Great increase of the tensile strength in the lamellar PI-coated FBG sensors

The pristine fiber has a tensile strength of 5 GPa while it can be reduced to 0.4 MPa after writing FBG by using the UV laser based phase mask technology. Herein, we report four lamellar polyimide (PI)-coated FBG sensors with great increase of the tensile strength. Our results show that the average tensile strength of the lamellar PI-coated FBG sensors is 2.8 times higher than the value of the uncoated FBG sensors. More importantly, compared with the uncoated FBG sensors, the lamellar PI-coated film can effectively protect the uncoated FBG sensors from a fracture at the grating area. In addition, the lamellar PI-coated FBG sensors also possess good force sensing capabilities, which indicate that the lamellar PI-coated FBG sensors can be considered as a candidate for force sensing applications.