Optimizing Graphene Ring Modulators: A Comparative Study of Straight, Bent, and Racetrack Geometries

Area of Science:

• Photonics
• Materials Science
• Electrical Engineering

Background:

• Graphene micro-ring modulators are key for optical interconnects due to their size, bandwidth, and compatibility.
• Current designs using straight bus coupling limit flexibility and require very small gaps for critical coupling.

Purpose of the Study:

• To compare straight, bent, and racetrack bus geometries for graphene-on-silicon nitride (Si3N4) micro-ring modulators.
• To demonstrate a racetrack design that enhances modulator performance and scalability.

Main Methods:

• Finite-difference time-domain (FDTD) simulations were used to analyze different bus geometries.
• Comparative analysis of coupling gap, graphene coverage, extinction ratio, and electrical bandwidth.

Main Results:

• The racetrack bus geometry enables critical coupling at larger gaps (up to 300 nm) without sacrificing modulation efficiency.
• Achieved extinction ratios up to 28 dB with only 6-12% graphene coverage.
• Supported electrical bandwidths approaching 90 GHz.

Conclusions:

• The racetrack geometry offers a flexible and efficient design for graphene photonic modulators.
• Co-designing coupling geometry and graphene coverage is crucial for high-speed, high-modulation-depth devices.
• This work provides a pathway for scalable integration of advanced graphene modulators in next-generation optical interconnects.