Analyzing network reliability up to 800G - Impact of SNR thresholds on BER for Coherent (16QAM) and Non-Coherent (PAM4) high speed transceivers under environmental variations#

Dr Gerhard Stein (Lead Research Engineer), co-author Thomas Weible (Chief Technology Officer)

• Why: As datacenter and DC-interconnect links move to 400G/800G, the margin between "link is up" and "link is silently degrading" narrows. This is one of the few operator-conference talks that quantifies that margin rather than asserting it, and the coherent-vs-PAM4 comparison maps directly onto DC/metro/WAN optics decisions the PM makes today.
• What: A measurement-driven analysis of how close to a low SNR threshold 100G/400G/800G transceivers can run while still holding a tolerable BER, and how temperature and cable length shift that threshold — used to estimate how long a link can reliably sustain a connection between two transceivers. Coherent (16QAM) and non-coherent (PAM4) parts are compared head to head (write-up based on the abstract and program page; slides are Flexoptix-branded and the data was gathered with a Flexbox, so the measurement apparatus is Flexoptix tooling).
• How: SNR is swept toward the failure threshold while BER is tracked, with temperature and cable length as controlled environmental variables, and the resulting curves are used to predict link reliability duration rather than a binary pass/fail.
• Where applicable: Broadly applicable to anyone specifying or commissioning 400G/800G optics for DC fabrics or DC-to-metro interconnect — the physics is vendor-neutral even if the measurement rig is not. Expect the practical numbers to depend on the specific transceiver families tested.