Understanding what is an optical module at its fundamental level is the starting point for understanding CPO. While traditional modules are independent, pluggable, external boxes, CPO represents a transition from a "modular system" to a "co-packaged chip system."

Why Do Traditional Pluggable Modules Hit Their Physical Limits?

Answer capsule approach:​ Traditional pluggable modules hit their physical limits at single-channel rates of 224Gbps because high-frequency electrical signals degrade rapidly over copper board traces, requiring power-hungry digital signal processors (DSPs) to restore signal integrity.

For the last 20 years, pluggable transceivers have been the bedrock of data communications. If a module broke, an engineer could pull it out and slide in a new one without shutting down the entire switch. This plug-and-play simplicity made scaling data centers incredibly easy.

However, as we push single-channel speeds toward 224Gbps, we run face-first into the laws of physics. High-frequency electrical signals suffer from extreme attenuation (loss of signal strength) when they travel through copper copper tracks on a printed circuit board (PCB).

At 224Gbps, the electrical signal deteriorates so fast that by the time it travels across 10 to 30 centimeters of copper board to reach the pluggable module, it is completely distorted. It arrives looking like a fuzzy mess of noise.

To solve this, traditional transceivers rely on a Digital Signal Processor (DSP) chip. The DSP acts like a high-speed reconstructor, using complex math to "guess" what the original signal looked like and clean it up.

But DSPs are incredibly power-hungry and expensive. A single DSP chip inside an optical module can consume between 5 to 10 watts of power. Multiply that by dozens of transceivers plugged into a single high-density switch, and you get a massive thermal problem. The switch faceplate turns into a virtual furnace.

Even our highly optimized 400G QSFP-DD transceivers push pluggable design to its absolute engineering limits. Beyond these speeds, trying to make copper traces work is no longer a matter of improving manufacturing; it is a physical bottleneck. CPO solves this not by trying to make copper better, but by removing the copper path almost entirely.

How Does CPO Save So Much Power?

Answer capsule approach:​ CPO saves power by reducing the electrical path from several centimeters to a few millimeters, allowing systems to remove or scale down energy-intensive DSPs and lower laser driver requirements.

The power-saving benefits of CPO come from two main areas:

1. Eliminating or Downsizing the DSP

Because the distance between the switch chip (ASIC) and the CPO optical engine is only a few millimeters, the electrical signal has almost no room to degrade. It arrives crisp and clean.

This means the system does not need a heavy, power-hungry DSP to perform complex signal restoration. In many CPO designs, the DSP can be completely eliminated. This instantly cuts 5 to 10 watts of power consumption per port.

2. Reducing Driver Power

When signal lines are short, the electrical amplifiers (drivers) do not need to push nearly as much voltage to get the signal across. This drops the driver power down to a fraction of what traditional systems require.

The real-world energy savings of this shift are dramatic:

Per-Port Savings:​ According to data released by NVIDIA, switching to a CPO-enabled design reduces individual port power consumption from 30 watts down to just 9 watts (a 70% decrease).

System-Wide Savings:​ In scale-up AI architectures, Meta's hardware analysis showed that an 800G traditional pluggable module consumes roughly 15W, whereas the optical engine inside Broadcom's Bailly CPO switch consumes only 5.4W per 800G of bandwidth delivered (a 65% power saving).

Saving power does not just lower your electric bill; it also lowers cooling costs. In massive AI training clusters, cooling the hardware often takes almost as much power as running the processors themselves. By eliminating the heat at the chip level, CPO makes green, highly sustainable AI computing a reality.

What Does a CPO System Look Like Inside?

Answer capsule approach:​ A standard CPO system consists of three core components: a silicon photonics engine for electro-optical conversion, a high-precision fiber optic array (FAU) for external connectivity, and an application-specific integrated circuit (ASIC) switch chip acting as the brain.

Inside a co-packaged optics design, the physical layout changes from a spread-out board to a highly dense, integrated micro-system. Here are the three pillars that make up its interior:

1. The Silicon Photonics Engine (PIC)

Unlike traditional transceivers that use individual, separate lasers and optical components, CPO relies on Silicon Photonics (SiPh). Photonic Integrated Circuits (PICs) are manufactured using standard CMOS silicon processes (the same factories that make computer CPUs). This allows engineers to print microscopic optical waveguides, modulators, and detectors directly onto a silicon chip.

