Chip-scale gyroscope using silicon-nitride waveguide resonator with a Q factor of 100 million

Recent breakthroughs in silicon photonics technology may soon lead to mass-producible chip-scale tactical-grade (or better) gyroscopes by using a CMOS-compatible fabrication process to print highly integrated high-sensitivity optical gyroscopes. This paper reports our progress on designing and building an optical gyro out of an SiN racetrack resonator of 37-mm perimeter with 1270 finesse (10⁸ intrinsic quality factor) using off-the-shelf fiber components (circulators, splitters, and modulators) and a semiconductor laser to achieve an angular random walk (ARW) of 80 deg/h/Hz, or 1.3 deg/h. To our knowledge, it is a record by a factor of 2 for the ARW per footprint area of a Sagnac-effect-based gyroscope on a chip. A balanced-detection scheme is employed to cancel 18 dB of gyroscope noise caused by laser phase noise converted into amplitude noise by residual backscatterers in the resonator. The backscattering coefficient was found to be very sensitive to wavelength, and therefore to the resonance used to probe the resonator. The lowest backscattering coefficient was measured to be more than 1,000 times lower than the mean. The use of this resonance, as well as an asymmetric phase-modulation scheme, greatly reduced the gyroscope's backscattering noise. Achieving this gyro's theoretical minimum ARW of 16 deg/h/Hz will likely require a lower backscattering coefficient or better means of cancelling backscattering noise. Further improvements to tactical-grade performance (and better) will likely require a larger resonator area, further reduction of backscattering, and/or a laser with reduced frequency noise.