A novel polarimetric dual-fibre coil sensor has been developed by use of highly birefringent single-mode fibre. A length of fibre is cut at its half-length and both halves of the fibre are connected again by splicing after rotating one fibre relative to the other by 90 degrees about its axis. The resultant fibre is doubled at the spliced location to make the paired fibres so that their birefringent axes may be arranged interchangeably with one another. A length of the paired fibres is coiled around a cylinder which is flexible in the direction of its diameter. The coil deformation turns into a change in bending-induced retardation. This polarimetric deformation sensor is immune to ambient temperature disturbances. The retardation linearity is considerably improved by incorporating a visible laser diode with a short coherence length.
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