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©Synopsys 2013 1
Simulation of Silicon Photonics
Chenglin Xu
Acknowledgements:
Evan Heller, Mayank Bahl, Mingming Jiang, Rob
Scarmozzino, Jigesh Patel, Dan Herrmann, and Ying Zhou
©Synopsys 2013 2
Outlines Outline
• Why silicon photonics
– Market demands
– Existing technologies
• What is silicon photonics and how to simulate it
• Summary
©Synopsys 2013 3
Why Silicon Photonics Market demands
• Moore’s Law
5 billions transistors!
Intel 62-core xeon phi, 2012
©Synopsys 2013 4
Why Silicon Photonics Market demands
• Limits of electronic interconnects
Inte
rcon
ne
ctio
ns
Se
mic
on
du
cto
r
Complexity limit
Clock rate saturated
Further increase?
Power consumption
becomes an issue. Speed limits
Multi-layers for interconnects!
©Synopsys 2013 5
Why Silicon Photonics Market demands
• Power Consumption Problem
Google’s Data Center in Dalles, Oregon
Power consumption > 100 MegaW
©Synopsys 2013 6
Why Silicon Photonics Alternatives
• Optical interconnects? ~1000 times faster!
2009 2013
©Synopsys 2013 7
Why Silicon Photonics Silicon is an optical material
©Synopsys 2013 8
Why Silicon Photonics Pros & cons
Transparent in 1.3~1.6µm range
CMOS compatible
Mature technology
High production volume
Low cost and large SOI wafer available
High-index contrast
Small footprint, high optical field confinement
No electro-optic effect
No detection in 1.3~1.6µm range
High-index contrast for fiber coupling
Lacks efficient light emission
©Synopsys 2013 9
Outlines Outline
• Why silicon photonics
• What is silicon photonics and how to simulate it
– Passive devices
– waveguide, couplers, filters, multiplexers, etc.
– Functional devices
– Modulators, tunable devices
– Active devices
– Lasers, detectors
– Photonics integrated circuit
• Summary
©Synopsys 2013 10
Passive Devices Waveguides
• Rib/ridge waveguide, mode by FemSIM
Straight mode
Bending loss
• Large core size
• Single mode
• Match fiber mode
Bending mode FemSIM:
• Arbitrary structure
• Propagation constant
and modal profile
• Bending mode and
bending loss
©Synopsys 2013 11
Passive Devices Waveguides
• Tricks and tips for bending modes
R x
n(x)
Calculate the straight mode first, use
it as initial guess for bending mode
Allowed Leaky Mode Use enough PML to ensure
no ripples in field amplitude
• Scan R from large to small
• Seed effective index
Don’t use MOST Cluster!!!
©Synopsys 2013 12
• Silicon wire, mode by FemSIM
Passive Devices Waveguide
Straight mode • Small core size
450nm x 220nm
(Industry standard)
• On-chip connects
Bending mode
Quasi-TE & Quasi-TM
• TM mode suffers
more bending loss
𝑬𝒛 ≠ 𝟎! 𝑯𝒛 ≠ 𝟎!
20𝑙𝑜𝑔𝑒−𝑛𝑖𝑘0
𝜋𝑅2 =-85.73
𝑛𝑖𝑅
𝜆dB
90o turn bending loss:
Straight-bent coupling loss excluded!
©Synopsys 2013 13
• Straight-Bent coupling loss, by FemSIM
– Calculate and save straight mode
– Create pathway and monitor
– Monitor file power(overlap with straight mode)
– Calculate bending mode
Passive Devices Waveguide
©Synopsys 2013 14
Horizontal spot (mode) size convertor (SSC or MSC)
• To effectively couple light between fibers and silicon wires on chip, a
spot size convertor is needed
Passive Devices Horizontal coupler
©Synopsys 2013 15
• SSC is way too big for FullWAVE, based on FDTD
• BeamPROP handle it easily
Passive Devices Horizontal coupler
©Synopsys 2013 16
• Vertical coupler is needed for board-board connection
• With both gratings and spot size converter
• Needs both BeamPROP and FullWAVE
– Cannot be handled by BeamPROP, because of omni-directional propagation
– Cannot be handled by FullWAVE, either, because it is too big
– BeamPROP for the spot size converter and FullWAVE for the gratings
Passive Device Vertical coupler
FullWAVE
BeamPROP
©Synopsys 2013 17
• FullWAVE simulation
– Waveguide Fiber
Passive Device Vertical coupler
D. Taillaert, et al, “Grating couplers for coupling
between fibers and nanophotonic waveguide,”
Japanese J. of Applied Physics, Vol. 45, No. 8A,
pp. 6071-6077, 2006.
