Leuven, Belgium — Imec has reported a C-band germanium-silicon electro-absorption modulator (GeSi EAM) fabricated on its 300 mm silicon photonics line that exceeds 110 GHz electrical bandwidth and delivers a net 400 Gb/s per lane. Designed for compact footprint, low latency, and high energy efficiency, the device targets short-reach IM/DD (intensity-modulation/direct-detection) optical links that tie together rack-to-rack and blade-server resources—exactly the traffic patterns exploding with AI training workloads.
Why this matters
Modern AI clusters demand ultra-fast, low-latency interconnects inside the data center. A pragmatic path is short-reach IM/DD at ~400 Gb/s per lane, minimizing complexity and cost versus coherent links. The new Imec modulator is positioned to be a building block for these scale-up fabrics.
What Imec built
- One device, C-band, beyond 110 GHz. A GeSi EAM that pushes well past 110 GHz measured bandwidth and supports 400 Gb/s per lane transmission.
- CMOS-friendly integration. Implemented on 300 mm Si-photonics, enabling wafer-scale manufacturability.
- Franz–Keldysh operation. The GeSi stack leverages field-induced absorption change to combine speed, small area, and low power.
Context vs. other modulators
- Thin-film LiNbO₃ MZMs: outstanding linearity/low loss/very high bandwidth, but large die area and contamination concerns can complicate co-packaged flows at wafer scale.
- Microring modulators: excellent density, yet typically need tight thermal/locking control, impacting energy efficiency.
- Imec’s GeSi EAM aims to blend high bandwidth + compactness + efficiency without heavy stabilization overhead.
Performance & setup
- Transmission demo: Net 400 Gb/s per lane in a PAM-4 IM/DD link using a wide-bandwidth test chain.
- First >110 GHz GeSi EAM operating in the C-band.
- First net 400 Gb/s-per-lane result demonstrated with a silicon-based EAM.
- Ceiling set by instruments: Imec notes the measurement gear—not the device—capped characterization at 110 GHz, suggesting headroom remains.
Behind the result
This milestone builds on years of parallel progress:
- Device engineering: footprint tuning, doping profiles, and epitaxial growth optimizations.
- System work: a robust end-to-end transmission bench to validate high-rate PAM-4 IM/DD performance.
What’s next
- Push the bandwidth window: Characterize beyond 110 GHz with higher-frequency equipment.
- Thermal realism: Evaluate under elevated temperatures representative of data-center environments.
- Ecosystem access: The GeSi EAM is being made available to partners on Imec’s 200 mm and 300 mm Si-photonics platforms to explore deployment in AI cluster interconnects.
Imec’s C-band GeSi EAM combines wafer-scale manufacturability, compact design, and >110 GHz performance to enable 400 Gb/s-per-lane IM/DD links—an attractive path for high-density, short-reach AI data-center connectivity.