Spun linear birefringence fibres and their sensing mechanism in current sensors with temperature compensation

A single-mode spun linear birefringence fibre is investigated as a periodic structure. By using coupled-mode theory, the modal fields and the propagation coefficients of the two eigenmodes in this fibre are given theoretically for the first time. A spun highly linear birefringence (SHB) fibre is capable of acting as a sensing coil of relatively high sensitivity and temperature stability in current sensors. The mechanism of compensation and the sensitivities of current with SHB fibres and temperature compensation are studied extensively with the above eigenmode theory. The relations of sensitivity and temperature stability to parameters of SHB fibres and light sources are derived. The averaging effect caused by the broadband spectrum of the light source, which effectively eliminate the temperature instability, is investigated quantitatively with the partial-coherent-light theory