High-quality optical modulation demonstrated using Graphene

Integrated optical modulators with high modulation speed, small footprint and broadband athermal operation are desired for future chip-level optical interconnects. Graphene is a promising material to achieve this, owing to its fast tunable absorption over a wide spectral range. Imec’s graphene-silicon EAM consists of a 50mm long graphene-oxide-silicon capacitor structure implemented on top of a planarised Silicon-on-Insulator (SoI) rib waveguide.

For the first time, high-quality optical modulation was demonstrated in a hybrid graphene-silicon modulator, at bit rates up to 10Gb/s. A competitive optical insertion loss below 4dB and extinction ratio of 2.5dB were obtained over a broad wavelength range of 80nm around 1550nm centre wavelength. Moreover, no significant changes in performance were observed for temperatures in the range of +20 to 49°C, implying a robust athermal operation. As such, imec’s graphene-silicon EAM outperforms state-of-the-art SiGe EAMs on thermal robustness and optical bandwidth specifications.

Imec’s research on high-bandwidth optical I/O explores optical solutions for realising high-bandwidth chip-level I/O. With support from its associated lab at Ghent University, the company aims to develop a scalable, manufacturable silicon-based optical interconnect technology for the telecomms and datacomms industries.

Imec’s portfolio includes low-loss strip waveguides, highly efficient grating couplers, 25Gb/s Mach-Zehnder modulators, 25Gb/s Ge photodetectors and more. Imec’s R&D on high bandwidth chip-level I/O is performed in co-operation with imec’s key partners in its core CMOS programmes including Intel, Samsung, TSMC, Globalfoundries, Micron, Sony, SK Hynix, Huawei.

Imec recently joined the Graphene Flagship, Europe’s €1bn programme covering the whole value chain from materials production to components and system. This will further strengthen imec’s strategic position in exploiting Graphene’s unique properties for optical interconnect applications.

“With this breakthrough result, imec has illustrated the huge potential of graphene optical EA modulators with respect to thermal, bandwidth, and footprint benefits,” said Philippe Absil, Department Director, 3D and Optical Technologies, imec. “This achievement underscores our dedicated work and industry leadership in R&D on high bandwidth chip-level optical I/O. Future work will focus on further improving the modulation speed of our graphene EAM, similar to the speed obtained in optimised Si(Ge) modulators.”