ROBERT HENDRY, GI LB ERT HEND RY, KEREN BERGMAN

LIGHTWAVE R ESEARC H LABCOLUMBI A 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 latency

HPEC 2011 2

Target Architectures

Optical link to memoryOptical interconnection

network on stacked memory

HPEC 2011 3

Ring Resonators

HPEC 2011 4

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

HPEC 2011 4

Photonic Communication

Light source Optical signal

Optical signal

Electrical control

detectors

filters

Photonic Network

10 Gb/s

x 3 = 30 Gb/s aggregate bandwidth

HPEC 2011 5

Optical Power BudgetO

ptic

al P

ower

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.

HPEC 2011 6

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]

HPEC 2011 9

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]

HPEC 2011 9

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]

HPEC 2011 9

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

HPEC 2011 10

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]

HPEC 2011 11

Insertion Loss Analysis

Worst-case insertion loss for a photonic mesh

[Biberman et al. 2011]

HPEC 2011 12

Insertion Loss Analysis

Worst-case insertion loss for a photonic mesh

[Biberman et al. 2011]

HPEC 2011 13

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

HPEC 2011 15

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

HPEC 2011 16

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

HPEC 2011 17

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

HPEC 2011 18

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

HPEC 2011 19

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

HPEC 2011 20

X-Y Buffering

Mesh topologyNo electronic links, other

than TDM clock distribution

Opt

ical

Pow

erDetector Sensitivity

Nonlinear Effects

Maximum Network-Level Insertion Loss

Ptotal = Pchannel × N

HPEC 2011 21

Photonic TDM vs. Photonic Circuit-Switched Insertion Loss

HPEC 2011 22

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

HPEC 2011 23

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

HPEC 2011 23

18 crossings 4 crossings

TDM Network Insertion Loss Analysis

4x4 Network 8x8 Network

16x16 Network 64x64 Network

HPEC 2011 25

Maximum Bandwidth (# of Wavelengths)

4x4 Network 8x8 Network

16x16 Network 64x64 NetworkHPEC 2011 26

Summary of Results

HPEC 2011 27

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