Incorporation of vanadium oxide films in optical fibers for temperature sensing and optical switching applications

Fiber optic temperature sensors were fabricated by depositing vanadium oxide thin films on the tips of optical fibers, and by incorporating vanadium oxide materials into the core of optical fibers. It was found that the properties of the initially amorphous vanadium oxide can be controllably converted to those of crystalline VOx compounds via the plasma arc of a fiber fusion splicer. These crystalline VOx compounds can then be over-coated with SiO2, and subsequently fused with another fiber to form an in-line fiber optic sensor. It was found that a well defined optical absorption edge was formed when the vanadium oxide (VOx) thin films were annealed using the plasma arc of a fusion splicer, suggesting the formation of crystalline VOx. Moreover, it was observed that the spectral position of this absorption edge varied with temperature in a reproducible way. The optical fiber devices described in this paper could also be employed for optical switching applications. Based on the spectral position of the band edge and the Raman spectra of the VOx films, deposited on the fiber optic tips, it was found that these annealed VOx films contained a mixture of different phases of vanadium oxide (VOx), in particular V2O5 and VO2. Furthermore, similar in-line optical fiber switches, based only on the insulator to metal phase transitions of VO2, can be fabricated by following the techniques described in this paper.