In this paper, we evaluate different thermal treatments in order to stabilize fiber Bragg gratings written by a femtosecond pulsed laser in specialty highly birefringent micro-structured optical fiber, targeting pressure monitoring at high pressure and high temperature environments. We have obtained a pressure sensitivity of 3.30 pm/bar up to 1400 bar and 290 °C. An effective thermal treatment has been experimentally implemented, yielding a nearly unchanged reflectivity at high temperature in combination with stable temperature and pressure readings: a standard deviation of 0.42 bar in the pressure reading was observed over 7 days at 280°C.

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In this article, we describe a NO2 sensor consisting of a coating based on lutetium bisphthalocyanine (LuPc2) in mesoporous silica. The sensor exploits the absorption spectrum change of this material which strongly and reversibly decreases in contact with NO2. NO2 is measured by following the amplitude change in the reflected spectrum of the coating deposited on the tip of a silica fibre. As diffusion of NO2 in LuPc2 is slow, the response time could be slow. To reduce it, the active molecules are dispersed in a mesoporous silica matrix deposited by a sol-gel process (Evaporation Induced Self Assembly) avoiding the formation of large crystals. Doing so, the response is fairly fast. As the recovery is slow at room temperature, the recovery time is reduced by exposure to UV light at 365 nm. This UV light is directly introduced in the fibre yielding a practical sensor sensitive to NO2 in the ppm range suitable for pollution monitoring.

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