High Density Silicon Photonics for Co-packaged Optics and ...

© 2020 Rockley Photonics Ltd.

High Density Silicon Photonics for Co-packaged Optics and Coherent Optical Engines

Aaron Zilkie

Rockley Photonics

ARPA-E ENLITENED Phase 2 Kick-off Meeting – Jan 13, 2021


CPO Drivers: Power, Cost & Density

2

Optics cost more than half of total switch cost

0%

20%

40%

60%

80%

2010 2012 2014 2016 2018 2020 2022

Per-port cost ratio between optics and populated switch

1G 10G 40G 100G 400G

Optics power exceedschassis power limit

Optics bandwidth density not scaling with switch capacity

Data sources:LightCounting Ethernet Optics Report Sep. 2019,Dell’Oro Datacenter Ethernet Switch Jul. 2019

640512 256

12801024

512

2560

2048

1024

FPP 400G FPP 800G CPO

Optics power per switch (W)

25.6 51.2 102.4

Images:edge-core

4RU128x

100G = 12.8T

400G = 51.2T

800G = 102.4T

2RU64x

100G = 6.4T

400G = 25.6T

800G = 51.2T



Rockley Photonics Platform Performance Advantages

3

Unique Benefits✓ Low loss: (< 0.2 dB/cm)

✓ Large-scale PIC capability, high levels of

integration

✓ Strong confinement: Tight packing and

turns as well as dense layout capability

▪ Low loss compact bends < 10-100 um Reff

✓ Low polarization dependent loss (PDL)

✓ Low loss, passive align fiber couplers

✓ Low wavelength sensitivity, accurate

WDM filters

▪ filters have 25x reduced λ sensitivity and

variations

✓ KGD III-V integration for high yield

actives

TE (neff = 3.4617) TM (neff = 3.4609)a) b)

y (m

icro

ns)

2

0

-2 -1 0 1 2 -2 -1 0 1 2-2

x (microns)x (microns)

Platform metrics - Si waveguides

TE and TM polarizations have near-degenerate neff and mode profiles



Technologies

Rockley Platform Technology Elements

4

Integrated Lasers• High-density WDM lasers• DFB, DBR lasers• Tunable lasers, broadband sources

Modulators• High-speed EAMs: Heterogeneous III-V 1310nm,

monolithic SiGe 1550nm• Carrier injection/depletion phase modulators

Mux / Demux / Filter Technologies• AWG• Echelle Grating• Mach Zehnder Interferometers• λ stable, process tolerant

Fiber Edge-couplers• Integrated V-groove mode matched to SMF

Other Passives• Splitters, taps, combiners, …

Echelle

AWG

MZIEAM

V-groove

edge-

coupler

Photodetectors• Monolithic Ge PD

Euler Bends• Tight waveguide bends for compact layouts

Analog Front End Electronics• TX: Modulator & laser driver ICs• RX: Transimpedance amplifier ICs

Receiver Architectures• Direct-detect• Coherent detection• Large arrays, high integration densities

Packaging• Wafer-level packaging• Integrated fanout• 2.5D/3D integration• Passive fiber attach

250 μm

106Gb/s

TIAs

106Gb/s

EAM

Drivers

Multi-𝛌 III-V

source on

silicon

Wide Range of Platform Technology Elements to Address Multiple Market Verticals

Opto-

Engine

CWDM Mux/Demux



0

20

40

60

80

0 0.2 0.4 0.6 0.8 1 1.2 1.4

Dev

ice

BW

(G

b/s

)

Pitch per ch [mm]

I/O Density: modulator technologies

III-V EA Modulators for Ultra High Density I/O

➢ Electrical switch size limited by BGA package, sets requirements on data density➢ XSR interconnects allows substrate up to double size substrate to

host CPO optical chips

➢ For 51Tb/s and 102 Tb/s switch ASICs with perimeter-integration:➢ Densities of 200 Gb/s/mm and 400 Gb/s/mm are needed for

optical I/O components

➢ Need compact modulators and detectors with pitches of ≤250 μm, channel rates of 100 Gb/s, and scaling to <125 μm and 200 Gb/s

Choose InP EAMs for high density Si Photonics for CPO

➢ Si MZMs can not meet the integration densities needed for future CPO generations

➢ Rockley half-ring EAM and Si RR modulators meet the density requirements, and are roughly the same size

➢ RRs are very sensitive to temperature and fabrication variations and require more control pads

➢ EAMs have wide operating bandwidth allowing open loop operation over 30C operating T range, 0-70C with T control

MZ (segmented LE)

snake LE MZEAM(1st and next gen)

RR*

Dev

ice

BW

(G

bau

d)

*RRs are bigger in area when consider more drive + control pads needed

250 μm

200 Gb/s/mm

Electrical Optical

Switch CPO Faceplate Pluggable

# lanesSerdes

rate (Gb/s)

capacity (Tb/s)

Electrical Data Density (Gb/s/mm)

Min Optical Data Density for XSR

(Gb/s/mm)lanes capacity modules

Faceplate size

256 50 12.8 100 50 8 400G 32 1RU

512 50 25.6 200 100 8 400G 64 2RU

256 100 25.6 200 100 8 800G 32 1RU

512 100 51.2 400 200 8 800G 64 2RU

1024 100 102.4 800 400 8 800G 256 4RU

1024 100 102.4 800 400 16 1.6T 128 2RU

512 200 102.4 800 400 8 1.6T 128 2RU

125 μm

400 Gb/s/mm

Rockley U-bend EAM


60 µm


Overcoming the Manufacturing & Yield Challenge

Challenges

❑ Materials integration, light coupling, manufacturability, yield, and assembly cost

❑ Integration with electronics: electrons require deep sub-micron design features while photons benefit from staying in microns dimension

Rockley’s Solution

✓ Multi-micron waveguide eases challenges of heterogenous integration on chip and getting light on and off the chip

✓ Separate photonic and electrical chips to take advantage of each silicon platform

6

AnalogElectronics

Silicon Photonics

Active Materials

Packaging

Digital(CMOS)

Rockley Photonics chipset solution provides high density I/O and is well suited for CPO and 400G and 800G Transceivers

Rockley 400Gb/s DR4 Transceiver chipset - now sampling!



