Design, Fabrication and Test of Transmissive Si₃N₄Waveguide Ring Resonator

The temperature-dependent polarization induced bias drift is a major factor affecting the long-term zero-bias stability of integrated optic gyro (RIOG). The silicon nitride (Si3N4) with high-aspect-ratio core geometry allows high polarization extinction ratio and ultra-low propagation loss. We start from suppressing the polarization noise of the RIOG and design a single polarization Si3N4 waveguide ring resonator (WRR) with a radius of 17.5 mm. We established the polarization model of the WRR. It is found through simulation that when the polarization-dependent loss of the Si3N4 waveguide reaches 800 dB/m, it can maintain the single-polarization performance, thereby suppressing the polarization noise of the gyroscope. And the relationship between the coupling coefficient of the coupler and the limit sensitivity, finesse and transmittance was determined. The cross-sectional size of the Si3N4 WRR is determined to be $4\,\,\mu \text{m}\,\,\times 40$ nm simultaneously by simulation. Finally, through its processing and testing, a single-polarization WRR with a finesse of 127, the quality factor is $1.31\times 10 ^{7}$ , a transmission loss of 2.5 dB/m, and a polarization-dependent loss of 810 dB/m is obtained. Meanwhile, we prove its single-polarization performance at different temperature. The successful design and fabrication of the WRR is expected to achieve high precision RIOG.