NPO vs CPO

Near-Packaged Optics (NPO) and Co-Packaged Optics (CPO) are two advanced optical interconnect architectures developed to address the electrical and thermal challenges created by rapidly increasing switch and accelerator bandwidth.

Both architectures move optical conversion closer to high-speed silicon than conventional front-panel pluggable optics. The fundamental difference is the degree of integration. NPO places the optical engine close to the host ASIC while keeping it physically separate from the ASIC package. CPO integrates the optical engines much more closely with the switching ASIC, typically on a common package or closely coupled package substrate.

This difference affects electrical reach, signal integrity, power efficiency, thermal management, serviceability, manufacturing, system design, and future scalability.

1. What Is NPO?

NPO stands for Near-Packaged Optics. The optical engine is positioned near the host ASIC or switching silicon, reducing the length of the high-speed electrical connection between the ASIC and optical interface.

NPO can use advanced board-level or near-package integration while keeping the optical engine separate from the ASIC package. The exact implementation can vary between system architectures.

2. What Is CPO?

CPO stands for Co-Packaged Optics. In a CPO architecture, the optical engine is integrated much more closely with the switching ASIC, generally through a common package or tightly coupled package-level structure.

The primary objective is to minimize the electrical distance between the ASIC SerDes and optical conversion point.

3. NPO vs CPO at a Glance

4. The Fundamental Difference

The simplest way to distinguish NPO from CPO is optical-engine placement.

NPO places the optical engine near the ASIC but normally keeps it physically separate. CPO integrates the optical engine much more tightly with the ASIC package.

This makes NPO an intermediate architecture between conventional pluggable optics and fully co-packaged optics.

5. Traditional Pluggable Optics

A conventional optical architecture can be simplified as:

ASIC → PCB → Electrical Connector → Optical Module → Fiber

The optical module is positioned at the front panel. At very high electrical lane rates, the distance between the ASIC and optical module can become a major signal-integrity constraint.

6. NPO Architecture

A simplified NPO architecture can be represented as:

ASIC → Short Electrical Path → Near-Package Optical Engine → Fiber

The optical conversion point is moved substantially closer to the ASIC, reducing the electrical channel that needs to carry the highest-speed signal.

7. CPO Architecture

A simplified CPO architecture can be represented as:

ASIC + Optical Engines → Fiber

The optical engines are placed directly on or very close to the ASIC package, significantly reducing the electrical distance between the SerDes and optical conversion circuitry.

8. Why Electrical Distance Matters

High-speed electrical signals experience loss and distortion as they travel through PCB traces, connectors, packages, vias, and other interconnect structures.

As lane speeds increase toward 200G and beyond, the available electrical channel margin becomes increasingly limited. Shortening the electrical path can therefore be an important architectural strategy.

9. NPO Reduces Electrical Reach

NPO reduces the distance that very high-speed electrical signals need to travel before being converted into optical signals.

This can reduce insertion loss, reflections, crosstalk, and other channel impairments and can provide greater margin for high-speed SerDes operation.

10. CPO Minimizes Electrical Reach Further

CPO takes the same principle further by placing the optical engine immediately adjacent to the ASIC package.

This greatly reduces the electrical connection between the switch silicon and optical engine and can become increasingly valuable as electrical lane rates continue to rise.

11. NPO and Signal Integrity

Signal integrity is one of the main reasons NPO is being considered for next-generation systems.

By moving the optical engine closer to the ASIC, NPO can shorten the PCB electrical path and reduce some of the loss that would otherwise occur between the ASIC and a front-panel module.

12. CPO and Signal Integrity

CPO minimizes the electrical path even further. The high-speed electrical signal can be converted to optical form very close to the ASIC.

This can provide strong electrical advantages for extremely high-speed interfaces where conventional board-level routing becomes increasingly difficult.

13. NPO vs CPO and SerDes

Both architectures are closely connected to host SerDes design.

