Theoretical Analysis of Slow-light in π-phase-shifted fiber Bragg grating for sensing applications

In this paper, a theoretical analysis of slow-light in pi-phase-shifted fiber Bragg grating (pi-FBG) for sensing applications has been presented. The coupled-mode theory (CMT) and transfer matrix method (TMM) have been used to establish the numerical modeling of slow-light in pi-FBG. The influence of slow-light grating parameters, such as grating length (L), index change (delta n), and loss coefficient (alpha), on the spectral and on the sensing characteristics of pi-FBG are studied in detail. The simulation results show that for the maximum slow-light sensitivity the optimum grating parameters are obtained as L = 5 mm, delta n = 1 x 10(-3) and alpha = 0.10 m(-1). The peak transmissivity of 0.55 and a remarkable group-index of 1477 is obtained from the optimized grating. The optimized pi-FBG is used for slowlight sensing applications. The highest values of slow-light strain and temperature sensitivity of 8.431 mu epsilon(-1) and 91.6435 degrees C-1, respectively are achieved. The slow-light sensitivity of proposed pi-FBG is the highest as compared to apodized FBGs reported in the literature. Therefore, the proposed slow-light pi-FBG shows great importance in sensing applications.