©Synopsys 2013 18
• FullWAVE simulation
– Fiber Waveguide
Passive Device Vertical coupler
D. Taillaert, et al, “Grating couplers for coupling
between fibers and nanophotonic waveguide,”
Japanese J. of Applied Physics, Vol. 45, No. 8A,
pp. 6071-6077, 2006.
©Synopsys 2013 19
Passive Devices Vertical coupler
3. Backward Propagation by BeamPROP
1. Forward Propagation by BeamPROP 2. Omni-Propagation by FullWAVE
Monitored powers
©Synopsys 2013 20
• Ring resonator is an add-drop filter
• Resonant wavelengths drop or add
• Off resonant wavelengths go through
Passive Devices Ring resonator
λ1, λ2, λ3 λ2
λ1, λ3
Resonance Off resonance
©Synopsys 2013 21
• Example simulated by FullWAVE
Passive Devices Ring resonator
B. E. Little, et al, IEEE Photon. Tech. Letts.
Vol. 11, No. 2, pp. 215-217, 1999
Simulation
Experiment
©Synopsys 2013 22
Passive Devices Disk resonator
• Disk resonator is similar to ring, Whisper Gallery Mode can be calculated
by FullWAVE
Resonances
Drawbacks: • Excitation dependent
• Long propagation to reach steady state
©Synopsys 2013 23
Passive Devices Disk resonator
• Resonances (Whisper Gallery Mode) can be calculated by
FemSIM for cavity modes, easily and efficiently
D
TE(1,2,45) mode
©Synopsys 2013 24
Passive Devices Array waveguide gratings
• AWG is an essential device for WDM (wavelength
division multiplexing)
• It is a passive circuit and can be simulated by AWG
Utility, based on BeamPROP.
Wavelength (nm)
1545 1548 1551 1554 1557
Tra
nsm
issio
n (
dB
)
50-
40-
30-
20-
10-
0 Output Port:
#1
#2
#3
#4
#5
#6
#7
#8
Output spectra
Field in
output star Field in
input star
©Synopsys 2013 25
Functional Devices Modulator
Mechanisms for Optical Modulation in Silicon
• Free-carrier concentration variation
– Applied field changes carrier density around PN junction
– Slow response (ms) for carrier recombination (forward bias)
– Fast response (ps) for carrier depletion (reverse bias)
– Holes change index more than electron
– Large index change, P=1018 -> n=2.1x10-3 @ =1.55m
p
Optical field
Hole density
Electron density
High speed modulators are carrier depletion type
©Synopsys 2013 26
Functional Devices Modulator
Validation: an SOI-based Mach-Zehnder Modulator
• The MZ modulator with 250m long branches, 500nm x 200nm
cross-section, set between lateral n- & p-contacts.
• The voltage between the contacts is 0-1.2 volts for one branch, and
0 volts for the other.
Modeling and Characterization of Mach-Zehnder Silicon
Electro-optical Modulators,” G.-R. Zhou et.al.,
CLEO/QELS 2008.
©Synopsys 2013 27
Functional Devices Modulator
Validation: an SOI-based Mach-Zehnder Modulator (cont’d)
• The structure, including geometry, refractive index, and doping is drawn
in the RSoft CAD.
• The Multi-Physics Utility computes the index change vs. applied voltage.
