LPO vs CPO

Linear Pluggable Optics (LPO) and Co-Packaged Optics (CPO) are two emerging approaches to solving the power, bandwidth, signal integrity, and scalability challenges of high-speed optical interconnects. Both are closely associated with AI clusters, high-performance computing, advanced switch ASICs, and rapidly increasing SerDes speeds, but they address the electrical and optical link in very different ways.

LPO keeps the optical connection in a pluggable module while removing the conventional high-speed DSP from the module in a typical implementation. CPO moves the optical engine much closer to the switch ASIC or accelerator and integrates optics and electronics within the same package or closely integrated package architecture. The shorter electrical path in CPO can reduce interconnect loss and enable a different system-level power and bandwidth architecture.

Although LPO and CPO are often discussed together, they are not simply two versions of the same technology. LPO primarily changes the signal-processing architecture of a pluggable optical module, while CPO fundamentally changes where the optics are physically integrated within the system.

1. What Is LPO?

LPO stands for Linear Pluggable Optics. In a typical LPO architecture, the high-speed DSP traditionally located inside a pluggable optical module is removed. Instead, the host ASIC or SerDes performs more of the signal-conditioning and equalization functions.

A simplified LPO transmit path is:

Host ASIC / SerDes → PCB / Connector → Linear Driver → Optical Engine → Fiber

The receive path is approximately:

Fiber → Photodetector → TIA → Connector / PCB → Host ASIC / SerDes

The exact implementation varies by product and ecosystem, but the key characteristic is the reduced reliance on a dedicated high-speed module DSP.

2. What Is CPO?

CPO stands for Co-Packaged Optics. CPO places optical engines directly alongside a high-speed switch ASIC, XPU, or other processing silicon rather than locating the optics at a removable front-panel pluggable module.

A simplified CPO architecture is:

Switch ASIC / XPU → Very Short Electrical Connection → Optical Engine → Fiber

Because the optical engine is located close to the processing silicon, the electrical path between the SerDes and optical interface can be dramatically shorter than in a conventional front-panel architecture.

CPO is therefore primarily an integration and packaging architecture rather than simply a signal-processing architecture.

3. The Core Difference Between LPO and CPO

4. LPO and CPO Solve Different Problems

LPO primarily addresses the power and latency overhead associated with high-speed signal processing inside pluggable optical modules.

CPO primarily addresses the electrical distance between high-speed silicon and optical conversion.

This distinction is important because a large amount of electrical loss is created before a signal reaches a traditional front-panel optical module. LPO removes the conventional module DSP but does not eliminate the physical distance between the switch ASIC and the pluggable module.

CPO attacks that distance directly by moving the optical conversion point closer to the ASIC.

5. Conventional Pluggable Optical Architecture

A traditional high-speed optical system can be represented as:

ASIC → Package → PCB → Connector → Module → DSP → Driver → Optical Engine

The signal must travel through several electrical interfaces before being converted from the electrical domain to the optical domain.

At moderate data rates, this architecture is relatively manageable. As SerDes speeds reach 100G, 200G per lane and beyond, electrical insertion loss and channel complexity increase significantly.

6. LPO Architecture

LPO removes the conventional high-speed DSP from the module:

ASIC → Package → PCB → Connector → Linear Driver → Optical Engine

This reduces module power and processing latency, but the ASIC-to-module electrical path remains.

As a result, LPO still requires careful control of PCB loss, connector loss, package loss, return loss, crosstalk, jitter, and other electrical parameters.

7. CPO Architecture

CPO goes one step further by moving the optical conversion point close to the ASIC:

ASIC → Short Electrical Path → Optical Engine → Fiber

The optical engine may be integrated on the same substrate or closely packaged with the switch silicon or XPU, depending on the specific architecture.

The objective is to minimize the high-speed electrical distance before optical conversion.

8. Why Electrical Distance Matters

High-speed electrical signals are affected by the physical transmission channel.

As the signal travels through PCB traces, connectors, vias, package substrates, and other structures, it experiences insertion loss, reflections, crosstalk, attenuation, and dispersion.

