Marc Epitaux

Silicon Photonics for Mid-Board Optical Modules

Chief Architect at Samtec, Inc

Outline

• Interconnect Solutions

• Mid-Board Optical Modules

• Silicon Photonics

o Benefits

o Challenges

• DragonFly Packaging Platform

• Conclusion

Interconnect Challenges

• Raw speed

• Distance

• Size

• Cooling and thermals

• Various environmental constraints

Why Miniature Mid-Board Optical Modules?

• Bring optics on board, closer to the chipset (opposed to the front-pluggable approach)

• Optical “flies over” to backplane or front panel

• Highest density

• Novel cooling options

• Qualified to Telcordia, sometimes MIL

standards

Form factor comparison between

MBOM & Front Pluggables

FireFly Optical Modules in array. Densest interconnect in the industry

Mid-Board Optics Standardization

Consortium for On-Board Optics

• Effort to standardize on-board optics

• Has adopted a two connectors mounting concept

• Two lane width proposed: 8x and 16x

• Three module length proposed

• 0.6mm pitch highspeed connector

• Full specification expected by mid-year with first

sample Q1’18

Why Silicon Photonics?

• Direct modulated laser diode is challenged with next

generation data rates (>28Gbps)

• Optical function integration: photodetection, WDM filter,

modulation, splitter

• Higher channel counts (8x, 16x)

• Enable advanced modulation: PAM, WDM, QAM,

DPSK

• Single mode operation allows longer reach (up to 2km)

• Volume manufacturing (wafer processing)

Silicon Photonics Challenges

• Circuit integration

o Platform and CAD tool homogenization

o Limited generic component offering

o Test infrastructure

• Light coupling

o Laser integration

o Single mode fiber coupling and alignment

• Packaging integration

o High speed signaling and interconnect

o Thermal management

Courtesy UCSB

Example: Laser integration

• Platform/PDK?

• Fabrication/foundry?

• Coupling approach?

• Test and Reliability?

DragonFly Packaging Platform

Architectural Features

• MBOM packaging

• Semiconductor manufacturing

• SiPho Engine (BGA’ed)

• Single mode optics

• Flip-chipped PMDs

• Backside illumination

• 4x 56G bandwidth

Development carried out in the IRT Nanoelec program

DragonFly Optical Layout

Optical Features

• Single mode fiber

• Free space optical layout

• Grating Coupler

o 1D output (3dB IL)

o 2D input (6dB IL)

o Mode converter

• Alignment Strategy

o Passive

o Active

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%

FIB

ER C

OU

PLI

NG

EFF

ICIE

NC

Y (%

)

% OF POPULATION

FIBER COUPLING EFFICIENCY FROM 10K MONTE CARLO

Design A Design B Design C Design D Design E

With same tolerances Design D would be better for Active Alignment

Design C: better for Passive Alignment

DragonFly Electrical Signal Integrity

Features

• Organic substrate

• 0.5mm edge connector

• BGA interconnect SiPho chip (200um)

Modeling & Simulation

• Modeled the system in HFSS

• IL: -1.55 dB Insertion loss @ 28 GHz

• RL: < -18 dB up to 28 GHz Nyquist.

DragonFly Thermal Management

200G DragonFly Est. Power

Driver + CDR 1’300mW

TIA + CDR 1’400mW

Laser Driver 400mW

Phase Shifter 100mW

Micro-Controller + IO Ctrl 150mW

Total 3’350mW

Autodesk CFD 360 Simulation

Power Density

• Multi-Gbps interconnect requires signal processing

and electronic compensation (CDR, CTLE, FFE,

DFE, PAM4,…)

• Smaller, integrated device increases drastically the

power density (1.7W/cm2 at the MBOM level)

Heatsink Alternatives

• Convection cooling (not sufficient)

• Conduction cooling

• Immersion

MBOM Implementation Example

Conclusion

• The combination of Mid-Board Optics packaging platform and Silicon Photonics is offering new high performance horizon for optical interconnect:

o Bring the fibers closer to the signal processor (ASIC, FPGA, switch)

o Increase the interconnect density

o Offer a path to 100Gbps and much beyond

o Extend optical link reach

• However the promises of photonics integration is still facing challenges:

o Circuit integration

o Light coupling

o Packaging integration

o A novel Mid-Board Silicon Photonics packaging platform has been presented which address most of those challenges

Thank you

Acknowledgments:• Samtec Team• IRT Nanoelec Partners