28 Gbaud PAM4 Real Time Optical Datacom Link up to 10 km (2018)

  
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John Pertessis, Shubhashish Datta, and Abhay Joshi
Discovery Semiconductors, Inc. 119 Silvia Street, Ewing, NJ 08628, USA

ABSTRACT

We present a forward error correction (FEC)-assisted, 10 km long, 28 Gbaud PAM4 optical link having error free performance over a wide dynamic range of -10 dBm to 0 dBm received optical power. The link was formed by driving a 1550 nm externally modulated laser with a commercial PAM4 transceiver chip. The optical signal was transmitted over 10 km long dispersion compensated fiber, fed to a low-noise 28 GHz linear receiver having variable gain, and routed back to the PAM4 transceiver chip. Real time bit error rate measurements demonstrate the advantage of employing linear receivers having automatic gain control (AGC).

INTRODUCTION

Ubiquitous 25 Gbps Non-Return to Zero Amplitude Shift Keyed (NRZ-ASK) optical links are not sufficient for satisfying the ever-increasing demand of data throughput in datacom severs. Several communication standards, including 100G Ethernet and Infiniband EDR, allow aggregating multiple parallel 25 Gbps lanes and enhance the data throughput. However, the maximum number of lanes that can be coalesced is ultimately restricted by interconnect density and crosstalk considerations. Increasing the NRZ-ASK bit rate to say 50 Gbps significantly increases the cost of the components, the printed circuit board, and connector technology to maintain necessary signal integrity, both in terms of signal to noise ratio (SNR) as well as crosstalk for multilane systems. Four-level Pulse Amplitude Modulation (PAM4) has emerged as an attractive alternative to NRZ-ASK for doubling the data throughput without increasing the analog bandwidth requirements, which will benefit both commercial datacom and net-centric defense platforms. This modulation format has been recognized as the path forward to achieve data rate of up to 400 Gbps by the IEEE 400 GbE standard [1, 2].
We present a forward error correction (FEC)-assisted, 10 km long, 28 Gbaud PAM4 optical link having error free performance over a wide dynamic range of -10 dBm to 0 dBm received optical power. The link was formed by driving a 1550 nm externally modulated laser with a commercial PAM4 transceiver chip. The optical signal was transmitted over 10 km long dispersion compensated fiber, fed to a low-noise 28 GHz linear receiver having variable gain, and routed back to the PAM4 transceiver chip. Real time bit error rate measurements demonstrate the advantage of employing linear receivers having automatic gain control (AGC).

REFERENCES


Event: SPIE Defense + Commercial Sensing Conference (15 - 19 April), 2018, Orlando, Florida, United States

 

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