• FemSIM or BeamPROP calculates the mode w & w/o index changes
V=0
V=1.2
©Synopsys 2013 28
Functional Devices Modulator
Validation: an SOI-based Mach-Zehnder Modulator (cont’d)
Measured & S-Device simulation
Multi-Physics Utility simulation
©Synopsys 2013 29
Functional Devices Modulator
Validation: an SOI-based Mach-Zehnder Modulator (cont’d)
• Frequency Response
Measured & S-Device simulation Multi-Physics Utility simulation
©Synopsys 2013 30
• Active Devices present an unusual challenge for the
semiconductor industry because light sources cannot be
implemented in silicon.
• A variety of other materials are required, such as GaAs,
GaN, InP (and their variants)
• Integration of non-silicon
devices into silicon chips
is difficult and expensive
(wafer bonding or fusing plane)
• Array of device specific challenges, such as; frequency
response, power consumption, noise, and on-chip real
estate.
Active Devices Lasers
©Synopsys 2013 31
Active Devices Lasers
Wafer bonded laser
• Simulation by LaserMOD
InGaAsP MQW
Layout in LaserCAD
Calculated optical mode Calculated L-I-V curves
Because of small overlap between optical mode and active region, threshold is very high
©Synopsys 2013 32
Active Devices Detectors
• Surface illuminated photodetectors
– Detection at output fiber optics
– Free space propagation
– Simulated by LaserMOD
– Could also be simulated by Solar Cell Utility
Vertical coupling Butt coupling
si si
• Integrated photodetectors
– Detection in integrated photonics
– Waveguide propagation
– Simulated by LaserMOD
©Synopsys 2013 33
Active Devices Detectors
Surface illuminated photodetectors
•Si/Ge Surface normal detector via
LaserMOD
•1.55um Signal
M. Oehme, et al, Appl. Phys. Lett. 141110 (2012)
©Synopsys 2013 34
Active Devices Detectors
Integrated photodetectors
•Si/Ge Waveguide detector via LaserMOD
•1.55um Signal
©Synopsys 2013 35
Active Devices CMOS sensor
Integrated CMOS surface illuminated sensor
– Optical performance can be simulated by
FullWAVE
– Electronics performance cannot be simulated
by LaserMOD, for now.
©Synopsys 2013 36
Active Devices CMOS sensor
Integrated CMOS surface illuminated sensor
• Simulated by FullWAVE
CAD Layout
Incident at 0o
Incident at 10o
Cross-talk
Contrast
©Synopsys 2013 37
Photonics Integrated Circuit Electronic-photonic integration
• No standard technology
• No combined tools
• No photonic circuit simulation
tool, yet
An IBM silicon photonics chip
combining optical and electrical circuits
Ph
oto
nic
s
laye
r
©Synopsys 2013 38
• Hybrid integrated circuits of active and passive devices
are available now (as shown below)
• No general (physical) hybrid circuit simulator
• Simple circuit can be simulated by combining our active
and passive tools vs scripting (vertical coupler)
• Customized utility for specific
devices/circuit
– Taper Layer Utility
Photonics Integrated Circuit Hybrid integration
T. Nakamura, et al, PETRA, 2011
©Synopsys 2013 39
• OptSim/ModeSYS, via co-simulation with other RSoft
tools, can estimate system performance of a device
design
Photonics Integrated Circuit Link simulator
©Synopsys 2013 40
• OptSim/ModeSYS, via co-simulation, can estimate
system performance of a CODE V lens design
Photonics Integrated Circuit Link simulator
©Synopsys 2013 41
• Passive devices
– FemSIM, finite-element mode solver
– BeamPROP, frequency domain wave propagation simulator
– FullWAVE, time-domain wave propagation simulator
– DiffractMOD, diffraction grating simulator
Summary RSoft software for silicon photonics
• Active devices
– LaserMOD, laser and detector simulator
• Functional devices
– Multi-Physics Utilities,
– Electro-optics, thermo-optics, stress-optics, and carrier-optics
• Photonics integrated circuit
– OptSim/ModeSYS for link simulation
– Combined tools via scripts
©Synopsys 2013 42
Thank You
