Imec shows 100 GHz Ge/Si APD for 400 Gbps optical links

Imec has presented a germanium-on-silicon avalanche photodiode (APD) that it says combines 100 GHz bandwidth, 5 V operating voltage and a responsivity of 1.8 A/W across both O-band and C-band wavelengths. The device was shown at the European Conference on Optical Communications (ECOC) on 21 September 2026, and imec describes it as the first Ge/Si APD to achieve this combination of speed, low voltage and gain.

Device architecture and claimed sensitivity gain

According to imec, the APD is built on a separate absorption, charge and multiplication (SACM) architecture that the research team re-engineered by scaling the multiplication layer to below 100 nm using a deeply-recessed germanium-in-silicon structure, and by removing the charge layer entirely. Imec's Joris Van Campenhout, VP R&D Optical Interconnects, attributes the resulting 1.8 A/W responsivity to roughly a twofold internal gain, and states the device delivers a 3 dB receiver-sensitivity improvement over a conventional photodiode. Imec says this margin could, depending on system design, be used to lower laser power or tolerate higher optical losses; this is presented as a vendor rationale rather than an independently verified system outcome.

Link demonstration and remaining work

To test system-level performance, imec paired the APD with its previously shown beyond-110 GHz C-band Ge/Si electro-absorption modulator, unveiled at ECOC in the prior year, to demonstrate what it describes as the first net 400 Gbps optical link using an APD receiver. This is a laboratory demonstration on imec's 300 mm silicon photonics (iSiPP300) platform, not a shipping component or finished interconnect product.

Imec states that further work will focus on improving the APD's reliability across a wider range of temperatures and optical input power levels, and on integrating the device with high-speed receiver electronics as part of more complete interconnect solutions aimed at AI data centre applications.