All-silicon carrier accumulation modulator based on a lateral metal-oxide-semiconductor capacitor

In silicon photonics, the carrier depletion scheme has been the most commonly used mechanism for demonstrating high speed electro-optic modulation. However, in terms of phase modulation efficiency, carrier accumulation based devices potentially offer almost an order of magnitude improvement over those based on carrier depletion. Previously reported accumulation modulator designs only considered vertical metal-oxide-semiconductor (MOS)-capacitors, which imposes serious restrictions on the design flexibility and integratability with other photonic components. In this work, for the first time we report experimental demonstration of an all-silicon accumulation phase modulator based on a lateral MOS-capacitor. Using a Mach-Zehnder interferometer (MZI) modulator with a 500-µm-long phase-shifter, we demonstrate high speed modulation up to 25 Gbit/s with a modulation efficiency (VπLπ) of 1.53 V-cm.