ABSTRACT
This chapter introduces the reader on how optical fibers are used as sensing elements in all-fiber current sensors; the particular specialty fiber types most commonly used; and their methods of conditioning and preparation. A common challenge is the suppression of Faraday-effect-quenching linear fiber birefringence. A particular focus is on spun highly birefringent fibers. Others are twisted fibers, helically wound fibers, helical-core fibers, flint glass fibers, spun low birefringence fibers, thermally annealed fibers, doped fibers with enhanced Faraday effect, multimode fibers, liquid core fibers, and microfiber coils. The light propagation and polarization evolution in the fibers is derived from coupled mode equations and illustrated on the Poincaré sphere. The influence of the fiber parameters and source spectral width on the polarization evolution and magneto-optic sensitivity is also discussed.
