Optical Fiber Polarizer With Fe–C Film for Corrosion Monitoring

The detection of early corrosion is a key issue to mitigate the damage induced by metal corrosion. This paper presents a corrosion sensor for steel based on an iron film-coated optical fiber polarizer. The polarizer is fabricated by sputtering a Fe-C film on a side-polished single mode fiber. The new fabricated polarizer shows highly birefringence, indicated by the difference of the transmission between the TE and TM modes, as well as the extinction ratio (ER). A series of simulations has been performed based on two models. The influences of the parameters of the sensor fabrication, the surrounding media, and film composition on the ER ratio and leakage are studied by the simulations. The accelerated corrosion experiments by immersing the polarizer into NaCl solution show that the polarizers become weakly birefringent after exposure. The results show that the ER and measured optical power decrease gradually during the corrosion process. The proposed polarizer can be used for monitoring the early stage of steel corrosion by building the relationship between the corrosion status and the polarization characteristics.