Kompetenzzentrum für optische Spezialfasern

It is presented a multimode interferometer based-fibre optic sensor with a silica tube section aimed to measure refractive index variations of surrounding liquids. The sensing head is a silica tube section fusion spliced to single mode fibres operating in transmission. In the splice regions tapers where made to allow the light to be guided in the silica tube while the core is formed by air. This configuration permits measurements of refractive index variations with sensitivities of 101.1 nm/RIU, 106.29 nm/RIU and 107.97 nm/RIU considering resonances with different wavelengths. The same resonances were tested with temperature variations with sensitivities achieved of 7.8 pm/ ºC , 8.7 pm/ ºC and 9.3 pm/ ºC respectively. The spectral variation associated with one degree temperature change corresponds to a refractive index change of ~ 5 8 10 ,   proving the low temperature dependence compared with sensitivity to RI variations.