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
3 © 2014 Oclaro Inc.
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
4 © 2014 Oclaro Inc.
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
5 © 2014 Oclaro Inc.
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
6 © 2014 Oclaro Inc.
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
7 © 2014 Oclaro Inc.
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
8 © 2014 Oclaro Inc.
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
9 © 2014 Oclaro Inc.
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)
10 © 2014 Oclaro Inc.
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
11 © 2014 Oclaro Inc.
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
12 © 2014 Oclaro Inc.
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).
2 © 2014 Oclaro, Inc.© 2014 Oclaro, Inc.