A high sensitivity fiber optic gyroscope on multiplexed telecommunication network

This paper presents a fiber optic gyroscope (FOG) on a 47 km single mode commercial fiber located in the urban area around the city of Turin, enclosing an area of 20 km² with a resolution of about 10^-8 (rad/s)/√Hz, without using complex instrumentation. The fiber is used for the Internet data traffic and is implemented on a dense wavelength division multiplexing (DWDM) architecture, in which the channel 44 was dedicated to the experiment. The setup is the same as for standard FOGs: laser radiation is split into two beams, that are injected in the telecom loop through optical add &drop multiplexers; the two beams travel over the loop in opposite directions, accumulating a phase difference due to Earth rotation, as predicted by the Sagnac effect. After a round trip, the two beams are extracted and recombined to detect the Sagnac phase. A well known technique of nonreciprocal phase modulation was used to this purpose. A closed loop system in which the nonreciprocal phase is compensated inserting a small frequency offset between the two beams is developed. This experiment shows the feasibility of a network of these type of sensors for seismic detection, placed side by side with traditional instrumentation, supported by the increasing activity on fiber networks for frequency metrology.