Cooling is critical for copackaged optics

The digital world is accelerating at a pace that seemed implausible just a few years ago. Artificial intelligence (AI) models are doubling in size, which is causing data center traffic to explode and the infrastructure that powers our connected lives to strain under this unprecedented demand. Behind every AI breakthrough, real‑time analytics engine, and cloud‑scale service lies a hidden bottleneck: the ability to move massive volumes of data efficiently and reliably.

As computing architectures continue to evolve toward higher density and speed, thermal management has emerged as a first-order design requirement. Cooling is no longer solely about removing heat. Instead, cooling directly impacts performance, reliability, scalability, and ultimately the economic viability of next-generation systems. From data centers to edge deployments, insufficient or imprecise thermal control now manifests as real limitations on bandwidth, power efficiency, and system longevity.

Where does thermal control matter most for CPOs?

In today’s copackaged optics (CPO) architecture, thermal areas of concern are largely associated with external laser sources (ELS), optical engines, and other discrete optical and electronic components. These elements often operate at high power densities and are sensitive to even modest temperature fluctuations. Variations in temperature can lead to wavelength drift, reduced signal integrity, and increased system margining to compensate for thermal uncertainty.

Looking forward, the center of thermal gravity shifts toward the application-specific integrated circuit (ASIC) itself as optical functions become increasingly integrated into compute and switching silicon. CPOs and interior lasers dramatically increase local thermal density while tightening operating tolerances. Heat is no longer distributed across a board. It’s now generated within millimeters—or microns—of bandwidth-critical logic. This transition fundamentally changes the cooling problem so that thermal gradients, not just absolute temperature, become performance-limiting factors. Without precise predictive cooling, bandwidth gains promised by advanced optics and integrated ASICs cannot be fully achieved within production environments.

CPO: Opportunity and challenge

CPO is one of the most transformative technologies to hit the data center world. By fusing photonics directly with silicon, CPO reimagines existing network architectures from the ground up. The result is a radical leap forward in bandwidth, energy efficiency, and system density.

Despite its advantages, CPO introduces new challenges, particularly in thermal management, photonic‑electronic co‑integration, and packaging design. The integration of high‑power ASICs with temperature‑sensitive optical components demands precise thermoelectric engineering. By moving photonic input/output (I/O) directly into the same package as switch or compute silicon, CPO eliminates long electrical pathways. But doing so introduces new engineering burdens: higher local power density, tighter thermal‑coupling constraints, and the need for ultrastable photonic operation within close proximity to hot ASICs.

Designing for this moment, whether it’s solutions to cool the laser or as part of a total package, requires deep thermal engineering knowledge and a wealth of real-world realistic modeling combined with in-market knowledge to ensure performance, enable solution scaling, and maximize uptime with no performance disruptions. While a technical issue with pluggable solutions begets a new pluggable, the blast radius of a failing CPO is much larger. Thermal component design is always imperative, but CPO takes this risk profile up a notch.

Core design criteria for CPO

Be mindful of these core design criteria for CPO: 

Designing for power density. CPO places optical modules and high‑power ASICs within extremely close proximity, which drives high local heat flux and requires precise thermal control to prevent optical‑device drift and signal degradation. Maintaining uniform temperatures is essential for reliability of 51.2-Tbit/s CPO systems, and liquid‑cooling and engineered heat‑sink designs are proven effective.

Ultrastable photonic operation within close proximity to hot ASICs. Optical components are highly sensitive to temperature fluctuations. Even small thermal shifts alter resonant wavelengths, degrade modulation contrast, and increase bit error rate (BER). CPO packaging demands tight thermo‑optic management, precise material selection, and architectural strategies to isolate photonics from ASIC heat sources.

Electrical‑to‑optical co‑integration. Integrating photonic dies with switch ASICs shortens electrical paths, but introduces new coupling challenges. The CPO environment requires careful signal‑integrity design, radio frequency (RF) optimization, and parasitic minimization, using multiphysics simulation to model electrical, thermal, and optical interactions simultaneously.

Packaging and interposer engineering. CPO performance depends heavily on substrate and interposer choices. Glass interposers, for example, offer a scalable path with controlled thermal behavior while maintaining RF performance up to 40 GHz. These design knobs directly impact heat flow, electrical loss, and manufacturability.

Scaling to multi‑terabit data rates. As interconnect speeds reach 1.6 T and beyond, the industry is hitting limits in power, signal integrity, and faceplate density. CPO inherits these challenges but addresses them by removing electrical losses and adding wavelength-division multiplexing (WDM) interconnects, which simultaneously introduces new constraints in cooling, thermal coupling, and high‑density photonics integration. Multi‑terabit scaling demands co‑optimization of photonics, thermals, and packaging from the outset.

Thermoelectric cooling for CPO

Thermoelectric cooling is well suited for CPO because it enables deterministic, highly localized thermal control at the component level. The absence of moving parts enhances system reliability, and combined with intrinsically high mean time between failures and the elimination of mechanical vibration, solid-state solutions are ideal for tightly integrated photonic-electronic packages.

With the ability to achieve sub-0.5°C temperature stability, thermoelectric coolers precisely regulate laser junction and photonic integrated circuit (PIC) temperatures to enable ultrahigh-performance (UHP) lasers to maintain signal integrity through the ring modulator. This precise thermal stabilization minimizes wavelength drift, preserves resonance alignment, reduces insertion loss, and sustains modulation efficiency. Thermoelectric cooling also supports a fast, closed-loop response to transient thermal loads inherent within high-bandwidth CPO systems, which makes it an effective solution for maintaining optical performance, yield, and reliability for advanced packaging environments.

In many ways, CPO is a technology that unlocks a new frontier. It allows AI clusters to grow without collapsing under power constraints, enables cloud networks to evolve at the pace of digital demand, and sets the stage for compute systems that are faster, cooler, denser, and dramatically more efficient. Thermoelectric cooling approaches are uniquely enabled to meet this moment—when and where needed most.