Polarization effects in the Sagnac-Michelson distributed disturbance location sensor

An analysis, based on Jones calculus, is presented of polarization effects in the merged Sagnac-Michelson interferometric sensor for distributed disturbance detection. The nature of birefringence biasing in the Sagnac interferometer is clarified: the cosine-response of the Sagnac interferometer can be biased to a sine-response by introducing birefringence with retardation equal to /spl pi//2 in the Sagnac-loop. In addition, the input light should be linearly polarized and both the direction of polarization and the optical axes of the birefringence region should be oriented at /spl pi//4 with respect to the plane of the fiber-loop.