Capillary encapsulating of fiber Bragg grating and the associated sensing model

In order to enhance temperature sensitivity of the bare fiber Bragg grating (FBG), a capillary encapsulating method was developed. The mechanism of temperature sensitivity enhancing was formularized based on the analysis of the thermal stress, a temperature sensing model of the encapsulated FBG was presented. For demonstrating the feasibility of the encapsulating method and verifying the sensing model, several FBGs were encapsulated using zinc capillary and different binders; the temperature sensing experiments of three typical encapsulated FBGs were conducted in a temperature controlled water bath. Results show, temperature sensitivity of the encapsulated FBGs was 18.25 pm/K, 21.87 pm/K and 35.13 pm/K, which was about 1.9, 2.3 and 3.6 times as that of the bare grating, respectively. The calculated values acquired from the model were 19.672 pm/K, 23.559 pm/K and 32.813 pm/K. Comparing the experimental results with the calculated values, the relative errors were within 9.1%, which verified the feasibility of the temperature sensing model.