CPO Enabling Packaging Technology

• Minimizes high speed interconnect length to maximize 100G

PAM4 channel performance

• 3-D, face-to-face photonic IC (PIC) and electrical IC (EIC)

assembly avoids TSVs

• Planar fiber array attach using Rockley fiber V-groove array

• Electrical Interface is LGA socketed, separable reworkable

interface to switch

• For future generations, can consider low loss optical

connector (no pigtail)

• Also applicable for compact high performance 800Gb/s

pluggable transceivers

7

Rockley LightDriver™ Optical Engine

Si Ph Tx and Rx

Driver and TIA ICs

Fiber arrays

Carrier and electrical interface


C. Minkenberg et al., “Co-Packaged Datacenter Optics:Opportunities and Challenges”,

C. Minkenberg, “Co-Packaged Datacenter Optics: Opportunities and Challenges.” IET Optoelectronics, to be published (2021)


CPO System Solution (OFC ’20 Demo)

LightDriver™ solution for 51.2 Tb/s system

• 16 OptoEngines: 3.2Tb/s full duplex, 100G PAM4 per lane, 8xDR4 & 8xFR4 compliant versions

• Remote Laser Source (RLS) in pluggable form factor

• 3D integration of EIC and PIC in OEngine

• Power: 10pJ/bit (50% savings vis-à-vis transceivers) for FR4

• Cost: <$0.52/Gbps (>60% savings)

• Co-packaged with Ethernet switch / OEM ASICs

8

Image of demo box; not reflective of 51T system

Image of demo box; not reflective of 51T system

Pluggable RLS module


C. Minkenberg “Reimagining datacenter topologies with integrated silicon photonics.” Journal of Optical Communications and Networking. 10(7) pp. B126-39. (2018)


High Density Coherent Tx with EAMs for ENLITENED

➢ Applications: High data-density Coherent CPO for datacenters and HPC, new more dynamic network architectures (add optical switching), longer I/O reaches using a common integrated platform

➢ Differentiators • At least 2x Higher linear density coherent solution with U-bend III-V

EAM compared to MZM solution, path to I/O densities of 10Tb/s with Rockley Compact U-bend EAM and integrated WDM MUXs/DEMUXs

• Simpler to control (no phase balancing and impedance matching needed), less phase variations in multi-micron platform

• Brings benefits of Rockley platform – CPO optical engine platform, polarization independence, low losses, high integration densities,

• Full range of integrated III-V actives allows for integrated III-V lasers and/or MZMs as well as needed

versus other approaches:

Schow group

S

P

Tx OUT

Tx OUT

pol. mux

S

P

EAM

EAM

EAM

EAM

MZM

MZM

MZM

MZM

4 lumped element diodes for 200 Gb/s

8 or more diodes for 200 Gb/s

➢ ARPA-E Project Objective: Apply Rockley Platform for alternative approach to UCSB INTREPID analog coherent interconnect, and alternate commercialization path with volume SI Photonics platform

➢ Tradeoffs – 6-8 dB higher Tx losses, higher laser power


(Not to scale)

9

Tx with parallel EAMs concept from Doerr at el. PTL 19 (15) p. 1184 (2007)

Details of MZM approaches in: Hirokawa at el. PTL 39 (2) p. 520 (2021)


High Density Coherent Rx for ENLITENED

10

➢ Monolithic Ge detectors in multi-micron platform ideal for coherent Rx:– Unique advantages:

1. Accurate MMI splitters for Coherent Hybrids with low variability

2. Reduced phase imbalances

3. Natively polarization independent

4. Inherently broad band

➢ Rockley’s TIA co-designed with 3-Terminal differential PD pair gives ultra-low balanced receiver dark current performance

➢ Rx PIC based on Rockley monolithic Ge PDs and compact passives supports data densities needed for Coherent solutions and CPO

Schow group

250 μm

2 5 0 μ m

-3

-2.5

-2

-1.5

-1

-0.5

0

0 10 20 30 40

S21 [dB]

Frequency [GHz]

-2 V

S21 3dB BW > 40 GHz

S21

[d

B]

SMF fibers passively aligned in V-grooves



QD lasers for remote lasers sources

11

BER plots for quantum dot Fabry-Perot laser (left)

and a commercial quantum well FP laser (right) in

back-to-back as well as 2 km transmission

experiments at 25 Gbps.

➢ advantages of QD DFB lasers for CPO RLS, transceivers, next gen Coherent WDM• better back reflection tolerance, removes need for isolator in integrated Si

Photonic PICs → lower $/Gb/s• Superior reliability for higher output powers• High power efficiency at high T → low pJ/bit• broadband comb laser sources for Coherent WDM links

➢ End goal to integrate into Rockley PICs to leverage Rockley III-V integration platform for further cost and size reductions

Rockley Pluggable RLS module1. Low pJ/bit and lower

cost RLS solution2. Comb sources for

high density Coherent WDM

=

J. Duan, et al. IEEE Photonics Technology Letters,

vol. 31, no. 5, pp. 345-348, 2019.



Thank-you

www.rockleyphotonics.com

High Density Silicon Photonics for Co-packaged Optics and ...

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