CPO for AI Data Centers: Building High-Bandwidth Optical Networks

Artificial intelligence infrastructure depends on fast, reliable communication between accelerators, memory systems and network switches. As AI clusters expand, the electrical connections used to move data across high-speed network equipment face increasing demands for bandwidth, signal integrity and energy efficiency. Co-packaged optics (CPO) addresses part of this challenge by placing optical engines close to a high-performance switch ASIC, shortening the electrical paths between switching silicon and optical conversion.

For AI data centers, CPO is a network architecture development rather than simply a replacement for a conventional optical transceiver. It changes the physical location of optical interfaces, the way electrical and photonic components are integrated, and how cooling, fiber attachment, maintenance and system validation are organized. Its practical value depends on the target network, bandwidth requirements, package design and operational priorities.

1. Why AI Data Centers Need Higher-Bandwidth Optical Interconnects

Large AI workloads distribute computation across many accelerators. Training jobs exchange model parameters, gradients and intermediate data, while inference systems move requests, cached data and intermediate results across compute and storage resources. Network performance therefore influences how effectively expensive computing resources remain utilized.

As the number of accelerators and the bandwidth of each connection increase, network equipment must support greater aggregate throughput without allowing interconnect power, cabling complexity or signal degradation to grow uncontrollably.

• Increasing port bandwidth: High-speed 400G, 800G and emerging 1.6T interfaces place greater demands on electrical channels and optical integration.

• Higher switch capacity: Dense switching platforms must connect more high-bandwidth ports within limited rack space and power budgets.

• Energy efficiency: Electrical signal conditioning, optical conversion, cooling and other supporting functions contribute to total network energy consumption.

• Signal integrity: Faster electrical interfaces are increasingly sensitive to channel loss, reflections, crosstalk, equalization and timing margins.

• Operational scale: Fiber routing, component access, fault isolation and replacement procedures become more important as the number of optical connections grows.

CPO targets the electrical and optical interface boundary inside the network device. Rather than routing high-speed electrical signals from a central switch ASIC across a relatively long board path to front-panel optical modules, CPO places optical engines close to the ASIC. Optical fibers then carry the converted signals toward other network endpoints.

2. How CPO Architecture Works

A CPO platform integrates the switch ASIC and multiple optical engines within a closely coupled package or package-level assembly. Electrical signals travel over short connections from the switching silicon to the optical engines, where electrical-to-optical conversion takes place. In the receive direction, incoming optical signals are converted into electrical signals and passed toward the switching circuitry.

The optical engines may incorporate photonic integrated circuits, electronic driver and receiver components, and fiber-coupling structures. Depending on the architecture, the light source may be integrated or provided by an external laser source. Optical fibers remain essential for carrying data beyond the package.

3. CPO in AI Scale-Up and Scale-Out Networks

AI data center networks typically involve different communication domains. Scale-up networking connects processors or accelerators within a tightly coupled compute system, while scale-out networking connects servers and racks through a switching fabric. The physical requirements, protocols and preferred interconnect technologies can differ significantly between these domains.

Scale-up interconnects

Scale-up systems provide high-bandwidth communication among accelerators or other closely coupled compute components. Their priorities can include high aggregate bandwidth, tightly controlled latency, synchronization and efficient data exchange. Optical I/O and CPO-related approaches may support future high-density connections where electrical reach and power become limiting factors.

However, a CPO-capable switch is not equivalent to an optical interface directly integrated into every accelerator. The complete scale-up solution depends on the compute architecture, switching topology, protocol, reach and the electrical or optical interfaces supported by each endpoint.

Scale-out networking

Scale-out networks connect servers, racks and larger groups of AI systems through network switches. Here, CPO can place optical engines near a high-capacity switch ASIC while providing many external optical connections through fiber.

This architecture is relevant when switch bandwidth and front-panel connectivity become difficult to scale within existing power and space limits. It can support dense optical fabrics, but system-level results still depend on link reach, routing topology, transceiver or optical-engine efficiency, switch power, cabling and network design.

4. The Main Benefits of CPO for AI Infrastructure

Shorter electrical paths

Conventional pluggable optics require high-speed electrical signals to travel from the switch ASIC through package connections, board traces and the module interface. CPO places the optical engine much closer to the ASIC, reducing the length of this high-speed electrical channel. A shorter channel can reduce insertion loss and the equalization effort needed to maintain signal integrity.

The achievable benefit depends on the electrical interface, package design and optical engine. It should be evaluated using the complete channel and measured power rather than assuming that every implementation delivers the same improvement.

Greater bandwidth density

Moving optical engines away from the front-panel module cages can create additional flexibility in arranging high-bandwidth optical interfaces around the switching silicon. This is important as network designers seek higher aggregate bandwidth within limited package and system footprints.

Higher bandwidth density also increases the demands on fiber attachment, optical routing, thermal design and automated manufacturing. Packaging and assembly capability must scale alongside the number of optical channels.

Potential reduction in link power

Reducing electrical channel length can lower the power associated with electrical signal conditioning, depending on the implementation. A CPO design may also change the power distribution between the switch package, optical engines and external laser subsystem.

System comparisons must include all relevant power consumers, including optical engines, laser sources, cooling hardware and supporting electronics. Lower power in one segment does not automatically translate into a proportionate reduction in total data center energy use.

Improved electrical signal conditions

Shorter high-speed electrical paths can reduce channel-loss and signal-integrity challenges. This may give designers more flexibility when allocating bandwidth across optical lanes, provided the package, SerDes and optical engine are engineered as a coordinated system.

5. CPO Compared with Pluggable Optical Transceivers

Pluggable transceivers and CPO solve related but different system-design problems. Pluggable modules provide replaceable optical interfaces at the equipment front panel. CPO places optical engines close to the switch ASIC to shorten electrical paths and increase integration density.

