The imec Report: Scaling Optical Interconnects for the AI Era
As artificial intelligence workloads continue to expand at an unprecedented pace, the semiconductor industry faces a critical challenge: moving massive volumes of data between compute elements without hitting the power and bandwidth walls of electrical interconnects. In its latest report, Belgian research institute imec outlines a roadmap for scaling optical interconnects to meet the demands of the AI era—a challenge that has only grown more urgent as we approach 2026.
The Bandwidth Bottleneck
AI training and inference workloads are inherently data-intensive. Large language models and multimodal systems require constant shuffling of terabytes of parameters and activations across GPUs, accelerators, and memory. Traditional copper-based electrical interconnects are approaching fundamental limits in reach, bandwidth density, and energy efficiency. As imec notes, the energy cost per bit must drop dramatically—by orders of magnitude—to sustain the projected growth of AI compute clusters.
Silicon Photonics as the Path Forward
Optical interconnects, which use light rather than electrons to transmit data, offer a compelling solution. Silicon photonics leverages mature CMOS manufacturing processes to integrate photonic components—modulators, waveguides, photodetectors—alongside electronic circuits. imec's report highlights several key scaling vectors:
- Co-packaged optics (CPO): Moving optical engines closer to the switch or compute ASIC, eliminating long electrical traces and reducing power consumption.
- Wavelength-division multiplexing (WDM): Increasing bandwidth density by transmitting multiple wavelengths over a single fiber.
- Advanced packaging: Integrating photonic and electronic dies using 2.5D and 3D packaging techniques, including through-silicon vias (TSVs) and fine-pitch microbumps.
- New materials and processes: Exploring heterogeneous integration with III-V materials for lasers and detectors, as well as novel modulator technologies.
2026 Context: The Road to Terabit-Class Optical I/O
By 2026, the industry has accelerated its transition toward optical I/O. Major foundries and packaging houses are ramping co-packaged optics for high-end switches, while hyperscalers are deploying optical interconnects in AI clusters. imec's roadmap anticipates that optical I/O will move from board-level and package-level integration toward chiplet-level and eventually intra-chip optical networks. Key milestones include:
- Demonstration of terabit-per-second optical links with sub-picojoule-per-bit energy efficiency.
- Standardization efforts for optical chiplets and interoperability.
- Maturation of 3D-integrated photonic-electronic platforms.
Challenges and Research Directions
Despite rapid progress, significant hurdles remain. Laser integration—whether via heterogeneous bonding or epitaxial growth—continues to be a yield and reliability concern. Thermal management of photonic integrated circuits, especially when co-packaged with high-power ASICs, requires careful co-design. Testing and known-good-die strategies for photonic chiplets are still evolving. imec's report calls for cross-disciplinary collaboration among materials scientists, device engineers, packaging experts, and system architects to address these challenges.
Conclusion
The AI era demands interconnect technology that can scale in bandwidth, density, and energy efficiency. Optical interconnects, driven by silicon photonics and advanced packaging, represent the most promising path forward. As imec's report makes clear, the transition from electrical to optical I/O is not a question of if, but when—and the industry must accelerate its efforts to stay ahead of the AI curve.