Photonics Integration and Evolution of the Optical Transceiver

Presented by: Giacomo Losio – ProLabs

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Optical Transceivers architecture is challenged

● Optical transceivers can’t continue to be a simple electro-optical converter

– Bandwidth increases, but cost, dimension and power need to go down

– Electrical interface beyond 10Gbit/s: need to compensate copper loss and distortion

– Electrical bottleneck: keep low pin count, boost lane speed

– Optics at 25Gbit/s and more: reduce cost, complexity and power

Driver

TIA

Laser

Photodiode Electrical Optical

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Electronics comes to the rescue

● Constant scaling of size and power of ICs now allows integration of new functions inside the transceiver

● Transmission impairments can be compensated at low cost in the electronic domain, permitting to relax optics performance

Source: Intel 1985 1995 2012 2012

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EDC

● Electrical and optical signal distortion can be compensated in the electrical domain

● Extends reach and relaxes component requirements

● Low power solutions are already possible in consolidated technologies

“A 25Gb/s 5.8mW CMOS Equalizer” J.W. Jung et al. ISSCC2014

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Forward error correction

● Forward error correction has been one of the key drivers of optical communication progress

● For cost and power reasons it has been used only in transport networks

● Current silicon node is compatible with transceiver real estate/power consumption

– FEC with >6dB gain,<100ns latency are feasible in less than 200mW @28nm (*) – 1mm2 silicon area – Can trade-off correction capability with latency

● Very important for multilevel modulation where SNR is reduced

(*) Wang et al. IEEE 802.3BM contribution, SEP. 2012

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Analog to Digital Converters

● Enable multi-level signalling

● Digital signal processing at receiver

● Low power implementation possible

– 10GS/s 6 bit ADC in 28nm FDSOI, STM(*)

• Power: 32mW • Area: 80x115 [μm]

– 90GS/s 8 bit ADC in 32nm SOI CMOS, IBM(**)

• Power: 667mW@90GS/s 345mW @70GS/s

• Area: 1.25x1.5 [mm]

Source: Globaltek

(*) “A 20GHz-BW 6b 10GS/s 32mW Time-Interleaved SAR ADC with Master T&H in 28nm UTBB FDSOI Technology” Le Tual et al., ISSCC2014 (**) “A 90GS/s 8b 667mW 64x Interleaved SAR ADC in 32nm Digital SOI CMOS” Kull et al., ISSCC2014

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The old and the new transceiver

● Every functional block will be impacted

Electrical Optical

TX IC

Cu equalization FEC Encoder Advanced Modulation TX signal conditioning Drivers

TX optical IC Optical circuits Mux Multichannel WDM

RX IC ADC EDC/DSP FEC decoder

RX optical IC Demux Integrated PD TIA

● Integrate μController and EEPROM in ICs to reduce transceiver real estate – ARM® Cortex®-M3 core @40nm consumes 7μW/MHz, 0.03mm2 die area

Driver Laser

TIA Photodiode

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Electronics success factors

● Progress of electronics has been incredible, optics lagged behind in a divided camp

● “Siliconize” Photonics to leverage CMOS investments

Enabling Technology Optics Semiconductor

IC

Building block Many (LD, PD, driver, modulator, etc.) Transistor

Material Many (InP, GaAs, InGaAs, Si, LiNbO3,…)

Silicon

Prevalent MFG process Many CMOS

Economy of scale NO YES

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Datacenter Optics can be Silicon Photonics killer app

● Multimode transceivers ruled Campus and Datacenter optics, but struggle to keep up with speed and distance

– 1000BASE-SX 550m on OM2 fiber

– 10GBASE-SR 300m on OM3 fiber

– 100GBASE-SR10 100m on OM3 fiber, 150m on OM4

● Datacenters are becoming huge installations: need 500m reach ore more

● Bandwidth inside Datacenter is unimaginable – One http request (1KB) can generate 1MB internal traffic (*)

● Big Data and IoT applications still haven’t unleashed all their potential

Datacenters need affordable, fast interconnects

(*)“Facebook’s Data Center Network Architecture” Farrington et al. 2012

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Transceiver Evolution to meet the Data Center challenge

● Push Bandwidth in every dimension – Lane Speed (Gbs) * Parallel Channels * WDM on each fiber

● Increase the throughput (Ports*BW) over front, mid- and backplanes – Evolving pluggable form factors: SFP+(1.6Tb) -> QSFP+(3.6T) –> CDFP(9.6Tb) – Transceiver will become ”pluggable ASICs” to enable optical front-, mid- and

backplanes with higher throughput

● Lower the cost of the transceiver: – Integration of electronics and optics – Eliminate sub-assembly and sub-components – Automate assembly and wafer scale semiconductor-like manufacturing

