Three-wave differential locking scheme in a 12-m-perimeter large-scale passive laser gyroscope

Large-scale laser gyroscopes with sufficiently high sensitivity for measurement of the rotation rate of the Earth ΩE are inertial sensors with the capability to provide Earth orientation parameters, i.e., rotation rate and polar motion in near real time. Larger-scale passive resonant gyroscopes (PRGs) theoretically have a lower shot-noise limit. However, the cavity perimeter fluctuations and laser frequency noise become challenges in a passive gyro. In this paper, we introduce a three-wave differential locking scheme for large-scale PRGs, resulting in an in situ measurement of the cavity perimeter with nanometer resolution. Furthermore, the laser frequency noise is effectively suppressed with an additional gain of 30 dB by a double-stage locking system, based on the three-wave differential locking scheme. Finally, the rotation rate resolution of our 3m×3m gyroscope improves to 1.1×10-9rad/s over 200 s. The simplicity, robustness, and effectiveness of the locking scheme are important to the long-term operation of large-scale PRGs aiming for applications in the geosciences.