Energy-Efficient VCSEL-based Transceivers for AI Datacenters

Author: Hideyuki Nasu, Fellow, Furukawa Electric Co., Ltd. Collection: 2026-OCP-EMEA-Summit-Photonics

Summary

Hideyuki Nasu, a Fellow at Furukawa Electric, presents the case for VCSEL (Vertical-Cavity Surface-Emitting Laser) technology as the energy-efficient optical interconnect for AI data center scale-up networks, arguing it occupies a compelling sweet spot between copper cables (short reach, high reliability) and silicon photonics (long reach, higher power). The talk is structured around three pillars: the maturity of 200 Gb/s-per-lane VCSEL technology, a thermal management solution enabling reliable VCSEL operation in CPO (Co-Packaged Optics) configurations, and demonstrated CPO transceiver prototypes using 1060-nm single-mode VCSELs with multi-core fiber (MCF).

On the technology side, Nasu documents that 850-nm GaAs VCSEL modulation rates have doubled approximately every 7–8 years from 1.25 Gb/s (802.3z, 1998) to 106.25 Gb/s (802.3db, 2022), with 200 Gb/s per lane now demonstrated at 2026 by Broadcom using 100 Gbaud PAM4. A parallel track using 1060-nm InGaAs VCSELs in a 48-channel 2D array with coupled-cavity architecture has achieved 200 Gb/s PAM4 eye patterns across all 48 channels simultaneously. Furukawa Electric's own contribution includes prototypes achieving 3.95 pJ/bit link energy at 106.25 Gb/s PAM4 over a 2-km 19-core multi-core fiber, with BER below the KP4-FEC threshold, as well as an 8-channel 106 Gb/s system using 980-nm single-mode fiber achieving 4.1 pJ/bit and maintaining open eye diagrams and sub-KP4-FEC BER at distances up to 2 km.

The thermal management challenge — historically cited as VCSELs' reliability Achilles heel — is addressed via a liquid-cooled CPO daughterboard architecture in which the transceiver case temperature is held below 40°C even when the switch ASIC dissipates up to 1,000 W. FIT (Failures In Time) data at 90% CL for 106G 850-nm VCSELs at 8 mA shows single-device FIT of 0.03 at 40°C rising to 0.14 at 85°C; for a 32-channel array the corresponding FIT values are 1.02 at 40°C and 4.48 at 85°C, which the author considers adequate for data center applications when temperature is controlled below 40°C.