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Xiang Zhou

Xiang Zhou

Xiang Zhou is currently a Tech Lead within Google DC optics group, leading Next-Gen optical interconnection technologies and roadmap development. Prior to join Google, He was with AT&T Labs-Research (Middletown, NJ, USA, 2001 to 2013), conducting research on various aspects of long-haul optical transmission and networking technologies, From 1999 to 2001, he was with Nanyang Technological University, Singapore, as a Research Fellow. Xiang Zhou received his Ph. D degree from BUPT in 1999. Dr. Zhou has extensive publications in top Journals and conferences in his field, including several record-setting ‘hero’ results, which have received wide media reports. He holds more than 50 US patents with a dozen more pending. He currently serves as an associate editor for J. Lightwave Technology and is an OSA fellow. He also served on the editorial board of Optics Express and in the Program Committee of a variety of technical conferences.
Authored Publications
Google Publications
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    Preview abstract This is an invited OFC 2024 conference workshop talk regarding a new type of lower-power datacenter optics design choice: linear pluggable optics. In this talk I will discuss the fundamental performance constraints facing linear pluggable optics and their implications on DCN and ML use cases View details
    Preview abstract This is an OIF 800G LR standard contribution. This contribution proposes to revise 800G LR1 baseline link loss budget from 6dB at C-band wavelength to 8dB at O-band wavelength View details
    Datacenter networks
    Journal of Optics (2023) (to appear)
    Preview abstract This is an invited paper section, as part of an industry white paper, 2023 Roadmap on Optical Communication, to be published in Journal of Optics. This paper section reviews, from a high level, technology challenges and possible solutions to continue to scale datacenter network View details
    Preview abstract We review state of art datacenter interconnect technologies for 800G, 1.6T and beyond networking speeds, with a special emphases on 200G per-lane IM-DD and 800G-LR1 coherent-lite View details
    Preview abstract We review state-of-the-art datacenter technologies for 800G, 1.6T and beyond interconnect speeds, focusing on 200G per-lane IM-DD (intensity modulated-direct detect) and 800G-LR1 coherent-lite transmissions. View details
    Preview abstract This is intended for IEEE802.3df contribution. In this contribution, we describe how to model four-wave-mixing (FWM) for datacenter interconnects systems, and why FWM could limit the achievable reach for 1.6Tb/s WDM-8 IM-DD systems View details
    Preview abstract This is intended for IEEE802.3df contribution. In this contribution, we describe the FEC requirements for 800GbE/1.6TbE optics from an operator's perspective, and how to make a fair comparison among different FEC options. View details
    Preview abstract This is on OFC conference workshop talk, discussing the use cases of low-latency optical interconnect technology in modern datacenter View details
    Preview abstract This is an OFC 2022 conference panel talk. We review from high level about the right technology choice for 1.6Tb/s data center optics interconnects View details
    800G LR1 Use Cases and Requirements Revisit
    Optical Internetworking Forum, https://www.oiforum.com/, https://www.oiforum.com/ (2021)
    Preview abstract This is contribution of campus networking application requirements to the OIF 800G-LR coherent-lite project. View details
    Beyond 1Tb/s Intra-Datacenter Interconnect Technology: IM-DD or Coherent Detection?
