Microring DWDM has long been seen as the densest but hardest-to-control route. NVIDIA's ECOC 2026 paper takes "too hard to control" apart piece by piece: nine rings find nine lasers on a chip that can't see the spectrum, then re-shuffle live through an 80°C temperature drift, with even the forwarded-clock handover running at zero bit errors.

The CPO race is no longer about optics—it is about whether packaging can reach volume at the next tier. This Nature Electronics review plots the pJ/bit of 2D, 2.5D, 3D TSV, hybrid bonding and monolithic integration on one chart, two orders of magnitude apart. We walk through all 24 figure panels and 2 tables, and flag where Taiwan's supply chain really fits.