Technique and Apparatus for Accurate Cross-Sectional Stress Profiling of Optical Fibers

The design and performance of a technique for determining 2-D cross-sectional stress distributions in optical fibers and fiber-based devices is described. The Brace-Kohler phase compensation method is implemented on a commercial polarization microscope to perform full-field measurements of the transverse retardations induced by the low levels of birefringence in optical fibers. Analysis of the region surrounding the fiber enables removal of the background retardation induced by the imaging optics. A custom microscope stage plate, fiber rotation apparatus, and compensator rotation apparatus allow for semi-automated measurements at various angular orientations of the fiber. Image analysis techniques are described that reduce the number of angular increments over which the compensator must be rotated, thus providing a more workable total data acquisition time. Computed tomography principles and the filtered backprojection algorithm are implemented to determine full cross-sectional axial stress distributions. The lateral spatial resolution of the technique is 0.46 mu m. The axial stress distribution in Corning SMF-28 fiber is presented. The resolution of the axial stress determined with the technique is estimated to be 0.24 MPa. The accuracy of the axial stress is estimated to be +/- 0.18 MPa.