These effects become increasingly significant as signaling speeds increase.

Reducing the electrical path therefore becomes an important strategy for maintaining signal integrity at very high lane rates.

9. LPO Does Not Eliminate the Electrical Channel

This is one of the most important differences between LPO and CPO.

LPO removes much of the signal processing from the optical module, but the electrical signal still travels from the host ASIC to the front-panel module.

This means that LPO depends heavily on host SerDes capabilities and the quality of the electrical channel.

CPO substantially shortens this electrical path and therefore addresses a different part of the system problem.

10. CPO Reduces the Electrical Path

In CPO systems, the optical engine can be placed immediately adjacent to the switch ASIC or processing silicon.

Instead of sending a very high-speed electrical signal across a large section of the PCB to a front-panel module, the electrical signal can be converted to optics much closer to its source.

This can reduce signal loss and simplify some of the high-speed electrical design challenges.

11. LPO and DSP

LPO is strongly associated with the removal of the conventional high-speed DSP from the pluggable module.

The host SerDes assumes greater responsibility for signal conditioning, while linear drivers and TIAs connect the electrical and optical domains.

This architecture can reduce module power and latency, but requires much tighter system-level design.

12. CPO and DSP

CPO should not be defined simply as an architecture with "no DSP."

CPO primarily defines the physical and packaging relationship between optics and processing silicon. Depending on the system architecture, different levels of signal processing may still exist.

Because the electrical path between the ASIC and optical engine is extremely short, the system may reduce or eliminate certain retimer or DSP functions that would otherwise be needed in a longer electrical channel.

The exact architecture depends on the CPO implementation.

13. Power Consumption Comparison

It is therefore more accurate to compare LPO and CPO based on total system power rather than simply comparing the power specifications of an individual module.

14. Why CPO Can Further Reduce Power

Removing the DSP from an optical module can reduce the module's power, but the electrical signal still needs to travel across the host platform.

CPO reduces this electrical distance at the physical level.

By moving optical conversion closer to the ASIC, CPO can reduce electrical loss and potentially reduce the amount of compensation required to maintain signal integrity.

This is one of the central reasons CPO is being evaluated for extremely high-bandwidth AI networking.

15. LPO and Power per Bit

As network bandwidth increases, power per bit becomes an important design metric.

An optical module carrying 800G or 1.6T cannot simply increase power indefinitely as bandwidth increases. High-density systems may contain hundreds or thousands of optical interfaces, making even small per-module power differences significant at the rack or data center level.

LPO attempts to reduce power by simplifying the module architecture, while CPO attacks the problem through physical proximity and deeper integration.

16. Latency Comparison

Both approaches can reduce latency compared with architectures that rely heavily on high-speed DSP processing, but they do so in different ways.

17. LPO's Main Latency Advantage

The major LPO latency advantage comes from eliminating the conventional high-speed module DSP processing stage.

The signal can travel from the host SerDes through the electrical channel directly into the linear optical driver or from the optical receiver through the TIA toward the host.

This simplifies the signal path inside the module.

18. CPO's Main Latency Advantage

CPO combines very short electrical paths with closely integrated optical conversion.

The signal does not need to travel from the ASIC across a large PCB region to reach a front-panel pluggable module.

As a result, CPO can reduce both electrical propagation distance and some signal-conditioning requirements.

19. Signal Integrity: LPO vs CPO

LPO remains sensitive to the electrical path between the ASIC and the module.

CPO substantially shortens that path.

20. Thermal Design in LPO

LPO can reduce the power dissipated by individual pluggable modules because the conventional DSP is generally removed.

This can simplify front-panel thermal management in high-density switches.

However, the host ASIC remains a major heat source. Higher-speed SerDes can consume substantial power, and additional host-side signal processing can contribute to system thermal requirements.

21. Thermal Design in CPO

CPO changes the thermal problem substantially because the optical engine is located close to high-power switching silicon.

