We report an optical fiber multiparameter sensor for refractive index and temperature measurements. The proposed sensor is composed by a microcavity in multimode fiber, assisted by Bragg gratings (FBGs) in singlemode fiber. The microcavity is engraved in a multimode optical fiber by using the femtosecond laser micromachining. The sensor is characterized through microcavity immersion in water and based on its temperature variation. The results show that it is possible to obtain refractive index and temperature measurements with sensitivities of 1625 μW/RIU (refractive index unit) and of 0.23 μW/°C, with resolution of 1.8 × 10<sup>-4</sup> RIU and of 1.3°C.
A 10 μm (length) × 75 μm (depth) open channel is fabricated in fibre Bragg gratings (FBG) by femtosecond laser micromachining. The FBG Fabry-Perot (FP) cavity formed by this complex structure has a length of 4 mm; value estimated from interference spectrum for the air open channel. Reflection spectra of FBG FP cavity as a function of the temperature shows the cavity phase change. The sensor is thermally characterized by filling polymer in the channel and subsequent UV curing; the results show a period shift of approximately 12 x10<sup>-3</sup>, value obtained of interferometer pattern for 30°C temperature range.
We report the fabrication of an hybrid fibre optic and T-shaped microstructrure inscribed in soda lime microscope slides by using femtosecond laser irradiation technique. that allow to construct true 3-D structures. Within the T-shaped structure a FBG was inserted and glued with photopolymer adhesive. The hybrid structure is sensitive to hydrostatic pressure. Calibration load tests were performed in the range 0 - 100 N.