Research of Ultra High-aspect-ratio Silicon Nitride Waveguide

The ultra high-aspect-ratio silicon nitride waveguide has the excellent performance of low loss and high polarization extinction ratio, and it is a feasible scheme to suppress the polarization noise in integrated optical gyroscope. In this paper, the mode field distribution, bending loss and fiber insertion loss of silicon nitride waveguide have been simulated and analyzed based on FEM and FDTD method. By optimizing the waveguide cross-section structures and using the micro-nano techniques of LPCVD and RIE, the single-mode silicon nitride waveguide with an aspect ratio of high to 100 has been successfully fabricated. The processes feasibility has been verified through characterizations and optical testing. The measured polarization extinction ratio of a 12 mm silicon nitride direct waveguide was up to be 3 dB. The results of this research have some significance for the application of ultra high-aspect-ratio silicon nitride waveguides in the integrated optical gyroscope and related polarizing devices.