Abstract
In this article, a self-referencing intensity-based fiber optic sensor relying on the principle of Fabry-Perot interference is proposed and demonstrated to measure curvature. The sensor is manufactured producing an air bubble cavity between two sections of multimode fiber. By detecting optical power variations at specific wavelengths, it was possible to measure curvature, enabling this sensor as a self-referencing system. For this setup, the achieved curvature sensitivity was 0.561 ± 0.014 dB/m-1, with a correlation factor up to 0.997, within the measurement range of 0.0-0.8 m-1. The proposed system has several features, including the self-referencing characteristic and its structure simplicity in terms of measuring procedure, making it a useful system. © 2017 IEEE.

Abstract
A reflective fiber optic sensor based on a Fabry-Perot cavity made by splicing two sections of multimode fiber is demonstrated to measure the needle curvature. The sensing structure was incorporated into a medical needle and characterized for curvature and temperature measurements. The maximum sensitivity of -0.152dB/m(-1) was obtained to the curvature measurements, with a resolution of 0.089m(-1). When subjected to temperature, the sensing head presented a low temperature sensitivity, which resulted in a small cross-sensitivity.

Abstract
In this work we demonstrate the multiplexing capability of new optical fiber Fabry-Perot interferometers based on air-microcavities using a commercial FBG interrogator. Three optimized air-microcavity interferometer sensors have been multiplexed in a single network and have been monitored using the commercial FBGs interrogator in combination with FFT calculations. Results show a sensitivity of 2.18 pi rad/m epsilon and a crosstalk-free operation.

Abstract
This work consists of using an optical fiber microsphere as a sensor for a wide range of curvature radii. The microsphere was manufactured in a standard fiber with an electric arc. In order to maximize system efficiency, the microsphere was spliced in the center of a taper. This work revealed that the variations of the wavelength where the maxima and minima of the spectrum are located varies linearly with the curvature of the system with a maximum sensitive of 580 +/- 20 (pm km). This is because the direction of the input beam in the microsphere depends on the system curvature, giving rise to interferometric variations within the microsphere.

Abstract
Hollow microsphere fiber sensors are Fabry-Perot interferometers ( FPI) that can be used for lateral loading, temperature, and refractive index sensing. In this work, graphene oxide (GO) is explored as a tunable platform for enhancing the spectral properties of hollow microsphere fiber sensors. GO offers similar mechanical and optical properties as graphene, with the advantage of a wider range of deposition methods and a lower cost. The influence of multilayer coatings of polyethylenimine (PEI) and GO, achieved with the layer-by-layer technique, on the reflectivity of the outer surface, and hence, on the spectrum of the FPI for maximum of 30 bilayers was studied. The obtained results revealed a change of the microsphere outer surface reflectivity and also of visibility of the reflected spectrum when varying the number of bilayers. A maximum signal amplitude of 3.9 dB was attained for the 13th bilayer, allowing to conclude that PEI/GO multilayer coatings can be used for enhancing desired properties of the three-wave FPI for different sensing applications.

Abstract
This work demonstrates the potential of combining a microsphere with a tip for the functionality of the contact sensor. This sensor consists of a tip aligned with the fiber core and a microsphere, which appears during tip formation. This new structure was produced using the electric arc machine. The sensor operation consists of the variation of the tip curvature, which causes a variation of the optical paths and, consequently, a change in the output signal. The study of this micro-cantilever consisted of an exploration of the contact mode. In addition, the sensor was characterized by temperature, which shows very low sensitivity and vibration. This last characterization was performed with two configurations parallel and perpendicular to the oscillating surface. The perpendicular case showed higher sensitivity and has an operating band of 0 Hz to 20 kHz. In this configuration, for frequencies up to 2 Hz, the intensity varies linearly with the frequencies and with a sensitivity of 0.032 +/- 0.001 (Hz(-1)). For the parallel case, the operating band was from 1.5 kHz to 7 kHz.