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Ultrafast and energy-efficient all-optical switching with graphene-loaded deep-subwavelength plasmonic waveguides

Abstract

All-optical switches have attracted attention because they can potentially overcome the speed limitation of electric switches. However, ultrafast, energy-efficient all-optical switches have been challenging to realize owing to the intrinsically small optical nonlinearity in existing materials. As a solution, we propose the use of graphene-loaded deep-subwavelength plasmonic waveguides (30 × 20 nm2). Thanks to extreme light confinement, we have greatly enhanced optical nonlinear absorption in graphene, and achieved ultrafast all-optical switching with a switching energy of 35 fJ and a switching time of 260 fs. The switching energy is four orders of magnitude smaller than that in previous graphene-based devices and is the smallest value reported for any all-optical switch operating at a few picoseconds or less. This device can be efficiently connected to conventional silicon waveguides and used in silicon photonic integrated circuits. We believe that this graphene-based device will pave the way towards on-chip ultrafast and energy-efficient photonic processing.

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Fig. 1: Schematic and simulation of a graphene-loaded metal–insulator–metal WG for all-optical control.
Fig. 2: SEM images of the fabricated samples.
Fig. 3: Measured linear absorption of graphene-loaded MIM-WGs.
Fig. 4: Saturable absorption and demonstration of all-optical switching.
Fig. 5: Demonstration of all-optical switching with femtosecond laser pulses.

Data availability

The data that support the plots within this paper and other findings of this study are available from the corresponding author upon reasonable request.

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Acknowledgements

We thank E. Kuramochi and T. Tamamura for support with the fabrication, K. Takata for support with the measurements and A. Shinya, N. Matsuda and Y. Ogawa for discussions. This work was supported by JSPS KAKENHI grant no. JP15H05735.

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M.O. designed and fabricated the sample, performed the experiment, analysed the data and wrote the manuscript. M.H. and M.T. numerically designed and fabricated the sample, performed the experiment and analysed the data. K.N. supported the measurement set-up and the discussion. H.S. and H.C. supported the graphene process and the discussion. M.N. conceived the work, designed the sample, analysed the data, wrote the manuscript and led the project.

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Correspondence to Masaaki Ono or Masaya Notomi.

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Performance comparison, graphene absorption analysis and insertion loss.

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Ono, M., Hata, M., Tsunekawa, M. et al. Ultrafast and energy-efficient all-optical switching with graphene-loaded deep-subwavelength plasmonic waveguides. Nat. Photonics 14, 37–43 (2020). https://doi.org/10.1038/s41566-019-0547-7

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