2. High-Precision Fiber Array Unit (FAU)

Once the silicon photonics engine converts electrical signals into light, that light must be funneled into glass fibers. The Fiber Array Unit (FAU) aligns dozens of individual fibers to the optical ports on the PIC with microscopic precision. Because the optical cores are only a few micrometers wide, even a tiny misalignment can ruin the connection.

When we manufacture high-density MPO and breakout fiber assemblies at COBTEL, micron-level end-face polishing is already a major engineering focus. In CPO systems, this precision is scaled directly onto the chip substrate.

3. The Switch ASIC (Core Brain)

This is the central processor that manages network routing. In CPO, this massive chip is placed directly next to the silicon photonics engine on a single multi-chip package substrate using advanced packaging technologies (like 2.5D or 3D stacking).

The External Laser Source (ELS): Putting the Bulb Outside the Oven

There is one major design challenge inside a CPO package: heat. The silicon switch ASIC gets incredibly hot (running like a small oven), but lasers are highly sensitive to temperature. If a laser chip gets too hot, its efficiency drops and its lifespan plummets.

To solve this, CPO architectures use an External Laser Source (ELS). The laser emitter is moved completely out of the hot chip package and placed onto the cool front panel of the switch. High-density fiber optic cables then guide the unmodulated laser light from the front panel into the CPO engine on the chip.

This design keeps the "heat-sensitive lightbulbs" safe from the "furnace," making the system much more reliable. To master these component dynamics, it is highly useful to study the main parts of an optical transceiver.

Main Packaging Structure Types of CPO Optical Modules

The way engineers physically arrange, connect, and stack the optical and electrical chips defines the CPO packaging structure. Today, the industry has settled on three primary structures: 2D, 2.5D, and 3D packaging.

1. 2D Packaging (Side-by-Side Integration)

In a 2D configuration, the Electronic Integrated Circuit (EIC) and the Photonic Integrated Circuit (PIC) are placed side-by-side on the same organic substrate or PCB.

Wire Bonding CPO:​ The EIC and PIC connect to the substrate, and thin gold wires bridge the gap between them. While this is highly flexible and simple to build, the wire loops create high parasitic capacitance, which limits high-speed performance.

Flip-Chip CPO:​ The chips are flipped upside down, and small metal bumps connect them to a ceramic substrate. This provides a shorter signal path and better thermals, but multi-layer ceramic substrates are expensive.

Fan-Out Wafer-Level Packaging (FOWLP):​ The PIC and EIC are molded into a synthetic polymer layer, and high-density metal lines (Redistribution Layers, or RDLs) are printed over them to link them. This completely eliminates wire bonds and bumps, creating a very thin, high-performance module.

Real-World Example: Broadcom's Bailly 51.2T CPO switch uses FOWLP to package eight optical engines around the central switch ASIC.

2. 2.5D Packaging (Interposer-Based Integration)

2.5D packaging introduces an extra layer called an interposer between the active chips and the bottom substrate. The active chips sit on top of this interposer, which contains incredibly dense, microscopic wiring to route signals between them.

Silicon Interposer:​ The PIC and EIC sit on a thin layer of silicon. This matches the thermal expansion of the chips perfectly, preventing physical warping. However, silicon is a semiconductor, which can cause high-frequency signals to bleed energy into the substrate.

Glass Interposer:​ Chips sit on a glass interposer. Glass is an exceptional electrical insulator, which keeps high-frequency signals clear.

OFC 2026 Milestone: Intel demonstrated a glass-substrate CPO prototype at the 2026 Optical Fiber Communication Conference, demonstrating a 10x increase in interconnect density.

EMIB (Embedded Multi-die Interconnect Bridge):​ Instead of a giant, expensive interposer, a tiny, thin silicon "bridge" is embedded inside the organic substrate right under the chip edges to link them. This saves money and maintains excellent signal integrity.

3. 3D Packaging (Vertical Stacking)

3D packaging represents the ultimate evolution of CPO. Instead of placing the optical and electrical chips side-by-side, engineers stack them vertically, one directly on top of the other.

PIC as the Interposer:​ The electronic chip (EIC) is stacked directly on top of the optical chip (PIC) using advanced copper-to-copper hybrid bonding.

Platform Standard: TSMC's COUPE (Compact Universal Photonic Engine) 3D platform uses this approach, dropping parasitic capacitance by an incredible 85% and cutting signal latency by 95%.

