The Belgian Microelectronics Research Center (imec) announced the successful demonstration of a C-band germanium-silicon (GeSi) electro-absorption modulator (EAM) with a bandwidth exceeding 110GHz. The component was manufactured on the 12-inch silicon photonics platform developed by imec.
Imec stated that the new modulator achieves a network transmission rate of 400Gb/s per channel and is optimized for compact design, low latency and high energy efficiency, laying the foundation for a new generation of optical intensity modulation direct detection (IM/DD) links that provide a simple and cost-effective way to interconnect data center racks and blade servers. This technology will be key to meeting the needs of AI applications that rely on faster and more efficient machine learning training.
Imec points out that artificial intelligence (AI) applications—and the machine learning (ML) training that drives them—require computing architectures that can exchange huge amounts of data with near-instant response. Meeting this challenge requires short-distance, vertically scalable interconnects between data center racks and blade servers that provide minimal latency and single-lane 400Gb/s bit rates (now widely considered the benchmark for future-ready deployments.) Optical IM/DD links powered by electroabsorption modulators are emerging as a key enabler.
Cedric Bruynsteen, a researcher at the IDLab of the imec research team at Ghent University, explained that developing the right modulator to assist these optical IM/DD links has been a major research focus because commonly used technology options have shortcomings. For example, thin-film lithium niobate Mach-Zehnder modulators (MZMs) provide excellent linearity, low optical loss and ultra-high bandwidth, but their large footprint and contamination challenges hinder their wafer-level integration with advanced CMOS logic components, challenging their future applications in co-packaged optical components (CPO) and optical I/O. On the other hand, micro-ring resonator modulators offer high integration density but require extensive stabilization control circuitry, which limits their energy efficiency.
The unique combination of ultra-high bandwidth, single-channel 400Gb/s IM/DD transmission and in-house wafer-level manufacturing of C-band components is driving the next generation of optical communications interconnects. Cedric Bruynsteen emphasizes that the C-band germanium silicon electroabsorption modulator we developed meets these challenges head-on. By fully utilizing the Franz-Keldysh effect, this modulator achieves compact design, high-speed and low-power transmission. And thanks to its germanium-silicon foundation, it also integrates seamlessly with the 12-inch silicon photonics platform we developed, enabling mass-market manufacturability.
Imec’s achievement combines two world firsts, the first demonstration of a 110GHz ultra-wideband germanium silicon electroabsorption modulator operating in the C-band, and the first use of a silicon-based electroabsorption modulator to achieve a single-channel 400Gb/s network transmission rate. This initiative is based on more than 10 years of R&D progress in both component integration and system level. In terms of component integration, imec researchers optimized the board area size, doping scheme and epitaxial growth process. On the system side, they developed a robust transmission setup to demonstrate the electroabsorption modulator's performance in achieving single-channel 400Gb/s network data transmission within a fourth-order pulse oscillator modulation (PAM-4) IM/DD link.
Imec further pointed out that these results clearly characterize the potential of our germanium-silicon electroabsorption modulator in realizing a new generation of vertically extended optical communication interconnections. Interestingly, though, the modulator itself was not the limiting factor in our test bandwidth. It was the measurement equipment that capped our bandwidth at 110GHz. Therefore, with access to higher frequency measurement tools, the next step is to uncover the true bandwidth limitations of this component and evaluate its performance at high temperatures such as those found in data centers. At the same time, imec is opening up this germanium-silicon electroabsorption modulator to partners on its 8-inch and 12-inch silicon photonics platforms, allowing them to explore the development potential of this device for vertically scalable networks within AI training R&D parks.