The switch ASIC may already generate significant heat, and integrating optical engines nearby creates additional thermal interaction within the package and system.

Therefore, CPO requires advanced thermal design involving package materials, heat spreading, optical engine placement, cooling systems, and fiber routing.

22. Why CPO Packaging Is More Complex

CPO integrates optical and electronic components at a much deeper level than conventional pluggable modules.

This creates challenges in assembly, optical alignment, thermal management, fiber attachment, package reliability, manufacturing yield, testing, and repair.

The benefits of shorter electrical paths therefore come with a substantially different manufacturing and operational model.

23. LPO Maintains the Pluggable Advantage

One of the biggest practical differences is serviceability.

An LPO module remains a pluggable component. It can be installed, replaced, tested, inventoried, and serviced similarly to other optical modules.

This makes LPO easier to integrate into existing network operational models than deeply integrated optical architectures.

24. CPO Changes Serviceability

In a CPO system, the optical engine is integrated into the switch or accelerator architecture.

Therefore, replacing an optical engine is not equivalent to replacing a standard pluggable transceiver.

System maintenance, failure analysis, manufacturing qualification, and field replacement require a different operational approach.

25. CPO and Fiber Management

CPO can significantly increase the number of optical connections emerging from a compact system.

This creates new requirements for fiber routing, connectorization, bend management, cable organization, mechanical protection, and service access.

The physical design of the optical system therefore becomes an integral part of the switch or accelerator architecture.

26. LPO and Fiber Management

LPO uses the familiar pluggable module and structured fiber-cabling approach used in conventional data center networks.

Fiber can be connected through standardized front-panel interfaces and replaced without replacing the entire switch platform.

This simplifies deployment and maintenance compared with highly integrated optical architectures.

27. LPO and CPO in AI Scale-Up Networks

AI scale-up networks connect GPUs, XPUs, switches, and other compute devices with extremely high bandwidth and low latency requirements.

These connections can operate within a highly controlled physical environment where the system designer can control the ASIC, PCB, module, cable, connector, and firmware ecosystem.

Such controlled environments are attractive for LPO because the electrical channel can be carefully optimized.

CPO is also relevant because the optical engine can move even closer to the compute or switching silicon.

28. LPO and CPO in AI Scale-Out Networks

AI scale-out networks connect multiple servers, racks, clusters, and network layers.

As the distance and interoperability requirements increase, pluggable optics retain important advantages.

Longer-reach and more diverse networking environments can place greater emphasis on interoperability, reach, optical budgets, and serviceability.

For these requirements, conventional DSP-based pluggable optics may continue to play an important role alongside LPO and CPO.

29. 800G LPO

800G is a major target for LPO because the power consumed by high-speed processing becomes significant at high bandwidth densities.

An 800G LPO implementation can use high-speed electrical lanes connected to linear drivers and optical engines without a conventional module DSP.

The exact implementation depends on the electrical lane rate, optical design, wavelength architecture, host SerDes, and target reach.

30. 800G CPO

800G-class switching and AI systems are also important applications for CPO.

By placing optical engines close to the switch ASIC, the system can reduce the electrical path associated with high-speed connections.

This approach can be particularly attractive as switch bandwidth and port density continue to increase.

31. 1.6T LPO

1.6T increases the pressure on the electrical channel because many implementations use 200G-class electrical lanes.

At these speeds, small differences in package loss, PCB loss, connector quality, and SerDes capability can significantly affect system margin.

LPO can address module power by removing the conventional DSP, but the resulting architecture requires careful host and module co-design.

32. 1.6T CPO

1.6T and higher bandwidth targets strengthen the motivation for shorter electrical connections.

CPO provides a physical architecture in which high-speed electrical signals can be converted to optical signals close to the switching or compute silicon.

This becomes increasingly important as traditional front-panel electrical paths become more difficult to manage at very high lane rates.

33. LPO vs CPO: Bandwidth Scaling

34. LPO Is Still a Pluggable Architecture

LPO changes the internal signal-processing structure of a pluggable module without abandoning the basic pluggable model.

