Calculation Method of Brillouin Power and Frequency Coefficients for Fiber Strain and Temperature Based on Multi-Layer Segmentation

Abstract

A novel theoretical calculation method is proposed to obtain Brillouin power and frequency coefficients for strain and temperature of optical fibers used in Brillouin optical time domain sensors. For a GeO2-doped single mode fiber with any kind of complex refractive index profile, if the profile of refractive index and dopants of the fiber is available, the power-strain and power-temperature coefficients can be, respectively, derived by observing the strain and temperature dependence of Brillouin power through the changes of fiber's effective refractive index, density, sound velocity, and acousto-optic effective area. The frequency-strain and frequency-temperature coefficients can be directly obtained by detecting the strain and temperature dependence of Brillouin frequency. The complex problem of the change of acousto-optic effective area is solved by multi-layer segmentation method. The single mode fiber-28 and large effective area fiber are taken as examples to validate the theoretical derivation. The validity of the proposed method is verified by comparing the calculation results of the Brillouin power and frequency coefficients for strain and temperature with the corresponding experimental results in the literature.