Lightmatter integrates optical engines into open rack hardware

Lightmatter has demonstrated two accelerator interconnect systems using its Passage co-packaged optical engines and Guide DR laser modules in hardware aligned with Open Compute Project rack specifications. The designs comprise a 204.8Tbps optical switch tray developed with Flex and a separate 102.4Tbps accelerator compute tray assembled through another manufacturing collaboration. Both are being shown at the 2026 Open Compute Project Global Summit, but their development and validation status differ.

The switch integrates eight bidirectional Passage engines in a liquid-cooled enclosure occupying one rack unit. Lightmatter and Flex developed it as a production validation platform to establish how co-packaged optics can fit within a manufacturable, standardised switch assembly. Lightmatter claims two to four times the rack faceplate bandwidth density of comparable arrangements using conventional external-laser small form factor pluggables and unidirectional fibre harnesses. The comparison is a company claim about packaging density, not a measured reduction in total system energy consumption.

The second system is a two-rack-unit accelerator tray with four accelerator ASICs, two CPUs and a combined 102.4Tbps scale-up optical interconnect. Its four bidirectional Passage engines take light from Guide DR laser modules. Rather than being a Flex-developed switch, this separate prototype uses Data Center Modular Hardware System infrastructure provided by another large original design manufacturer, whose name Lightmatter has not disclosed.

In conventional high-bandwidth rack designs, short copper connections carry signals between processors or switching components. Higher transmission speeds increase the effects of conductor losses, crosstalk and equalisation requirements, while longer copper routes become increasingly difficult to engineer. Moving selected scale-up connections onto optical paths changes those constraints, but it adds photonic engines, laser sources, fibre routing and serviceable interfaces that must be integrated into the same mechanical and cooling envelope.

Co-packaged optics place optical conversion close to high-performance semiconductor devices, shortening some electrical paths. Lightmatter uses separate Guide DR modules to supply the laser light, while Passage engines provide bidirectional optical connectivity within the switch or compute assembly. Separating the light source from the co-packaged engine has implications for service access and heat removal; the full design must still account for optical coupling loss, connector reliability and the combined power of the electrical and optical portions.

Both trays follow Open Rack Version 3 and Modular Hardware System arrangements, allowing their mechanical interfaces and supporting infrastructure to be evaluated in a common rack environment. The compute prototype demonstrates blind-mating optical connections when inserted into the rack. Such an arrangement must maintain alignment, acceptable insertion loss and repeatable connections across removal and replacement cycles if it is to offer the servicing behaviour expected of production compute equipment.

Lightmatter has also incorporated its detachable vClick optics into the compute tray. Developed with SENKO, the optical interface is intended to make dense fibre arrays compatible with advanced semiconductor packaging and replacement operations. SENKO and Corning provide fibre connections and connector elements across the two systems. The contribution of these partners is distinct from Flex’s manufacturing work on the switch tray, and the arrangement has not been reported as a single jointly developed product.

The 204.8Tbps and 102.4Tbps figures describe specified aggregate optical bandwidth in the respective demonstrators. They do not establish realised application throughput, accelerator utilisation or performance under an installed cluster workload. Environmental qualification, thermal performance, fibre management and interoperability across different suppliers remain relevant tests as the designs move from integrated demonstrations towards possible commercial systems.

Lightmatter has been developing the wider Passage and Guide architecture and participating in the Open Silicon Photonics for AI Systems initiative, whose supporters span component, connectivity and manufacturing companies. The new milestone is the placement of those technologies in open rack switch and compute form factors, rather than the first announcement of the individual engines or laser modules. The switch now has a stated production validation purpose, while the accelerator tray remains a proof of concept; neither announcement provides a customer shipment timetable.