This means data center operators can maintain familiar module installation, replacement, cabling, and inventory processes.

For existing switch architectures, this can be an important transition path toward lower-power optics.

35. CPO Is an Architectural Change

CPO is a much deeper change to the system.

Instead of treating the optical module as a removable peripheral component, optics become part of the switch or accelerator package architecture.

This affects chip packaging, board design, fiber routing, thermal management, manufacturing, test, serviceability, and system-level qualification.

36. LPO and NPO

Near-Packaged Optics (NPO) places the optical engine closer to the ASIC than a conventional front-panel pluggable module but does not necessarily integrate the optics within the same package.

NPO can therefore be considered an intermediate architecture between pluggable LPO and CPO.

A simplified evolution can be represented as:

DSP Pluggable → LPO → NPO / OBO → CPO

These categories are architectural concepts, and real products may use different terminology or hybrid implementations.

37. LPO and OBO

On-Board Optics (OBO) mounts optical engines directly on the system board or very close to the switch silicon.

This reduces electrical path length compared with a front-panel optical module while retaining some separation between the optical engine and the silicon package.

OBO can provide an intermediate approach between pluggable optics and CPO.

38. LPO, NPO, OBO, and CPO

39. Interoperability Differences

LPO requires careful interoperability testing because the host electrical channel directly affects optical performance.

Different ASICs, PCB layouts, connectors, SerDes implementations, and firmware environments can produce different results with the same LPO module.

CPO takes interoperability in another direction. Because the optical engine is integrated into the platform, the system ecosystem becomes more tightly controlled.

This can simplify optimization inside a specific platform while reducing the modularity available to customers.

40. Standardization Requirements for LPO

LPO depends on clearly defined electrical and optical interfaces so that switches, NICs, optical modules, drivers, TIAs, and other components can work together.

Multi-source agreements and industry specifications are therefore important for building a broader LPO ecosystem.

Without sufficient interoperability, LPO can become highly platform-specific.

41. Standardization Challenges for CPO

CPO has additional standardization challenges because the optical engine is deeply integrated with the host silicon.

Different vendors may use different package structures, optical engine architectures, fiber interfaces, thermal systems, and manufacturing processes.

As a result, CPO interoperability involves not only optical specifications but also packaging, electrical, mechanical, thermal, and manufacturing considerations.

42. Manufacturing Complexity: LPO

LPO modules still require conventional optical manufacturing capabilities such as optical alignment, laser integration, TIA integration, high-speed driver design, firmware or management interfaces, EEPROM programming, thermal validation, and production testing.

The absence of the conventional module DSP simplifies part of the architecture but does not eliminate the complexity of manufacturing high-speed optical modules.

43. Manufacturing Complexity: CPO

CPO introduces additional manufacturing requirements because optical engines and high-speed silicon must be integrated within a tightly controlled package and system environment.

Optical coupling, package assembly, thermal expansion, fiber routing, yield management, reliability testing, and field handling become critical manufacturing considerations.

This is one reason why CPO requires coordination across semiconductor, photonics, packaging, fiber, connector, and system manufacturers.

44. Testing LPO Systems

LPO testing should cover the complete host-to-optics electrical and optical path.

Important parameters include:

Insertion loss

Return loss

Crosstalk

Jitter

PAM4 eye quality

Transmitter linearity

Receiver performance

BER

Optical power budget

Temperature performance

Because the host electrical channel is important, module-only testing may not fully represent real-world LPO performance.

45. Testing CPO Systems

CPO testing covers an even broader set of parameters.

In addition to electrical and optical performance, CPO requires verification of package reliability, thermal behavior, optical coupling, fiber routing, mechanical stress, system yield, and long-term operating stability.

The integrated architecture makes it necessary to validate the package and optical system as a whole.

46. Reliability Considerations

47. Cost Structure of LPO

LPO can reduce the bill of materials associated with the optical module by removing a conventional high-speed DSP.

However, additional platform-level engineering may be necessary to meet electrical channel and interoperability requirements.

