The novel microstructured optical fibres (MOF) with suspended core design guiding linear and quasi-circular polarized
modes has been developed which demonstrates linear birefringence scalable in a range 5×10<sup>-4</sup> to 2×10<sup>-2</sup> by tuning the
core size. The SPUN type of this MOF exhibits a high magneto-optical effect for sensitive coil diameter of 5 mm and
shows no degradation of performance, e.g. optical losses and magneto-optical sensitivity, for turns number of 10<sup>2</sup>÷10<sup>4</sup>.
The transmission losses are 2÷4 dB/km and the magneto-optical sensitivity approaches the value of 70% of theoretical
limit for small diameter coil. The potential applications of such MOF in gyro and optical current transformer will be
In this article we propose the way to measure the beat length of the embedded linear birefringence in optical Spun fibers
and give theoretical basis of this method. This explanation is based on the model of helical structure of the birefringence
axis. The measurement method is based on a measuring of the period of fringe pattern that obtained by passing the light
through the Spun fiber placed between two polarizers.