Miniature Fabry-Perot interferometer strain sensor based on an elliptical air bubble

We demonstrated a high-robustness Fabry-Perot interferometer strain sensor based on an in-fiber elliptical bubble that was created by splicing together two sections of standard single mode fibers. Such a FPI could be used to develop a high-robustness strain sensor with a low cross-sensitivity between temperature and tensile stain. The sensitivity of this strain sensor was ~2.4 pm/με, and exhibited low thermal sensitivity (less than 1.0 pm/°C) reducing the cross sensitivity between tensile strain and temperature. Moreover, such a strain sensor has a broad operation wavelength range ~36 nm, fringe contrast ~38dB, and super-high mechanical robustness. The robustness of the strain sensor based on the air mini-cavity is demonstrated up to 9800 με until the single mode fiber was fractured.