Pluggable optics remain valuable where modular replacement, flexible port configuration and established maintenance processes are priorities. CPO becomes attractive when electrical channel limits, bandwidth density and system-level power objectives justify a more tightly integrated architecture.

For current network designs using conventional optical modules, relevant product categories include 800G OSFP optical transceivers, 800G QSFP-DD optical transceivers and 1.6T OSFP-RHS optical transceivers. These pluggable form factors are distinct from CPO and should be selected according to the target equipment and interface requirements.

6. External Laser Sources and Optical Reliability

An external laser source (ELS) separates the laser from the optical engine and the hottest part of the switch package. Light is delivered to the optical engine through a fiber connection or a dedicated optical interface. This can help isolate laser heat and allow the laser subsystem to be serviced separately in suitable architectures.

External laser placement does not eliminate every thermal or reliability concern. The optical engine still contains heat-generating components, and the light-delivery path introduces requirements for optical power, coupling loss, connector or blind-mate design, fiber routing and laser-source reliability.

Important design considerations include:

• Optical power margin: Ensure that source output and delivery losses meet the optical engine's input requirements under expected operating conditions.

• Wavelength and stability: Validate source characteristics against the photonic platform and supported optical channel plan.

• Redundancy: Define how the system handles laser-source degradation or failure, including whether redundancy is supported by the architecture.

• Service access: Make external sources accessible without disturbing sensitive package-level optical connections.

• Fiber reliability: Control connector cleanliness, bend radius, mechanical stress and coupling repeatability.

7. Thermal Management and Package Integration

AI switches can concentrate substantial power in the ASIC, while optical engines operate close enough to experience thermal interaction. The result is a package where electronic heat removal and photonic temperature stability must be planned together.

Depending on total power and the system design, CPO may use air cooling, liquid-cooled cold plates or hybrid cooling. A cooling method that controls the ASIC temperature does not necessarily provide the best temperature uniformity across every optical engine.

Thermal design should evaluate local hotspots, temperature gradients, material expansion and the stability of fiber-to-chip coupling. Thermal interface materials, heat spreaders and cold-plate pressure must be selected to control thermal resistance without introducing unacceptable package stress or deformation.

Qualification should combine thermal simulation with physical tests. Measurements can include component temperatures, optical output, wavelength where relevant, link error performance and cooling-system behavior under realistic operating profiles. The acceptable limits must follow the specifications of the implemented components and system.

8. Manufacturing, Testing and Serviceability

CPO changes the way optical interfaces are assembled and tested. Because the optical engines are integrated close to the switch ASIC, manufacturing yield and repair strategy become closely linked to package-level processes. Optical coupling and high-speed electrical performance must be verified across a dense assembly rather than only at the front-panel module level.

Manufacturing and qualification priorities

• Known-good components: Characterize photonic and electronic components before final integration where the manufacturing flow permits.

• Assembly alignment: Control fiber-array and optical-engine positioning to achieve repeatable coupling performance.

• Electrical validation: Measure high-speed channel performance, including insertion loss, return loss and crosstalk where applicable.

• Optical validation: Verify output power, receiver performance and bit error rate under the specified operating conditions.

• Thermal qualification: Test temperature stability, thermal cycling and optical performance across the required environmental range.

• Repair strategy: Define whether a failure requires replacement of an external laser, a fiber assembly, an optical subassembly or a larger package or system.

Automated test coverage and fault isolation are particularly important for large AI deployments. A design that offers high bandwidth but requires complex package replacement for routine faults may introduce operational costs that reduce its system-level value.

9. Practical CPO Deployment Considerations

CPO adoption should be based on measurable system requirements rather than bandwidth targets alone. Network architects need to compare the electrical, optical, thermal and operational characteristics of the complete platform against the existing deployment model.

1. Define the target network. Specify whether the use case involves scale-up, scale-out, inter-rack connectivity or another optical interconnect domain.

2. Set bandwidth and reach requirements. Determine aggregate switch capacity, per-link rate, fiber type, transmission distance and supported optical interfaces.

3. Build a complete power model. Include the switch ASIC, optical engines, laser sources, signal-conditioning circuits and cooling infrastructure.

4. Evaluate package and cooling limits. Check heat density, optical temperature sensitivity, fiber attachment and service access.

5. Verify interoperability. Confirm protocol support, optical characteristics, management functions and system-level compatibility rather than relying on bandwidth labels alone.

6. Plan qualification and maintenance. Establish optical, electrical, thermal and reliability tests together with practical fault-isolation and replacement procedures.

CPO is most compelling where its integration benefits solve a clearly identified system constraint. If the deployment instead prioritizes flexible module replacement, incremental upgrades or familiar qualification procedures, pluggable optics may remain the more suitable choice.

10. Frequently Asked Questions

11. Conclusion

CPO is an important architectural option for AI data centers that need higher-bandwidth switching, dense optical interfaces and more efficient high-speed electrical interconnects. By placing optical engines close to the switch ASIC, it can reduce electrical channel length and create opportunities to improve bandwidth density and link-level energy efficiency.

These benefits come with additional design requirements in thermal management, optical coupling, package integration, test coverage and field maintenance. External laser sources and coordinated electrical-optical-thermal design can help address some of these challenges, but the complete system must still be validated against its network and operational requirements.

For existing high-speed optical networks, selecting between CPO and pluggable optics requires a system-level assessment of bandwidth, reach, power, reliability and serviceability. The right architecture is the one that meets the target AI workload and deployment constraints with a verifiable performance and maintenance strategy.

For optical interconnect and transceiver-related inquiries, review the optical transceiver product catalog or Contact C-LIGHT.