Broadband graphene optical modulator on silicon

At this week’s IEEE International Electron Devices Meeting (IEDM 2014), nanoelectronics research center imec and its associated lab at Ghent University have demonstrated the industry’s first integrated graphene optical electro-absorption modulator (EAM) capable of 10Gb/s modulation speed. Combining low insertion loss, low drive voltage, high thermal stability, broadband operation and compact footprint, the device marks an important milestone in the realization of next-generation, high-density low-power integrated optical interconnects. Integrated optical modulators with high modulation speed, small footprint and broadband athermal operation are highly 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 50µm long graphene-oxide-silicon capacitor structure implemented on top of a planarized 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 center wavelength. Moreover, no significant changes in performance were observed for temperatures in the range of 20-49°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. “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, 3D and Optical Technologies department director at imec. “This achievement underscores our dedicated work and industry leadership in R&D on high bandwidth chip-level optical input/output. Future work will focus on further improving the modulation speed of our graphene EAM, similar to the speed obtained in highly optimized Si(Ge) modulators (30-50 Gb/s).” Imec’s research on high-bandwidth optical input/output (I/O) explores optical solutions for realizing high-bandwidth chip-level I/O. With support by its associated lab at Ghent University it aims at developing a scalable, manufacturable silicon-based optical interconnect technology for the telecom and datacom industry. 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 input/output is performed in cooperation with imec’s key partners in its core CMOS programs including Intel, Samsung, TSMC, Globalfoundries, Micron, Sony, SK Hynix, Huawei. Imec recently joined the Graphene Flagship, Europe’s 1 billion EUR 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.