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We briefly discussed CPO optical engines from the perspective of module industry development. Many colleagues have mentioned Alibaba’s 3.2T NPO switches, whose adopted optical engines are developed in line with OIF’s standard specifications for CPO optical engines. Yet they are named NPO instead of CPO.
It is easy for beginners to confuse NPO and CPO, mainly because switch manufacturers and optical module suppliers view them from different perspectives. In this issue, we will sort out the differences between CPO and NPO and analyze their correlation from multiple perspectives.

2. Concept Definition: What are NPO and CPO?

We have already defined CPO (Co-packaged Optics): it refers to integrating optical systems together with customer-side ASIC chips in the same package.
As for NPO (Near-Packaged Optics): it means packaging optical systems close to customer-side ASIC chips.
What does "near" mean, and what does "co-packaged" mean? The term "near" is relatively ambiguous. Many may wonder how close counts as near, and whether a certain proximity equals co-packaging. This is a common misunderstanding. To clarify this, we can refer to the schematic diagrams of NPO and CPO.
OIF has formulated clear standard protocols for CPO, while NPO is an intermediate transition form evolving from pluggable optical solutions toward CPO, without complete unified standard protocols.
From the perspective of electrical interconnection:
In NPO switches, both optical engines and ASICs are mounted on the host PCB with independent packaging substrates respectively.
In CPO switches, ASICs and optical engines must share one identical packaging substrate.
The core difference between CPO and NPO lies in whether they share a packaging substrate. Short-distance electrical interconnection is only an additional advantage, which is also the main reason for widespread confusion between the two technologies.
Whether optical engines can share a packaging substrate with ASICs does not depend on the packaging design of optical engines, but on how clients define the matching relationship between optical engines and ASIC chips.