Passive chip-scale resonant optical gyroscope with sub-20-deg/hour/√Hz performance

This paper describes the progress made in developing a resonant optical gyroscope fabricated with a silicon-nitride (SiN) waveguide using CMOS-compatible processes. The ultra-low loss of SiN waveguides allows ring resonators to be fabricated with small footprints (~1 cm²) while achieving higher Q-factors (~10⁸) than similar resonators made from other materials. For this reason, SiN is a very promising platform for developing a miniaturized optical gyroscope with tactical-grade specifications, which require an angular random walk (ARW) of 0.05 deg/h/√Hz and a drift of 10 deg/h. Our first-generation SiN ring gyro, reported in 2022, had an affective diameter of 11.6 mm, a perimeter of 37 mm and a finesses of 1270. When interrogated with a 10-kHz linewidth laser, it had a measured ARW of 1.3 deg/h/√Hz and a drift of 4000 deg/h, and its dominant noise was backscattering noise. In this paper, we present a second-generation of SiN gyro with a longer ring waveguide and a lower finesse to reduce the backscattering noise. This multi-turn ring has the shape of a spiral with 33 turns and an average diameter of 12.2 mm, a waveguide length of 1.2 m, and a finesse of 30. The laser linewidth was also decreased to 100 Hz to reduce the dominant noise sources, including laser frequency noise and backscattering noise. The reported ARW of this new gyro is 0.28 deg/√h, which is a factor of 4.5 lower than that of the first-generation gyro. After splicing several of the components together to reduce instabilities due to mechanical connectors, the drift was reduced to 500 deg/h. This work provides an incentive to move towards integrating more components on the chip. With continued research, this technology could soon meet the performance requirements of a wide variety of navigation-related applications.