400G ZR+ BiDi does not exist, it can't hurt you. Or can it?#

Nicola von Thadden (PFALZKOM), Arjan Koopen (i3D.net / Stichting EventInfra)

• Why: A creative, out-of-spec experiment: a 400G link over a single fiber using ZR+ coherent optics, since 400G BiDi doesn't exist as a product. Directly relevant to the PM's optics interests — demonstrates what coherent optics tolerate outside their specified operating envelope, useful when fiber count is constrained.
• What: For the WHY2025 hacker summer camp in the Netherlands, the speakers built a 400G link over a single fiber. Since 400G BiDi doesn't exist, they built something out-of-spec using ZR+ optics. A lightning talk. (from abstract and page only — no slides or detailed technical writeup available)
• How: Not detailed in the abstract — presumably two wavelengths (one per direction) with coherent ZR+ modules on a single fiber pair, a non-standard but functional configuration.
• Where applicable: Limited direct applicability — proof-of-concept in a temporary event network. The demonstrated envelope-pushing of coherent modules is useful knowledge for DCI planning where fiber count is constrained or when troubleshooting marginal coherent links.