Fiber-Based Cavity Ring-Down Technique for Refractive Index Sensing at 1953nm Using Tapered Fibers

摘要

Conventional and amplified fiber-based cavity ring-down techniques (CRDT) are demonstrated for the first time in the 2-m wavelength region. The evanescent field in tapered fibers, used as an intra-cavity element, is utilized to perform refractive index (RI) measurement. These longer wavelengths have larger mode field diameter. This results in larger value of the evanescent field and higher sensitivity, confirmed by the numerical simulations. The effect of tapered fiber diameter is investigated both numerically and experimentally. It is found that smaller diameters provide higher sensitivity. The best detection limit achieved experimentally is 4.8 10 RIU at RI of 1.31 with a tapered fiber of length 4 mm and a diameter of 5.35 μm, in conjunction with amplified CRDT. The detection limit can be further improved when the cavity is designed with components and fiber that are optimized for minimal loss at these wavelengths.