Silicon photonics and the data- centric datacenter · L. Zhou et al. “Towards athermal...

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Silicon photonics and the data-centric datacenter

Marco Fiorentino, HP LabsDate: 04/15/2011


Google (2009)

“In the last 7 years online data increased 56 times”


Data-centric computing

• Data grows faster than computation

• Data-centric workloads

• From performance to efficiency

• Scalability

3


4

Optical interconnects

$$$¢

100 101 103 104 105 10610-110-210-3

Distance (m)

Cost pressure

State of the art

Advantages

More bits per “wire” Less power per bit Better signal integrity


Outline

5

• Architectures

• Devices• Waveguides• Modulators• Detectors• Lasers

R. G. Beausoleil “Large-Scale Integrated Photonics forHigh-Performance Interconnects,” to be published in ACM Transactions on Computational Logic


Architectures

6


Network-on-Chip link topologies

Point-to-point

Sun/Oracle, MIT

Switched network

Cornell

Broadcast bus

Cornell, Northwestern

Multiple sender single receiver

HP


MIT Local mesh to global switchArchitecture example 1

8

− Point-to-point plus passive mesh− DRAM-centric architecture− 20W power envelope (network)− 10x improvement over electrical

Batten 2009


HP CoronaArchitecture example 2

9

Opticalhub

Arbitration

2 fixed drop filters

64 variable drop filters/detectors

L1-I

Core 0

Core 1

Core 2

Core 3

L1-D

L1-D

L1-I

L1-I

L1-D

L1-D

L1-I

L1 ↔

L2

Inte

rface

Hub

MC

NI

Through Silicon Via Array

Directory

L1 ↔

L2

Inte

rface

My

X-b

ar

Con

nect

ion

Pee

r X-b

ar

Con

nect

ionL2

Cache

Data&

Control

ModulatorsModulators


Modulators

Modulators


Modulators

Detectors

0123

N-1

NN+1

616263

4-waveguidebundles

Broadcast

Modulators Detectors

Splitters

Off-Chip

Modulators Detectors

Splitters

Fiber I/O’s to OCMs or Network

Package

Memory Controller/Directory/L2 Die

Processor/L1 Die

Analog Electronics Die

Optical DiepgcTSVs

Face to Face Bonds

Heat Sink

Laser

pgcTSVs

sTSVs

− Multiple-sender single-receiver links− 1 byte/flop on chip and to memory− 250W power envelope (compute + network)− 20x improvement over electrical

Vanatrease 2009


HP HyperXArchitecture example 3

•Crossbar used in high-radix switches

•Switch enables high connectivity topology

10

Optical Data Crossbar128 channels

inpu

t buf

fer

& ro

utin

g

inpu

t buf

fer

& ro

utin

g

inpu

t buf

fer

& ro

utin

g

inpu

t buf

fer

& ro

utin

g

outp

utbu

ffer

outp

utbu

ffer

outp

utbu

ffer

outp

utbu

ffer

….. 128 ….

….. 128 ….

Ahn 2009


Technology requirements

•DWDM: bandwidth density

•Silicon photonics: cost and scalability

•Ring resonators: technology of choice

11

SiGe Doped

Modulator OFF Modulator ON Switch Detector

III-V

Laser


Devices

12


Low-loss waveguides

Cladding

Core

Substrate

Cladding

Core

Substrate

Silicon wire

Loss 1 dB/cm

Rib waveguide

Loss 0.2 dB/cm

Cladding

Substrate

Slot

Slot waveguide

Loss 6.5 dB/cm

SWG waveguide

Loss 2.1 dB/cm (Bock 2010)


Modulation mechanisms

14

Carrier injection

Cornell, HP

Carrier depletion

Sandia, Kotura

Carrier accumulation

Lightwire

Electro-optic polymer

Intel

metal metal

EO polymer


HP modulators results

10 μm silicon ring resonators

Results• 45 fJ/bit• 6 Gbps modulation (with pre-emphasis)

0

0.2

0.4

0.6

0.8

1

1.2

1318.3 1318.5 1318.7 1318.9

Nor

maliz

ed in

tens

ity

Wavelength (nm)

0V

1.1V

ON

OFF

Eye diagram NRZ 6 Gbps CW tuning

E-beam litho Photolitho


A detectors’ menagerie

16

Intel Yin2007Vertical Ge PIN on rib WG BW 31 GHz

CEA-LETI & Paris Vivien2007Vertical Ge PIN coupled to wire BW 42 GHz

Lincoln Lab Geis2009Damaged silicon detector BW 35 GHz

Damaged silicon

n p

A*STAR Wang2008Horizontal Ge PIN BW 18 GHz


Laser: integrated vs. external

Integrated laser• The contenders

• Bonded lasers (UCSB, Intel, Ghent)• Germanium laser (MIT)• III-V grown on Si (Michigan)

• Pro• Less packaging• Cheaper

• Cons• Thermal issues• Fabrication issues

17

External laser• The contenders

• Telecom grade commercial lasers• Quantum dot (Innolume)• Modulated (UC Davis)

• Pro• Power and thermal independent• Established technology

• Cons• Complexity• Cost

Van Campenhout 2008Zhou 2009


Integrated laser example: HP

• Idea: Hybrid Si/III-V laser with 12.5 Gb/s data rate• Wafer bonding + self-aligned process

• Results• 2.5 mW output, • < 4 mA min threshold• 5 GHz BW achieved, 10–12.5 GHz expected

• Future directions• Integration• Silicon on diamond

18

CWDM optical engine

Cost ~ Area ~ 0.015 mm2

Power ~ 2 pJ/bit

Hybridmicrorings

Liang 2010


External laser example: Innolume

19

• Idea: quantum dot FP laser• MBE grown

• Results• 80 Ghz spacing• 8 lines• >-10dBm per line• Low RIN (-110 dB/Hz)

• Future directions• Add wavelengths

Wojcik 2009


Open problems and future directions

Work to be done• Integration

• How do we put it all together?

