Advanced Modulation Formats in Data Centre Communications Michael J. Wale Director Active Products Research

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1 Advanced Modulation Formats in Data Centre Communications Michael J. Wale Director Active Products Research 2 nd Symposium on Optical Interconnects in Data Centres ECOC, Cannes, 23rd September Oclaro, Inc.

2 Agenda Motivation Strategies: Photonic Integration, Advanced Modulation Formats 400Gbit/s Ethernet with Advanced Modulation Formats: Proposal and Experimental Verification Acknowledgments Conclusions Oclaro Inc.

3 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 Microsoft c/o Google Oclaro Inc.

4 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 TL DP-I&Q Modulator CONTROL ELECTRONICS Integrated Coherent Receiver TL CFP2 Transceiver employing InP PICs for coherent 100Gbit/s transmission using DP-QPSK Oclaro Inc.

5 FRAMER FEC DSP ADCs FRAMER FEC DSP DACs 100/200G Digital Coherent Hardware for Line-Side Telecom TxDATA ASIC TL DP-I&Q Modulator CONTROL ELECTRONICS RxDATA Integrated Coherent Receiver TL 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 Oclaro Inc.

6 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 PM-QPSK 2x2 bits/symbol PAM-4 2 bits/symbol PM-16QAM 2x4 bits/symbol Oclaro Inc.

7 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 Center Wavelengths -FR4 CWDM -LR4 LANWDM L nm nm L nm nm L nm nm L nm nm Block Diagram Oclaro Inc.

8 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 Oclaro Inc.

9 Interface FEC (TBD) DSP DAC Optics Optics ADC DSP FEC (TBD) Interface Nyquist PAM4 for Single Channel 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) Nyquist Modulation Nyquist PAM4 Reproduce Decision/Timing regeneration 56 GBaud 56 GBaud 28 GHz GHz Frequency spectrum 17.9 ps Transmitter waveform 17.9 ps Reproduced waveform Oclaro Inc.

10 OMA Experimental results Experiment using commercially available 25G EML and pin-tia receiver at Gbit/s (l=1310nm) Demonstrated capability of 8.9dB link budget with estimated WDMmux/demux insertion loss of total 3dB Pav OMA Power Tx power (w/o MUX) Rx (w/o demux) Tx power minus Rx sensitivity +3.4 dbm +3.8 dbm -8.5 dbm -8.1 dbm 11.9dB Pattern length 2 15 bits Eye Pattern P av (*) Strong FEC is required Experimental values (Hirai_3bs_01_0914) Oclaro Inc.

11 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 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 Oclaro Inc.

12 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) Oclaro Inc.

13 Oclaro, Inc.