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.