Multiplexed FBG-FFPI strainmeter array for field observation

Mining mass data of the earth's surface deformation is a promising approach for earthquake early-warning, raising an urgent demand for developing large-scale optical fiber strainmeters. This paper presents the implementation and results of large-scale, ultrahigh-resolution, real-time multiplexed fiber Bragg grating-based Fabry-Perot interferometer (FBG-FFPI) strainmeter arrays for field observation. The Pound-Drever-Hall technique locks master and slave single-sideband lasers onto the FBG-FFPI resonance peaks for precise strain measurement. A 10-channel array was successfully utilized for field observation at Lijiang National Seismic Station, which accurately recorded over 100 earthquakes and the earth's daily tide signal. The FBG-FFPIs have a strain resolution of 4.80 pε/√Hz @ 30 Hz with a 0.22-m cavity length. A 4-channel array with a longer cavity length of 1.4 m was also established at Heqing Seismic Station, showing advantageous performances. These results demonstrate the significant potential of FBG-FFPI strainmeter arrays in providing geophysical data for earthquake early-warning and hazard mitigation.