Application of Optical Frequency Domain Reflectometry for the Study of Polarization Maintaining Fibers

Polarization maintaining fibers (PMF) are used in various fields of photonics and telecommunications, so the study of the propagation of optical radiation in such fibers and the determination of the parameters of these fibers is an important task. Therefore, for example, to work with a Mach–Zehnder interferometer, it is important to know the time delay or the difference in arm lengths. One of the methods that solve this problem is optical frequency domain reflectometry, which has a high spatial resolution, sensitivity, and measurement speed. A new method for determining the difference in the lengths of PMF during measurements by the method of optical reflectometry in the frequency domain is presented. If the fibers under study are adjusted at an angle of 45° to the optical axes of the output fibers of the reflectometer, then the detected signal exhibits beat frequencies caused by intermode interference of light fields with orthogonal polarizations. The beat frequencies obtained by analyzing the detected signal contain information about the delay time and the total length of the studied optical fibers. A model is proposed that explains the physical nature of the occurrence of beat frequencies, demonstrates the high accuracy of agreement between numerical calculations and experimental results, and shows the influence of certain parameters on the position and magnitude of these frequencies on the reflectogram. To improve the accuracy of determining the parameters of the studied optical fibers, various methods were used to compensate for the nonlinearity of the laser tuning using an asymmetric interferometer.