Noise Analysis and Optical Design of an Optical Fiber Seismometer with a Super-Long Refraction Arm

In this paper, we proposed an fiber seismometer based on a fiber-optic interferometer with a super-long arm to detect seismic waves. The interferometer was composed of a sensing fiber which was wrapped between two measurement points, and a reference fiber which was completely isolated from the vibration. The seismic signal could be obtained by directly detecting the strain and vibration between two measurement points fixed on rocks without an inertial pendulum. The strain and vibration were amplified due to the multi-layer wrapped sensing fiber. We studied the optical structure and parameter design of the fiber seismometer, analyzed the effect of thermal noise, Rayleigh noise and shot noise, and optimized the sensitivity and resolution. The experimental results indicated that the measurement resolution of the seismometer with the interference arm length of 1000 m was higher than 100 pm/Hz(1/2).