Belgian researchers raise speed limit in European datacentres

Researchers have developed a prototype of an optical receiver that will help datacentres process data at a much higher rate

Partially funded by grants from the European Commission, Belgian research and technology organisation (RTO) imec recently completed work that demonstrates powerful new concepts that can now be used by manufacturers to speed up data networks.

The aim of the research project was to reduce costs, improve yield and lower power consumption. Now, the fruits of the work are expected to be used over short distances to speed up datacentres – and then over greater distances for applications related to 5G. 

A team of researchers at the internet technology and data science lab (IDLab) presented their prototypical optical receiver, which achieves a gross data rate of 200Gbps, at the European Conference on Optical Communication (ECOC) in Glasgow during the week of 2-6 October 2023. IDLab is a part of the imec research group at Ghent University in Belgium. 

Not only is this new approach ultrafast, but it is also highly scalable. Speed and scalability are the two primary prerequisites for any technology used to meet the soaring requirements of performance-hungry applications. The new optical receiver works by co-integrating a travelling-wave SiGe Bi-Complementary metal-oxide-semiconductor (BiCMOS) transimpedance amplifier with a silicon photonics Ge photodetector.  

“The use of mainstream SiGe BiCMOS makes the technology more scalable, which also makes it more affordable,” said Peter Ossieur, programme manager for high-speed transceivers at IDLab. “Manufacturers can integrate more features and at the same time produce a higher volume of chips.” 

Why speed is so important 

Modern applications – including artificial intelligence, cloud computing and 5G – consume vast quantities of data and need to process that data at ever-growing rates. While processing power continues to increase at astounding rates, that evolution alone will never keep up with demand.

And even though specialised chips are being developed to meet the requirements of specific applications, many algorithms rely on fast data exchange between different computing and storage elements in a datacentre.  

Optical communication networks, which are delivering increasingly higher levels of performance, are a big part of the solution. Optical technology already provides the backbone for communication within virtually all datacentres. But some of the shortcomings of optical technology are development time and cost and power consumption. 

“The highest-performing optical datacom transceivers today use eight channels carrying 100Gbps each, for a total data rate of 800Gbps,” explained Ossieur.

“Our innovation doubles the channel capacity to 200Gbps, which allows manufacturers to reduce the number of channels, while maintaining the same data rate. This means transceiver complexity can be reduced to improve manufacturing yield and lower unit costs. The other advantage is that power consumption also comes down.” 

A culture of research that promises even faster networks 

“We look at the transceiver as a whole – the photonics front end and electronics all the way to the CMOS speed chip and we’re looking for ways in which we can bring innovation,” said Ossieur. “Our goal is to develop intellectual property that can be licensed by industry.”

“Our research focuses on the electronics, which is closely co-developed with photonic integrated circuits – and that combination is what allowed us to deliver results,” he added. “The demonstrator combines electronics that we developed in our team with photonics from other teams at imec.” 

Imec has a number of different optical platforms and produces its own optical devices at wafer scale in its in-house 200mm and 300mm CMOS pilot lines. These include high-performance devices that operate at over 50GB for a range of applications – including light modulation, switching, coupling, filtering and detection.

Production is at low volume for research purposes. But the research organisation is always keeping an idea on industry, maintaining a repository of device components, designs and software that can be licensed and customised by manufacturers. 

“For the prototype we developed, the main focus was on the SiGe BiCMOS electronics,” said Ossieur. “We’ve shown that using a travelling wave approach, we can meet specifications for devices that need 200Gbps per channel. This is a prototype chip. Customers can license the underlying technology for short reach interconnect inside datacentres, with potential use for coherent transceivers where the link distances are far longer.”  

According to Joris Van Campenhout, fellow and programme director for optical I/O at imec, the new optical receiver is just one of many things imec is doing to ready its silicon photonics platforms for even more demanding applications.

“These latest results represent one more data point showcasing the capability of imec’s silicon photonics platform [iSiPP] to operate at lane rates of 200Gbps, a key requirement for upcoming pluggable and co-packaged optics,” he said.

Another promising research area is in programmable photonic chips. While photonics provides an ideal medium for moving data around very quickly, developing new photonic integrated chips is a slow and costly process.

Researchers at imec are using microelectromechanical systems (MEMS) and liquid-crystal-based solutions to develop low-power building blocks that can be reconfigured to serve different applications, making the photonic chips reusable. These techniques can help serve applications in a range of industries beyond high-performance computing – including biosensing. 

Last but not least, imec is also working on wireline data converters for fast networking applications. These converters operate at very high speed in highly scaled CMOS. Researchers are designing prototypes in 5nm (nanometre) CMOS and plan to start working on 3nm CMOS during the next year.

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