    Hong Liu
    Ryohei Urata
    IEEE/SOA J. Lightwave Technology (2020) (to appear)
    Preview abstract We discuss technology options and challenges for beyond 1Tb/s intra-datacenter interconnect bandwidth scaling, with a focus on pulse amplitude modulation (PAM)-based intensity modulation-direct detection (IM-DD) and baud-rate digital signal processing (DSP)-based coherent technology. We show that a flexible PAM (FlexPAM) technique with fine granularity of bandwidth/spectral efficiency (in terms of bits/symbol) could bring significant value for 200Gb/s per lane or per dimension bandwidth scaling. For baud-rate sampled coherent technology, we propose a much simplified DSP architecture which could bring down coherent DSP power close to that of IM-DD PAM technology. We also propose two new phase noise tolerant, 5 bits per symbol, 2D coherent modulation formats to lower the requirement on laser linewidth. To conclude, we present a comparative study of IM-DD PAM versus coherent PM-QAM (polarization multiplexed-quadrature amplitude modulation) for 200Gb/s per dimension throughput scaling in terms of achievable link loss/reach budget, power consumption, implementation complexity, as well as fan-out granularity. View details
    Beyond 1Tb/s Datacenter Interconnect Technology: Challenges and Solutions
    Hong Liu
    Ryohei Urata
    OFC 2019 conference proceedings, OSA, The Optical Society 2010 Massachusetts Ave, NW Washington, DC 20036 USA (2019)
    Preview abstract We discuss challenges and solutions for beyond 1Tb/s intra-datacenter bandwidth scaling, with a focus on the FlexPAM-based direct detection and the baud-rate DSP enabled coherent detection. View details
    Scaling Large Data Center Interconnects: Challenges and Solutions
    Hong Liu
    Ryohei Urata
    Sara Zebian
    Optical Fiber Technology (2017)
    Preview abstract Increasing demands for web and cloud-based services have been driving exponential growth of datacenter bandwidth. This paper discusses, from Google’s perspective, emerging challenges and possible technical solutions to scale intra-datacenter and intra-campus interconnection network bandwidth. View details
    Preview abstract In this presentation, we will review the evolution of Google’s intra-datacenter interconnects and networking over the past decade, then outline future technology directions which, along with a more holistic design approach, will be needed to keep pace with the requirements and growth of the datacenter. View details
    Preview abstract In this workshop talk we will discuss the potential and value of flexible modulation formats and constellation shaping for datacenter interconnection bandwidth scaling View details
    Datacenter Optics: Requirement, Technology and Trend
    Hong Liu
    Ryohei Urata
    Chinese Optics Letters (2017)
    Preview abstract This paper reviews over decade of technology evolution and advancement of datacenter optical interconnect, which is mainly driven by the explosive bandwidth demand growth of web and cloud based services. Emerging trend and technical options to scale bandwidth well beyond 400Gb/s have also been discussed. View details
    Datacenter Interconnect and Networking: from Evolution to Holistic Revolution
    Ryohei Urata
    Hong Liu
    Amin Vahdat
    OFC 2017 Proceedings (2017)
    Preview abstract In this presentation, we will discuss Google’s intra-datacenter networks and interconnect. We will first review the evolution of datacenter interconnects and networking over the past decade, then outline future technology directions which will be needed to keep pace with the requirements and growth of the datacenter. View details
    Preview abstract This book chapter presents a systematic review on carrier recovery technologies recently developed for high-spectral efficiency coherent transmission systems. View details
    Scaling Large Data Center Interconnect: Technology Options and Challenges
    Hong Liu
    Frontiers in Optics: The 100th OSA Annual Meeting, OSA (2016)
    Preview abstract This is an invited OSA annual meeting talk. This talk reviews technology options and challenges to scale bandwidth and power for large-scale data center interconnects. View details
    Pluggable DWDM: Considerations For Campus and Metro DCI Applications
    Hong Liu
    ECOC 2016 workshop presentation, VDE, Germany, Stresemannallee 15 60596 Frankfurt/Main Germany (2016)
    Preview abstract This is a ECOC workshop talk. We will discuss, from Google’s perspective, the challenges facing datacenter campus and metro interconnection networks, and the potential of using pluggable tunable DWDM for both campus and metro applications View details
    Advanced DSP for 400Gb/s and beyond Optical Networks
    Lynn Nelson
    JOURNAL OF LIGHTWAVE TECHNOLOGY, vol. Vol. 32 (2014), pp. 2716-2725
    Preview abstract This paper presents a systematic review of several digital signal processing (DSP)-enabled technologies recently proposed and demonstrated for high spectral efficiency (SE) 400Gb/s – class and beyond optical networks. These include 1) a newly proposed SE-adaptable optical modulation technology ⎯ time-domain hybrid quadrature amplitude modulation (QAM), 2) two advanced transmitter side digital spectral shaping technologies ⎯ Nyquist signaling (for spectrally-efficient multiplexing) and digital pre-equalization (for improving tolerance toward channel narrowing effects), and 3) a newly proposed training-assisted two-stage carrier phase recovery algorithm that is designed to address the detrimental cyclic phase slipping problem with minimal training overhead. Additionally, this paper presents a novel DSP-based method for mitigation of equalizer-enhanced phase noise impairments. It is shown that performance degradation caused by the interaction between the long-memory chromatic dispersion (CD) compensating filter/equalizer and local oscillator (LO) laser phase noise can be effectively mitigated by replacing the commonly used fast single-tap phase-rotation-based equalizer (for typical carrier phase recovery) with a fast multi-tap linear equalizer. Finally, brief reviews of two high-SE 400Gb/s-class WDM transmission experiments employing these advanced DSP algorithms are presented. View details
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