Efficient graphene electro-optic modulation via maximized optical mode overlap.

Integrating more components in one silicon photonic chip is critical for processing exponentially growing data in optical communications and photonic computing. One of the key components in the chip, the electro-optic modulator, suffers from an oversized footprint (in millimeters). Graphene modulators are more compact, with device sizes at hundreds of micrometers. However, conventional graphene-on-top configurations, where graphene only couples to the weak evanescent field of the waveguide, have limited modulation efficiency and hinder the continuing efforts of reducing device footprint. Here, we present a design where graphene layers are positioned inside the optical mode to maximize light-graphene interaction. This architecture enhances the effective refractive index modulation and shows 30% increased efficiency compared to the conventional design, which facilitates a 3 dB bandwidth exceeding 30 GHz. Wafer-scale manufacturing with graphene integrated at the Back End of Line (BEOL) is achieved. As an additional proof-of-concept demonstration, a silicon-platform embedded graphene modulator achieves a modulation efficiency of 0.096 V·cm. We believe this work provides a pathway for graphene integrating to high-density, foundry-level silicon photonic circuits.