Optical Modules of Core Switches

Core switches use high-speed optical modules—ranging from pluggable transceivers to co-packaged optics—to deliver scalable, low-latency, and high-bandwidth connectivity in modern data centers.

Types of Optical Modules

Pluggable Optical Modules: Traditional modules like SFP, SFP+, QSFP28, and OSFP are widely used in core switches for Ethernet connectivity. They support speeds from 1Gbps to 400Gbps and can accommodate various optical architectures such as DR, FR, LR, SR, and ZR, enabling flexible point-to-point or point-to-multipoint connections . Pluggable modules are hot-swappable, allowing quick replacement or upgrades without taking the entire switch offline . eXtra-dense Pluggable Optics (XPO): XPO modules are designed for next-generation AI data centers, delivering up to 12.8Tbps per module using 64 electrical lanes. They provide extremely high front-panel density, enabling up to 204.8Tbps of switching capacity in a single rack unit, while maintaining field pluggability and operational flexibility . Co-Packaged Optics (CPO): CPO integrates optical and electronic components directly alongside the ASICs on the same substrate or interposer. This reduces the distance between the optical engine and the switch core, lowering latency, insertion loss, and power consumption. CPO modules are not hot-swappable but offer higher bandwidth density and energy efficiency, making them suitable for hyperscale and AI workloads . The optical engine typically includes photonic integrated circuits (PICs) and electronic ICs (EICs), which can be stacked or co-located on silicon interposers to optimize signal integrity and reduce electrical trace losses .

Key Considerations

• Bandwidth and Density: XPO and CPO modules significantly increase bandwidth per unit area compared to traditional pluggable optics, addressing the growing demands of AI and machine learning workloads .
• Power and Cooling: High-density modules like XPO may require integrated liquid cooling to handle 400W+ power consumption, while CPO designs must carefully manage heat dissipation from stacked optical and electronic components .
• Serviceability: Pluggable modules are easier to replace in the field, whereas CPO modules, being integrated, require more complex maintenance procedures .
• Scalability: Both XPO and CPO support pay-as-you-grow deployment models, but CPO offers higher long-term scalability for ultra-high-speed interconnects due to reduced electrical bottlenecks .

Summary

Optical modules in core switches range from conventional pluggable transceivers to advanced high-density solutions like XPO and CPO. Pluggable optics provide flexibility and ease of maintenance, while XPO and CPO address the extreme bandwidth, density, and efficiency requirements of modern AI and hyperscale data centers. Choosing the right module depends on trade-offs between bandwidth, power, serviceability, and deployment scale.