The total cost therefore depends on module volume, host architecture, qualification effort, PCB design, testing, and deployment model.

48. Cost Structure of CPO

CPO has the potential to improve bandwidth density and reduce power per bit, but the package and manufacturing processes are more complex than those used for conventional pluggable modules.

Investment in packaging, optical integration, thermal design, automated assembly, test, and yield optimization can significantly affect total system economics.

CPO economics therefore depend strongly on high-volume manufacturing and the specific system architecture.

49. Deployment Flexibility

50. LPO for Existing Pluggable Ecosystems

LPO is compatible with the general concept of pluggable optical networking.

This means network equipment manufacturers can develop lower-power optical interfaces while retaining a familiar physical deployment model.

For data centers that already use large numbers of pluggable optical modules, this characteristic can simplify migration planning.

51. CPO for New System Architectures

CPO is more naturally suited to new switch or accelerator platforms designed around deep optical integration.

Because the optical engines are part of the system architecture, CPO is not simply an optical-module upgrade.

The ASIC package, optical engines, power delivery, cooling, fiber connections, and system enclosure may need to be designed together.

52. LPO and AI Cluster Density

AI systems can contain large numbers of high-speed links operating simultaneously.

In these environments, reducing optical-module power can reduce the thermal load associated with front-panel optics.

LPO therefore has strong relevance to applications where high bandwidth, short reach, low latency, and controlled electrical channels exist together.

53. CPO and AI Cluster Density

CPO can provide extremely high optical bandwidth density because many optical channels can be integrated directly around high-bandwidth switching or compute silicon.

This is particularly relevant as switch bandwidth grows and the number of optical channels required by a system increases.

The trade-off is that optical integration becomes a structural part of the system rather than a replaceable module function.

54. LPO vs CPO for Short-Reach Connectivity

Both LPO and CPO can target short-reach AI connectivity, but they approach the problem differently.

LPO keeps the optical interface modular while reducing signal-processing complexity.

CPO reduces the physical electrical path and integrates the optical conversion closer to the silicon.

The choice therefore depends on whether the system places greater emphasis on modular deployment or deeper physical integration.

55. LPO vs CPO for Longer Reach

LPO is primarily associated with controlled short-reach environments.

CPO can also drive optical signals into longer fiber links after conversion, but the main advantage of CPO comes from reducing the electrical distance between silicon and optics rather than inherently increasing optical transmission distance.

For long-reach optical networking, pluggable DSP-based modules and coherent architectures remain important because advanced digital signal processing can address optical impairments over longer distances.

56. CPO Does Not Mean All Optical Modules Will Disappear

CPO is not a direct replacement for every type of pluggable optical module.

Data centers contain many different network layers and reach requirements. Some links benefit from deeply integrated optics, while others require removable modules with different reach, wavelength, interoperability, or serviceability characteristics.

Pluggable optics therefore remain an important part of the broader optical connectivity ecosystem.

57. LPO Does Not Mean CPO Is No Longer Needed

LPO and CPO can coexist.

LPO can address links where the host electrical channel remains manageable and pluggability is important. CPO can address systems where electrical loss becomes a dominant constraint and much deeper integration is justified.

The two architectures can therefore occupy different positions within future AI and data center network designs.

58. LPO vs CPO and Optical Engine Integration

In LPO, the optical engine remains inside a pluggable module.

In CPO, the optical engine is moved much closer to the ASIC or accelerator.

This distinction influences almost every part of the system, including electrical routing, thermal design, optics packaging, manufacturing, testing, maintenance, and fiber management.

59. Evolution from DSP Pluggables to CPO

The development of high-speed optical connectivity can be viewed as a series of architectural transitions:

DSP-Based Pluggable → LPO → NPO / OBO → CPO

This sequence does not mean every system must follow the same path. Instead, each architecture addresses a different balance between electrical reach, optical integration, power, latency, modularity, and system complexity.

60. LPO vs CPO: Overall Architecture Comparison

61. How to Evaluate LPO and CPO

The evaluation should begin with the complete network architecture rather than the optical interface alone.

