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