Co-packaged optics

Notes

Serviceability is the sticking point, because a failed in-package optic cannot be swapped like a pluggable module.

Overview

Co-packaged optics (CPO) is a way of building network switches and accelerators in which the optical engines that turn electrical signals into light sit inside the same package as the main chip, instead of in pluggable transceiver modules at the front of the equipment. Shortening the electrical path from the chip to the optics cuts the power spent driving signals across a circuit board. CPO is being adopted first in high-bandwidth AI and data centre switches, where interconnect power has become a major constraint.

How it works

In a conventional switch, each port's signal leaves the switch chip through a SerDes, crosses the circuit board and a connector, and reaches a pluggable module that holds the laser, modulator, photodetector and their electronics. In CPO, optical engines are mounted on the same substrate as the switch or accelerator die, close around it. Each engine pairs a photonic integrated circuit, which modulates and detects light in waveguides, with an electronic chip holding drivers and receivers, and fibres leave the package directly.

The laser is often kept outside the package in a separate pluggable unit, away from the heat of the main chip and easy to replace, with its light fed in by fibre. OIF has published implementation agreements for a 3.2 Tb/s co-packaged module and for an external laser small form factor pluggable to support this split.

CPO brings real difficulties. The optical engines sit next to a very hot chip, fibre alignment must hold across temperature, materials with different thermal expansion stress the assembly, and a failed engine cannot simply be unplugged and swapped like a module. Assembly yield across many dies in one package matters a great deal, and test and inspection of the photonic parts add new steps to the packaging flow.

Examples

• NVIDIA's Spectrum-X Photonics Ethernet and Quantum-X Photonics InfiniBand switches, announced in March 2025 with co-packaged silicon photonics.
• A switch design that feeds its in-package optical engines from external laser modules in a pluggable form factor.
• Live co-packaging and external laser demonstrations by OIF members at OFC 2025.
• Inspection of V-grooves, waveguides and micro-lenses during CPO module assembly.

Why it matters

Switch and accelerator makers are turning to CPO because moving data optically close to the chip promises large savings in network power and better signal integrity at very high port speeds. System architects, packaging engineers, silicon photonics designers and the driver and receiver circuit designers all have to work as one team, and data centre operators must plan for a different service model.

Related terms

• Optical engine
• Optical I/O
• Optical transceiver
• Silicon photonics
• Advanced packaging

Where it appears on the Hub

Used on 13 pages of the Hub. In each group, the pages that mention it most come first.