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CERN-EP R&D program on High Speed Links

Silicon Photonics

Carmelo Scarcella

9th February 2018

Outline

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Silicon Photonics roadmap

Silicon Photonics for datacenters

Packaging

Optical coupling

Electrical connections

Silicon photonics roadmap - 2018

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Silicon photonics stakeholders - 2018

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State of the art of Silicon photonics for datacenter

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Luxtera/Molex

Free carries dispersion MZMz

28 Gbps OOK electrical speed – variety of combinations with WDM and PAM4 with modules reaching 100s of Gbps per module

Fragmented phase shifter?

Kotura/Mellanox

SiGe EA modulator at 1550 nm. Working on the edge of a bandgap, suitable for a wide temperature range of operation?

50 Gbps OOK per channel

Intel

Free carries dispersion MZMs

100 Gbps QSFP28 modules. 4 parallel lines or CWDM option. 2 km reach

Macom

Free carrier dispersion MZMs, ring modulators, WDM. Selling chips. Acquired BinOptics with Etched Facet Technology (EFT) DFB. Patented Self-Alignment EF

Sicoya

Carrier injection MZMs

A number of options available: WDM, PAM, all based on the electrical speed of 25 Gbps. Driver electronics requires strong equalization.

Rockley Photonics

ROCKLEY PHOTONICS AND HENGTONG OPTIC-ELECTRIC FORM JOINT VENTURE to manufacture high performance optical transceiver modules

based on its silicon photonics technology.

“innovative monolithic fiber attach technologies and an all-CMOS electrical chipset”

Inphi

COLORZ® Delivers up to 4Tb/s of bandwidth over a single fiber – 25 or 80 km reach, inter data centres interconnection!

Caliopa/HUAWEI?

LightWire/Cisco?

IBM?

Form factors

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QSFP and OSFP parallel channels (MPO) or duplex

Optical engines - OptoPHY

Consortium for On-Board Optics (COBO) is working to develop specifications

to permit the use of board-mounted optical modules – New standard!

- low cost

- small size

- heat spreading

- electronics and optics co-packaging

http://onboardoptics.org/

http://www.luxtera.com

http://www.luxtera.com

http://www.intel.com

Grating Couplers – Narrow band ~ 30 nm – Active alignment – allows 2D array for high density I/Os

Luxtera Active alignment of fibre array onto grating couplers

Fibers off-vertical

Requires dedicated production lines for optical coupling

Good throughput: 1 million modules already delivered in 2016

Tyndall Active alignment of planar fibre arrays using total internal reflection at the fiber facet

Active alignment, not used for volume production

In the long run there might be issues with facet contamination

Edge coupling – Wideband – Passive alignment possible with custom chip fabrication

Mellanox Former Kotura, shut down the business in 2018

3 µm thick SOI, edge coupling and active alignment

IBM Passive edge coupling alignment: on-chip V-grooves for fiber alignment

On-chip spot size converter to 10 µm (Si etching under SiO2 BOX)

Reuse of standard pick-and-place assembly lines for C-MOS!

Under reliability testing

Intel Passive alignment edge coupling

Flipped die

On-chip guides for fiber alignment pins

Already used in production?

State-of-the-art of fiber coupling for commercial products

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Note: CW Laser remotely connected through fiber array

‘Fancy’ research approaches not yet demonstrated to be suitable for volume production not mentioned

The first two methods do not require special mechanical features on chip and can be implemented with any technology

Optical coupling in 2025

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Companies providing packaging services?

PIXAPP EU project – ‘Photonics Packaging Pilot Line’ is addressing this point!

Addressing needs for applications with relative small volumes (~ 10s of thousands), like biomedical, quantum optics, sensing, etc.

Multicore fibers? Space Division Multiplexing SDM

Becoming very popular for high density optical interconnections

Good fit with silicon photonics fiber coupling

True pluggable connection using microlens

Demonstrated at the research level – wafer bonding of MLAs, on-chip polymer lens writing TPA, Fresnel lenses

Many companies developing scalable processes

Passive alignment

Today only for custom processes (e.g. IBM, Intel) for spot size conversion and on-chip alignment features

IBM is sharing the process with AIM photonics

New methods suitable for any fabrication platform?

