Experimental examination of the variation of the spontaneous Brillouin power and frequency coefficients under the combined influence of temperature and strain

Interpretation of Brillouin-scattering-based distributed strain and temperature measurements so far has been based on the premise that the Brillouin coefficients used to describe the influence of strain or temperature remain constant under circumstances where a sensing fiber is subjected to the combined influence of both temperature and strain. We examine the validity of these assumptions by experimentally evaluating the Brillouin coefficients under combined temperature and strain influence. In order to illustrate the importance of correcting the Brillouin coefficients for estimation of true values of applied strain and change in temperature, arbitrarily chosen values of change in frequency and percentage change in intensity are used to calculate the values of applied strain and change in temperature by using both corrected and uncorrected Brillouin coefficients.