Influence of the mode field diameter on the strain and temperature sensitivity of different fibres

Summary form only given. Fibre sensitivity to the temperature, longitudinal strain or pressure, is a very important fibre feature in many applications, such as sensing application or telecommunication. The most common way to modify (either mitigate or strengthen, depending on application) this sensitivity is to change the material properties by doping or to employ microstructured fibres. In some cases the precise adjustment of a doping level and sophisticated design of air-hole arrangement is needed to obtain required features of a fibre, for example to increase sensitivity to the hydrostatic pressure and avoid cross-sensitivity to the temperature [1].In this paper we investigate, for the first time to the best of our knowledge, the influence of the mode field diameter (MFD) on the fibre sensitivity. To do so, we engage a dedicated all-fibre interferometer [2] which enables the measurement of the sensitivity of different types of fibres (including conventional and microstructured fibres with different core diameters) to the different factors (e.g. temperature, longitudinal strain or pressure). To calculate fibre sensitivity we used the formula [3]: l dφ Sp= L dp, (1) where L is the fibre length which is exposed to the factor X, dij is the phase change caused by the this factor and dX is the factor change. Results of measurements of the fibre sensitivity to the longitudinal strain (Sİ) for different fibres as well as images of these fibres are demonstrated in Fig. 1. The strain sensitivity calculated with the use of Eq. (1) clearly depends on the MFD, which is evidenced in Table 1.The larger is the MFD, the more sensitive is the fibre to the longitudinal strain. We have kind of relation in measurements also observed the same of the temperature sensitivity. In addition to the measurement results we present in the paper the complex analysis of this phenomenon and we discuss its consequences and possibilities of application .