The polarization dependence of the coherent detection in optical frequency-domain reflectometry can be exploited to measure the local beatlength along an optical fiber. Reproducibility of the results is given for high and low polarization-mode coupling fibers, and the influence of several effects on beatlength measurement precision, such as spatial reflectometer resolution,fiber twist, and the presence of circular birefringence, is discussed. The experimental results seem to indicate that the typical assumption that the fiber birefringence can be treated as purely linear might not be fully justified. Beatlength overestimates of 10% and more can result.
M. Wegmuller, M. Legre, and N. Gisin, "Distributed Beatlength Measurement in Single-Mode Fibers With Optical Frequency-Domain Reflectometry," J. Lightwave Technol. 20, 800- (2002)