Advanced Modulation Formats in Data Centre Communications

1 © 2014 Oclaro, Inc.© 2014 Oclaro, Inc.

Advanced Modulation Formats in Data Centre CommunicationsMichael J. WaleDirector Active Products Research2nd Symposium on Optical Interconnects in Data CentresECOC, Cannes, 23rd September 2014

2 © 2014 Oclaro Inc.

Agenda

• Motivation

• Strategies: Photonic Integration, Advanced Modulation Formats

• 400Gbit/s Ethernet with Advanced Modulation Formats: Proposal and Experimental Verification

•Conclusions

•Acknowledgments


Motivation

• Internet traffic growth ~50%/year

• Growth in cloud services

• Corresponding growth in data

centre capacity, size and power

efficiency demands at minimum

cost

• Optical transport vital within data

centres as well as between

centres

• Equipment density extremely

high

• Need to maximize optical

transport capacity per fibre and

per transceiver

c/o Google

c/o Microsoft


Strategies to increase capacity & packing density

• Photonic integration

– Monolithic integration on InP

– e.g. Tunable laser/Mach Zehnder modulator in XFP, SFP+ telecom modules

– Silicon photonics

• Advanced Modulation Formats

– Higher capacity per optical carrier without increasing basic signalling rate or electronic speed

– Electronic processing for data recovery and impairment mitigation

– Industry standard for long-haul 100Gbit/s telecom, widely used in copper interconnect for datacom

ILMZ wafer

Integrated laser-MZ modulator in XFP transceiver

CFP2 Transceiver employing InP PICs for coherent 100Gbit/s transmission using DP-QPSK

DP-I&QModulator

CONTROL ELECTRONICS

Integrated Coherent

Receiver

TL

TL


100/200G Digital Coherent Hardware for Line-Side Telecom

• I&Q Mach-Zehnder modulator for TX and 90º optical hybrid for RX

provide flexible building blocks capable of arbitrary modulation formats

• Transmit DACs on ASIC provide for software-defined networking

– Utilize PM-QPSK, 16QAM,… depending on requirements for reach,

spectral efficiency, filtering tolerance, etc.

DP-I&QModulator

CONTROL ELECTRONICS

Integrated Coherent

Receiver

TL

DA

Cs

AD

Cs

TL

ASIC

FE

C

DS

P

FR

AM

ER

FE

C

DS

P

FR

AM

ERRxDATA

TxDATA


Advanced modulation formats

• Line-side telecommunications needs

very high spectral efficiency (~100 l

across band), very high resilience to

dispersion, PMD, nonlinear effects …

– Coherent transmission with phase

modulated (QPSK) or QAM; dual

polarization operation, powerful DSP

• Data communications require high

capacity per channel, shorter links (2-

10km), ultra-compact components,

lowest cost

– Focus on multi-level pulse amplitude

modulation (PAM) with direct detection

– PAM4: 4 amplitude levels

– Transmits 2 bits/second/Hz

• 2x2 bits/symbol

PM-QPSK

• 2x4 bits/symbol

PM-16QAM

• 2 bits/symbol

PAM-4


Data Communications: Proposal for 400Gbit/s Ethernet

• We propose 400GBASE-FR4 and –LR4 with single mode fibre (SMF)

4-lane Wavelength Division multiplexing (WDM)

Each lane transmits and receives 100Gbit/s data using Nyquist PAM4

Optical Fiber Wavelengths

400GBASE-FR4 2m to 2km SMF CWDM

400GBASE-LR4 2m to 10km SMF LANWDM

-FR4 -LR4

CWDM LANWDM

L0 1271 nm 1295.56 nm

L1 1291 nm 1300.05 nm

L2 1311 nm 1304.58 nm

L3 1331 nm 1309.14 nm

Center Wavelengths

Block Diagram


Why Nyquist PAM4?

• PAM4 has good tolerance to

channel impairments but requires

very high sampling rate

(>100GSa/s)

• Nyquist PAM4 reduces signal

spectral width, allowing a lower

sampling rate at the receiver

• Permits technology reuse of

100GbE LR4 devices

• Sensitivity can be improved using

DSP EQ technologies

• Study confirms 400GbE using

Nyquist-PAM4 is possible with

existing components


Nyquist PAM4 for Single Channel

Transmitter waveform Frequency spectrum

28 GHz

0 16 32 -16 -32 GHz

17.9 ps

Op

tics

DA

C

AD

C

Op

tics

DSP

Inte

rfac

e

Inte

rfac

e

DSP

Reproduced waveform

Nyquist Modulation Nyquist PAM4 Reproduce Decision/Timing regeneration

FEC

(TB

D)

FEC

(TB

D)

17.9 ps

56 GBaud 56 GBaud

• Proposal and features – Filter PAM4 at the TX side

Transmitter output spectrum width is reduced by half with Nyquist pulse shaping • Optical devices will require about 28GHz bandwidth.

ISI is not degraded due to reduced spectrum (Zero ISI criteria compliance)

– Regenerate signal at RX side with 56-62GSa/s (Nyquist-Shannon theorem)

– Strong FEC is required; DSP requirements modest (0.6M gates)


Experimental results

• Experiment using commercially available 25G EML and pin-TIA receiver

at 102.4 Gbit/s (l=1310nm)

• Demonstrated capability of 8.9dB link budget with estimated WDM-

mux/demux insertion loss of total 3dB

Pav OMA

Tx power (w/o MUX)

+3.4 dBm +3.8 dBm

Rx sensitivity @BER=2E-3* (w/o demux)

-8.5 dBm -8.1 dBm

Tx power minus Rx sensitivity

11.9dB

Experimental values (Hirai_3bs_01_0914)

Eye Pattern

Pav

Power

OM

A

(*) Strong FEC is required Pattern length 215 bits


Summary

• Growth in data center traffic requires continuous innovation in

optical interconnection techniques

• Photonic integration and advanced modulation formats are key

tools, as they are in telecommunications systems

• As an example, we propose 400GbE for 2km and 10km links

using single-l 100G channels with Nyquist-PAM4 modulation

– Nyquist filtering at the TX side lowers the device BW to 28GHz

– Regenerate signal at RX side at 56-62 GSa/s

– Can apply currently available ADC, DAC & DSP technologies

– Additional DSP power consumption with Nyquist filtering is low

• Sensitivity can be further improved with equalization technologies

such as DFE, FFE and MLSE

• Interplay of optics and electronics becomes ever-more important


Acknowledgements

• Many thanks to everyone at Oclaro engaged in the design,

development and production of these components

• Special thanks to Ram Rao and Takayoshi Fukui (Oclaro) and

Riu Hirai and Nobuhiko Kikuchi (Hitachi, Ltd.) for their work on

400GbE using Nyquist PAM4

• Our proposals on 400GbE using Nyquist PAM4 for 2km and

10km were presented at the IEEE P802.3bs 400Gb/s Ethernet

Task Force meeting, 8-13 September 2014

• Please see ECOC paper by Nobuhiko Kikuchi and Riu Hirai,

“Intensity-Modulated / Direct-Detection (IM/DD) Nyquist Pulse-

Amplitude Modulation (PAM) Signaling for 100-Gbit/s Optical

Short-Reach Transmission” (P4.12).

Advanced Modulation Formats in Data Centre Communications

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