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Harnessing plasma absorption in silicon MOS ring modulators


High-bandwidth, low-power and compact silicon electro-optical modulators are essential for future energy-efficient and densely integrated optical data communication circuits. The all-silicon plasma-dispersion-effect ring resonator modulator is an attractive prospect. However, its performance is currently limited by the trade-off between modulation depth and switching speed, dictated by its quality factor. Here we introduce a mechanism to leap beyond this limitation by harnessing the plasma absorption induced in a silicon metal–oxide–semiconductor waveguide to enhance the extinction ratio of a low-quality-factor, high-speed ring modulator. The fabricated devices demonstrate a modulation depth of ~27 dB for a bias of ~3.5 V. Modulation enhancement has been observed for operation frequencies ranging from kilohertz to gigahertz, with data modulation up to 100 Gbit s−1 on–off keying demonstrated, paving a way to the evolution of optical interconnects to 100 Gbaud and beyond per wavelength.

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Fig. 1: Integrated silicon MOS modulator.
Fig. 2: Static EO response of the MOS ring modulator.
Fig. 3: Frequency response of absorption enhancement.
Fig. 4: EO bandwidths of the inversion and accumulation modes.
Fig. 5: Optical-eye diagrams and EO bandwidth.

Data availability

The data that support the results within this paper are available in the Supplementary Information and at the University of Southampton repository ( Source data are provided with this paper.


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This work was supported by funding from Rockley Photonics and the EPSRC through the Prosperity Partnership (EP/R003076/1), EPSRC Platform Grant (EP/N013247/1), EPSRC Strategic Equipment Grant (EP/T019697/1) and European Commission H2020 PICTURE Project (780930). D.J.T. acknowledges funding from the Royal Society for his University Research Fellowship (UF150325).

Author information

Authors and Affiliations



W.Z. contributed to the idea, simulation, fabrication, device testing and manuscript preparation. K.L. contributed to device testing. M.E., B.C., X.Y., H.D., M.B., D.T.T. and C.G.L. contributed to device fabrication. A.S., G.Y., R.S., A.Z. and G.R. contributed to the discussion, and G.R. manages the Silicon Photonics Group at Southampton. D.J.T. provided high-level project supervision and manuscript revision.

Corresponding author

Correspondence to David J. Thomson.

Ethics declarations

Competing interests

Authors A.S., G.Y., R.S., A.Z., G.R. and D.J.T. are shareholders of Rockley Photonics Holdings Limited (NYSE: RKLY), a global leader in photonics-based health monitoring and communications solutions.

Peer review

Peer review information

Nature Photonics thanks Stanley Cheung and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

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Supplementary information

Supplementary Information

Supplementary discussion, Supplementary Figs. I-1, I-2, I-3, I-4, I-5, I-6, I-7, I-8, II-1, II-2, III-1, III-2, III-3, III-4, III-5, IV-1, IV-2 and IV-3 and Supplementary Tables III-1 and IV-1.

Supplementary Data

Original data for Fig. I-1.

Supplementary Data

Original data for Fig. I-2, Fig. I-3, Fig. I-4.

Supplementary Data

Original data for Fig. I-5.

Supplementary Data

Original data for Fig. I-6.

Supplementary Data

Original data for Fig. I-7.

Supplementary Data

Original data for Fig. I-8.

Supplementary Data

Original data for Fig. III-1.

Supplementary Data

Original data for Fig. III-3/4/5.

Supplementary Data

Original data for Fig. I-1.

Supplementary Data

Original data for Fig. I-2.

Supplementary Data

Original data for Fig. I-3.

Source data

Source Data Fig. 1

Source data of image of the device in Fig. 1.

Source Data Fig. 2

Source data of optical transmission data in Fig. 2.

Source Data Fig. 3

Source data of optical transmission and image containing data in Fig. 3.

Source Data Fig. 4

Source data of bandwidth and eye diagram image of Fig. 4.

Source Data Table.1

Source data of bandwidth and eye diagram image of Fig. 5.

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Zhang, W., Ebert, M., Li, K. et al. Harnessing plasma absorption in silicon MOS ring modulators. Nat. Photon. 17, 273–279 (2023).

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