Measuring the third-order optical nonlinearities in silicon nitride for photonic integrated circuits

Nonlinear effects in photonic integrated circuits (PICs), particularly third-order nonlinear effects, play a vital role in various applications. In this paper, we investigate nonlinear effects in PICs, focusing on third-order susceptibility and its impact on device performance. We employ an efficient measurement technique based on continuous-wave (CW) excitations of a silicon nitride racetrack resonator to evaluate the effective third-order nonlinear susceptibility, providing a deeper understanding of the nonlinear response of materials used in PICs. The effective values of these nonlinearities in integrated devices differ from those of bulk materials and depend on the polarization of the guided light, the operating wavelength, and the waveguide dimensions. Complementary to the experimental analysis, we simulate both the optical and electrical characteristics of the waveguide structures, developing a comprehensive model of their behavior under various conditions. The simulation results are then fitted to the measured data to ensure compatibility, refining the model for improved accuracy. Furthermore, we explore the scaling of the DC-Kerr effect, a key nonlinear phenomenon in silicon nitride waveguides. Additionally, using nonlinear coupled equations for the racetrack cavity, we establish an analytical model that defines the conditions-input power levels and applied DC voltages for the efficient measurement of third-order nonlinear susceptibility.