High Spatial Resolution Distributed Birefringence Measurement in km Level Length PM Fiber Based on Polarization OFDR

This paper proposes a distributed birefringence measurement method for long-distance polarization maintaining fiber (PMF) based on polarization optical frequency domain reflectometry (P-OFDR). Distinguished from the existing ways, the method characterizes birefringence by the internal strain of the PMF, and cuts off the dependence of birefringence measurements on the wavelength of the interrogated laser. It obtains the internal strain through the cross-correlation of the Rayleigh backscattering (RBS) spectra from the two orthogonal axes of polarization. The measured internal strain is converted to birefringence according to the parameters of the PMF. In addition, a delay correction method is proposed for overcome the degradation of the RBS spectra correlation due to birefringence delay, and extends the measurement distance. In the experiments, the distributed birefringence measurement in 5020m PMF is achieved with a spatial resolution of 10cm and a measurement accuracy of 1.4×10-7. The single sweep is faster at only 1 second and offers excellent stability. Finally, we demonstrate the application of the method in a fiber coil. The measured distributed birefringence of the coil is symmetric. Stress concentration due to temperature variations and winding defects is clearly visible in the results. The method is helpful for quality evaluation of polarization maintaining devices and PMF, as well as potentially applying to birefringence-based distributed sensing.