Lightmatter joined the Open CPX Multi-Source Agreement (MSA) and introduced the Passage L20 CPX optical module in a September 17, 2026 announcement, which the company described as the first Open CPX module for AI infrastructure to use bidirectional (BiDi) optical link technology. Lightmatter said the module halves the fiber and connectors required in AI scale-up networks.
The Passage L20 CPX is powered by the Passage L20 optical engine, the near-package optics (NPO) platform Lightmatter announced in March, which the company said delivers 6.4 terabits per second (Tbps) in a single socketed module.
Nick Harris, Lightmatter’s founder and CEO, said in the announcement that AI infrastructure is growing beyond what copper can support, describing co-packaged optics (CPO) as the answer and CPX as the route to getting optics, fiber, and the supply chain into production ahead of it. “It gets the optics, the fiber, and the supply chain into production now, so that when CPO arrives, the hard parts are already proven,” Harris said. He said the bidirectional design carries transmit and receive over a single fiber, halving fiber requirements and, at cluster scale, speeding bring-up and reducing failures.
In a conventional optical link, one fiber carries the transmit signal and a second fiber carries the receive signal. Bidirectional technology places both directions on one fiber by giving each direction its own wavelength of light. In a 512-GPU scale-up pod, the company’s analysis found the approach takes the pod from about 130,000 fibers to 65,000, with approximately 16,000 fewer connectors, saving more than 200 miles of fiber. Lightmatter said this reduction cuts roughly 15 percent from total scale-up interconnect network cost, speeds deployment, and simplifies fiber plant maintenance.
Copper Reach and the 512-GPU Pod Analysis
The announcement draws on a technical brief that Lightmatter authors Taylor Groves and Lars Johnsson published on September 14, 2026. The brief states that at 200 gigabits per second per lane, copper’s reach of roughly one meter limits an electrically connected scale-up domain to one or two racks, or 72 to 144 GPUs. Linking 512 or more accelerators across racks, the authors wrote, leaves photonic interconnects as the only viable option.
The brief calculates that a 512-GPU pod built with conventional unidirectional (UniDi) optics carries 131,072 data fibers and 32,768 connector endpoints that must be cleaned and tested during deployment, work the authors estimate at more than 1,000 hours for a single pod. According to the brief, BiDi reduces the pod to approximately 65,536 fibers and eliminates 16,384 connectors along with the shuffle boxes that route them, cutting the number of passive optical components that can fail by about half. The authors estimate the smaller fiber plant can also remove more than a week of integration and test time from each pod.
The brief attributes roughly a 15 percent reduction in total scale-up network spending for the 512-GPU cluster to BiDi, a figure spanning switches, fibers, connectors, and shuffle interconnects. It also cites a May 2024 Broadcom white paper that found optics cost savings of 15 percent for a 512-GPU cluster, with savings growing alongside fiber length and pod footprint.
Passage L20 CPX Specifications
The Passage L20 CPX is designed to deliver 12.8 Tbps of total bandwidth (6.4 Tbps transmit and 6.4 Tbps receive) across 32 optical lanes per direction at a 212.5 Gbps PAM4 line rate. The module implements 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 is managed through OIF-CMIS protocols.
The module operates on the 1331- and 1311-nanometer O-band wavelengths and works with Lightmatter’s Guide DR laser module or other compatible external laser sources. The Passage L20 is also available in an XPO form factor. According to the technical brief, the two BiDi wavelengths sit 20 nanometers apart, and each optical engine is programmable at the port level to transmit on either wavelength, a design the authors said leaves switch topology and radix unchanged.
Lightmatter noted that the specifications in the release are preliminary and that its performance and cost figures are based on internal testing or modeling under specific conditions.
Open CPX MSA Purpose and Membership
The Open CPX MSA defines a standardized form factor for co-packaged and near-package optical modules that sit directly beside the host ASIC, switch, or GPU to provide high-bandwidth, low-latency input and output, with modules mounting to the circuit board or substrate. According to the announcement, because faceplate area caps bandwidth density in pluggable systems, moving near-package optics next to the processor lifts that cap while cutting cost and power relative to conventional pluggable transceivers.
The Open CPX MSA presents itself as an international organization working to ease adoption of optical engines through shared mechanical and performance parameters for ecosystem suppliers and end users. Its stated goal is to cut power, cost, and latency while raising the bandwidth density, capacity, and reliability of high-speed co-packaged and near-package interconnects in AI data center applications. The group has published the Open CPX Specification 1.0 covering co-packaged and near-package connector and optics modules. Its site lists Ciena, Coherent, Marvell, Molex, Samtec, and TeraHop as founding members and lists Lightmatter among contributor members that also include Dell, Hewlett Packard Enterprise, Intel, and Qualcomm.
Sameh Boujelbene, vice president at Dell’Oro Group, said in the announcement that as AI clusters grow, the binding constraints are moving from compute to surrounding physical infrastructure such as power, cabling, and pod bring-up time. “Standardization efforts like the Open CPX MSA are critical to commercializing optics close to the package across a broad multi-vendor ecosystem,” Boujelbene said, adding that halving fiber counts without sacrificing bandwidth speaks to a cost and complexity problem operators face directly.
Lightmatter said Passage L20 CPX module evaluation kits are anticipated to ship to customers in the first quarter of 2027.
