Chip-Scale Resonant Optical Gyroscope With Near Earth-Rate Sensitivity

This article reports progress toward developing a passive chip-scale resonant optical gyroscope with a measured noise approaching tactical-grade specification. The gyroscope consists of a ring resonator fabricated with an ultra-low-loss silicon-nitride (SiN) waveguide tightly wound in a spiral with a length of 1.2 m, an average radius of 6.1 mm, and a Q factor of 60 million. We previously reported an earlier version of this spiral gyro with a measured noise and drift of 210°/h/<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\surd $ </tex-math></inline-formula>Hz and 4000°/h, respectively. The noise was reduced by one order of magnitude by interrogating the gyro with a more coherent source, which simultaneously decreased the two dominant noise sources (laser-frequency noise and backscattering noise). Improvements made to the experimental setup, including the optimization of the modulation frequencies and the placement of some optical components, further reduced the noise by a factor of more than 2. Additionally, the drift was improved by more than one order of magnitude when several of the mechanical fiber connectors, which contribute to polarization-coupling drift, were replaced with polarization-maintaining splices. The measured noise of this improved spiral gyro is 6.7°/h/<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\surd $ </tex-math></inline-formula>Hz, which is among the lowest reported values for a resonator with this footprint, and less than a factor of 3 from meeting the tactical-grade angular random walk (ARW) requirement. The measured drift is 250°/h. The next-generation SiN gyroscope will be designed specifically to further improve the drift by reducing the component and connector count. This work demonstrates that a miniature CMOS-compatible optical gyroscope with tactical-grade specifications is within reach.