Metallic nanoparticles show a peak in the absorption spectrum due to the Localized Surface Plasmon Resonance (LSPR) effect. The position of this peak depends on the shape, size and the type of the nanoparticles as well as on the refractive index of the surrounding media. From the dependence of the position of the peak with the external refractive index, it is possible to use these nanoparticles as a sensor element to measure the refractive index of liquids and gas. A refractive index sensor was developed with nanoparticles deposited at the end face of an optical fiber. These nanoparticles, fabricated from a heated gold film deposited at the end face of the fiber, have a non homogenous distribution of size and form. In order to obtain a better control of the size and form of the fabricated metallic nanoparticles, aiming the development of an optical sensor with control of the involved parameters, it was investigated in this work the formation of silver nanoparticles by chemical synthesis. Furthermore, extending the investigation of fiber optics systems with applications on sensing, it was performed a simulation of the deformation of elliptical air cavities, formed in the interior of optical fibers, under the effect of longitudinal stress along the fiber. This type of system can be used as a deformation sensor due to the multiple interference reflections in the interior of the cavity.