--- title: "Co-Packaged Optics Explained: What It Changes in AI Networks" url: https://syntaxradar.com/radar/co-packaged-optics-silicon-photonics-gpu-cluster-bandwidth-wall author: "Abdul Rehman, Lead Systems Architect and Technical Director" publishedAt: 2026-10-25T08:05:00.000Z dateModified: 2026-10-29T10:33:58.900Z category: "#HARDWARE-CHIPS" topic: "co-packaged optics" primarySource: https://convergedigest.com/nvidia-debuts-spectrum-x-and-quantum-x-photonics-switches/ summary: "Co-packaged optics explained: what it is, how Nvidia and Broadcom use it in AI switches, the power savings they claim, and the trade-offs still open." --- # Co-Packaged Optics Explained: What It Changes in AI Networks **Short answer:** Nvidia and Broadcom have announced network switches that put the light-emitting parts inside the switch package instead of plug-in modules. Both claim large power savings for AI data centers, though the figures are vendor-reported. **Takeaway:** Co-packaged optics moves the light conversion next to the switch chip to save power, but the savings are vendor-reported and serviceability remains the open question. **Key figures (as reported by the source):** - Nvidia claimed power efficiency gain: 3.5x - Broadcom claimed optics power reduction: More than 70% - Broadcom Davisson switching capacity: 102.4 Tbps Co-packaged optics (CPO) is a way of building network switches so that the parts that turn electricity into light sit inside the same package as the switch chip, instead of in plug-in modules on the front panel. Nvidia and Broadcom have both announced switches built this way, and both say the main payoff is lower power use in AI data centers. Those power figures come from the vendors themselves, and independent measurements are scarce. ### What is co-packaged optics? A network switch is the box that moves data between servers. Today, most switches send data to a plug-in module called a pluggable transceiver. The module converts the electrical signal into pulses of light that travel down a fiber cable. This design moves that conversion next to the switch chip. According to [Converge Digest's coverage of Nvidia's launch](https://convergedigest.com/nvidia-debuts-spectrum-x-and-quantum-x-photonics-switches/), the optical parts are integrated into the switch package, so fiber connects directly to it and the separate pluggable modules disappear. The optical parts are built with silicon photonics, which means making tiny light-handling components (modulators that encode data onto light) on silicon, the same material as ordinary chips. That lets them be manufactured with chip-making equipment. ### Why do AI clusters need a different way to connect chips? Training a large AI model means thousands of GPUs (graphics processors) constantly swapping data. The network that links them has to carry enormous traffic, and each link burns power. A [Wevolver explainer](https://www.wevolver.com/article/what-is-co-packaged-optics-architecture-benefits-challenges-and-performance) describes the structural problem with pluggables. A signal has to cross roughly 15 to 30 cm of circuit board trace to reach the module on the front panel. At today's speeds that requires power-hungry signal-cleaning chips called DSPs (digital signal processors) and retimers. The article also notes that the front panel only has room for so many modules, and each one adds heat. Placing the optics beside the switch chip shortens the electrical path to millimeters, according to the same source. A shorter path needs less signal cleanup, and less cleanup means less power. ![Rows of server racks with bundles of fiber optic cables in a dimly lit data center aisle](https://images.unsplash.com/photo-1544197150-b99a580bb7a8?w=1600&auto=format&fit=crop&q=85) ### How much power does co-packaged optics actually save? The vendors report large savings, and the numbers differ by product and by what is being measured. Nvidia says its Spectrum-X Photonics and Quantum-X Photonics switches deliver 3.5 times better power efficiency than traditional networking, as [Converge Digest reports](https://convergedigest.com/nvidia-debuts-spectrum-x-and-quantum-x-photonics-switches/). The same article quotes Nvidia chief executive Jensen Huang saying the technology could cut up to 60 MW per AI data center, which it equates to the power of 100 Rubin Ultra racks. Broadcom's figures, relayed by [Converge Digest from its Tomahawk 6 Davisson launch](https://convergedigest.com/broadcom-unveils-102-4-tbps-davisson-cpo-switch-for-ai-clusters/), say optics power is more than 70% lower than with pluggables and overall interconnect power is 3.5 times lower. The Wevolver article cites an experiment in which a 30 W pluggable was replaced by a 9 W co-packaged link, a 70% reduction. It also lists energy per bit (the power needed to move one bit of data) of 15 to 20 picojoules for pluggables against 5 to 10 for co-packaged optics. A picojoule is a trillionth of a joule. These are vendor and research claims, and none comes from an audited production data center. The "3.5 times" and "70% lower" figures describe different slices of the system, so they cannot be added or compared directly. ### What did Nvidia and Broadcom actually announce? Nvidia announced its photonics switches at GTC in March 2025. According to Converge Digest, Quantum-X Photonics is a liquid-cooled InfiniBand switch with 144 ports at 800 Gbps each, and Spectrum-X Photonics is an Ethernet switch with up to 400 Tbps of total bandwidth. (A Tbps is a trillion bits per second.) The article lists partners including TSMC, Coherent, Corning, Foxconn, Lumentum and SENKO. It says Quantum-X was due in 2025 and Spectrum-X in 2026. Broadcom introduced Tomahawk 6 Davisson on October 