Lightmatter Introduces Industry's First Bidirectional CPX Optical Engine

Lightmatter, a leader in photonic computing, has joined the Open CPX Multi-Source Agreement (MSA) and introduced the Passage L20 CPX, the industry's first Open CPX module for AI infrastructure with bidirectional (BiDi) optical link technology. This innovation aims to address the growing constraints in AI cluster infrastructure, particularly in fiber requirements.

The Passage L20 CPX, powered by Lightmatter's near-package optics (NPO) platform, delivers 6.4 terabits per second (Tbps) in a single socketed module, halving the optical cabling in AI scale-up networks. By combining transmit and receive on a single fiber, the module uses different wavelengths of light for each direction, significantly reducing the number of fibers and connectors needed.

Nick Harris, Ph.D., Founder and CEO of Lightmatter, explained, "AI infrastructure is scaling faster than copper can follow, and co-packaged optics is the answer. CPX is the on-ramp. It gets the optics, the fiber, and the supply chain into production now, so that when CPO arrives, the hard parts are already proven."

According to Lightmatter's analysis, in a 512-GPU scale-up pod, the Passage L20 CPX can save over 200 miles of fiber, reducing the number of fibers from approximately 130,000 to 65,000. This reduction also means fewer connectors, lowering the potential failure points and saving about 15 percent of the total scale-up interconnect network cost. Additionally, the module simplifies fiber plant maintenance and reduces long-term operational costs.

Sameh Boujelbene, Vice President at Dell'Oro Group, commented, "Standardization efforts like the Open CPX MSA are critical to commercializing optics close to the package across a broad multi-vendor ecosystem. A bidirectional architecture that halves fiber count without giving up bandwidth addresses a cost and complexity problem that operators feel immediately."

The Open CPX MSA defines a standardized CPO/NPO module form factor for high-bandwidth, low-latency I/O placed directly adjacent to the host ASIC, switch, or GPU. The Passage L20 CPX is built on the Passage L-Series optical engine platform, delivering 12.8 Tbps of total bandwidth (6.4 Tbps transmit and 6.4 Tbps receive) and 32 optical lanes per direction at a 212.5 Gbps PAM4 line rate. It uses the Type 2 single RF+MP pin field defined by the MSA, reaches beyond 500 meters over single-mode fiber, follows the IEEE 802.3dj DR link architecture, and uses the OIF-CMIS management protocols. The module supports O-band wavelengths 1331 nm and 1311 nm and can pair with Lightmatter's Guide® DR laser module, or other compatible external laser sources. The Passage L20 is also available in an XPO form factor.

Passage L20 CPX module evaluation kits are anticipated to ship to customers in the first quarter of 2027. Specifications in this release are preliminary and subject to change. Performance and cost figures are based on internal testing or modeling under specific conditions, and actual results may vary by configuration and deployment.

This innovative solution from Lightmatter is expected to significantly impact the AI infrastructure landscape, making it easier and more cost-effective to scale up AI clusters.