Temperature sensing experiment of Fiber Bragg Grating packaged by copper capillary without strain

In consideration of bare Fiber Bragg Grating being fragility, an approach of polymer and copper capillary package for FBG is proposed in this paper. FBG is coated with acrylate. After second coating, FBG is packaged into a blank copper capillary. FBG can expand or contract freely without strain. The second coating protects bare FBG from damage. The comparison of the experimental results between coated FBG and bare FBG indicates that the temperature sensitivity of coated FBG is nearly same as that of bare FBG. The thin coating thickness guarantees that coating thickness is uniform and the spectrum of coated FBG has a good shape. The influence on measurement precision of temperature from strain is decreased. The empirical results show that the coefficient between wavelength and temperature is 0.99929, and measurement sensitivity is 13.675 pm/°C. The temperature sensor has a good repeatability.