• Co-design• Drivers and receivers

• Fabrication• What happens if we try to build 1000s of devices on a chip?

• Power consumption and thermal

…and most importantly• Business case• Solution roadmap• Supplier ecosystem

20


Thank you


BibliographyReview paperR. G. Beausoleil “Large-Scale Integrated Photonics for High-Performance Interconnects,” to be published in ACM Transactions on Computational LogicArchitectureC. Batten et al. “Building many-core processor-to-DRAM networks with monolithic CMOS silicon photonics,” IEEE Micro 29 8 (2009).D. Vantrease et al. “Corona: System implications of emerging nanophotonic technology,” In Proceedings of the 35th International Symposium on Computer Architecture (2009) 153A. V. Krishnamoorthy et al.“Computer Systems Based on Silicon Photonic Interconnects,” In Proceedings of the IEEE 97 p.1337 (2009)N. Kirman et al.“On-chip optical technology in future bus-based multicore designs,” IEEE Micro 27 56 (2007)Y. Pan et al. “Firefly: Illuminating Future Network-on-Chip with Nanophotonics,” In Proceedings of the 36th International Symposium on Computer Architecture (2010) 429K. Bergman et al. “Power effiecient photonic networks on-chip,” In Proc. Soc. Photo-Opt. Instrum. Eng. 6898 689813 (2008)J. H. Ahn et al.“HyperX: topology, routing, and packaging of efficient large-scale networks,” In Proceedings of the Conference on High Performance Computing Networking, Storage and Analysis (SC). ACM 1 (2009)WaveguidesR. Ding et al. “Low-loss strip-loaded slot waveguides in Silicon-on-Insulator,” Opt. Express 18 25062 (2010)P. J. Bock et al. “Subwavelength grating crossings for silicon wire waveguides,” Opt. Express 18 16146 (2010)M. Gnan “Fabrication of low-loss photonic wires in silicon-on-insulator using hydrogen silsesquioxane electron-beam resist,” Electron. Lett. 44 115 (2008)U. Fischer ”0.1 dB/cm waveguide losses in single-mode SOI rib waveguides,” IEEE Photon. Technol. Lett. 8 647 (1996)ModulatorsQ. Xu “Micrometre-scale silicon electro-optic modulator,” Nature 435 (2005) 325M. Watts “ Low-voltage, compact, depletion-mode, silicon Mach-Zehnder modulator, ” IEEE J. Select. Topics Quantum Electron. 16 159 (2010)D. D'Andrea “CMOS photonics today & tomorrow,” In Proceedings of the Optical Fiber Communication Conference (OFC) (2009)B.A. Block et al. “Electro-optic polymer cladding ring resonator modulators” Opt. Express 16 18326 (2008)


Bibliography (continued)DetectorsM. W. Geis et al. "Silicon waveguide infrared photodiodes with >35 GHz bandwidth and phototransistors with 50 AW-1 response," Opt. Express 17, 5193 (2009) J. Wang et al. “Low-voltage high-speed (18 GHz/V) evanescent-coupled thin-lm-Ge lateral PIN photodetectors integrated on Si waveguide,” 20, 1485 (2008)T. Yin et al. "31 GHz Ge n-i-p waveguide photodetectors on Silicon-on-Insulator substrate," Opt. Express 15, 13965-13971 (2007)L. Viviene et al. "High speed and high responsivity germanium photodetector integrated in a Silicon-On-Insulator microwaveguide," Opt. Express 15, 9843-9848 (2007)LaserL. Zhou et al. “Towards athermal optically-interconnected computing system using slotted silicon microring resonators and RF-photonic comb generation,” Appl. Phys. A 95, 1101 (2009)J. Van Campenhout et al. “Electrically pumped InP-based microdisk lasers integrated with a nanophotonic silicon-on-insulator waveguide circuit” Opt. Express 15, 6744 (2007)Jun Yang et al. "Integration of epitaxially-grown InGaAs/GaAs quantum dot lasers with hydrogenated amorphous silicon waveguides on silicon," Opt. Express 16, 5136 (2008)G. L. Wojcik et al. “A single comb laser source for short reach WDM interconnects,” In Proc. Soc. Photo-Opt. Instrum. Eng. 7230, 723021 (2009)J. Liu et al. "Ge-on-Si laser operating at room temperature," Opt. Lett. 35, 679(2010)D. Liang et al. “Electrically-pumped compact hybrid silicon microring lasers for optical interconnects,” Opt. Express 17, 20355 (2009)

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