Fiber-Optic Sagnac Interferometry for Gravity Gradient Measurements

We report a design for gravity gradient measurements based on Sagnac interferometry. A structure with two masses is designed to convert the effect of gravity gradients into rotational motion. Sagnac interferometry based on optical fibers is introduced to probe its rotational motion. The systematic effects are analyzed theoretically and validated by the static observation of an experimental apparatus. In a 37-day record, we achieve a noise level of $5\,\, \times 10^{-12}$ rads $^{-2}$ Hz $^{-1/2}$ under a room temperature environment without any vibration isolation and magnetic shielding devices. The corresponding contribution for the gravity gradient measurement is estimated to $1\,\, \times 10^{-2}$ EHz $^{-1/2}$ .