Measurements of fundamental thermal induced phase fluctuations in the fiber of a Sagnac interferometer

We demonstrate measurements of fundamental thermal induced phase fluctuations in the fiber-loop of a Sagnac interferometer. Loop lengths of 1.1 and 2.2 km are considered, showing phase noise levels between /spl sim/0.2-1.4 μrad rms//spl radic/(Hz) in the frequency range 1-100 kHz. Good agreement between theory and experiment is demonstrated. We show that the frequency dependent noise floor can have a considerable impact on threshold detection's for a Sagnac based sensor for detection of reciprocal measurands, as well as on the random walk coefficient in fiber optic gyroscopes.