EIC as the Interposer:​ The PIC is stacked on top of the EIC. This allows the hot electronic chip to connect directly to the bottom substrate for easier cooling.

Organic Substrate Embedding:​ Silicon photonics are embedded directly inside an organic substrate, using built-in polymer waveguides to route light. This is highly cost-effective but prone to warping under intense heat.

Here is a summary of the tradeoffs across these three structural approaches:

Who Is Building CPO? The Global Ecosystem Map

CPO is not a localized effort; it has sparked a massive global collaboration across silicon design, advanced packaging, laser manufacturing, and physical cabling infrastructure.

1. International Silicon and System Giants

NVIDIA:​ The most aggressive driver of CPO commercialization. NVIDIA's Quantum-X800 Q3450-LD liquid-cooled CPO switch (using TSMC's 3D COUPE platform) delivers 115.2 Tbps of total bandwidth across 144 ports, completely removing the DSP to save over 3 kilowatts of power per switch rack.

Broadcom:​ The early pioneer. Following its Bailly 51.2T CPO switch, Broadcom introduced the Tomahawk 6 Davisson CPO ASIC, achieving single-channel speeds of 200Gbps and cutting optical power consumption by 70%.

Intel:​ Capitalizing on over 20 years of research, Intel is focusing on Optical Compute Interconnects (OCI) to link CPU and GPU chips directly using high-bandwidth optical paths.

Cisco & Marvell:​ Building custom SiliconOne CPO routers and integrated 3D Silicon Photonics engines directly inside customized XPUs.

2. Semiconductor Foundries

TSMC:​ Providing the foundational manufacturing engine with its COUPE platform, enabling high-volume 3D hybrid bonding of optical and electrical circuits.

GlobalFoundries (GF Fotonix) & Tower Semiconductor:​ Offering open, highly standardized silicon photonics design platforms for key tech builders.

3. Supply Chain & Component Leaders

Precision Alignment (FAUs):​ Tianfu Telecom is a global leader in high-precision FAU manufacturing and 1.6T light engines, serving as a core supplier for high-end AI CPO systems.

Laser Emitters (ELS):​ Lumentum and Coherent are leading developers of external laser sources. Meanwhile, companies like Yuanjie Technology have built a strong market position supplying CW-DFB laser chips.

Switch and Cooling Infrastructure:​ Ruijie Networks, H3C, and cooling specialists like Envic provide CPO-ready liquid cooling setups to manage high heat loads.

4. COBTEL's Role in the Ecosystem

As an OEM manufacturer of advanced optical components, COBTEL plays a crucial role in the physical infrastructure layer. CPO systems utilize incredibly high fiber counts to route laser light and signals. Our high-precision MPO fiber patch cords and custom server cabinets are specifically engineered to support the sub-micron tolerances and high density required by CPO switches and AI accelerators.

Will CPO Completely Replace Traditional Pluggable Modules?

Answer capsule approach:​ No, CPO and pluggable optical modules will co-exist for the foreseeable future, as pluggables remain ideal for long-distance, highly flexible, and hot-swappable links, while CPO targets short-reach, ultra-dense AI clusters.

Despite the massive excitement surrounding co-packaged optics, it is not a "one-size-fits-all" replacement for traditional pluggable modules. Instead, the two technologies will co-exist, each serving different roles in the network.

Pluggables: King of Long Distance and Flexibility

For long-distance data center interconnects (DCI)-such as linking two data centers across a city or state-traditional pluggable modules like our high-capacity 800G optical transceiver will remain the standard.

These links do not need ultra-dense chip integration, but they do require high flexibility. If a long-distance transmitter fails, swapping a front-panel pluggable module takes seconds and keeps the rest of the switch running.

CPO: Master of Short-Distance, Ultra-High Bandwidth

CPO's home is inside the AI cluster. For connecting GPUs to other GPUs, or linking spine switches inside a single hall where distances are short (under 100 meters), bandwidth density and power savings are the ultimate priorities.

In this space, CPO is unmatched.

Industry analysts estimate that CPO will account for roughly 1% of AI-related optical modules shipped. However, as 1.6T and 3.2T architectures scale up, CPO market penetration is projected to climb to 20%–35% between 2028 and 2030.

The Stepping Stone: Near-Packaged Optics (NPO)

Because the leap from traditional pluggables to full CPO is technically complex, the industry has embraced an intermediate step called Near-Packaged Optics (NPO).