METHOD AND DEVICE FOR MEASURING MODE DOUBLE REFRACTIVE INDEX OF BIREFRINGENT FIBER

摘要

PURPOSE:To measure a mode double refractive index of optional wavelength with high accuracy and to easily obtain the transmission characteristics of the birefringent fiber by performing the Fourier transform of two interferograms measured by a Michelson interferometer. CONSTITUTION:Projection light from the birefringent fiber to be measured is made incident on the Michelson interferometer consisting of a beam splitter 14 and two right-angle concave mirrors 15 and 16. Incident light beams are propagated through different optical paths and multiplexed to interfere with each other. In this case, interferograms are formed nearby the origin of the difference l=0 between the two optical paths in the interferometer and at a point slightly distant from the origin as one concave mirror 16 of the interferometer is moved as shown by an arrow. Those two interferograms are measured and processed by Fourier transform and its ratio is calculated, so that a component with slow variation is generated in the phase term of the ratio. The mode double refractive index is found from the element of a position term with the slow variation and the value is as accurate as the variation is slow. Further, the loss ratio of both modes is found from the ratio after the Fourier transform.