The main goal of our thesis is to develop a fiber optic sensor, more precisely a vibration sensor. The thesis consists on developing a working prototype using two different technologies, with two different optical circuits: the first uses two facing fibers, one in transmission and one in reflection, the second instead is based on a Bragg gratings, therefore the fiber is sensitive to contraction/expansion. The first arrangement is rawer and it is based on Plastic Optic Fibers (POF), it is cheaper and easier under both designing and manufacturing aspects. The second one, instead, exploits glass single mode fibers: it has a cost that is orders of magnitudes larger and requires a lot more effort to manage the optical components, because they must be fiber coupled.