A low cost rotational seismometer for seismic exploration

In recent years, with the development of rotation direct measurement instruments, rotational seismology has gradually become a hot field, and it is proposed that observation needs high sensitivity. The rotational seismometer based on fiber optic gyroscopes (FOG) has gradually become the preferred choice for seismic rotation observation due to its insensitivity to translational motion, fully solid state and high sensitivity. In order to meet the demands of multi station observation network in seismic exploration, the FOG which is the core sensing element of the rotational seismometer, needs to have the characteristics of high sensitivity and low cost. In this paper, a budget-friendly dual-polarization FOG scheme based on a Lyot depolarizer is proposed, and the ports difference method is employed to suppress the short-time noise and improve the sensitivity. The experiment adopts 2km polarization maintaining fiber ring, and the two ports have stable output. After the difference of the two port signals, the self-noise over 0.03Hz~50Hz is reduced from 260nrads^-1Hz^-1/2 to 120nrads^-1Hz^-1/2. It shows that the rotational seismometer using this structure has low cost and high sensitivity, and has a good application prospect.