Fibre Bragg gratings written in highly birefringent microstructured fiber as very sensitive strain sensors

The possibility of manufacturing highly birefringent (HB) microstructured optical fibers (MOF) made these fiber types very attractive for use in sensing applications. In contrary to traditional optical fibre sensors, properly designed MOF based components do not need temperature compensation as their birefringence remains insensitive to temperature changes. Furthermore the polarimetric strain sensitivity can significantly increase (even two orders of magnitude according to our previously reported results) for higher order modes, as their mode maxima get closer to the holey region of the fiber, hence are subjected to higher strain distribution. In this paper we present the results of numerical modeling of the propagation conditions in the HB dual-mode MOF including effective refractive index, confinement losses and birefringence calculations. Furthermore we show and discuss the spectral characteristics of fiber Bragg grating (FBG) structures written in the dedicated fiber with two technologies (with a nanosecond and femtosecond UV laser sources). A comparison of the theoretical and experimental values of effective refractive index and birefringence of the fundamental and second order modes is also included. We show the preliminary results of the fabricated structures strain response measurements and discuss ideas of increasing the structures strain sensitivity.