A High-Sensitivity Giant Interferometric Fiberoptic Gyroscope for Seismic Observation

Optic gyroscopes are widely used in geophysics. Compared with ring laser gyroscopes, interferometric fiber optic gyroscopes (IFOGs) have advantages such as low cost and full solid-states. In this paper, we focus on the design, noise suppression, and implementation of IFOGs and establish a high-sensitivity giant IFOG system for seismic observation. The diameter of the giant IFOG is 2 m, and it uses 20.68 km of polarization-maintaining optical fiber to provide a sensing area of up to 10300 m <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$ ^{2}$</tex-math></inline-formula>. The highest sensitivity of the giant IFOG can reach <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$ 1\times 10^{-9}$</tex-math></inline-formula> <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$ \mathrm{rad/s/\sqrt{Hz}}$</tex-math></inline-formula> in the frequency range of 0.01–0.6 Hz, and angular random walk (ARW) and bias instability (BI) reach <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$ 3\times 10^{-9}$</tex-math></inline-formula> <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\mathrm{rad/\sqrt{s}}$</tex-math></inline-formula> and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$ 4\times 10^{-11}$</tex-math></inline-formula> <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$ \mathrm{rad/s}$</tex-math></inline-formula>, respectively. It is currently the best performing giant IFOG publicly reported. Based on the developed giant IFOG, we successfully observed the Pn and Pg coda waves in the vertical component of natural seismic rotation, which indicates that high-sensitivity giant IFOGs have significant advantages in seismic observation. This paper provides a theoretical and experimental foundation for achieving high-sensitivity giant IFOGs and it offers new measurement parameters and methods for geodesy and geophysics.