Ultra-Short Fiber Bragg Grating Composed of Cascaded Microchannels in a Microprobe for Refractive Index Measurement

An ultra-short fiber Bragg grating (US-FBG) refractive index (RI) sensor is presented and demonstrated. The US-FBG is composed of a series of cascaded microchannels which carved by femtosecond (fs) laser in the microprobe. According to the simulation results, an US-FBG with length/period of 149.8/5.35 μm is fabricated and used to measure refractive index (RI) of liquids. The experimental results show that the sensitivity of the proposed sensor can reach 600.5622 nm/RIU with a linear response range of 1.3323 to 1.3787. Such a compact size, high sensitivity and the inherent high reliability and ease of modulation of the US-FBG is expected to be used in the field of biosensing related to RI.