Enhancing SiN waveguide optical nonlinearity via hybrid GaS integration

Silicon nitride (SiN) has been demonstrated as an exceptional low-loss platform for integrated photonics, however, its relatively small nonlinear refractive index limits its full potential in applications such as all-optical phase modulation, supercontinuum generation, and frequency combs. Here, we demonstrate that through hybrid integration with wide-bandgap 2D materials such as gallium sulfide (GaS), the nonlinear refractive index of the hybrid waveguide can be greatly increased (by five-fold in our experiment). We fabricate high quality factor SiN/GaS microring resonators, with low two-photon absorption at telecom wavelengths, to demonstrate enhanced all-optical modulation. We show that the hybrid platform is suitable for assessing the nonlinear properties of 2D materials, and we have used it to quantify, for the first time, the nonlinear refractive index (n ₂) of GaS. For GaS, n ₂ = $12\times {10}^{-19}{\text{m}}^{\text{2}}{\text{W}}^{-\text{1}}$ , which is ten times larger than that of SiN. (paper)