NPO reduces the electrical channel requirements by moving optics closer to the ASIC, while CPO minimizes that channel to an even greater degree. The result is a tighter relationship between the ASIC, optical engine, package, and system design.

14. Power Consumption

Power efficiency is another major reason to investigate NPO and CPO.

When electrical channels become longer and faster, more signal-conditioning power can be required. Moving optics closer to the ASIC can reduce some of this electrical transmission burden.

The actual power advantage depends on the complete architecture and should be evaluated at system level.

15. NPO Power Characteristics

NPO can reduce power associated with long high-speed electrical channels while maintaining more separation between the optical engine and ASIC than CPO.

This provides a balance between electrical efficiency and implementation flexibility.

16. CPO Power Characteristics

CPO can provide a very short electrical path and therefore has strong potential for energy-efficient high-bandwidth interconnects.

However, CPO also introduces additional package, thermal, manufacturing, and optical-management requirements that can influence total system power.

17. NPO vs CPO Latency

Both NPO and CPO can reduce latency associated with long electrical interconnects.

CPO has the shortest electrical path, while NPO also provides a substantial reduction compared with front-panel architectures. Actual end-to-end latency still depends on SerDes, optical conversion, switch processing, fiber propagation, and system architecture.

18. Optical Engine Placement and Latency

The physical propagation delay across a PCB section is only one part of total latency.

The more important advantage of moving optics closer to the ASIC can be the reduction in required electrical signal conditioning and the ability to simplify the high-speed channel rather than simply reducing physical propagation time.

19. Thermal Management

NPO and CPO create different thermal challenges because the optical engines are moved closer to the high-power switching silicon.

This changes the location of heat sources and requires closer coordination between the optical engine, ASIC, heatsink, PCB, package, airflow, and system cooling infrastructure.

20. NPO Thermal Design

NPO can place optical engines on the host board near the ASIC rather than inside front-panel modules.

This requires careful board-level thermal planning but can provide more physical separation between the optical engine and the hottest portion of the ASIC package than a tightly integrated CPO design.

21. CPO Thermal Design

CPO places optical engines extremely close to the ASIC, creating a highly integrated thermal environment.

The optical components must operate within their temperature limits while the ASIC itself may generate substantial heat. Thermal coupling between these components therefore becomes a major packaging consideration.

22. Why Thermal Design Is Difficult for CPO

In a conventional pluggable architecture, the optical module has its own mechanical and thermal environment.

With CPO, the optical engine is physically close to the switching ASIC, which means the thermal solution must support both components simultaneously.

23. Serviceability

Serviceability is one of the largest practical differences between NPO and CPO.

An NPO optical engine may remain separately replaceable depending on the implementation. CPO integrates the optics much more tightly with the ASIC package, making field replacement considerably more complex.

24. NPO Serviceability

NPO can preserve a degree of modularity because the optical engine does not necessarily have to be part of the same package as the ASIC.

This can make repair, rework, testing, or replacement more manageable than a fully integrated package architecture.

25. CPO Serviceability

CPO reduces the independence of the optical engine from the switching silicon.

If the optical engine, package, or ASIC has a major failure, repair can become a board- or assembly-level operation rather than a simple front-panel module replacement.

26. Front-Panel Architecture

NPO can reduce the dependence on traditional front-panel optical modules by moving the optical engines closer to the ASIC.

CPO goes further and can remove a significant portion of the traditional optical-module architecture from the front panel.

27. Cable Connectivity

Both NPO and CPO still require external fiber connections.

The difference is where the optical-to-electrical conversion occurs. In both architectures, the optical engine converts high-speed electrical signals into optical signals before they travel through external fiber.

28. Fiber Management

Moving optical engines toward the ASIC changes fiber routing inside the system.

NPO requires carefully designed fiber routing from the near-package engines to external interfaces. CPO can require even tighter fiber-management solutions because many optical connections originate from a densely integrated package.

