Abstract
We discuss technology options and challenges for scaling intra-datacenter interconnects beyond 1 Tb/s bandwidths, with focus on two possible approaches: pulse amplitude modulation (PAM)-based intensity modulation-direct detection (IM-DD) and baud-rate sampled coherent technology. In our studies, we compare the performance of various orders of PAM modulation (PAM4 to 8). In addition to these fixed PAM signaling options, a flexible PAM (FlexPAM) technique leveraging granularity in spectral efficiency (SE) is proposed to maximize link margin. For baud-rate sampled coherent technology, we propose a simplified digital signal processing (DSP) architecture to bring down power consumption of the coherent approach closer to that of IM-DD PAM. We also propose two new phase noise tolerant 2D coherent modulation formats to relax the laser linewidth requirement. In closing, a comparative study of fixed IM-DD PAM versus coherent polarization multiplexed-quadrature amplitude modulation (PM-QAM) is presented for a 1.6 Tb/s solution (200 Gb/s per dimension), with consideration of link loss/reach budget, power consumption, implementation complexity, as well as fan-out granularity.
Highlights
I N THE past decade, datacenters (DCs) have become the key technology enabler for internet-based applications
Given the above implementation complexities facing flexible PAM (FlexPAM), a fixed pulse amplitude modulation (PAM) signaling design remains a viable option for 200 Gb/s per lane scaling if the link loss/reach budget can be satisfied with the available components
For coherent polarization multiplexed (PM)-32QAM, we show the results with different laser power splitting ratios
Summary
I N THE past decade, datacenters (DCs) have become the key technology enabler for internet-based applications. By increasing the baud rate from 25 Gbaud to 50 Gbaud/s, single lane 100 Gb/s could be achieved for SMF transceivers (more challenging with VCSEL/MMF technology) using optical and electrical components with higher bandwidth and better linearity. This will enable 800 Gb/s bandwidth in an OSFP form factor. Scaling in the parallelization axis requires doubling the number of optical and electrical components (assuming no changes in encoding or detection techniques) This will result in an approximately linear increase in cost and power. A judicious combination of the three techniques is the most likely path forward
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