Flexible Dispersion Engineering in Thin GaP-OI Frequency Comb Resonator Design

Thickness-constrained waveguides enable ultralow loss photonics while suffering severe chromatic issues nowadays. We present a concentric ring configuration to reduce the dispersion requirements for the core waveguide thickness. This approach employs a second ring to squeeze light into additional anti-bonding modes to manifest the dispersion profile with lateral coupling parameters such as the 2nd ring width as well as the gap size. We then applied this method to a 200 nm-thick SiO2-passivated concentric coupled GaP-OI resonator design for Kerr soliton frequency comb generation which gives rise to an anomalous dispersion span of 150 nm. The dispersion profile could be further optimized by changing the gap of the coupled rings, demonstrating the design flexibility. Our concentric microrings approach can find anomalous dispersions on thickness-constrained materials, opening the possibilities for novel integrated nonlinear photonic applications.