With the rapid advancement of AI large language models, high-performance computing (HPC), and hyperscale data centers, traditional electrical switching architectures are increasingly constrained by bandwidth, power consumption, and latency bottlenecks. To overcome these limitations, optical interconnect technologies have emerged as the core direction for future network evolution.

In today’s data center and AI networking landscape, OCS (Optical Circuit Switch) and CPO (Co-Packaged Optics) are two of the most widely discussed technologies. Many people confuse the two, but in reality, they operate at different layers and target distinct challenges.

So, what exactly is the difference between OCS and CPO? What problems do they each solve? And how will they evolve and collaborate in the future?

1. What is OCS (Optical Circuit Switch)?
OCS, or Optical Circuit Switch, is a technology that establishes end-to-end optical paths directly through optical switches. It enables data switching entirely at the optical layer, minimizing or eliminating frequent optical-electrical-optical (O-E-O) conversions.
In conventional networks, data typically undergoes multiple conversions:
· Optical → Electrical → Switching Chip → Electrical → Optical
· OCS aims to reduce or bypass these intermediate electrical switching stages as much as possible, achieving all-optical switching.

Core Characteristics of OCS:
· Ultra-low power consumption: By drastically reducing SerDes (Serializer/Deserializer) and DSP (Digital Signal Processor) electrical processing, OCS consumes significantly · less power than traditional electrical switches.
· High bandwidth scalability: Ideal for massive interconnects between tens of thousands of GPUs in AI clusters.
· Low latency: Eliminates queuing and buffering delays caused by multi-stage electrical switching.
· Dynamic optical path scheduling: Can dynamically reconfigure network topology based on real-time AI training workloads.

OCS is particularly effective in scenarios with relatively stable, high-volume traffic patterns, such as collective communication in AI model training.

2. What is CPO (Co-Packaged Optics)?
CPO, or Co-Packaged Optics, is an advanced packaging technology that integrates optical engines (lasers, modulators, photodetectors, etc.) with switching ASIC chips on the same substrate or even within the same package.
In traditional switches, high-speed electrical signals must travel relatively long distances between the switching chip and front-panel pluggable optical modules. As switch capacities scale to 51.2T, 102.4T, and beyond, this approach encounters severe challenges:
· Significant signal loss and degradation
· Increasingly difficult PCB trace routing
· Sharply rising power consumption
· Intensified thermal management pressure

CPO’s core objective is to dramatically shorten the electrical connection distance between the switching chip and the optical engine, thereby addressing signal integrity and efficiency issues at the source.

3. Essential Differences Between OCS and CPO
Although both belong to next-generation optical interconnect technologies, they tackle fundamentally different problems. Here is a clear comparison:

In simple terms:
· OCS answers “How to switch data” at the network level.
· CPO answers “How to connect switching chips and optical modules more efficiently” at the device level.

They are not competing alternatives but complementary advancements in different dimensions.

4. Why AI Data Centers Need Both OCS and CPO
AI networks are experiencing explosive growth in bandwidth and power demands. A large-scale AI cluster may contain tens of thousands of GPUs, creating challenges such as:
· Enormous switching power consumption
· Network congestion
· High latency
· Exploding cabling complexity

The industry is therefore advancing both technologies in parallel:
CPO – Internal Revolution of Switches
CPO primarily optimizes:
· High-speed connections between chips and optical engines
· Power consumption of ultra-high-speed SerDes
· Front-panel port density limitations

It represents an evolutionary upgrade inside individual switches.

OCS – Network-Wide Revolution
OCS focuses on:
· Interconnections between GPU clusters
· Dynamic network reconfiguration
· Large-scale all-optical interconnects

It drives a fundamental architectural transformation across the entire data center fabric.

5. Will OCS and CPO Replace Each Other?
The answer is no. They are highly likely to coexist for the long term.

· CPO acts as an “enhanced switch”: Even with CPO, data still passes through electronic switching chips, and the network remains primarily packet-switched. CPO does not change the overall switching architecture.
· OCS represents a “new network architecture”: It reduces reliance on large electronic switching chips, builds more flexible optical-layer networks, and enables lower-power, large-scale AI interconnects. OCS brings architectural-level innovation.

6. Future Trend: Synergistic OCS + CPO Development
Future AI data centers are expected to adopt a “CPO + OCS” hybrid architecture:
· Use CPO inside switches for internal high-efficiency interconnects.
· Deploy OCS across the data center network for dynamic optical-layer scheduling.

This combination delivers:
· Lower overall power consumption (by reducing SerDes and electrical switching losses)
· Higher bandwidth to support million-GPU-scale clusters
· Reduced latency, improving AI training efficiency
· Greater scalability for next-generation AI infrastructure

7. Why OCS Is Gaining Rapid Attention
Compared to CPO, OCS has seen surging interest in recent years for several key reasons:
Changing AI Traffic Patterns
·AI training involves massive All-to-All communication, frequent GPU-to-GPU interactions, and dynamic bandwidth demands. Traditional fixed topologies struggle to keep up. · OCS enables real-time optical path adjustment via high-speed MEMS switches, optimizing bandwidth allocation and improving GPU utilization.

Intensifying Power Pressure
In hyperscale AI data centers, network power consumption has become a critical challenge. OCS’s all-optical switching advantage positions it as a vital technology for reducing overall data center energy use.

8. Conclusion
Although both OCS and CPO are next-generation optical interconnect technologies, they address entirely different issues:
· CPO is an “packaging upgrade” inside switches.
· OCS is an “architectural upgrade” for the entire data center network.

The future of AI data centers will not be an “either-or” choice. Instead, it will likely be: “CPO enhances individual switch performance, while OCS reconstructs the overall optical network architecture.” As AI cluster scales continue to expand, the value of OCS in ultra-large-scale optical interconnects is becoming increasingly prominent. Optical switches are set to become one of the core devices in future intelligent optical networks. The all-optical era of data centers is approaching. Understanding and leveraging both OCS and CPO will be essential for organizations aiming to build efficient, scalable, and sustainable AI infrastructure.