Effect of Dynamic Strain on Fiber Bragg Grating Reflection Spectra (Effekten avDynamisk Toeyning pa Refleksjonspekteret til Fiberoptiske Bragg-Gitre)

摘要

We investigate the effect on fiber Bragg grating reflection spectra of dynamicstrain. We argue that the grating length should be significantly shorter than the wavelength of the dynamic strain. Under this condition we subject the gratings to linear and quadratic chirp to approximate the strain in nodes and antinodes of a strain wave. The analysis is performed using a graphical bandgap method and numerical simulations of the grating spectra. We analyze two different uniform gratings equivalent gratings with a Gaussian index modulation envelope. We also develop a criterion for the maximum strain and vibration frequency a uniform grating should be able to measure. We find that the Gaussian gratings can be used to measure larger values of strain and vibration frequencies, and that relatively strong uniform gratings with unstrained reflectance of 100%, should be applicable for sensing of strain up to 1% at frequencies below 100kHz.