29. Manufacturing Complexity

NPO requires tighter coordination between optical engines, PCB design, high-speed routing, mechanical components, fiber routing, and system testing.

CPO adds another level of integration because the optical engine and ASIC package must operate as a closely coupled assembly.

30. Packaging Requirements

NPO can take advantage of advanced PCB and socketed or modular approaches while keeping some separation between the ASIC and optical engine.

CPO requires advanced packaging technologies capable of handling high-speed electrical interfaces, optical coupling, thermal management, mechanical tolerances, and manufacturing yield.

31. NPO and Open Ecosystems

NPO can provide more separation between the switching ASIC and optical engine than CPO.

This can make it easier to develop modular architectures in which different optical engines or components can be evaluated without completely redesigning the ASIC package.

32. CPO and Ecosystem Integration

CPO creates a much tighter dependency between the ASIC vendor, package technology, optical engine, fiber coupling, thermal system, and equipment manufacturer.

This can improve system optimization but also increases the number of components and organizations that need to coordinate on the same platform.

33. NPO vs CPO Upgrade Flexibility

NPO generally provides greater upgrade flexibility because the optical engine can remain more independent from the ASIC package.

CPO architectures are more tightly tied to the specific ASIC package and optical implementation, so a major optical or ASIC upgrade can require a more substantial system redesign.

34. NPO for 800G

800G is a practical generation for evaluating near-package optical architectures because the corresponding electrical lane rates already create significant board-level signal-integrity challenges.

NPO can reduce the ASIC-to-optics electrical distance while preserving more modularity than CPO.

35. CPO for 800G

800G can also be implemented in CPO architectures, particularly where switch bandwidth density and energy efficiency are major priorities.

However, the decision involves more than the optical data rate because thermal, packaging, fiber coupling, serviceability, and manufacturing requirements become part of the system design.

36. NPO for 1.6T

At 1.6T, the electrical interface becomes significantly more demanding.

NPO can help by shortening the electrical path between the high-speed ASIC and optical engine, making near-package placement increasingly relevant to high-density switch and AI architectures.

37. CPO for 1.6T

CPO is also relevant to 1.6T systems because the electrical distance between the ASIC and optics becomes an increasingly important constraint.

The extremely short path can help address signal-integrity limitations, although thermal and packaging complexity also increases.

38. 200G-per-Lane Signaling

As electrical signaling moves toward 200G-per-lane operation, PCB traces and connectors consume a larger portion of the electrical link budget.

NPO and CPO address this problem by moving the optical conversion point closer to the SerDes, with CPO providing the most aggressive reduction in electrical reach.

39. Beyond 1.6T

Future systems are expected to explore even higher aggregate bandwidth and signaling rates.

As electrical reach becomes more restrictive, architectures that place optics closer to silicon become increasingly relevant. This includes NPO, CPO, and other emerging optical-engine integration approaches.

40. NPO vs CPO for AI Data Centers

AI data centers require high-bandwidth connections among switches, GPUs, accelerators, NICs, and other infrastructure.

NPO can provide a compromise between electrical efficiency and modularity, while CPO can maximize the integration between the switching ASIC and optical engines.

41. NPO vs CPO and Rack-Level Scaling

Higher port bandwidth increases the amount of data that can be moved through a switch without proportionally increasing the number of physical ports.

Both NPO and CPO can therefore contribute to higher bandwidth density, although CPO offers deeper integration than NPO.

42. NPO vs CPO and Optical Port Density

NPO and CPO can change the relationship between the optical engine and the traditional front panel.

Instead of placing all optical conversion in front-panel modules, the optical engines can be distributed around the ASIC. This can support higher aggregate bandwidth in a limited system footprint.

43. NPO vs CPO and Maintenance

NPO can retain more modular maintenance characteristics because the optical engine may be separately accessible.

CPO requires a more integrated service model, which can increase the difficulty of replacing individual optical components without affecting the surrounding package or system assembly.

