Proposal of Polarization Optical Correlation-Domain Reflectometry (POCDR)

We propose a new scheme for polarization-sensitive distributed fiber-optic sensing, called polarization optical correlation-domain reflectometry (POCDR), and experimentally demonstrate its fundamental operations. In this scheme, the states of polarization (SOPs) of reference lights are controlled so that they are uniformly distributed on the Poincaré sphere using a calibration method, which cancels the effect of unknown birefringence in the fibers used in the system. Then the SOP of spontaneous Brillouin scattering in a sensing fiber is estimated using a least-squares method, by measuring the interference powers for the multiple reference lights with different SOPs. As a pilot demonstration, the SOP transitions along a fiber including a three-paddle polarization controller are measured under different conditions. We also measure the SOP transition of a fiber wound on a bobbin and calculate its polarization beat length, which agrees well with the theoretical value. By exploiting its unique nature called random accessibility, high-speed measurement of the roundtrip birefringence between two arbitrary points in a sensing fiber will be potentially achieved.