[Research on the reflection spectrum of linear chirped fiber bragg grating under the impact of dynamic stress].

Dynastic stress field detection based on the linear chirped fiber Bragg grating (LCFBG) was proposed. Firstly, the reflectance spectra strain sensing model of LCFBG adopting the transfer matrix method was constructed, and attenuation sine function was used to simulate the dynamic stress field along LCFBG. In the simulation experiment, the responding character of LCFBG reflection spectrum to different amplitude, different attenuation coefficient and different propagation speed of dynamic stress was studied in detail. The simulation results show that the reflectivity, wavelength and spectral shape of LCFBG reflection spec- trum are related to the dynamic stress. However, the LCFBG reflection spectrum has different response to different parameters of dynamic stress. In a range, maximum reflectivity of LCFBG reflectance spectra increases when the amplitude and propagation speed of dynastic stress field becomes larger, but it decreases when the attenuation coefficient increases. Eventually, vibration sensor using LCFBG as the sensing element was designed, and then LCFBG dynamic stress fluctuations experiment platform was build. The data obtained from experiment agrees with the simulation results. Therefore, a novel detection method of dynamic stress field through real-time acquisition of LCFBG full spectral information is proposed in this article.

[Research on the phase-shifted fiber grating spectrum characteristics in the inhomogeneous strain fields].

Based on the transfer matrix method, the spectrum characteristics of phase-shifted fiber grating were analyzed systematically, and the reflection spectra of phase-shifted fiber grating under uniform strain, linear strain, secondary strain and cubic strain were simulated respectively. The regularity conclusion that the influence of different strain distribution functions on reflectivity, transmission bandwidth, wavelength of transmission window and spectral shape came out. In order to verify the simulation result, strain-tuning equipment was designed based on cantilever with different structures. Finite element method was carried out to simulate the strain distribution of phased shift fiber grating fixed on the surface of cantilever during the strain-tuning experiment. Experiment result demonstrated that the reflection spectra of phase-shifted fiber grating under uniform strain, linear strain and secondary strain exhibited a regular change, which is in agreement with simulation results.