A Large Area Fiber Optic Gyroscope on multiplexed fiber network
  We describe a fiber optical gyroscope based on the Sagnac effect realized on a multiplexed telecom fiber network. Our loop encloses an area of 20 km^2 and coexists with Internet data traffic. This Sagnac interferometer achieves a sensitivity of about 1e-8 (rad/s)/sqrt(Hz), thus approaching ring laser gyroscopes without using narrow-linewidth laser nor sophisticated optics. The proposed gyroscope is sensitive enough for seismic applications, opening new possibilities for this kind of optical fiber sensors 
Cecilia Clivati, Davide Calonico, Giovanni A. Costanzo, Alberto Mura,   Marco Pizzocaro, Filippo Levi
physics.optics