The Optical Networking and Communication
Conference & Exhibition

San Diego Convention Center,
San Diego, California, USA

2018 Rump Session

2018 Rump Session

When Will Coherent Replace Direct Detection in the Data Center?

Organizer:  Chris Cole, Finisar Corp., USA

Provocateurs:  Sudeep Bhoja; InPhi Corporation, USA; Peter De Dobbelaere; Luxtera Inc., USA; Chris Doerr; Acacia Inc., USA; Fotini Karinou; Huawei Technologies Co. Ltd., Germany; George Papen; UCSD, USA;  Bardia Pezeshki; Kaiam Corporation, USA; Martin Schell; Fraunhofer HHI, Germany; Haoli Qian; Credo Semiconductor Inc., USA; Chongjin Xie; Alibaba Group Holding Ltd., China

Over time, optics has replaced copper cables starting with long reach transmission, followed by regional, metro, inter-facility, and finally all links inside the data center except for server interconnect. Even server I/O is under challenge by active optical cables. Replacement of IMDD (Intensity Modulated Direct Detection) optics by Coherent optics appears to be following the same trend, but on a delayed time line. Coherent has now replaced IMDD in long reach transmission, regional, and metro applications. Coherent vs. IMDD for 20km, 40km and 80km links at 100G and 400G is the subject of intense industry debate including in standards bodies and tough competition in the market place. Will the trend continue, and when if ever will Coherent replace IMDD for 500m, 1km and 2km data center links?
Questions for Discussion:
  • Coherent has superior sensitivity to IMDD. Does that matter for data center loss budgets of 3dB to 7dB?
  • Coherent has superior impairment mitigation (CD, PMD) to IMDD. Does that matter for 500m to 2km reaches?
  • Power is becoming the dominant performance metric in the data center. Which is inherently lower power -- Coherent or IMDD?
  • Analog techniques have traditionally led to the lowest power. Is analog easier for Coherent or IMDD? Which can more easily eliminate DSP?
  • Coherent requires IQ modulation which imposes physical dimension requirements on modulator implementations. Does that lead to a cost disadvantage for transmitter implementations?
  • Low latency links are becoming increasingly important for applications requiring large data base searches and machine learning. Which has inherently lower latency -- Coherent or IMDD?
  • Optical switching and hybrid electrical/optical topologies are becoming increasingly important for managing cost and power in the data center. Which has inherently faster locking speed -- Coherent or IMDD?
  • Does IMDD enable use of weak or no FEC for lowest latency links?
  • Short introductory presentation by session organizer.
  • One slide presentations from diverse group of industry provocateurs.
  • Vigorous audience participation after each presentation, with organizer facilitating wide ranging discussion.
  • Attendees come prepared with tough questions and insightful comments, and challenge the presenters.

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