Allan variance analysis of a nuclear magnetic resonance oscillator

Nuclear magnetic resonance (NMR) oscillator is an optical atomic sensor which is developed to measure inertial angular velocity with navigation grade accuracy. It utilizes semiconductor laser, miniaturized magnetic shield and atom vapor cell to realize nuclear magnetic resonance, optical pump and detection in a very small volume (about 10cc to 100cc). NMR oscillator is much more compact than other classic gyros such as fiber optic gyro (FOG), so it is a potential substitution of FOG in the next generation compact navigation grade IMU. To achieve this goal, it is essential to analyse the short-term noise and long-term drift performance of the NMR oscillator. It is also necessary to decompose and track the random error source for further improvements of the device. We propose using the Allan Variance (AVAR) method to both analyse the drift performance and characterize the short-term noise. We also built an NMR oscillator prototype to test and verify the method's accuracy. Theory analysis and experimental results are compared with the classic FOG for deeper comprehension of the differences between these two inertial sensors. We hope this is helpful for those who design the IMU system.