Important questions include the host SerDes rate, electrical channel length, PCB loss, system bandwidth, optical reach, thermal budget, required latency, maintenance model, optical density, and expected operating environment.

The decision should also consider whether the equipment needs interchangeable optical modules or whether a tightly integrated optical architecture is acceptable.

62. When LPO Is a Suitable Architecture

LPO is particularly relevant when the system requires:

High bandwidth

Short optical reach

Low module power

Low module latency

Strong host SerDes capability

A controlled electrical channel

Pluggable serviceability

These characteristics align closely with short-reach AI and high-performance computing environments.

63. When CPO Is a Suitable Architecture

CPO becomes particularly relevant when:

ASIC bandwidth is extremely high

Electrical channel loss is becoming a dominant limitation

Optical port density is very high

Power per bit is a major system parameter

Deep ASIC and optical co-design is acceptable

The system can support advanced packaging and thermal solutions

These conditions are increasingly relevant to large-scale AI and high-performance networking platforms.

64. The Main Advantage of LPO

The defining advantage of LPO is the ability to reduce module-level signal-processing power and latency while maintaining the pluggable optical architecture.

It provides a transition toward more linear optical connectivity without requiring the optical engine to become part of the ASIC package.

65. The Main Challenge of LPO

The main challenge is the electrical channel between the host and pluggable module.

At very high lane rates, this channel can become increasingly difficult to manage. The performance of the LPO system therefore depends strongly on the ASIC SerDes, PCB, connectors, module electrical interface, and complete signal path.

66. The Main Advantage of CPO

The primary architectural advantage of CPO is proximity.

The optical engine is placed close to the processing silicon, minimizing the high-speed electrical path before optical conversion.

This can support higher bandwidth density and reduce some of the power and signal-integrity constraints associated with longer electrical interconnects.

67. The Main Challenge of CPO

The main challenge is integration.

CPO transforms optics from a replaceable module into a tightly integrated part of the system. This creates additional challenges in packaging, thermal management, manufacturing, testing, fiber routing, reliability, and serviceability.

68. The Future Relationship Between LPO and CPO

The future optical architecture of AI data centers is unlikely to consist of a single technology.

Different network layers can require different solutions.

Pluggable DSP optics can provide reach and signal-processing capability. LPO can reduce power and latency in controlled short-reach connections. NPO and OBO can shorten the electrical channel without full package integration. CPO can provide deeper integration for systems where bandwidth density and electrical path limitations dominate.

69. LPO vs CPO for Next-Generation AI Infrastructure

As AI systems move toward higher switch bandwidth, higher SerDes speeds, and larger numbers of optical channels, the distinction between electrical and optical system design becomes increasingly blurred.

LPO represents a move toward linear, host-driven optical connectivity.

CPO represents a move toward deeply integrated optical computing and networking architectures.

Both approaches are part of the broader effort to reduce power per bit and maintain signal integrity as bandwidth continues to increase.

70. Conclusion

LPO and CPO address the challenges of high-speed optical connectivity from different directions.

LPO keeps the optical engine inside a pluggable module while removing the conventional high-speed DSP from the module in a typical implementation. This can reduce module power and latency while preserving the serviceability and deployment flexibility of pluggable optics.

CPO places optical engines much closer to the switch ASIC or XPU, greatly shortening the electrical path between high-speed silicon and optical conversion. This can reduce electrical loss and support high bandwidth density and power-efficient architectures, but requires substantially deeper integration across silicon, photonics, packaging, thermal management, manufacturing, and system design.

The most important distinction is therefore simple: LPO primarily changes how a pluggable optical link processes the signal, while CPO primarily changes where the optical conversion occurs.

For 800G, 1.6T, and future AI networking architectures, LPO, CPO, NPO, OBO, and DSP-based pluggable optics should be viewed as complementary architectures serving different combinations of bandwidth, reach, power, latency, interoperability, and serviceability requirements.

71.LPO vs CPO Q&A