Spectral-domain measurement of beat length in polarization-maintaining fibers

A spectral white-light interferometric (WLI) method for measuring the beat length in high birefringence polarization-maintaining fibers (PMFs) is presented. The approach is based on the stress-induced polarization mode coupling between the two polarization eigenmodes and utilizes their spectral interferograms. By recording the spectral interferograms before and after the displacement of the force, the beat length can be obtained by the displacement of the force and the relative phase variation retrieved from the two spectral interferograms. According to the principle that the phase difference between adjacent fringes peaks is 2π, the phase can be retrieved from the interferograms simply. The factors affecting the measurement precision of this method and the main source of errors are investigated in detail.

► Beat length in PMFs is measured by spectral-domain interferometric.
► A simple method is used to retrieve the relative phase variation.
► Long fibers can be measured, and distributed measurement can be achieved.
► The factors that limit the beat length measurement range are discussed in detail.