Fiber-optic distributed sensing by a two-loop Sagnac interferometer.

A two-loop Sagnac interferometer is proposed for fiber-optic distributed sensing. The location of a disturbance can be determined from the two output phase signals of the two Sagnac loops, and the amplitude of the disturbance can be obtained by integration of the phase signal. A prototype distributed impact sensing system has been tested based on the two-loop Sagnac interferometer.