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A graphene-based broadband optical modulator

Abstract

Integrated optical modulators with high modulation speed, small footprint and large optical bandwidth are poised to be the enabling devices for on-chip optical interconnects1,2. Semiconductor modulators have therefore been heavily researched over the past few years. However, the device footprint of silicon-based modulators is of the order of millimetres, owing to its weak electro-optical properties3. Germanium and compound semiconductors, on the other hand, face the major challenge of integration with existing silicon electronics and photonics platforms4,5,6. Integrating silicon modulators with high-quality-factor optical resonators increases the modulation strength, but these devices suffer from intrinsic narrow bandwidth and require sophisticated optical design; they also have stringent fabrication requirements and limited temperature tolerances7. Finding a complementary metal-oxide-semiconductor (CMOS)-compatible material with adequate modulation speed and strength has therefore become a task of not only scientific interest, but also industrial importance. Here we experimentally demonstrate a broadband, high-speed, waveguide-integrated electroabsorption modulator based on monolayer graphene. By electrically tuning the Fermi level of the graphene sheet, we demonstrate modulation of the guided light at frequencies over 1 GHz, together with a broad operation spectrum that ranges from 1.35 to 1.6 µm under ambient conditions. The high modulation efficiency of graphene results in an active device area of merely 25 µm2, which is among the smallest to date. This graphene-based optical modulation mechanism, with combined advantages of compact footprint, low operation voltage and ultrafast modulation speed across a broad range of wavelengths, can enable novel architectures for on-chip optical communications.

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Figure 1: A graphene-based waveguide-integrated optical modulator.
Figure 2: Static electro-optical response of the device at different drive voltages.
Figure 3: Dynamic electro-optical response of the device.
Figure 4: Spectrum characterization of the optical modulator.

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Acknowledgements

This work was supported by the National Science Foundation Nano-scale Science and Engineering Center (NSF-NSEC) for Scalable and Integrated Nano Manufacturing (SINAM) (grant no. CMMI-0751621) and by the US Department of Energy, Basic Energy Sciences Energy Frontier Research Center (DoE-LMI-EFRC) under award DOE DE-AC02-05CH11231. M.L. thanks Y. Rao for discussions.

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M.L. and X.Z. contributed to the experimental ideas. M.L. fabricated device samples. M.L. and X.Y. carried out measurements, analysed the experimental data and prepared the manuscript. B.G., L.J. and F.W. prepared graphene film. All authors contributed to discussions and manuscript revision.

Corresponding authors

Correspondence to Feng Wang or Xiang Zhang.

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Liu, M., Yin, X., Ulin-Avila, E. et al. A graphene-based broadband optical modulator. Nature 474, 64–67 (2011). https://doi.org/10.1038/nature10067

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