44. NPO vs CPO and Testing

Testing becomes more complex as optical engines move closer to the ASIC.

NPO requires high-speed electrical, optical, thermal, and fiber testing at the board level. CPO adds package-level optical alignment, coupling, thermal, and manufacturing-yield considerations.

45. Reliability Considerations

Reliability depends on more than optical component quality.

NPO and CPO must also account for thermal cycling, mechanical stress, optical coupling stability, fiber routing, electrical integrity, package reliability, and manufacturing consistency.

46. NPO vs CPO Cost

The cost comparison cannot be reduced to the price of the optical engine.

NPO may require advanced boards, optical routing, high-density connectors, and specialized assembly. CPO introduces additional packaging, coupling, thermal, and manufacturing requirements.

The meaningful comparison is total system cost, including manufacturing, cooling, maintenance, service, and upgrade requirements.

47. NPO vs CPO and Supply Chain

NPO can maintain more separation between the ASIC and optical components, potentially allowing a broader set of suppliers to participate in different parts of the system.

CPO requires close coordination between ASIC packaging, optical engines, package substrates, fiber coupling, thermal systems, and manufacturing processes.

48. NPO vs CPO Architecture Comparison

49. NPO vs CPO vs LPO

NPO, CPO, and LPO solve different parts of the optical-interconnect scaling problem.

50. Why NPO Is Between Pluggable Optics and CPO

NPO can be viewed as an intermediate architecture because it moves the optical engine closer to the ASIC without requiring the same degree of package integration as CPO.

This can provide some of the electrical benefits of CPO while preserving more modularity and potentially simplifying manufacturing and service.

51. Is NPO Better Than CPO?

NPO and CPO are designed around different system priorities.

NPO emphasizes a balance between short electrical reach, modularity, and system integration. CPO emphasizes maximum integration between optical engines and switching silicon.

The appropriate architecture depends on bandwidth, electrical reach, power, cooling, serviceability, manufacturing, and network deployment requirements.

52. Is CPO Always More Power Efficient?

CPO can provide strong energy-efficiency potential because the electrical path between the ASIC and optics is extremely short.

However, system power also includes optical engines, cooling, packaging, fiber coupling, control electronics, and other infrastructure. Therefore, total energy efficiency must be evaluated across the complete system.

53. Is NPO Easier to Maintain?

NPO generally offers more serviceability than tightly integrated CPO architectures because the optical engine can remain more physically separated from the ASIC.

The actual maintenance model depends on whether the NPO system uses socketed, modular, or fixed optical engines.

54. NPO vs CPO Selection Factors

When comparing NPO and CPO, evaluate the following system parameters:

ASIC lane rate, electrical channel loss, optical engine placement, power consumption, thermal coupling, fiber routing, package technology, serviceability, manufacturing yield, interoperability, system cost, and future bandwidth requirements.

55. NPO vs CPO Summary

56. Conclusion

NPO and CPO are both designed to bring optical conversion closer to high-speed switching silicon, but their integration levels are different. NPO places the optical engine near the ASIC while keeping greater physical separation and potential modularity. CPO integrates the optical engine much more closely with the ASIC package to minimize the electrical path as much as possible.

NPO therefore represents a balance between electrical performance and serviceability, while CPO emphasizes maximum integration, electrical reach reduction, and bandwidth density. The trade-offs appear in thermal management, manufacturing, fiber routing, maintenance, cost, and upgrade flexibility.

For 800G systems, both architectures can be relevant as data center bandwidth requirements increase. As electrical interfaces move toward 1.6T, 200G-per-lane operation, and future higher-rate technologies, reducing the electrical distance between the ASIC and optical engine becomes increasingly important.

The future optical interconnect landscape is therefore unlikely to depend on a single architecture. LPO, NPO, CPO, and other optical-engine placement strategies can coexist, with each addressing different combinations of bandwidth, power, electrical reach, thermal constraints, serviceability, and system integration.

57.NPO vs CPO Q&A