8, 2025, calling it its third-generation CPO Ethernet switch. Converge Digest reports 102.4 Tbps of switching capacity, built from 16 optical engines of 6.4 Tbps each. Broadcom says a fourth generation with 400 Gbps per channel is in development. Broadcom's reliability claim comes with a named customer. Converge Digest reports that Meta confirmed one million cumulative 400G CPO port-device hours with zero link flaps (brief drops in a connection). ![Engineer in a clean room inspecting a small silicon wafer under bright light](https://images.unsplash.com/photo-1518770660439-4636190af475?w=1600&auto=format&fit=crop&q=85) Converge Digest describes Nvidia's switches as using microring resonator modulators, tiny ring-shaped structures that switch light on and off to carry data, and says they are made with TSMC's 3D COUPE process, which stacks electronic and photonic chips together. That stacking is what lets the optical engine sit so close to the switch silicon. Broadcom describes a different route to the same goal. Its Davisson chip combines the Tomahawk 6 switch silicon with sixteen 6.4 Tbps silicon photonics engines, per the same outlet. Both designs share the central idea of fiber leaving straight from the package. ### Why are lasers moved out of the package? Lasers are the least dependable part of an optical link, and they produce heat. The Wevolver article says early designs put lasers on the photonic chip itself, where they were the least reliable component and added heat near the modulators and the switch chip. Most designs have since shifted to external laser sources that can be replaced on their own. Broadcom's Davisson follows this pattern with field-replaceable ELSFP laser modules, which Converge Digest says keep the light source away from the hot switch package and improve serviceability. External lasers bring a cost of their own. Light has to travel by fiber from the laser to the optical engine, and Wevolver notes that the loss along that path has to be managed, so moving the lasers away from the heat solves one problem while adding another. ### What are the downsides of co-packaged optics? Serviceability is the most cited concern. A pluggable can be swapped in seconds, while Wevolver says permanently bonded fiber attachments need far more intervention, and detachable versions add signal loss, which means a failed part is harder to deal with than a plug-in module that can simply be swapped. The article reports that operators cite this as a reason to stay with pluggables. Heat is another. Photonic parts are sensitive to temperature, and Wevolver says wavelength drift can hurt performance, which often pushes designs toward liquid cooling. Nvidia's Quantum-X switch is liquid-cooled, as noted above. The same article lists fiber density, manufacturing yield, immature standards and higher per-port cost as open challenges. Wevolver expects pluggables to coexist with co-packaged optics for most of this decade. ### What to watch next Wevolver reports Quantum-X Photonics reaching availability in early 2026 and Spectrum-X in the second half of 2026, while its adoption estimates for the larger scale-up links inside a GPU cluster range from 2027 to 2030. Wevolver notes that connecting tens of thousands of GPUs with pluggables would consume hundreds of megawatts, so even a partial cut would matter to operators who are already limited by the power they can get from the grid. - Independent power measurements from an operator running co-packaged switches at scale. - Field failure and replacement data, since serviceability is the main objection. - Broadcom's 400 Gbps-per-channel generation and whether it ships on schedule. - Whether the technology moves from switches to the links between GPUs themselves. For background on the clusters this network has to serve, see [what xAI's Colossus supercomputer looks like](/radar/inside-grok-bot-xai-colossus-supercomputer-real-time-ai) and how Cerebras approaches very large models. ## Frequently asked questions ### What is co-packaged optics? Co-packaged optics is a switch design in which the components that convert electrical signals to light sit in the same package as the switch chip. Fiber connects straight to that package, so the plug-in transceiver modules on the front panel are no longer needed, which is meant to cut power use and space. ### How is co-packaged optics different from pluggable optics? Pluggable optics put the electrical-to-light conversion in a removable module on the front panel, so signals travel 15 to 30 cm across a circuit board first, according to Wevolver. Co-packaged optics shortens that path to millimeters, which reduces the signal cleanup and power needed, but makes swapping parts harder. ### Who is building co-packaged optics switches? Nvidia announced Spectrum-X Photonics and Quantum-X Photonics switches in March 2025, working with partners including TSMC, Coherent, Corning, Foxconn, Lumentum and SENKO. Broadcom introduced its third-generation Tomahawk 6 Davisson switch with 102.4 Tbps of capacity on October 8, 2025, according to Converge Digest. ### Will co-packaged optics replace pluggable transceivers? Not soon. Wevolver expects pluggables to coexist with co-packaged optics for most of this decade, and cites serviceability, heat, cost and immature standards as obstacles. Adoption estimates for links inside GPU clusters range from 2027 to 2030. ## Source Based on Nvidia and Broadcom launch coverage. https://convergedigest.com/nvidia-debuts-spectrum-x-and-quantum-x-photonics-switches/ --- Published on SyntaxRadar (https://syntaxradar.com). Canonical URL: https://syntaxradar.com/radar/co-packaged-optics-silicon-photonics-gpu-cluster-bandwidth-wall. Last modified 2026-10-29T10:33:58.900Z.