This work focuses on how to measure a phisical parameter using a special optical fiber as a trasducer. The goal is to study a system that can be used to access to very small volumes where other sensors can not because of their phisical dimensions. Moreover, there are other advantages of using the optical fiber technology like the absence of electromagnetic interference and the very high sensibility and response speed of the sensor itself. ?? The optical fiber used in this work is like any other optical fiber used for example for digital high speed communication: the fiber is the medium through which the information propagates.