The signal that propagates in a single-mode optical fiber is characterized by circular polarization, which in conditions of stability of the cable is either static or rotates very slowly; conversely, the state of polarization can vary extremely rapidly in the presence of stresses such as vibrations, pressures, tensions, etc.

The patent consists in a system that uses an optical fiber as a sensitive element that is at the same time a signal carrier, even over long distances. It converts the polarization variation (expensive to read) into information that is more limited but simpler to read, such as power variation, using a Polarization Beam Splitter (PBS). PBS is an optical element that divides the signal into two components: one containing only the vertically polarized signal and the other containing only the horizontally polarized signal. A polarization rotation shifts power from one component to the other, keeping the total power unchanged. Two photodiodes, placed one at each output of the PBS, allow to measure these power imbalances in a cost-effective manner.

An interesting feature of this solution is that the PBS can be made of silicon, making it a low-cost solution in case of mass production.