# From 800G to 6.4T: How CPO Is Redefining Optical Testing and Manufacturing

**By APEX GROUP LIMITED | Industry Insights | June 2026**

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The closer Co-Packaged Optics (CPO) gets to mass production, the more the "unsexy" challenges — testing, alignment, yield screening — move to center stage.

The driving force is clear: AI data centers are generating data movement demands that are pushing traditional pluggable optical modules to their physical limits. While the industry has been focused on silicon photonics engines, switch ASICs, and external laser sources, the real bottleneck emerging as links scale from 800G to 1.6T, 3.2T, and 6.4T is not whether we can build the optical engine — but whether we can test it, align it, and manufacture it at scale.

## CPO: Solving Distance, Shifting Cost

The problem with pluggable optics is straightforward: high-speed electrical signals must travel from the switch ASIC to the front-panel module across copper traces. As data rates climb, those traces become increasingly problematic.

**CPO changes the equation by bringing the optical engine next to the ASIC:**

| Metric            | Traditional Pluggable | CPO                 |

| ----------------- | --------------------- | ------------------- |

| Electrical Path   | ~100mm+ copper trace  | ~10mm or less       |

| Energy Efficiency | ~20 pJ/bit            | Under 5 pJ/bit      |

| System Power      | Baseline              | 50%+ savings target |

| Latency           | Baseline              | 15%+ improvement    |

But the benefit comes with a trade-off. Testing that used to happen at the module level must now be distributed across wafer, die, package, module, and system levels.

## The Real Challenge: Multi-Level Testing

CPO isn't just about placing a PIC, EIC, laser source, and ASIC together. It requires simultaneous management of high-speed electrical signals, optical coupling, thermal dissipation, mechanical stress, and packaging yield.

**The test chain breaks down into five critical stages:**

- **Wafer Level:** KGD (Known Good Die) screening to eliminate defective dies early

- **Chip Level:** PIC/EIC electro-optical conversion verification

- **Package Level:** Post-encapsulation coupling efficiency, thermal drift, mechanical stress

- **Module Level:** BER, FEC performance, Ethernet protocol compliance, interoperability

- **System Level:** Full integration testing with switch ASIC, optical engine, and external laser source

## Alignment: The Underestimated Bottleneck

Light is not electricity. Electrical connections can compensate through solder joints, traces, and connectors. Optical connections, once misaligned, suffer from insertion loss, crosstalk, and power budget degradation that cannot be recovered.

**Edge Coupler demands:**

- Insertion loss: under 1.0 dB

- Supports: 128-core FAU (Fiber Array Unit)

- Challenge: Sub-micron alignment precision required

## WDM: More Bandwidth, More Complexity

- Wavelength coverage: 1270nm through 1410nm (8+ wavelengths)

- Critical KPI: Crosstalk maintained at -20dB

- Testing scope: Center wavelength, spectral drift, insertion loss, crosstalk, power budget

## Modulator Choices

| Type | Size      | Advantage              | Test Challenge    |

| ---- | --------- | ---------------------- | ----------------- |

| MZI  | 1-3mm     | Good linearity, mature | Large footprint   |

| MRM  | 10-20μm  | Ultra-compact          | Thermal stability |

| EAM  | 50-100μm | Compact                | PAM4 linearity    |

## Apex Perspective: Optical Modules in the CPO Era

At APEX GROUP LIMITED, we are closely tracking the CPO transition. While pluggable optics remain dominant today, the long-term trajectory is undeniable.

**What matters for our customers today:**

- **800G and 1.6T pluggable modules** remain the backbone of AI data center interconnects

- **CPO-ready infrastructure** investments are accelerating among hyperscale customers

- **Supply chain integration** across Hisilicon, Accelink, Acacia, Coherent, Eopolink, and other key brands positions Apex to support this transition

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**APEX GROUP LIMITED** — Your partner for 800G/1.6T optical modules and optical communication solutions.

�� Optical@apexallinone.com | �� www.apexallinone.com

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*Keywords: CPO co-packaged optics, 800G optical modules, 1.6T transceivers, silicon photonics, AI data center optics, WDM optical modules, Apex optical modules*