Abstract
The proposed technique consists in an optical fiber resonator interrogated for sensor characterization, implementing an alternative technique for dynamic range improvement. Such technique relies on the analysis of an added-signal caused by signal saturation, which occurs due to the broadening of the laser pulse. A wide study for different pulse widths is presented in this work, namely for 100 ns, 5 mu s and 20 mu s, being the last one related to the emergence of an added-signal for the proposed configuration. The behavior of the waveform in the presence of an intensity sensor is also characterized.

Abstract
Small sections of suspended twin-core fiber are used in reflection configurations to create two parallel Fabry-Perot cavities. Situations where both cores are excited and where only one core is excited are analyzed and compared. When both cores are excited, two parallel and equivalent cavities are formed and an interference pattern with higher visibility is obtained. The structure is also characterized with respect to temperature and a sensitivity of 12.4 pm/K is achieved.

Abstract
A curvature sensor based on a Fabry-Perot interferometer is proposed. A capillary tube of silica is fusion spliced between two single mode fibers, producing a Fabry-Perot cavity. The light propagates in air, when passing through the capillary tube. Two different cavities are subjected to curvature and temperature. The cavity with shorter length shows insensitivity to both measurands. The larger cavity shows two operating regions for curvature measurement, where a linear response is shown, with a maximum sensitivity of 18.77pm/m(-1) for the high curvature radius range. When subjected to temperature, the sensing head produces a similar response for different curvature radius, with a sensitivity of 0.87pm/degrees C.

Abstract
A cantilever structure in 3D printed based on a fiber Bragg grating (FBG) sensor embedded in polymer material is proposed. The FBG sensor was embedded in 3D printed coating and was tested under three physical parameters: displacement, temperature and vibration. The sensor was tested in displacement in two different regions of the cantilever, namely, on its midpoint and end point. The maximum displacement sensitivity achieved was (3 +/- 0.1) pm/mm for end point displacement, and a temperature sensitivity of (30 +/- 1) pm/degrees C was also attained. In the case of vibration measurements it was possible to obtain a 10.23Hz-low frequency oscillation.

Abstract
In this paper, two techniques for interrogation and multiplexing of fiber loop mirror (FLM) intensity sensors based on optical time domain reflectometer (OTDR) are proposed. These configurations enable series and parallel FLM sensor interrogation. A fiber taper characterized as a displacement sensor was used as the intensity sensor. The OTDR parameters were optimized in order to obtain the best results. The optimized parameters were 100-ns pulse width and 10-dB input signal attenuation which permitted to attain similar to 18 dB dynamic range in the operating wavelength of 1550 nm. The results show a linear behavior for both configurations with similar slope, -15.3 dB/mm, in the normalized displacement range of 0.2 to 0.7 mm. It was also achieved a displacement resolution of 0.027 and 0.093 mm, for the series and parallel configurations, respectively. Sensors multiplexing are demonstrated for both configurations and the systems do not present crosstalk. Based on the experimental results, the best configuration is the parallel one. The proposed approach is a viable alternative for multiplexing and interrogation of remote fiber sensors.

Abstract
A brief review in the fibre cavity ring-down (CRD) technique is presented. It addresses the latest developments in CRD technique for sensing applications, undergone at INESC TEC. The CRD is based on the conventional configuration with the possibility of adding amplification in order to compensate the output signal losses induced by the sensing head. The results obtained for strain, curvature and refractive index sensing are presented, corresponding to distinct sensing structures, namely, a chirped fibre Bragg grating (FBG), a long period grating (LPG) and a multimode interference (MMI) based sensor.