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Optics vs. electronics
in high-speed
switching and signal processing
Rod Tucker
University of Melbourne
Take-Home Messages
• Energy is too often overlooked
• Speed is over-rated
- the “Electronic Bottleneck” is an urban myth
• Electronics is improving more rapidly than optics
- at least an order of magnitude left in Moore’s law
• Optical processing promising in simple high-speed circuits
- electronics wins as complexity increases
• Size matters
Overview
• Key requirements on digital signal processing devices
• Comparing optical and electronic signal processing
• Energy density and circuit power consumption
• Energy and signal processing
– Logic functionality
• AND, NAND, OR, etc.
– Cascadability
• Retain logic levels when
cascading multiple devices
– Fan-out > 2
• Device output can drive input of
at least two devices
• Typical fan-out for CMOS ~ 10
– Logic level restoration
5V
5V
00 In
Out
In Out
OutIn
In
In
Out
Out
Requirements on Digital Devices
Digital
Optical
Circuit
Comparing Optical and Electronic Circuits
O/E
O/E
O/E
E/O
E/O
E/OOptical
Inputs
Optical
Outputs
Optical
Outputs
Optical
Inputs
• Potentially high speed
• Accepts optical inputs
• Energy consumption
• Footprint
• Energy consumption
• Footprint
• Powerful digital capabilities
• Low cost
• Slower speed
• Requires O/E, E/O, and
possibly MUX/DEMUX
• Energy consumption?
+
+
-
-
Digital
Electronic
CircuitDE
MU
X
MU
X
Optics
Switch Fabrics Buffers
Wavelength
Demutiplexers Wavelength
Multiplexers
Fibers
Forwarding Engine
J
Switch
Fabric
O/E
Converters
Reduced bit rate (i.e. parallel processing)
Electronic (DE)MUXing in Routers
Speed (throughput) is not a limitation
Electronics
DEMUX MUX
Energy and Digital Signal Processing
Artist’s impression of optical IC
Intel I7 chip
774 million transistors
3 GHz / 95W / 296 mm2
Photo : Intel Corporation
Optical
Devices
Optical Signal Processing Circuit
aggregateB
Aggregate input
bit rate
supply
bit op device
aggregate
PE N E
B
Total energy per bit
processed
Device operations per bitDevice energy
per bit
supplyP Optical Output portsOptical Input ports
Electronic
Devices
Optical Output ports
Electronic Signal Processing Circuit
Optical Input portssupplyP
aggregateB
Aggregate input
bit rate
/ / ( )O E O DE MUX
bit op device
aggregate
P PE N E
B
Total energy per bit
processed
Device operations
per bit
Device energy
per bit
MUX
MUX
MUX
DEMUX
DEMUXO/E
E/O
E/O
E/O
O/E
/ /O E OP ( )DE MUXP
Comparing Optics and Electronics
Total energy per bit processed
/ / ( )bit op device O E O DE MUXE N E E E
bit op deviceE N E
Device energy per bit
Device Operations per bit
wavelength
converter
FEC ~ 104
~ 1
Optical Signal Processing Electronic Signal Processing
MUX
MUX
MUX
E/O
E/O
E/O
DEMUX
DEMUXO/E
O/E
Edevice = Ei + EsupplyTotal device
switching energy
DeviceInput energy , Ei
Supply energy, Esupply
Energy in Switching Devices
Input Energy = Switching Energy
SOAInput Output
Pump
Pin ~ 160 µW IDC = 300 mA
PDC = 600 mW
Total Switching
Energy per bit = 0.6/40x109 = 15 pJ
>103 larger
Input Energy per bit
= 160x10-6/40x109 = 4 fJ
Semiconductor
Optical Amplifier
“We demonstrate an all-optical wavelength converter at 50
Gb/s. The device uses cross-gain modulation in a
semiconductor optical amplifier. The wavelength converter
has a world record low switching energy of 4 fJ”
Fatal flaw: total energy per bit > 10 nJ/bit
I Was Wrong
Optical
TDM
Electronic
TDM
4 x 4 Gb/s = 16 Gb/s
1988
“The Electronic Bottleneck”
Fatal flaw: Large power dissipation
“The Electronic Bottleneck”
DEMONSTRATION OF PHOTONIC FAST
PACKET SWITCHING AT 700 Mbit/s DATA
RATE
W. L. HA
R. M. FORTENBERRY
R. S. TUCKER
Photonics Research Laboratory
The University of Melbourne
Parkville, Victoria 3052, Australia
Fatal flaws: No optical RAM, large power dissipation
Energy in CMOS Gates
gateC
Device energy per
transition
(per bit for NRZ)
Supply energy
(ESupply)Input energy
(Ei)
VDD
LWEI1
Wire capacitance
Cw per unit length
(ESupply)
212( )device gate w w DDE C C L V
Electronic vs All-Optical Signal Processing
10-20
10-19
10-18
10-17
10-16
10-15
10-14
2000 2010 2020
9065
4532
22
130
18
10-13
10-12
10-11
1970 1980 1990
12-mm
PMOS
Sw
itch
ing
en
erg
y E
devic
e,
J
Year
11
Feature
size in nm
CMOS gate
energy
Total CMOS energy
including wires
45
11
2232
10-10
2030
All-optical Devices
Si NanowirePPLNSOA
HNLF
Sources: ITRS ’97-’09 Roadmaps; Hinton et al., JSTQE 2008;
Möller; OFC 2010, Tucker, JSTQE, 2010
SiGe?
