What Is a CPO Switch? A Plain-Language Guide to Co-Packaged Optics

Micas Networks 51.2T co-packaged optics (CPO) switch. — A 51.2T CPO switch: 128 × 400G ports, fiber connected at the front panel, no transceivers.

AI data centers are running into a wall, and it isn't compute. It's the power and space it takes to move data between switches. Co-packaged optics (CPO) is the industry's answer, and in 2025 it moved from lab demos to shipping hardware.

This guide explains what a CPO switch is, how it differs from the switches most data centers run today, why it saves so much power, and what the tradeoffs are.

What is a CPO switch?

DefinitionA CPO switch is a network switch whose optical engines sit inside the same package as the switch chip (ASIC), instead of in separate plug-in modules on the front panel.

Every data center switch has to turn electrical signals into light to send data over fiber. In a traditional switch, that conversion happens in optical transceivers plugged into the front of the box. In a CPO switch, it happens millimeters from the switch chip itself, and fiber connects almost directly to the chip package.

Diagram of a co-packaged optics package: the optical engine sits on the same ASIC substrate as the ASIC die, beneath a shared heat sink. — Inside a CPO package: the optical engine shares the ASIC substrate with the switch die, so the signal never crosses the circuit board. Source: Micas Networks.

How is a CPO switch different from a traditional switch?

The difference comes down to how far the electrical signal has to travel before it becomes light.

	Traditional switch (pluggable optics)	CPO switch
Where optics live	Transceiver modules in front-panel ports	Optical engines inside the switch chip package
Electrical path	Centimeters of circuit board traces to the front panel	Millimeters from chip to optics
Signal processors (DSPs)	Needed in every transceiver to clean up the signal	Not needed
Parts to buy	Switch plus one transceiver per port	Switch with fiber connections built in
Servicing optics	Swap a module by hand	Handled at the system level

At low speeds, the traditional design works fine. At 51.2 Tb/s and beyond, pushing signals across the board and cleaning them up again takes a large share of the switch's total power.

Why does CPO save power?

CPO switches use over 50% less power than traditional switches with the same specifications. That figure comes from Micas testing at 40 °C ambient with full line-rate bidirectional traffic. In that test, a Tomahawk 5 switch with 400G DR4 pluggable optics drew 3,267 W, and the Tomahawk 5 CPO switch drew 1,626 W, a 50.23% reduction.

Power comparison: TH5 M2-W6940-128QC with 400G DR4 pluggables at 3,267 W versus TH5 CPO M2-W6940-128X1-FR4 at 1,626 W, a 50.23% reduction. — Pluggable vs. CPO, same Tomahawk 5 switch chip: 3,267 W vs. 1,626 W. Ambient 40 °C, full line-rate throughput, bidirectional traffic. Source: Micas Networks.

The savings come from two places:

No DSPs. Each pluggable transceiver carries a digital signal processor to recover signals that degraded on their way across the board. With the optics next to the chip, those DSPs aren't needed.
Shorter electrical paths. Less distance means less power spent driving signals, and less heat to remove from the system.

Less heat also changes cooling. The Micas 51.2T CPO switch ships as an air-cooled 4RU system, so it fits existing data center racks without a move to liquid cooling.

There's a cost benefit too. Because the optics are built in, there are no transceivers to buy for each port.

What are the tradeoffs?

The biggest question buyers ask about CPO is reliability. In a pluggable switch, a failed transceiver is a quick swap. In a CPO switch, the optics are part of the chip package, so a failure matters more.

That's why reliability testing has been central to CPO's path to production. For the Micas 51.2T CPO switch:

cumulative 400G-equivalent port device hours, link flap-free, in hyperscaler and OEM testing

<0.1 FIT

laser field failure rate across 100 billion field device hours, from more than 4M lasers shipped since 2016

3/3

key components passed qualification: pluggable laser source, photonic IC, optical connector

Laser and component qualification data: Broadcom.

The laser source, the component most likely to wear out, also stays pluggable, so it can still be serviced from the front of the box.

Where is CPO today?

CPO is no longer a research project. In March 2025, Micas Networks put the industry's first 51.2T CPO switch system into volume production, developed with Broadcom.

Micas 51.2T CPO switch	Specification
Switch device	Broadcom Tomahawk 5 Bailly (BCM78909)
Optical engines	Eight 6.4 Tb/s silicon photonics chiplets
Ports	128 × 400G FR4
Form factor	4RU, air-cooled
Fiber connectors	LC or MPO
Manufacturing	Micas co-owned factory in Malaysia
Availability	In volume production since March 2025

NVIDIA and Broadcom are also bringing CPO to next-generation platforms, a sign that CPO is becoming a standard part of AI networking.

Frequently asked questions

What does “CPO switch” mean?

CPO stands for co-packaged optics. A CPO switch builds its optical engines into the switch chip package instead of using plug-in transceivers.

What does CPO stand for in electronics?

In networking and semiconductors, CPO means co-packaged optics: optical components packaged together with a chip on a single substrate.

Is CPO better than pluggable optics?

For high-bandwidth AI networks, CPO uses far less power and removes per-port transceiver costs. Pluggable optics are simpler to service and are still used on the server side of most networks.

Are CPO switches available now?

Yes. The Micas 51.2T CPO switch has been in volume production since March 2025.

See the Micas 51.2T CPO switch

Micas Networks builds data center switches for AI-scale networks, including the industry's first CPO switch in volume production. Explore the specs or talk to our team about your deployment.

Explore the CPO switch →

Power: >50% reduction vs. traditional switches with the same specifications, per Micas testing at 40 °C ambient, full line-rate bidirectional traffic. Reliability: 4M cumulative 400G-equivalent port device hours (hyperscaler and OEM testing); laser field failure rate <0.1 FIT across 100 × 10⁹ field device hours and 4M+ lasers shipped since 2016 (data source: Broadcom).