Rib waveguides for Kerr nonlinear optics

Optical amplifiers are fundamental to high-throughput optical communication systems, but traditional rare-earth-doped amplifiers with limited optical bandwidth increasingly constrain the scalability of next-generation fiber networks. Integrated optical parametric amplifiers (OPAs), based on Kerr nonlinear optics, can address this challenge by offering broadband gain across arbitrary wavelengths. However, their performance is currently limited by optical losses in meter-scale waveguides, which limits the maximum achievable gain. In this work, we challenge the conventional preference for strip waveguides in Kerr-based systems and demonstrate with numerical studies that rib waveguides fabricated on the silicon nitride (Si₃N₄) platform can offer substantially higher gain, despite a lower effective nonlinear coefficient. To accommodate the longer waveguide lengths required, we introduce a meander-style spiral concatenation, and we also show how to avoid active stitching error compensation in electron-beam lithography. We further investigate the fabrication tolerance of group velocity dispersion in both geometries and show that rib waveguides maintain comparable performance. These results pave the way not only for practical OPAs but also for other devices based on χ(³) nonlinearity such as wavelength converters and optical sampling oscilloscopes by simultaneously providing high gain, broad bandwidth, and low noise figure.