Proposal for phase-sensitive heterodyne detection in large-scale passive resonant gyroscopes.

Large-scale passive resonant gyroscopes (PRGs) have been utilized in the measurement of Earth rotation. We report on a scheme of phase-sensitive heterodyne detection in large-scale PRGs. By injecting three separated beams into different longitudinal modes of the ring cavity and self-demodulating the detected signals, the backscattering disturbance and the cavity length fluctuation effect both can be isolated. With the implementation of this new scheme, we can obtain the Earth rotation signal with a Sagnac frequency that is twice of that of the traditional scheme, which enhance the equivalent scale factor of the laser gyroscopes. On the other hand, the quantum noise limit of the instrument can also be further suppressed due to the improvement of the signal-to-noise ratio. With this new scheme, the theoretical rotational sensitivity of a 3 m × 3 m large scale PRG can be as low as 10 rad/s/Hz. With this rotational sensitivity, the measurement of the length of day or the test of the general relativity can be realized.