InP HBT E(DE)MUX
EO/E/O
Comparing Optics and Electronics
Total energy per bit processed
/ / ( )bit op device O E O DE MUXE N E E E bit op deviceE N E
Device energy per bit
Device Operations per bit
Optical Signal Processing Electronic Signal Processing
MUX
MUX
MUX
E/O
E/O
E/O
DEMUX
DEMUXO/E
O/E
Electronic vs Optical Signal Processing
Year
Nonlinear optical devices
Sources: ITRS ’97-’09 Roadmaps; Hinton et al., JSTQE 2008;
Möller; OFC 2010, Tucker, JSTQE, 2010
10-16
10-15
10-14
2000 2010 2020
10-13
10-12
10-11
1970 1980 1990
Sw
itch
ing
en
erg
y E
de
vic
e,
J EO/E/O
E(DE)MUX
10-10
2030
xx
x
x
x
xx2 PJ
x 20 fJTotal CMOS energy
including wires
Energy and Integrated Circuits
Number of operations per bit, Nop
10-13
1 10 100 1,000
10-12
10-11
10-10
10-9
Tota
l energ
y p
er
bit p
rocessed ,
E
bit
(J)
Edevice = 2 pJ
Edevice = 20 fJ
O/E/O + (DE)MUX
10,000
Optical
Electronic
(2020)
Electronic
(2010)
Chip Energy Density
Device
Pitch, d
Optical or
electronic chip
Psupply
Optical or
electronic device
Tucker, PTL 2008
Electronic IC: Energy consumption dominated by CV2 energy in interconnects
Optical IC: Energy consumption dominated by supply energy
PD = 100 W/cm2,
Optical and Electronic Integrated Circuits
Source: Tucker, PTL 2008
Energ
y p
er
Bit,
Esu
pp
ly (J)
10-17
10-16
10-15
10-14
10-610-7 10-5 10-4
10-13
10-3 10-2
10-12
10-11
Device Pitch, d (m)
Nonlinear Optical DevicesActivity factor
2 pJ/b
20 fJ/b
Optical and Electronic Moore’s LawN
um
ber
of
De
vic
es p
er
1-c
m2
Chip
Year
1970 1980 1990 2000 2010
1010
108
106
104
102
1.9 Billion (Intel SRAM)
2020
11-nm CMOS
energy limit
Infinera (~ 102)
Nonlinear
optics energy
limit: 1 GHz
1 GHz
100 GHz
Nonlinear
optics energy
limit:100 GHz
20 fJ/b
20 fJ/b
2 pJ/b
2 pJ/b
Source: Hinton, Raskutti & Tucker, JSTQE 2008
10-8
Sw
itchin
g E
nerg
y/b
it (
J)
Device Size (m)
104102110-210-410-610-8
10-10
10-12
10-14
10-16CMOS (ITRS)
Nonlinear Fibre
Semiconductor
Optical Amplifier
Si nanowire (FWM)
Periodically Polled
Lithium Niobate
Device Switching Energy and Size
Take-Home Messages
• Energy is too often overlooked
• Speed is over-rated
- the “Electronic Bottleneck” is an urban myth
• Electronics is improving more rapidly than optics
- at least an order of magnitude left in Moore’s law
• Optical processing promising in simple high-speed circuits
- electronics wins as complexity increases
• Size matters
Optical and Electronic Integrated Circuits
Artist’s impression of optical IC
operating at excessive power density
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