid Integration

61. AIM
Academy
Germanium Laser
 Ge-on-Si for Si integration
 High n-doping required
 Demonstrated lasing from 1520 to 1700 nm
with electrical pumping
 Demonstrated 8mW laser peak power at
1620nm
J.F. Liu, X. Sun, R. Camacho-Aguilera, L. C. Kimerling, J. Michel, “A Ge-on-Si laser
operating at room temperature” Optics Lett. 35 (2010)
R. E. Camacho-Aguilera, Y. Cai, N. Patel, J. T. Bessette, M. Romagnoli, L.C. Kimerling, and
J. Michel, “An electrically pumped Germanium laser”, Opt. Exp. 20, 11316 (2012)
L-I curve at 300K
Germanium Laser

62. AIM
Academy
QW and QD Lasers on Silicon
 GaAs directly grown on Si
 InGaAs QW with n and p
contact
 Current emission wavelength
between 800nm and 1100nm
 Electroluminescence
demonstrated
 Optically pumped lasing
reported
L. C. Chuang et al., “InGaAs QW Nanopillar Light Emitting Diodes
Monolithically Grown on a Si Substrate,“ OSA/CLEO/QELS 2010 CMFF6
InGaAs Nanopillar QW Laser InAs QD Laser
Alan Y. Liu et al., “High performance continuous wave 1.3 mm quantum
dot lasers on silicon“ APPLIED PHYSICS LETTERS 104, 041104 (2014)
QW and QD Lasers on Silicon

63. AIM
Academy
Frequency Comb Generation
T. Herr, et al., NP, 145, 2014 & K. Saha, et al., OE, 1335, 2013
Frequency Comb Generation

64. AIM
Academy
Near IR Comb Generation
using SiN
Nanophotonic Optical Parametric Oscillator
• SiN
• CMOS-compatible material
• n~2, on-chip, high confinement
waveguides
• Very low propagation losses (0.1 dB/cm)
• Broad transparency window
• n2 ~ 2x10-19 (cm2/W), γ ~ 1 W-1m-1
• Source with many independent
wavelengths in the C-band
• Suitable for use in Si network-on-chip
• Flexible pump wavelength: visible to IR
J. S. Levy, A. Gondarenko, et al., “CMOS-compatible multiple-wavelength oscillator for
on-chip optical interconnects,” Nature Photonics., v.4(1), pp. 37-40 (2010).
Near IR Comb Generation using SiN

65. AIM
Academy Book Recommendation
Handbook of Silicon Photonics
CRC Press
Series in Optics and Optoelectronics
Published: April 26, 2013 by Taylor &
Francis
Editor(s): Laurent Vivien, Lorenzo Pavesi