Unik APD lægger fundamentet for næste generation af optisk interkonnektering
imec præsenterer 100 GHz Ge/Si avalanche fotodiode (APD), der baner vejen for 400 Gbit/s datamodtagelse med operation ved kun 5 V (in english).
At the European Conference on Optical Communications (ECOC), imec - a world-leading research and innovation hub in advanced semiconductor technologies - presented the world's first Ge/Si avalanche photodiode (APD) to combine 100 GHz bandwidth, low-voltage (5 V) operation and a responsivity of 1.8 A/W across both the O- and C-bands.
Delivering a 3 dB receiver-sensitivity improvement, the device was used to demonstrate the first net 400 Gbps optical link employing an APD receiver. This breakthrough marks an important step toward next-generation optical interconnects for AI data centers, where vast amounts of data must be exchanged with ever-higher speed and energy efficiency.
As AI workloads continue to scale, data centers require optical links that can move massive amounts of data between racks and blade servers with low latency and growing per-lane data rates. Imec addresses this need by developing key silicon photonics building blocks, including high-speed modulators and photodetectors, for next-generation optical interconnects.
At last year’s ECOC, imec demonstrated a beyond-110 GHz C-band Ge/Si electro-absorption modulator (EAM), strengthening the transmit side of future short-reach, scale-up optical links.
At the receiving end of those links, however, the challenge is no less demanding, as receivers must simultaneously maintain high sensitivity while operating at ever-higher bandwidths.
Avalanche photodiodes offer an attractive solution because their built-in signal amplification improves receiver sensitivity. Traditionally, though, achieving this amplification has come at the expense of bandwidth, higher operating voltages, or both.
The world's first Ge/Si APD to combine 100 GHz bandwidth, low-voltage operation & meaningful gain
- The team started from the well-established SACM (separate absorption, charge and multiplication) APD architecture, but re-engineered the device at its core, explains Joris Van Campenhout, VP R&D Optical Interconnects at imec.
- By scaling the multiplication layer width to below 100 nm - leveraging a deeply-recessed germanium-in-silicon structure - and eliminating the charge layer, we were able to simultaneously achieve 100 GHz bandwidth, 5 V operation and a responsivity of 1.8 A/W, corresponding to approximately a twofold internal gain. An additional advantage is that the device delivers comparable performance in both the O-band and C-band, giving system architects greater flexibility when designing future optical interconnects.
The first demonstration of a net 400 Gbps optical link employing an APD
To demonstrate the technology's system-level potential, imec combined its APD with the beyond-110 GHz C-band Ge/Si EAM it unveiled at last year’s ECOC. Together, the devices were used to demonstrate the first net 400 Gbps optical link employing an APD.
Joris Van Campenhout continues:
- Delivering a 3 dB receiver-sensitivity improvement, the APD provides additional link margin compared with a conventional photodiode. Depending on system requirements, this margin can be used either to reduce laser power consumption or to accommodate higher optical losses. Combined with its high bandwidth and low operating voltage, this makes the device particularly attractive for future scale-up optical interconnects.
Looking ahead, imec's researchers will focus on further improving the APD’s reliability across a wider range of temperatures and optical input power conditions. Future work will also tackle integration of the APD with high-speed receiver electronics as part of more complete optical interconnect solutions.
In parallel, the team will continue to leverage imec's 300 mm silicon photonics (iSiPP300) platform to mature the technology and accelerate the adoption of optical interconnect technologies that help address the bandwidth and energy-efficiency challenges facing future AI infrastructure.
