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Proceedings Paper

Scaling single-wavelength optical interconnects to 180 Gb/s with PAM-M and pulse shaping
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Paper Abstract

Faced with surging datacenter traffic demand, system designers are turning to multi-level optical modulation with direct detection as the means of reaching 100 Gb/s in a single optical lane; a further upgrade to 400 Gb/s is envisaged through wavelength-multiplexing of multiple 100 Gb/s strands. In terms of modulation formats, PAM-4 and PAM-8 are considered the front-runners, striking a good balance between bandwidth-efficiency and implementation complexity. In addition, the emergence of energy-efficient, high-speed CMOS digital-to-analog converters (DACs) opens up new possibilities: Spectral shaping through digital filtering will allow squeezing even more data through low-cost, low-bandwidth electro-optic components. In this work we demonstrate an optical interconnect based on an EAM that is driven directly with sub-volt electrical swing by a 65 GSa/s arbitrary waveform generator (AWG). Low-voltage drive is particularly attractive since it allows direct interfacing with the switch/server ASIC, eliminating the need for dedicated, power-hungry and expensive electrical drivers. Single-wavelength throughputs of 180 and 120 Gb/s are experimentally demonstrated with 60 Gbaud optical PAM-8 and PAM-4 respectively. Successful transmission over 1250 m SMF is achieved with direct-detection, using linear equalization via offline digital signal processing in order to overcome the strong bandwidth limitation of the overall link (~20 GHz). The suitability of Nyquist pulse shaping for optical interconnects is also investigated experimentally with PAM-4 and PAM-8, at a lower symbol rate of 40 Gbaud (limited by the sampling rate of the AWG). To the best of our knowledge, the rates achieved are the highest ever using optical PAM-M formats.

Paper Details

Date Published: 7 March 2016
PDF: 12 pages
Proc. SPIE 9775, Next-Generation Optical Networks for Data Centers and Short-Reach Links III, 977506 (7 March 2016); doi: 10.1117/12.2208876
Show Author Affiliations
Stefanos Dris, National Technical Univ. of Athens (Greece)
Paraskevas Bakopoulos, National Technical Univ. of Athens (Greece)
Nikolaos Argyris, National Technical Univ. of Athens (Greece)
Christos Spatharakis, National Technical Univ. of Athens (Greece)
Hercules Avramopoulos, National Technical Univ. of Athens (Greece)


Published in SPIE Proceedings Vol. 9775:
Next-Generation Optical Networks for Data Centers and Short-Reach Links III
Atul K. Srivastava, Editor(s)

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