Abstract

To investigate the error in temperature and strain simultaneous measurement based on Brillouin scattering and Brillouin dynamic grating (BDG), the error estimation for birefringence-induced frequency shift in BDG reflected spectra is systematically investigated. In view of the validity of characterization of the BDG reflected spectra by the coupled-wave equations and estimation of birefringence-induced frequency shift by Gaussian model, the BDG reflected spectra with different values of frequency sweep span, signal-to-noise ratio (SNR), linewidth and number of sweeps are numerically generated based on solving of the coupled-wave equations. The birefringence-induced frequency shift is estimated by fitting the Gaussian model to the numerically generated spectra. The relationship between the error in the birefringence-induced frequency shift and the above factors is obtained by the least-squares fit. The results reveal that the birefringence-induced frequency shift error decreases exponentially with increasing SNR. The error is approximately proportional to linewidth. The error decreases as a power of the number of sweeps and the exponent is −0.5. Too narrow or wide frequency sweep span corresponds to a large error. The frequency sweep span is suggested to be set to one linewidth. An estimation formula for birefringence-induced frequency shift error in BDG reflected spectra is proposed based on a large number of generated spectra.

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