Because the manufacturing technology of commercial optical fiber device and polarization-maintaining fiber fusion splicing technology based on 40 μm polarization-maintaining fiber are not mature

general polarization-maintaining fiber parameter measurement methods are difficult to directly apply. In this paper

a simple polarization interference device is constructed by accomplishing Superluminescent Diode（SLD） source coupling and making optical fiber polarizer online on a 40 μm polarization-maintaining fiber. The beating length and refractive index temperature coefficient of polarization-maintaining fiber can be both measured using the modulated spectrum. The measuring method is elaborated in theory and verified via the experiment

which is also applicable for polarization-maintaining fibers with other diameters.