Double-cone tapered single-mode fibers are common in many telecommunication components and offer an alternative sensor to typical fiber optic strain gauges, which are susceptible to temperature and pressure and require expensive and complex signal acquisition systems. Cavity ring-down spectroscopy is a technique often used for highly sensitive chemical analysis and has the advantage of detection sensitivity, which can be used to improve the strain measurement of double-cone tapers. By combining these two techniques in a spatially extended resonator, we demonstrate a minimum detectable change in ring-down time of 0.08%, corresponding to a minimum detectable displacement of 4.8 nm and a sensitivity to strain as low as 79 nε/mm of tapered length at 5 Hz.
