Co-Packaged Optics (CPO) and the Future of Fiber Connectivity
Co-packaged optics (CPO) moves the optical engines from front-panel pluggable modules to the switch package, right beside the ASIC. Fiber now runs from inside the switch to the faceplate. The lasers stay outside, in front-panel external laser source (ELS) modules. The fiber count leaving the switch does not drop: a 102.4T switch at 200G per lane still needs about 1,024 data fibers (example). For the cabling plant, structured single-mode MPO trunks, cords and breakout harnesses stay. The changes are inside the box and at the faceplate.
Pluggable vs Co-Packaged: What Moves
| Pluggable optics | Co-packaged optics | |
|---|---|---|
| Where the optics sit | In each front-panel module | Optical engines on the switch package |
| Electrical path ASIC → optics | Long board trace to the faceplate | Very short, inside the package |
| Electrical loss (one maker's figure) | about 22 dB | about 4 dB |
| Laser | Inside each module | External, in front-panel ELS modules |
| What you plug at the faceplate | Transceiver, then a cord | Fiber connector (and ELS modules) |
| Service | Swap a module | Swap an ELS module; optical engines are not field parts |
Two switch makers ship or announce 102.4T CPO switches. One quotes 128 ports of 800G and 3.5× better power efficiency than pluggable optics. The other quotes 16 optical engines of 6.4T, 200G per link, field-replaceable ELS modules and more than 3.5× lower optical interconnect power. These are maker claims, not independent test results. One maker plans Ethernet availability in the second half of 2026.
External Laser Sources
Lasers run hotter and fail more often than silicon, so most CPO designs keep them out of the package. The OIF ELSFP (External Laser Small Form Factor Pluggable) implementation agreement defines a faceplate module that sends continuous-wave light into the switch:
- Field replaceable, with a blind-mate optical connector at the rear of the module.
- 1 or 2 MT-compatible ferrules, so one module can feed one or more optical engines.
- Design goal of 16 modules per row in an 18-inch rack.
- First published August 2023; version 2.0 in January 2025.
The laser fibers inside the switch are typically polarization-maintaining fiber. One maker uses one laser for every eight data links. For a 102.4T switch at 200G per link, that is 512 ÷ 8 = 64 laser channels (example).
Fiber Count: It Does Not Go Down
| 102.4T switch (example) | Data lanes | Fibers out of the faceplate |
|---|---|---|
| 64 × 1.6T DR8 pluggables | 512 × 200G | 64 × 16 = 1,024 |
| CPO, 200G per lane, parallel single-mode | 512 × 200G | 512 × 2 = 1,024 |
Both rows are derived examples. Industry white papers already put 51.2T CPO switches at "hundreds to over 1,000 fibers". Inside the box, the switch maker routes every fiber from the optical engines to the faceplate through a fiber shuffle: a managed bundle or flex circuit that maps engine lanes to faceplate ports. That is the switch maker's part, not the data center's.
What This Means for the Cabling Plant
- Structured MPO cabling stays. CPO lanes are parallel single-mode, like DR4 and DR8. Trunks, panels and APC cords look the same as in a 1.6T pluggable design.
- Read the faceplate connector from the switch datasheet. It may be MPO-12, MPO-16 or a very small form factor connector. See VSFF connectors.
- Breakouts move to harnesses. One maker states its CPO switch is interoperable with 400G and 800G Ethernet, so a CPO port often feeds pluggable modules in servers. That link needs a cord or breakout harness mapped to the module port.
- Cleanliness matters more. A dirty faceplate connector on a CPO switch cannot be fixed by swapping a module. Inspect and clean every end face before mating.
- Plan density. More ports per switch means more fibers per rack. See MMC and SN-MT density vs MPO and the 802.3dj guide.
Related reading: CPO is one of several shifts summarised in data center fiber trends for 2026. CPO switches often sit in liquid-cooled racks, and hollow-core fiber is a separate route to lower latency.
Frequently Asked Questions
What is co-packaged optics?
CPO places the optical engines on the switch package next to the ASIC, instead of in front-panel pluggable modules. Fiber connects inside the switch and runs to the faceplate.
Does CPO reduce the number of fibers?
No. Fibers follow lanes. A 102.4T switch at 200G per lane needs about 1,024 data fibers either way (example), plus laser fibers inside the box.
What is an external laser source?
A front-panel module that holds the lasers and feeds light to the optical engines over fiber. The OIF ELSFP agreement defines one, with a blind-mate MT-compatible connector.
Do I still need MPO cables with CPO switches?
In most designs, yes. CPO links are parallel single-mode, so structured MPO trunks, APC cords and breakout harnesses still connect switches, panels and servers. Check the switch datasheet for the faceplate connector.
When will CPO switches be common?
102.4T CPO switches were announced in 2025, and one maker plans Ethernet availability in the second half of 2026. Pluggable optics will remain in use alongside them.
Huawellux Cables for CPO-Era Networks
Huawellux builds OS2 MPO-12/APC and MPO-16/APC cords, trunks and breakout harnesses to order for links between switches, panels and pluggable modules. Send the switch and module port types, and we confirm connector, gender, fiber count and polarity in the quotation. Huawellux can also supply bend-insensitive fiber.
Huawellux's specification for MPO and MTP® assemblies (identical for both) is insertion loss ≤0.35 dB for single-mode and multimode, with return loss >60 dB single-mode (OS2, APC) and >30 dB multimode (OM3/OM4/OM5). LC and SC patch cords are listed at insertion loss ≤0.35 dB and return loss ≥50 dB (single-mode UPC), ≥60 dB (single-mode APC) and >30 dB (multimode). Every Huawellux product receives end-face visual inspection under a 400x video microscope and is tested for insertion loss (IL) and return loss (RL) before it ships. Interferometric end-face geometry (fiber height, coplanarity, end-face angle and radius) is checked by sample-based testing in standard production, and 100% interferometer testing of a batch is available on request. Dust caps are fitted on every connector, and a formal test report is available on request.
Huawellux replies to inquiries within 24 hours. Custom orders typically take 1–5 business days to complete production, with final timing confirmed case by case in the quotation. For special/custom requirements, MOQ is 2 km of fiber length. Standard listed patch cords have no formal MOQ. The sample fee is credited against the bulk order.
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