| Summary: | Silicon nitride waveguide (Si<sub>3</sub>N<sub>4</sub>), 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 Si<sub>3</sub>N<sub>4</sub> 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 Si<sub>3</sub>N<sub>4</sub> waveguide resonator. We use the Fimmprop module of the simulation software Photon Design to simulate the relationship between the back-reflection coefficient of Si<sub>3</sub>N<sub>4</sub> waveguide and different tilt angles. The simulation result shows that when the end face of the Si<sub>3</sub>N<sub>4</sub> waveguide is oblique cut by 15°, 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 Si<sub>3</sub>N<sub>4</sub> can be suppressed by the oblique cutting of the end face by 15°. The conclusion can lay a foundation for improving the performance of RIOG based on Si<sub>3</sub>N<sub>4</sub> waveguide resonator.
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