The coupling measurement system for ring laser gyro

The lock-in effect can reduce the performance of ring laser gyros. The lock-in effect is a result of backscattering. Self-consistent equations for ring laser gyro show that the intensity of the opposite beams has AC modulation at the frequency of beat frequency signal because of the backscattering. The amplitude and phase of the AC modulations have important information about the backscattering. Comparing to the DC component in intensity signal, The AC components are much smaller, it is not suitable to measure the AC components directly using analog to digital conversion. A novel synchronous demodulation method is proposed which taking advantage of the heterodyne read-out signals in quadrature. The coupling modulation under different rotation rate is measured, experiments of this system show that this system works well and we can draw beneficial conclusion from the experiments.