Advancements in silicon-nitride photonics technology, in particular reduction in waveguide scattering and loss below 1 dB/m, have opened the door to developing tactical-grade chip-scale optical gyroscopes for applications such as inertial navigation for a variety of self-driving vehicles. The first generation (2021) of the chip-scale ring gyroscope was fabricated with an ultra-low-loss waveguide in the shape of a racetrack with a length of 37 mm and finesse of 1270. The gyro was interrogated with a 10-kHz linewidth laser that was tuned to a resonance with a low backscattering coefficient, and balanced detection was used to reduce reciprocal noise in the two counter-propagating signals. The lowest measured angular random walk (ARW), or minimum detectable rotation rate, was 80 deg/h/√Hz, and the gyro output was limited by backscattering noise. This defense will discuss the different techniques that were implemented to reduce backscattering noise and demonstrate the first passive chip-scale gyro to achieve earth-rate sensitivity. 

The two dominant noise sources in a ring gyro output, when using a probe laser with sufficiently low relative intensity noise, are backscattering noise and laser frequency noise. A key parameter is the laser linewidth because it can be optimized to minimize these two dominant noise sources, which have opposite responses to the linewidth. To reduce backscattering noise, a second-generation gyro was fabricated with a lower finesse. The new device had a multi-turn spiral design with a total length of 1.2 m coiled on a 6.1-mm diameter footprint, and a finesse of 30. Other sources of noise and drift were investigated and reduced, including replacing mechanical connectors between components with fusion splices, reducing the laser frequency noise by using a laser with a narrower linewidth, and optimizing the electro-optic modulators, balanced detectors, and other components. When the multi-turn ring gyro was interrogated with a 100-Hz linewidth laser, the lowest measured ARW was 17 deg/h/√Hz. 

This seminar is sponsored by the Department of Applied Physics and the Ginzton Laboratory