the principle axis of the selected fiber is aligned in the direction of the externally applied stress by detecting a null output from the power detecting apparatus application_number US 80535991 A description alignment of preferred birefringent axis of the coupler fiber is a precursor to the fusion and tapering process accurate alignment of the birefringent axes of the two fibers at the pre determined locations of fibers was accomplished with the in house developed computer controlled fiber alignment setup the setup is capable of determining slow or fast axis of the coupler fiber to better than 0 1 degree accuracy the fibers are prepared for alignment by the following step by step procedure 1 stripping away 20 mm length of the fiber jacket at the center of two fibers each of which is 2 meters long 2 cleaning the stripped regions such that all contaminations and the jell particles from the jacket are removed fig1 shows a schematic diagram of the polarization maintaining fiber alignment system which is capable of determining the birefringent axis orientation to within 0 1 degree accuracy determination of the slow or fast axis of a pm fiber is based on the principle of elasto optic effect described in carrara et al 34.