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Pushing Bandwidth in every Dimensions Line Rate (Gb/s)

Wavelength Channel

Physical Channel

100

1 80

24

100G Transceiver (4x25G)

4

40/56G SR Transceiver 56 40

100G (4x25G) WDM Transceiver, 2Km

4

25

400G Transceiver

300G MBOM (12X25G)

Mellanox is pushing the boundary on every dimension to increase the bandwidth of the transceiver

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Photonics Integration eliminates 100s of piece parts

Heat Sink Block

Fiber Ribbon Holder

SIP Rx

SIP Tx

Driver / TIA

Microprocessor TX (Modulator) RX (Detector)

Making 100Gb/s Deployments as Easy as 10Gb/s

Silicon Photonics Integration

• One laser drives multiple parallel channels

• Monolithic integration of detectors and waveguides

• Integrated WDM capabilities

• No subassembly i.e. No TOSA/ROSA

• No lenses, no isolator, no TEC

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Photonics Integration: one laser for four channels

Lasers

Modulators

Splitter

Scalable and efficient silicon photonics platform: • Simple FTTH style laser drives multiple channels

• Flip-chip bonded die

• Passive alignment

• No isolator, no laser subassembly

• Splitter to make four separate channels

• Tap and power monitor

• Easily accommodates arrays

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Photonics Integration: Tiny FK modulators scale to >50 GHz

• Franz-Keldysh modulator is >>10x smaller than MZI

• Only 40 um long

• Provides 5dB ER

• Integrates well with WDM section

25Gb/s Eye

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Photonics Integration: germanium detectors scale to >50 Gb/s

1300 1350 1400 1450 1500 1550 16000

0.2

0.4

0.6

0.8

1

1.2

Wavelength(nm)

Resp

onsiv

ity(A

/W)

TETMLimit

1300 1400 1500 1600-2

-1

0

1

2

Wavelength(nm)

PDR(

dB)

Frequency (GHz)

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WDM on each fiber

● WDM allows for many wavelengths over a single fiber

– 100’s of wavelengths can be applied – The 1550nm band provide the best density

● With gratings WDM can be integrated into silicon photonics

– Scale from 4 to 40+ wavelength

– Mellanox has demonstrated > 1Tb/s WDM devices

– 10x smaller than AWGs

– Very low cross talk

input

output Reflective facet

Slab

........................

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Higher throughput over Front-, Mid- and Backplanes . . . by using pluggable transceivers inside Servers and Swithes

QSFP

CPU

Memory

NIC

Switch-to-NIC/Server over optical backplane

Switch

Electrical connections

Optical connections

Front panel

Transceiver (pluggable and board mount)

Mid- or Back plane

The pluggable transceiver enables:

• Front panels with passive optical connectors (LC or MPO) with higher port density than QSFP

• Mid- and Back planes with optical, scalable and denser connectivity. Higher speed and longer distances

• Better signal integrity. Electrical high speed signals are shorter and get offloaded by the transceiver close to the ASIC or CPU

Switch Node

Compute Node

LC or MPO

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Transceiver as a “pluggable ASIC”

Transceiver Characteristics:

Bandwidth

• 336Gbps bidirectional (up to 28G/ch)

• 12ch full duplex optical engine

Advanced features:

• Retiming and equalizer

• Intelligent link features

• BERT

Reach

• 60m (MMF, 850nm)

• 500m (SMF, 1550nm)

Power consumption

• 5.2 mW/Gbps (w/o retiming)

16mm

24mm

24mm

The intelligent link

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Application • Test and locate • Green cable • Fiber testing and

TX power adjust • Link authentication • OAM

Low Speed Communication Features

● Low speed communication

– Beacons and ”morse” when not running full speed

– Laser safety for MBOM ● Sub band modulation

● System level

Primary 28G modulation

Sub band modulation

High speed standard compliant signal path

µC µC

Control Path

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Application examples: automatic link adjustment

● Receiver evaluates performance – Most receivers are equipped with eye monitoring, can estimate BER – Can be inferred by taps of RX filters – FEC counters

● Information is back-propagated to Transmitter – Simple “in-band” protocol

● Transmitter optimizes performance – Regulate TX power and eye to overcome transmission impairments – Optimize FEC correction capability vs. power/latency

● Benefits – Better utilization of link resources – Lowest power consumption/cooling needs OPEX reduction

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Transceiver will no longer be a “dumb” electro-optical converters

● Optical transceivers will – Incorporate more electronics – Have more optical circuits/ components

– Protect investment in networking equipment

● Transceivers will become a “pluggable ASIC” – Solve ICs bandwidth bottleneck – Increase port density

● Optics & electronics integration helps to reduce cost – Silicon Photonics puts optics on the same trajectory of ICs

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Thank you !