Ultra-high sensitivity strain sensor based on biconical fiber with a bulge air-bubble

An ultra-high sensitivity Fabry–Perot interferometer (FPI) strain sensor is proposed and experimentally demonstrated. It is composed of a biconical fiber with a bulge air-bubble at its waist. Because of the good stress concentration capability of the tapered fiber, the bulge air-bubble is easily deformed when it is stressed, resulting in an ultra-high strain sensitivity of 101.7 pm/µɛ, which is the highest strain sensitivity among the direct wavelength interrogation-based strain sensors reported so far, to the best of our knowledge. Moreover, the proposed sensor has a low temperature sensitivity of ∼ 1 p m / ∘ C ; thus an extreme low temperature cross sensitivity of less than 10 nɛ/°C can be achieved.