ROBERT HENDRY, GILBERT HENDRY, KEREN BERGMAN

LIGHTWAVE RESEARCH LABCOLUMBIA UNIVERSITY

HPEC 2011

TDM Photonic Network using Deposited Materials

Motivation for Silicon Photonics

• Performance scaling becoming extremely difficult

• Data movement cost increasingly expensive

• On/off-chip communication bandwidth limited

Photonics offers: Higher bandwidth density

High datarate and parallel wavelengths

Low operating power

Low latencyHPEC 2011 2

Target Architectures

Optical link to memoryOptical interconnection

network on stacked memory

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Ring Resonators

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waveguide

light source

modulator

waveguide

signal

switch

waveguide

signal

switch

Off resonance

On resonance

waveguide

signal

filter

opticalmessage

electriccontrol

electriccontrol

Photonic Communication

Light source Optical signal

Optical signal

ring-resonatormodulators

Electrical control

detectors

filters

Photonic Network

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Photonic Communication

Light source Optical signal

Optical signal

Electrical control

detectors

filters

Photonic Network

10 Gb/s

x 3 = 30 Gb/s aggregate bandwidth

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Optical Power BudgetO

pti

cal P

ow

er

Detector Sensitivity

Nonlinear Effects

Total Injected Power

Received Power

Maximum Network-Level Insertion Loss

Injected Power Per Wavelength

Ptotal = Pchannel × N

1 dBm

1 mm

0.68 dBm

waveguide propagation-1.0 dB/cm

total insertion loss0.32 dB

waveguide crossing-0.05 dB each

passing by a ring -0.01 dB each

The total injectable power Ptotal must remain below a threshold to avoid non-linear effects. Ptotal is then divided among the N wavelengths of a WDM packet, where each channels injects at Pchannel.

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Silicon Photonics Technologies

Crystalline Silicon Best electrical and optical properties

Unable to deposit

Material Propagation Loss

CrystallineSilicon

1.7 dB/cm[Xia et al.

2007]

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Silicon Photonics Technologies

Crystalline Silicon Best electrical and optical properties

Unable to deposit

Polycrystalline Silicon Can deposit

Very lossy

Material Propagation Loss

CrystallineSilicon

1.7 dB/cm[Xia et al.

2007]

Polycrystalline

Silicon

6.45 dB/cm[Fang et al.

2008]

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Silicon Photonics Technologies

Crystalline Silicon Best electrical and optical properties

Unable to deposit

Polycrystalline Silicon Can deposit

Very lossy

Silicon Nitride Very low loss

Can deposit

Not useful active devices

Material Propagation Loss

CrystallineSilicon

1.7 dB/cm[Xia et al.

2007]

Polycrystalline

Silicon

6.45 dB/cm[Fang et al.

2008]

SiliconNitride

0.1 dB/cm[Shaw et al.

2005] [Gondarenko et

al. 2009]

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Poly-Si / SiN Combination approach

We can use silicon nitride and polycrystalline silicon in combination

SiN for non-active wave guides

Poly-Si for active devices (e.g. ring-resonator based switch)

Designs for a layered modulatorand switch

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Poly-Si / SiN Combination approach

Waveguide crossings eliminated

Insertion loss, crosstalk both incurred heavily in waveguide crossings

• However, .1 dB insertion loss per vertical coupling [Sun et al. 2008]

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Insertion Loss Analysis

Worst-case insertion loss for a photonic mesh

[Biberman et al. 2011]

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Insertion Loss Analysis

Worst-case insertion loss for a photonic mesh

[Biberman et al. 2011]

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Photonic TDM NoC Architecture

Mesh topologyNo electronic links,

other than TDM clock distribution

TIM

E

Time slot 1

Time slot 2

Time slot 3

Time slot 4

Time slot 5

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Photonic TDM NoC Architecture

Mesh topologyNo electronic links,

other than TDM clock distribution

TIM

E

Time slot 1

Time slot 2

Time slot 3

Time slot 4

Time slot 5

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Photonic TDM NoC Architecture

Mesh topologyNo electronic links,

other than TDM clock distribution

TIM

E

Time slot 1

Time slot 2

Time slot 3

Time slot 4

Time slot 5

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Photonic TDM NoC Architecture

Mesh topologyNo electronic links,

other than TDM clock distribution

TIM

E

Time slot 1

Time slot 2

Time slot 3

Time slot 4

Time slot 5

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Photonic TDM NoC Architecture

Mesh topologyNo electronic links,

other than TDM clock distribution

TIM

E

Time slot 1

Time slot 2

Time slot 3

Time slot 4

Time slot 5

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Photonic TDM NoC Architecture

Mesh topologyNo electronic links,

other than TDM clock distribution

TIM

E

Time slot 1

Time slot 2

Time slot 3

Time slot 4

Time slot 5

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X-Y Buffering

Mesh topologyNo electronic links,

other than TDM clock distribution

Op

tica

l Po

wer

Detector Sensitivity

Nonlinear Effects

Maximum Network-Level Insertion Loss

Ptotal = Pchannel × N

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Photonic TDM vs. Photonic Circuit-Switched Insertion Loss

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Single-Layer Switch vs. Multi-layer Switch

Single-layer TDM Switch Multi-layer TDM Switch

Control

East

1

25

6

3

7

4

8

North

South

West

Gateway

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Single-Layer Switch vs. Multi-layer Switch

Single-layer TDM Switch Multi-layer TDM Switch

Control

East

1

25

6

3

7

4

8

North

South

West

Gateway

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18 crossings 4 crossings

TDM Network Insertion Loss Analysis

4x4 Network 8x8 Network

16x16 Network64x64 Network

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Maximum Bandwidth (# of Wavelengths)

4x4 Network 8x8 Network

16x16 Network 64x64 Network

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Summary of Results

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Conclusions

Poly-Silicon and Silicon Nitride in conjunction are a good choice of materials for photonic interconnection networks Low-loss = more wavelengths = higher bandwidth

We’ve shown that our best network, when at large scale, can be improved with a multi-layer implementation

Future work: We expect the elimination of waveguide crossings to significantly reduce crosstalk across a wide variety of network architectures

HPEC 2011 28