Fiber Optic Seismometer Based on π-Phase-Shifted FBG and Swept Optical SSB-SC Interrogation Technique

A fiber optic seismometer based on π-phase-shifted FBG (π-FBG) is proposed. The static wavelength/strain of the π-FBG is measured by swept optical suppressed carrier single sideband (SSB-SC) interrogation technique with a reference FBG resonator. A broadband (DC-50 Hz) wavelength/strain with 0.0006 pm (0.47 nε) resolution is demonstrated. As a reasonable double-diaphragm acceleration model is realized, the seismometer works from 20 s to 50 Hz and reaches a noise level of -130 dB@1 Hz (re: 10×log m2s-4/Hz) which meets the earth’s background noise. The proposed seismometer has the ability to record the close small earthquake with high signal-noise ratio (SNR).