Suppression of Back-Reflection From the End Face of Si3N4 Waveguide Resonator

Silicon nitride waveguide (Si3N4), is used as the most important sensitive device because of its excellent high-polarizing characteristics. It has the potential to build the miniaturized, high-precision resonant integrated optical gyroscope (RIOG) in recent years. However, the back-reflection caused by the refractive index difference between the Si3N4 waveguide and the pigtail fiber has a non-negligible impact on the accuracy of the gyroscope. In this paper, we propose a method to suppress the back-reflection of the end face of the Si3N4 waveguide resonator. We use the Fimmprop module of the simulation software Photon Design to simulate the relationship between the back-reflection coefficient of Si3N4 waveguide and different tilt angles. The simulation result shows that when the end face of the Si3N4 waveguide is oblique cut by 15 degrees, the back-reflection is the minimum, about -67 dB. The back-reflection obtained through the experiments are about -65 dB, consistent with the simulation result. Together, our data suggested that the back-reflection noise of the Si3N4 can be suppressed by the oblique cutting of the end face by 15 degrees. The conclusion can lay a foundation for improving the performance of RIOG based on Si3N4 waveguide resonator.