Photonic interposers/motherboard?

Imec

16 cores

56 Gbps

896Gbit/s

OFC 2017

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Optical coupling - Comparison with VL/VL+

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Submicron alignment tolerances

Active alignment

Dedicated production machines

Established technology

Many companies providing assembly services

Pluggable connection

Single channel

Single-mode

~ 5 µm alignment tolerances

Passive alignment

Standard vision based production machines

Established technology

Many companies providing assembly services

Pluggable connection

Single channel

Multimode

Submicron alignment tolerances

Active alignment

Dedicated production machines

Not established technology

Lack of companies providing assembly services

Pigtailing

Multichannel

Single-mode

~ 5 µm alignment tolerances

Passive alignment

Standard vision based production machines

Established technology

Many companies providing assembly services

Pluggable connection

Multi-channel

Multimode

Fiber attachment for silicon photonics presents the same difficulty of single-mode TOSA packaging!

The lack of a standardized package/form factor prevents from having companies providing fiber attachment service for Silicon Photonics

State of the art of electronic packaging

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Hybrid integration of electronic and photonic ICS (Flip chip bonding) most used method

Wire bonding between PCB and photonic IC

All standard processes used in electronics

http://www.luxtera.com

2025 electronic packaging

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Nowadays the photonic IC size is generally larger than the electronic IC size

Free carrier dispersion modulators are relatively large devices > 1 mm

Fiber attachment has a large footprint onto the photonic chip

Area on electronic IC is in general more expensive than on PIC

Hybrid integration is currently preferred to monolithic integration of electronics and photonics devices

Scaling of Photonic IC size might bring advantages for monolithic integration of electronics and photonics

Through Substrate Via (TSV) to replace wire bonding and minimize parasitic?

https://www.3dincites.com/2014/01/lessons-learned-trenches-3d-ic-manufacturing-sensor-applications/

FABULOUS D4.1.4 Dissemination kit

Electronic packaging comparison with VL/VL+

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Process complexity compoarable between SiPh and VL or VL+:

VL VL+ SiPh

High resolution

VL VL+ SiPh

Die attachment High resolution opto-die attachment

onto TO-Can

1 step per channel

High resolution (< 5 µm) die attachment

1 step per module (4 dies per module)

Photonic die attachment onto

substrate - no high accuracy

1 die per module

Electronic ASIC flip-chip onto

photonic die – established process

1 step per module

Wire bonding Opto-die wire bonding into TO-Can

1 step per channel

Electronic packaging of Laser driver

into QFN

1 step per channel

Wire bonding of dies to the substrate

1 step per module

Photonic IC wire bonding to the

substrate

1 step per module

Soldering TOSA/ROSA manually soldered Fully automated Fully automated

6 steps per module 2 steps per module 3 steps per module

Electronic packaging for Silicon Photonics is more efficient in comparison with VTRx and of the same difficulty level compared to VL+

Performances comparison with VL/VL+

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VL VL+ SiPh

Size and mass Relatively large Compact Compact

Power consumption TX ~ 50 pJ/bit (250 mW/channel)

RX ~ 20 pJ/bit (100 mW/channel)

TX ~ 5 pJ/bit (50 mW/channel)

RX ~ 20 pJ/bit (100 mW/channel)

20 ÷ 5 pJ/bit

Speed 5 Gbps 10 Gbps per channel (DML Max 10

Gbps)

25 Gbps electrical data rate

Easy WDM or PAM

implementation

Reach 400 m (MM)

3 km (SM)

200 m ~ 2 km

# channels Single channel Multichannel Multichannel

In progress, rough estimation…

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Polarization diversity

Carrier depletion phase shifter

Polarization control with

Thermo-optic phase shifters

2D Grating coupler

IMEC design kit IL = 6 dB

Luxtera demonstrated IL = 2.6 dB

TE

TE

The input MZM recombines in phase the optical power in the two arms

The optical power coupled in the high-speed modulator is constant with any input polarization

No optical insertion loss from MZM input, extra electronic control loop need to be implemented

1D Grating coupler

IMEC design kit IL = 2.5 dB

Luxtera demonstrated IL = 1 dB

Quadrature point biasing

IL ~ 0IL 4 dB/mm ÷ 1.5 dB/mm