Measurement of the Kerr Nonlinear Refractive Index and its Variation Among 4H-SiC Wafers

The unique material property of silicon carbide (SiC) and the recent demonstration of low-loss SiC-on-insulator integrated photonics platform have attracted considerable research interests for chip-scale photonic and quantum applications. Despite the impressive progresses made in SiC photonics, some of its beneficial photonic properties are yet to be fully explored. Here, we carry out a thorough investigation of the Kerr nonlinearity among 4H-SiC wafers from several major wafer manufacturers, and reveal that their Kerr nonlinear refractive index can be significantly different. By eliminating various measurement uncer-tainties in the four-wave mixing experiment, the best Kerr nonlinear refractive index of 4H-SiC wafers is estimated to be approximately 4 times, instead of the prior estimate of 2 to 3 times, of that of stoichiomet-ric silicon nitride in the telecommunication band. In addition, experimental evidence is developed that the Kerr nonlinearity in 4H-SiC wafers can be stronger along the c axis than that in the orthogonal direction. Our examination of the Kerr nonlinear refractive index also compels a useful correction to the existing model in high-index-contrast waveguides; otherwise, considerable errors can be introduced.