Analysis of effects of Young modulus variations on Brillouin power and Brillouin frequency shift changes in optical fibers

Abstract

Brillouin scattering mechanism and Young modulus variations in optical fiber distributed sensing systems are directly affected by ambient temperature and thermal strain formations. Generally, in such sensing systems where temperature and strain formations are detected and measured simultaneously, Brillouin frequency shift and Brillouin power changes of backscattered optical signal are used due to their temperature and strain dependencies. In this research, a different point of view has been developed and effects of Young modulus variations of the sensing fiber core on the Brillouin power and the Brillouin frequency shift changes have been analyzed. In this study, positioning five heating units at different locations along a 1000 m G.652 type single-mode fiber operating at 1550 nm, a sensing system model has been constructed. On this model, simulations related to Young modulus variations along the sensing fiber depending on temperature fluctuations generated by heating units have been performed using Matlab 2010 and results have been obtained for 1000 different points with a spatial resolution of 1 m. For 40 degrees C- 47 degrees C operating temperature range of the sensing fiber, the Young modulus of the fiber core changes from 73.205 GPa to 73.283 GPa. Furthermore, using the analytical method, linear formula between the Young modulus and Brillouin parameters, i.e. Brillouin power and Brillouin frequency shift changes, of the backscattered optical signal have been derived. Thus, for the system model constructed, Matlab simulations analyzing relations between Young modulus variations and Brillouin parameter changes have been performed under specified operating conditions. For Young modulus variations in 73.205 GPa - 73.283 GPa range, values of Brillouin power and Brillouin frequency shift changes have been obtained in ranges of 13.950 % - 16.273 % and 69.00 MHz - 85.72 MHz, respectively. Moreover, temperature and thermal strain resolutions along the sensing fiber have been acquired as similar to 0.7 degrees C and similar to 40 mu epsilon, respectively.