Single-Mode-Multimode Silica Rod-Single-Mode High Refractive Index Fiber Sensor

This paper reports a robust high refractive index (RI) sensor based on a multimode silica rod structure. The sensor was fabricated by splicing a segment of multimode silica rod between two single-mode fiber (SMF) leads. The measurement of high-RI is realized by monitoring the change of power spectrum caused by the reaction of leaky modes to different surrounding high-RI. The 0.5-cm long multimode silica rod sensing element exhibits a sensitivity of up to 115.12 dBm/RIU for high-RI ranging between 1.450 and 1.531. The sensor also demonstrated its potential in power transformer application by distinguishing various ageing levels of transformer oil. The leaky modes mechanism in all-silica based structure is essentially temperature insensitive, and therefore very practical to be deployed in extreme temperature conditions.