TWISTING AND ANNEALING OPTICAL-FIBER FOR CURRENT SENSORS

We demonstrate that twisting a fiber a few turns per meter before it i s annealed largely eliminates the residual linear birefringence. This dramatically improves the yield of annealed toils used for current sen sing and makes it possible to use fibers that previously had large res idual linear birefringence. Twisting the fiber is effective because th e residual birefringence, associated with core ellipticity, is reduced to near zero by twisting. A theoretical model of the twisted and anne aled fiber current sensor is compared to experimental data, We also sh ow good temperature stability for a sensor made with this new techniqu e.