Abstract
The continued growth in Hyperscale data center (HDC) deployment is expected to drive world-wide Internet traffic to an astounding 21 zettabytes by 2021. This growth will place increased demands on data center interconnects (DCIs) and drive the capacity of the underlying electronic application specific integrated circuit (ASIC) switch chips that route DCI ethernet traffic, from 12.8 Tbps per chip today to 100 Tbps and beyond in the future. This astounding growth will push the limits of today's incoherent fiber link technologies that connect switches, including power dissipation, density, and practical engineering solutions. To overcome these limits, high capacity coherent WDM, traditionally relegated to the metro and long-haul networks, will need to move into the DCI. However, migrating coherent WDM into the DCI, particularly for link distances less than 2 km, will require elimination of power consuming and costly technologies like the digital signal processor (DSP). Additionally, new photonic integration technologies will be needed to co-locate the coherent optical interfaces directly with switch ASICs to alleviate the bandwidth, power, and density limits. In this article, we introduce a new approach to DSP-free coherent WDM for the DCI called FRESCO: FREquency Stabilized Coherent Optical Links for Low Energy DCIs. FRESCO utilizes spectrally pure, ultra-stable light source technology, normally associated with high-end scientific applications like atomic clocks, to enable high capacity high-order WDM QAM with low bandwidth, low power electronics normally associated with RF links. Terabits per second FRESCO links based on shared, stabilized sources and high-density coherent WDM silicon photonic coherent transceivers that are co-located with the switch ASIC will pave the way to a DSP-free coherent WDM scalable DCI solution.
Highlights
H YPERSCALE data centers are expected to support 21 Zettabytes per year and represent over 50% of share of installed data center base in 2021 [1]
We propose utilizing ultra-high frequency stability to bring coherent WDM into the data center interconnects (DCIs) without the high cost, large footprint and power consuming technologies associated with traditional coherent WDM systems including digital signal processors (DSPs) and high bandwidth analog and high speed digital electronics [11], [12] as well as employing highly integrated co-packaged switch/optics [6], [8]
We have described FRESCO, a new approach that leverages the properties of spectrally-pure highly-stable light developed for large scale physics experiments, to bring ultra-high capacity long-haul coherent optical solutions into the DCI without energy consuming electronics
Summary
H YPERSCALE data centers are expected to support 21 Zettabytes per year and represent over 50% of share of installed data center base in 2021 [1]. The scale of this challenge is equivalent to integrating onto a single electronic chip package, the electronic switching and interface subsystems (buffering, switching, scheduling, etc.) of the 92 Tbps Cisco CRS-1 and CRS-3 [3] that occupied up to 72 interface/buffer equipment racks and 8 switch equipment racks The capacity of these packet routing systems was limited in large part by the “power spreading problem” [4], a practical set of design constraints where increases in on-chip capacity leads to the chip exceeding the allowable power dissipation per area (e.g., 100 Watts per cm). The ARPA-e OPEN funded FRESCO: FRequency Stabilized Coherent Optical WDM links for energy efficient DCIs, is designed to provide a power envelope and chip/fiber-count complexity that scales the switch ASIC optical I/O to 100 Tbps and beyond. We propose utilizing ultra-high frequency stability to bring coherent WDM into the DCI without the high cost, large footprint and power consuming technologies associated with traditional coherent WDM systems including digital signal processors (DSPs) and high bandwidth analog and high speed digital electronics [11], [12] as well as employing highly integrated co-packaged switch/optics [6], [8]
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