Fun with Optics#

Patrick Prangl (Arista Networks)

• Why: A concise, current state-of-the-industry view on the optics-to-1600G transition — covering 800GbE standardization, LPO/LRO/CPO, and ZR/ZR+ DCI evolution. Essential physical-layer DC context for anyone planning high-density switching and interconnect over the next 3–5 years.
• What: A survey covering merchant silicon roadmaps (51.2T shipping, 102.4T expected 2025, 204.8T in 2027), 800GbE standards status (IEEE 802.3ck/df, 800GBASE-ETC-R), the 50G→100G→200G SerDes transition, Linear-drive Pluggable Optics (LPO) as a 50%+ power-reduction alternative to DSP-based transceivers, and the ZR/ZR+ coherent DCI ecosystem from 100G-ZR to 1.6T.
• How: LPO removes the DSP from the module (typical 800G-DR8 at 7.5W vs 14–16W DSP-based), relying on clean <20dB die-to-die electrical channels — the same channel requirement as NPO and CPO, with packaging position being the only difference. At 200G-PAM4, LPO needs careful channel design (fly-over cables on switches). ZR/ZR+ coherent evolution extends from 400G-ZR (120km) through 800G-ZR/ZR+ (up to 1000+km) to 1.6T Coherent Lite, with spectrum widths growing from 75GHz to 300GHz.
• Where applicable: Any DC operator planning 800G/1600G port deployments, especially for AI clusters where power per port is a constraint. Arista-branded but the data draws on MSA specs, IEEE standards, and multi-vendor plug-fest results.